Sustainable automotive components for interior door trims

Sustainable automotive components for interior door trims University of Porto | Faculty of Engineering Mechanical Engineering Department Sustainable automotive components for interior door trims Dissertation submitted to the Faculty of Engineering of the University of Porto for obtaining the degree of Doctor of Philosophy in Leaders for Technological Industries of the MIT-Portugal Program Nuno Alexandre de Oliveira Calçada Loureiro Mechanical Engineer | Master in Industrial Design PORTO, 2013 Supervisor Professor José Luís Soares Esteves Assistant Professor | Mechanical Engineering Department Faculty of Engineering | University of Porto | Portugal Co-Supervisors Professor Júlio César Machado Viana Associate Professor | Polymer Engineering Department Engineering School | University of Minho | Portugal Professor Satyabrata Ghosh Head of Research and Development | Carborundum Universal Limited| India This work has been done under the Engineering Design and Advanced Manufacturing (EDAM) focus area of MIT-PORTUGAL Program. This program is an international collaboration of Massachusetts Institute of Technology, Faculty of Engineering of University of Porto, University of Minho and Instituto Superior Técnico. This work has the financial support of the Portuguese Foundation for Science and Technology (Fundação para a Ciência e Tecnologia) through the PhD Grant SFRH/BD/42978/2008 and through the project MIT-Pt/EDAM-SMS/0030/2008 - Assessment and Development of integrated Systems for Electric Vehicles on the scope of QREN – POPH – Topology 4.1 Advanced Formation Scope. (Co-participated by the European Social Found and by MEC national founds). ~ Ao meu filho João Dinis, para que sempre saiba que, com trabalho, todos os sonhos se concretizam. To my son, João Dinis, to always know that, with work, all dreams come true. Sustainable automotive components for interior door trims xvi Abstract In the last few years, biomaterials have been a target of interest at scientific, technological research and industrial level. The increasing of the environmental concern and the excessive use of petrol resources have conducted to the development of new materials, biocomposites, which will achieve a great importance into the future. It’s a fact that, allied to weight reduction, the automotive industry can benefit from the inclusion of these materials in cars, not only because of the installed fear of decline and extinction of oil reserves, but also because of the strong legislation that forces an increasing incorporation of these materials in automobiles. This topic presents a big potential because it seeks to find solutions for a sustainable development with environmental concerns in order to be able to obtain biodegradable solutions for the interior door trims. Since the main purpose of this work is to create a bio-composite that is suitable to replace the existing interior door trims, the work has focused on obtaining that bio-composite, taking account into the raw-materials cost reduction and the maintenance of the manufacturing process of current door trims. Therefore PLA and PHA blends mechanical and morphological behavior have been studied in order to define the best matrix for use in this study. Subsequently it was studied the incorporation of cellulosic fiber to adjust the properties to meet the required values. Throughout this report, it’s possible to find a description of the various tasks performed in the development of this project. The work began with a review of the literature about biocomposites materials. Then it’s presented the experimental work. The study of the choice of matrix and processing parameters, followed by the study of the fibers incorporation is presented. Having defined the composite the work ends with the production of an interior door trim made into this bio-composite to demonstrate the potentiality of these materials. In conclusion it verifies that the matrix containing 70% PLA and 30% PHA (weight fraction) has the best properties for the interior door trims. The incorporation of 20% of fiber improves the thermal behavior of the composite, proving that it is possible to replace the petrol-based polymers for these biocomposites without compromising the mechanical behavior of interior door trims. Nuno Calçada Loureiro xvii Résumé Les biomatériaux sont devenus un sujet d’intérêt, au cours des dernières années, soit dans la recherche scientifique et technologique, soit dans l’industrie. Les préoccupations croissantes avec l’environnement et l’utilisation excessive des ressources pétrolières sont à l’origine de la recherche et développement des matériaux nouveaux, les bio-composites, très importants pour l’avenir. L’industrie automobile bénéficiera de l’utilisation de ces matériaux, notamment par la réduction du poids des voitures. En plus, ils pourront être une alternative face à la crainte de diminution et épuisement des réserves de pétrole et répondront favorablement à la forte législation qui oblige à une incorporation progressive de ces matériaux dans les voitures. Ce sujet présente un grand potentiel, puisque il permet de trouver des solutions pour un développement durable, avec des préoccupations écologiques, afin d’obtenir des solutions biodégradables pour les panneaux intérieures des voitures. Étant donné que l’objectif de ce travail est la création d’un bio-composite qui permet le remplacement des panneaux de portes des voitures, toutes les démarches ont eu comme objectif l’obtention de ce biocomposite, en tenant compte la réduction des dépenses en matières premières et le maintient du processus de fabrication des panneaux actuels. Ainsi, on a étudié mécaniquement et morphologiquement les mélanges de PLA e PHA afin de définir la matrice la plus correcte pour l’application désirée. Ensuite, on a étudié l’incorporation des fibres pour l’ajustement des propriétés nécessaires. Le long du texte, il est possible de trouver la description des différents procédés d’investigation au niveau de ce projet. Le travail a commencé par une analyse attentive de la littérature sur les matériaux bio-composites. Ensuite, on présente le travail expérimental réalisé. Le choix de la matrice et des paramètres du processus, suivi de l’étude de l’incorporation des fibres. Une fois le composite défini, on a terminé le travail par la production d’une pièce pour démontrer le potentiel de ces matériaux. En conclusion, on vérifie que la matrice composée de 70% PLA et 30% PHA (fraction massique) présente les propriétés idéales pour l’application proposée. L’incorporation de 20% de fibre dans cette matrice permet une amélioration importante du comportement thermique de ce matériel, en prouvant, ainsi, qu’il est possible de remplacer des polymères d’origine pétrolière par ces bio-composites, sans, toutefois, compromettre le comportement mécanique et thermique des panneaux intérieures des portes des voitures. Sustainable automotive components for interior door trims xviii Abstrakt Biomaterialen wurden das interessenziel in den letzten Jahren im umfang der wissenschaftlichen und technologischen Forschung und in der Industrie. Steigende umweltbewusstsein und den übermäßigen Einsatz von Öl-Ressourcen führte zu einer erhöhten Entwicklung neuer Materialien, Biocomposites, die eine große Zukunft Bedeutung haben wird. Es ist eine Tatsache, dass, gepaart mit der Gewichtsreduktion, die Automobilindustrie kann von der Einbindung dieser Stoffe in Autos profitiert, nicht nur wegen der Angst vor Verfall und Auslöschung installiert Ölreserven, sondern auch wegen der starken Rechtsvorschriften, die erfordert eine zunehmende integration dieser Materialien in Autos. Dieses thema stellt ein großes potenzial, weil es um Lösungen für eine nachhaltige Entwicklung zu finden mit Umweltbelangen, um in der Lage sein, biologisch abbaubare Lösungen für die Innenverkleidung des Autos erhalten soll. Da der Hauptzweck dieser Suchung auf eine Bio-Composites schaffen die bestehende Macht Autoinnenraum Platten ersetzen kann, hat die Suchung über den Erhalt derartiger bio-Verbund konzentriert, unter Berücksichtigung der Kostenreduktion von Rohstoffen und Wartung von Herstellungsprozess der aktuellen Zellen. Daher wurden Mischungen aus PLA und PHA morphologisch und mechanisch untersucht, um die besten Matrix zur Verwendung bei der Untersuchung zu definieren. Anschließend wurde die Einbindung von cellulosefasern untersucht, um die gewünschten Eigenschaften einzustellen. In diesem Bericht finden Sie eine Beschreibung der verschiedenen Aufgaben bei der Entwicklung dieses Projektes durchgeführt. Die Arbeit begann mit einer gründlichen Analyse der Literatur über Biocomposites Materialien. Dann stellen wir die experimentelle Arbeit. Die Wahl der Matrix und Verarbeitungsparameter, durch Untersuchung der Einbindung von Fasern folgt. Nach der Definition der Verbund wurde Werkstück Produktion beendet, um die Fähigkeit dieser Materialien zu demonstrieren. Abschließend, es scheint, dass die Matrix mit 70% PLA und 30% PHA (Gewichtsanteil) die besten Eigenschaften für die Anwendung unter Berücksichtigung hat. Die Einarbeitung von 20% Faser in dieser Matrix verbessert die thermische Leistung des Materials, was beweist, dass es möglich ist, die Polymere aus Erdöl gewonnene für diese Biocomposites ohne die mechanischen Türinnenverkleidungen ersetzen. Nuno Calçada Loureiro xix Contents LIST OF SYMBOLS ....................................................................................................................................... XXIII LIST OF ABBREVIATIONS ............................................................................................................................. XXV LIST OF FIGURES ........................................................................................................................................ XXVII LIST OF TABLES .......................................................................................................................................... XXXI CHAPTER 1. INTRODUCTION ............................................................................................................................ 1 1.1 I NTRODUCTION ................................................................................................................................................. 1 1.2 P ETROL TREND .................................................................................................................................................. 1 1.3 A UTOMOTIVE C OMPONENTS ............................................................................................................................... 3 1.4 T HE FUTURE FOR A UTOMOTIVE C OMPONENTS ........................................................................................................ 8 R EFERENCES ......................................................................................................................................................... 11 CHAPTER 2. LITERATURE REVIEW ................................................................................................................... 13 2.1 I NTRODUCTION ............................................................................................................................................... 13 2.1.1 E NGINEERING P LASTICS ............................................................................................................................. 15 2.2.2 T YPES OF P OLYMERS ................................................................................................................................. 15 2.2 B IODEGRADABLE P OLYMERS .............................................................................................................................. 17 2.2.1 B IODEGRADABLE P OLYMERS USED ............................................................................................................... 19 2.3 P OLY (L ACTIC A CID ) .......................................................................................................................................... 19 2.3.1 PLA P RODUCTION .................................................................................................................................... 20 2.3.2 PLA P ROPERTIES ...................................................................................................................................... 22 2.3.3 PLA B IODEGRADATION ............................................................................................................................. 23 2.3.4 PLA B ASED C OMPOSITES ........................................................................................................................... 25 2.4 P OLY H YDROXY A LKANOATE (PHA) ...................................................................................................................... 26 2.4.1 PHA PROPERTIES ..................................................................................................................................... 29 2.4.2 PHA BIODEGRADATION ............................................................................................................................. 29 2.4.3 PHA BASED C OMPOSITES .......................................................................................................................... 30 2.5 N ATURAL F IBERS ............................................................................................................................................. 31 2.5.1 F IBERS C LASSIFICATION ............................................................................................................................. 32 2.5.2 C ELLULOSIC FIBERS : A DVANTAGES AND D ISADVANTAGES ................................................................................. 35 2.5.3 C ELLULOSIC FIBERS : P ORTUGUESE M ARKET AND E XTRACTION T ECHNOLOGY ........................................................ 36 2.6 C OMPOSITE M ATERIALS .................................................................................................................................... 39 2.6.1 M ATRICES .............................................................................................................................................. 39 2.6.2 R EINFORCEMENTS .................................................................................................................................... 40 2.6.3 T HERMOPLASTIC M ATRIX C OMPOSITES ........................................................................................................ 40 2.6.4 C OMPOSITE P RODUCTION INTO THE AUTOMOTIVE INDUSTRY ............................................................................ 42 2.6.5 B ULK M OULDING C OMPOUNDING / S HEET M OULDING C OMPOUNDING ............................................................. 42 2.6.6 I NJECTION M OULDING .............................................................................................................................. 44 R EFERENCES ......................................................................................................................................................... 46 Sustainable automotive components for interior door trims xx CHAPTER 3. MOTIVATION, OBJECTIVES AND RESEARCH APPROACH.............................................................. 49 3.1 M OTIVATION AND OBJECTIVES ........................................................................................................................... 49 3.2 R ESEARCH A PPROACH ...................................................................................................................................... 49 3.3 T HESIS S TRUCTURE .......................................................................................................................................... 51 R EFERENCES ......................................................................................................................................................... 52 CHAPTER 4. MATERIALS AND METHODS ........................................................................................................ 53 4.1 M ATERIALS .................................................................................................................................................... 53 4.1.1 P OLYHIDROXYALKANOATE – PHA ................................................................................................................ 53 4.1.2 P OLY (L ACTIC A CID ) – PLA ......................................................................................................................... 54 4.1.3 C ELLULOSIC F IBERS ................................................................................................................................... 54 4.1.4 P REPARATION OF THE B LENDS .................................................................................................................... 54 4.1.5 P REPARATION OF THE C OMPOSITE M ATERIAL ................................................................................................ 55 4.2 D ETERMINATION OF M ECHANICAL P ROPERTIES ..................................................................................................... 57 4.2.1 T ENSILE T EST ........................................................................................................................................... 57 4.2.2 F LEXURAL T EST ........................................................................................................................................ 58 4.2.3 I MPACT T EST ........................................................................................................................................... 58 4.3 D ETERMINATION OF T HERMAL P ROPERTIES .......................................................................................................... 59 4.3.1 H EAT -D EFLECTION T EMPERATURE ............................................................................................................... 59 4.3.2 D IFFERENTIAL S CANNING C ALORIMETRY ....................................................................................................... 60 4.4 D ETERMINATION OF M ORPHOLOGICAL P ROPERTIES ............................................................................................... 61 4.4.1 O PTICAL M ICROSCOPY .............................................................................................................................. 61 4.4.2 W IDE -A NGLE X-R AY D IFFRACTION .............................................................................................................. 61 4.4.3 S CANNING E LECTRON M ICROSCOPY ............................................................................................................. 62 R EFERENCES ......................................................................................................................................................... 64 CHAPTER 5. MECHANICAL CHARACTERIZATION OF PHA/PLA BLENDS............................................................ 65 5.1 M ECHANICAL PROPERTIES PREDICTION MODELS ..................................................................................................... 66 5.1.1 R ULE OF M IXTURES .................................................................................................................................. 66 5.1.2 K ERNER -U EMURA -T AKAYANAGI MODEL ....................................................................................................... 66 5.1.3 N ICOLAIS -N ARKIS MODEL .......................................................................................................................... 67 5.1.4 B ÉLA -P UKÁNSKY MODEL ............................................................................................................................ 67 5.2 M ECHANICAL T ESTING ...................................................................................................................................... 68 5.2.1 F LEXURAL P ROPERTIES .............................................................................................................................. 68 5.2.2 T ENSILE P ROPERTIES ................................................................................................................................. 68 5.2.3 I NSTRUMENTED P ROPERTIES ...................................................................................................................... 69 5.2.4 H EAT D EFLECTION T EMPERATURE (HDT) M EASUREMENTS .............................................................................. 69 5.3 R ESULTS AND D ISCUSSION ................................................................................................................................. 69 5.4 C ONCLUSIONS ................................................................................................................................................. 77 R EFERENCES ......................................................................................................................................................... 79 CHAPTER 6. MORPHOLOGICAL CHARACTERIZATION OF PHA/PLA BLENDS .................................................... 81 6.1 I NTRODUCTION ............................................................................................................................................... 81 6.2 M ORPHOLOGICAL C ALCULATIONS BASED ON DSC RESULTS ...................................................................................... 82 6.3 R ESULTS AND D ISCUSSION ................................................................................................................................. 82 Nuno Calçada Loureiro xxi 6.3.1 WAXD M EASUREMENTS ........................................................................................................................... 82 6.3.2 DSC OF I NJECTION M OLDED PHA/PLA BLENDS ............................................................................................ 83 6.4 C ONCLUSIONS ................................................................................................................................................. 90 R EFERENCES ......................................................................................................................................................... 91 CHAPTER 7. CHARACTERIZATION OF PHA/PLA – CELLULOSIC FIBERS COMPOSITES........................................ 93 7.1 I NTRODUCTION ............................................................................................................................................... 93 7.2 M ECHANICAL PROPERTIES PREDICTION MODELS ..................................................................................................... 94 7.2.1 M ODIFIED H ALPIN -T SAI E QUATION ( M HT) ................................................................................................... 94 7.2.2 I SHAI AND C OHEN MODEL (IC M ) ................................................................................................................. 95 7.2.3 R ULE OF M IXTURES (ROM) ...................................................................................................................... 95 7.3 R ESULTS AND D ISCUSSION ................................................................................................................................. 96 7.3.1 T ENSILE BEHAVIOR .................................................................................................................................... 96 7.3.2 F LEXURAL BEHAVIOR ................................................................................................................................. 98 7.3.3 I MPACT BEHAVIOR .................................................................................................................................. 100 7.3.4 H EAT D EFLECTION T EMPERATURE (HDT) MEASUREMENT .............................................................................. 103 7.3.5 M ICROSCOPY ANALYSIS ........................................................................................................................... 104 7.4 C ONCLUSIONS ............................................................................................................................................... 106 R EFERENCES ....................................................................................................................................................... 107 CHAPTER 8. APPLICATION OF BIO-COMPOSITES INTO AUTOMOTIVE INTERIOR PARTS ................................ 109 8.1 R ESULTS COMPILATION ................................................................................................................................... 109 8.2 P RODUCTION T ECHNOLOGY ............................................................................................................................. 111 8.3 C OMPOSITE S ELECTION ................................................................................................................................... 112 8.4 A UTOMOTIVE PART ........................................................................................................................................ 113 8.5 C ONCLUSIONS ............................................................................................................................................... 114 CHAPTER 9. FINAL REMARKS AND FUTURE WORKS ..................................................................................... 117 9.1 F INAL R EMARKS ............................................................................................................................................ 117 9.2 F UTURE W ORKS ............................................................................................................................................ 118 APPENDIXES ................................................................................................................................................ 119 A.1 D ATASHEET OF P OLYHYDROXYALKANOATE .......................................................................................................... 121 A.2 D ATASHEET OF P OLY (L ACTIC A CID ) ................................................................................................................... 123 A.3 D ATASHEET OF A CYLONITRILE B UTADIENE S TYRENE ............................................................................................. 127 A.4 D ATASHEET OF P OLY P ROPYLENE ...................................................................................................................... 133 A.5 G ENERAL R EFERENCES .................................................................................................................................... 139 A.6 P UBLICATIONS DUE TO THIS WORK .................................................................................................................... 141 Sustainable automotive components for interior door trims xxii Nuno Calçada Loureiro xxiii List of Symbols $ United States Dollar ΔC P [J.ºC.g - 1 ] Heat Capacity ΔH cc [J.g - 1 ] Enthalpy of Cold Crystallization ∆ H   [J.g - 1 ] Enthalpy of melting ΔH m [J.g - 1 ] Enthalpy of fusion σ b [Pa] Blend Maximum Stress σ c [Pa] Composite Maximum Stress σ f [Pa] Fiber Maximum Stress σ m [Pa] Matrix Maximum Stress σ max [Pa] Maximum Stress υ [ ] Poisson Coefficient υ d [ ] Dispersed Phase Poisson Coefficient υ m [ ] Matrix Poisson Coefficient Ø [%] Weight Fraction Ø f ib [%] Fiber Weight Fraction Ø d [%] Dispersed Phase Weight Fraction Ø max [%] Nielson maximum packaging fraction ζ [ ] Einstein Coefficient B [ ] Béla-Pukásnky Load-bearing capacity C P [kJ.(kg.K) - 1 ] Specific Heat at Constant pressure E [Pa] Young’s Modulus E c [Pa] Composite Young’s Modulus E b [Pa] Blend Young’s Modulus E d [Pa] Dispersed Phase Young’s Modulus E f [Pa] Flexural Young’s Modulus E fib [Pa] Fiber Young’s Modulus E m [Pa] Matrix Young’s Modulus H [kJ.kg - 1 ] Enthalpy K [ ] Nicolais-Narkis Interaction Constant Q [kg.h - 1 ] Mass flow rate T c T cc [ºC] Cold Crystallization Temperature T g [ºC] Glass Transition Temperature T m [ºC] Melting Temperature V f [%] Fiber Volume Fraction x c [%] Crystallinity wf w f [%] Weight fraction Sustainable automotive components for interior door trims xxiv Nuno Calçada Loureiro xxv List of Abbreviations A ABS Acrylonitrile Butadiene Styrene ASTM American Society and Testing Materials B bbl barrel BIW Body-in-white BMC Bulk Molding Compound BP Béla-Pukánsky Model BTU British Thermal Unit C CIM Compound Injection Moulding CO 2 Carbon Dioxide D DSC Differential Scanning Calorimetry E ELV End-of-Life Vehicle EU European Union F FAO Food and Agriculture Organization of the United Nations FEUP Faculty of Engineering of University of Porto FRP Fiber Reinforced Plastic H HDT Heat-Deflection Temperature I ICm Ishai and Cohen model ISEP School of Engineering of Polytechnic Institute of Porto ISO International Organization for Standardization ISPGaya Polytechnic Superior Institute Gaya IUPAC International Union of Pure and Applied Chemistry K KUT Kerner-Uemura-Takayanagi Model Sustainable automotive components for interior door trims xxxii Nuno Calçada Loureiro 1 Chapter 1. Introduction 1.1 Introduction The preservation of our environment requires that we stop using materials that will last indefinitely. In the last years the ecological concerns develops a natural interest to the natural materials and eco-solutions. Into the automotive area, researches are exploring natural fibers, such as flax, hemp and kenaf, [1] as an ecoalternative to glass fibers. The Kyoto Protocol has pushed the European Union Member States to find ways to reduce emissions. As expected the transport sector, who in 2004 was responsible for 30% of UK energy-consumption, is one of the first areas to be studied[2]. 1.2 Petrol trend It’s easy to understand that petrol price rules all the other prices. Energy, plastics, assembling lines and metallic materials prices are directly or indirectly connected with the petrol price. It’s possible to verify that in 2008 the financial crises originated by the crash of Lehman Brothers drives to a crash of the oil prices. The financial speculation leads the oil prices to increase and it’s expected that it will continues this trend for the next years. Sustainable automotive components for interior door trims 2 Figure 1.1 – Evolution of Oil Price (source: US Energy Information Administration) Since the plastics use in automotive parts are manly Polypropylene(PP) or Acrilonitrile-Butadiene-Styrene (ABS) and these are petrol-based polymers it’s easy to understand that with the increase of the oil price, the price of PP, ABS and energy will also increase. Figure 1.2 – Evolution of PP price per ton (source: www.plastmart.com) Nuno Calçada Loureiro 3 Figure 1.3 – Evolution of energy price (source: US Energy Information Administration) With all this figures it’s easy to achieve that the future of automotive industry goes to create lighter cars that are not dependent of petrol-based polymers and with engines that will spend less fuel. 1.3 Automotive Components The substitution of automotive components made from glass-fiber composites for the natural fibers composites, in addition to the reduction of the problems due to recycling of the vehicles, drives to a decrease of fuel consumption and gases emission. That means that this substitution contributes for a better life quality. The natural fiber-filled thermoplastics are 35-40% lighter than the glass fiber analogs[1]. Associating the weight decreasing to a better crash absorbance and sound insulation it’s possible to realize the profit achieved when applied to door trims, instrument panels, package trays, glove boxes, arm rests and seat backs. The first attempt to use “natural” composite materials probably was made by Henry Ford in the early 1930s. Henry Ford walked into his company’s research laboratory with a bag of chicken bones, dumped them on the desk and asked his technicians to see what they could make out of them. They responded by experimenting with a variety of natural materials including cantaloupes, carrots, cornstalks, cabbages and onions in a search of materials to build an organic car body. In 1940, Ford scientists discovered that soybean oil could be used to make high-quality paint enamel and could also be molded into a fiber-base plastic. In 1941, composites, particularly those based on natural fibers reinforcements received increased attention. During the World War II, seats and fuselages into aircrafts were made in those materials due to the shortage of aluminum at that time. An example is the “GORDON-AEROLITE” a composite of unidirectional, unbleached flax yarn impregnated with phenolic resin and hot pressed. This material was used in aircraft fuselages. At that time also appears a cotton-polymer composite, which was reportedly the first fiber-reinforced plastic used by the military, for aircraft radar. In 1942, Henry Ford developed the first prototype composite car made from hemp fibers. The car didn’t go to general production due to economic limitations at the time. Sustainable automotive components for interior door trims 4 Between 1950 and 1960 in Europe, the body of the East German “Trabant” car was one of the first to be built form materials containing cotton fibers into a polyester matrix. In 1996, the E-Class vehicle from Mercedes integrates a jute-based door panels. In the last decade, bio-fiber reinforced polymer composites have been embraced by European car makers for door panels, seat backs, headliners, package trays, dashboards, and trunk liners. Table 1.1 – Automotive manufactures, models and components using bio-fibers [3-4] Automotive Manufacturer Model and Application Audi TT, A2, A3, A4, A4 Avant,, A4 Variant (1997), A6, A8 (1997) , Roadster, Coupe: Seat Back, side and back door panel, boot lining, hat rack, spare tire lining. BMW Serie 3, Serie 5, Serie 7: Door insert, Door panels, Headliner panel, boot lining, seat back. Citroen C4 (2001) Daimler - Chrysler Class A, Class C, Class E, Class S: Door panels, windshield, Dashboard, business table, pillar cover panel; Class A, Travego Bus: Exterior underbody protection trim; Class M: Instrumental panel Class S: 27 parts manufactured from bio fibers Fiat Punto, Brava, Marea, Alfa Romeo 146 and 156, Sportwagon Ford Mondeo CD 162 (1997); Focus; Cougar (1998); Mondeo (2000), : Door inserts, Door panels, Bpillar and cover, Boot liner, parcel tray, motor protection (cover under shield) MAN Bus (1997) Mitsubishi Space Star: Door panels; Colt: Instrumental panels Nissan Miscellaneous models Opel / Vauxhall Astra, Vectra, Zafira: Headliner panel, door panels, door inserts, pillar cover panel, instrumental panel, rear shelf panel, column cover; Peugeot New 406 model Renault Clio, Twingo Rover Rover 2000 and others: Insulation, rear storage shelf and panel Saab Coupe (1998): door inserts; door panels SEAT Door panels, door inserts, seat backs Toyota Miscellaneous models Volkswagen Golf A4, Passat Variant, Golf A4 Variant (1998), Bora: Door panel, Door inserts, seat back, boot lid finish panel, boot liner, rear flap lining, parcel tray; Volvo C70, V70, Coupe (1998): Door inserts, parcel tray; Nowadays, in the USA more than 1.5 million vehicles are the substrate of choice for biofibers such as kenaf, jute, flax, hemp and sisal and thermoplastic polymers such as polypropylene and polyester. Bio fibers composites are, nowadays, used also in the exterior components of an automotive. DaimlerChrysler’s innovative application of abaca fibers in exterior under floor protection for passenger cars has been recently recognized. Nuno Calçada Loureiro 5 Figure 1.4 – Automotive door in-liner, instrumental panel made from bio-fiber reinforced composites [4] Figure 1.5 – Under floor protection trim of Mercedes A Class made from banana fiber [4] Other exterior parts (front bumper, under floor trim of bus) from flax fiber reinforced composites will follow. The automotive company Ford is using composites of kenaf fibers and polypropylene for the door panels of the Ford Mondeo. The Mercedes S-Class has, actually, 27 components manufactured in bio-fibers reinforced composites with a total weight of 43 kg representing an increasing of 73% composite weight. Sustainable automotive components for interior door trims 6 Figure 1.6 – Mercedes S Class components made from different bio-fiber reinforced composites [4] Figure 1.7 – Model U Ford Hybrid-Electric Car. Corn based materials are used into the interior roof fabric and floor matting. Soy and corn-derived resins replace carbon black in the tires. Synthetic polyester is use to cover seats [5] Nowadays approximately 18 million of automobiles and Lorries are manufactured in Europe per year. Each unit possesses between 5 to 10 kg of fiber which indicates a potential market of 90.000 to 100.000 tons per year of fiber. Taking into account the 37 million of cars and light vans that are manufactured in the rest of the world the global potential market for natural fibers rises to 250.000 to 500.000 tons per year. Nuno Calçada Loureiro 7 Each automobile is about 8% plastics and composites, which can be translated in around 245 lbs(79kg)/vehicle. [6] The potential of composites materials provide a wide range of parts and components – body panels, suspension, steering and brakes among others. The assessment of the viability of composites in automotive applications is based on the very limited cost information currently available. Figure 1.8 – Cost Structure Comparisons of BIW designs [6] The comparative study, whom some results are presented into figure 1.8, of two composite monocoque Bodyin-white (BIW) indicates that the material cost contributes with 60% for the total cost of carbon fiberreinforced thermoplastics, but contributes only 27% with stell unibody and 29% if used glass fiber-reinforced thermosets. The next table compares the costs of various BIW designs on USD/lb basis. Table 1.2 – Cost Component comparisons of various BIW designs (USD/lb) [6] BIW Design Material Labor Eqpt Tooling Other Total Steel Unibody 0,60 0,42 0,37 0,40 0,45 2,24 Glass-reinforced Thermoset Monocoque 1,38 1,64 0,36 0,57 0,74 4,68 Carbon-reinforced Thermoplastic Monocoque 4,55 1,61 0,30 0,44 0,65 7,55 (source: Dieffenbach et al. (1996a)) The recyclability of thermoplastics shows a great promise but the work should develop the cost-effective means of recycling including the fiber separation. Sustainable automotive components for interior door trims 8 1.4 The future for Automotive Components Faced with pressures to produce fuel-efficient, low-pollution vehicles and “green” cars, the automotive industry is looking for eco-friendly composites. The usual composites present a polluted and intensive energy production. Glass, carbon and aramid fiber reinforced polyester, epoxy or similar resins are difficult to recycle and hard to dispose. [5] The European Union regulations require that, by 2015, all new vehicles should be 95% recyclable. For that the use of thermoplastics, that can be thermally recycled to produce new products, will be good solution for that. For reinforce instead using the non-recyclable common fibers, the automotive manufactures are also seeking for new materials. The new generation of fibers, based on agricultural products is already being in with mechanical properties that are suitable for some automotive applications. Table 1.3 – Comparison of properties of various natural and synthetic fibers [5] Fiber Specific Gravity [g.cm -3 ] Tensile Strength [GPa] Specific Strength [GPa/(g.cm -3 )] Tensile Modulus [GPa] Specific Modulus [GPa/(g.cm -3 )] Spruce pulp 0,60 0,98-1,77 1,63-2,95 10-80 17-133 Sisal 1,20 0,08-0,50 0,07-0,42 3-98 3-82 Flax 1,20 2,00 1,60 85 71 E-Glass 2,60 3,50 1,35 72 28 Kevlar® 49 1,44 3,90 2,71 131 91 Carbon (standard) 1,75 3,00 1,71 235 134 Lightweight, strong and low-cost the bio-fibers are poised to replace glass and mineral fillers in numerous interior parts. [4] In the last decade, bio-fiber reinforced polymer composites have been embraced by the European car manufactures for several interior parts (door panels, seat backs, headliners, package trays, dashboards, trunk liners, etc). This trend reaches actually the North America. In the USA more than 1,5 million vehicles are the substrate of choice for biofibers. On average each automotive can use around 20 m 2 of fibers or fabrics, woven or non-woven based composites. This is an increasing trend due to the advantages of lightweight, high strength and day-by-day lowering costs of textile products [4]. The European and North American market for bio-fibers reinforced plastics composites reached 685000 ton in 2002 with a value of 775 million USD. The major automotive manufacture European country – Germany – is increasing the consumption of bio-fibers (from 4000 ton into 1996 to 18000 ton into 2003). Nuno Calçada Loureiro 9 Figure 1.9 – Total consumption of bio-fibers within Western Europe; 2005 and 2010 are predictions [4] Many automotive components are now made from bio-fiber reinforced composite materials. However, these composites present a thermoplastic matrix but not a biodegradable one. That drives us to a stage that the automotive part can be reutilized, reprocessed but not decomposed without affecting the environment. Figure 1.10 – LFTs applications in automotive parts [7] Long fiber reinforced thermoplastics (LFT), used primarily in automotive applications, continue to show strong growth as they replace metal, short fiber reinforced thermoplastics, and thermoset plastics such as SMC and BMC. R. Babinsky [7] estimates consumption was 160.000 – 190.000 metric tons of LFTs in 2006. The same study estimates that in North America and Europe, about 80% of the regional volume of LFTs goes into automotive applications. Sustainable automotive components for interior door trims 16 • Thermosets - These polymers when heated, suffer irreversible chemical reactions that origin intermolecular cross-connections. The result is a reticulated structure which is infusible; • Thermoplastics – These polymers when heated melts, and they can be heated and cooled anytime. These polymers, due to these characteristic, can be processed by the traditional methods: Injection, extrusion and rolling; The properties of the engineering plastics are strictly connected with the raw-monomer and the chemical reaction used to produce the polymer. Nowadays it’s possible to process polymers by three chemical processes: • Polyaddition – The monomers presents a double-connection carbon-carbon. In this process, the formation of sub-products doesn’t exist and the final molecular weights can reach a magnitude of 10 5 - 10 6 ; • Polycondensation - In this process, the formation of sub-products exists, and these sub-products must be removed of the reaction environment. The molecular weights reach a magnitude of 10 4 ; • Chemical modification – This process consists in the polymers chemical modification. The changes on the molecular weight, the physical and mechanical behavior of the modify polymers allows a hugh diversification of the polymers applications; As said before theses polymers can be divided into three groups: Elastomers, thermoplastics and thermosets. Figure 2.4 - European Plastics Demand by Segment and resin type 2011 2 2 Source: PlasticsEurope Market Research Group (PEMRG) Nuno Calçada Loureiro 17 As already related into Chapter 1, the automotive industry is using thermoplastic polymers for the automotive plastic parts. For that reason the focus will be settled on this kind of materials. 2.2 Biodegradable Polymers Biodegradable polymers (biopolymers) are thermoplastic polymers obtained from renewable resources, synthesized microbially, or synthesized from petroleum-based chemicals. Through blend of two or more biopolymers a new biopolymer may be designed for specific requirements. Thus biodegradability is not only a function of origin but also of chemical structure and degrading environment. Biodegradable polymers can be define as those polymers that are capable of undergoing decomposition primarily through enzymatic action of microorganisms in to CO 2 , methane, inorganic compounds, or biomass, in a specified period of time. As seen into figure 2.5, it’s possible to obtain several biopolymers from different sources, even from petrol. Figure 2.5 - Classification of Biopolymers [1-2] Sustainable automotive components for interior door trims 18 The automotive industry, as discussed into Chapter 1, is trying to have green parts. For achieving that objective its necessary not only that the polymer presents biodegradable properties but also that the origin is also green, reason why the present state-of-art will focus the renewable source polymers only. Originally, biopolymers were intended to be used in packaging industries, farming, and other applications with minor strength requirements. The basic idea behind the biopolymers is taken from nature’s cycle. Every year 100 billion of tones of organic material are generated by photosynthesis all over the globe. Most of this material is converted back into starting products, carbon dioxide and water by micro-organisms. This cycle is the role-model for biopolymers, which are made from renewable raw materials obtained from agricultural production or agricultural sub-products or waste. When the biopolymer parts as reach its end, it can be composted, closing the loop. Figure 2.6 - Ideal closed loop life-cycle of biodegradable products [1] The, yet, high cost of biopolymers and the performance limitations are major barriers for the widespread acceptance as substitute for traditional non-biodegradable polymers by the biodegradable polymers. However the high cost is not due to the raw material but it is mainly attributed to the low volume of production. Nuno Calçada Loureiro 19 2.2.1 Biodegradable Polymers used The use of biodegradable polymers from renewable resources to replace the petro-source polymers is increasing worldwide. The actual growing of petroleum cost and the overuse of landfills combined with environmental factors and policies are making a swift on the general sense of the use of biopolymers[3]. Several biopolymers and their blends are being used into a large spectrum of utilities. This new type of polymers allied to the life-cycle-analysis is making a turnover in the polymer industry. However, it’s mandatory to find biopolymers blends with properties that fulfill the product´s technical specifications at a low price, decreasing the ratio price/quality. From the universe of biodegradable polymers from natural resources, the Polyhydroxyalcanoate (PHA) presents mechanical properties that can replace a large spectrum of petro-source polymers, namely in the automotive industry. However, due to its actual price, the solution isn’t economically viable for mass consumption. Polylactic acid (PLA) is a lower cost polymer but does not meet fully the requirements of polymers for automotive components, for example, in terms of temperature resistance. To make a competitive solution is necessary to reduce the price of the final polymer. One way is to blend PHA with a less expensive biopolymer, such as PLA. Most of the biodegradable polymers contain hydrolysable linkages such as amide, ester, urea and urethane along the polymer chains. However, the use of aliphatic polyesters (such as PLA) due to their useful biodegradability and their versatility regarding physical, chemical and biological properties is most attractive. 2.3 Poly(Lactic Acid) Poly(lactic Acid) (PLA) is a polymer derived from lactic acid (2-hydroxy propionic acid). PLA is a rigid thermoplastic biodegradable polyester polymer that can be semi-crystalline or totally amorphous, depending on the stereopurity of the polymer backbone. PLA is the first commodity polymer produced from annually renewable resources. The PLA production presents numerous advantages: 1It can be obtained from a renewable agricultural source – corn, sugarcane, starch; 2The production consumes carbon dioxide; 3It provides significant energy savings; 4The PLA is recyclable and compostable; 5It can help improve farm economies; 6The physical an mechanical properties can be manipulated through the polymer architecture; The next figure presents a life-cycle model of PLA. Sustainable automotive components for interior door trims 20 Figure 2.7 - Life-cycle model of PLA [4] 2.3.1 PLA Production The PLA can be manufactured by carbohydrate fermentation or chemical synthesis. In 1780 the first building block of PLA that was isolated from sour milk by the Swedish chemist Scheele and the first commercialization has been in 1881. [5] Lactic acid is the simplest hydroxyl acid with an asymmetric carbon atom and it exists in two optically active configurations, the L (+) and D (-) isomers. Figure 2.8 - Polymerization of L-Lactic acid to L-PLA by direct condensation or by ring opening via the L-lactide [6] Nuno Calçada Loureiro 21 The L-Lactic Acid (2-hydorxy propionic acid) is the simplest hydroxyl and the natural and most common form of this acid. The asymmetric carbon atom drives to production of two optical isomers: the L-Lactic Acid (+) produced by mammalian and the D-Lactic Acid (-) produced by mammalian and other microorganisms. Figure 2.9 - Chemical Structure of L (left) and D (right) Lactic Acid [4] The lactic acid is made by bacterial fermentation of carbohydrates. The fermentation processes to obtain lactic acid can be classified according to the type of bacteria used. In the Heterofermentative method less than 1.8 moles of lactic acid per mole of hexose is produced along with significant levels of other metabolites such as acetic acid, ethanol, glycerol, mannitol and carbon dioxide. In the Homofermentative method an average of 1.8 moles of lactic acid per mole of hexose and minor levels of other metabolites are produced. This conversion yields 90 g lactic acid per 100 g glucose. Since homofermentative pathways lead to greater yields of lactic acid and lower levels of byproducts, these pathways are mainly used by industry. The majority of the fermentation processes nowadays use a genus of Lactobacilli which yields a high rate of lactic acid. These bacteria are classified as homofermentative, and the general processing conditions include a pH of 5.4 to 6.4, a temperature of 38 to 42 ºC and a low oxygen concentration. The main sources are, in general, simple sugars such as glucose and maltose from corn or potato, sucrose from cane or beet sugar and lactose from cheese whey. The production rate depends of the production type. Generally, batch processes produce 1 to 4,5 g /(l.h) of lactic acid while continuous processes produce 3 to 9,0 g/(l.h) . It’s possible to reach a rate of near to 76 g/(l.h) if it’s use cell recycle reactors. Sustainable automotive components for interior door trims 22 Figure 2.10 – Non-solvent process to prepare Poly(Lactic Acid) [4] In order to produce PLA for industrial processes is necessary that the polymer possess adequate thermal stability to prevent degradation and maintain the molecular weight and properties. PLA undergoes thermal degradation at temperatures above 200 ºC by hydrolysis, lactide reformation, oxidative main chain scission and intraor intermolecular transesterification reactions. [5] The PLA homopolymers presents a T g around 55ºC and a T m of 175ºC. 2.3.2 PLA Properties PLA is a unique polymer that in many ways behaves like PET, but also performs a lot like PP. The properties of PLA are determined by the polymer architecture (i.e. the stereochemical makeup of the backbone) and the molecular mass, which is controlled by the addition of hydroxylic compounds. The ability to control the stereochemical architecture allows a precise control over the speed of crystallization and the degree of crystallinity. That ability allows, also, the control of the mechanical properties and the processing temperatures of the material. It’s possible also to control the degradation behavior since it is strongly dependent of the crystallinity of the polymer. Due to its good strength properties, film transparency, biodegradability, biocompatibility and availability from renewable sources, the PLA is commercially interesting. The physical characteristics of PLA are very dependent on its transition temperatures for common qualities such as density, heat capacity and mechanical and rheological properties. Nuno Calçada Loureiro 23 In the solid state PLA can be either amorphous or semicrystalline depending on the stereochemistry and thermal history. For the amorphous PLA the glass transition temperature (T g ) determines the upper use temperature for most commercial applications. Figure 2.11 – Metastable states of amorphous PLAs [4] For semicrystalline PLAs, both T g (aprox. 58 ºC) and melting point (T m ), 130-230 ºC are important for determining the use temperatures across various applications. T g and T m are strongly affected by the overall optical composition, primary structure, thermal history and molecular weight. Figure 2.12 – Metastable states of semicrystalline PLAs [4] 2.3.3 PLA Biodegradation As mentioned earlier, the biopolymers are polymers that are chemically synthesized or biosynthesized during growth cycles of all organisms. Some micro-organism and enzymes, already identified, are capable of degrading them. Under typical use conditions, PLA is very stable and will retain its molecular weight and physical properties for years. However under conditions of high temperature and high humidity PLA will degrade quickly and disintegrate within weeks to months. PLA and its copolymers degrade to non-toxic breakdown products under certain conditions of temperature and moisture content. The degradation occurs initially by a non-enzymatic hydrolytic process. However the mass and the shape of the PLA part can be preserved until extensive degradation has taken place. Sustainable automotive components for interior door trims 24 The primary mechanism of degradation is hydrolysis and cleavage of the ester linkages in the polymer backbone, followed by bacterial attack on the fragmented residues. In the initial phase, the high molecular weight polyester chains hydrolyze (to a lower molecular weight oligomers) and after water penetration this molecular weight decrease rapidly due the PLA solubility in water only at very low molecular weight. Figure 2.13 – PLA Hydrolysis and molecular weight loss [4] The rate of hydrolysis is determined by its intrinsic rate constant, water concentration, acid or base catalyst, temperature and morphology. Since PLA is very water permeable this hydrolysis reaction is autocatalytic. Figure 2.14 – Autocatalytic Hydrolysis reaction [1] In the next steps of the degradation several enzymes can catalyze PLA hydrolysis. The most common enzymes are the Proteinase K, Pronase and Bromelain. The enzymes are large molecules and are unable to diffuse through the PLA crystalline regions. Enzymatic involvement can produce pores and fragmentation making more polymer regions accessible to the enzymes. Nuno Calçada Loureiro 25 2.3.4 PLA Based Composites The PLA composites can be categorized into two different groups: one in which products are mainly used in the field of medical applications and a second group in which applications are in the field of structural plastics intended for other uses. PLA composites for medical applications have often been reinforced with bioactive mineral fillers like zirconia, magnesium oxide, tricalcium phosphate or hydroxyapatite. The reinforced by carbon fibers is also used. The main reason for the use of these types of composites is to mimic the mechanical properties and behavior of the bones in surgical applications. There are several reasons to use PLA as a matrix into natural fiber biocomposites. • PLA is nowadays the most advanced biopolymer in terms of commercialization; • PLA has good mechanical properties that are similar to those of the polystyrene; • PLA can be melt-processed with standard processing equipments at temperatures below those at which natural fibers start to degrade; There are innumerous studies of PLA composites. Bledzki and Jaszkiewicz studied the composites of PLA reinforced with Jute, Abaca or Man-made cellulose. [7] They concluded that by adding 30% (wf) of man-made cellulose, an increase in tensile strength of up to 50% can be achieved, and in average it’s possible to obtain an improvement of around 30%. Figure 2.15 – Stress-strain curves of the tested composites [7] Oksman, Skrifvars and Selin [8] investigates if PLA can be used as matrix in composite systems where natural fibers are used as reinforcements. They concluded that PLA works very well as matrix material for natural fiber composites. The composite strength is about 50% better compared to similar PP/flax fiber composites, which are used today in many industrial applications. The stiffness of PLA is increased from 3.4 to 8.4 GPa with an addition of 30 wf.% flax fibers. Generally these results indicate that PLA natural fiber composites have mechanical properties high enough for use instead of conventional thermoplastic composites. Sustainable automotive components for interior door trims 32 This new dilemma drives to the re-born use of natural fibers, not only for the applications from the past, but also to produce new composite materials. The use of natural fibers from vegetable sources in the production of composite materials has increasing during the last decade, especially into the automotive industry. Due to the commitment between the resistance, stiffness and weight, the composites reinforce with natural fibers form vegetable sources are competing with the “conventional composites” in particular with the ones that are reinforced with glass-fiber. Natural fibers such as flax, hemp, jute, sisal or cotton are from renewable nature, cheaper, with a minor density, have better specific stiffness and a minor environmental impact since that they are biodegradable and easily recyclable. Table 2.4 - Mechanical Properties of Natural Fibers [6] [21] Fiber Specific Gravity Tensile Strength (MPa) Modulus (GPa) Elongation at break (%) Specific Modulus Jute 1,3 393 55 1,16 - 1,5 38 Sisal 1,3 510 28 3 – 7 22 Flax 1,5 344 27 2,7 – 3,2 50 Sunhemp 1,07 389 35 --- 32 Pineapple 1,56 170 62 --- 40 The natural fibers presents some limitations than need to be resolve so they can effectively compete with glass fibers. The three major limitations are: • The weak interfacial adhesion with the synthetic polymers – specially the thermoplastics; • The high capability of water absorption; • The low thermal resistance due to its organic nature; To overcome these limitations, the natural fibers can be submitted to superficial treatments that allows the development of composites with good mechanical properties, bigger durability and reliability due to the operating conditions. 2.5.1 Fibers Classification Natural fibers are subdivided based on their origins as expressed into figure 2.20: Figure 2.20 - Fibers classification [1] [22] Nuno Calçada Loureiro 33 All plant fibers (vegetable) are composed of cellulose while animal fibers consist of proteins (hair, silk and wool). Plant fibers can include bast (or stem) fibers, leaf or hard fibers, wood, cereal straw and other grass fibers. Natural fibers can be compared with a composite material consisted by cellulose fibrils embedded in lignin matrix. [17] The cellulose fibrils are aligned along the length of the fiber, and the reinforcing efficiency is related to the nature of cellulose and its crystallinity. Table 2.5 - Commercially Important Fiber Sources [1] Fiber Species World Production (10 3 ton) Origin Wood ( >10,000 species) 1,750,000 Stem Bamboo ( > 1,250 species) 10,000 Stem Cotton lint Gossypium sp. 18,450 Fruit Jute Corchorus sp. 2,300 Stem Kenaf Hibiscus cannabinus 970 Stem Flax Linum usitatissimum 830 Stem Sisal Agave sisilana 378 Leaf Roselle Hibiscus sabdariffa 250 Stem Hemp Cannabis sativa 214 Stem Coir Cocos nucifera 100 Fruit Ramie Boehmeria nivia 100 Stem Abaca Musa textiles 70 Leaf The vegetable/plant fibers can be further sub-divided into subgroups, as showed in the next figure: Figure 2.21Vegetable fiber classification [1] The most important of the natural fibers in terms of automotive industry are, with no doubt, the stem fibers subgroup. They are called by that name because their origin is the stem of the plant. The plant stem is composed of an inner woody core surrounded by bundles of long hollow fibers and an outer protective skin. Sustainable automotive components for interior door trims 34 Figure 2.22 – Structure of biofiber [22] Since the main function of the stem is to stabilize the plant, it’s logical that the stem have plant fibers with good mechanical properties. This attribute in conjunction with a low density ensures that stem fibers have the potential to be outstanding reinforcements in lightweight composite parts. The advantages of using stem fibers in the automotive industry are: • Renewable and sustainable plant fiber resource; • Recyclable; • Weight saving between 10 and 30%; • Cost savings; • Abundant supply which is accessible to car manufacturing plants in many regions of the world; Table 2.6 – Fiber characteristics and growing area of commercially available fibers [4] Nuno Calçada Loureiro 35 Nowadays an increasing market is appearing due to the vegetable fibers. Figure 2.23 - Total consumption for natural fibers in Europe [1] The world’s supply of natural resources is being depleted, the demand for sustainable and renewable materials continues to rise. Figure 2.24 - Use of natural fibers in the German automotive industry 1996– –– –2002 (tonnes) [33] 2.5.2 Cellulosic fibers: Advantages and Disadvantages The biofiber world is full of examples where cells or groups of cells are designed for strength and stiffness. Cellulose is a natural polymer with high strength and stiffness per weight, and it’s the building material of long fibrous cells. Sustainable automotive components for interior door trims 36 In general, the fiber consists of a wood core surrounded by a stem. Within the stem there are a number of fiber bundles, which contain individual fiber cells or filaments. These filaments are made of cellulose and hemicellulos, bonded together by a matrix, normally lignin or pectin. The principal differences between the individual fibers are: fiber qualities, lignin content and odor. The increasing of interest in lignocellulosic fibers is due mainly to their economical production with few requirements for equipment and low specific weight, which results in a higher specific strength and stiffness when compared to glass reinforced composites. The biofibers, such as the cellulosic fibers, are nonabrasive to mixing and molding equipment. They have a positive environmental impact and with a production that requires little energy. However the inherent polar and hydrophilic nature of lignocellulosic fibers and the non-polar characteristics of the common thermoplastics results into a compounding difficulties leading to non-uniform dispersion of the fibers within the matrix which impairs the efficiency of the composite. This is probably the major disadvantage of biocomposites. Another problem is related to the processing temperatures that for this type of fibers are restricted to 200 ºC once that the vegetable fibers degrade at high temperatures. This will frame the matrix choice. Another setback is the high moisture absorption of the biofibers leading to swelling and presence of voids at the interface, which leads to a poor mechanical properties and reduces dimensional stability of the composites. Is clear that the advantages outweigh the disadvantages and most of the shortcomings have remedial measures in the form of chemical treatments. 2.5.3 Cellulosic fibers: Portuguese Market and Extraction Technology The best way to obtain cellulosic fibers is to use the pulp wastes from the paper plants. In the north of Portugal and in the Galiza region (Spain) is possible to count 824000 ha of Pine trees and 468000 ha of Eucalyptus trees. [23] To process and transform the wood in paper this euro-region counts with 9 industrial plants. From these 9 plants, 2 are thermochemical paper pulp plants. The other 7 can be divided in 5 plants to produce MDF and 2 to produce fiberboard. Nuno Calçada Loureiro 37 Figure 2.25 – Northern Iberian Peninsula Wood Transformation Plants Geo-localization [23] The process to extract fibers from the wood is a chemically heavy and requires a parallel system to purify the produced wastes to decrease the environmental impact. The process is quite similar if we are extracting pine fibers or eucalyptus fibers. The main differences are at the chemical compounds used. In figure 2.26 it’s presented a simplified diagram of a typical pulp and paper process. For composite applications the fibers don’t goes through all process described but after bleaching the pulp goes to the secondary market pulp. Sustainable automotive components for interior door trims 38 Figure 2.26 – Simplified diagram of a typical pulp and paper process [24] Nuno Calçada Loureiro 39 2.6 Composite Materials A Composite Material (or composite) can be defined as a micro or macroscopic combination of two or more distinct materials. The association of these materials aims to create a new material with better properties than the ones who origin it. The composite materials exist and they are being used for several centuries. Probably the oldest reference to composite materials appears in the Holly Bible, and describe that the Jewish slaves are forced by the Egyptians to produce bricks from the mixture of straw and mud. 5 In the VII Century the Japanese sabers were made by steel and iron. Nowadays it’s possible to find composite materials everywhere, starting in the glass of our house windows, passing by the concrete use in construction. The composite materials are, technically, heterogeneous and anisotropic materials and that means that the mechanical properties are depending of the direction and the place where the solicitation occurs. Typically, a composite material is constituted by a matrix - a homogeneous resin or polymer material, and reinforcement – a strong material bonded into the matrix to improve its mechanical properties. 2.6.1 Matrices The purpose of a Composite Matrix is to bind the reinforcement together. This binding is made due to the cohesive and adhesive characteristics of the matrix material. When under load, resins may microcrack and craze. Due to the coalescence of microcracks, the matrix may form larger cracks. It’s also possible to have a debonded of the reinforce fiber. If anyone of these factors occurred it’s possible to have a composite with properties far lower than the desired ones. That’s way the matrix is the “weak link” of any composite material. Nonetheless, the matrix resin provides many essential functions. The composite matrix is responsible for keep the reinforce into the proper orientation and position, to distribute the load more or less evenly among the fibers, provides resistance to crack propagation and damage, and also provides all of the interlaminar shear strength of the composite. Furthermore, it’s matrix responsibility the overall service temperature limitations. 5 Exodus 5,7 Sustainable automotive components for interior door trims 40 2.6.2 Reinforcements One of the objectives of the reinforcements is to support most of the load that are applied into the composite material. Since the reinforcements are, by default, fragile materials they don’t contribute to the impact behavior of the composite. However, the reinforcements are more rigid and stiffener than the matrix material. These characteristics give to the composite a high mechanical behavior. To a material reinforce effectively a matrix, it must have the following characteristics: • A Young Modulus higher than the matrix (minimum twice bigger); • Tensile Stress bigger than the matrix tensile stress; • A geometry that allows the combination with the matrix and with the final form of the part; • Have a good adhesion with the matrix; • Don’t react chemically with the matrix; Normally, the reinforce addition, occurs to improve the mechanical behavior, stiffness, corrosion resistance, thermal conductivity, creep and fatigue resistance. 2.6.3 Thermoplastic Matrix Composites The composites can be divided into classes in various manners. The first division, and the most common one, is to dived by the matrix material. In this case the division is thermoplastic matrix composites and thermoset matrix composites. Other division is too dived by the reinforce material. In this case the division is much more complex since it’s possible to have an innumerous number of reinforce materials. Thermoplastic resins are potentially useful as matrices for advanced composites. Thermoplastic resins present three advantages when compared to thermosets resins. • Processing can be faster since no curing reaction is required. Thermoplastic composites only require heating, shaping and cooling; • The mechanical properties are attractive, in particular, high delamination resistance and damage tolerance, low moisture absorption and the excellent chemical resistance of semicrystalline polymers; • Thermoplastic composites offer advantages in terms of environmental aspects. They have very low toxicity since they do not contain reactive chemicals (therefore storage life is infinite). Because it is possible to remelt and dissolve such thermoplastics, their composites are also easily recycled or combined with other recycled materials; In the automotive industry, thermoplastic composites are used extensively, because they allow fast processing cycles for fairly large components. In the field of injection molded components, the thermoplastic composites, normally, are used with short fibers (5-10mm) in molding pellets. Nuno Calçada Loureiro 41 Thermoplastics resins can have an amorphous or a semi-crystalline structure. If the structure is amorphous, the polymer chains don’t present long-range order, which may be viewed as polymer glasses and, in the absence of color pigments, these polymers, are usually transparent. On the other hand, crystalline polymers have regions of molecular order. Due to the large size of polymer chains inhibits the perfect crystallization; the crystalline thermoplastics correctly must be described as semi-crystalline, since the degree of crystallinity never reaches 100%. So, the semi-crystalline thermoplastics are really a two-phase materials with a crystalline and an amorphous phase. Table 2.7 - Characteristic temperatures for thermoplastic resins [25] Polymer IUPAC designation Structure T g (ºC) T m (ºC) Processing Temperature (ºC) Polyamide 6,6 PA6,6 Crystalline 55 265 270-320 Polyamide 12 PA12 Crystalline 35 180 220-260 Polyamide-imide PAI Amorphous 275 None 350-400 Polybutylene terephthalate PBT Crystalline 20 240 260-290 Polycarbonate PC Amorphous 150 None 280-330 Polyether Ether Ketone PEEK Crystalline 143 343 380-400 Polyetherimide PEI Amorphous 217 None 335-420 Polyether-sulphone PES Amorphous 220 None 300-320 Polyethylene terephthalate PET Crystalline 70 265 280-310 Polyphenylene Sulfide PPS Crystalline 90 280 300-340 Polypropylene PP Crystalline -10 165 200-240 Polysulphone PSU Amorphous 190 None 300-350 The use of polymer composites is of great interest in the view of a more intelligent utilization of environmental and financial resources. Several works have being done to create full biodegradable composites by the replacement of the petrol-based polymers and synthetic fiber reinforcement for renewable-source polymers and fibers. These green composites, yet, presents some limitations regarding mainly ductility, processability and dimensional stability [26]. It can be stated that the commercial market is still in an opening phase (especially in Europe) for these types of composites. Therefore much can still be done in order finding new applications, improving the properties, the appearance and the marketability of these materials. All of these issues require, and continue to require, significant research efforts in order to: • find new formulations (virgin or recycled polymers, traditional or biodegradable polymers; type, appearance, quality and amount of the fillers); • Correctly characterize at all terms the new composites; • Apply them for the most suitable applications; • Refine and readjust the processing techniques. As soon as the market for these composites increases, reduction of costs and improvement of the quality will be achieved. Sustainable automotive components for interior door trims 48 Nuno Calçada Loureiro 49 Chapter 3. Motivation, Objectives and Research Approach 3.1 Motivation and objectives The motivation of this work arises the fact that all the OEM’s are trying to input more eco-friendly materials into the cars. Although the research on this area is hugh it is focus on natural fibers composites or petrol-based thermoplastics so they can achieved the legal imposed environmental indexes without using the petrol-based polymers. The use of only one renewable-source polymer will drive us to a much more expensive polymer. The main objectives of this work are easy to state. It’s necessary to develop a new composite material that possesses the minimal properties to replace the petrol-based polymers used into the interior door trims. That new composite must be processed by the usual technological process for manufacturing these type of pieces – injection molding. Allied to that, this new composite material must be biodegradable and must have a renewable-source origin. 3.2 Research Approach This section describes the research approach used to achieve the goal of this thesis. As already describe into chapter 2, the PLA is the cheaper biodegradable polymer. However the neat PLA doesn’t fulfill all the interior door trims requirements. The blending with PHA tries to reach the mechanical requirements. The PLA/PHA blends have the mechanical capability to replace the used petrol-base polymers but in terms of service temperature stays lower than the required value. The incorporation of cellulosic fibers will try to improve the service temperature and mechanical behavior. Sustainable automotive components for interior door trims 50 Once that the idea is to optimize a three material composite, the combinations of the three components can be translated into an enormous sets of samples, tests and data analysis that can take too much time to analyses. Figure 3.1– Variable interaction for reaching the optimal solution As possible to conclude by analysis the figure 3.1, to reach to a good substitute of the petrol-based polymers actually in use for interior door trims, it’s necessary to make a composite with a polymer blend as a matrix and the correct weight fraction of cellulosic fibers. The approach that is been chosen starts with a two variable model, and with that the matrix polymer blend will be optimize. After that the weight fraction of fibers will be determined based into a one variable model. Since the matrix is responsible for the mechanical behavior of the composite the blended polymer matrix will be optimized comparing the mechanical behavior with the mechanical behavior of the actual polymers used into interior door trims. After that, the thermal behavior will be optimized by the addiction of the fibers. All the tests were performed taking account the ASTM or ISO standards. For the matrix, eleven different samples were prepared, with intervals of 10% of variation of the phases, starting in pure PHA samples and ended in the pure PLA samples (PHA/PLA ratios of [100:0] to [0:100]). The values between the ratios were extrapolated from the nearby data. After chosen the best PHA/PLA ratio, the introduction of the fibers starts with the best PLA/Fiber ratio described in the literature (20% wf) [1] and, after that, a ± 10% fiber weight fiber were tested. The data extrapolation will give us the best matrix/fiber ratio. The research approach can be summarized into the next figure. Nuno Calçada Loureiro 51 Figure 3.2 – Scheme of thesis research strategy 3.3 Thesis Structure To reflect all this research work, this thesis starts, in chapter 1, to explain the motivation that energizes all the work. In chapter 2 it’s presented the literature review of all topics that are related with this work and in chapter 3 it is presented the path to reach the final objective. The used materials and the performed tests and specifications are presented into chapter 4. Chapter 5 and chapter 6 presents, respectively, the mechanical and morphological characterization of PHA/PLA blends that drives to the selection of the best composite matrix. Chapter 7 presents the study of the fiber incorporation and the selection of the best matrix/fiber relation. On chapter 8 the production of a demonstration part is related. This work ends in, chapter 9, with the final remarks and the indication of some future works that might be done. Sustainable automotive components for interior door trims 52 References [1] D. Guimarães, Efeito das condições de injecção nas propriedades de PLA reforçado com fibras celulósicas, Master Thesis in Polymer Engineering, University of Minho, Portugal (2009) Nuno Calçada Loureiro 53 Chapter 4. Materials and Methods This chapter describes the materials, experimental protocols and characterization techniques used in this thesis. 4.1 Materials 4.1.1 Polyhidroxyalkanoate – PHA The Polyhydroxyalkanoate used is produced by Natureplast® (France) under the trade name PHI002. PHI002 is a thermoplastic resin of PHA made from bacterial fermentation and is specifically developed for injection molding. The detailed datasheet can be found in the Appendix A.1. However, the main properties are transcribed into table 4.1 Table 4.1 – PHA Technical data Melt temperature (ºC) 145 - 155 Degradation temperature (ºC) 200 Tensile Strength at break (MPa) 35 Tensile elongation at break (%) 2 Tensile Modulus (MPa) 2950 HDT A (1,8 MPa) (ºC) 72,5 Density 1,25 (±0,05) MFI (190 ºC/2.16 kg) (g/600 s) 15-30 Sustainable automotive components for interior door trims 54 4.1.2 Poly(Lactic Acid) – PLA The Poly(Lactic Acid) used is produced by NatureWorks LLC® (USA) under the trade name INGEO biopolymer 3251D. INGEO 3251D is designed for injection molding applications. This grade presents a higher melt flow capability and a higher flow capability. The detailed datasheet can be found in the Appendix A.2. However, the main properties are transcribed into table 4.2 Table 4.2 – PLA Technical data Melt temperature (ºC) 188 - 210 Tensile Strength at break (MPa) 48 Tensile elongation at break (%) 2,5 Density 1,24 MFI (190 ºC/2.16 kg) (g/600 s) 30-40 4.1.3 Cellulosic Fibers The cellulose fibers used in this work come from the Portucel Kraft paper factory, located in Viana do Castelo and it origin is the Eucalyptus Globulus trees. They have been removed of the production line after the final chemical treatment and before enter in the paper production line, which means that the fibers were bleached and disintegrated. The bulk fibers are composed essentially of cellulose (~85%) and glucuronoxylan (~15%). The main properties are expressed into table 4.3 Table 4.3 – Eucalyptus Globulus fiber general properties [1-2] Average fiber diameter (μm) 10,9 Average fiber length (mm) 0,66 Tensile Strength at break (MPa) 160 Tensile elongation at break (%) 5,2 Tensile Modulus (GPa) 17,4 Flexural Modulus (GPa) 16 Flexural Strengh at break (MPa) 130 Density 1,6 4.1.4 Preparation of the Blends The polymers were dried into an oven ate 60ºC for 24 hours before processing and kept into separate Ziploc bags. Just before the injection, the polymers are weighed and then mix into a rotational chamber. When the mixture period ends the blend is injected into a Ferromatik Milacron K85 injection machine, being produced tensile test specimens. Nuno Calçada Loureiro 55 The mold temperature was 20 ºC and the injection temperature profile is described in figure 4.1. Figure 4.1 – Injection Temperature profile The temperature profile was established by combining the melting temperature of the polymers, the degradation temperature and the injection molding conditions suggested by the supplier´s datasheets. The other injection parameters were the following: injection velocity: 20 mm/s (corresponding to an injection flow rate of 6,3 cm3/s). Eleven different samples were prepared with intervals of 10wt% of variation of the material´s ratios: PHA/PLA ratio of: [100:0] (pure PHA), [90:10], [80:20, [70:30], [60:40], [50:50], [40:60], [30:70], [20:80], [10:90] and [0:100] (pure PLA). The blends were injection molded in the form of specimens with dimensions according to the respective standard. Figure 4.2 – Used tensile specimen injection mold 4.1.5 Preparation of the Composite Material To prepare the Bio-composite the process used was the same of the preparation of blends. However before injection it was necessary to extrude the bio-composite and palletize it. The extrusion takes place into a twin screw Coperion Extruder (Werner & Pfleiderer). Figure 4.3 – Coperion Extruder Sustainable automotive components for interior door trims 56 The extruder temperature profile used is expressed into figure 4.4. Figure 4.4 – Extruder Temperature Profile This particular equipment possesses three independent hoppers, one for each component. Figure 4.5 – Hoppers System Adjusting the feeding throat of each hopper it’s possible to adjust the weight fraction of the extruded composite. The used mass flow rate is expressed into table 4.4. Table 4.4 – Extrusion flow rates Q total Q PHA Q PLA Q Fiber 90% Matrix / 10% Fiber 4 kg/h 1,08 kg/h 2,52 kg/h 0,4 kg/h 80% Matrix / 20% Fiber 4 kg/h 0,96 kg/h 2,24 kg/h 0,8 kg/h 70% Matrix / 30% Fiber 1 kg/h 0,21 kg/h 0,49 kg/h 0,3 kg/h After the composite extrusion, material goes to extruder incorporated palletizer to be catted and the keep it into Ziploc bags until starts the injection preparation procedure. Nuno Calçada Loureiro 57 Figure 4.6 – Palletizer cutting System 4.2 Determination of Mechanical Properties 4.2.1 Tensile Test The measurement of the tensile properties was made according to ASTM D638. For that it has been used a Shimadzu AG-X 10 kN universal testing machine, equipped with a 50 mm extensometer. Figure 4.7 – Tensile test Apparatus According to the standard the sample geometry was a type III, with a grip distance of 150 mm. The crosshead velocity was of 5 mm/min and the tests were performed in a standard laboratory atmosphere of 23±2ºC and 50±5% relative humidity. Sustainable automotive components for interior door trims 64 References [1] H. Savastano Jr., P.G. Warden, R.S.P. Coutts, Brazilian waste fibres as reinforcement for cemente-based composites, Cement & Concrete Composites, vol.22, pp. 379-384 (2000) [2] V. Agopyan, H. Savastano Jr., V.M. John, M.A. Cincotto, Developments on vegetable fibre-cement based materials in São Paulo, Brazil: an overview, Cement & Concrete Composites, vol.27 , pp. 527-536 (2005) [3] ASTM standard D 638 – 03 Standard Test Method for Tensile Properties of Plastics (2010) [4] ASTM standard D 790 – 10 Standard Test Method for Flexural Properties of Unreinforced and Reinforced Plastics and Electrical Insulating Materials (2010) [5] ISO standard 6603 – 2 Determination of multiaxial impact behavior of rigid plastics - Part 2: Instrumented puncture test (2000) [6] ISO standard 75 - 2 Determination of temperature of deflection under load - Part 2: Plastics and ebonite (2004) [7] ASTM D7426-08 – Standard Test Method for assignment of the DSC procedure for determining T g of a polymer or an elastomeric compound (2008) Nuno Calçada Loureiro 65 Chapter 5. Mechanical Characterization of PHA/PLA Blends 8 This chapter presents an investigation about the mechanical behavior of PHA/PLA blends. The blend mechanical properties can be optimized trough the variation of the PHA contents on the blend. The flexural and tensile properties were estimated by different models: Rule of Mixtures, Kerner–Uemura– Takayanagi model, Nicolai-Narkis model and Béla-Pukánsky model. This aimed at investigating the adhesion between the two material phases. The results anticipate a good adhesion between both polymeric phases when PHA is the disperse phase. For tensile modulus, a linear relationship is found, following the rules of mixtures (or a KUT model with perfect adhesion between phases) denoting a good adhesion between the 8 Adapted from N.C. Loureiro, J.L. Esteves, J.C. Viana, S. Ghosh: “Mechanical Characterization of Polyhydroxyalkanoate and Poly(Lactic Acid) Blends”, Journal of Thermoplastic Composite Materials (accepted) Sustainable automotive components for interior door trims 66 phases over the composition range. The incorporation of PHA in the blend leads to a decrease of the flexural modulus but, at the same time, increases the tensile modulus. The impact energy varies over 157% over the entire blend composition. For blends with PHA weight fraction lower than 50% the impact strength of the blend is higher than the pure base polymers. The highest synergetic effect is found when the PLA is the matrix and PHA the disperse phase for the blend PHA/PLA of 30/70. The second maximum is found for the inverse composition of 70/30. PLA has a Heat Deflection Temperature substantially lower than PHA. For the blends, the HDT increases with the increment upon the % of incorporation of PHA. Up to 50% PHA (PLA as matrix), the HDT is practically constant and equal to PLA value. Over this point (PHA matrix), the HDT of the polymer blends increases linearly with % of addition of PHA. 5.1 Mechanical properties prediction models The mechanical properties of the blends (indicated by subscript b) can be predicted by usual models assuming different interfacial behaviors: • Well disperse phases with perfect adhesion (rules of mixtures) • spherical inclusions of one polymer in a continuous polymer matrix with perfect adhesion or no adhesion (KUT model) • spherical inclusions with variable interphase interactions, ranging from poor to good adhesion (NN model); These models will be described in the following. They will be used to interpret the adhesion between the polymers phases within the blend. 5.1.1 Rule of Mixtures The rule of mixtures (ROM) considers perfect adhesion between the matrix (indicated by subscript m) and the dispersed phase (indicated by subscript d) and a perfect dispersion of the spherical inclusions in the matrix. This model can be used to predict the initial modulus and the tensile stress, respectively. E  =   E  E  − 1  × ∅  + 1  × E  (5.1) σ  =   σ  σ  − 1  × ∅  + 1  × σ  (5.2) where E b is the initial modulus of the blend, E d is the initial modulus of the disperse phase, E m is the initial modulus of the matrix, Ø d is the volume fraction of the disperse phase, σ b is the maximum stress of the blend, σ d is the maximum stress of the disperse phase, and σ m is the maximum stress of the matrix. 5.1.2 Kerner-Uemura-Takayanagi model Nuno Calçada Loureiro 67 The Kerner–Uemura–Takayanagi (KUT) model treats the blends as spherical inclusions of one polymer, having an initial module of Ed, in a continuous matrix of another polymer having Em. The Poisson’s ratio of the matrix (υm) is taken to be 0,49 [1]. This model has two variations. One assumes perfect adhesion (eq.5. 3) at the blend interface and the other assumes no adhesion. (eq.5.4). E  = E     ! υ " # $ " %  & ' υ " # $ (   ! υ " #  $ " $ ( # ∅ (  7 − 5 υ m # E m +  8 − 10 υ m # E d +  8 − 10 υ m #  $ " $ ( # ∅ ( - (5.3) E  = E     ! υ " # $ "   ! υ " #  $ " # ∅ (  7 − 5 υ m # E m +  8 − 10 υ m #  $ " # ∅ ( - (5.4) 5.1.3 Nicolais-Narkis model In the Nicolais–Narkis (NN) model, the interphase interaction constant – K - is a function of the blend structure. For spherical inclusions, K= 1.21 stands for the extreme case of poor adhesion; interphase adhesion takes place for values of K < 1.21. When K=0, the adhesion is sufficient so that the polymer matrix strength will not decrease, that is, . / =. 0 That means that the better adhesion appears when K is low[1]. The NN model assumes that both phases are of a no-adherent type and the maximum stress is a function of either the area fraction or the volume fraction of the dispersed phase. The NN model is given by: σ  = 1 1 − K ∅  3 4 ⁄ 6 × σ  (5.5) In this work, the calculation of K values by adjustment of equation 5.5 to the experimental data gives a measure of the adhesion between both phases. 5.1.4 Béla-Pukánsky model In the Béla-Pukánsky (BP) model, the maximum tensile stress of the blend is determined by the maximum stress of the matrix, the volume fraction of the dispersed phase and the effective load-bearing cross section: 7 8 = 7 9  : − ∅ ; : + < . > ∅ ;  ?  @ ∅ ; # (5.6) B is a parameter that relates the load-bearing capacity of the disperse phase and depends on the size of the contact surface between the polymer and the disperse phase and on the properties of the interphase that is formed. The lower the B parameter the lower is the phase´s adhesion (i.e., no-adhesion case). The highest B is, the better is the adhesion between phases. The aggregation decreases the surface available for the polymer, and therefore drives a decreasing of the value of B. [1] Sustainable automotive components for interior door trims 68 The calculation of this factor allows the estimation of the load-bearing capacity of the dispersed phase in the blend. Table 5.1 resumes the models adopted in this work and the information that they give for the interpretation of the blend structure. Table 5.1 – Models used in this work to interpret blend structure. Model Eq. Blend structure Interpretation Use ROM (5.1) (5.2) Spherical polymer inclusions in a continuous polymer matrix with perfect adhesion perfect adhesion and dispersion Fit to the model for E and σ KUT (5.3) (5.4) Spherical polymer inclusions in a continuous polymer matrix with perfect adhesion or no adhesion a) perfect adhesion b) no adhesion Fit to the model for E NN (5.5) Spherical inclusions with variable interphase interactions, ranging from poor to good adhesion K - interphase interaction constant, function of the blend structure K adjustment for σ values: K= 1.21 – no adhesion K < 1.21 – phase´s adhesion K=0 – no property decrement BP (5.6) Blend stress determined by the matrix stress, dispersed phase volume fraction and the effective load-bearing cross section B - load-bearing capacity of the disperse phase. It depends on the size of the contact surface and interphase properties B adjustment (for σ values): Lowest B means lower adhesion Highest B means better adhesion 5.2 Mechanical Testing 5.2.1 Flexural Properties A Universal Tiratest 2705 5kN Machine was used to measure the flexural properties according to ASTM D790 standard. It has been used a 3-point flexural test, with a crosshead speed of 2,56 mm/min and a spam of 96 mm. Tests were performed at room temperature (23 ºC). The envisaged flexural properties assessed were the initial modulus, the maximum stress and the strain at maxim stress. At least 11 specimens were tested for each blend composition. 5.2.2 Tensile Properties To measure the tensile properties according to ASTM D638, a universal mechanical testing machine Shamidzu AG-X 100kN, equipped with a 50 mm Shamidzu extensometer, was used. The crosshead velocity used was of 5 Nuno Calçada Loureiro 69 mm/min and the testes were performed at room temperature (23 ºC). A grip distance of 150 mm was used. The envisaged tensile properties assessed were the initial modulus, the maximum/yield stress and the strain at break. At least 11 specimens were tested for each blend composition. 5.2.3 Instrumented Properties Instrumented impact tests are performed according ISO 6603-2 standard in a CEAST Fractovis plus pendulum impact machine (velocity of 1 m/s). All performed tests were carried out in a standard laboratory atmosphere of 23±2ºC and 50±5% relative humidity. From the force-displacement curve, the impact toughness was calculated. The impact data presented are the average of 7 measurements. 5.2.4 Heat Deflection Temperature (HDT) Measurements To measure the Heat Deflection Temperature, HDT, according to ISO 75-2, RAY-RAN HDT apparatus was used. This test used the method HDT A with a stress state of 1,8 MPa and an increasing temperature speed of 120ºC/h. The tests were carried out in a standard laboratory atmosphere of 23±2 ºC and 50±5 % relative humidity. The presented HDT results are the average values of three measurements. 5.3 Results and Discussion The results of the tensile tests of the PHA/PLA blends are given in Table 5.2. Table 5.2 – Tensile properties of PHA/PLA blends PHA/PLA Blend [Mass Fraction] Tensile Modulus [GPa] Maximum Stress [MPa] Strain at maximum Stress [%] [0:100] 3,62 ± 0,03 59,17 ± 0,7 2,5 ± 0,03 [10:90] 3,15 ± 0,21 51,35 ± 1,0 2,4 ± 0,07 [20:80] 3,32 ± 0,06 43,61 ± 0,6 2,0 ± 0,13 [30:70] 3,36 ± 0,07 46,02 ± 1,5 2,0 ± 0,06 [40:60] 3,63 ± 0,05 43,19 ± 0,6 1,9 ±0,10 [50:50] 3,55 ± 0,05 40,36 ± 4,1 1,7 ± 0,39 [60:40] 3,62 ± 0,06 43,02 ± 0,4 1,9 ± 0,02 [70:30] 3,69 ± 0,08 39,21 ± 0,4 1,8 ± 0,06 [80:20] 3,73 ± 0,25 35,99 ± 5,6 1,6 ± 0,26 [90:10] 3,74 ± 0,11 28,04 ± 3,7 1,3 ± 0,14 [100:0] 3,81 ± 0,12 29,19 ± 0,2 1,6 ± 0,19 Based on the predictive models, the estimated mechanical properties are presented in Table 5.3. Table 5.3 – Predicted Tensile Modulus PHA/PLA Blend [Mass Fraction] Tensile Modulus [GPa] ROM KUT perfect adhesion KUT no adhesion [0:100] 3,62 3,62 3,62 [10:90] 3,64 3,64 3,06 [20:80] 3,66 3,66 2,56 [30:70] 3,68 3,68 2,11 Sustainable automotive components for interior door trims 70 [40:60] 3,70 3,70 1,72 [50:50] 3,72 3,72 1,43 [60:40] 3,73 3,73 1,80 [70:30] 3,75 3,75 2,22 [80:20] 3,77 3,77 2,69 [90:10] 3,79 3,79 3,21 [100:0] 3,81 3,81 3,81 Fig.5.1 shows the evolution of the initial modulus with the PHA weight fraction, based on the data from tables 5.2 and 5.3. Figure 5.1 –Tensile initial modulus results and predicted values from models The increase of PHA on the blend results in a general increase of the initial tensile modulus. This is expected since the initial modulus of PHA is slightly higher than PLA. In Figure 5.1 are also presented the predictions of E based on the abovementioned models: ROM and KUT models with perfect and no adhesion between phases. Two main issues can be withdrawn: i) the KUT model with no adhesion does not give good predictions of E; ii) the ROM and KUT model with perfect adhesion both give good predictions of the variation of E with the weight faction of PLA in the blend. The maximum deviation between the KUT perfect adhesion prediction and the experimental value is about 5 %. These results anticipate a good adhesion between both phases in the PHA/PLA blends. Nevertheless, for low levels of incorporation of PHA (up to 30%), where PLA is expectantly the matrix, the experimental data seems to deviate from the perfect adhesion models, suggesting a decrease on the adhesion between both polymeric phases when PHA is the disperse phase. The maximum stress of the blends can be estimated from the above presented prediction models. From the NN and BP models, the parameters K and B can be calculated giving estimations of the interphase interaction and of the load-bearing capacity of the disperse phase, respectively. The calculated values are expressed in Table 5.4 for each blend. Table 5.4 – Calculated Values for K and B for PLA/PHA blends PHA/PLA Blend [Mass Fraction] K (NN model) B (BP model) [10:90] 0,55 2,0 Nuno Calçada Loureiro 71 [20:80] 0,74 1,7 [30:70] 0,47 2,3 [40:60] 0,48 2,3 [50:50] 0,49 2,3 [60:40] 0,37 4,0 [70:30] 0,42 4,0 [80:20] 0,44 4,2 [90:10] 0,56 2,9 AVERAGE 0,50 2,1 (PLA Matrix) 3,8 (PHA Matrix) Figure 5.2 shows the variation of K and B with the weight fraction of PHA. K values are always lower than 1.21, meaning that a good adhesion between both phases is achieved. The values of B parameter are also relatively high, indicating a good adhesion between phases. Furthermore, in the PLA fraction 50-60% the values of K show a drop and that of B a sudden increment, which can be attributed to phase inversion in the blends. Again, for the low levels of incorporation of PHA (PHA as disperse phase) the K values are higher indicating a lower adhesion between both phases when PLA is the matrix. For this dilution regime, the B values are lower, indicating a lower load-bearing capacity of the PHA disperse phase, also due to the low tensile strength of this phase. Figure 5.2 –Variations of K and B parameters of NN and BP models with weight fraction of PHA In Table 5.5 are presented the predictions of the tensile stress for ROM, NN (with different K values) and BP (with average B value) models for the various PHA/PLA mass fractions. For percentages of incorporation of PHA higher than 60% (PLA as matrix), the NN and BP models do not give good agreement with experimental data. Table 5.5 – Models predictions of Maximum Stress PHA/PLA Blend [Mass Fraction] Maximum Stress [MPa] ROM NN BP K=0 K=0,5 K=1,21 B=2,3 [0:100] 59,17 58,26 58,26 58,26 58,26 [10:90] 56,17 58,26 51,98 43,07 52,79 [20:80] 53,17 58,26 48,29 34,15 49,22 Sustainable automotive components for interior door trims 72 [30:70] 50,18 58,26 45,20 26,67 46,46 [40:60] 47,18 58,26 42,44 19,99 43,85 [50:50] 44,18 58,26 39,91 13,85 40,89 [60:40] 41,18 [70:30] 38,19 [80:20] 35,19 [90:10] 32,19 [100:0] 29,19 Fig. 5.3 shows the variations of the tensile maximum stress with % of PHA and respective models predictions. Figure 5.3 – Tensile Maximum Stress Results and Predicted Values The increase of PHA on the blends drives to a general decreasing of the Maximum Stress. The ROM fits well with the experimental data for the larger amounts of incorporation of PHA, suggesting a very good adhesion between PHA matrix and the PLA disperse phase. For low % of PHA the phase adhesion is small, the experimental data deviates from ROM. In this regime, the values of K and B were adjusted in order to fit better the models predictions. Values of K = 0,5 and B=2,3 were found up to %PHA of 50% (above this value, a best fit is obtained for K=-1,2 and B=4,0). These values regarding both NN and BP models corroborate that the interphase adhesion is promoted when PLA is the disperse phase. The flexural test results of the blends are given in Table 5.6. The experimental variation of the flexural module as function of the PHA fraction is small, of 3,52%. Table 5.6 – Flexural Properties of PHA/PLA blends PHA/PLA Blend [Mass Fraction] Flexural Modulus [GPa] Maximum Stress [MPa] Strain at maximum Stress [%] [0:100] 3,59± 0,06 80,52 ± 2,6 2,3 ± 0,1 [10:90] 3,41 ± 0,08 57,36 ± 3,1 2,2 ± 0,1 [20:80] 3,46 ± 0,06 70,87 ± 4,7 2,6 ± 0,2 [30:70] 3,53 ± 0,02 62,30 ± 7,1 2,1 ± 0,4 Nuno Calçada Loureiro 73 [40:60] 3,79 ± 0,01 55,31 ± 2,6 1,6 ± 0,1 [50:50] 3,61 ± 0,08 79,93 ± 2,4 3,1 ± 0,1 [60:40] 3,56 ± 0,11 46,49 ± 3,0 1,3 ± 0,1 [70:30] 3,42 ± 0,03 66,10 ± 0,6 2,4 ± 0,1 [80:20] 3,42 ± 0,10 47,32 ± 2,9 1,5 ± 0,1 [90:10] 3,44 ± 0,22 53,94 ± 3,5 2,2 ± 0,4 [100:0] 3,40 ± 0,10 53,97 ± 0,6 2,2 ± 0,1 Fig.5.4 shows the variations of E f with % of PHA and respective models predictions. Conversely, to the tensile modulus, here for the flexural modulus the ROM does not applies over the full range of compositions. Only for high % of incorporation of PHA (as matrix), the ROM is valid. In the case of PHA as disperse phase, the variations of E f with PHA fraction are not conclusive. The E f of the blends seems to be more sensitive to the morphology of the low fraction component (e.g., dispersion, size, aspect ratio). Also, ROM and KUT-adhesion models give the same predictions of E f as function of PHA fraction, with maximum error of 7.9% (an average of 2.1%). Figure 5.4 - Flexural Young’s Modulus Results and Predicted Values. Fig. 5.5 shows the variations of maximum flexural stress with % of PHA and respective models predictions. Again, the increase of PHA on the blends drives to a general decreasing of the Maximum Stress. As for the flexural modulus, the variations of σ max with % of PHA are subjected to high fluctuations. In general, the ROM does not give satisfactory predictions, even for larger amounts of incorporation of PHA. For low % of PHA the experimental values are always smaller than the ones predicted by ROM, this evidencing a low level of adhesion between both phases. This also happened in the tensile response: when PHA is the disperse phase, the adhesion is small. In this regime, the values of K and B were also adjusted in order to fit better the models predictions. Values of K = 0,48 and B=2,2 were found up to %PHA of 50% for both NN and BP models, respectively. These values are very close to the obtained on the tensile tests (K = 0,45 and B=2,3). Adjustments for the case of PLA as disperse phase, gives K= 0,22 and B=2,6. The K value is reduced substantially when compared with PHA as disperse phase, this meaning a better adhesion between phases; B slightly increases as a reflex of this better adhesion, but the load-bearing capacity of the disperse phase seems to remain Sustainable automotive components for interior door trims 80 Nuno Calçada Loureiro 81 Chapter 6. Morphological Characterization of PHA/PLA Blends 9 6.1 Introduction Poly (lactic acid), PLA, is a polymer produced by the fermentation of simple sugars, such as glucose and maltose from corn or potato, sucrose from cane or beet sugar and lactose from cheese [1]. It’s a linear aliphatic polyester thermoplastic used as packaging materials and in production of cloths, carpet tiles, surgical and biomedical devices among others. The PLA has a melting temperature ranging from 188º a 210 ºC, and the glass transition temperature, Tg, of 55-60 ºC (these temperatures are dependent upon the optical composition, the primary structure, the molecular weight, and the thermomechanical history upon cooling). PLA has been blended with other polymers in order to obtain better mechanical properties and/or cost reduction. Several studies have been made on blends of PLA with poly(ε-caprolactone), PCL[2], poly(butylacrylate), PBA [3], and acrylonitrile butadiene styrene, ABS[4]. Polyhydroxyalkanoate, PHA, is a generic designation of polyester polymers produced by the bacterial fermentation of sugars and lipids. These polyesters are a carbon storage and energy reserves in bacteria, such as Ralstonia Eutropha, Bacillus Megaterium, Azotobacterchroococum. By controlling the copolymers composition is possible to tailor most of the mechanical properties of PHA [5].The PHAs are highly crystalline polyesters (above 50%) with melting temperatures ranging from 120º to 180ºC, depending on the chemical composition [6]. The Tg is around 5ºC. The blending of these two polymers, PHA/PLA, allows obtaining materials with improved properties, being less costly than chemical modifications or synthesis of tailor-made copolymers. The properties of the PHA/PLA 9 Adapted from N.C. Loureiro, J.L. Esteves, J.C. Viana, S. Ghosh, Morphological study on Polyhydroxyalkanoates and Poly(Lactic Acid) blends obtained by injection moulding, Journal of Macromolecular Science, Part B - Physics (submitted) Sustainable automotive components for interior door trims 82 blends can be easily modified by changing the polymers or co-polymers molecular weight or by varying the blend composition. [7-8] In this chapter, the morphology development during injection molding of blends of PHA/PLA has been investigated. 6.2 Morphological Calculations based on DSC results From the DSC thermograms several parameters were evaluated. The degrees of crystallinity (x A ) of the pure polymers were estimated using eq.6.1 B C   ∆ D E ∆ D FF ∆ D E G (6.1) where, o m H∆ is the enthalpy of 100 % crystalline PHA as 146 J.g-1 [3], and PLA had 93 J.g-1, respectively [10]. ∆H 0 is the enthalpy of fusion. For the PHA/PLA blends a different approach was followed. In this case, since the cold crystallization is due to PLA and the crystallization to PHA and PLA, it’s necessary to take into account not only the crystallization behavior of the base polymers alone, but also the interaction of the two polymers into the blend. For that, in a first approach, the degree of crystallinity of the blends is given by: B C  ∆ H 0  ∆ H CC ∆ H 0 , JKL  ∙ ∅ JKL  ∆ H 0 , JDL  ∙ ∅ JDL (6.2) This equation relates the enthalpy of fusion of the blend (ΔH m ) and the enthalpy of cold crystallization (ΔH cc ) with the enthalpy of melting of the neat polymers ( and ) and their weight fraction (Ø PLA and Ø PHA ). The weighting of the enthalpy of melting of the base polymers through the weight fraction of both polymers will give a more realistic value for the enthalpy of melting of the considered blend. 6.3 Results and Discussion 6.3.1 WAXD Measurements Figure 6.1 reveals the diffractogram of the as-molded injection molded samples of neat PLA, neat PHA, and PHA/PLA blends. The scan shows no peak for neat PLA samples, suggesting that PLA is amorphous under the thermomechanical conditions of injection molding. On the contrary, PHA crystallized to a significant extent, with diffraction peaks at 2θ values at 13.52º and 16.88º [11-12]. The most intense peak for PHA is at 2θ values at 13.52º, originating from 020 plane. The weak reflection peaks at 2ϴ=16.88º are originating 110 plane. Nuno Calçada Loureiro 83 10 12 14 16 18 20 0 / 100 10 / 90 20 / 80 30 / 70 40 / 60 50 / 50 60 / 40 70 / 30 80 / 20 90 / 10 13.52 o 16.88 o 100 / 0 Intensity (arb. unit.) 2 θ (؛) PHA / PLA Figure 6.1 - WAXD traces of injection molded PHA/PLA blends. For blends, the scans can be divided into two different regimes: (i) the increasing fraction of PLA in PHA, (ii) the other is increasing fraction of PHA in PLA. The addition of PLA in PHA revealed that the intensity of reflection at 2θ =13.52º remained relatively same or more intense up to 70/30 PHA / PLA composition, compared to neat PHA. However, the intensity of the peak at 2θ =13.52º decreases monotonically with increasing fraction PLA, and the peak almost disappears with 40/60 PHA/PLA composition. It is worth to mention here that PLA is a semicrystalline polymer with a slow rate of crystallization. PLA crystallizes significantly from miscible polymer blends with the most intense Bragg peak of 2θ=16.88º [13-14], however is possible to note that neat PLA does not crystallize during standard operating conditions of injection molding. The reason for “the apparent increase peak intensity at 2θ=13.52º, and gradual decrease in peak intensity at 2θ=16.88º” requires further structural experimentation to establish. From 40 / 60 to 90 /10 PHA/PLA composition, the only reflection peak is at 2ϴ=13.52º. The suppression of peak at 2θ=16.88º, which is the most peak of crystalline PLA and a less intense of PHA suggests the following: (a) there is a strong interaction between PLA and PHA crystals, and (b) PLA do not crystallize from PHA/PLA blends, under the present thermomechanical environment of injection molding. 6.3.2 DSC of Injection Molded PHA/PLA blends The first heating of PLA revealed the typical thermal transitions along the temperature axis: (i) a glass transition, (ii) an exothermic cold crystallization, and (iii) an endothermic melting – see Fig. 6.2. The degree of crystallinity of PLA was 1.5 %, estimated from Eq. 1. This low degree of crystallinity of injection molded PLA is fairly in good agreement with the results reported elsewhere [10]. Sustainable automotive components for interior door trims 84 90PHA 80PHA 70PHA 60PHA 50PHA 40PHA 30PHA 20PHA 10PHA 0PHA 100PHA -20 0 20 40 60 80 100 120 140 160 180 200 Endo Heat Flow (W.g -1 ) Temperature ( o C) 1W .g -1 Figure 6.2 – DSC thermograms of the PHA/PLA blends in the heating run. (from top to bottom the weight fraction of PLA increases and the weight fraction of PHA decreases) Table 6.1 – DSC data of PHA, PLA and PHA/PLA blends. PHA wt (%) PLA wt (%) T g (ºC) ΔC P (J.g -1 .ºC) T cc (ºC) ΔH cc (J.g -1 ) T m (ºC) ΔH m (J.g -1 ) x c (%) PHA PLA Fox eq. PLA PHA PLA 0 100 - 63.7 63.7 0.575 97.9 29.5 177.7 30.9 1.5 10 90 7.5 61 33.0 0.229 0.254 -- 27.6 172.5 40.7 13.8 20 80 7.5 45.8 22.3 0.204 0.255 102.2 15.5 170.5 46.2 31.7 30 70 6.5 55.2 16.8 0.215 0.307 105.8 18.9 172.3 45.4 27.0 40 60 - 58.9 13.5 0.129 0.215 112.1 10.1 172.5 51.3 41.3 50 50 - 54.6 11.3 0.095 0.19 97.4 13.8 171.2 53.9 39.6 60 40 7.0 53.7 9.7 0.404 1.01 72.5 15.9 169.9 62.6 45.4 70 30 6.5 57.5 8.5 0.366 1.22 90 10.4 171.2 69.7 56.8 80 20 6.2 56.2 7.6 0.34 1.7 88 1.8 171.5 66.2 60.8 90 10 - 58.6 6.8 0.329 3.29 100 -- 177 67 62.3 100 0 6.2 - 6.2 -- -- -- -- 170.3 65.5 60.1 Within the scan range, the injection molded PHA showed only an endothermic melting peak at 170.3 ºC. It is worth to mention that the T g of PHA was detected in the scan at 6.2 ºC. The degree of crystallinity of injection molded PHA was 60.1 %. The mold temperature, 20 ºC i.e. well above the T g allowed the highly flexible PHA segments to crystallize significantly. Figure 6.3 reveals that the Tg of PLA shows a trend to decrease with increasing fraction of PHA. Similarly, the Tg of PHA shows an upward trend with increasing fraction of PLA. The blend T g between the T g, PHA (6.2 ºC) and the T g, PLA (63.7 ºC) indicate that PLA and PHA were partially miscible in the processed blends. Nuno Calçada Loureiro 85 Figure 6.3 – Variation of the two glass transition temperatures with the weight fraction of PHA in the blend. The blend miscibility can be derived from the comparison of measured T g values with those predicted by the Fox equation [16], given by: 1 N O , /PQRS  ∅ JKL N O , JKL  ∅ JDL N O , JDL (6.3) Where T g , T g,PHA and T g,PLA are the glass transition temperatures of the blend, PHA and PLA respectively. For T g,PHA and T g,PLA the values are obtain experimentally and are, respectively, 6,2ºC and 63,7 ºC. The weight fractions of the base polymers in the blend are given by Ø PLA and Ø PHA , respectively. The Fox equation calculates the T g of the blend assuming that the base polymers are completely miscible one in the other. When comparing the experimental data with the theoretical Fox model (Table 2) is possible to observe that when PHA is the matrix polymer (%PHA>60%) the blend presents some miscibility. This miscibility is confirmed by the shifting of the T g from the neat polymer value. The phase inversion of the blends is not easy to identify in Fig. 6.3. Fig. 6.4 shows the effect of increasing the PHA weight fraction in the heat capacity at the PLA glass transition, ΔC p . Pure PLA shows the highest heat capacity, ΔC p = 0,575 (J.g -1 .ºC). The heat capacity at the glass transition is a measure of the fraction of the amorphous phase (of PLA in this case) that relaxes at T g . Interestingly, two regimes can be found in Figure 6, depending upon the type of matrix in the blend. For low percentages of incorporation of PHA, PHA is the dispersed phase and PLA is the matrix. Adding a small amount of PHA to the blend (10PHA/90PLA) is enough to reduce its heat capacity by 60%, indicating that the amorphous phase of PLA becomes less mobile. Increasing the amount of PHA further reduces ΔC P of the blend. For the 50PHA/50PLA blend the lowest ΔC P is obtained, being reduced by 84%. Then, between 50-60% fraction of PHA, PLA becomes the dispersed phase and PHA the matrix. This corresponds to a change on the heat capacity of PLA in the blend that suddenly increases, but still being lower than that of pure PLA (reduction of 30% for the 60PHA/40PLA). Phase inversion is clearly identified by changes on ΔC P of this PHA/PLA blend. Furthermore, the Sustainable automotive components for interior door trims 86 amount of mobile PLA amorphous phase at T g is reduced when PLA is the disperse phase, but not as much when it is the matrix. Increasing more the amount of PHA, further reduces ΔC P , but not reaching the same decrement as PLA as matrix (reducing more than 43% for 90PHA/10PLA). It’s possible to assume that, since ΔC P is directly connected with the mobility of the chains of the blend, the PLA matrix blends are more flexible that the PHA matrix blends. Figure 6.4 – Variation of the heat capacity at the glass transition of PLA with the weight fraction of PHA in the blend. Figure 6.5 shows the variation of the cold crystallization temperature of PLA with the percentage of incorporation of PHA. Again two distinct evolutions are evident. When PLA is the matrix, T cc increases with %PHA, starting from pure PLA T cc . This increment on T cc means a delay on the cold crystallization of PLA and an expectant reduction on its degree of crystallinity with increasing of %PHA. At 50-60% PHA, phase inversion occurs with a high decrement upon T cc of PLA. PHA becomes the matrix and the cold crystallization of the PLA dispersed phase occurs at a lower temperature, inducing the crystallization. As the %PHA still increases, T cc increases again. Figure 6.5 – Variation of the cold crystallization temperature of PLA with the weight fraction of PHA in the blend. The variation of the cold crystallization enthalpy of PLA, ΔH cc with %PHA is shown in Figure 6.6 (ΔH cc data was been weighted by the amount of PLA in the blend). Generally, ΔH cc decreases with %PHA increment. This 0,0 0,1 0,2 0,3 0,4 0,5 0,6 0,7 0 10 20 30 40 50 60 70 80 90 100 Cp - PLA/J.g -1 K -1 % PHA Nuno Calçada Loureiro 87 decrement means that PLA crystallizes more during the processing stages as PHA is added to the blend. The variations are higher when the PLA is the matrix (from 30 to 7 J/g). Figure 6.6 – Variation of the cold crystallization enthalpy of PLA with the weight fraction of PHA in the blend . Considering the melting peak, T m of the blends does not change significantly over the blend’s compositions (between 170.3-172.5 ºC), close to the melting temperature of PHA of 170.3 ºC. Note that the melting temperature of PLA is around 175-180 ºC and this peak should be overlapped by the melting peak of PHA. It can be concluded that the blend composition does not have an effect on thickness of crystalline structures of PHA (i.e., T m is constant). As expected, the pure PHA presents a higher degree of crystallinity, X C =60.1%, than PLA, X C =1.5%, which is essentially amorphous. Figure 6.7 shows the variations of the degree of crystallinity of the blends with the %PHA (weighted by the composition according to equation 2) and considering only the contribution of PHA for the melting peak. In both cases, X C increases with %PHA. The degree of crystallinity of PLA is lower when it is the dispersed phase, which can be explained by the nucleating action of PHA in the PLA matrix or by the different cooling conditions that PLA experiences when cold down from the blended melt. Sustainable automotive components for interior door trims 88 Figure 6.7 – Variations of the degree of crystallinity of the blend with the weight fraction of PHA. χ c was calculated assuming a weighted contribution of the two polymers and single contribution of PHA for the melting peak. Figure 6.8 presents the fracture surfaces of neat polymers and their blends. The SEM images show interestingly a clear change on the blend morphology at the phase inversion (c.a. 50%PHA) where a lamellar morphology is developed. This morphology develops in the blends only when PHA is the matrix and becomes more evident as the amount of PLA increases, and a result of the thermomechanical environment applied during processing, with a preferential orientation in the flow direction. On the other hand, a more fine structure of the PHA dispersed phase is revealed in the PLA matrix blends. It is also evident the more brittle character of the neat PLA, which feature a highly smooth fracture surface, when compared with the rough one of the neat PHA. This is also shown by the blends: when PHA is the matrix the fracture surfaces are rougher. It is expected a different toughness of the blends. 0 10 20 30 40 50 60 70 0 20 40 60 80 100 Xc (%) % PHA pure polymers blend weighted (eq. 2) blend-PLA Nuno Calçada Loureiro 89 Figure 6.8 – SEM images of fracture surfaces of PHA/PLA blends (magnification of 500x). 100 % PHA 90 % PHA 80 % PHA 70 % PHA 60 % PHA 50 % PHA 40 % PHA 30 % PHA 20 % PHA 10 % PHA 0 % PHA Sustainable automotive components for interior door trims 96 7.3 Results and Discussion 7.3.1 Tensile behavior The results of the tensile tests of the composites are given in Table 7.1. An experimental stress-strain demonstrative curve for each specimen is shown into figure 7.1. The horizontal step represents the time of extensometer removal during the test. Figure 7.1 – Tensile Stress-Strain Curves obtained experimentally Table 7.1 - Tensile Properties of PHA/PLA composites reinforced with cellulosic fiber Fiber ratio [Mass Fraction] Tensile modulus [GPa] Maximum stress [MPa] Strain at maximum stress [%] 0 % 3.36 ± 0.07 40.00 ± 1.5 2.0 ± 0.06 10 % 4.29 ± 0.37 44.21 ± 1.4 2.7 ± 0.33 20 % 5.14 ± 0.31 49.01 ± 1.6 2.4 ± 0.31 30 % 10.01 ± 0.34 79.72 ± 1.2 1.9 ± 0.18 Based on the predictive models, the estimated mechanical properties are presented in Table 7.2. Table 7.2 – Predicted and Experimental tensile modulus Reinforce Fiber [Mass Fraction] Tensile Modulus [GPa] experimental ROM mHT ICm 0 % 3.36 ± 0.07 3.36 3.36 3.36 10% 4.29 ± 0.37 4.72 4.34 3.69 20% 5.14 ± 0.31 6.09 5.38 4.14 30% 10.01 ± 0.34 7.45 6.47 4.72 Nuno Calçada Loureiro 97 Fig. 7.2 shows the evolution of the modulus, E, with the reinforced fiber weight fraction. Figure 7.2 – Experimental tensile modulus, E, results and predicted values from the micromechanical models The increase of fiber content results in a general increment on the initial tensile modulus of the composite. This is expected because the fiber contributes to the stiffness of the final composite. In Fig. 7.2 are also presented the predictions of E based on the above mentioned models: ROM, mHT and ICm. ROM model supposes that the fiber and the matrix present a perfect adhesion. The ICm is based in a cubic approximation. The results show that this model provides the lowest predication, meaning that the based hypothesis of the model is not suitable for this specific composite. mHT equation supposes that the fiber presents a homogenous distribution through the matrix. The mHT equation gives an excellent prediction of E for incorporation until 20% (wf) of cellulosic fibers. Analyzing only until 20% (wf) of fiber incorporation, the maximum deviation between mHT equation and the experimental values is only about 3.5%, and for the ROM this deviation reaches 18%. This anticipates a homogenous dispersion of the fiber through the matrix. For 30 wt% of fibers, the models underpredict the experimental value. This may result from several factors including, not only the data obtain from the fibers, but also from the geometric assumptions from the adopted models. In Table 7.3 are presented the experimental values and the predictions of the maximum tensile stress for ROM and mHT models for the various fiber incorporation ratios. Table 7.3 – Experimental and Predicted tensile Stresses Reinforce Fiber [Mass Fraction] Tensile Stress [MPa] Experimental ROM mHT 0 % 40.00 ± 1.5 40.00 40.00 10% 44.21 ± 1.4 49.54 44.83 20% 49.01 ± 1.6 59.52 49.91 30% 79.72 ± 1.2 69.97 52.24 Sustainable automotive components for interior door trims 98 Fig. 7.3 shows the variations of the maximum tensile stress with the wt% of fiber and respective models predictions. Figure 7.3– Tensile Maximum Stress Results and Predicted Values The maximum stress of the composites can be also estimated with an excellent agreement from the above presented prediction models, namely the mHT equation. This equation gives very good predictions incorporation of fibers until 20 wt%. Until this percentage, the maximum deviation between mHT equation and the experimental values is about 1.3%, and for the ROM is about 20%. Again, for 30 wt% of fibers, the models under predict the experimental value. 7.3.2 Flexural behavior The flexural test results of the blends are given in Table 7.4. An experimental stress-strain demonstrative curve for each specimen is depicted into figure 7.4. Nuno Calçada Loureiro 99 Figure 7.4 – Flexural Stress-Strain Curves obtained experimentally Table 7.4 – Flexural Properties of PHA/PLA composites reinforced with cellulosic fiber Fiber ratio [Mass Fraction] Flexural Modulus [GPa] Maximum Stress [MPa] Strain at maximum Stress [%] 0 % 3.09 ± 0.13 77.49 ± 1.54 4.00 ± 0.29 10% 4.44 ± 0.07 82.51 ± 1.22 3.14 ± 0.22 20% 5.59 ± 0.09 89.02 ± 1.36 2.78 ± 0.12 30% 6.35 ± 0.19 85.36 ± 1.57 2.11 ± 0.04 Fig. 7.5 shows the variations of E f with % of fiber and respective values of the prediction model (ROM). As for the tensile modulus, the ROM suggests that for fiber incorporation superior to 20% the fiber distribution is non-homogeneous. Conversly, to the tensile modulus, the ROM models gives acceptable predictions up to 30% of incorporation of fibers. Sustainable automotive components for interior door trims 100 Figure 7.5 – Flexural Modulus, E f , Results and Predicted Values from model Fig. 7.6 shows the variations of maximum flexural stress with % fiber and respective models predictions. Again, the increment on the fiber content leads to a general increasing of the maximum flexural stress of the composite. However the incorporation of more than 20% of fiber results on a reduction on the maximum flexural stress, and a divergence from the theoretical predictive value. In general, the ROM gives very good predictions for fiber incorporation levels below 20%. Figure 7.6 – Flexural Maximum Stress Results and Predicted Values 7.3.3 Impact behavior Figure 7.7 presents the impact force over time during the impact test of the composites. The incorporation of fiber improves the energy absorption capabilities of the composites. However due to the non-homogeneous distribution of the fiber in the 30% fiber-composite, the impact toughness appears to decrease because the fiber bundles may act as stress concentrators, leading to fracture of the composite. Nuno Calçada Loureiro 101 The impact results of the tested composites are given in Table 7.5. The impact energy (or toughness) establishes the amount of energy that the material can absorbed until it breaks. Table 7.5 – Composite Impact properties Fiber ratio [Mass Fraction] Impact energy [J] Deflection at break [mm] 0 % 1.7 ± 0.2 4.6 ± 1.4 10% 2.8 ± 0.5 4.8 ± 0.4 20% 2.8 ± 0.2 4.4 ± 0.8 30% 2.3 ± 0.3 3.2 ± 0.8 Figure 7.7 – Experimental impact force versus time for the instrumented impact tests The variations of the impact toughness with fiber weight fraction are depicted in Fig. 7.8. The maximum toughness is found for composites with 10 and 20 wt% of fibers. The incorporation of 30% of fibers leads to a composite with a bad impact behavior with 18% less capability of absorbing energy considering the other fiber incorporations. Sustainable automotive components for interior door trims 102 Figure 7.8 – Impact toughness. The variations of the maximum deflection with fiber wf are depicted in Fig. 7.9. The addition of cellulosic fibers decreases the maximum deflection of the composites. Figure 7.9 – Impact maximum deflection of various eco-composites. The incorporation of 30% of fibers drives to a composite with decreasing on the deformation capabilities at break of around 33%. Nuno Calçada Loureiro 103 7.3.4 Heat Deflection Temperature (HDT) measurement The Heat Deflection Temperature (HDT) results are given in Table 7.6 and Fig. 7.10 for all fiber compositions. Table 7.6 – Heat-Deflection Temperature of composites Fiber ratio [Mass Fraction] HDT [ºC] 0 % 48.5 ± 0.9 10% 49.2 ± 0.6 20% 56.0 ± 0.2 30% 51.7 ± 0.2 Figure 7.10 – Experimental HDT evolution over fiber composition As expected the incorporation of fibers increases the HDT. The maximum synergetic effect is obtained with the incorporation of 20% of fibers leading to an increasing of 15% on the HDT value. Sustainable automotive components for interior door trims 104 7.3.5 Microscopy analysis The previous mechanical characterization highlights the effects of the adhesion between the polymeric matrix and the cellulosic fiber and of the dispersion of fibers. The optical microscopy analysis images are shown in Figure 7.11 and SEM analysis in fig.7.12. The incorporation of 30% wf of fiber leads to a non-homogeneous composite and the incorporation until 20% wf drives to a homogeneous composite. Figure 7.11 – Optical microscopy analysis (magnification 20x). As possible to verify in figure 7.12, the matrix is a perfectly miscible one. Is not possible to identify a PLA or a PHA phase in the matrix. The SEM analysis also corroborates that the fiber dispersion is homogenous until reach the 20% wf. After that the dispersion starts to random and lost the homogeneity. As seen in fig. 7.13 the SEM analysis reveals that the fibers are deboned of the matrix inducing a lower interfacial adhesion. This interfacial behavior justifies the deviation of the experimental data and the predicated values based into perfect adhesion. 10% fiber 20% fiber 30% fiber Nuno Calçada Loureiro 105 Figure 7.12 – SEM Analysis . Figure 7.13 – Detail of the interface matrix-fiber obtain in SEM Analysis (20% fiber wf) Sustainable automotive components for interior door trims 112 Figure 8.2 – CIM equipment 8.3 Composite Selection Based in tables 8.1, 8.2 and 8.3 is possible to plot a 6 dimension radar chart (figure 8.3) that will emphasize the relation of all these parameters. As seen in the figure, the values of the impact absorbed energy are quite different. That difference can have originated in the velocity of the test which is not indicated into the consulted database. In this work it was used an impact velocity of 1m/s but is common into the generic polymer industry that this velocity rounds the 4,4 m/s. Regarding the HDT, is possible to see that the ABS presents the highest value. However the value presented is an average of all ABS grades actually in the market. It’s possible to have an ABS with a HDT lower than the studied composites. By analyzing the radar chart is possible to conclude that the composite with 20% fiber (light-gray shadow) is the one that present better or equal properties in all the dimensions. For producing the automotive parts it’s going to be used the composite that presents the equal or better properties in all dimensions. By analyzing the 6D radar chart is possible to conclude that the composite with 20% fiber (gray shadow) is the one that fulfill the previous statement. The only dimension that this composite present a weaker behavior is on impact, but as have been said before these values needs some confirmation that outbound the aim of this thesis. Nuno Calçada Loureiro 113 Figure 8.3 – 6 Dimension radar chart materials comparison 8.4 Automotive part To demonstrate the possibility of using this composite and the CIM technology a part was injected. It was chosen a cabin light support part from a well-known OEM from a 2008 model. The original part is produced in an ABS/PA6 blend by injection moulding. Figure 8.4 – Original Part Sustainable automotive components for interior door trims 114 Using the injection parameters already optimized in the previous chapters on a CIM equipment with a composite material formed by a [PHA:PLA] [30:70] matrix and a ratio of 20% wf of cellulosic fiber is possible to obtain the same part but into bio-degradable composite. Figure 8.5 – eco-composite part As can be seen by comparing figure 8.4 and 8.5 the part produce in eco-composite presents the same geometry. That allows the easy replacement of the actual part for this one and also allows the incorporation of the systems and parts that are integrated into the cabin interior light part. Is possible to see, in fig. 8.6, that even the small details can be reproduced with this composite. Figure 8.6 – eco-composite part detail As happens nowadays the part color can be adjust with pigments. 8.5 Conclusions The feasibility of producing interior parts on the studied eco-composites has been investigated. Composites with a [30:70] [PHA:PLA] matrix and with a fiber content of 10% and 20% (wf) were compared with the most used petrol-based polymers for automotive interior parts (PP and ABS) Nuno Calçada Loureiro 115 The incorporation of 20% wf fiber leads to an eco-composite that presents the best properties of all biopolymer blends and biocomposites studied. When compared with ABS and PP, this eco-composite, normally, presents equal or better properties, excluding the impact absorbed energy. Is possible to conclude that this composite can reveal himself an option for replace the petrol-based polymers in some cabin interior parts applications has demonstrated in this part case-study. Sustainable automotive components for interior door trims 116 Nuno Calçada Loureiro 117 Chapter 9. Final Remarks and Future Works 9.1 Final Remarks The principals expected result of this thesis is focus on the development of a concept of an eco-efficient automotive door interior trim using 100 % of renewable sources materials, whilst meeting actual applicable crashworthiness standards and aesthetics requirements. The work reported in this thesis proof that the properties of biodegradable composites can be tailored by a careful selection of the neat polymer or polymer blends that compose the matrix and the correct incorporation of reinforce fibers. For the matrix a blend of PHA and PLA were chosen recurring to a study over the full ratio of compositions. The mechanical and morphological behavior were study and the [PHA:PLA] [30:70] blend was chosen to be the matrix of the biodegradable composite that will be developed. As mentioned before ([10], chapter 7), taking account previous works, the fiber incorporation can’t be superior to 30% (wf). To asset the best fiber fraction incorporation composites with a [PHA:PLA] [30:70] matrix and with a fiber content until 30% (wf) were investigated. Sustainable automotive components for interior door trims 118 Comparing all the results is possible to conclude that for automotive interior parts, the best biodegradable composite that this work achieves is a composite with a matrix compose by [PHA:PLA] [30:70] (wf) and with a fiber incorporation of 20% (wf). Using the actual production process is possible to process automotive interior parts with this composite as demonstrated in the case-study. Therefore is possible to stat that the primary objective of this work has been achieved and the formulation of a 100% renewable-source composite capable of replace the petrol-based polymers use into interior door trims has been identified. 9.2 Future Works For future works based in this thesis is possible to works in six different areas: 1 st area – Directly connected with this work: Study the mechanical behavior of the injected composite into the CIM equipment. Study the influence of the Impact Velocity on the Absorbed Energy to compare with petrol-based polymers. Study the interface between fiber and matrix. Optimize the adhesion between the matrix and the fiber recurring to chemical and thermo-physical fibers treatments. 2 nd area – Matrix: In this section is possible to study other renewable-source polymers, such as PHB, PGA, PBA, to replace PHA and/or PLA. 3 rd area – Fibers: Study the incorporation of other fibers such as coconut, flax, cotton, hemp, jute, sisal among others. Is also possible to study the incorporation of woven and pre-impregnated fibers. 4 th area – Other applications: Developed and test this composite for structural parts use it in moderate stress states. Study the incorporation of this composite into other transport systems and others industrial sectors. 5 th area – Processing Technology: I suggest the study of processing this composites and composite parts, by other technologies such as compression moulding, Vacuum conformation, etc. 6 th area – Long Term Composite Characterization: Study the long term behavior such as fatigue, creep, real degradation process, solar exposition, moisture degradation and chemical degradation occurring by the contact with lubricants and other environmental agents. Nuno Calçada Loureiro 119 Appendixes Sustainable automotive components for interior door trims 120 Nuno Calçada Loureiro 121 A.1 Datasheet of Polyhydroxyalkanoate