Characterization of metallized polypropylene films

Universidade do Minho Escola de Ciências Sílvia Patrícia Gonçalves dos Santos March 2021 Characterization of metallized polypropylene films Sílvia Patrícia Gonçalves dos Santos Characterization of metallized polypropylene films UMinho|2021 Universidade do Minho Escola de Ciências Sílvia Patrícia Gonçalves dos Santos March 2021 Characterization of metallized polypropylene films Under orientation of: Professor Doctor Maria Manuela Silva Engineer José Aurélio Campos Master thesis: Master in Characterization Techniques and Chemical Analysis ii DIREITOS DE AUTOR E CONDIÇÕES DE UTILIZAÇÃO DO TRABALHO POR TERCEIROS Este é um trabalho académico que pode ser utilizado por terceiros desde que respeitadas as regras e boas práticas internacionalmente aceites, no que concerne aos direitos de autor e direitos conexos. Assim, o presente trabalho pode ser utilizado nos termos previstos na licença abaixo indicada. Caso o utilizador necessite de permissão para poder fazer um uso do trabalho em condições não previstas no licenciamento indicado, deverá contactar o autor, através do RepositóriUM da Universidade do Minho. Licença concedida aos utilizadores deste trabalho Atribuição-NãoComercial-SemDerivações CC BY-NC-ND https://creativecommons.org/licenses/by-nc-nd/4.0/ iii ACKNOWLEDGMENT My acknowledgment to all who gave me positive energy to overcome this challenge and never give up. All are important for me! To my parents Rosário e Pedro, who gave me strength to believe all these years that it could be possible. To my husband Carlos, who was always here, for all his patient and love. My daughter Inês and my son Simão, my life! To my brother João Pedro and his wife Joana, even far from here, in France, always sending me comforting messages. My all family and friends, for their patience and good times during this hard and strange year. My teacher, Professor Doctor Maria Manuela Silva for being my supervisor, always available and very cooperating. To Engineer José Aurélio Campos who gave me this opportunity, to never deny me a lesson or a meeting, always present and specially to believe in me. To Professor Doctor Susana Costa and Dr. Daniela Carvalhal, always available to explain me all questions and doubts concerning the master. To Vishay Electrónica Portugal, Lda which gave me the opportunity to make the master thesis. Thank you to Dr. Vítor Morais and Dr.Cláudia Cruz, Engineer Vítor Araújo, Engineer Geraldo Silva, Engineer José Lagido, Engineer Geert Stevens, Doctor Atul Killedar and Engineer Marc Vanoosthuyse. To my colleagues from Process Engineer and Research & Development departments, as well as, Production, Quality, Logistics and Maintenance departments. To all Vishay Electrónica Portugal team. Thank you. iv STATEMENT OF INTEGRITY I hereby declare having conducted this academic work with integrity. I confirm that I have not used plagiarism or any form of undue use of information or falsification of results along the process leading to its elaboration. I further declare that I have fully acknowledged the Code of Ethical Conduct of the University of Minho. v Characterization of metallized polypropylene films ABSTRACT The main goal of a capacitor is to store energy and release it in a circuit when needed. There are in the market several types of capacitors, as film capacitors, ceramic capacitors and electrolytic capacitors. For this study, it will be presented a metallized film capacitor. Film capacitors are electronic components with a high importance in a lot of electronic devices. They are used in different applications as, for instance, in televisions, radios, automotive industry, renewable energy devices, like solar panels and in hybrid and electrical cars. Different materials and components can be part of a film capacitor, as a plastic case, an epoxy, a thin plastic film metallized with metal alloys, solder, wires, and terminals. The focus of this work is the body of the film capacitor, which is the plastic film, metallized with a very thin metal layer. The intend of this work was to study six different polypropylene grades, from several suppliers, using different characterization techniques, as Differential Scanning Calorimetry, Fourier Transform Infrared Spectroscopy, Atomic Force Microscopy and Scanning Electron Microscopy. These techniques allow a better understanding of the behaviour and performance of each material, throughout the life of a film capacitor and prevent the failures during its life cycle. Thus, they had shown that there are some properties that influence the behaviour of each sample, as for instance, the surface roughness, the BOPP fabrication process (sequential stretching versus simultaneous stretching) and thickness, which influence crystals grains and the polymer chain orientation, that in turn, influence the crystallinity. All these techniques gave an important contribute for the understanding of the different polypropylene samples, concluding that sample 5 seems to be the best material to be used in a film capacitor, due to its high crystallinity, constant roughness, high Young Modulus and low shrinkage. Keywords: BOPP, film capacitors, metallized film capacitor, polypropylene. vi Caracterização de bases de fita de polipropileno metalizadas RESUMO O principal objetivo de um condensador é armazenar energia e libertá-la num circuito quando for necessário. Existem no mercado vários tipos de condensadores, como condensadores de filme, condensadores cerâmicos e condensadores eletrolíticos. Para este estudo, será apresentado um condensador de filme metalizado. Os condensadores de filme são componentes eletrónicos de grande importância em muitos dispositivos eletrónicos. São usados em diferentes aplicações como, por exemplo, em televisores, rádios, indústria automóvel, dispositivos de energia renovável, como painéis solares e em carros híbridos e elétricos. Diferentes materiais e componentes podem fazer parte de um condensador de filme, como uma caixa de plástico, um epóxi, um fino filme plástico metalizado com ligas metálicas, soldas, fios e terminais. O foco deste trabalho é o corpo do condensador de filme, que é o filme plástico, metalizado com uma camada de metal muito fina. O objetivo deste trabalho foi estudar seis amostras de polipropileno, de diversos fornecedores, utilizando diferentes técnicas de caracterização, como Calorimetria Diferencial de Varrimento, Espectroscopia de Infravermelho por Transformada de Fourier, Microscopia de Força Atómica e Microscopia Eletrónica de Varrimento. Estas técnicas permitem uma melhor compreensão do comportamento e desempenho de cada material, ao longo da vida de um condensador de filme e evitam falhas durante o seu ciclo de vida. Assim, elas mostraram que existem algumas propriedades que influenciam o comportamento de cada amostra, como por exemplo, a rugosidade superficial, o processo de fabricação do BOPP (estiramento sequencial versus estiramento simultâneo) e a espessura que influenciam os grãos dos cristais e a orientação da cadeia polimérica, que por sua vez, influenciam a cristalinidade. Todas estas técnicas deram um importante contributo para a compreensão das diferentes amostras de polipropileno, concluindo que a amostra 5 parece ser o melhor material para ser utilizado num condensador de filme, devido à sua elevada cristalinidade, rugosidade constante, elevado Módulo de Young e baixo encolhimento. Palavras-chave: BOPP, condensador de filme metalizado, condensadores de filme, polipropileno. vii CONTENT ABSTRACT .......................................................................................................................... v RESUMO ............................................................................................................................ vi FIGURES CONTENT ........................................................................................................... ix TABLE CONTENT .............................................................................................................. xii ABREVIATION LIST ............................................................................................................ xiv CHAPTER 1INTRODUCTION ............................................................................................. 1 1. Introduction ............................................................................................................. 1 1.1. The company: Vishay´s history ............................................................................ 1 1.2. Scope .................................................................................................................. 1 1.3. Thesis organization .............................................................................................. 2 CHAPTER 2STATE OF ART ............................................................................................... 3 2. State of art............................................................................................................... 3 2.1. Film Capacitor ..................................................................................................... 3 2.2. Materials.............................................................................................................. 7 2.2.1. Polypropylene film ................................................................................................... 8 2.2.2. iPP as a dielectric film ............................................................................................ 11 2.3. Characterization techniques ............................................................................... 15 2.3.1. Differential Scanning Calorimetry ................................................................................. 16 2.3.2. Fourier Transform Infrared Spectroscopy ..................................................................... 17 2.3.3. Scanning Electron Microscopy ..................................................................................... 18 2.3.4. Atomic Force Microscopy ............................................................................................ 19 2.4. Mechanical tests ........................................................................................................ 20 CHAPTER 3MATERIALS AND METHODS ......................................................................... 23 3. Materials and methods .......................................................................................... 23 3.1. Metallized PP film samples ................................................................................. 23 3.2. Characterization Techniques .............................................................................. 23 3.2.1. Differential Scanning Calorimetry analysis .............................................................. 23 3.2.2. Fourier Transform Infrared Spectroscopy analysis ................................................... 25 3.2.3. Scanning Electron Microscopy and Energy Dispersive Spectroscopy analysis ........... 26 xiv ABREVIATION LIST A Area Al Aluminium element AFM Atomic Force Microscopy aPP Atactic polypropylene ASTM American Society for Testing and Materials ATR-FTIR Attenuated Total Reflectance-Fourier Infrared Spectroscopy BOPP Biaxially oriented polypropylene %C Percentage of crystallinity D Distance DSC Differencial Scanning Calorimetry Е Young Modulus EDS Energy Dispersive Spectroscopy EDX Energy Dispersive X-Ray Spectroscopy ε Strain εo Vacuum permittivity εr Dielectric constant ESR Equivalent series resistance F Frequency FTIR Fourier Transformed Infrared Spectroscopy ∆Hf Entalpy of fusion HDPE High density polyethylene iPP Isotactic polypropylene ISO International Standards Organization IR or RIS Insulation resistance IUPAC International Union of Pure and Applied Chemistry LDPE Low density polyethylene MD Machine direction MDO Machine direction orienter MKP Metallized Polypropylene film MKT Metallized Polyester film MPa Mega Pascal PBT Polybutylene terephthalate PET Polyethylene terephthalate PP Polypropylene PPS Polyphenylene sulfide PS Polystyrene Ra Roughness average RIS Resistance insulation RMS or Rq Root mean square 𝑠 Standard deviation SE Secondary electron SEM Scanning Electron Microscopy SnZn Alloy of Tin and Zinc xv SnCu Alloy of Tin and Copper sPP Syndiotactic polypropylene tan δ Dissipation factor TD Transverse direction TDO Transverse direction orienter Tg Glass transition temperature U Voltage x Average Xc Capacitive reactance Zn Zinc element ZnAl alloy Alloy of Zinc and aluminium 𝜎 Stress % Percentage xvi “To Dream To Dare To Do “ (By Dr. Felix Zandman) 1 CHAPTER 1INTRODUCTION 1. Introduction 1.1. The company: Vishay´s history Vishay Intertechnology, Inc. is a worldwide company which was growing through acquisitions of some companies as Roederstein, Dale, BCComponents and General semiconductor [1]. Discrete semiconductors and passive components represents the Vishay´s portfolio brands [2]. Its founder was Dr. Felix Zandman, who was born in 1928 and passed away in 2011. Doctorated in Mechanical Physics by University of Paris in 1953, he had a very important portfolio in the electronic industry [3]. Dr. Felix Zandman was a survivor of Holocaust horror. An example of strength, struggle, persistence, work and hope. His experience is described in his book ”Never the Last Journey” [4]. Vishay Electrónica Portugal, Lda, is located in Portugal, near Vila Nova de Famalicão, in Calendário. It belongs to Vishay Intertechnology, Inc [5]. Roederstein was acquired by Vishay Intertechnology in 1993 and since that time it is Vishay Electrónica Portugal, Lda. In 2019, Vishay Intertecnology celebrated the fiftieth anniversary. Vishay Electrónica Portugal, Lda celebrated the historical event in September 2019 [6]. In Portugal, Figure 1, it has around 200 workers and it produces film capacitors to electronic equipment’s, as solar panels energy, televisions, radios and automotive industry. Vishay is growing and getting stronger and very competitive in the electric and hybrids automotive industry. Figure 1Vishay Electrónica Portugal, Lda [7] 1.2. Scope The main goal of this work was to study and understand the different polypropylene (PP) films that are used in film capacitors. To evaluate different suppliers and grades, different techniques, as Differential Scanning Calorimetry (DSC), Fourier Transformed Infrared Spectroscopy (FTIR), Scanning Electron Microscopy 2 (SEM), Atomic Force Microscopy (AFM) and mechanical measurements were applied. Furthermore, the knowledge of chemical and physics polypropylene properties was important too in this study. 1.3. Thesis organization The thesis is divided in 6 chapters, as presented in the Figure 2. Figure 2Overview of the thesis chapters •The company : Vishay´s history •Scope of this investigation •Thesis organization 1-Introduction •Film capacitor and production process •Materials •Polyproplylene polymer •Caracterization tecnhiques: DSC, FTIR, SEM, AFM, mechanical tests 2-State of art •Materials used in the investigation •Methods details 3-Materials and Methods •Discussion and analysis of the results 4-Discussion and results •Overview and final conclusions of the results obtained. 5-Conclusion •Suggestions for further investigation and development 6-Future work 3 CHAPTER 2STATE OF ART 2. State of art 2.1. Film Capacitor A film capacitor is a passive component, meaning that it cannot introduce power into a circuit or either amplifying the flow of the electrical current or either capable of electrically controlling. It is able to store energy and release it in the circuit when needed[8]. The Figure 3 shows a scheme of a film capacitor. A capacitor consists in two electrodes (position 1) working as two conductive plates, separated by the dielectric (position 2), the insulating material. The distance between the electrodes is given by position 3. Figure 3Scheme of a film capacitor [9] For a better understanding of a metallized film capacitor, it will be described the steps involved to produce it. The Figure 4 demonstrates the steps for manufacturing a film capacitor. 4 Figure 4Steps for a film capacitor manufacturing [10] The first step is the metallizing, where the metal layer is deposited in one side of the plastic film, under a vacuum deposition system. The result is a metallized film called as dielectric. After that, the metallized mother roll is cutted in several parts (film slitting) and packaged to be winding later on, in the same factory or to be sold. Vishay Electrónica Portugal buys the metallized film from several suppliers. The third step is the winding and here starts the production in Vishay Electrónica Portugal. They are winded the right and left metallized rolls with a high-speed machine. The product at this stage is called as cell. Cells which are cylindric, are going to be flattened, in the flattening. After that, they will be involved in a masking paper and the sides (contact layer) are going to be sprayed with a metal layer, “schoopage”. Then, cells are tested in a machine, the healing step, to select the good ones and separate the cells with defects, as burnings. Some types, go to the impregnation, which is defined as giving a bath in a silicon oil tank. A wire or a terminal will be soldered in the contact layer (terminal welding step), before being casted with an epoxy, inside a box. Finally, the capacitor makes the electrical end test, 5 where it is tested in a specific electrical equipment which measures, for example, the capacitance and the dissipation factor. Figure 5, presents a scheme of a film capacitor, after its manufacturing. Figure 5Scheme of a film capacitor[10] Electrical tests are important to evaluate the good conditions of a capacitor. There are three important characteristics which are measured at the final production of a capacitor: the capacitance (C), the tangent delta (tan δ) and the insulation resistance (IR or RIS). The capacitance is the capacity to store electric charges. It is expressed in Farad (F) and its value is proportional to the dielectric constant of the material,𝜀𝑟, to vacuum permittivity, 𝜖0 , and electrodes area, 𝐴,and inversely proportional to the distance between the electrodes, 𝑑, as expressed in Equation 1[11]. ∁=𝛆𝐫𝛜𝟎𝐀 𝐝 Equation 1 The dissipation factor or tangent delta, tanδ, expressed in percentage (%) depends of the equivalent series resistance (𝐸𝑆𝑅) and the capacitive reactance, 𝑋𝑐 (Equation 2). 𝐭𝐚𝐧𝛅=𝐄𝐒𝐑 𝐗𝐜 Equation 2 The 𝑋𝑐 , in ohms, is the impedance of the capacitor and it is inversely proportional to the capacitance and frequency, f . It is defined as the inertia against the flow of the current and it is given by Equation 3 [12], [11]. 𝐗𝐜=𝟏 𝟐 𝒇𝑪 Equation 3 (PP) 6 The lower the ESR, the lower the tangent delta, the better the capacitor and the lower the losses. The value indicates losses of the resistance between the metallized film, metal spray layer and terminals, as well as, losses of the polarization in the dielectric[13]. The insulation resistance (IR), expressed in ohms (Ω) is related to the applied voltage, 𝑈 , and the leakage current, 𝐼, given by Equation 4. 𝐑𝐈𝐒 =𝐔 𝐈 Equation 4 An increase in 𝐼 leads to a decrease in the IR, therefore, more heat is produced and the more the temperature increases leading in possible failures, as melting of the dielectric [14]. During the manufacturing and the lifetime of a metallized film capacitor, there are some failures modes which can occur, as shown in Figure 6. Figure 6Failure modes, causes, effects and consequences which can occur in a metallized film capacitor [14] Figures 7 and 8 show some failures in the metallized film, which can damage a metallized film capacitor. 7 Figure 7Metallized film with electrode corrosion due to the presence of moisture [14] Figure 8Metallized film which was demetallized due to corona arcing [14] 2.2. Materials Materials are selected according to the application of the film capacitor. The Table 1 shows some of the materials used to produce film capacitors. Table 1Example of materials used in a film capacitor Material To be used in PP (or PET) metallized with ZnAl /Al Cell Cu tinned Terminal or wire ZnAl/ Al/SnZn/SnCu Alloy Metal spray layer PBT (or PPS) with glass fiber Case Epoxy resin/ Polyurethane Resin PPPolypropylene; PETPolyethylene Terephthalate;ZnAlZinc Aluminium; AlAluminium; CuCopper; SnZnTin Zinc; SnCuTin Copper; PBTPolybutylene Terephthalate; PPSPolyphenylene Sulfide. 14 Figure 18Influence of the orientation in the dielectric strength[33] The Figure 18 demonstrates that the orientation plays an important rule on the dielectric strength improvement. An oriented dielectric film has higher dielectric strength, with a survival frequency of 99%, when compared with an oriented packaging film (or even with an unoriented packaging film, which cannot survive more than 95%). To prevent the film from stretching, a higher Young Modulus value is preferred. Higher orientation level and higher modulus prevent the film from having permanently deformations. The stretching causes wrinkles in the wounded roll and it is responsible for the non-desirable capacitance. Furthermore, the shrinkage of the dielectric during the manufacturing can decrease the capacitance of the capacitor or it can lead to flashover shorts. For semi-crystalline polymers, as PP, the volume is reduced 20 to 25%, when cooled from the processing temperature to the room temperature, Figure 19 [30]. Figure 19Influence of the shrinkage ( specific volume versus temperature with no pressure) [30] 15 The shrinkage depends from the rate solidification and this can cause internal stress which can lead to void formation and tearing. A low shrinkage is desirable. The surface roughness tends to affect the dielectric and physical strengths. To improve the impregnation and preserves the strength of the film, in a dielectric liquid impregnated electrical capacitor, for example, a morphological phenomenon, called as hazy PP film, is used as a dielectric medium. This provides an irregular surface on PP, but it is uniform in all film. As a BOPP is metallized with a thin layer of aluminium, for example, is desirable a strong adherence between the metal layer and the BOPP to improve the contact. The hazy film provides a good contact between the materials and improves the winding and the drying cycle of the material as it provides surface lack for removal of vapours [34]. Hazy film allows the dielectric oil penetrates into the capacitor due to one side of the film has an open fibrillar structure, Figure 20 [33]. Figure 20Hazy film: Open fibrillar structure on the film surface (General electric)[33] In this case, the fibrillar surface depends of the resin characteristics and process parameters, while the oil cooperates to a good capacitance. Other important point to consider, it is the contamination during manufacturing or present in the resin, which can lead to dissipation factors. During the manufacturing of the films is not allowed regrind material. 2.3. Characterization techniques For the characterization of the polypropylene films, all samples were subjected to several techniques such as Differential Scanning Calorimetry (DSC), Fourier Transform Infrared spectroscopy (FTIR), Scanning Electron Microscopy (SEM), Atomic Force Microscopy (AFM) and mechanical tests. It is going to be described a summary of each technique, which one, very useful to characterize materials. 16 2.3.1. Differential Scanning Calorimetry DSC is a thermal analysis technique, very important in pharmaceutical and polymer fields, used in quality control methods, development and manufacturing of polymeric materials. It is able to measure the response of a material when heated or cooled, allowing to study physical properties, estimates the lifetime and curing processes for example, as well as, to study thermal and mechanical histories of a material [35]. The Figure 21 shows a typical thermogram for an organic polymer. It measures the transitions and enthalpy changes, occurred in a sample as a function of temperature and time. Figure 21-DSC response of an organic polymer [30] At a constant heating and cooling rates, this technique allows the measuring of the glass transition (Tg), the melting, the crystallization, degradation, oxidation and the heat capacity of a material, providing a full thermal characterization of a material [30]. To study a polymer, it is made a first heating curve of a DSC measurement, to see the mechanical or thermal history, and then a second heating curve to determine the properties of the material, under certain conditions [36]. Many materials have crystalline and amorphous regions. The crystalline structure and the morphology (as spherulites dimensions) have a significant influence in the mechanical properties of semicrystalline polymers, as PP [37]. For PP, there are four different types of spherulites [22]. The DSC can measure the degree of crystallization of a structural order of a solid, becoming possible the study of polymer properties. It is influenced by the thermal history and the chemical structure. By Equation 5, it can be obtained the relative percentage of crystallinity (%C) by measuring the enthalpy of fusion of a sample (∆Hf) and comparing it with the enthalpy of the pure crystalline material (∆Hf 100%). The enthalpy for 100% crystalline PP is 207J/g [38]. 17 %𝐂= ∆𝑯𝒇 ∆𝑯𝒇𝟏𝟎𝟎%𝐱𝟏𝟎𝟎 Equation 5 The higher the percentage of crystallinity, more brittle is the material but stronger and stiffer is. Moreover, it influences the density, transparency and hardness of a material [37]. 2.3.2. Fourier Transform Infrared Spectroscopy FTIR is used in a wide range of industries, as an example, pharmaceuticals, food, chemicals, materials, forensic labs and at academics. It covers chemical applications for organic compounds and polymers. It allows, for instance, the investigation of adulterants in the food, analyze product formulation, identify product contaminants and solve manufacturing problems [39]. It is a non-destructive technique that measures the interaction of infrared light with the material, through the vibrational transitions of molecules. It consists in passing an infrared radiation through a sample, while some radiation is transmitted and other is absorbed by the atoms. This absorption is detected by the detector, which gives a signal of the molecular “fingerprint” of the sample, the spectrum. This can be done by handling compressed alkali metal halide pellet method (using for example Bromine Potassium (KBr)) or use an Attenuated Total ReflectanceFourier Transform Infrared Spectroscopy (ATR-FTIR). By the measuring of the vibrations of atoms is possible to determine the functional groups and obtain an infrared spectrum, as shown in Figure 22 [40]. The frequency is measured as wavenumbers, over the range of 4000cm-1 and 600cm-1, typically. Figure 22Infrared spectrum of n-heptane, by ATRFTIR [41] 18 The main regions of the infrared spectrum is listed in Figure 23. Figure 23IR regions and respectively functional groups positions[42] 2.3.3. Scanning Electron Microscopy Morphological aspects of a material can be determined by SEM, a non-destructive technique, very useful for the characterization of materials, as it is able to give detailed images of the sample which is being analyzed. Electron microscope has the same principle of an optical microscope, but due to its electrons with very shorts wavelengths it allows higher resolution image than the optical microscope[43]. Atoms present in the surface of the sample interact with the electron beam producing several signals on the surface of the solid sample giving information about, for example, the chemical composition, morphology, crystallinity structure and orientation of the materials[44]. SEM can be coupled with energy dispersive spectroscopy (SEM-EDS). EDS can be also designated as energy dispersive X-ray spectroscopy (EDX). It allows the identification and the quantification of each element present in the sample and it useful for instance, for contamination analysis, material defects and tin whiskers analysis[45]. EDX consists in bombarded, with X-ray radiation, the surface of a sample, in keV, through an electron beam. The X-rays emitted depend on the acceleration voltage of the electron beam, as well as, on the material which is being analyzed and the elements found near the surface of the sample. For example, metals like gold, zinc are very easy to be detected by this technique, while elements with low atomic number are more difficult to be detected [46]. Figure 24 presents the electromagnetic spectrum, showing the distribution of the electromagnetic radiation in function of frequency and wavelength. The higher the frequency the shorter the wavelength, as observed for X-rays [47]. 19 Figure 24Electromagnetic spectrum [47] 2.3.4. Atomic Force Microscopy AFM characterizes the surface topography of samples through, for example, the determination of the roughness [48]. As SEM, it allows the analysis of the surface with a high accuracy. Figure 25 presents a scheme of an AFM system. The sample is placed in the AFM and, by a piezo actuator with displacement in XYZ positions, scans the surface of the sample. An optical system, with laser beam and a photo detector, determine the deflection level of the cantilever, according the surface topography. Finally, a specific software will translate the information and give the image of surface topography[49]. Figure 25AFM scheme [50] 20 There are height parameters able to characterize the surface topography. Figure 26 shows some of principle parameters, where M is the mean line and L is the sampling length (L)[51]. Most common parameters are the roughness average (Ra), which is defined as the arithmetic average of the absolute values of the profile heights, measured from the mean line; the root mean square deviation (RMS or Rq), which corresponds to the standard deviation of the surface height measured from the mean line[52]. The maximum roughness depth (Rmax) is the difference between the highest and the lowest vertical distance point of the profile. Figure 26Example of a Ra and Rq measurement [51] 2.4. Mechanical tests During the development and research of plastics materials, it is very important to study and know more about the properties and the behavior of each material to predict future problems as ruptures or breaks. There are some characteristics as Young Modulus (or Tensile Modulus), tensile strength and elongation at breaks which are very useful to understand how the material reacts under compression or even tension. Of course, these properties can be influenced by the process used later on, but normally they are given by the raw material supplier. The Young Modulus, 𝐸, is measured in Pascal (Pa) and evaluates the elasticity of solid materials [53]. The Young Modulus is determined by the Equation 6. It gives a measure of the resistance to deformation of a material and it is defined as the deformation 𝜀 (strain), of a material and the force 𝜎 (stress), needed to deform it [30]. 𝐄=𝛔 𝛆 Equation 6 21 Tensile strength, measured in MPa, is the maximum stress that a material can handle. It is the maximum value just before the rupture. The elongation at breaks, measured in percentage (%), is the elongation that a material can withstand before its break. The Figure 27 shows a stress-strain curve of a material. This analysis provides information about the mechanical behavior. A sample, with a known dimension, is deformed at a given rate while the strength needed to induce the deformation is recorded. Figure 27Stressstrain curve of a material [53] The elastic behavior is the first yield point, where the material can return to the initial state if released the applied force. Then the second yield point is the plastic behavior where the material will have a permanent deformation. The third yield point is the rupture point, which means that the strength applied was too high. After the rupture point, the material will break. Figure 28 shows a scheme of stress-strain curves, depending on the polymer. 22 Figure 28Examples of stress-strain curves for different polymers [30] In conclusion, the elongation at break is related to the polymer plasticity and its ability to extend before breaking. Young Modulus is related to the elasticity while the tensile strength is related to the mechanical strength of a polymer [47]. The stiffer the material, the greater the Young Modulus value. 23 CHAPTER 3MATERIALS AND METHODS 3. Materials and methods 3.1. Metallized PP film samples PP film rolls with a thin metallization layer presenting 36.0mm width, with different thicknesses (2.4µm to 3.0µm) were the samples used for the investigation, as presented in Figure 29. Figure 29Metallized polypropylene film samples All samples were identified from 1 to 6, according to Vishay code number, as listed in the Table 3. Table 3Samples identification Sample Vishay Code nr. 1 80920622 2 80920625 3 80921546 4 80933978 5 80932744 6 80920623 3.2. Characterization Techniques 3.2.1. Differential Scanning Calorimetry analysis DSC curve of the samples was recorded with a differential scanning calorimeter from PerkinElmer, model 6000, equipped with an intracooler (Figure 30). 30 Figure 38DSC result for sample 1, Vishay code nr. 80920622, using program 1 All thermograms, using program 1, are presented in annex I, of this thesis. To have an overview of results, Table 6 and Table 7 present the melting and the crystallization peaks of each sample, using program 1, during the first and the second run, respectively. As it can be seen, there were some differences for Tm, Hm and consequently, crystallinity percentage variation (table 8) of the structure. Increasing the onset melting temperature in BOPP films can be the result of transition of structures of stacked lamellae into fibrillar structures which are oriented along transverse [57], but the DSC technique is not sensitive to detect these changes. Table 6First run for the melting and crystallization, for the program 1, for each sample First run Heating (melting) Cooling (crystallization) BOPP sample Onset (±0,01°C) End (±0,01°C) Tmelting (±0,01°C) Area (mJ) ΔHm (J/g) Onset (±0,01°C) End (±0,01°C) Tcrystallisation (±0,01°C) Area (mJ) ΔHc (J/g) 180920622 157.97 176.77 172.49 1029.42 128.68 122.63 112.90 117.59 988.21 123.53 280920625 170.09 176.49 172.46 830.12 105.08 121.48 112.57 117.18 863.25 109.27 380921546 160.08 174.23 170.79 917.82 99.76 119.78 110.13 114.51 909.01 98.81 480933978 167.05 176.06 173.05 784.84 120.74 121.15 111.52 116.28 767.16 118.02 580932744 163.62 174.42 171.47 726.97 111.84 120.19 111.34 115.79 747.71 115.03 680920623 167.00 177.48 173.87 991.65 116.66 120.39 110.61 115.23 973.90 114.58 31 Table 7Second run for the melting and crystallization, for the program 1, for each sample Second run Heating (melting) Cooling (crystallization) BOPP sample Onset (±0,01°C) End (±0,01°C) Tmelting (±0,01°C) Area (mJ) ΔHm (J/g) Onset (±0,01°C) End (±0,01°C) Tcrystallisation (±0,01°C) Area (mJ) ΔHc (J/g) 180920622 159.18 170.77 166.48 988.17 123.52 122.09 112.54 116.92 980.00 122.50 280920625 160.52 171.04 166.54 864.16 109.39 122.15 112.80 116.54 870.62 110.21 380921546 157.29 169.71 164.55 850.58 92.45 119.97 110.33 114.34 912.26 99.16 480933978 158.05 169.97 165.04 775.73 119.34 121.46 111.65 115.95 767.31 118.05 580932744 157.47 168.49 163.40 716.89 110.29 120.42 111.45 115.46 748.92 115.22 680920623 158.74 171.56 166.67 917.01 107.88 120.24 110.52 114.90 978.78 115.15 With this information (Tables 6 and 7) is possible to calculate the crystallinity of each BOPP sample, by Equation 5, considering ∆Hf of PP is 207 J.g-1 and presented in table 8. Table 8Crystallinity results for the first and second run during the heating BOPP sample ΔHm(J/g) 1st run % C ΔHm (J/g) 2nd run % C 1-80920622 128.68 62.16 123.52 59.67 280920625 105.08 50.76 109.39 52.84 3-80921546 99.76 48.19 92.45 44.66 4-80933978 120.74 58.33 119.34 57.65 5-80932744 111.84 54.03 110.29 53.28 6-80920623 116.66 56.36 107.88 52.12 Figure 39 shows the percentage of crystallinity of the six samples studied with the program 1. Figure 39Percentage of crystallinity, using the program 1 0 10 20 30 40 50 60 70 Sample 180920622 Sample 280920625 Sample 380921546 Sample 480933978 Sample 580932744 Sample 680920623 % C 1st run 62,16 50,76 48,19 58,33 54,03 56,36 % C 2nd run 59,67 52,84 44,66 57,65 53,28 52,12 Percentage of crystallinity(%) 32 Sample 1 has the highest percentage of crystallinity, followed by sample 4. Samples 5 and 6 have similar crystallinity, while the lowest crystallinity is observed in sample 3. Polymers which are more ordered tend to lead to high degree of crystallinity. The first run and the second run have the same rate of cooling, so it is not seen significant differences between the runs, in terms of crystallinity. Considering the program 2, Figure 40 presents the thermograms of all samples, from Table 3. Figure 40-DSC results from all Vishay BOPP samples, obtained with the program 2 For example, considering sample 1, 80920622, it was determined the thermogram of Figure 41. Figure 41DSC result for sample 1, Vishay code nr. 80920622, using program 2 -40 -30 -20 -10 0 10 20 30 40 -50 050 100 150 200 250 300 Heat Flow Endo Up (mW) Temperature (⁰C) 80920622 80920625 80921546 80933978 80932744 80920623 33 All thermograms, using program 2, are presented in annex II, of this thesis. To have an overview of results, Tables 9 and 10, present the melting and the crystallization peaks of each sample, using program 2, during the first and the second run, respectively. Table 9First run for the melting and crystallization, for the program 2, for each sample First run Heating (melting) Cooling (crystallization) BOPP sample Onset (±0,01°C) End (±0,01°C) Tmelting (±0,01°C) Area (mJ) ΔHm (J/g) Onset (±0,01°C) End (±0,01°C) Tcrystallisation (±0,01°C) Area (mJ) ΔHc (J/g) 180920622 157.62 175.39 171.92 831.03 125.92 104.07 91.79 99.23 777.09 117.74 280920625 157.84 175.87 171.70 888.19 120.03 103.19 91.57 99.04 938.62 126.84 380921546 156.92 174.14 170.34 782.28 110.18 102.41 90.04 97.24 806.65 97.24 480933978 168.64 175.10 172.34 733.56 114.62 105.30 89.62 97.99 769.38 120.22 580932744 157.62 175.39 171.92 831.03 125.92 104.07 91.79 99.23 777.09 117.74 680920623 157.84 175.87 171.70 888.19 120.03 103.19 91.57 99.04 938.62 126.84 Table 10Second run for the melting and crystallization, for the program 2, for each sample Second run Heating (melting) Cooling (crystallization) BOPP sample Onset (±0,01°C) End (±0,01°C) Tmelting (±0,01°C) Area (mJ) ΔHm (J/g) Onset (±0,01°C) End (±0,01°C) Tcrystallisation (±0,01°C) Area (mJ) ΔHc (J/g) 180920622 156.73 170.62 165.75 652.15 98.81 122.59 113.92 117.65 770.37 116.72 280920625 157.62 170.56 165.40 830.37 112.21 121.93 113.67 117.38 819.64 110.76 380921546 156.58 169.40 163.27 694.51 97.82 121.25 112.25 115.77 723.15 101.85 480933978 157.04 170.45 164.79 605.48 94.61 122.37 112.20 117.38 732.39 114.44 580932744 156.73 170.62 165.75 652.15 98.81 122.59 113.92 117.65 770.37 116.72 680920623 157.62 170.56 165.40 830.37 112.21 121.93 113.67 117.38 819.64 110.76 It can be checked that, for program 2, there is almost no variation in the onset temperature, possible meaning that the lamellae crystals are more uniform between them. With the information, from Tables 9 and 10, is possible to calculate the crystallinity of each BOPP sample, by Equation 5, considering ∆Hf of PP is 207 J.g-1 and presented in the Table 11. 34 Table 11Crystallinity results for the first and second run during the heating BOPP sample ΔHm (J/g) 1st run % C ΔHm (J/g) 2nd run % C 1-80920622 125.92 60.83 98.81 47.73 280920625 120.03 57.98 112.21 54.21 3-80921546 110.18 53.23 97.82 47.26 4-80933978 114.62 55.37 94.61 45.70 5-80932744 98.04 47.36 83.61 40.39 6-80920623 131.34 63.45 118.76 57.37 Figure 42 shows the percentage of crystallinity of the six samples studied with the program 2. Figure 42Percentage of crystallinity, using the program 2 With program 2, the percentage of crystallinity is different, when compared with the results of program 1. Sample 6 has the highest percentage of crystallinity, followed by the samples 1, 2 and 4, while the lowest crystallinity is observed in sample 5. By the DSC, the first heating, which gives the information about the material as it is, shows that the polymer is an iPP, as the melting point of a perfect iPP is 171ºC. During the first heating are visible two peaks that can give an indication of two different crystal morphologies of the iPP. Normally commercial iPP has a melting point around 160-166ºC, and this can be observed in the second heating (which gives information about the behavior of the material). The program used can influence the 0,00 10,00 20,00 30,00 40,00 50,00 60,00 70,00 Sample 180920622 Sample 280920625 Sample 380921546 Sample 480933978 Sample 580932744 Sample 680920623 % C 1st run 60,83 57,98 53,23 55,37 47,36 63,45 % C 2nd run 47,73 54,21 47,26 45,70 40,39 57,37 Percentage of crystallinity(%) 35 crystallinity of the polymer, as proved by using different cooling’s at program 1 and program 2. The first cooling allows the molecular orientation, gives information about the recrystallization of the iPP and delete the thermal history of the material[58]. The cooling run provides information about the manufacturing process, where it can be seen a crystallization peak which proves that manufacturing process was too fast and gave no time to occur the crystallization of the iPP. Molecules cannot have time to organize themselves and this can lead to thermal and mechanical failures. Samples 4 and 5 have the lowest area in the melting point region, during the endothermic reaction. The crystallinity of the PP is around 40-60%, as the results show, samples 1 and 6 have the highest crystallinity and therefore more brittle is the sample[58]. The higher the crystallinity the stiffer is the sample and the better the material resistance. Fast cooling can lead to crystallinity problems because the material cannot have time to crystallize in total. The program 1 has a slow cooling, 10ºC/min, which can influence the crystallinity and can give time for the molecular chain organization, as well as, crystalline structures. This is shown by the high percentage of crystallinity, during the second run. For example, sample 1 has a % C of 62.16/59.67, during first and second run in program 1, respectively, while the same sample, with program 2, has a %C of 60.83/47.73 during first and second run, respectively. The processing conditions, as cooling/heating rate and time, and the thickness of samples can influence the results obtained, as shown with different cooling rates. Other important factor that can affect the crystallinity is the thickness of PP film, the higher the thickness the lower the crystallization. This can explain the low crystallinity observed in sample 3, which is the thicker sample. In the first heating run, it is visible two different melting peaks which can be justified as two different crystal morphologies of the polymer. The first melting peak disappears in the second heating run, probably due to high energy and imperfect crystals. Considering the total area during the heating, it can be observed that the area in first run is higher than in the second run, for both programs. As samples were not normalized, it cannot be said that the lower the area, the less quantity of material was melted. However, it can be observed that the second melting peak is thinner than the first melting peak. This technique demonstrates that the polymer studied is a PP and samples have different crystallinities, which can influence the mechanical properties of each sample. 36 4.2. Fourier Transform Infrared Spectroscopy FTIR measurements were used to evaluate the vibrational characteristic bands of the samples and the Figure 43 shows the spectrum obtained for all samples, which confirms that it is a PP sample. As PP is an alkane, it has only C-C and C-H bonds. From the ATR-FTIR spectrum, and checking literature, it can be observed that samples have four peaks between 3000cm-1 and 2800cm-1, which are related to the CH3 asymmetric stretching vibration (2950cm-1), CH3 symmetric stretching vibration (2867cm-1), CH2 asymmetric stretching vibration (2918cm-1), CH3 symmetric stretching vibration (2838cm-1),respectively. The peak at 1453cm-1 can be attributed to the CH2 scissor vibrations or to CH3 asymmetric deformation vibrations, while the peak at 1375cm-1 is attributed to CH3 asymmetric deformation vibrations. Between 1200cm-1 to 750cm-1 there are several small peaks. The peak at wavenumber around 1167cm-1 can be justified by the CH3 asymmetric rocking vibration or C-H wagging vibration or even due to the C-C asymmetric stretching vibration. The peak at wavenumber around 998cm-1 can be attributed to CH3 asymmetric rocking vibrations. The peak at wavenumber around 972cm-1 is due to the C-C asymmetric stretching and the CH3 asymmetric rocking vibrations, while the peak at 899cm-1 is due C-C asymmetric and symmetric stretching vibrations and CH3 asymmetric rocking vibrations. Finally, the peaks at 848cm-1 and 809cm-1 are related to CH2 rocking vibrations. [59] Figure 43ATR-FTIR spectrum: overview of all BOPP samples 70 75 80 85 90 95 100 105 5001000150020002500300035004000 Transmitance (%) Wavenumber (cm-1) ATR-FTIR Spectrum 80920622 80920625 80921546 80933978 80932744 80920623 37 Splitting the samples of Figure 43, it can be observed that they have the same spectrum, with different transmittances. For example, in Figure 44, sample 1 (80920622) has the same transmittance of sample 5 (80932744). Sample 2 (80920625) has the same transmittance of sample 6 (80920623). Sample 3 (80921546) has the same transmittance of sample 4 (80933978). The comparison, for example, of sample 1(80920622) with sample 3 (80921546) shows high transmittance for sample 3. This happened because the spectrums were not normalized by equalizing the height of the absorption peak at 2918cm-1. Figure 44ATR-FTIR spectrum: examples of the comparison between two samples For sample 1, it is shown in Figure 45, the spectrum taken from the FTIR software. 70 80 90 100 5001000150020002500300035004000 Transmitance (%) Wavenumber (cm-1) ATR-FTIR Spectrum 80920622 80932744 70 80 90 100 5001000150020002500300035004000 Transmitance (%) Wavenumber (cm-1) ATR-FTIR Spectrum 80921546 80933978 70 80 90 100 5001000150020002500300035004000 Transmitance (%) Wavenumber (cm-1) ATR-FTIR Spectrum 80920625 80920623 70 80 90 100 5001000150020002500300035004000 Transmitance (%) Wavenumber (cm-1) ATR-FTIR Spectrum 80920622 80921546 38 Figure 45Spectrum of a BOPP sample (sample 1) All samples spectrum are presented in annex III, of this thesis. 4.3. Scanning Electron Microscopy Figures 46 to 57 show surface morphological studies of samples, per area, evaluated by SEM. Element mapping of the particles was performed by SEM-EDS and the chemical composition results are summarized, per sample and per area, in Tables 12 to 17. The pictures (SEM) evidence different surface morphologies depending on the samples and suppliers. The surface of layer in the BOPP film is very smooth, and wrinkles and other defects are few, as shown in the picture in Figure 46 and 47, and for low magnification. 39 Sample 1Areas A and C Area A (between segments) C (not segmented) SEM image EDS image Figure 46SEMEDS images obtained in the Sample 1 – areas (A) and (C). . 46 Sample 4Area B Area B(in segments) SEM images EDS image Figure 53SEMEDS images obtained in the Sample 4 -area (B) The high-magnification SEM picture (Figure 53) shows that PP lamellae grow to the fiber axis. Table 15Identification and quantification of each element present in sample 4 Element Element weight (%) A Area B1 Area B2 Area C Area C 96.2 97.7 96.7 88.6 Zn 0.0 0.0 0.0 6.9 O 3.0 2.2 2.3 3.5 Al 0.8 0.1 1.0 0.9 47 Sample 5 -- Areas A and C Area A (between segments) C (not segmented) SEM images EDS image Figure 54SEMEDS images obtained in the Sample 5 -areas (A) and (C) 48 Sample 5Area B Area B(in segments) SEM images EDS image Figure 55SEMEDS images obtained in the Sample 5 area (B) In Figure 55, SEM analyses of the cross sections (B) confirmed uniform distribution of clusters inside the sample. Table 16Identification and quantification of each element present in sample 5 Element Element weight (%) A Area B1 Area B2 Area C Area C 95,6 98,8 95,8 88,3 Zn 0 0 0 6,7 O 3,6 1,2 3,5 4,2 Al 0,8 0,1 0,7 0,8 49 Sample 6 - Areas A and C Area A (between segments) C (not segmented) SEM images EDS image Figure 56SEMEDS images obtained in the Sample 6 -areas (A) and (C) 50 Sample 6Area B Area B(in segments) SEM images EDS image Figure 57SEMEDS images obtained in the Sample 6 -area (B) The high-magnification SEM picture (Figures 56 and 57) show that PP lamellae grow to the fiber axis. Table 17Identification and quantification of each element present in sample 6 Element Element weight (%) A Area B1 Area B2 Area C Area C 96.6 98.7 96.3 88.0 Zn 0.0 0.0 0.0 7.9 O 2.7 1.2 3.2 3.2 Al 0.7 0.1 0.6 0.8 51 Considering the Table 18, with the EDS identification and quantification of each element, it can be observed, that sample 1 and sample 2 don´t have zinc (Zn) in C area, meaning that they are metallized only with Al. Samples 3 to 6 have Zn in C area, meaning that they were metallized in ZnAl. Observing the images from the morphological aspect, they suggest that all samples are from different suppliers, as they have different morphological aspect. The same conclusion was observed with DSC and ATR-FTIR techniques, as all samples shown different thermograms and spectrums, respectively. PP lamellae grow to the fiber axis and they are visible in almost all films, however samples 1 and 2 seems to have more than the other samples. Then appears sample 6 and 3, however the most homogeneous samples seem to be samples 5 and 4. Considering B area, sample 4 has almost no PP lamellae in B1 area and sample 5 has no PP lamellae in B1 and B2 areas. Samples 4 and 5 show a special treatment or process in area B. This difference can give an indication about different metallization processes. It is interesting to observe B1 area, specially sample 5, as it has clusters, very well defined and uniform. It would be interesting to check the element composition in this area (dark and white part). Sample 1 and 2 seem to have the same metallization process as the EDS is very similar. Samples 4 to 6 have the lowest Al percentage in B1 area (0.1%) against samples 2 and 3 (0.2%) and sample 1 (0.3%), which can give an indication about the cleaning of the segments. Comparing samples 3 to 6 metallized with ZnAl, it can be observed that sample 3 has the highest weight of Zn in C area (10.9%), against the lower quantity of Zn presented in sample 5 (6.7%). Considering the weight of Al in these samples, it is visible that the Al is more uniform in sample 5 in all the extension of the film, from the A area to the C area (0.7% and 0.8%) and almost no Al in B1 area (0.1%). This can suggest that the process is controlled. For example, in sample 4, the Al weight from A are to C area vary between 0,8% and 1.0%. The deterioration of Al caused by oxidation is not desirable, hence, to prevent the oxidation and improve the humidity resistance of the metallized film it is used Zn [60], [61]. 52 Table 18Overview of EDS Identification and quantification for each sample in graphs Sample 1 Sample 2 Sample 3 Sample 4 Sample 5 Sample 6 91 92 93 94 95 96 97 98 99 100 101 Area A Area B1 Area B2 Area C Element weight (%) Al O Zn C 88 90 92 94 96 98 100 102 Area A Area B1 Area B2 Area C Element weight(%) Al O Zn C 75 80 85 90 95 100 105 Area A Area B1 Area B2 Area C Element weight(%) Al O Zn C 82 84 86 88 90 92 94 96 98 100 102 Area A Area B1 Area B2 Area C Element weight(%) Al O Zn C 82 84 86 88 90 92 94 96 98 100 102 Area A Area B1 Area B2 Area C Element weight(%) Al O Zn C 80 82 84 86 88 90 92 94 96 98 100 102 Area A Area B1 Area B2 Area C Element weight(%) Al O Zn C 53 4.4. Atomic Force Microscopy Figures 58 to 63 and Tables 19 to 24, present AFM images of each sample area, as well as, the surface roughness values of each sample area, respectively. Tests were performed in transverse direction of the BOPP film. • Sample 1 A B C Figure 58Optical AFM topography images and surface roughness of the sample 1, into three different areas: (A), (B) and (C). Image size: 5×5 μm Table 19Surface roughness of the sample 1, into three different areas (A), (B) and (C) S1 A B C Rq (nm) 4.18 7.91 4.92 Ra(nm) 3.28 6.22 3.98 Rmax (nm) 42.80 70.80 39.40 54 Sample 2 A B C Figure 59Optical AFM topography images and surface roughness of the sample 2, into three different areas: (A), (B) and (C). Image size: 5×5 μm Table 20Surface roughness of the sample 2, into three different areas (A), (B) and (C) S2 A B C Rq (nm) 3.97 7.37 3.51 Ra(nm) 3.16 6.04 2.83 Rmax (nm) 36.50 61.00 30.70 55 • Sample 3 A B C Figure 60 - Optical AFM topography images and surface roughness of the sample 3, into three different areas: (A), (B) and (C). Image size: 5×5 μm Table 21Surface roughness of the sample 3, into three different areas (A), (B) and (C) S3 A B C Rq (nm) 4.78 7.57 9.32 Ra(nm) 3.82 6.22 7.23 Rmax (nm) 46.60 55.80 91.00 62 extension of the film (around 4.6nm for Ra; 6.0nm for Rq and 55 Rmax). Roughness is needed in a PP film, but high roughness is not desirable, as this can lead in electrical failures. Considering the results seems that a constant Ra among all film, of around 4,6nm is desirable for a metallized PP film. Analyzing AFM and SEM results, sample 5 is the most homogeneous sample in both techniques, this can be explain by the possible simultaneous stretching of the sample which lead to fiber orientation in transverse and longitudinal directions. 4.5. Mechanical tests From Table 25 to Table 31, it is presented the results of the mechanical tests obtained for sample 1 to 6, respectively, including the average and the standard deviation. All tests were performed in transverse direction of the film. The Table 25 show the results in sample 1, for each mechanical test. Table 25Mechanical results obtained for sample 1 Specimen Tensile Modulus or Young Modulus (MPa) Tensile stress at Yield (Offset 0.2 %) (MPa) Tensile strength (MPa) Strain at maximum load or elongation at break (%) Strain at break (%) 1 3124.04 32.19 126.71 48.13 48.13 2 3588.76 38.77 95.83 21.86 21.85 3 3651.71 36.79 127.03 40.73 40.73 4 3983.11 42.88 149.24 53.73 53.73 5 3814.16 43.44 98.00 21.16 21.16 6 3188.59 41.47 92.87 22.92 22.92 7 3787.97 40.78 137.42 50.00 50.00 𝐱 3591.19 39.47 118.16 36.93 36.93 𝐬 323.01 3.95 22.48 14.52 14.52 63 Figure 70 presents the strain-stress curve for the 7 specimens of sample 1. Figure 70Tensile strain vs tensile stress graph for specimen of sample 1 The Table 26 shows the results in sample 2, for each mechanical test. Table 26Mechanical results obtained for sample 2 Specimen Tensile Modulus or Young Modulus (MPa) Tensile stress at Yield (Offset 0.2 %) (MPa) Tensile strength (MPa) Strain at maximum load or elongation at break (%) Strain at break (%) 1 3335.00 34.57 66.92 18.50 18.50 2 3629.26 34.71 138.26 87.03 87.03 3 3033.38 34.62 135.53 88.24 88.24 4 3286.39 39.70 124.48 67.70 67.70 5 3155.33 35.26 128.26 81.49 81.49 6 2906.95 35.94 125.10 78.56 78.53 7 2597.86 34.55 80.50 31.20 31.20 𝐱 3134.88 35.62 114.15 64.67 64.67 𝐬 331.28 1.87 28.36 28.26 28.26 64 Figure 71 presents the strain-stress curve for the 7 specimens of sample 2. Figure 71Tensile strain vs tensile stress graph for specimen of sample 2 The Table 27 shows the results in sample 3, for each mechanical test. Table 27Mechanical results obtained for sample 3 Specimen Tensile Modulus or Young Modulus (MPa) Tensile stress at Yield (Offset 0.2 %) (MPa) Tensile strength (MPa) Strain at maximum load or elongation at break (%) Strain at break (%) 1 2958.44 26.95 61.22 30.83 30.83 2 2638.43 34.9 94.54 71.3 71.29 3 3453.38 31.37 81.75 50.69 50.66 4 3174.76 35.43 113.02 90.83 90.83 5 3185.16 27.31 102.94 90.86 90.86 6 3498.51 40.6 136.71 109.13 108.78 7 2915.1 28.89 115.26 104.95 104.92 𝐱 3117.68 32.21 100.78 78.37 78.31 𝐬 305.95 5.02 24.57 28.98 28.92 65 Figure 72 presents the strain-stress curve for the 7 specimens of sample 3. Figure 72Tensile strain vs tensile stress graph for specimen of sample 3 The Table 28 shows the results in sample 4, for each mechanical test. Table 28Mechanical results obtained for sample 4 Specimen Tensile Modulus or Young Modulus (MPa) Tensile stress at Yield (Offset 0.2 %) (MPa) Tensile strength (MPa) Strain at maximum load or elongation at break (%) Strain at break (%) 1 4000.51 41.03 65.2 13.41 13.39 2 3635.76 26.87 48.92 12.89 12.87 3 3464.92 44.45 153.2 105.87 105.87 4 3526.07 33.08 66.64 25.15 25.15 5 3128.08 39.71 61.56 14.32 14.32 6 3901.33 32.37 67.19 24.42 24.41 7 3799.9 32.37 80.15 37.96 37.94 𝐱 3636.65 35.70 77.55 33.43 33.42 𝐬 297.06 6.17 34.60 33.18 33.18 66 Figure 73 presents the strain-stress curve for the 7 specimens of sample 4. Figure 73Tensile strain vs tensile stress graph for specimen of sample 4 The Table 29 shows the results in sample 5, for each mechanical test. Table 29Mechanical results obtained for sample 5 Specimen Tensile Modulus or Young Modulus (MPa) Tensile stress at Yield (Offset 0.2 %) (MPa) Tensile strength (MPa) Strain at maximum load or elongation at break (%) Strain at break (%) 1 3979.96 38.38 64.79 8.18 8.16 2 3581.4 36.75 123.07 37.79 37.79 3 3644.13 28.81 78.78 20.16 20.15 4 3935.7 36.69 126.15 40.18 40.18 5 4487.97 44.37 125.22 32.69 32.69 6 3925.9 31.98 111.73 32.84 32.82 7 3762.43 46.26 163.88 57.71 57.7 𝐱 3902.50 37.61 113.37 32.79 32.78 𝐬 299.97 6.22 32.93 15.63 15.63 67 Figure 74 presents the strain-stress curve for the 7 specimens of sample 5. Figure 74Tensile strain vs tensile stress graph for specimen of sample 5 The Table 30 shows the results in sample 6, for each mechanical test. Table 30Mechanical results obtained for sample 6 Specimen Tensile Modulus or Young Modulus (MPa) Tensile stress at Yield (Offset 0.2 %) (MPa) Tensile strength (MPa) Strain at maximum load or elongation at break (%) Strain at break (%) 1 3578.22 34.71 56.08 11.56 11.52 2 3658.58 38.81 124.92 80.57 80.57 3 3409.16 37.91 119.22 79.98 79.98 4 3076.15 32.24 55.99 18.73 18.73 5 3699.15 35.72 100.76 54.61 54.61 6 3454.75 33.67 77.5 36.46 36.45 7 3176.68 32.63 96.06 56.36 56.36 𝐱 3436.10 35.10 90.08 48.32 48.32 𝐬 236.93 2.53 27.96 27.43 27.44 68 Figure 75 presents the strain-stress curve for the 7 specimens of sample 6. Figure 75Tensile strain vs tensile stress graph for specimen of sample 6 An overview of the average and standard deviation of each sample is presented in the Table 31. Table 31Average (𝐱) and standard deviation (𝐒) overview for each sample Sample Vishay Code nr. Tensile Modulus or Young Modulus (MPa) Tensile stress at Yield (Offset 0.2 %) (MPa) Tensile strength (MPa) Strain at maximum load or elongation at break (%) Strain at break (%) 1 80920622 x 3591.19 39.47 118.16 36.93 36.93 s 323.01 3.95 22.48 14.52 14.52 2 80920625 x 3134.88 35.62 114.15 64.67 64.67 s 331.28 1.87 28.36 28.26 28.26 3 80921546 x 3117.68 32.21 100.78 78.37 78.31 s 305.95 5.02 24.57 28.98 28.92 4 80933978 x 3636.65 35.70 77.55 33.43 33.42 s 297.06 6.17 34.60 33.18 33.18 5 80932744 x 3902.50 37.61 113.37 32.79 32.78 s 299.97 6.22 32.93 15.63 15.63 6 80920623 x 3436.10 35.10 90.08 48.32 48.32 s 236.93 2.53 27.96 27.43 27.44 69 Figures 76 to 78 show the variation and the comparison of all samples. Figure 76Overview of all characterisitics performed in mechanical tests. per sample Figure 77Young Modulus obtained per sample 70 Figure 78Tensile strength obtained per sample Figure 79Elongation at Break obtained per sample High Young Modulus is desirable, as it prevents deformations and cause less stretching, which in turn, can cause wrinkles and problems in capacitance of a capacitor. The higher the Young Modulus the less the material deforms and the higher the degree orientation. It depends from the crystal 71 orientation of the material. High elongation at break and high tensile strength leads to high toughness and a ductile material [62]. Samples 1, 4 and 5 have the highest Young Modulus, verified by the highest degree of crystallinity, as shown with DSC results, with program 1. Moreover, they have the lowest elongation at break. Samples 1, 2 and 5 have the highest tensile strength values. Sample 3 has the lowest Young Modulus, high tensile strength and the highest elongation at break values. The crystallinity and the thickness of the samples can explain the results obtained. 4.6. Shrinkage Regarding the shrinkage of films, in machine direction, results are presented in Table 32, using Equation 9 and considering 0% of shrinkage at 25°C. Table 32Measurement, in percentage, of the length of each film Sample Temperature 25 ⁰C 85 ⁰C 105 ⁰C 120 ⁰C 180920622 0% -0,95% -2,08% -3,34% 280920625 0% -0,81% -1,57% -2,71% 380921546 0% -0,74% -2,70% -3,37% 480933978 0% -0,92% -1,49% -2,04% 580932744 0% -0,74% -1,21% -1,76% 680920623 0% -0,47% -1,06% -1,68% The Figure 80 shows the shrinkage of all samples for the different temperatures. Shrinkage depends on the materials properties and polymer composition. The lower the shrinkage the better the capacitance of the capacitor and the less the internal stress of the film. 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[62] Y.H.Zhao, E.J.Lavernia, “The mechanical properties of multi-scale mettalic materials", Nanostructured Metal and Alloys, Processing, Microstructure, Mechanical Properties Applications, Elsevier, Chapter 13, 2011. 80 ANNEX I Thermograms obtained with program 1 • Sample 1 • Sample 2 81 • Sample 3 • Sample 4 82 • Sample 5 • Sample 6 83 ANNEX II Thermograms obtained with program 2 • Sample 1 • Sample 2 84 • Sample 3 • Sample 4 85 • Sample 5 • Sample 6 86 ANNEX III Spectrum • Sample 1 • Sample 2 87 • Sample 3 • Sample 4