Production of melt-spun fibers with heat conduction properties

Universidade do Minho Escola de Engenharia Tomás Ramos Ribeiro Production of melt-spun fibers with heat conduction properties november 2023 UMinho | 2023 Tomás Ramos Ribeiro Productiont of melt-spun fibers with heat conduction properties Tomás Ramos Ribeiro Production of melt-spun fibers with heat conduction properties Dissertação de Mestrado Mestrado Integrado em Engenharia de Polímeros Trabalho realizado sob a orientação de: Professora Doutora Maria Conceição Paiva Mestre Sofia Silva Universidade do Minho Escola de Engenharia november 2023 i 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-CompartilhaIgual CC BY-NC-SA https://creativecommons.org/licenses/by-nc-sa/4.0/ ii Acknowledgements Throughout my life, I always had people beside me that helped me in every step of the way, and the development of this work was no exception. With that being said, I would like to thank everyone that, directly or indirectly, guided and supported me in the conclusion of this important stage of my life. My genuine thanks to everyone. First and foremost, I would like to express my sincere gratitude to my parents, Helena, and Paulo, for the values and all the education they passed on to me and for their willingness to share their experiences and insights that help me become the person I am today. To my sister, Carolina, for the sense of responsibility and fraternity. And, by extension, to all my family. I must thank my advisor, PhD professor Maria Conceição Paiva, for all the guidance, support, and outstanding feedback during my master’s thesis work. To CeNTI, for all the conditions provided and to all the Functional Fibers team for welcoming me and for all the help provided. A special thanks to Sofia and Cíntia for guiding me during the development of this work, for letting me learn from my mistakes and for the immense sharing of knowledge. I would like to highlight my friend José who has offered me invaluable advices that will benefit me during my whole life and for making this journey much more enjoyable. To my group of friends “Glassware”, for the friendship and companionship during this last five years. In addition, I would like to mention my group of friends “Não tejas medo” for always having my back and making me understand the real meaning of friendship. Lastly, to my girlfriend Lara, for the love and unconditional support. Without all of you this would not be possible. My deepest and sincere appreciation. iii 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. University of Minho, October 2023 Tomás Ramos Ribeiro iv Resumo O objetivo deste trabalho consiste na produção de fibras pela técnica melt-spinning , baseadas em nanocompósitos polímero/nanopartículas de carbono. com propriedades de condução de calor, através do Efeito de Joule. O motivo deste trabalho envolve dar o seguimento da produção de nanocompósitos condutores até às fibras multifilamento, que ainda é um tema pouco abordado. Primeiramente, a preparação dos nanocompósitos foi dividida em duas etapas: (i) produção de compósitos com poli(butileno tereftalato) (PBT) e nanotubos de carbono de parede múltipla (MWCNTs) para determinação do limiar de percolação elétrica; (ii) produção de compósitos híbridos com MWCNTs e grafite, PBT/MWCNTs/G, para estudar o efeito da grafite na condutividade elétrica dos nanocompósitos. O limiar de percolação elétrico do compósito PBT/MWCNTs encontra-se abaixo de 1 %(m/m) de MWCNTs, observando-se um aumento da condutividade elétrica em 10 ordens de grandeza (de 1 x 10-15 para 2,11 x 10-5 S/m). O valor máximo de condutividade elétrica foi 1,75 S/m no compósito com 5 %(m/m) de MWCNTs. A adição de grafite no composto PBT/MWCNTs selecionado (PBT/2%MWCNTs) teve um efeito negativo, reduzindo a condutividade elétrica entre 2 e 4 ordens de grandeza. Para estudar esta diminuição, a morfologia dos compósitos híbridos foi caracterizada para avaliar a presença de aglomerados. Por último, para selecionar o composto com melhor resposta térmica, os nanocompósitos PBT/MWCNTs com composição próxima do limiar de percolação (1, 2 e 3 %(m/m)) foram submetidos a testes de aquecimento para analisar a ocorrência do Efeito de Joule. Os resultados demonstraram melhor resposta térmica para o compósito PBT/3%MWCNTs, atingindo uma temperatura de 41,2 °C com uma tensão de 12 V. A última etapa do trabalho consistiu na produção de multifilamentos pela técnica de meltspinning . As propriedades elétricas, térmicas e mecânicas dos multifilaments foram analisados. Foram obtidos multifilamentos com condutividade elétrica de 2,86 x 10-4 S/m. No entanto, os ensaios mecânicos de tração indicaram que a adição dos MWCNTs na matriz de PBT reduziu a tenacidade e o alongamento à rutura dos multifilamentos. Os testes de aquecimento demonstraram que o efeito de Joule não era significativo nos multifilamentos, pois a temperatura permaneceu inalterada (≈ 26 °C) mesmo com a aplicação de uma tensão de 48 V. Palavras-chave: condutividade elétrica, Efeito de Joule, fibras multifilamento, melt-spinning v Abstract The objective of this study was to produce melt-spinning fibers, based on nanocomposites polymer/carbon nanoparticles with heat conduction properties, by Joule effect. The development of this work was motivated since there are few researches involving heat conduction in melt-spun fibers. Firstly, the nanocomposites preparation was carried in two steps: (i) production of composites with poly(butylene terephthalate) (PBT) and multi-walled carbon nanotubes (MWCNTs) and determination of the electrical percolation threshold; (ii) production of hybrid composites with MWCNTs and graphite, PBT/MWCNTs/G, to study the effect of graphite in the electrical conductivity of the nanocomposites. The electrical percolation threshold of the PBT/MWCNTs nanocomposites was reached below 1 wt.% with an increase of the electrical conductivity of 10 orders of magnitude (from 1 x 10-15 to 2,11 x 10-5 S/m). The highest value of electrical conductivity was 1,75 S/m with a filler content of 5 wt.% of MWCNTs. The addition of graphite into the selected PBT/MWCNTs nanocomposite (PBT/2%MWCNTs) had a negative effect, decreasing the electrical conductivity between 2 and 4 orders of magnitude. To study this decrease, the hybrid nanocomposites morphology was characterized to evaluate the presence of agglomerates. Lastly, in order to select the nanocomposite with the best thermal response, the PBT/MWCNTs nanocomposites with a filler content near the electrical percolation threshold (1 wt.%, 2 wt.% and 3 wt.%) were submitted to heating tests to analyze the occurrence of the Joule Effect. The results showed better thermal response for the PBT/3%MWCNTs, reaching a temperature of 41,2 °C with a voltage of 12 V. The last stage of this work consisted in the production of multifilament fibers using the melt-spinning technique. Afterwards, the produced fibers were characterized by their electrical, thermal, and mechanical properties. It was possible to produce multifilaments with an electrical conductivity of 2,86 x 10-4 S/m. However, the mechanical tests of the multifilaments proved that the MWCNTs addition to the PBT matrix reduced the tenacity and elongation at break of the multifilaments. The heating tests showed that the Joule effect was not significant in the multifilaments, since the temperature remained stable (≈ 26 °C) even with an applied voltage of 48 V. Keywords: electrical conductivity, Joule Effect, melt-spinning, multifilament fibers. vi Content I. Introduction 1 1. Background 1 2. Objectives and Work Planning 3 3. Dissertation Structure 4 II. Literature Review 5 4. State of art 5 4.1. Nanocomposites 6 4.2. Conductive fillers 6 4.3. Electrical conductivity in nanocomposites 7 4.4. Heat conduction in nanocomposites and multifilaments 11 4.5. Dispersion of carbon nanoparticles 12 4.6. Melt-spinning technique 13 4.7. Materials selection 16 4.7.1. Poly(butylene terephthalate) 16 4.7.2. Carbon nanotubes 17 4.7.3. Graphite 19 III. Materials and Methods 20 5. Materials 20 6. Nanocomposites preparation 21 7. Melt-spinning process 23 8. Nanocomposites characterization 26 8.1 Electrical conductivity measurements 26 8.2 Melt flow index characterization 27 xiii PBT - Poly(butylene terephthalate) PET - Poly(ethylene terephthalate) PP - Polypropylene PTT - Poly(trimethylene terephthalate) SD - Standard Deviation Tm - Melting Temperature wt.% - Weight Percentage 1 I. Introduction 1. Background Since the beginning of times, mankind found clever and innovative ways to evolve, and this is consequence of the constant evolution we face every day. From our daily tasks to the most complex and challenging assignments, we constantly seek for perfection. As result, the development of new materials like composites, create new technological and scientific opportunities to upgrade equipment or even to improve parts that can have a better overall performance. The properties obtained in composite materials are ideal to answer these demands. These materials combine complementary properties of its constituents, which cannot be achieved with the isolated components [1]. Thanks to their light weight, corrosion resistance and easy processability, polymer composites are being used in several applications such as power electronics, electric motors and generators, heat exchangers, automotive, military and so on [1], [2]. Polymeric materials are known to have excellent mechanical properties despite being electrically insulating. Therefore, it is necessary to combine them with a conductive filler in order to obtain a conductive polymer composite. Carbon nanoparticles such as carbon nanotubes (CNTs), graphene, graphite, and carbon black (CB) have shown a positive impact in the electrical properties of polymeric composites [3]. These highly conductive fillers can not only turn an insulating polymer into an electrically conductive composite, but also give them the ability to transfer heat, by the Joule heating effect. The passage of electrical current through a conductive nanocomposite can also produce heat adding new functionalities and enabling new areas of application such as sports, healthcare, transportation, and automobiles [4]. However, the dispersion of nanoparticles is the biggest issue involving the performance of the composites. There is a wide variety of articles covering this topic because both electrical and thermal conductivity are significantly affected by the degree of dispersion of the conductive fillers in the matrix [2]. Dispersion is also critical when producing polymeric fibers using the melt- 2 spinning technique since the spinneret is composed of several holes in the micrometer range and the appearance of agglomerates will cause the fibers to break and will also affect the stretching given by the take-up rolls [5]. Although there has been a considerable number of studies on thermally conductive composites, this research does not extend to conductive melt-spun fibers, which motivated the development of this work. 3 2. Objectives and Work Planning The main objective of this work is the development and further characterization of polymer/nanoparticle composites with electrical conductivity using melt extrusion, and to produce multifilament fibers with this composite by multifilament extrusion using the meltspinning technique and characterization of the Joule heating effect for heated car seats. The work was divided into the following steps: 1. Literature review of the most promising applications for the use of these thermally conductive fibers. Material selection, process parameters (melt compounding and meltspinning) and characterization methods; 2. Planning definition of the work in progress, in order to define the necessary steps for the fulfillment of the established objectives; 3. Development of the electrically conductive nanocomposites by melt compounding: 3.1 Determination of the electrical percolation threshold of PBT/MWCNTs nanocomposites (production of nanocomposites with 1 wt.% to 5 wt.%); 3.2 Production of hybrid nanocomposites PBT/MWCNTs/Graphite to study possible synergy between both fillers; 4. Thermal and rheological characterization of the nanocomposites in order to evaluate if they meet the requirements for the melt-spinning process; 5. Production of thermally conductive multifilament fibers by melt-spinning; 6. Characterization and validation of the electrical, thermal, and mechanical properties of the fibers. 4 3. Dissertation Structure This work is composed of five chapters. The first chapter covers a brief introduction to the work, consisting of the background, the objectives and organization of this dissertation. The second chapter describes the characteristics and main properties of PBT, carbon nanotubes, and graphite, as well as a literature review of the theoretical principles of production and characterization of polymeric nanocomposites. A compilation of studies on the production of nanocomposites filled with conductive nanoparticles is also described in this chapter. The third chapter lists the materials and equipment’s used in the production of these nanocomposites, as well as a description of the experimental characterization techniques used. The fourth chapter presents and analyzes the experimental results obtained. Lastly, the fifth chapter presents the main conclusions from the work done, as well as proposals for future work. 5 II. Literature Review 4. State of art Composite materials combine the properties of its constituents, producing a new material and allowing it to have strengths from both of them while often overcoming their weaknesses. Composites are commonly identified by the type of matrix that holds the filler together. These composites can have a metallic, ceramic, or polymeric matrix [6]. Since polymers have excellent mechanical properties, good processability and elevated corrosion resistance they are seen as a good option to replace metals and other materials in very distinct applications such as construction, military, automotive, aerospace and so on [1]. Generally, polymeric materials are known to be thermal and electrically insulating (<0,5 W/mK, ≈ 1015 Ω.cm, respectively). However, thermal conductivity is one of the most important properties in many applications and it is getting considerable attention. Despite existing many strategies to enhance the thermal conductivity of polymers, the most efficient way is to combine conductive fillers within the polymer matrix [3]. The incorporation of these fillers in insulating matrixes can reduce their volume resistivity as well as increase thermal conductivity while improving mechanical, chemical, and thermal properties. Therefore, materials like polypropylene (PP), low-density polyethylene (LDPE), high-density polyethylene (HDPE), polyethylene terephthalate (PET) among other polymers have been widely used to create thermally conductive composites [7], [8] when combined with conductive fillers, especially carbon-based fillers such as graphite, graphene, carbon nanotubes or carbon black [9]. When the filler has at least one dimension below approximately 100 nm, it can be classified as a nanocomposite [10] . To ensure a reliable performance of the nanocomposites it is essential to establish a strong interfacial adhesion and a proper dispersion between matrix and filler [11]. Melt spun multifilament fibers are known to have a wide variety of properties that can be used in different industries like textile (underwear, sportswear, and fabrics), automotive (seat belts), sports equipment (climbing ropes and racquet strings) and fishing lines. Among the benefits of these fibers, the mechanical and electrical properties are the most important ones. There are several procedures to create electrically conductive fibers, for example using an intrinsic conductive polymer (ICP), melt mixing an insulating polymer with conductive fillers 6 (carbon black, graphite, carbon nanotubes, etc.) or even coating a fiber with conductive materials. However, the incorporation of conductive nanofillers has gained a lot of interest due to the quickness and ease of the process [12], [13]. 4.1. Nanocomposites Currently, emerging industries are looking for new thermally conductive materials to replace, for example, metals in parts that require heat dissipation. Since polymer composites are somewhat easy to process and can be integrated in parts with complex geometry, are lightweight, and have a good corrosion resistance they are suitable for areas like LED devices, electronic assembly and packaging, battery, and solar applications [14]. Polymer nanocomposites can be produced using three distinct methods: melt compounding, in situ polymerization or solution mixing [15]. Solution mixing is a process where the nanoparticles are dispersed into polymer solutions through ultrasonication and shearing depending on the solubility of the respective particles in the solvents [16]. On in situ polymerization the nanoparticles are previously dispersed in a monomer solution and then the nanocomposite material is formed via standard polymerization procedures [17]. Lastly, the melt compounding process is the most popular method to produce nanocomposites by virtue of being environmentally friendly (does not require organic solvents) and its compatibility to a large-scale production. This technique consists in combining the melted polymer with the desired nanoparticle by means of an extruder [18]. Despite of all the advantages of the melt compounding process, the main disadvantage is the limitations to the dispersion of the filler in the polymer melt, with higher viscosity compared to solution methods [19]. 4.2. Conductive fillers Metals (or conductive materials) are known to have high electrical conductivity making them extremely important in electronic areas. Semiconductor materials include the nanocomposites since they are highly dependent of the type of filler and its concentration on the matrix. These materials represent an intermediate state between conductors and insulators. Finally, insulators (e.g. polymers) are materials that block the passage of electrical current because of their high resistivity. The typical electrical conductivity values (in S/m) of each class of materials can be seen in Figure 1. 7 Figure 2 – Schematic representation of carbon allotropes: Graphite, graphene, and carbon nanotube. Taken from [21]. Electrical conductivity is one of the most important properties when producing nanocomposites with heat conduction. Therefore, to create conductive polymer composites it is necessary to introduce highly conductive fillers into their matrix [14]. These fillers can be classified into three distinct categories depending on their constituent material: carbon-based, metallic, and ceramic. Carbon-based fillers include carbon nanotubes, graphite, graphene, and carbon black (Figure 2) [15]. [ Carbon nanoparticles have shown a positive impact in physical and chemical properties, emphasizing the improvement in mechanical, thermal, and electrical properties [3], [22]-[23]. [21] 4.3. Electrical conductivity in nanocomposites The percolation threshold (Figure 3) is described by the critical conductive filler content where an insulating material becomes conductive. When this critical filler concentration is achieved, a continuous network is created where the electrical current can pass through [24]. Given the problems of dispersion it is important that the percolation threshold is reached with the lowest possible filler concentration to prevent the appearance of agglomerates [5]. Figure 1 – Typical values of electrical conductivity of commonly known materials. Taken from [20]. 8 Figure 3 – Theoretical behavior of the electrical resistivity with increasing filler concentration. Taken from [25]. Several studies have been conducted in order to study the electrical percolation threshold of carbon nanoparticles in polymer composites and some will be presented below. Seo et al . [26] produced polypropylene (PP) and MWCNTs nanocomposites and obtained a percolation threshold between 1 and 2 wt.% of MWCNTs and were able to decrease the volume resistivity from approximately 107 Ohm.cm to 102 Ohm.cm, respectively. Above 2 wt.%, the volume resistivity was maintained even with nanocomposites with 5 wt.% of MWCNTs. Zhang et al. [27] prepared composites of HDPE (high density polyethylene) and SWCNTs using spray coating. The electrical conductivity of neat HDPE is 1 x 10-14 S/cm and this value increased drastically by adding a filler content of 4 wt.% of SWCNTs reaching 1 x 10-5 S/cm. Over 6 wt.% of SWCNTs, the electrical conductivity tended to stabilize. Hu et al. [28] investigated the percolation threshold of a PET/MWCNTs composites. The electrical conductivity of neat PET is 8,6 x 10-17 S/cm and it was possible to achieve 10-5 S/cm with just 2 wt.% of MWCNTs. The low percolation threshold of this composite is explained by the high aspect ratio of the MWCNTs and their homogenous dispersion in PET matrix. With a filler content of 1 wt.%, the composite exceeded the antistatic criterion for thin films. Allaoui et al. [29] dispersed MWCNTs in an epoxy polymer matrix. The value of percolation threshold of this composite was between 0,5 and 1 wt.% obtaining a value of 1 x 10-3 S/cm with a filler loading of 1 wt.%. Composites with 4 wt.% only improved the conductivity value by an order of magnitude. This high MWCNTs content would negatively affect the mechanical properties of the overall composite achieving a “saturation effect.” Dorigato et al. [30] prepared PBT/MWCNTs using the melt compounding process and 9 were able to decrease the electrical resistivity of neat PBT from 1015 to 104 Ω.cm with 0,5 wt.% of MWCNTs. For the PBT/3%MWCNTs nanocomposites, the value of resistivity only reduced by two orders of magnitude achieving a percolation threshold below 0,5 wt.%. Dorigato et al . [31] conducted a previous study on PBT/MWCNTs and were not able to reach this type of values. This time, only with a filler content of 6 wt.% of MWCNTs it was possible to reach a value of 103 Ω.cm. Moreover, regarding the carbon black nanocomposites, it was possible to achieve a value of 104 Ω.cm but with a 15 wt.% of CB. These values were not as satisfactory as their previous study probably due to the use of a twin-screw extruder in this more recent work which led to a better filler dispersion within the PBT matrix. Hybrid nanocomposites are thought to enhance thermal conductivity through the synergistic effect of both fillers. Che et al. [3] prepared ternary composites using high density polyethylene (HDPE), expanded graphite (EG) and multi-walled carbon nanotubes. Two different binary composites (HDPE/CNTs and HDPE/EG) were produced to study both electrical and thermal conductivity. It was observed that with a low filler content of CNTs (2,5 wt.%) was possible to reach values of electrical conductivity of approximately 101 S/m. On the other hand, to get the same value of electrical conductivity with EG it was needed a much larger filler content (around 25 wt.%). Concerning the thermal conductivity, the opposite effect occurs. HDPE/EG reaches greater values of thermal conductivity (≈ 2,25 W/mK with 20 wt.%) when compared with HDPE/CNTs (≈ 1,0 W/mK with 20 wt.%). Taking that into consideration, ternary composites where prepared fixing the EG content in 10, 15 and 20 wt.% and adding small concentrations of CNTs to study their electrical and thermal conductivity. In summary, these ternary composites were able to increase both conductivities due to great synergy between both carbon nanoparticles and graphite as shown in Figure 4. Table 1 summarizes the research done regarding the electrical conductivity in polymer nanocomposites. 16 4.7. Materials selection Since the main goal is to produce multifilaments with heat conduction properties, it is necessary to select the best materials (polymer matrix and conductive filler) for heated car seats. As stated previously, carbon nanoparticles (CNTs and graphite) are the best conductive filler for electrical and thermal applications in polymer composites because of their excellent properties such as low density, high elastic modulus, a good thermal stability and, most importantly, outstanding thermal and electrical conductivity [11], [46], [47]. Regarding the polymer matrix, polyesters (PET and PBT), polyolefins (PP, LDPE and HDPE), and polyamides (PA 6 and PA 6.6) are the most commonly used polymers for the meltspinning technique [42], [48], [49]. Polyolefins are mostly used in medical applications for surgical gowns and masks while the polyamides are particularly used for textile applications. Polyesters can be used in a wider variety of applications and have excellent mechanical, thermal, and chemical properties [42]. Since the crystalline structures favor the electrical conductivity [50] and PBT has a faster, easier and better crystallization rate than PET [22], [42], it makes it more interesting for the electrically conductive nanocomposites. 4.7.1. Poly(butylene terephthalate) Nowadays, polyesters are among the most economically important classes of polymers. Polyesters can be classified into two types: (i) thermoplastic polyesters and (ii) unsaturated polyesters. The most widely known are the thermoplastic which includes polyethylene terephthalate (PET), poly(trimethylene terephthalate) (PTT) and poly(butylene terephthalate) (PBT) [51]. As previously stated, PBT (Figure 7) is a semicrystalline thermoplastic polyester that appeared in the late 1960s and became a commonly used material because of its easy processability and fast crystallization which makes it suitable for very structural applications like automotive, electrical, and electronic industries. PBT is prepared by polycondensation of 1,4butanediol with terephthalic acid or dimethyl terephthalate [30], [52], [53]. 17 Figure 7 – Chemical structure of PBT. Taken from [52]. PBT-based composites are described by high stiffness and strength, excellent electrical properties, chemical resistance, and low moisture absorption [30]. Additionally, PBT has good electrical and dielectric properties demonstrating particularly good creep current resistance and does not initiate any electrolytic corrosion [52]. This polymer can be blended, mainly, with carbon nanoparticles such as carbon nanotubes, carbon black, graphite, and graphene, forming nanocomposites that can be used in electrically conductive applications [3], [31], [54], [55]. PBT composites can be applied in electronic applications such as EMI shielding [56], in packaging films or sensitive electronic parts [30], but also in the automotive and medical industries [22]. 4.7.2. Carbon nanotubes In 1991, Sumio Iijima was one of the pioneers of the modern technology for the production of carbon nanotubes [57]. Since its discovery, CNTs have been studied and further developed [58] becoming particularly useful in a wide range of applications including reinforcing fibers, electromagnetic shields, smart clothing [12], sensors, electronics on flexible substrates, etc. [59]. The excellent properties of carbon nanotubes (Table 2) make them an extremely versatile filler due to low density (0,8 - 1,8 g/cm3), high electrical and thermal conductivity (102 - 106 S/cm and 2000 - 6000 W/mK, respectively), excellent thermal stability (up to 2800 °C), and extraordinary Young’s modulus (1-2 TPa) [11], [60]. 18 Figure 8 – Simple structural representation of carbon nanotubes. Rolling one or several (a) sheets of graphene forms (b) SWCNTs, (c) DWCNTs and (d) MWCNTs. Adapted from [61]. Table 2 – Properties values comparison between SWCNTs and MWCNTs. Adapted from [61]. Properties SWCNTs MWCNTs Relative density (g/cm3) 0,8 – 1,3 1,8 – 2,6 Specific area (m2/g) 400 – 900 200 – 400 Young’s modulus (Pa) ≈ 1000 ≈ 1000 Tensile strength (Pa) (3 – 50) x 1010 (1 – 15) x 1010 Thermal conductivity (W/mK) 3000 – 6000 2000 – 3000 Electrical conductivity (S/cm) 102 – 106 103 – 105 Thermal stability temperature in air (°C) 550 – 650 550 – 650 CNTs can be structurally classified in three distinct types (Figure 8): single-walled carbon nanotubes (SWCNTs), double-walled carbon nanotubes (DWCNTs) and multi-walled carbon nanotubes (MWCNTs). As the name suggests, SWCNTs are composed of single layer of graphene sheet rolled up around itself while DWCNTs are made of two layers of graphene and MWCNTs consist in three or more layers rolled up concentrically [59]. [62] 19 4.7.3. Graphite Graphite (Figure 9) is a carbon filler that exists naturally but can equally be synthetically produced. Structurally, it consists of thousands of parallel layers of graphene sheets with sp2hybridized carbon bonded hexagonally which are held together through Van der Waals forces. Therefore, graphite has excellent properties including its elastic modulus (1TPa), low electrical resistivity (≈ 50 µΩcm at room temperature) [46], high thermal and electrical conductivity (5300 W/mK and 104 S/cm) [47], and excellent thermal stability under inert atmosphere and in the vacuum. Figure 9 - Schematic illustration of graphite structure. Taken from [63]. 20 III. Materials and Methods 5. Materials The polymer matrix used was a low viscosity poly(butylene terephthalate) (PBT), grade Crastin® FGS600F40 NC010, provided by Dupont. The relevant properties of the material are shown is Table 3. Table 3 – Properties of PBT Crastin® FGS600F40 NC010, obtained from the technical datasheet. The nanofillers used, both in powder form, were NANOCYL® NC7000™ MWCNTs (multiwall carbon nanotubes) produced by catalytic chemical vapor deposition (CCVD), supplied by Nanocyl S.A, and graphite, grade GraphTHERM® 23/99.9 supplied by LUH. Their relevant properties are represented in Table 4: Table 4 – Properties of Nanocyl® NC7000™ MWCNTs and graphite GraphTHERM® 23/99.9 based on the technical datasheets. PBT Melt flow rate (g/10 min) 33 Tensile Modulus (MPa) 2400 Melting temperature (°C) 223 Glass transition temperature (°C) 55 Density (g/cm3) 1,29 Volume resistivity (Ω.cm) 1 x 1016 Water absorption (%) 0,4 MWCNTs Graphite Average diameter (nm) 9,5 Carbon content (%) 99,9 Average length (µm) 1,5 Ash (%) 0,1 Carbon purity (%) 90 Moisture (%) 0,5 Surface area (m²/g) 250 – 300 Surface area (m²/g) 5 – 6,5 Volume resistivity (Ω.cm) 10-4 Tamped density (g/cm3) 0,95 – 1,05 Thermal conductivity (W/mK) 3000 Size (µm) 10 – 50 21 Figure 10 – Corotating twin-screw extruder by Rondol Technology Ltd, 21 mm. 6. Nanocomposites preparation The nanocomposites were prepared by melt compounding using a corotating twin-screw extruder (Figure 10) with a screw diameter of 21 mm and a length to diameter ratio (L/D) of 25 from Rondol Technology Ltd. This screw configuration used two chaotic mixture screws. The extruder is made up of four heating zones along the length of the cylinder, excluding the spinneret, and peripheral feeders. The extruded filament was then cooled in a water bath and collected for further characterization. The operating limits of the extruder used are presented in Table 5. Table 5 – Operating limits of the extruder. Condition Maximum Temperature (°C) 450 Screw rotation speed (rpm) 300 Torque (%) 100 Pressure (bar) 90 22 Prior to processing, the PBT pellets were dried in a dehumidifier Piovan DPC30 at 120 °C for 4h. After the drying process, the humidity of the pellets was measured to ensure the absence of water in the nanocomposite preparation. To ensure a controlled feed rate, two feeders were used – a gravimetric for the MWCNTs powder and a volumetric for the PBT pellets. Since the density of the materials varies depending on the type and percentage of fillers incorporated, the feeders had to be calibrated beforehand to ensure the desired flow rate. The processing conditions (Table 6) were set based on the melting temperature of the PBT (specified in datasheet) and supported with the analysis of previous works that cover identical topics. The screw rotation speed was set to 140 RPM in order prevent backflow of material. Table 6 – Processing conditions of the nanocomposites. Firstly, as stated in [38], to help the MWCNTs dispersion, a nanocomposite with a high filler content of 6 wt.% of MWCNTs was produced as a masterbatch to form the nanocomposites with the designated concentrations. The extruded material was cooled in a water bath at 50 °C and pelletized. Then, the PBT/6%CNTs was diluted with neat PBT to produce nanocomposites with lower filler concentration (5; 4; 3,5; 3; 2 and 1 wt.%). After evaluating the electrical percolation threshold of the PBT/MWCNTs nanocomposites, hybrid nanocomposites were produced by adding three different graphite concentrations. The processing conditions were the same as the binary composites. A high concentration nanocomposite was produced with 5 wt.% of graphite. This composite was cooled in a water bath at 50 °C and then pelletized. Later, the dilution process was performed with neat PBT to create lower filler contents of 1 and 2 wt.% of graphite. From this first processing, a sample of each hybrid nanocomposites (with 1; 2 and 5 wt.% of graphite) were collected to perform the electrical characterization. This filler contents of graphite were selected based on the melt-spinning extruder requirements, since it is not recommended to used nanocomposites with a total filler Condition Value Temperature profile (°C) 210, 215, 220, 225, 230 Screw rotation speed (RPM) 140 Feed rate (kg/h) 3 Cooling bath (°C) 50 23 content above 7 wt.%. However, to study the effect of a second processing in the electrical conductivity, the ternary nanocomposites were reprocessed because a second shear force could help improve the dispersion. All the nanocomposites produced in this step of the work are presented in Table 7. Table 7 – Designation and information about the nanocomposites produced in all steps of this work. MWCNT content (wt.%) Graphite content (wt.%) Nanocomposite name Step 1 (Masterbatch 6%) 2 processing’s 5 - PBT/5%CNTs 4 - PBT/4%CNTs 3,5 - PBT/3,5%CNTs 3 - PBT/3%CNTs 2 - PBT/2%CNTs 1 - PBT/1%CNTs Step 2 (Hybrid nanocomposites) 2 processing’s 2 1 PBT/2%CNTs/1%G 2 2 PBT/2%CNTs/2%G 2 5 PBT/2%CNTs/5%G Step 3 (Reprocessed hybrid composites) 3 processing’s 2 1 PBT/2%CNTs/1%G (R) 2 2 PBT/2%CNTs/2%G (R) 2 5 PBT/2%CNTs/5%G (R) 7. Melt-spinning process The polymer multifilaments were processed using a single screw multi-component fiber extruder model TRC with a length to diameter ratio (L/D) 30:1 and a pump capacity of 2,9 cm3/rot, from Hills Inc, Co. As Figure 11 suggests, the draw-down ratio DDR is the ratio between the speed of the roll 1 (feeding roll) and the extrusion speed – induces hot stretching. The colddraw ratio (CDR) is the ratio between the velocity of the stretching roll (roll 2) and the feeding roll. This ratio of speeds causes a cold stretching on the multifilaments. Lastly, between roll 3 (relaxation roll) and roll 2 is where the relaxation of the fiber is applied. 24 Figure 11 – Schematic representation of the melt-spinning extruder. Prior to fiber processing, the PBT with 3 wt.% CNTs and neat PBT were dried in a dehumidifier Piovan DPC30 at 120° C for 4h. Then, the humidity was measured using a Radwag MA 50/1.X2.A.WH moisture analyzer to ensure the effectiveness of the drying process. The meltspinning equipment is composed by seven heating zones in total: four heating zones along the length of the cylinder plus the pump, transfer line and spinning pack. The temperature profile was set based on the melting temperature of the PBT (specified in datasheet) and in order to ensure a controlled pump pressure (Table 8). The spinning pack used has a mono-component multifilament spinneret with 36 holes with 0,6 mm of diameter each. The process began when the all the parameters were set and the multifilaments started to exit the spinneret. Afterwards, they were cooled by an air quenching chamber and collected by a take-up roll. After, the multifilaments are drawn in two different zones (DDR and CDR) with different temperatures and speeds. Finally, the multifilament was wounded in a bobbin (Figure 11). 25 Table 8 – Temperature profile of the melt-spinning process. Zones Temperature (°C) Zone 1 215 Zone 2 220 Zone 3 225 Zone 4 235 Pump 240 Transfer Line 215 Spinneret 220 By varying the pump speed, the extrusion speed also changes inducing different DDR and this was done in order to evaluate how the different stretching conditions affect the mechanical properties. The increase of temperature of roll 2 was performed in order to provide mobility for the conductive particles. The other parameters were fixed. The spun fibers were processed with variable pump speeds (10, 14 and 18 rpm), that consequently affected the feed rate. Also, a smaller change in the temperature of the second roll was employed (V2) (40 to 55 °C) while the temperature of the first roll (V1) was set at 60 °C and the third roll (V3) was kept at room temperature. 32 Figure 17 – Setup used for the electrical characterization of the multifilaments. 9. Multifilaments characterization 9.1 Electrical characterization The electrical characterization of the multifilaments was performed based on the ISO 3915-1981 standard, used for the electrical measurements of the nanocomposites. In this characterization, five samples of each fiber type were cut with 3 cm length each and placed on a glass slide (Figure 17). Then, twisting was applied to ensure the contact between the multifilaments. Then, the silver ink was applied to both ends (Cl 1036 Highly Conductive Silver Ink) to facilitate the contact between the multifilament and the measuring system, before going through a thermal curing process at 120 °C for 20 minutes. After carrying out the electrical measurements, to assess fibers longitudinal cross-section geometry (Figure 18) that is necessary to calculate the volume resistivity, a Leica DM2500 M microscope with an incorporated camera was used. The multifilaments diameter was considered as cylindrical. 33 Figure 18 - Representative image of the measurement of the longitudinal cross-section geometry of the multifilaments. 9.2 Mechanical characterization The mechanical characterization was carried out in a universal mechanical testing machine, model AGXV-50kN from Shimadzu, to determine the mechanical properties of the multifilaments, following the ASTM 3822:07 standard. The length between the rubber coated grips was 25 mm, the tensile test speed was 250 mm/min, and a load cell of 100 N was used. The main mechanical properties, elongation at break (%) and tenacity (cN/dtex), were studied. Elongation at break corresponds to the increase in length of the test specimen compared to its starting length (expressed in %), while applying a deformation at the indicated speed. Tenacity is described as the specific stress corresponding to the maximum force in a stress-strain curve. For this result, it is important to consider the linear density of the multifilaments in calculating tenacity, since each multifilament can have a different linear density and diameter [66]. For each fiber, at least, 12 samples were tested in standard atmosphere conditions (room temperature: 25,5 ± 0,05 ºC; relative humidity: 60,0 ± 0,05 %). Prior to the tensile tests, the linear density of each fiber was measured. The linear density, whose unit is decitex (dtex), corresponds to the weight in grams per 10000 meters of multifilament. These measurements were performed in a wrap reel test model 161M from Mesdan. 34 9.3 Joule heating tests for multifilaments The Joule heating tests of the multifilaments was conducted in an identical way as for the nanocomposites. The setup for this characterization consisted in an acrylic part (Figure 19 a)) with two sides covered with copper tape. Then, the multifilament was rolled around this acrylic part (Figure 19 b)) and the highly conductive silver ink was applied to the zones of the multifilament that were in contact with the copper tape. Then, the silver ink was cured in an oven at 120 °C for 20 minutes and, lastly, the multifilaments were again covered with copper tape. The measurements were carried out using a power source connected to two ends of the copper tape and three test of 5 minutes each were carried out applying three different voltages (12V, 24V and 48V). A FLIR A700 thermal camera was used to record the temperature variations of the multifilaments and, finally, the results were examined in the FLIR Tools software. Figure 19 – Setup used for the thermal characterization of the multifilaments: a) acrylic part and b) final setup. 35 IV. Results and Discussion 10. Characterization of PBT/CNTs nanocomposites 10.1 Study of the electrical percolation threshold The values of electrical conductivity of the PBT/MWCNTs are presented in Figure 20 and it shows that the incorporation of MWCNTs significantly increased the electrical conductivity of the nanocomposites. Figure 20 – Electrical conductivity as a function of MWCNTs concentration. The value of electrical conductivity of neat PBT is 1 x 10-13 S/m. The electrical percolation threshold occurred between 0 wt.% and 1wt.% with an increment from 1 x 10-13 to 1,91 x 10-5 S/m. The maximum value of electrical conductivity was 1,75 S/m with a filler content of 5 wt.%. With the addition of a small filler content of MWCNTs it was possible to obtain a transition from an insulating to a semiconductor material, with the electrical conductivity increasing approximately 8 orders of magnitude relative to the raw polymer. The addition of MWCNTs to the PBT matrix caused an increase of the electrical conductivity by creating a continuous network of contacts between the MWCNTs. 1,75E+00 1,03E+00 5,26E-01 2,87E-01 2,61E-02 1,91E-05 1,00E-13 1,00E-13 1,00E-10 1,00E-07 1,00E-04 1,00E-01 1,00E+02 0 1 2 3 4 5 𝜎(S/m) MWCNTs (wt.%) 36 25 50 75 100 125 150 050 100 150 200 250 300 Temperature (ºC) Time (s) 12V 24V 48V 10.2 Heating evaluation The heating test was carried out in order to evaluate the heat dissipation in the nanocomposites when submitted to different voltages. The results of these test are presented in Figure 21 and only the PBT/3%CNTs was characterized since was not possible to create a setup with a low enough resistance with the other nanocomposites (PBT with 1 and 2 wt.% of MWCNTs). Previously, a target temperature was established between 35 and 40 °C and the time that took to reach that temperature was also obtained with the FLIR Tools software as well as the maximum temperature reached by the setup (Table 10). Table 10 – Maximum temperature and time taken to reach the target temperature in each test. Test Maximum Temperature (°C) Time to reach 40 °C (s) 12 V 41,2 120 24 V 75,9 7 48 V 128,7 2 Figure 21 – Temperature variation over time during the Joule heating tests for the PBT/3%CNTs. 37 0 10 20 30 40 50 60 MFR (g/10 min) Neat PBT PBT/3%CNTs Reprocessed PBT/3%CNTs Figure 22 – Comparison between melt flow rate values of the neat polymer and the nanocomposite. As it is possible to observe in Figure 21, with a voltage of 12 V, the nanocomposites were able to reach the target temperature established previously in 120 s. The tests performed with 24 V and 48 V demonstrate that the nanocomposites quickly heat up to 40 °C (7 and 2 seconds, respectively) and, after this, achieve a plateau stage at a higher temperature. As described in chapter II, it was observed that the nanocomposites presented the Joule heating effect, since the applied electrical current to the nanocomposites was converted to dissipated heat. 10.3 Melt flow index The MFI measurements were performed in order to evaluate the spinnability of the nanocomposite as well as to study the influence of the MWCNTs on the PBT viscosity. The results are presented in Figure 22. The PBT/3%CNTs was tested in order to study the effect of a second processing in the melt flow rate values and because it was the only composite capable of heating up by Joule effect, as will be discussed in the next subchapter. The results show that the melt flow rate decreases when the MWCNTs are added to the PBT matrix reaching values of 13 g/10min and 15,8 g/10min for PBT/3%CNTs and reprocessed PBT/3%CNTs, respectively, showing that the composites are within the operating window of the multifilament production equipment. Thus, these melt flow rate values are acceptable for the melt-spinning technique. 38 10.4 Macrodispersion The optical microscopy was employed to study the presence of agglomerates in the PBT/3%CNTs nanocomposite. Figure 23 displays representative images of the nanocomposite obtained during the morphological analysis. Figure 23 – Images obtained with OM of the PBT/3% nanocomposite (magnification 20x). By analyzing the images, it is possible to observe some agglomerates with different sizes. Therefore, a quantitative analysis was performed in order to examine the distribution of the agglomerate areas and the results are represented in the histogram in Figure 24. The area distribution of the agglomerates is obtained by the number of agglomerates (normalized per mm²) versus the different agglomerates area classes (each class corresponds to 250 µm²). 39 1E+0 1E+1 1E+2 1E+3 1E+4 N of agglomerates (per mm2) Area of agglomerates (µm²) Figure 24 – Number of agglomerates (per mm2) as a function of the area of agglomerates of the PBT/3%CNTs nanocomposite. When analyzing Figure 24, it is noticeable that the majority of agglomerates are represented in the first area classes (smaller agglomerate areas) which can be problematic to the melt-spinning technique. The presence of a few larger agglomerates is also observed, which could mean that the nanocomposite is reaching a saturation level and is no longer able to disperse individual MWCNTs into the bulk composite. This was expectable since 3 wt.% of MWCNTs is already above the percolation threshold (between 0 and 1 wt.%) which can lead to an excessive concentration of MWCNTs and, consequently, the formation of larger agglomerates. 40 11. Influence of graphite addition 11.1 Electrical conductivity The results obtained for the electrical conductivity of the hybrid composites are presented in Figure 25 and it displays the effect of the addition of graphite to the PBT with 2 wt.% of MWCNTs nanocomposites. The selection of this nanocomposite was based on the fact that it was expected that the electrical conductivity of the multifilaments would decrease when compared to the nanocomposite rods [44]. Figure 25 – Electrical conductivity as a function of graphite concentration (purple line represents the ternary nanocomposites with 1 processing; blue line represents the hybrid nanocomposites with 2 processing steps). When compared to the electrical conductivity of the PBT with 2 wt.% of MWCNTs (Figure 20), it is observed that the addition of graphite had a negative impact on the electrical conductivity, decreasing it by 3 orders of magnitude (from 2,61 x 10-2 to 2,67 x 10-5 S/m) for the hybrid composites (purple line) and 4 orders of magnitude (from 2,61 x 10-2 to 3,00 x 10-6 S/m) for the reprocessed hybrid composites (blue line). It was expected that the addition of graphite could increase the electrical conductivity of the PBT with 2 wt.% of MWCNTs nanocomposite (or at least nor decrease it), since it is expected that graphene sheets help dispersing the MWCNTs, separating the entangled nanotubes, and forming an effective conductive pathway, as Liu et al. reported [67]. 2,67E-05 2,49E-04 3,97E-04 1,30E-05 3,00E-06 2,03E-05 2,61E-02 1,00E-06 1,00E-05 1,00E-04 1,00E-03 1,00E-02 1,00E-01 1,00E+00 0 1 2 3 4 5 6 𝜎(S/m) Graphite (wt.%) PBT/2%CNTs/xG PBT/2%CNTs/xG (R) PBT/2%CNTs 41 Conversely, Joseph et al. [68] concluded that this synergy between graphene sheets and carbon nanotubes is only achievable when using concentrations below the percolation threshold, since above this value, a decrease of the electrical conductivity is verified. Therefore, the results presented in Figure 25 are not in line with the previous studies probably because the filler content of MWCNTs was above the electrical percolation threshold. 11.2 Macrodispersion The morphological analysis was conducted to evaluate the presence of agglomerates in the ternary composites. The images in Figure 26 correspond to the cross-section of the hybrid nanocomposites obtained by OM. Figure 26 – Representative images obtain by OM of the ternary nanocomposites (magnification 20x): a) PBT/2%CNTs/1%G; b) PBT/2%CNTs/5%G. Figure 26 presents the cross-section of the samples studied in this work, which were the PBT with 3 wt.% of carbon nanoparticles (2 wt.% of MWCNTs and 1wt.% of graphite – a)) and with 48 V. Conclusions The main objective of this work was the production of multifilaments with heating conduction properties by the melt-spinning technology. The Joule heating tests were performed with the objective of checking the nanocomposites response for heating as induced by an electric current. The results of these tests showed that the PBT/3%CNTs nanocomposite can heat up when submitted to an electric current proving the possibility of applying the Joule heating effect. This nanocomposite reached a temperature of 41,2 °C in 5 minute in a test where a voltage of 12 V was applied. This test was the most important for the selection of the nanocomposite that would be used for the production of multifilaments which, ultimately, demonstrated that the PBT/3%CNTs composites were adequate for the application, despite of the expected decrease of the electrical conductivity in the meltspinning technique. After the selection of the polymer matrix and the conductive filler, the nanocomposites preparation was divided into 2 steps. Firstly, a study of the electrical percolation threshold was conducted by melt compounding and characterization the PBT/CNTs nanocomposites with the following filler contents: 5; 4; 3,5; 3; 2 and 1 wt.%. The electrical characterization showed an increase of the electrical conductivity by 8 orders of magnitude from the raw polymer (1 x 10-13 S/m) to the PBT with 1 wt.% of MWCNTs nanocomposite (2,11 x 10-5 S/m), meaning that the electrical percolation threshold is below 1 wt.% of MWCNTs. Afterwards, based on these results, the PBT with 2wt.% of MWCNTs was selected to combine with graphite to produce the hybrid nanocomposites with concentrations of 1, 2 and 5 wt.% of graphite. Then, another electrical characterization was performed with this hybrid composites to examine the effect of the addition of graphite. It was observed that the graphite did not enhance the electrical conductivity comparatively to the PBT/CNTs nanocomposites decreasing the value from 2 (4,85 x 10-4 S/m) to 4 (3,41 x 10-6 S/m) orders of magnitude. Therefore, it was observed that the addition of the conductive fillers increased the electrical conductivity of the PBT matrix, but no synergistic effect was observed with graphite since a filler content of MWCNTs above the electrical percolation threshold was used in the hybrid nanocomposites. The morphological analysis was carried out with the purpose to evaluate the presence of agglomerates in the nanocomposites. The increase of smaller sized agglomerates (< 1000 µm2) in the hybrid nanocomposites is related to the large content of graphite nanoflakes, and it is 49 possible that these composites are reaching a saturation level for the MWCNTs dispersion in the PBT bulk. The same was observed for the PBT/3%CNTs morphological analysis since the presence of relatively large agglomerates was observed. Finally, after all the characterization tests of the nanocomposites, the production of the multifilaments was carried out. Six different multifilaments were produced by varying the pump speed and the temperature of the second roll. These two variables showed that the lower pump speed favored the electrical conductivity, reaching the highest values (1,4 x 10-4 and 2,86 x 10-4 S/m). Also, comparatively to the values of electrical conductivity of the nanocomposites, the electrical conductivity of the multifilaments decreased 3 and 4 orders of magnitude which is a very satisfactory result, when compared to the literature review. On the other hand, the mechanical characterization showed that the MWCNTs did not have an obvious reinforcement effect in the PBT composite. To conclude, the Joule heating tests of the multifilaments demonstrated that the fibers produced could not heat up when submitted to an electrical current, despite carrying out a test where a voltage of 48 V was applied. 13. Proposal for future work With the purpose of obtaining composites with improved electrical properties it is suggested that the melt compounding conditions of the nanocomposites should be analyzed in order to optimize them to reduce the presence of agglomerates and enhance the electrical conductivity. Another possibility is to functionalize the CNTs to promote a better dispersion and adhesion to PBT. The thermogravimetric tests would be useful in order to evaluate the real percentage of nanoparticles incorporated in the polymer matrix as well as transmission electron microscopy (TEM) or scanning electron microscopy (SEM) to observe the individual dispersion state and interface of the carbon nanoparticles in the polymer matrix. 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Materials technical datasheet 1.1 PBT DuPont™ Crastin® FGS600F40 NC010 64 1.3 Graphite GraphTHERM® 23/99.9 technical datasheet 65 1.4 Cl 1036 Highly Conductive Silver Ink technical datasheet 66 67 2. Characterization data 2.1 Melt flow index data Neat PBT Test MFR (g/10 min) MVR (cm3/10 min) Melt density (g/cm3) Mass (g) 1 53,334 48,306 1,104 2,354 2 54,669 51,243 1,067 2,270 3 51,916 47,162 1,101 2,347 4 55,086 50,191 1,098 2,340 5 55,625 52,614 1,057 2,254 Average 54,126 49,903 1,085 2,313 SD 1,340 1,964 0,019 0,042 PBT/3%CNTs Test MFR (g/10 min) MVR (cm3/10 min) Melt density (g/cm3) Mass (g) 1 11,741 10,625 1,105 2,356 2 12,272 11,077 1,108 2,362 3 11,599 10,715 1,083 2,308 4 13,205 11,860 1,113 2,374 5 14,843 13,811 1,075 2,290 6 13,634 12,301 1,108 2,363 7 13,943 12,591 1,107 2,361 Average 13,034 11,854 1,106 2,345 SD 0,266 0,226 0,001 0,003 Reprocessed PBT/3%CNTs Test MFR (g/10 min) MVR (cm3/10 min) Melt density (g/cm3) Mass (g) 1 13,433 12,110 1,109 2,365 2 14,138 13,016 1,086 2,316 3 16,252 15,211 1,068 2,278 4 14,333 12,921 1,109 2,365 5 14,303 12,921 1,107 2,360 6 15,546 14,299 1,087 2,318 7 15,821 14,421 1,097 2,339 Average 14,832 13,557 1,093 2,334 SD 0,899 0,951 0,013 0,028 68 2.2 Mechanical tests data OS_01 Name Maximum Force Elongation at break Tenacity Unit cN % cN/dtex R1 997 256 1,13 R2 1062 281 1,20 R3 1105 270 1,25 R4 1065 264 1,20 R5 1057 250 1,19 R6 927 231 1,05 R7 971 235 1,10 R8 1026 291 1,16 R9 FALSE R10 FALSE dtex 885 OS_02 Name Maximum Force Elongation at break Tenacity Unit cN % cN/dtex R1 915,322 7,45303 0,42 R2 900,633 10,3043 0,42 R3 795,494 9,2258 0,37 R4 890,15 10,3601 0,41 R5 937,994 7,34307 0,43 R6 963 11 0,44 R7 963 10 0,44 R8 898,81 9,91483 0,41 R9 FALSE R10 FALSE dtex 2168 69 OS_03 Name Maximum Force Elongation at break Tenacity Unit cN % cN/dtex R1 1199,35 10,3036 0,48 R2 1260,41 10,093 0,51 R3 1186,86 8,91237 0,48 R4 1184,03 10,3617 0,48 R5 1272 10 0,51 R6 1161 10 0,47 R7 1274 9 0,51 R8 1262 10 0,51 R9 1182 8 0,48 R10 FALSE dtex 2487 OS_04 Name Maximum Force Elongation at break Tenacity Unit cN % cN/dtex R1 1526,6 9,64893 0,49 R2 1553,86 9,13473 0,50 R3 1503,67 9,5532 0,48 R4 1501 9 0,48 R5 1477 9 0,47 R6 1468 11 0,47 R7 1468 8 0,47 R8 1406,21 9,29873 0,45 R9 FALSE R10 FALSE dtex 3135 70 OS_05 Name Maximum Force Elongation at break Tenacity Unit cN % cN/dtex R1 945,61 8,0503 0,57 R2 945,153 9,6009 0,57 R3 986,293 10,2851 0,59 R4 969 8 0,58 R5 916 9 0,55 R6 929,018 9,15907 0,56 R7 948,878 8,81017 0,57 R8 933,333 8,92997 0,56 R9 970,843 10,8646 0,58 R10 FALSE dtex 1667 OS_06 Name Maximum Force Elongation at break Tenacity Unit cN % cN/dtex R1 1223,75 11,3358 0,40 R2 1165,55 9,6707 0,38 R3 1279 10 0,41 R4 1356,82 10,2795 0,44 R5 1194,46 10,9608 0,39 R6 1353,13 10,166 0,44 R7 1205,08 10,1304 0,39 R8 1227,95 9,29847 0,40 R9 1263,21 10,883 0,41 R10 FALSE dtex 3090 71 OS_07 Name Maximum Force Elongation at break Tenacity Unit cN % cN/dtex R1 1514 10 0,54 R2 1434,97 7,895 0,51 R3 1541,95 9,61263 0,55 R4 1411,69 8,4471 0,50 R5 1390,35 7,93217 0,49 R6 1583,95 8,23287 0,56 R7 1336,29 9,43367 0,47 R8 1453,64 8,76803 0,51 R9 1635,7 9,28587 0,58 R10 FALSE dtex 2829 Tenacity (cN/dtex) Elongation at break (%) Maximum Force (cN) AV SD CV AV SD CV AV SD CV OS_01 1,16 0,06 0,05 259,6 20 0,08 1026 55 0,05 OS_02 0,42 0,02 0,06 9,4 1 0,13 908 50 0,06 OS_03 0,49 0,02 0,04 9,6 1 0,07 1220 43 0,04 OS_04 0,47 0,01 0,03 9,2 1 0,07 1488 42 0,03 OS_05 0,57 0,01 0,02 9,2 1 0,10 949 21 0,02 OS_06 0,41 0,02 0,05 10,3 1 0,06 1252 64 0,05 OS_07 0,52 0,03 0,06 8,9 1 0,08 1478 92 0,06 72 2.3 Electrical characterization data PBT/CNTs mm Resistance (Ohm) Resistivity (Ohm.m) Conductivity (S/m) AV SD CV (%) d1 d2 AV Area (m2) PBT/5%CNTs 1 2,15 2,17 2,16 1,46574E-05 5,88E+02 5,74E-01 1,74E+00 1,75E+00 0,270 15,371 2 2,2 2,17 2,185 1,49987E-05 7,20E+02 7,20E-01 1,39E+00 3 2,18 2,15 2,165 1,47254E-05 6,62E+02 6,50E-01 1,54E+00 4 2,11 2,14 2,125 1,41863E-05 6,05E+02 5,72E-01 1,75E+00 5 2,13 2,19 2,16 1,46574E-05 5,43E+02 5,31E-01 1,88E+00 6 2,17 2,15 2,16 1,46574E-05 6,19E+02 6,05E-01 1,65E+00 7 2,11 2,15 2,13 1,42531E-05 6,35E+02 6,03E-01 1,66E+00 8 2,21 2,18 2,195 1,51363E-05 4,55E+02 4,59E-01 2,18E+00 9 2,15 2,18 2,165 1,47254E-05 4,51E+02 4,43E-01 2,26E+00 10 2,22 2,19 2,205 1,52745E-05 6,62E+02 6,74E-01 1,48E+00 PBT/4%CNTs 1 2,22 2,2 2,21 1,53439E-05 6,84E+02 7,00E-01 1,43E+00 1,03E+00 0,228 22,016 2 2,19 2,25 2,22 1,5483E-05 1,07E+03 1,11E+00 9,03E-01 3 2,18 2,2 2,19 1,50674E-05 9,75E+02 9,79E-01 1,02E+00 4 2,23 2,26 2,245 1,58337E-05 8,81E+02 9,30E-01 1,08E+00 5 2,17 2,19 2,18 1,49301E-05 8,10E+02 8,06E-01 1,24E+00 6 2,26 2,26 2,26 1,6046E-05 9,14E+02 9,78E-01 1,02E+00 7 2,25 2,27 2,26 1,6046E-05 7,46E+02 7,98E-01 1,25E+00 8 2,2 2,23 2,215 1,54134E-05 1,69E+03 1,74E+00 5,75E-01 9 2,19 2,2 2,195 1,51363E-05 1,19E+03 1,20E+00 8,32E-01 10 2,21 2,24 2,225 1,55528E-05 9,70E+02 1,01E+00 9,94E-01 73 mm Resistance (Ohm) Resistivity (Ohm.m) Conductivity (S/m) AV SD CV (%) d1 d2 AV Area (m2) PBT/3,5%CNTs 1 2,11 2,15 2,13 1,42531E-05 1,94E+03 1,84E+00 5,44E-01 5,26E-01 0,113 21,541 2 2,17 2,12 2,145 1,44545E-05 1,90E+03 1,83E+00 5,46E-01 3 2,21 2,2 2,205 1,52745E-05 1,58E+03 1,61E+00 6,22E-01 4 2,17 2,17 2,17 1,47934E-05 2,52E+03 2,48E+00 4,03E-01 5 2,2 2,25 2,225 1,55528E-05 2,21E+03 2,29E+00 4,36E-01 6 2,14 2,18 2,16 1,46574E-05 1,73E+03 1,69E+00 5,93E-01 7 2,22 2,21 2,215 1,54134E-05 2,01E+03 2,07E+00 4,83E-01 8 2,15 2,17 2,16 1,46574E-05 1,40E+03 1,37E+00 7,31E-01 9 2,18 2,15 2,165 1,47254E-05 1,73E+03 1,70E+00 5,88E-01 10 2,18 2,18 2,18 1,49301E-05 3,16E+03 3,15E+00 3,18E-01 PBT/3%CNTs 1 2,18 2,2 2,19 1,50674E-05 7,51E+03 7,54E+00 1,33E-01 2,87E-01 0,074 25,865 2 2,19 2,2 2,195 1,51363E-05 2,62E+03 2,64E+00 3,79E-01 3 2,16 2,23 2,195 1,51363E-05 2,42E+03 2,44E+00 4,10E-01 4 2,19 2,19 2,19 1,50674E-05 4,02E+03 4,04E+00 2,48E-01 5 2,2 2,19 2,195 1,51363E-05 4,12E+03 4,16E+00 2,41E-01 6 2,1 2,19 2,145 1,44545E-05 3,54E+03 3,41E+00 2,94E-01 7 2,1 2,17 2,135 1,43201E-05 3,97E+03 3,79E+00 2,64E-01 8 2,17 2,17 2,17 1,47934E-05 3,16E+03 3,12E+00 3,21E-01 9 2,23 2,14 2,185 1,49987E-05 3,07E+03 3,07E+00 3,26E-01 10 2,16 2,15 2,155 1,45896E-05 3,97E+03 3,87E+00 2,59E-01 80 Bobbin Conditions Diameter (m) Area (m2) Resistance (Ohm) Resistivity (Ohm.m) Conductivity (S/m) AV SD CV OS_6 Bomba: 14 rpm Rolo 1: 100 m/min Rolo 2: 100 m/min Rolo 3: 100 m/min CDR: 1 DDR: 25 0,00083 0,00000054 3,50E+08 6,26E+03 1,60E-04 7,85E-05 5,81E-05 0,760 2,30E+09 4,11E+04 2,43E-05 1,90E+09 3,40E+04 2,94E-05 1,60E+09 2,86E+04 3,50E-05 4,18E+08 7,47E+03 1,34E-04 OS_7 Bomba: 18 rpm Rolo 1: 100 m/min Rolo 2: 100 m/min Rolo 3: 100 m/min CDR: 1 DDR: 20 0,00091 0,00000066 1,70E+09 3,71E+04 2,69E-05 3,08E-05 1,14E-05 0,369 1,80E+09 3,93E+04 2,54E-05 9,50E+08 2,07E+04 4,82E-05 1,20E+09 2,62E+04 3,82E-05 3,02E+09 6,59E+04 1,52E-05 81 2.4 Heating tests data PBT/3%CNTs – 12 V 82 PBT/3%CNTs – 24 V 83 PBT/3%CNTs – 48 V