This work deals with isothermal and non-isothermal crystallization kinetics of electrically conductive polyvinylidene fluoride/poly(ethylene terephthalate) (PVDF/PET) based composites. It completes our previous work in which we related the crystallinity of these conductive PVDF/PET based composites to their through-plane resistivity [1]. Isothermal crystallization was described using the logarithmic form of the Avrami equation and it was observed that the crystallization rate of the PVDF phase inside the composite became slower compared to that of neat PVDF. In nonisothermal crystallization, the Avrami exponent of PVDF phase did not show any noticeable variation; however, that of PET phase, which contains the major part of the conductive carbon black (CB) and graphite (GR) additives, showed an evident decrease compared with neat PET. It was also observed that, at the same cooling rate, the crystallization rate of PVDF and PET phases inside the composite was slower than that of neat PVDF and PET.

In this work, we showed how the functionalization of multiwall carbon nanotubes (MWCNT) by nitric acid (HNO 3 ) and their predispersion into poly (butylene terephthalate) (PBT) improved the through-plane electrical conductivity and mechanical properties of co-continuous morphology polyvinylidene fluoride (PVDF)/poly (ethylene terephthalate) (PET)/carbon black (CB)/graphite (GR)/MWCNT nanocomposites. First, when MWCNT were functionalized with HNO 3 then premixed with PBT, they showed no aggregations inside the PBT matrix due to their improved interfacial interactions and chemical compatibility with the PBT matrix. Then, when PBT/ (HNO 3 -functionalized MWCNT) mixture was added in small quantities to (PET/PVDF)/(CB/GR) composites, it decreased significantly their through-plane resistivity and enhanced their impact and flexural properties. Its synergistic effect also led to the best proton exchange membrane fuel cell bipolar plate prototypes (smoother surface, without any cracks). | INTRODUCTIONProton exchange membrane fuel cell (PEMFC) technology is considered as one of the most promising future technologies for industrial and transportation applications. A lot of work has been done to develop lightweight and good performance PEMFC components.Bipolar plates (BPPs) are ones of the main components that got more research focus. Bipolar plates comprise the major part, by weigh and volume, of PEMFC stack. They also represent 40% to 50% of its cost. 1 Thus, the development of appropriate and low cost materials for BPPs becomes a key factor for PEMFCs commercialization.To date, metals, graphite (GR), and polymer composites are the 3 types of materials that are mainly used for the fabrication of BPPs.Metallic BPPs could offer a good electrical conductivity, excellent mechanical properties, and ease of fabrication. However, their operating environment exposes them to a pH of 2 to 3 for temperatures around 80°C, leading to their corrosion or even their dissolution. This could poison the membrane and considerably affect its ionic conductivity if the BPPs are not protected with expensive corrosion-resistant metallic coatings.1-3 Although they have excellent corrosion resistance and high electrical conductivity, BPPs made from GR are heavy, brittle, and require precise machining of flow channels, leading to higher costs. Mighri et al 4 tested different conductive additives with thermoplasticcomposites based on polypropylene and polyphenylene sulfide. The lowest through-plane resistivity was obtained by using a combination of high surface area carbon black (CB) and synthetic GR. However, due to the high CB/GR concentration needed, the blends viscosity largely increased so that BPP manufacturing became more difficult.To find a compromise between blends processability and their corresponding BPP properties, Bouatia et al 5 developed poly (ethylene terephthalate) (PET)-based blends by twin-screw extrusion process. In addition to CB/GR combination, silver-coated glass particles were also added to decrease BPP through-plane resistiv...

This study aims at developing lightweight and high performance electrically conductive nanocomposites for proton exchange membrane fuel cell (PEMFC) bipolar plates (BPPs). These composites were made from an optimized co-continuous mixture of Polyethylene terephthalate (PET) and polyvinylidene fluoride (PVDF) reinforced with highly conductive carbon additives composed of carbon black (CB) and synthetic graphite (GR). Multiwall carbon nanotubes (MWCNT) were functionalized then used to improve BPPs electrical conductivity and their mechanical properties, such as flexural and impact strengths. It was observed that the best BPP prototype was obtained using nitric acid (HNO 3 )-functionalized MWCNT. The latter led to the smothest BPP surface, the lowest through-plane resitivity (0.12 X cm) and the highest impact and flexural strengths. These results are attributed to the improved dispersion of the functionalized MWCNT, a result of their best compatibilization with the (PET/PVDF) polymeric phase. V C 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 43624.