Thermal post treatment of highly filled compounds for fuel cells.

Functionalized polymers in general are claiming more and more novel applications; for example they can function as a metal replacement. Especially the E&E- market or the so-called “green technologies” require highly engineered polymers for many new needs such as a high level of thermal or electrical conductivity in polymers. To functionalize an intrinsic isolating polymer high loadings of conductive fillers, like graphite, carbon blacks, CNTs, metals and/or others, are necessary. For fuel cell application filler contents of more than 80 wt% in a thermoplastic polymer are needed. The mixtures, so-called compounds, exhibit a significantly different behavior in processing and in their properties compared to neat polymer. Especially viscosity sensitive processing techniques such as injection molding are often limiting the amount of filler that is applicable and therefore also limiting achievable conductivity. A low resistivity is critical for the use in fuel cells. At ZBT a new thermal post treatment technique was developed that can decrease resistivity of injection molded bipolar plates significantly. Reduction of resistivity ranged up to 76%. The influence of filler content, particle size, morphology, time and temperature of treatment were investigated extensively and the mechanism behind the temperature treatment was studied in detail. Using DSC and XRD method the change in crystallinity was found to be the driving factor suggesting that percolation in filled compounds is not only based upon degree of filling but also crystallinity of polymer. Furthermore temperature treatment showed great promise for implementation in future injection molding process of highly conductive compounds as even short times of thermal post treatment lead to a significant effect. [ABSTRACT FROM AUTHOR]