Poly(vinylidene fluoride) and thermoplastic polyurethane composites filled with carbon black-polypyrrole for electromagnetic shielding applications

This study aims to investigate the electromagnetic interference shielding properties of composites based on immiscible polymer blends of poly(vinylidene fluoride) (PVDF) and thermoplastic polyurethane (TPU) filled with carbon black doped with polypyrrole (CB-PPy) prepared by compression molding and fused filament fabrication. Composites of PVDF/CB-PPy and TPU/CB-PPy were also prepared for comparison. Rheological measurements showed that although the rheological behavior of PVDF/TPU composites was an intermediate behavior between PVDF/CB-PPy and TPU/CB-PPy composites, the effect of the conductive filler was much more pronounced in PVDF than in TPU. Moreover, the addition of CB-PPy was found to increase the storage modulus of the composites leading to more rigid materials, and to decrease the Tg values of the composites due to the reduction of the mobility of the polymeric chains. In addition, PVDF/TPU composites presented an intermediate behavior when compared to composites based on the neat polymers demonstrating that the addition of TPU to PVDF contributes to the development of composites with improved flexibility. Furthermore, the addition of CB-PPy increased the electrical conductivity of all composites. However, the electrical conductivity of PVDF/TPU 50/50 vol% co-continuous blends was higher than the electrical conductivity of PVDF/TPU 38/62 vol% composites with the same amount of conductive filler. Composites with higher electrical conductivity showed better shielding from electromagnetic radiation. As expected, composites based on the co-continuous blend displayed higher EMI shielding efficiency than the 38/62 vol% composites. The main mechanism of shielding was absorption for all composites. Overall, composites based on the PVDF/TPU 50/50 vol% co-continuous blend showed a better combination of EMI shielding efficiency and mechanical properties. Moreover, specimens prepared by fused filament fabrication displayed diminished electrical conductivity and EMI-SE responses when compared to compression-molded samples with the same composition. This difference is attributed to the presence of voids, defects, and overlapping layers, which can hamper the electron flow.