Improved piezoresistive sensing behavior of poly(vinylidene fluoride) / carbon black composites by blending with a second polymer

Abstract

For the production of low-cost conductive polymer composites (CPCs), carbon black (CB) is a suitable conductive filler that provides higher piezoresistive sensitivity compared to highly anisotropic fillers such as carbon nanotubes. However, the use of CB containing CPCs as sensor materials is limited by high electrical percolation threshold (Φc) and poor signal linearity. In this work we demonstrate that the addition of either amorphous poly(methyl methacrylate) (PMMA, 20 wt%) or partially crystalline poly(butylene succinate) (PBS, 30 wt%) tunes the piezoresistive behavior of composites based on partially crystalline poly(vinylidene fluoride) (PVDF) and CB (3 and 4 wt%), due to a changed phase morphology and network arrangement. Significantly improved piezoresistive linearity compared to the corresponding composites with a pure PVDF matrix was achieved. Thereby, the sensitivity at small initial strains is not compromised. Furthermore, the addition of 30 wt% PBS reduced the electrical percolation threshold significantly, so that samples with the low amount of 1.5 wt% CB became available for piezoresistive testing. This blend composite shows a nearly linear piezoresistive behavior with a significantly enhanced relative electrical resistance change ΔR/R0 of 71.8 ± 7.1% at 5% strain. This value is much higher than those achieved in the PVDF-CNT (1–2 wt%) or PVDF-CB (3–4 wt%) composites (ΔR/R0 lower than 40%).