具有高灵敏性且稳定可重复的正温度系数效应的PVDF/CF导电复合材料

以碳纤维(CF)为填料,聚偏氟乙烯(PVDF)为基体,通过熔融共混法制备PVDF/CF导电复合材料.所得复合材料具有显著的正温度系数(PTC)效应,温度上升到聚合物熔点附近时,电阻率对温度变化敏感.在转折温度区间(155.5~171.0oC,(35)(28)15.5oC)内,其体积电阻率的增加速率约为1.3×105?cm K-1.在不同CF含量下,复合材料表现出不同的PTC行为.随着CF含量的增加,其峰值电阻略有下降.高导电粒子含量下,无负温度系数(NTC)效应.在冷却循环过程,导电网络的重构性良好.复合材料即使经过多次热循环,依然表现出良好的PTC特性重现性.

PVDF/CF Conductive Composites with High Sensitivity and Stable Reproducibility of Positive Temperature Coefficient Effect

Application of polymer based composites with positive temperature coefficient (PTC) effect is greatly limited because of the drawbacks such as slow change of the resistivity in the transition temperature range,low PTC intensity,poor PTC reproducibility.In this work,the composite composed ofpolyvinylidene fluoride (PVDF) as matrix and carbon fiber (CF) as conductive filler was prepared by melt mixing to obtain high PTC intensity and stable reproducibility of PTC effect.The resulted PVDF/CF composites,with CF content from 13.1 vol％ to 18.2 vol％,which was above the percolation threshold of 3.93 vol％,showed remarkable PTC effect without significant negative temperature coefficient (NTC) effect during heating processed.A fast transition from conductor to insulator was obtained when the temperature was close to the melting point of PVDF matrix,namely,the increase rate of volume resistivity was 1.3 × 105 Ω cm K-1 in the transition temperature range (155.5-171.0℃).To our knowledge,this study is the first to report such phenomena in CF filled composites.The transition temperature ranges for all composites,determined by the melt temperature range and melting point of PVDF matrix,were almost the same owing to the presence of CF,and showed no effect on the crystallization behaviour of PVDF matrix.The room temperature resistivity and PTC intensity of composites with low CF content showed dependences on the thermal-cooling cycles,but they showed almost the same pattern and PTC intensity for the composites with high CF content.Desired reconstruction of CF network in the PVDF melt during cooling process and the excellent PTC reproducibility were observed even after 9 thermal-cooling cycles.