炭黑/二氧化硅/环氧树脂基复合材料的PTC效应

PTC effect in carbon black/silica loaded epoxy resin

在25～200℃范围内，炭黑／二氧化硅／环氧树脂基复合材料的电阻率随温度的升高而增加，表现出正的温度系数效应（PTC）。当温度低于80℃，低碳含量复合材料（14％和19％，基于聚合物的质量）的温度稳定性较好，这是因为炭黑用量的减少，将有利于环氧树脂与异佛尔酮二异氰酸酯之间亲核加成反应的发生，材料中形成了更多的交联链，在一定程度上限制了聚合物骨架的运动性，降低了其对炭黑形成的导电通路网的破坏作用。当温度高于160℃，高碳含量复合材料（24％和33％，基于聚合物的质量）的温度稳定性好，这是因为高温条件促进了热激发的电子越迁过程，在一定程度上抵消由于组分热膨胀性差异而引起的对导电通路的破坏作用；而热激发的电子越迁过程对炭黑颗粒间距小的高碳复合材料的影响更为显著。扫描电镜、红外光谱和差示扫描热量法分析结果支持上述结论。

Electrical resistivity of carbon black （CB）/sihca filled epoxy resin composites increases with the increase of temperature in 25 - 200℃ （Positive Temperature Coefficient, PTC）. At low temperature （ 〈 80℃）, lower CB content of composites （ 14% and 19% ,on mass of resin） exhibits beuer temperature stability in contrast to higher CB loaded composites. As low CB content aids the nucleophilic addition reaction between epoxy resin and isophomne diisocyanate and subsequently the development of cross-links which will restrict the mobility of polymer matrix and reduce its detrimental effect on electrical conducting networks developed by CB. At high temperature （ 〉 160℃）, higher CB content composites （24% and 33%, on mass of resin） display better temperature stability, which may result from the thermally activated electron hopping procedure. The electron hopping counteracts the increase in resistivity resulting from the thermal mismatch between polymer and CB, and this effect is more prominent in composite with high CB content as the interparticle gaps are smaller. SEM,FY-IR and DSC analyses evidence for the conclusions.