纤维状填料/HDPE复合体系的导电渗流与流变渗流行为的关系

研究了纤维状导电材料不锈钢纤维(SSF)填充高密度聚乙烯(HDPE)导电复合体系的导电渗流与流变渗流行为之间的关系,并与颗粒状导电颗粒炭黑(CB)/HDPE导电复合体系进行了比较.发现当SSF含量极低(0.3vol%)时,SSF/HDPE体系即发生导电渗流现象,且导电渗流转变区域极窄;而仅当SSF含量达到4.8vol%时,该复合体系才表现出流变渗流现象,这一结果与CB/HDPE体系及纳米级导电纤维填充体系截然不同.此外,通过正温度系数效应的研究发现SSF形成的导电通路稳定性高于CB/HDPE体系.我们认为,SSF/HDPE体系呈现的这些特点均与SSF较大的直径及长径比且其导电通路及流变渗流网络的形成机理不同有关.

RELATIONSHIP BETWEEN ELECTRICAL CONDUCTIVE AND RHEOLOGICAL PERCOLATIONS FOR FIBRES/HDPE COMPOSITES

The linear viscoelastic behavior and electrical conductivity of high-density polyethylene (HDPE) filled with stainless steel fibers (SSF) were investigated and compared with those of carbon black (CB) filled HDPE composites system.It is found that CB/HDPE composites show two electrical conductivity percolation values (φ c1 and φ c2 ) and a wide percolation range.However,SSF/HDPE composites present an extremely low threshold of the electrical conductivity percolation (only 0.3 vol%) and a narrow percolation range.Only one conductivity percolation value (φc) was observed.The speciality of conductivity percolation behavior of SSF/HDPE composites owes to the formation of conducting channels of SSF/HDPE composites.It is well recognized that the rheological percolation threshold is identical to the percolation threshold of electrical conductivity for CB/HDPE composites.Whereas,for SSF/HDPE composites,dynamics storage modulus (G') becomes almost independent of frequency in the low frequency region as the SSF loading increases up to 4.8 vol%,suggesting an onset of solidlike behavior in SSF/HDPE composites.By plotting G' versus SSF loading,the rheological threshold is determined as 4.8 vol%,which is much lower than the percolation threshold of electrical conductivity,i.e. 0.3 vol%.Additionally,the positive temperature coefficient (PTC) effect was measured for SSF/HDPE and CB/HDPE composites.It reveals that the conductivity channels formed by SSF show a higher stability than those formed by CB particles in HDPE matrix.The difference in the percolation threshold and the stability of conductivity channels are understood in terms of the larger L/D of SSF and the particular conductive mechanism of SSF/HDPE composites