流变-导电同步测试法研究炭黑填充高密度聚乙烯的等温结晶行为

采用流变-导电同步测试法,研究炭黑(CB)填充高密度聚乙烯(HDPE)在124.3～125.3℃范围的等温结晶行为,发现应变、频率与预降温速率均显著影响等温结晶过程中动态流变与导电行为.动态储能模量(G')与电阻均在结晶过程中发生显著变化.其中,CB粒子在熔体中发生扩散,造成原有逾渗网络结构破坏,导致复合体系电阻在结晶诱导期内增大.随结晶度增加,G'在结晶诱导期附近开始显著增大,其临界时间对应1%～2%相对结晶度;同时,CB粒子在无定形区相互聚集而形成渗流网络结构,使得复合体系电阻显著降低.电阻的变化被认为与CB粒子在熔体中的迁移以及在HDPE晶体生长过程中的聚集行为有关,且比依时性动态流变行为更敏感.

STUDY ON ISOTHERMAL CRYSTALLIZATION OF CARBON BLACK FILLED HIGH DENSITY POLYETHYLENE THROUGH RHEOLOGY-ELECTRICAL CONDUCTION SIMULTANEOUS MEASUREMENT

Isothermal crystallization behavior of carbon black(CB) filled high density polyethylene(HDPE) at a narrow temperature range from 124.3 ℃ to 125.3 ℃ was investigated using a rheology-electrical conduction simultaneous measurement method to detect the formation of percolation network and its influence on viscoelastic evolution involving in crystallization of polymer matrix.The results show that strain,frequency and pre-cooling rate have significant influences on both rheological behavior and electrical resistance evolutions as a function of time.The dynamic storage modulus(G′) and resistance(R) exhibit abrupt changes upon crystallization of HDPE.R increases during the crystallization induction period,which is assigned to CB particle diffusion in the polymer melts resulting in a partial breakdown of the original percolation network.On the other hand,G′ remains constant until induction time of crystallization and the dyanmic rheological method can detect the structural variation only when relative crystallinity reaching 1%~2%.With proceeding of crystallization,G′ increases while R decreases markedly and the later is assigned to CB exclusion from the crystalline phase and aggregation in the amorphous phase.Both the rheological and electric donduction behaviors undergo interconnected changes during isothermal crystallization of filled HDPE while the R variation is much more sensitive than that of dynamic rheological behavior to detect the structural evolution because it can reflect the CB diffusion in the melts before crystallization and the CB aggregation in the amorphous phase upon crystallization.