Studies On Dynamic Rheological Behaviors And Crystalline Properties Of PE/CSW Composites

In this work, calcium sulfate whisker(CSW) was used as a kind of filler andfilled with four kinds of polyethylene with different structure of molecular chain(HDPE, mPE, LLDPE, LDPE-1, LDPE-2). PE/CSW composites were prepared usingmelt blending method. The influence of filler content and structure of polyethylene(PE) on Payne effect, like solid behavior, shear thinned behavior and the temperaturedependence of viscosity was discussed. The microstructure of the composite sampleswas observed by scanning electron microscopy (SEM). In addition, melting andcrystallization behavior of four composites were investigated.The results of dynamic rheological experiments of PE/CSW composites showedthat: all composites except LDPE-2/CSW composites showed Payne effect andpseudo solid-like behavior when the volume percentage of whisker (Φ) reaches acertain value. In dynamic strain sweep, storage modulus decreased sharply with theincrease of strain. In dynamic frequency sweep, storage modulus of composites hadbeen improved greatly and modulus of platform was seen in the low-frequency region.While, Payne effect and pseudo solid-like behavior was not seen in LDPE-2/CSWcomposites. It was found that percolation threshold(ΦC) which was tested in dynamicrheological test was the same with the value of whisker content(ΦP) when Payneeffect appeared in all composites. The results of shear thinned behavior studies ofPE/CSW composites showed that: mPE/CSW and LLDPE/CSW composites appearedsignificant shear thinned behavior in low frequency region when whisker content washigher than15vol%. But all samples of LDPE-1/CSW and LDPE-2/CSW compositesshowed obvious shear thinned behavior. The shear thinned phenomenon ofLDPE-1/CSW composites was more significant in higher filler content samples. Theinvestigation of temperature dependence of viscosity showed that: when the volumecontent of whisker was under15vol%, the viscous flow activation energy of PE/CSWcomposites decreased with increase of whisker content; when the volume content ofwhisker was higher15vol%, the viscous flow activation energy of PE/CSWcomposites increased with increase of whisker content.The morphology structure of the composites’ fracture surface was also observed.There was obvious phase interface between whiskers and polymers in HDPE/CSW,mPE/CSW and LLDPE/CSW composites in which aggregate structure of whiskers was formed. There was no phase interface between whiskers and polymers inLDPE-1/CSW and LDPE-2/CSW which proved that whisker had good compatibilitywith LDPE. Whiskers in LDPE-2/CSW composites orientation very well and surfaceof each whiskers surface coated with polyethylene tightly. But distribution ofwhiskers in LDPE-1/CSW composites was random and a phenomenon of aggregationwas seen.The melting and crystallization behavior of PE/CSW composites were alsoinvestigated. The melting point of all composites was improved slightly when5vol%whiskers were filled. While,the melting point decreased when whisker content washigher than5vol%. With the increase of whisker content, the crystallinity of HDPEdcreased, but the crystallinity of mPE and LLDPE increased. Influence of whiskers onmelting and crystallization behavior was not obvious.