Influence of interfacial condition on rheological instability behavior of UHMWPE/HDPE/nano-SiO2 blends in capillary extrusion

In this study, rheological behaviors and capillary extrusion flow instabilities of ultra-high molecular weight polyethylene (UHMWPE)/high-density polyethylene (HDPE)/SiO 2 composites containing modified nano-SiO 2 or pure nano-SiO 2 are investigated. Effects of interfacial conditions between the dispersed nano-SiO 2 phase and PE matrix on rheological behaviors are analyzed. The results show that modified nano-SiO 2 in the PE matrix has a relatively strong interfacial interaction with the polymer chains compared with pure nano-SiO 2 , thus causing a more pronounced shear thinning behavior and reducing extrudate swell during capillary extrusion. Nanocomposite extrudates experience the transition of smooth- sharkskin- oscillating distortion—overall melt fracture with the increase of shear rate (or shear stress). The interfacial interaction allows a more storage of elastic energy as the melt flow through the die, resulting in sharkskin distortion and oscillating distortion to occur prematurely at critical shear rates. It also restricts the elastic recovery of the melt after leaving the die, thus delaying sharkskin distortion under shear stress. At high shear rates, the modified nano-SiO 2 particles begin to roll, and some of the unmodified particles move and embed to the wall. It is believed that the interfacial adsorption effect and the wall-slip effect of nanoparticles exist simultaneously in the whole extrusion process.