Studies On Melts Extension Rheological Behaviors And Mechanisms Of Polyethylene Blends And Its Nanocomposites

Polymer elongational flow widely exists in many processing, such as spinning and blow molding, which significantly impact the quality of the final products. Rheological behavior of polymer multiphase systems including blends and composites in extensional flow field are more complicated. Therefore, it is necessary to investigate the elongational rheological behavior and its mechanism of polyethylene multiphase systems.In this paper, low density polyethylene/linear low density polyethylene(LDPE/LLDPE) blends, low density polyethylene/high-density polyethylene(LDPE/HDPE) blends and low density polyethylene blends/nano-zinc oxide(LDPE/nano-ZnO) nano-composite materials were prepared by a twin-screw extruder. A Rheotens device was used to test the elongational rheological behavior of these three systems with melt spinning method. The impacts of extentional strain rate, temperature, die extrution velosity and materials weight fraction on the extensional rheological properties of polyethylene multiphase systems were well investigated.The extensional stress of LDPE/LLDPE blends increased with the increasing strain rate and the LDPE weight fraction, while decreased with the increasing temperature. The dependence of the melt elongation viscosity and melt strength on temperature roughly obeyed the Arrhenius equation, and it increased with increasing extensional strain rate and the LDPE weight fraction. Dependence of melt strength on the die extrution velosity roughly obeyed the exponential equation. The drawability of the blends melt decreased with the LDPE weight fraction and the die extrution velosity, while increased with the increasing temperature.When the LLDPE weight fraction was less than 40%, LDPE plays a dominant role in the extentional flow behavior of the blends.The dependence of the melt elongation viscosity and melt strength of LDPE/HDPE on temperature could not obey the Arrhenius equation, and it increased with increasing extensional strain rate. The dependence of the melt strength on temperature roughly obeyed the Arrhenius equation and it increased with the increase of die extrution velosity. Though when the HDPE weight fraction was higher than 20%, it had a significant effect on the extensional flow behavior of the blends, LDPE still plays a dominant role in the extentional flow behavior of the blends.The dependence of the melt elongation viscosity and melt strength of LDPE/nano-ZnO nanocomposites on temperature roughly obeyed the Arrhenius equation. Due to the weakness of the interfacial force between nano-ZnO and LDPE and the ‘roll’ effect, after adding nano-ZnO, the elongational viscosity and the melt strength of LDPE nanocomposites were lower compared to LDPE.The Rheotens grandmastercurves were applicable for LDPE/LLPDE blends, LDPE/HDPE blends, LDPE/nano-ZnO nanocomposites. The relationship between the shift factors b and temperature T as well as lgb and lgv0 were linear.Many factors influence the extensional flow-induced crystallization behavior, including the die temperature, die extrusion rate and stretch ratio. A appropriately enhanced die temperature and the suitable draw ratio will cause the increase of deformation, orientation along the flow direction and higher level extending of the macromolecular chains, so that the effect of stretching flow-induced crystallization increased, resulting in the increasing crystallinity;The results would enrich the rheology in polymer processing. In addition it is a practical value for guiding the preparing, film blowing and melt spinning of polymer blends and its nanocomposites.