Effect Of Ultrasonic Oscillations On Rheological Behavior And Structure As Well As Properties Of Metallocene-Catalyzed Polyethylene And Its Blends With Low Density Polyethylene And Polypropylene

An ultrasonic oscillations extrusion equipment developed in our lab is optimized to improve the processing properties of metallocene-catalyzed polyethylene (mPE). Effect of ultrasonic oscillations on rheological, processing behaviors and structure & properties development of mPE and its binary blend with low density polyethylene (LDPE) and polypropylene (PP) are studied.In the presence of ultrasonic oscillations, molecular weight of mPE decreases at first and then increases, its distribution becomes wider, branching and crosslinking content in mPE molecules increase, resulting in different multiple-step isothermal crystallizing behaviors.The experimental results show that ultrasonic oscillations as well as die materials have great influence on the rheological and processing behavior of mPE. The die pressure, apparent viscosity, flow activation energy of mPE and its blends reduce greatly, productivity increases in the presence of ultrasonic oscillations during extrusion. Polytetrafluoroethylene (PTFE) die can greatly inhibit the occurrence of melt fracture or surface distortion of mPE extrudate, the surface appearance of mPE extrudate gets greatly improved, and the critical shear rate increases nearly 3 times. Slip velocity between mPE melt and die capillary wall increases in the presence of ultrasonic oscillations and much greatly when mPE melt extruded through PTFE die. Ultrasonic oscillations can conduce POE to disperse more finely and evenly in mPE matrix.Molecular weight, branching and crosslinking content of mPE increase slightly after extrusion in the presence of ultrasonic oscillations. Dynamic rheological results indicate that mPE melt, which extruded in the presence of 200W ultrasonic oscillations, has lower dynamic cross modulus, longer characteristic time, higher complex viscosity and zero shear viscosity. Ultrasonic oscillations can reduce complex viscosity and zero shear viscosity of mPE/LDPE or mPE/PP blends and improve their compatibility. DSC, TG and DMTA results show that ultrasonic oscillations have distinct influence on crystallizing, thermal and relaxing behaviors of mPE. Mechanical properties of mPE get improved in some degree due to ultrasonic oscillations effects during extrusion.Ultrasonic oscillations have different influences on crystallizing and mechanical properties of mPE/LDPE and mPE/PP blends. Crystalline phase of LDPE contains more branching mPE molecular segments. Impact strength of PP gets improved due to the addition of mPE, and that of blends increases greatly in the presence of ultrasonic oscillations. The addition of LDPE or PP has nearly no effect on outstanding impact strength of mPE. Film processing property of mPE gets improved and mechanical properties reduce slightly due to the addition of LDPE, and film mechanical properties of LDPE increase due to the addition of mPE.