Studies On The Dynamic Rheological Properties Of UHMWPE/HDPE Composites

Polymer dynamics rheology is an effective method to study the relation of the evolution of its morphology and the rheological behavior, especially for multi-phase polymer system.In recent years, many study focused on the dynamic rheological properties of polyolefins (mainly polyethylene) blends. Mostly concentrated in the relation of thermal rheological behavior of blends and the phase behavior. It was lack necessary research to the relation of the evolution of its morphology and the rheological behavior in the processing.In this article, high-density polyethylene/ultrahigh molecular weight polyethylene (HDPE/UHMWPE), high density polyethylene/ultrahigh molecular weight polyethylene/calcium carbonate (HDPE/UHMWPE/CaCO3) blends was intended to take as a model. The influence of the processing parameters, including the processing temperature, screw shear rate, filler content, on the dynamic rheological behavior of the blends has been investigated. On this basis, the evolution of morphological structure on the system has been extrapolated.Study showed that for HDPE/UHMWPE blends (90/10wt%), the change of processing temperature or screw shear rate maked the dynamic rheological behavior of this system obviously transform.The results showed that the dispersion of UHMWPE improved with the increase of screw speed. The composite melts behaved various dynamic rheological behaviors. The storage moduli (G'), loss moduli (G"), zero shear viscosity (η0) of the HDPE/UHMWPE composite melts increased obviously at low frequency region, while the transition point of the viscoelasticity moved to low frequence region. Due to the dispersion improvement of UHMWPE, the initial crystallization temperature of HDPE/UHMWPE composites shifted to high temperature and the isothermal crystallization process was accelerated. The morphology of nascent UHMWPE powder was examined by scanning electronic microscopy (SEM). A morphology model has been proposed for these composites. The secondary UHMWPE particles could be gradually destroyed by the screw shear and resulted in better degrees of UHMWPE dispersion in these composites.However for the HDPE/UHMWPE (96/4wt%) blends, the changes of processing parameters had no significant effective on dynamic rheological properties of this blends. The addition of calcium carbonate has caused significant changes of dynamic rheological behavior. The results showed that CaCO3 can not change the rheological behavior of HDPE. While HDPE/UHMWPE/CaCO3 composites had various rheological behavior with different processing. At low frequency region the dependence of storage modulus on frequency for the blends tended to be weakened with the increase of the screw speed of torque rheometer. And the storage moduli (G'), loss moduli (G"), zero shear viscosity (η0) of the blend melts increased obviously, while the tangent (δ) decreases. This corresponded to changes from more liquid-like behaviors for HDPE/UHMWPE/CaCO3 composites to solid-like behaviors. These phenomena reflected macromolecular chains entanglement enhancement. The change of the structure of the blend melt further identified that the macromolecular chains interacted much more . The interaction affected the mobility of macromolecular chains. So the the stress relaxation time increased and the isothermal crystallization process was accelerated. The viscoelastic transition of melt was related to the interaction of UHMWPE and CaCO3 rigid particle. With the content increasing of Calcium carbonate, the dynamic rheological properties significant changed, which may be related to the forming of the network between calcium carbonate filler and ultra-high molecular weight polyethylene.