Extensional-shear coupled flow-induced morphology and phase evolution of polypropylene/ultrahigh molecular weight polyethylene blends: Dissipative particle dynamics simulations and experimental studies

Abstract

The property of ultrahigh molecular weight polyethylene (UHMWPE)-based materials are significantly dependent on the morphology and phase behavior evolution subjected to extensional-shear coupled flow fields. In this study, we utilize polypropylene (PP)/UHMWPE blends as model and present a combination of numerical simulation and experimental study on their association behavior under extensional-shear coupled flow field. In terms of simulation, combined molecular dynamics (MD) and dissipative particle dynamics (DPD) method are applied, where two kinds of extensional-shear coupled flow fields are produced, named as coupledⅠand coupled Ⅱ. In response to coupled Ⅰ, shear-stretched alignment of PP chains is observed at shear rate of γ˙ = 0.01, followed by a quick disordering transition with increasing the shear rates and a final phase-separation at shear rate of γ˙ = 0.1. When subjected to coupled Ⅱ, the weak segregation start to connect with the adjacent ones, giving a homogeneous phase when further increasing the applied pressure. The presence of pressure-driven flow helps in bridging different chains, causing the percolating polymer network reinforcement. Besides, experimental studies by means of Raman spectroscopy, Raman mapping and rheological measurement are compared with the above simulations. It confirms that it is more efficiently broken for melted drops under an extensional dominated coupled flow than those under a shear dominated coupled flow, in which an effective lubricating phase forms, leading to the induced miscibility in polymer blends and reduction in storage modulus and viscosity. These experimental findings are consistent with simulation results.