Large scale formation of various highly oriented structures in polyethylene/polycarbonate microfibril blends subjected to secondary melt flow

Abstract

A strong shear flow was imposed on the melt of polycarbonate (PC) microfibril reinforced high density Polyethylene (HDPE) during a secondary melt flow process, i.e. gas assisted injection molding (GAIM). Classic shish-kebabs and typical transcrystallinity were simultaneously observed in the entire thickness of the GAIM HDPE/PC microfibril composites, which were closely related to the strong shear flow that was further amplified and distributed by incorporated PC microfibrils. Interestingly, some nano-sized ultrafine PC microfibril inclined to absorb extended chain bundles to form shish nuclei on its surface first, which subsequently evolved into hybrid shish-kebab superstructures. It was deemed that the induced formation of hybrid shish-kebab superstructures on nano-sized ultrafine PC microfibril was due to the absorbing of extended chain bundles for hybrid shish nuclei with the strong shear flow serving as the driving force. Importantly, large scale formation of these highly oriented crystalline superstructures can bring significant mechanical reinforcement in GAIM HDPE/PC microfibril composite. For GAIM HDPE/PC microfibril composites, its yield strength is increased by 68% and 66%, compared to the GAIM HDPE parts and the common injection molded (CIM) HDPE/PC composites, respectively; meanwhile, the Young's modulus is enhanced by 253% and 17%, compared to the GAIM HDPE parts and the CIM HDPE/PC composites, respectively.