Preferential alignment of two-dimensional montmorillonite in polyolefin elastomer tube via rotation extrusion featuring biaxial stress field

Abstract

Preferential alignment of two-dimensional (2D) nanofillers in polymer matrix is essential to realize the transition of distinct properties from individual nanofiller into bulk nanocomposites, but this is an impossible task in conventional melt-processing because 2D nanofillers with two degrees of freedom experience transition and rotation movements along or around the two axes of the plate. Here, we proposed a flow manipulation strategy to control the preferential alignment of 2D montmorillonite (MMT) plates in polyolefin elastomer (POE) tube by superposing a hoop drag flow from rotation of mandrel and die onto axial flow caused by conventional extrusion. The biaxial stress field simultaneously restricted the axial and hoop rotation movements of the major and minor axes of the MMT plates, leading to preferential alignment along the hoop and longitudinal directions with the planar surface perpendicular to radial direction of the tube. As a result, the as-prepared tube exhibited strong resistance to various mechanical deformations (hoop kinking, axial and radial compression) as well as enhanced barrier property, holding the promising potential as an advanced tube in clinical interventional therapy and transportation of polar substances. Compared with the state-of-the-art techniques with complicated process and low productivity efficiency, this flow manipulation strategy for tailoring preferential alignment of 2D nanofillers was featured with a simple melt-processing, which was suitable for massive production and easily extended to the other composite tubes.