Structure and properties of biaxial stretched submicron thin UHMWPE membranes

Producing thinner polymer membranes has been a research hotspot to satisfy the increasing demand from diverse application scenarios in the industry. This work used biaxially stretching with an exceptionally high draw ratio near melting point to thin down the excessively petrolatum-swollen UHMWPE gel from millimeters to hundreds of nanometers. Of which the meso- and micro-structural evolution during stretching processing was systematically investigated, especially within the thickness range from microns to submicrons, threading through the micron-thickness boundary. These membranes consisted of oriented smooth fibrils without identifiable overgrowth lamellae but with two obvious melting points, being different from the conventional bead-fiber shape of the typical shish-kebab super-crystalline structures. Moreover, an ionic rejection phenomenon of submicron UHMWPE was observed, which was attributed to the surface potential that emerged when thinning down PE membrane below the threshold of 800 nm. It is the first report of emerging surface potential for the nonpolar neutral polymers as a function of reduced thickness within the submicron range. This work provides insight into the processing of submicron-thin polymer membranes, with the unique structure and properties distinguished from the bulk revealed and explained. These findings may also help the processing and structure-property analysis of submicron membranes of other polymer materials.