The development of voidage and capillary size within extruded plastic films

This paper describes how both capillary diameter and voidage can be manipulated by downstream mechanical processing of plastic microcapillary films (MCFs). MCFs are a novel thermoplastic extrudate that have been manufactured by the entrainment of gas within nozzles positioned in an extrusion die; the film resembles a plastic tape but contains an array of equally spaced parallel microcapillaries that run along its entire length. The low-voidage MCFs manufactured from linear low density polyethylene were made by melt drawing the polymer to produce an essentially isotropic MCF. This MCF could then be subsequently mechanically drawn to form small diameter MCFs. By altering process conditions an anisotropic high voidage MCF was produced. This MCF was brittle when drawn in the capillary direction but showed unusual mechanical transverse drawing. The paper presents experiment details for the manufacture of the different MCF structures together with mechanical properties and X-ray orientation data. From this, qualitative explanations for the mechanisms to achieve the different structures are given.