GB1333059A - Plexifilamentary structures - Google Patents

Abstract

1333059 Plexifilaments E I DU PONT DE NEMOURS & CO 3 Nov 1970 52244/70 Heading B5B A plexifilament made by "flash-spinning" a solution of a non-crystalline (as determined by X-ray diffraction) thermoplastic synthetic organic polymer comprises a plurality of fibrils positioned parallel to the plexifilament axis and interconnected at their ends to form a three-dimensional plexus, the fibrils being less than 5Á thick and composed of film-fibrils less than 1Á thick which are oriented substantially only along their longitudinal axes. The plexifilament has a minimum surface area of 2m<SP>2</SP>/g, a minimum tenacity of 0À1 gpd, a minimum free fibril count of 50/thousand/0À1 mm. length and a density within 2% of that of the solid material from which it is made. The solvent should have a b.p. below the flow temperature of the polymer, be inert and have sufficient solvent power to form a single phase solution at the extrusion temperature and pressure but still form a twophase solution at the same temperature when the pressure is released. As described a 10-40% polymer solution within 40‹C of the solvent critical temperature and above the two-phaseboundary at this temperature by e.g. 200-300 p.s.i., is extruded first into aregion about 200p.s.i. below said boundary to produce a two-phasesolution which is then "flash-spun". The polymer may be a polycarbonate, polysulphone, PVC, polystyrene, or polymethylmethacrylate (solvent methylene chloride) or polyacrylonitrile (solvent aqueous acetonitrile). The power of the solvent may be adjusted by additives, e.g. fluorotrichloromethane on 1, 1, 2- trichloro-1, 2, 2-trifluoroethane in the case of methylene chloride.