Morphology of polytetrafluoroethylene before and after irradiation

Supramolecular structure and morphology of as-polymerized, sintered, and gamma-irradiated suspension PTFE were studied with scanning electron microscopy. Irradiation was performed both below and above melting point of crystal phase. Fibrillar supramolecular structure of as-polymerized PTFE is preserved after its sintering. In contrast to as-polymerized FIFE, in the sintered polymer some segments of fibrils form lamellae of thickness 100-300 nm and length up to several microns, with fibrils arranged perpendicularly to a lamella. Irradiation below the melting point (20 and 200 degrees C) does not change quantitatively PTFE morphology. In both cases and also in the case of pristine FIFE, dense and loose (porous) regions are present in its morphology. Dense regions are packages of irregular shape and consist of densely packaged fibrils. Loose regions consist of individual ribbons and fibrillar lamellae. Irradiation at 200 degrees C increases greatly the width of lamellae. PTFE, structure rearrranges drastically under irradiation above the melting point. New morphology units, spherulites of size about 50 mu m, are formed, the spherulites consisting of radially extending fibrils, and porosity decreases substantially. Formation of spherulites is ascribed to radiation-induced chain scission and decrease in molecular mass and viscosity of polymer. (C) 2011 Elsevier Ltd. All rights reserved.