Ultra-high molecular weight polyethylene – Evidence for a three-phase morphology

The phase composition of ultra-high molecular weight polyethylene of two different molecular weights has been estimated using Raman spectroscopy. Materials have then been irradiated in air to give a received doses of 3.5 and 10 Mrad, and crystallinity change with time has been monitored by differential scanning calorimetry (DSC), wide and small angle X-ray diffraction (WAX and SAX) and Raman spectroscopy. Analysis by DSC and X-ray diffraction involved melting and re-crystallisation. Raman spectroscopy demonstrated that the material consists of three phases, fully crystalline, fully amorphous and an intermediate all-trans non-crystalline phase. Following irradiation the mass fraction of this latter phase reduces as total crystal content increases. SAX results indicate a refinement of the original lamellae and the emergence of a population of smaller crystals. It is thought that the all-trans material exists as an interfacial phase and that scission within this phase facilitates the observed crystal changes.