Structure–property behaviour of electron beam irradiated polytetrafluoroethylene and polytetrafluoroethylene-co-hexafluoropropylene

Abstract

The effect of various doses of electron beam (EB) irradiation in air on the structure, thermal and mechanical properties of polytetrafluoroethylene (PTFE) and polytetrafluoroethylene-co-hexaflouropropylene (FEP) has been investigated. IR spectroscopic analysis of EB irradiated polymers showed an absorption band due to carbonyl group (CO) stretching as a result of irradiation and hydrolysis of the COF groups to carboxylic acid groups. While EB irradiated PTFE displayed higher thermal stability than unirradiated polymer, an opposite behaviour was observed in the case of FEP polymer as shown by thermogravimetric analysis (TGA) thermograms. However, unirradiated PTFE polymer is more stable against thermal decomposition than unirradiated FEP polymer within the same range of temperatures. The calculated activation energies of the thermal decomposition reaction for both polymers give further support to these trends and indicate that the reaction is temperature-dependent and follows zero-order kinetics. The stress–strain curves of both PTFE and FEP either before or after EB irradiation showed no yield properties. Meanwhile, exposing both polymers to a dose of 125 kGy causes a dramatic drop in stress and strain at break suggesting the occurrence of oxidative degradation during EB irradiation. However, PTFE polymer is highly sensitive to EB irradiation compared to FEP polymer exposed to the same dose.