Effect of gamma radiation and annealing on ultra‐oriented polyethylene

Abstract

AbstractFilaments of ultra‐oriented high density polyethylene were solid‐state extruded at an extrusion (draw) ratio of 26 and subsequently irradiated under vacuum by a cobalt‐60 source at doses of 10,15, 20, 40 and 60 megarads (MRad). Several identically prepared but unirradiated strands were also tested. One set of samples at each dose was immersed in a silicone oil bath for one half hour at 128°C and one set was given no post‐irradiation thermal treatment. Characterization of the resultant morphologies included differential scanning calorimetry (DSC), birefringence, thermomechanical analysis (TMA), and tensile testing. Results from DSC measurements indicate that initial radiation crosslinking only slightly disrupts the crystal lattice, but on subsequent melting and re crystallization, the chains are unable to recrystallize effectively in their former habit. In all cases, melting point and crystallinity decrease with increasing radiation dose. Birefringence and TMA results indicate that orientation is not disrupted by irradiation. For unannealed samples, Young's modulus increases slightly then levels off while tensile strength and elongation at break increase initially, then drop, For annealed irradiated samples, Young's modulus rises at first, then levels off at higher doses. Tensile strength and elongation at break increase significantly with increasing radiation treatment, then essentially reach constant values at highest doses.