Photo-mechanical degradation of thermoplastic elastomers
Jim R White, Anil K Bhowmick
University of Newcastle upon Tyne, UK
UK

Keywords: photodegradation, TPEs, rubber


The photomechanical degradation of thermoplastic elastomers (TPEs) consisting of blends of a rubber and a polyolefin has been studied using laboratory UV exposures in the unstrained state and under tensile strains of fairly high magnitudes (25% and above). The experiments have shown that photomechanical degradation rather than ozone cracking dominates under these conditions. Tests have been conducted on experimental TPEs based on blends of natural rubber and polyethylene and containing various stabilizers; and on commercial TPEs based on synthetic rubbers and polypropylene, and designed for outdoor applications. Strained exposure to UV caused reduction of the strain to failure in subsequent tensile tests in all of the materials studied. The pattern of degradation behaviour was rather similar to that displayed by an elastomeric blend containing natural rubber and a butadiene rubber that does not display thermoplastic behaviour.

All of the stabilizers tested with the experimental TPEs produced considerable improvement in photo-resistance. The most effective one was IPPD, a stabilizer for rubber, even though the continuous phase in these blends is polyethylene. The effect was to slow down degradation; there was no apparent change in the nature of the micromechanism of the degradation process. Again this replicated observations made with the blend of natural rubber and butadiene rubber, which was tested in unmodified form and also in the form of compounds containing combinations of carbon black and stabilizer.