Degradation Analysis for Polyethylene of Raised Temperature Resistance After Long-term Hot Water Immersion and Hot Air Exposure Tests

Polyethylene of raised temperature resistance（PE-RT）which is non-crosslinked polyethylene for hot water application was used for an aging test for 3000 hours to 35000 hours under hot water immersion and hot air exposure to clarify the mechanism of long-term degradation. The tensile strengths were increased up to 3000 hours, and after that, they were reached to the almost constant value due to crystallization. On the other hand, the tensile elongations at break were slightly decreased as a testing time. The decrease of anti-oxidation ability under hot water immersion was more rapid than hot air exposure until 10000 hours. It was caused by the elution of antioxidation additives to hot water from FT-IR mapping analysis. The Raman mapping method was used to examine the distribution of crystallinity. It was found that the dispersion was greater than that of initial. T2 results obtained by the 1H-pulsed NMR method showed the amorphous component of 16000 h testing samples was bigger than that of initial. It was presumed that these results were related with the decrease of elongations at break. The initial oxidation was realized by the FT-IR analysis at 35000 hours. The ester C = O group signal mainly emerged at the surface of the samples after hot air exposure. The carboxylic acid C = O signal was also seen after hot water immersion. The ESR results revealed that the auto-oxidation reaction was activated under hot air exposure although it was inactive under hot water immersion because of its poor dissolved oxygen.