Oxidative resistance of Bimodal HDPE and silane crosslinked bimodal HDPE under exposure to hot chlorinated water

Abstract

Experiments were performed in an attempt to identify the reactive intermediate(s) involved in the degradation of bimodal HDPE (B-HDPE) and silane crosslinked bimodal HDPE (SXB-HDPE) in chlorinated water. These studies, demonstrated that chlorination is one reaction that ultimately contributes to HDPE degradation. In this case, the intermediates involved could either be Cl2 or NaOCl. Available information also indicates that, for many polymers, free chlorine, chemically generated from NaOCl, could likewise be involved as an intermediate in a degradation reaction. Thus, tests were undertaken to specifically address this latter issue with respect to HDPE degradation. The degradation of HDPE was monitored under a variety of conditions by DSC and FT-IR spectroscopy. Furthermore, the effect of hot chlorinated solution on mechanical properties was investigated by performing drop impact and tensile tests on unexposed and exposed specimens. Surface inspection was being carried out using SEM. The rate of degradation was found to be temperature and time dependent, and degradation was most pronounced at temperature >50°C and the time duration >500 hours. DSC showed that a small increase in crystallinity, melting point and melting peak broadening of the samples subjected to more severe chlorine oxidative treatment. The FTIR experiments showed formation of carbonyl groups. Moreover. FTIR measurements suggested that transformation of the hydroxyl groups leads to a weakening of the overall hydrogen bonding strength in the degraded samples. The data strongly pointed to Cl2 as the key intermediate in the surface oxidative degradation.