Oxidative Resistance of Bimodal Hdpe and Silane Crosslinked Bimodal HDPE Under Exposure to Hot Chlorinated Water

Abstract

Eksperimen telah dijalankan untuk mengenalpasti elemen perantaraan yang reaktif dalam degradasi bimodal HDPE (B–HDPE) dan bimodal HDPE bersambung–silang (SXB–HDPE) dalam air berklorin. Kajian menunjukkan pengklorinan merupakan faktor penyumbang terhadap degradasi HDPE. Dalam kes ini, media perantaraan kemungkinan ialah Cl₂ atau NaOCl. Maklumat menunjukkan bagi kebanyakan polimer, ‘klorin bebas’ yang terhasil daripada tindak balas kimia NaOCl merupakan media perantaraan dalam tindak balas degradasi. Oleh itu, ujikaji DSC dan spektroskopi FTIR dijalankan pada keadaan yang berbagai untuk mengenalpasti degradasi HDPE. Kesan ‘larutan berklorin panas’ terhadap sifat mekanikal polimer turut juga dikaji, antaranya ialah ujian ketegasan dan ujian hentaman impak terhadap sampel yang mengalami proses pengoksidaan klorin dan tanpa pengoksidaan klorin. Kajian terhadap permukaan sampel degradasi dijalankan dengan SEM. Kadar degradasi didapati berkadaran dengan suhu dan masa. Kadar degradasi paling nyata pada suhu >50°C dan masa >500 jam. DSC menunjukkan terdapat sedikit peningkatan terhadap tahap pengkristalan, suhu peleburan kristal dan suhu peleburan puncak bagi sampel yang mengalami kesan pengklorinan yang kritikal. Ujian spektroskopi FTIR menunjukkan kemunculan kumpulan berfungsi karbon pada sampel yang mengalami degradasi. Spektroskopi FTIR menunjukkan transformasi kumpulan hidroksi mengurangkan ikatan hidrogen dalam sampel degradasi. Data ini menunjukkan Cl₂ ialah medium perantaraan dalam degradasi pengoksidaan permukaan. Kata kunci: Bersambung silane; air berklorin; bermodal HDPE; ujikaji pengklorinan; pengoksidaan degradasi 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. Key words: Silane crosslinked; chlorinated water; bimodal HDPE; Chlorination; Oxidative degradation