Evolution of the chemical and morphological changes of HDPE when subjected to digestion in a strong acid medium

High-density polyethylene (HDPE) is the polymer most used for geomembranes, and one of the tests to determine its applicability is its long term resistance to oxidation. In this sense, this work focuses on the study of the chemical and morphological changes that PE films may experiment when subjected to digestion in nitric acid, simulating the severe ambient conditions of a landfill. The effect of digestion of HDPE, on its chemical and morphological structure, was evaluated. It was observed that the molecular weight of HDPE decreases, forming acid and nitro groups, as the time of digestion increases. Also, the oxidative degradation first produced a bimodal MW distribution, but as the time of strong acid treatment increases, a trimodal MW distribution appears, at lower molecular weights. Finally, as time of digestion continued, a bimodal MW distribution appears again, but at much lower molecular weights. The crystal size of the treated HDPE is directly related to the HDPE molecular weight, that is, as time of digestion increases, the molecular weight decreases and the crystal size decreases. In addition, the heterogeneity of molecular weights, such as bimodal and trimodal distributions, and the presence of chemical groups other than the normal -CH2- strings of pure PE produced defects in the unit cell parameters a and b. (C) 2011 Wiley Periodicals, Inc. J Appl Polym Sci 123: 3248-3254, 2012