The hydrophilic nature of water trees [in polyethene]

The water tree phenomenon is examined by investigating its hydrophilic nature. Experimental findings lead to a model which involves both the chemical composition and the physical structure of water trees. Carboxylate groups were found in all water trees considered. The concentration depended greatly on the type of polyethene; the carboxylate groups are thought to be end groups of the polymer. An interaction between water and carboxylate groups was assessed. This also was done for groups which absorb in the 1000-1200-cm¹ range; these groups are probably ionic sulfur-oxygen groups. It is shown that the hydrophilic nature of watertrees may be explained completely by the presence of chemically or physically bonded ionic groups. The oxidative stability of polyethene is reduced locally by water treeing. The results obtained support the idea of oxidation occurring during watertreeing if carboxylate groups and ionic sulfur-oxygen groups are regarded as possible oxidation products. Water trees can be selectively permeable to different entities; they seem to bear a close resemblance to ionomer membranes locally