THE INFLUENCE OF CRYSTALLINE MORPHOLOGY ON THE GROWTH OF WATER TREES IN PE

A small amount of phenolphthalein, acting as a nucleating agent, was a dded to low density polyethylene (LDPE) to modify the size and number of spherulites. The crystalline morphology was observed and analyzed w ith the aid of a chemical etching method. It was found that the growth of water trees is faster in LDPE samples in which spherulites are lar ger and the number of the spherulites is lower. In contrast, water tre es grow more slowly in other LDPE samples in which spherulites are sma ller in size and greater in number. On the other hand, three different kinds of additives, weak electrolyte and hydrophilic or hydrophobic s ubstances, were added to the LDPE materials to investigate the influen ce of typical spherulite boundary regions on the growth of water trees . It was verified experimentally that during the process of crystalliz ation, these three different additives are rejected and finally settle d near the spherulite boundaries. Therefore, three kinds of boundary r egions with different characteristics are formed. It has been conclude d that hydrophillic boundary regions can strongly inhibit the gTowth o f water trees, while the other two boundary regions (weak electrolyte, hydrophobic) have little influence on the water tree growth.