Mechanical aspects of water treeing

The initiation and growth of water trees in a clear polyester resin are correlated with the mechanical properties of the material. The mechanical properties of the resin were varied systematically by the addition of controlled amounts of a plasticizing polyester. The polymer was in contact with 0.1-M NaCl solution and a 50-Hz AC voltage was applied to each specimen. It was found that the initiation time for water trees decreased (and the growth rate increased) with the plasticizer content. A correlation has been made between the initiation time and the tensile strength, both of which decreased due to plasticization, based on the assumption that initiation occurs when the osmotic pressure in a cavity at the water needle tip exceeds the mechanical strength of the material