EFFECTS OF WATER ON THE FRACTURE OF POLYSTYRENE

Abstract

In hot-pressed polystyrene strips, effects of water on the fracture of polystyrene have been studied in terms of the transparency, the mechanical property and the fracture surface morphology.Various kinds of defects may be observed when the sample is soaked in water. Form, size and amount of the defects vary with the conditions of the soaking, e. g., soaking temperature and time.The size of defects becomes smaller as the soaking temperature becomes higher and the size of defect becomes larger as the soaking time becomes longer.Three kinds of defects different in shape appear by the soaking and these defects give rise to complicated changes in the transparency, the mechanical properties and the development of the fracture. The first defects are small spherical holes about 0.1_??_0.51μ in diameter. The amount of these defects have the maximum value at 94°C. These defects lower the transparency of the sample but are not related to the mechanical properties. The second defects are cracks about 1_??_20μ in length. A maximum amount of these defects is produced at 80°C. These defects are little related to the transparency since they undergo apparent restoration for the prolonged soaking. In such a case, however, mechanical properties go down. The third defects occur with the growth of the second defects.These defects are cracks about 25_??_50μ in length and the maximum amount of these defects appears at about 70°C.Both of the transparency and the mechanical properties go down with the occurrence of these defects.Because the appearance and the growth of these three kind defects follow their own timetables, the transparency and the mechanical properties of a sample change complicatedly with time.