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How to Test Plastic Properties
\Water Absorption data may be obtained by immersion of 24 hr or longer in water at 73.4 °F. Upon removal, specimens are dried and weighed immediately. The increase in weight is reported as percent age gained.
Various plastics absorb varying amounts of water, and the presence of absorbed water may affect plastics in different ways. Electrical properties change most noticeably with water absorption, and this is one of the reasons that polyethylene, because it absorbs almost no water, is highly favored as a dielectric. Plastics which absorb relatively larger amounts of water tend to change dimension in the process. When dimensional stability is required in products made of such plastics, grades with less tendency to absorb water are chosen. The water absorption rate of acetal type plastics is so low as to have a negligible effect on properties. ASTM D-570.