Chemically Cross-Linked Heat-Shrinkable Polyethylene Tubes

摘要

The memory effect of heat-shrinkable tubes made of low density polyethylene obtained by irradiation with accelerated electrons is presented. The dependence of the cross-linked polyethylene contraction force on time, temperature, degree of cross-linking, etc., is emphasized. Some mechanical, electrical and chemical properties of the irradiated polyethylene are evident. Within the temperature range where the polymers have a thermoelastic behavior, their imprinted deformations lead to macromolecular orientations. These orientations stay after cooling, hence strong inner tension occurs. Through heat, the polymer tends to relax which cancels almost entirely the previous imprinted deformations. This feature is known as plastic materials' memory. The memory phenomenon has been noticed with a large number of polymers such as polyethylene; polypropylene; vinyl-poly-chloride; vinyliden-poly-fluoride; poly-tetra-fluor ethylene; polyurethene; ethylene copolymers with vinyl-acetate, with ethyl-acrylate and with butanyene; neoprene rubber; fluoride rubber; silicone rubber, etc. The experiment shows that the memory effect grows stronger with the increasing number of cross-linking in the polymer.