Memory effects in irradiated polyethylene

摘要

AbstractThe memory of irradiated polyethylene has been studied with emphasis on the magnitude of the restoration force exerted by the deformed polymer during the process of restoration to the nonstressed state and on the degree of completeness with which restoration occurs. The particular form of the memory effect studied has involved the deformation of the heated polymer followed by “locking‐in” of the memory via cooling. Subsequent heating restores the deformed specimen to the undeformed state. The memory effect has been studied under both nontransparency (NT) and transparency (T) deformation conditions. The effects of parameters such as the polymer properties (Tm, density, molecular weight), radiation dose, and deformation and restoration conditions on the degree of restoration and restoration force have been investigated. The results of this study may be summarized as follows. Restoration temperatures equal to or above the crystalline melting point (Tm) of the polymer are required in order to obtain complete restoration. The restoration temperature increases with increasing polymer crystalline melting point. The degree of restoration increases with increasing restoration temperature for NT deformed specimens. T deformed specimens do not begin to restore until the temperature approaches theTmof the polymer. The restoring force increases with decreasing deformation temperature. NT deformation results in larger restoring forces and faster restoration relative to T deformation. The restoring force increases with increasing radiation dose for both T and NT deformations, the effect being greater for NT deformation. Radiation dose, however, above a minimum value does not affect the degree of restoration. The restoring force increases with increasing polymer initial molecular weight for T deform