The role of intramolecular crosslinking in the radiolysis of bulk crystallized high density polyethylene

Abstract

Intramolecular crosslinks have been suggested to occur in bulk crystallized, irradiated, high density polyethylene (HDPE) and to account for the low rates of gel formation, especially those of previously annealed samples when compared with that manifested by the same resin when previously quenched from the melt. Such crosslinks do not contribute to the development of gel and contribute to only a limited extent to the elastic properties above the crystalline melting point when compared with intermolecular crosslinks, but, if the mesh size of the intra- and inter-molecular networks are comparable, are fully reflected in the rupture elongation. The rupture elongations of a wide range of HDPE resins, for a given sol fraction or elastic modulus, are found to be at least as high as and often higher than those of low (LDPE) or linear low (LLDPE) polyethylene resins, indicating that intramolecular crosslinking of this type does not occur to a significantly greater extent in these higher crystallinity resins. Other factors more likely to account for the reduced rates of inter alia gel formation in some HDPE resins are discussed.