Dicumyl peroxide-initiated crosslinking reaction of low density polyethylene

Abstract

Low density polyethylene (LDPE) was crosslinked with dicumyl peroxide (DCP) by the gas (nitrogen) curing method. In order to prevent the formation of microvoids, crosslinking reactions were carried out under 50 psi pressure. The reaction kinetics of the crosslinking process was evaluated by dynamic differential scanning calorimetry (DSC) method (measuring exothermic heat of reaction and the soluble fraction in the crosslinked polymer. Thus one can calculate the expected sol fraction of a specific crosslinking process if the reaction temperature, time, DCP concentration, number average molecular weight (Mn) and polydispersity index of LDPE are known. The degree of crosslinking, density, crystallinity and methanical properties of the crosslinked polymers were also studied. The degree of crystallinity and density of the crosslinked polymers decreased with increasing DCP concentration. The elongation at break and tensile strength were found to be influenced by the combined effect of crosslink concentration and crystallinity change. The elongation at break reached maximum at 1.0 PHR DCP concentration and decreased as the crosslinked polymer became brittle at higher crosslink concentration. The melting point depression was also noted as the degree of crosslinking increased and an empirical equation was derived correlating Tm and the concentration of the crosslinking initiator.