Component interactions and properties of crosslinked vinyl systems

Abstract

Compositions based on PVC, containing DIDP or TOTM plasticizers, and in several cases also containing chlorinated polyethylene (CPE) as property modifier, have been crosslinked by irradiation, using di- and tri-functional acrylic crosslinking agents. Crosslinking effectiveness has been analyzed by solvent swelling data, and the effects of irradiation up to dosages of about 10 Mrad on the mechanical properties of the systems have been recorded. The interaction potential of components used in these systems has been determined by recently-developed methods of inverse gas chromatography (IGC). These classify PVC and CPE as electron acceptors, and the plasticizers as donors. Expectedly, increased moduli and decreased elongational properties follow exposure to gamma-rays. The plasticizers reduce the effectiveness of crosslinking, the magnitude of the reduction being related to the degree of acid/base interaction between PVC and plasticizing fluids. When present, CPE competes with PVC for plasticizer so that for given quantities of DIDP or TOTM, the fraction available to solubilize the host polymer is reduced. In compounds with CPE, therefore, the crosslinking effectiveness of irradiation is raised, consistent with the acid/base balance of interactions, as given by the IGC results. Twin yield points have been observed in the stress-strain curves of compounds containing CPE. It is postulated that distinct, interpenetrating crosslink networks are formed when these polymers are subjected to gamma irradiation.