Surface graft copolymerization of low density polyethylene films and its relevance to auto-adhesion

Abstract

The surfaces of low density polyethylene (LDPE) films were modified first by ozone pretreatment, followed by thermally-induced graft copolymerization with the amphoteric monomer, 3-dimethyl(methacryloylethyl)ammonium propanesulfonate (DMAPS). The DMAPS graft copolymerized LDPE films were capable of exhibiting adhesive-free adhesion when brought into contact in the presence of water and subsequently dried. Lap shear adhesion strengths in excess of 100 N/cm 2 were achieved for lamination carried out at elevated temperature (60°C). It was also demonstrated that when two ozone-pretreated LDPE films were brought into contact in the presence of a small quantity of the aqueous DMAPS solution at an elevated temperature (70°C and above), surface graft copolymerization with concurrent lamination were achieved under atmospheric conditions and in the complete absence of an added polymerization initiator or oxygen scavenger. The adhesion strengths in both cases were governed by the concentration-dependent chain diffusion and entanglement, as well as by the electrostatic interaction, at the lapped interface. The graft copolymerized surfaces in both cases were characterized by X-ray photoelectron spectroscopy (XPS).