Surface modification of low-density polyethylene films by UV-induced graft copolymerization and its relevance to photolamination

Abstract

Surface modification of ozone-pretreated low-density polyethylene (LDPE) films were carried out via a novel technique of UV-induced graft copolymerization with acrylamide (AAm), Na salt of styrenesulfonic acid (NaSS), 3-dimethyl(methacryloylethyl)ammonium propanesulfonate (DMAPS), acrylic acid (AAc), N,N-dimethylacrylamide (DMAA), and 2-(dimethylamino)ethyl methacrylate (DMAEMA) under atmospheric conditions and in the complete absence of an added initiator or oxygen scavenger. Photografting with concurrent photolamination in assemblies containing a monomer solution sandwiched between two LDPE films was demonstrated. The chemical composition and microstructure of the graft copolymerized surfaces were studied by angle-resolved X-ray photoelectron spectroscopy. For LDPE films with high graft concentrations, such as those graft copolymerized with AAm, DMAA, and DMAEMA, surface chain rearrangement to form a stratified surface microstructure with a higher substrate to graft chain ratio at the outermost surface than in the subsurface layer was observed. The photolamination strengths depend on UV illumination time, monomer concentration, and the chemical nature of the monomer being graft copolymerized. Lap shear photolamination strength of about 90 N/cm2 could be readily achieved in the LDPE/DMAPS(aq)/LDPE assembly after UV illumination. The failure mode of the photolaminated surfaces was either cohesive or adhesional in nature, depending on the type of monomer used in the photolamination assembly.