SURFACE MODIFICATION OF LOW-DENSITY POLYETHYLENE FILMS BY UV-INDUCED GRAFT-COPOLYMERIZATION AND ITS RELEVANCE TO PHOTOLAMINATION

Surface modification of ozone-pretreated low-density polyethylene (LDP E) films were carried out via a novel technique of UV-induced graft co polymerization with acrylamide (AAm), Na salt of styrenesulfonic acid (NaSS), 3-dimethyl(methacryloylethyl)ammonium propanesulfonate (DMAPS) , acrylic acid (AAc), N,N-dimethylacrylamide (DMAA), and 2-(dimethylam ino)ethyl methacrylate (DMAEMA) under atmospheric conditions and in th e complete absence of an added initiator or oxygen scavenger. Photogra fting with concurrent photolamination in assemblies containing a monom er solution sandwiched between two LDPE films was demonstrated. The ch emical composition and microstructure of the graft copolymerized surfa ces were studied by angle-resolved X-ray photoelectron spectroscopy. F or LDPE films with high graft concentrations, such as those graft copo lymerized with AAm, DMAA, and DMAEMA, surface chain rearrangement to f orm a stratified surface microstructure with a higher substrate to gra ft chain ratio at the outermost surface than in the subsurface layer w as observed. The photolamination strengths depend on UV illumination t ime, monomer concentration, and the chemical nature of the monomer bei ng graft copolymerized. Lap shear photolamination strength of about 90 N/cm(2) could be readily achieved in the LDPE/DMAPS(aq)/LDPE assembly after UV illumination. The failure mode of the photolaminated surface s was either cohesive or adhesional in nature, depending on the type o f monomer used in the photolamination assembly.