Surface modification of polymer films by graft copolymerization for adhesive-free adhesion

Abstract

The surfaces of low density polyethylene (LDPE), poly(carbonate) (PC), polytetrafluoroethylene (PTFE) and emeraldine (EM) base films of poly(aniline) are modified by graft copolymerization with N,N-dimethylacrylamide (DMAA), Na salt of styrenesulfonic acid (NaSS), 3-dimethyl(methacryloylethyl)ammonium propanesulfonate (DMAPS) and acrylic acid (AAc). Two surface graft copolymerized films are capable of exhibiting ‘adhesive-free’ adhesion or auto-adhesion when brought into contact in the presence of water and subsequently dried. The development of the lap shear adhesion strength depends upon the concentration of the surface graft, the contact adhesion (drying) time, the nature of the substrate, the microstructure of the graft copolymerized surfaces and the extent of molecular interaction (dispersive, electrostatic, etc.) at the lapped junction. Lap shear adhesion strengths in excess of 90 N cm −2 were readily achieved between films graft copolymerized with the amphoteric DMAPS, as well as between a DMAPS graft copolymerized EM film and an AAc graft copolymerized PTFE film. X-ray photoelectron spectroscopy (x.p.s.) analysis of the delaminated surfaces suggests that the failure mode involves the fracture of the graft chains at the substrate-graft interface.