Bonding of highly oriented polypropylene sheets by epitaxial crystallization of polyethylene

The bonding of highly oriented polypropylene (PP) by means of a thin epitaxial polyethylene (PE) interlayer, was investigated. Epitaxy occurred in HDPE over a range of molecular weight, including ultra-high molecular weights. It was also observed for LDPE, although the epitaxy was less well-developed than for HDPE. Laminates of highly oriented PP thinly coated with PE and treated to induce cross-hatchng of PE showed much improved adhesion, compared with uncoated PP treated in a similar fashion. The PE epitaxy is believed to be responsible for this behaviour. The adhesive performance was also shown to be a function of the molecular weight and its distribution of PE, as well as of the annealing treatment of the PE coat.