SPECIFIC INTERACTIONS, INITIAL AND EQUILIBRIUM BOND STRENGTH IN POLYMER POLYMER ASSEMBLIES/

This paper reports on bonding characteristics of assemblies using as s ubstrates poly(vinyl chloride) (PVC), acrylonitrile-butadiene-styrene (ABS) and polypropylene (PP), and as melt adhesives an ethylene-vinyl acetate (EVA) copolymer, a polyurethane (PUr), and low density polyeth ylene (LDPE). Peel strength measurements on freshly assembled joints w ere compared with results for samples aged under inert and humid condi tions. Significant time-dependent variations of bond strength were obs erved in all cases, but the direction of change varied among the assem blies. Those involving only dispersion-force materials displayed losse s of bond strength, attributable to the gradual accumulation of cohesi vely weak layers at the substrate/adhesive interface. In assemblies in volving materials able to interact by non-dispersion (acid/base) force s, as indicated by inverse gas chromatographic data, a variety of resp onses was obtained. These have been rationalized by the ability of the EVA and PUr adhesives to reorient when in contact with an appropriate polymer substrate. Reorientation, leading to bond strength increments , was associated with substrate/adhesive pairs (e.g., PVC/EVA and ABS/ PUr), in which significant acid/base interaction could take place.