Polymer diffusion and the evolution of adhesive bond strength

An attempt has been made to establish the role of diffusion across the polymer interface as a contributing factor to lap-shear bond strength. The assemblies studied were polypropylene/linear low-density polyethylene (PP/LLDPE); polystyrene/polyvinyl chloride (PS/PVC); polystyrene/polymethyl methacrylate (PS/PMMA); and polyvinyl chloride/polyvinylidene fluoride (PVC/PVDF). Initial bond strength measurements were followed by measurements on joints that had been annealed for up to 72 h at temperatures in the range of 60-160°C. Following induction times of tens of minutes where bond characteristics remained constant, substantial increments in bond strength were observed for PP/LLDPE and for PS/PVC but not for PS/PMMA or PVC/PVDF. Results point to a significant contribution to bond strength arising from diffusion when dispersion forces and favorable acid/base interactions act at the interface. The times required to establish the apparent diffusion effects far exceed normal bonding times and may account for the...