Evaluation of latex adhesives containing hydrophobic cores and poly(vinyl acetate) shells: potential to improve poly(vinyl acetate) performance

Various experimental poly(vinyl acetate) (PVAc) latices containing relatively rigid polystyrene (PS) domains were investigated in order to evaluate whether the presence of PS domains improves the performance, especially the creep resistance, of PVAc adhesives. The effects of a range of PS content, PS/PVAc morphologies and core-shell polymerisation approaches were examined by evaluating thin-film mechanical properties and adhesive performance. The results have shown that up to 50% PS (by mass) can be incorporated into a PVAc latex without compromising adhesive strength. Mechanical testing of films indicated the presence of PS maintains film performance at elevated temperature (60°C). Polymers formed using a chain transfer agent during the second stage styrene polymerisation had a concentric core-shell morphology and these performed better than either copolymers having an acorn morphology or a simple blend of PS and PVAc. Incorporation of PS domains into a commercial PVAc adhesive by second-stage polymerisation of styrene did not greatly diminish the performance of the conventional adhesive. While performance advantages acquired by adding PS into PVAc particles were demonstrated during creep testing at high humidity, the presence of PS did not impart any improved resistance to water or to heat, as determined by accelerated exposure water soak testing and shear block testing above 70°C.