An analysis of the role of wax in hot melt adhesives

In order to model the peel strength of hot melt adhesives, a systematic study has been carried out to elucidate the morphological features developed for blends of wax and ethylene vinyl acetate (EVA) random copolymer. The presence of wax enables the overall blend to crystallize rapidly. However, matching the specific molecular weight of the wax to an appropriate crystallizable methylene segment's length in the EVA, a random copolymer, the overall degree of crystallinity can be increased beyond the expected sum from the two individual components. In this study we found the combination of EVA that contains 28 wt% vinyl acetate groups matching particularly well with model alkanes of 32–36 carbons which can cocrystallize. The overall degree of crystallinity of the blend is higher than the value found for the individual components. This provides the structural and thermal stability needed in various hot melt applications. In addition, specific waxes possessing different structural features have been studied to demonstrate the performance gained for only those samples which match the most probable crystallizable polymethylene segments in EVA.