Role of n-alkane-based additives in hot melt adhesives

A systematic study has been carried out to understand the morphological features developed for blends of wax/ethylene vinyl acetate (EVA) random copolymer. This system is commonly used in hot melt adhesives. It was determined that in all cases, wax enhanced the crystallization kinetics, an important consideration when used in hot melt adhesives to control the setting speed. A number of well characterized n-alkanes have been used to follow the crystallization behavior of wax/EVA blends. Using a mixed crystal study, the infrared analysis revealed the presence of co-crystallization for long (~30 carbons) n-alkanes. This is supported by the high spatial resolution Raman imaging studies. However, cocrystallization only occurs for specific longer chain alkanes. When shorter ones are employed the traditional picture emerges, i.e. the wax additive nucleates the crystallization process of EVA, forming a phase separate structure.