Institute of Fundamental Technological Research

This paper studies the interrelationships between the molecular weight, rheology, crystallinity, and tackiness of three types of commercial thermoplastic hot melt adhesives. The hot melt adhesives employed here differ in their compositions and molecular weights, even though all are copolyesters primarily based on poly(butylene terephthalate). Differences in the composition were found to influence the adhesives’ crystallization and melting behavior. These structural variations can translate into different thermal responses and processing characteristics relevant for tailoring adhesive selection to application requirements. Furthermore, adhesives with higher molecular weight were observed to possess larger elasticity, leading to significantly enhanced tackiness properties, as evidenced by the higher values of tensile modulus, peak stress, and work of debonding. This elevated tackiness was linked to the increased fibrillation process observed in polymers with higher molecular weights. Additionally, all tested adhesives exhibited storage moduli below the Dahlquist threshold (G′ < 3.3 × 105 Pa), which supports their ability to achieve measurable tackiness during the initial bonding process. The results presented in this study underscore the diversity among hot melt adhesives and the critical properties that should be considered when selecting adhesives for specific applications.

Hot melt adhesives, copolyester, polybutylene terephthalate, tack properties, rheology, crystallinity