Reactive polyurethane hot-melt adhesives with high biogenic carbon content

The use of water-based or solvent-based polyurethane adhesives is widely extended in the footwear industry. However, reactive polyurethane hot-melt adhesives (RPHMA) represent a good option to substitute both technologies as they are solvent-free. Their environmental footprint can be further improved with the use of renewable raw materials for their synthesis. A typical RPHMA formulation includes macroglycols and isocyanates as raw materials, both of which are based on petroleum derivatives. Against this background, this work focuses on the development of RPHMAs based on polyols from renewable sources, which considerably improves their content in biogenic carbon. The evaluation of the new adhesives properties was conducted using different experimental techniques such as FTIR, TGA, DSC, CLSM, XRD, plate-plate rheometry, R&B softening point, biogenic carbon content (ASTM D6866–22, method B) and T-peel strength of adhesive joints (EN 1392:2007), before and after aging. The partial substitution of one of the conventional petroleum-based polyols by a bio-based polyol leads to a change in the segmented structure of polyurethane and an increase in the polyurethane thermal resistance and crystallinity. Furthermore, the new adhesives based on reduced fossil content meet the standard quality requirements on adhesive properties for footwear, according to EN 15,307:2015.