Low-Temperature-Curing Sustainable Waterborne Adhesives with Phase Change Properties for Leather Applications and Its Life-Cycle Assessment

Developing waterborne adhesives capable of curing at low temperatures remains a significant challenge, especially for heat-sensitive substrates, such as leather. In this work, we report a novel and sustainable adhesive system based on aza-Michael and amine-epoxide chemistries. Acrylate-based emulsion (GPS) was synthesized using poly(ethylene glycol methyl ether) methacrylate (PEGMA), glycidyl methacrylate (GMA), and stearyl methacrylate (SM), yielding particles of 90 nm. This emulsion was reacted with gelatin to produce nanocomposites (GPS-GEL100 and GPS-GEL200) that served as the adhesives, curing effectively at 50 °C. The resulting adhesives exhibited peel (0.54–0.64 N/mm) and lap shear (172–284 KPa) strengths comparable to conventional and commercial synthetic rubber adhesives used in the footwear industry. Replacing gelatin with leather waste further enhanced the peel strength and lap shear strength to 0.66 N/mm and 586 KPa, respectively. Glycerol and guar gum, incorporated as a plasticizer and a viscosity modifier, respectively, had minimal positive impact on peel and lap shear strengths. Thermal analyses revealed stability between a wide range of temperatures from −34 to 220 °C and phase change material (PCM) behavior, enabling both adhesive and thermal energy storage functionalities. Chemical, structural, thermal, and morphological analyses were performed using FTIR, DLS, FESEM, TGA, DSC, and TEM. Life-cycle assessment (LCA) demonstrated a favorable sustainability profile compared with commercial counterparts. This water-based adhesive system offers strong potential for sustainable leather applications requiring low-temperature curing and thermoregulating performance.