Sustainable Copolyester Hot-Melt Adhesives: Tunable Design, Robust Bonding, and Closed-Loop Recyclability

The pervasive use of adhesives creates significant environmental sustainability challenges including the depletion of resources and the generation of adhesive-derived microplastics. In response, hot-melt adhesives (HMAs) for PVC or PC substrates were developed by synthesizing a series of poly(trimethylene succinate-co-terephthalate) (PTST) copolyesters. The balance between the crystallinity, mechanical strength, and degradability of the PTST copolyester was achieved by modulating the ratio of terephthalic acid (TPA) and succinic acid (SA). And introducing SA induced a brittle-to-tough transition in fracture behavior. The PTST HMAs exhibit bonding strength comparable to that of traditional adhesives on PVC or PC substrates, consistently enabling substrate fracture. Contact angle analysis, rotational rheology, and molecular dynamics (MD) simulations were utilized to elucidate the adhesion mechanism. Both physical and chemical recyclings were achieved at low temperatures. For physical recycling, the rebonding strengths are comparable to the initial adhesion. Chemical recycling was achieved by alkaline hydrolysis using the KOH-EtOH system, which enabled the recovery of TPA and SA monomers, achieving closed-loop recyclability of the substrate materials bonded by the HMAs.