Syringic-Based Copolyesters for Oxygen-Rich Low-Temperature Hot-Melt Adhesives: Synthesis, Adhesion Properties, and Enzymatic Depolymerization

Biobased polyesters are emerging as sustainable alternatives for hot-melt adhesives (HMAs) owing to their tunable adhesion properties, facile processing, and versatile end-of-life options. Here, we report on the design of low-temperature (100 °C) HMAs, derived from oxygen-rich lignin-based copolyesters synthesized via copolymerization of a syringic acid-derived aromatic monomer with biobased aliphatic monomers, adipic acid, and 1,4-butanediol. Copolyesters containing more than 60 mol % syringic units exhibited high adhesion to paper and various metal substrates, achieving a peak strength of ∼5.4 MPa on aluminum. After use, the adhesive can be easily removed with some acetone, enabling convenient debonding and surface cleaning. Enzymatic depolymerization using Humicola insolens cutinase (HiCut) at 70 °C showed a decreasing depolymerization rate as the aromatic syringic content increased. This observation was further rationalized through molecular docking simulations of representative aliphatic and aromatic chain segments. These findings demonstrate a viable approach for developing HMAs from oxygen-rich syringic acid that achieve a balance between performance and biodegradability.