Dynamic cross-linked polyurethane hot-melt adhesive with high biomass content and high adhesive strength simultaneously

Polyurethane hot-melt adhesives (PU-HMAs) have been widely used due to their outstanding advantages, however, the high dependence on non-renewable petrochemical resources has limited their green and sustainable development. It is still a challenge to achieve high adhesive strength and high biomass content of PU-HMAs simultaneously. Herein, a bio-based dynamically cross-linked polyurethane hot-melt adhesive (DPU) was constructed by the bio-based vanillin oxime (VO) and soybean oil polyol (SBOH), along with polytetrahydrofuran (PTMG) and isophorone diisocyanate (IPDI). The highest lap shear strength of the DPU adhesive reached up to 6.55 ± 0.88 MPa only after 30 min curing, while the biomass content reached 25 wt% of the total mass, which is significantly higher than that of previous reports. Especially, the oxime group of VO reacts with isocyanates to form the reversible oxime-carbamate covalent bonds, which endows the adhesive with excellent self-healing and repeatable adhesion properties. The lap shear strength remained at 5.56 ± 0.89 MPa after 7 complete breaking-repairing cycles, which exceeded 80 % of the initial lap shear strength. Moreover, the DPU adhesive also displayed excellent resistance to low temperatures and solvents, and better adaptability on different substrate surfaces than commercial PU-HMA Lubrizol-5173 and Loctite-3542. Therefore, this work provided a new route for developing high-performance and self-healing bio-based PU-HMAs.