Comparison and investigation of H-bond assisted reusable PU adhesives with high shear strength

Hot-melt adhesive (HMA) is commonly used in industrial manufacturing due to its ease of use. However, the direct factors that affect shear strength have been unclear in recent years, making it difficult to prepare hot melt adhesives with high shear strength, which are mostly lower than 6 MPa. In this study, three types of polyurethane HMAs, differing in the position of H-bond motifs, ureidopyrimidinone (UPy), were synthesized and characterized, the most central factor for shear strength, Young's modulus, was firstly found out and proved. Side-chain UPy provides better flexibility and more chain entanglement. The lap shear strength of SPU was about 13.48 MPa, which was the highest shear strength of PU HMA, and remained 73.4 % even after 4 cycles. Compared to the other two samples, the side-chain motifs improved the possibility of forming hydrogen bonds with adherends and increased chain mobility. This led to a more efficient wetting process and strengthened Young's modulus directly, enhancing adhesive property incomparably. This work provides a satisfactory method for achieving high shear strength in HMA.