Silane-catechol synergy: Enhanced multi-substrate adhesion mechanisms of cationic polyurethane adhesives co-modified by KH550 and DBA

Cationic waterborne polyurethane (CWPU) adhesives are characterized by their environmental benefits and excellent adhesion, enabled by their inherent positive charges that grant a strong affinity for negatively charged substrates such as glass and metal oxides. However, poor water resistance and emulsification limit their development. Herein, we developed an organosilicon-modified high-adhesion CWPU using polyester polyol polybutylene adipate (PBA, Mn = 2000), isophorone diisocyanate (IPDI), chain extender DMAP (imparting cationic groups for water dispersibility), γ-aminopropyltriethoxy silane (KH550, 0-7 wt% as end-cappers), and neutralizing agents acetic acid and catechol-structured 3,4-dihydroxybenzoic acid (DBA). FT-IR and 1 H NMR confirmed successful synthesis. Organosilicon and alkyl groups improved water resistance and thermal stability, while cationic properties conferred antibacterial efficacy. The results of the research indicated that adding 3 wt% of KH550 yielded the optimal adhesion effect. Specifically, in the T- peel strength on non-polar PVC materials, reached 53.5 N/cm. Meanwhile, the lap shear strengths on rigid materials (steel, aluminum, wood, and copper) were 11.42 MPa, 6.91 MPa, 5.88 MPa, and 6.72 MPa, respectively.