DIFFERENT APPROACH TO THE MECHANISM OF ADHESION OF SURFACE TREATED WITH TRICHLOROISOCYANURIC ACID SOLUTION RUBBER AND POLYURETHANE ADHESIVE JOINTS

Although the effects produced by the surface treatment of rubber with organic solvent solutions of trichloroisocyanuric acid (TCI) leading to improved adhesion to polyurethane (PU) adhesive have been established, the mechanism of adhesion involved is still unclear. In this study, the reaction of TCI species on the rubber surface with the polyurethane adhesive leading to the formation of chemical bonds was proposed as the relevant mechanism of adhesion. As a model, TCI was added to polyurethane adhesive (PU + TCI), and a polyurethane film was immersed in TCI solution (PU − TCI), their surface, structural, and viscoelastic properties were monitored for different times. The formation of chemical bonds between the polyurethane chains and TCI species derived from the solid TCI crystals on the rubber surface during bonding formation, and the crosslinking/hardening of the polyurethane surface were evidenced. The reaction with TCI species increased the surface energy on the polyurethane, mainly the polar component, similar surface energies were obtained in both PU + TCI and PU − TCI after 7 days. The enhanced surface energies on the PU that reacted with TCI were ascribed to the creation of new C–Cl and C=O species, their percentages were higher on PU + TCI than on PU − TCI surface. On the other hand, new N–H stretching and carbonyl species were produced; this indicated that TCI species interacted with the hard segments. Furthermore, the crystallization peaks in PU + TCI and PU − TCI at higher temperatures and lower enthalpies than in the PU indicated the disruption of the interactions between the soft segments. Therefore, the structural changes in the PU caused by reaction with TCI species affected their degree of phase separation and viscoelastic properties. The addition of solid TCI to the PU caused a noticeable degradation and hardening, the extent of degradation was more marked by increasing the time, this led to lower mechanical properties.