Curing behaviors and functional performance of crosslinker-free epoxy coatings

Abstract

To determine the feasibility of crosslinker-free epoxy systems as an applied coating solution, this study investigated the cure-by-design behaviors and functional performance of anionically catalyzed crosslinker-free epoxy functional coatings. A fusion boned epoxy (FBE) powder platform was utilized, and formulation index (FI)-oriented optimizations were performed, with the FI extended to infinity (or ∞), which corresponds exclusively to 100% epoxy self-crosslinking from an applied chemistry standpoint. Depending on the catalyst type and loading, the cure kinetics and rheology of these homogeneous crosslinker-free systems varied significantly from those of heterogeneous crosslinker-containing coatings. In addition to thermal curing responses (including viscoelastic gelation and vitrification), the structural properties, particularly glass transition temperature (T_g), flexibility, cohesive toughness, impermeability, and adhesion, are closely correlated to the T_g-capability or -potential of their formulations, as well as the chemical structures, molecular weights (MWs), epoxy equivalent weights (EEWs), and functionality (f) of the underlying epoxy resins or monomers. Other interesting findings, such as the concurrence and sequences of epoxy-crosslinker copolymerization and epoxy-epoxy homo-polymerization by differential scanning calorimetry (DSC) exothermic profile analysis, are reported and explained.