2D gradient and correlation FTIR analyses for optimizing thermal curing process of commercial-grade polyurethane coatings for automotive interior parts

Soft-feel coatings for automotive interior parts are a crucial factor in consumer purchase preferences owing to the growing awareness of human sensibility ergonomics. Herein, the thermal curing of commercial-grade polyurethane (PU) coatings was optimized using advanced spectroscopic tools. Conventional FTIR spectra were collected at various curing temperatures and times, and analyzed using two-dimensional (2D) gradient maps and 2D correlation spectroscopy (2D COS); while the former demonstrates the spectral variation trend with curing time, the latter provides whole spectral sequences that inform the cure reaction mechanism. The thermal curing continued for 50 min at 60 and 70 °C, and was halted after 30 min above 80 °C. According to the 2D COS and kinetic model fitting, the cure reaction was initiated by solvent evaporation and followed nucleation and growth mechanisms. PUs cured at lower temperatures were ductile owing to incomplete reactions, whereas PUs cured above 80 °C exhibited brittle features. Consequently, the optimal curing process was determined to be at 80 °C for 30 min. The 2D FTIR analytic tools can be useful in the development of high-quality soft-feel coatings for automotive interior parts.