Molecular-Level Insights into Temperature-Dependent Polyurethane Interactions with Nylon and Alumina at Interfaces.

Two-component polyurethane (PU) adhesives are widely used in transportation, construction, and packaging due to their tunable strength and cost-effectiveness. In automotive, aerospace, and industrial applications, these adhesives must maintain good performance across typical usage temperatures (-40 to 80 °C). However, many commercial PU adhesives lose adhesion at elevated temperatures. This study uses sum frequency generation (SFG) vibrational spectroscopy, supported by Fourier transform infrared spectroscopy (FTIR) and adhesion testing, to investigate molecular-level mechanisms of such loss of PU adhesion to alumina and nylon. At the PU/nylon interface, adhesion loss correlates with reduced SFG signals from nylon C═O groups, suggesting interfacial disordering. In contrast, the PU/alumina interface shows no spectral change, indicating that adhesion loss likely stems from weakened van der Waals interactions. These findings offer insight into temperature-induced adhesion failure at buried PU interfaces, providing knowledge for developing PU adhesives with improved performance.