Monitoring the curing process of polyurethane materials based on terahertz technology

Polyurethane materials possess excellent insulation, heat resistance, and durability, making them excellent adhesives for composite structural materials in high-temperature and high-pressure environments. The quality of adhesion at the interface is closely related to its curing state. Therefore, non-contact monitoring of the transition from the liquid to solid state prevents issues like weak bonding at the adhesive interface, significantly enhancing the adhesion quality and safety of composite structural materials. Such monitoring finds extensive applications in various fields, including aerospace, energy, and power, among others. In this study, the reflection-mode terahertz time-domain spectroscopy technique was employed to monitor the curing reaction process of polyurethane materials. Additionally, refractive index spectra of samples at different curing times were extracted, and the relationship between the refractive index and curing reaction time was established. Furthermore, a comparison was made with the material loss factor obtained through a rheometer to determine the correlation between the refractive index and the material loss factor. The experimental results indicate that during the curing process, the refractive index demonstrates a gradual decrease and stabilizes after 225 minutes of curing. The correlation coefficient between the refractive index and the material loss factor exceeds 0.9. As the curing reaction progresses, the refractive index accurately reflects the curing process of polyurethane materials. This study provides an effective means for monitoring the curing process of polyurethane materials.