Estudo de processos cinéticos de fotocura de resinas poliméricas através da espectroscopia fotoacústica

Abstract

In this work, photocuring processes of polymer resins are studied by photoacoustic spectroscopy (PAS). In a photocuring process, the photons absorbed by the photoinitiator, present in the resin composition, may trigger a thermal de-excitation process, which generates heat sources in the material, or a process of chemical de-excitation, which generates chemical bonds in the material. In this second de-excitation process, can occur release of heat during curing reactions of the resin. In this way, these two de-excitation processes will contribute to the generation of the photoacoustic signal. The main goal of this work is a qualitative study of the kinetics of curing of these photocurable materials, where it is sought to monitor the competition of these two mechanisms of de-excitation involved in the process of absorption of the electromagnetic radiation. For this, three photocuring systems were studied: epoxy resins; urethane resins; and metacrylic resins. Before the monitoring, absorption spectra were obtained for each photocure system. The monitoring was performed at different modulation frequencies, for a fixed wavelength of the curing light. Also, by setting the modulation frequency, the wavelength of the curing light was varied in the monitoring. Finally, for the fixed modulation frequency and fixed wavelength of the curing light, the wavelength of the saturating light was varied, in the cases of the monitoring with the presence of the positive effect. The dependence of the amplitude and phase of the photoacoustic signal with the time of exposure to the curing light was quite varied in the photocuring systems studied, in relation to the modulation frequency changes. This temporal dependence of the photoacoustic signal with the time of exposure to the curing light was discussed qualitatively. However, the results obtained show the capacity and potential that the PAS technique has in monitoring kinetic processes such as the photocuring processes of the polymer resins.