Stereolithography Somos 7110 photosensitive resin: study of curing kinetic and thermal degradation

Different types of photopolymers, also called photosensitive resins, have been used in the stereolithography process to obtain specimens with specific size and application. The Somos 7110 resin evaluated in this study was characterized by infrared (IR) and nuclear magnetic resonance (NMR) spectroscopy, indicating the presence of epoxy and acrylic functional groups, as well as, aromatics and aliphatic ether groups. Infrared spectroscopy was also used as the technique to evaluate the curing process and identify the components of thermal degradation of liquid and cured resin. Thermogravimetric analysis was other complementary procedure used to quantify the components formed in the degradation process and determines the related physicochemical parameters. The kinetic studies indicated that this solvent-free polymerization was diffusion-controlled during the chemical crosslinking, due to the reaction order of the curing process, which was very close to unity. The cured resin had only one degradation stage with activation energy of 100-125 kJ mol−1 in the weight loss fraction of 0.20-0.85, in contrast to the second degradation stage observed for liquid resin above the 0.5-weight loss fraction. This second degradation stage gives Ea-values in the range 210-260 kJ mol−1. The higher weight loss temperature of the cured resin compared with the liquid resin and the single decomposition stage suggest different decomposition mechanisms and a stability of the cured resin at higher temperatures compared to the liquid resin.