Photopolymerization kinetics of an epoxy based resin for stereolithography

Abstract

Curing reactions of photoactivated epoxy resins are assuming an increasing relevance in many industrial processes, such as coatings, printing, adhesives. Besides these processes, stereolithography makes use of photoactivated resins in a laser induced polymerization for 3D building. The kinetic behaviour of photocuring is a key point for a full comprehension of the cure conditions occurring in the small zone irradiated by the laser beam. Furthermore, the kinetic analysis is very important in order to determine the cure time needed for part building in a stereolithographic equipment. The mechanisms involved in a cationic photopolymerization are complex when compared with radical photopolymerization. In this paper the photoinitiated polymerization of a commercially available epoxy based resin for stereolitography has been studied by means of differential scanning calorimetry (DSC). The polymerization rate and the amount of unreacted monomer are determined directly from the conversion vs. time curves during DSC isothermal scans. Kinetic characterization of epoxy photopolymerization has been carried out as a function of the temperature and experimental results have been compared with an original mathematical model.