Solubility of Irgacure ® 2959 photoinitiator in supercritical carbon dioxide: Experimental determination and correlation

Abstract

CIBA photoinitiator Irgacure ® 2959 is a highly efficient radical photoinitiator for UV curing systems. Furthermore, and due to its proven low cellular toxicity, this photoinitiator can also be employed in the photopolymerization of polymers and copolymers intended for biomedical and tissue engineering applications, not only in conventional pharmaceutically accepted liquid solvents, but also in supercritical CO 2 (scCO 2). In this work we report the experimental measurement and correlation of the solubility of Irgacure ® 2959 in scCO 2. Results were obtained using a static analytical method, at 308.2, 318.2 and 328.2 K, and in a pressure range from 10.0 up to 26.0 MPa. Experimental data were correlated with three density-based models (Chrastil, Bartle and Méndez-Santiago–Teja models) and with an equation-of-state (EOS) model: the Peng–Robinson cubic equation of state (PR-EOS) together with the conventional van der Waals mixing and combining rules. Several different sets of solid properties, estimated by different methods available in literature, were used in EOS correlations. The importance of the estimation methods used for the determination of solid properties (namely sublimation pressure) was discussed in terms of correlation results quality. To the best of our knowledge, these are the first experimental scCO 2 solubility results for this class of initiators and the obtained solubility results indicate the feasibility of using this photoinitiator in free radical polymerization reactions carried out in scCO 2 like, for example, dispersion and precipitation polymerizations, or in the development of interpenetrating polymer networks (IPN's).