Photo-Curing Kinetics of 3D-Printing Photo-Inks Based on Urethane-Acrylates.

In this study, photo-curing kinetics for urethane-acrylate-based photo-inks for 3D printing were evaluated using a photo-differential scanning calorimetry analysis. Initially, the photopolymerization kinetics of di- and monofunctional monomers were separately studied at different temperatures (5-85 °C). Later, the photo-curing kinetics and mechanical properties of photo-inks based on different monomer mixtures (40/60-20/80) were evaluated. The results showed that urethane-dimethacrylate (UrDMA) and urethane-acrylate (UrA) had no light absorption in the region of 280-700 nm, making them a proper crosslinker and a reactive diluent, respectively, for the formulation of 3D-printing photo-inks. The kinetics investigations showed a temperature dependency for the photo-curing of UrDMA, where a higher photopolymerization rate ( R p,max : from 5.25 × 10 -2 to 8.42 × 10 -2 1/s) and double-bound conversion ( DBC total : from 63.8% to 92.2%) were observed at elevated temperatures (5-85 °C), while the photo-curing of UrA was independent of the temperature (25-85 °C). Enhancing the UrA content from 60% to 80% in the UrDMA/UrA mixtures initially increased and later decreased the photopolymerization rate and conversion, where the mixtures of 30/70 and 25/75 presented the highest values. Meanwhile, increasing the UrA content led to lower glass transition temperatures ( T g ) and mechanical strength for the photo-cured samples, where the mixture of 30/70 presented the highest maximum elongation ( ε max : 73%).