Controlling photopolymerization reaction in layer-by-layer photopolymerization in 3D printing

Today, controlling the photopolymerization process during the 3D printing in vat photopolymerization is a key challenge. In this work, it is shown that using a relatively limited set of parameter, it is possible to estimate key factors involved in such process. On the basis of 16 formulations containing different concentrations of photoinitiator and UV filter, attempt was made to rationalize the photonic parameters used in the 3D printing process, that is, the depth of penetration Dp and the critical energy Ec. It is shown that the experimental Dp values can be correlated with calculated ones from Bouguer–Beer–Lambert law. Real-time Fourier-transform infrared spectroscopy (RT-FTIR) experiments were performed under similar conditions as in 3D printing. The conversion profiles were used to estimate the Ec values. The limits of this approach was discussed as a function of the UV filter concentration. Finally, the RT-FTIR curves are exploited to predict the in-depth conversion of the different 3D printed layers and compared to experimental results obtained by confocal Raman microscopy.