Predicting 3D printing critical parameters from Basic photochemical principles in vat photopolymerization

Vat photopolymerization technologies have emerged rapidly in the field of additive manufacturing. In this technology, the Jacobs working curve is considered the cornerstone for defining printing parameters. Understanding the underlying mechanisms occurring during 3D printing becomes mandatory. In this work, attempt was made to highlight the factors governing the critical energy and the depth of penetration. By systematically varying coinitiator concentrations in the isopropylthioxanthone (ITX) /coinitiator system —and thus modifying photopolymerization efficiency— we investigate their influence on maximum conversion, polymerization rate, and critical energy (Ec). A central finding is the direct correlation between inhibition time, quantum yield of radicals, and critical energy, establishing a predictive framework for resin reactivity. The results indicate that inhibition time strongly dictates Ec, providing an improved understanding of polymerization initiation in oxygen-inhibited environments. Furthermore, while ITX achieves high efficiency when combined with coinitiators such as N-phenylglycine (NPG) or ethyldimethylaminobenzoate (EDB), it is shown that it can initiate the photopolymerization alone, although at lower extent. These findings offer valuable insights for optimizing resin formulations in vat photopolymerization 3D printing, where precise control over polymerization kinetics is essential for print fidelity, layer adhesion, and mechanical performance.