Impact of oxygen inhibition on (meth)acrylate photopolymerization in tomographic volumetric printing

Abstract

Oxygen inhibition in (meth)acrylate photopolymerization gives rise to a gelation threshold by delaying polymerization until the accumulated light dose exceeds a critical value, thereby enabling 3D printing with tomographic volumetric additive manufacturing (TVAM). While this thresholding behavior is essential to TVAM, its underlying kinetics have not been thoroughly studied. In this work, we systematically examine how photoinitiator (PI) concentration and light intensity govern the time required to deplete oxygen in (meth)acrylate photoresins, and evaluate their impact on print quality. To investigate these effects, we derive theoretical results elucidating oxygen inhibition, which remain valid even at low PI concentrations typical in TVAM printing, and can be used to estimate the oxygen concentration in the photoresins. We compare these predictions with photo-rheology experiments and observe good agreement. The findings reveal that at low PI concentrations, decreasing PI concentration dramatically increases oxygen depletion times, thereby extending oxygen diffusion periods and leading to poor printing quality; a similar trend is observed with reduced light intensity. While higher PI concentrations and increased light intensity can improve print quality, they are constrained by penetration depth limits and illumination restrictions of LED-based projection sources. This study also highlights the challenges of printing larger parts in TVAM, where oxygen inhibition and limited light penetration narrow the usable PI concentration range. These insights help optimize TVAM parameters to improve print quality and expand the technology's capabilities.