Photocuring of di-acrylate in presence of oxygen

Abstract

A model is presented for photocuring of a hexanediol diacrylate (HDDA) film, where in the presence of oxygen liquid monomer cures into a solid polymer network. The model is based on an earlier version (Iedema et al., 2018) that has been validated in absence of oxygen. The oxygen from ambient air inhibits the polymerization in the top part of the film causing conversion gradients across the film, which is a problem in the manufacture of large scale prints. In the current work results of the curing of thin HDDA films (10 μm) exposed to ambient air with initiator Irgacure 819, bis(acylphosphine oxide) under irradiation intensity varying in a range of 1000–6000 W·m−2 are presented. The average conversion of vinyl groups in bulk of the films was registered by real-time Fourier Transformed Infrared (FTIR) in transmission mode, while simultaneously the conversion in the non-exposed bottom part was measured by real-time FTIR with attenuated transmission reflectance (ATR). The bulk data were used to estimate the kinetic and transport parameters of the model, which enables it to correctly describe the bulk and bottom cure as measured by FTIR. The model accounts for local swelling and shrinking of the created polymer due to the conversion gradient. By Raman spectroscopy the conversion gradient after the photocuring process was also directly measured, again confirming the considerable conversion difference between top and bottom of the film predicted by the model as caused by oxygen inhibition. Initially dissolved small amounts oxygen throughout the whole film turns out to be a negligable role.