Addressing sustainability in photopolymerization: comparative LCA study of six synthetic routes of 1-hydroxycyclohexyl phenyl ketone as photoinitiator for copolymer applications

Photoinitiators have long been investigated as alternatives to thermal initiators with the aim of reducing polymerisation temperatures and, consequently, heat consumption. The synthesis of poly(vinyl acetate-co-crotonic acid) represents a suitable case for exploring photoinitiation strategies. In this context, the performance of various commercial photoinitiators has been experimentally tested, and hydroxycyclohexyl phenyl ketone (HCPK) demonstrated its effectiveness with respect to other alternatives. Then, life cycle assessment (LCA) was applied to compare six alternative synthetic routes to produce HCPK, considering three different data sources: laboratory scale, advanced process calculation, and software-assisted modelling, with the latter two representative of the industrial scale. Among the six synthetic routes analysed, the pathway involving an initial α-chlorination of cyclohexyl phenyl ketone followed by a nucleophilic substitution emerges as the environmentally preferable option. As expected, a general decreasing trend in environmental impacts is observed when moving from laboratory-scale modelling to software-assisted industrial-scale modelling, likely due to process optimization at larger scales. Overall, the study demonstrates that the synthesis of poly(vinyl acetate-co-crotonic acid) is feasible through photopolymerization and that HCPK behaves better than thermal initiators like benzoyl peroxide under the same conditions. While laboratory-scale LCA constitutes a valuable preliminary screening tool, more accurate early-stage LCA modellling is likely achieved through industrial-scale simulation.