Evidence for Material Circularity in Photopolymer Additive Manufacturing: Material-Loop Closure, Recovery Mass Balance, Recovered-Feedstock Identity and Property Retention

Claims of circular photopolymer additive manufacturing often compress several different operations into one word. Network cleavage or dissolution demonstrates processability of an article, not recovery of a defined material fraction. Isolation of a liquid or oligomeric fraction demonstrates recovery, not its identity or suitability as feedstock. Fabrication of a second object demonstrates reprinting, not equivalence of composition, yield or performance. Similar properties after one cycle do not establish repeatability or an environmentally preferable system. Primary studies have demonstrated materially different loop architectures, including recovery of functional oligomers followed by replenishment of a complementary reactant, and depolymerisation of photocured lipoate networks to chemically characterised reprintable resin across repeated cycles. These studies also expose why evidence must be route-neutral: fresh inputs, recovered species, purification losses, additives and changes in print behaviour differ between chemistries. ER-198 proposes a qualification architecture based on a declared loop boundary, targeted-material mass balance, recovered-feedstock identity, transparent make-up accounting, reprinting as an observed process step and state-matched property retention. It excludes life-cycle assessment and does not treat recyclability as proof of sustainability.