Repair Coatings and Recoat Interfaces on Aged Photopolymers: Surface Reactivation, Chemical Compatibility and Structural Recovery

An aged printed photopolymer is not the same bonding substrate as a freshly printed surface. Conversion, oxidation, hydrolysis, contamination, extractive loss, absorbed water, residual stress, cracking and previous service can change surface reactivity and the load-bearing structure. Abrasion, cleaning, plasma or UV-ozone treatment, primer application and a compatible repair resin can improve a particular interface, but no treatment is universally beneficial. A high initial lap, shear or flexural result may reflect cohesive failure outside the interface, favourable specimen geometry or a repair material that has not itself been aged. This review defines a non-compensatory qualification architecture for repair coatings and recoat interfaces on aged photopolymers. It treats the aged substrate as a measured material state; separates cleaning, mechanical preparation, chemical reactivation and coupling; requires repair-material compatibility and cure to be evaluated independently of apparent bond strength; and distinguishes local interfacial recovery from recovery of part-level stiffness, strength, toughness, dimensional function and failure mode. Direct evidence from aged and repaired 3D-printed methacrylate and permanent dental resins is combined with bounded adjacent evidence for polymer-surface activation. The repaired assembly must be re-aged and retested in the intended environment. No universal abrasion, plasma, primer, recoat-window, bond-strength, cure or service-life value is established.