Environmental Ageing and Property Retention in Vat Photopolymerisation: Resin Storage, Photooxidation, Hydrothermal Conditioning and State-Resolved Qualification
Segurola, Juan
2026-08-27 · Informe · Versión 1.1
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Vat photopolymerisation converts a liquid formulation into a network whose measured properties continue to depend on time and environment after printing. The starting resin may age during storage; the green print may undergo additional reaction during washing and post-curing; the solid network may physically relax; water may reversibly plasticise the material or irreversibly promote hydrolysis, leaching and interfacial damage; and ultraviolet-visible exposure in oxygen can change chromophores, colour, surface chemistry and mechanics. These processes are frequently collapsed into broad claims such as stable, UV-resistant, non-yellowing or durable. The resulting data can be misleading when the initial material state, exposure boundary and recovery step are not declared. This review separates five states: stored resin, green print, post-cured baseline, environmentally aged specimen and recovered or reconditioned specimen. Direct VPP evidence shows that storage-aged resin can change realised geometry and mechanics even when bulk viscosity changes little; post- cure can improve stiffness while introducing shrinkage; dry physical ageing can increase modulus; water immersion can reduce stiffness without measurable surface hydrolysis; elevated-temperature hydrothermal exposure can produce severe cracking and mechanical loss; and wet-dry cycling can yield a different endpoint from continuous immersion. Weathering studies further show that photoinitiator chemistry, stabilisation, post- cure history and resin class control whether optical and mechanical degradation evolve together. The proposed framework requires an exact resin and process identity, a frozen initial condition, fully specified spectrum-dose-temperature-humidity history, state-resolved dimensional, optical, chemical and mechanical measurements, and an explicit recovery step before irreversible degradation is assigned. Reporting aids are proposed for property retention, dimensional retention and post-ageing recovery, but raw values and complete curves remain mandatory. Existing ISO methods cover weathering, water absorption, chemical immersion, tensile testing, dynamic mechanical analysis and colour measurement; none by itself establishes a transferable VPP service life. The central principle is: exposure time is not material age unless the starting state, mechanism and recovery path are known.