Accelerated Ageing and Life-Claim Validity for Printed Photopolymers: Acceleration Factors in a Material Whose State Is Still Evolving

Accelerated ageing of a printed photopolymer contains a confound that is easy to miss: the elevated temperature, radiation or humidity intended to accelerate degradation can also continue cure, relax residual state, change free volume or alter transport. A specimen can therefore become stiffer or stronger during an ageing exposure even while another degradation process is occurring. ER-170 does not review the degradation mechanisms themselves; those remain in ER-072 and neighbouring reviews. It asks the narrower qualification question: when does an accelerated exposure preserve enough mechanism and material state that an acceleration factor or service-life claim is defensible? The controlled VPP ageing corpus shows that post-cure history, water state, geometry, temperature and recovery protocol can move the measured endpoint independently of degradation. It also establishes that one laboratory hour cannot be converted into service time merely because a property changes faster at elevated severity. A valid acceleration model requires a frozen initial state, mechanism equivalence across severities, an unchanged failure mode, an appropriate transport regime and uncertainty sufficient for the intended life claim.