Micro-SORS-Based Protocol for the Noninvasive Depth-Resolved Study of Degraded ABS in Cultural Heritage

In the field of cultural heritage, there is an urgent need to enhance our understanding of the composition of plastic materials and their degradation processes, especially given their susceptibility to relatively rapid deterioration. Among these materials, acrylonitrile-butadiene-styrene (ABS), commonly found in museum collections, is particularly vulnerable to photoaging, primarily affecting the polybutadiene (PB) phase through oxidation and cross-linking, significantly compromising its mechanical properties. While noninvasive techniques have been successfully applied to characterize surfaces of ABS-based objects, a major limitation exists in terms of assessing the depth and spatial distribution of degradation without invasive sampling. This study introduces microspatially offset Raman spectroscopy (micro-SORS) as a noninvasive method to investigate artificially aged turbid ABS-based objects at both the surface and the subsurface level. First, micro-SORS spectra were collected using both a benchtop and an in-house-developed micro-SORS portable prototype, demonstrating the potential of the method for in situ diagnostics. Then, a simplified physical model based on light transport in turbid material is developed to describe the UV-vis photo-oxidation process. Lastly, a protocol is proposed for estimating the degradation depth in turbid ABS-based materials by interpreting micro-SORS measurements through the UV-vis degradation model. The model is initially calibrated through a few sacrificial samples to estimate the physical parameters. Then, the approach operates fully noninvasively, providing quantitative insights into subsurface aging phenomena. By providing a new strategy for depth-resolved aging assessment, this work bridges a key methodological gap in polymer conservation and paves the way for more informed treatment strategies and future noninvasive diagnostic applications.