Multi-analytical approach for the morphological, molecular, and mechanical characterization after photo-oxidation of polymers used in artworks

For a proper preservation of plastics objects, it is essential to study the degradation processes involved in both exposed and hidden areas of the polymeric materials. In fact, surface properties can differ significantly from the bulk and can have a strong effect on the artistic perception and the correct conservation strategy. In this work, a multi-analytical investigation, including spectroscopic techniques, optical, and electronic microscopic observations and mechanical tests, was carried out to deeply investigate changes in the physic-chemical and mechanical surface properties of selected polymers used in design objects and contemporary artworks. Accelerated photo-oxidative ageing was performed on acrylonitrile butadiene styrene (ABS), poly(vinyl chloride) (PVC), polypropylene (PP), high density polyethylene, and linear low density polyethylene. Overall, the analyzed materials have shown different behaviors following photo-oxidation. The molecular and microscopic analyses highlighted the formation of different products of oxidation due to the dissimilar patterns of ageing leading to surface cracking and strong yellowing of the specimen, mainly for ABS, PVC, and PP. Moreover, mechanical properties, such as the variation of hardness and elastic modulus, were investigated at different depth scales (from 100 down to 1 μm) by using different techniques such as microscratch, micro-, and nanoindentation. The selected polymers showed different mechanical behavior at different depth scales.