Raman spectral mapping reveal molecular changes in cellulose aging induced by ultraviolet and extreme ultraviolet radiation

In the framework of a study on the aging phenomena of textiles we used Raman spectral mapping to analyze changes in the chemical bonds of cellulose of flax fabrics exposed to ultraviolet (UV) radiation in air, and extreme ultraviolet (EUV) radiation in vacuum. Our results show that both UV and EUV produce photolysis of cellulose bonds, which in turn triggers photochemical oxidation and dehydration, in a kind of “accelerated aging” and oxidative degradation of flax. In particular, we detected the formation of a large number of carboxyl and carbonyl groups, which, when conjugated, act as chromophores and give flax a yellowish hue. Remarkably, the mapping of Raman spectra makes it possible to identify the relative weights of molecular reactions responsible for the generation of oxidized groups and aging of cellulose. In particular, the comparison of spatially-resolved Raman spectra after irradiations UV in air and EUV in vacuum provides direct and quantitative evidence of the role of oxygen in the molecular changes leading to flax aging due to UV illumination. As an example, we found that atmospheric oxygen does not affect the change of the degree of polymerization of cellulose nor the formation of carboxyl and carboxyl groups. These results help to assess the possible benefit, if any, of preserving and exposing ancient cellulosic cloths in an inert, oxygen-free atmosphere.