Evaluating the Impacts of Alcohol-Based Solutions on Silk: Chemical, Mechanical and Wettability Changes before and after Artificial Ageing

Due to the COVID-19 pandemic, since 2020, alcohol-based sanitisers have been frequently used in museums and historic sites. Although they provide a safer environment for visitors, the impact of the (components in) sanitisers on the cultural heritage on open display is still uncertain. The current study investigated the effects of ethanol and isopropanol solutions on silk artefacts specifically in relation to possible mechanical changes and to their long-term impact based on artificial ageing. Thus, samples from three modern silk fabrics were treated through spraying and immersion with six solutions, two of which contained benzalkonium chloride (BZK), a surfactant suggested by Italian national guidelines in the formulation of sanitisers for museums. The impact of the treatment was studied from a chemical perspective, i.e., through spectroscopic techniques, and considering changes in the mechanical strength through uniaxial tensile testing. In addition, water wettability was measured. To study whether the contact with the solutions can affect the degradation path of silk, after the treatment, samples were exposed to light ageing and were stored at medium and high RH, i.e., 55% and 80%. Furthermore, treated and untreated silk textiles were placed in the Museum of Palazzo Mocenigo (Venice) to define the behaviour in an actual museum environment. The results show that, even when silk is immersed in the solutions for 180 min, no relevant chemical and physical changes can be observed on silk fibres. Variations noted at the end of the light ageing occurred regardless of the treatments with the solutions, so they are not affected by the contact with sanitisers. Nevertheless, when treating the samples (also through spraying) with solutions containing BZK, the surfactant is adsorbed by the textile. Once adsorbed, BZK significantly increases the water wettability of silk, causing a persistent modification of the property as also observed at the end of the ageing and in situ tests.