From microfibres to nanogels-conservation cleaning of plastics heritage

Surveys of the condition of plastics heritage in Europe indicate that 70- 75% of collections require cleaning. Oily fingerprints, carbonaceous dirt and crystalline degradation products on plastic objects and artworks reduce their significances, chemical and physical stabilities. However, it is essential to balance the need to clean against the risks of mechanical damage from cleaning tools particularly scratches and of inducing chemical changes from aqueous- or solvent-based agents by mobilizing additives and solubilizing degraded polymers. Conservators must therefore consider scientific, aesthetic and ethical factors before developing a cleaning strategy for plastic objects and artworks.
Until around 2000, research into cleaning of plastics heritage used visual examination alone as an evaluation tool and concluded that dry mechanical cleaning was the most effective treatment offering the lowest risk of damage. In 2012, the EU 7th Framework Programme project POPART used optical- and scanning electron microscopy, changes in surface energy and gloss to conduct an exhaustive evaluation of mechanical, aqueous and non-aqueous cleaning techniques for their effectiveness at removing sebum and carbonaceous soils from cellulose acetate, polyethylene, PVC, polystyrene and polymethylmethacrylate. POPART concluded that applying anionic and nonionic detergent solutions with polyester microfiber cloth, cleaned more effectively and produced fewer scratches than using dry cleaning tools. Polyethylene and PS were the plastics found most vulnerable to scratching. In 2018, the Horizon 2020 research project NANORESTART added nanogels and -gums to the cleaning tools examined in POPART and infrared spectroscopy to the suite of instruments. The project concluded that nanogels based on polyvinyl alcohol, loaded with anionic detergent solutions and applied to plastic surfaces for between 5 and 20 minutes, were equally effective as microfiber cloths at removing sebum and carbonaceous soils but produced significantly fewer scratches. It is clear that twenty years of conservation research has dramatically increased the range of cleaning tools and cleaning agents available. In addition to the latest findings, this paper will use case histories to discuss how developments in conservation cleaning science influence cleaning practice for plastics heritage.