Inhibiting the inevitable: current approaches to slowing the deterioration of plastics

Once plastics objects are registered in museum collections, the institution becomes responsible for their long term preservation, until the end of their useful lifetime. Plastics appear to deteriorate faster than other materials in museum collections and have a useful lifetime between 5 and 25 years. Preventive or inhibitive conservation involves controlling the environments in which objects are placed during storage and display, with the aim of slowing the major deterioration reactions. Once in progress, degradation of plastics cannot be stopped or reversed, so the aim of preventive conservation is to ‘buy time’ for the object. Inhibitive conservation of plastics involves the removal or reduction of factors causing or accelerating degradation including light, oxygen, acids, relative humidity and acidic breakdown products. Specific approaches to conservation have been developed for cellulose nitrate, cellulose acetate, PVC and polyurethanes by considering the most effective action to inhibit their major degradation pathways. The purpose of this article is to outline the main factors causing degradation of the least stable plastics in museum collections and present an overview of the conservation treatments established to date. Recent research has suggested that some of the conservation practices to slow the rate of deterioration in use today, particularly those for cellulose nitrate and acetate, are poorly effective and that alternatives should be evaluated. One alternative is low temperature storage.