Inhibiting the deterioration of plasticized poly (vinyl chloride)-a museum perspective

Plasticized polyvinyl chloride (PVC) has been one of the most economically and technically important synthetic materials since the 1950s . Proportions of plasticizer in commercial PVC formulations range from 15% to 50% by weight. Examples of these various formulations are present in many international museum collections, in the form of protective clothing and footwear, inflatable furniture, cable insulation, toys, medical tubing and sculpture. Most plasticized PVC formulations are designed to function for less than 10 years; this is a concern to museums where all collections should be preserved for at least 50 years. The present study outlines a strategy for prolonging the useful lifetime of plasticized PVC objects with di-2-ethylhexyl phthalate (DEHP).

Examination of deteriorated PVC in museums suggested that migration, loss and chemical breakdown of plasticizer were the major mechanisms of deterioration . Model formulations were developed to represent the range of plasticized PVC objects in museum collections. The extent, rate and mechanisms of deterioration were examined during accelerated thermal ageing in various environments, typical of those used to store and display plastics and other materials in museums. Environments included a closed flask, freezer, with silica gel, activated carbon and Ageless ® oxygen absorber, at high relative humidity, on glass and in polyethylene bags. In addition, two naturally aged ‘objects’, also plasticized with DEHP and exhibiting deterioration, were included in the experimental work to examine the effect of the environments on non-ideal materials.

A non-destructive analytical technique was developed using Attenuated Total Reflection Fourier Transform infrared (ATR-FTIR) spectroscopy to quantify the concentration of DEHP at the surfaces of samples. Weight loss was used to quantify total loss of plasticizer. Changes in the distribution of DEHP were mapped using low-vacuum scanning electron microscopy (LV-SEM). Densitometry was used to quantify darkening of the PVC component of samples.

Degradation of model formulations and naturally degraded objects was inhibited by enclosure in a non-adsorbent material such as glass, containing non-agitated air. Enclosing plasticized PVC objects, whatever their level of deterioration, is inexpensive to implement, of low practical complexity and allows public accessibility to plastics objects.