Aging of plasticized polyvinyl chloride in heritage collections: The impact of conditioning and cleaning treatments

The degradation kinetics of plasticized PVC films naturally aged for about 30 years old in museum conditions and displaying surface exudates was studied during an artificial aging treatment consisting in a temperature cycle (2 days at 80 °C/1 day at 25 °C) and under controlled relative humidity (65%). The role of the enclosure was investigated by placing the films either in a closed vessel or by freely hanging them in the climatic chamber, while the effect of a preliminary mechanical surface cleaning to remove the exudates was also studied. Plasticizer migration and PVC degradations were characterized every week by coupling thermo-gravimetric analysis, gas chromatography, dynamic mechanical thermal analysis, infrared and UV-visible spectroscopy, atomic force microscopy and contact angle measurements. The results show that there is a significant slowing down of PVC aging in a closed container with respect to an open environment. Plasticizer loss and thus changes in mechanical properties are thus strongly delayed in a closed environment while PVC dehydrochlorination leading to sample yellowing also evolves at a slower pace. Concerning the effect of the preliminary PVC surface cleaning, it appears effective and has no effect on the kinetics of further PVC degradation. In particular, the removal of the exudates does not accelerate the further plasticizer loss. This study brings significant insights for conservation strategies. Indeed, the lifetime of soiled PVC-base heritage artifacts can be extended through a soft mechanical cleaning of the surface allowing retaining their visual appearance. Moreover, preservation of PVC artifacts in a closed container is preferable to slow their degradation process.