Study of plasticizers, loss and exudation in plasticized polyvinylchloride-based heritage objects

International audiencePlasticized polyvinyl chloride (PVC) is widely present in contemporary Art collections but its conservation condition is often considered as poor. The project aims to deepen the understanding of thermal degradation mechanisms of plasticized PVC objects and to recommend preservation conditions and restoration treatments.Our research was carried out on plasticized PVC films naturally aged (around 30 years old) and exhibiting surface exudates. Plasticizers such as 13% di-iso-octylphthalte (DOP) and 15% di-octyl azelate (DOZ) were identified by Gas Chromatography and Mass Spectrometry, both within the material and the exudates. Plasticizer migration and PVC degradation were studied during a cyclic thermal artificial aging (2 days 80°C/1 day 25°C at 65% RH). PVC films were placed either in an open or a closed vessel, and whether or not submitted to a preliminary cleaning with a microfiber cloth.This study shows that all samples undergo a similar degradation process, which is significantly slowed in a closed packaging with respect to an open one, in agreement with previous studies[1]. Regardless of any packaging condition, no effect of the preliminary cleaning is evidenced. In an open packaging, a significant plasticizer loss is thus observed, since almost no plasticizer is detected in the samples after 15 weeks of thermal aging. This migration is accompanied by a α-relaxation temperature increase up to a value close to the one measured for unplasticized PVC, which is consistent with the absence of plasticizer at this stage. Dehydrochlorination is evidenced from with Infrared and UV-visible spectroscopies, in agreement with the PVC yellowing. No exudation phenomenon related to plasticizer migration is observed with the naked eye however dendritic structures attributed to the migration of hindered amine light stabilizers are detected by Atomic Force Microscopy. Future work is devoted to study the effect of the wrapping materials.Reference[1]Y.R. Shashoua, Polym. Degrad. Stab. 81 (2003) 29-3