A comparison between TGA, SEM-EDX and Raman spectroscopy to assess PVC plasticizer loss

Abstract

The migration of DINP and ESO plasticizers from PVC in contact with different wrapping materials was studied during artificial aging by combining three analysis methods. Silk paper, LDPE and PET were selected since these materials are widely used to protect PVC in heritage collections. First, Scanning Electron Microscopy (SEM) images and Energy Dispersive X-ray (EDX) analyses confirmed the presence of a plasticizer film at the surface of aged PVC whatever the wrapping material. Plasticizer loss during aging was then investigated after PVC surface cleaning. The overall loss of plasticizers was determined from Thermogravimetric Analysis (TGA) however it appeared to be skewed by the dehydrochlorination state. EDX analysis allowed to follow the plasticizer loss through the oxygen to carbon ratio although an external contamination was detected for some samples. Raman spectroscopy was the only technique providing the quantification of both ESO and DINP plasticizers across aging time. The combination of the three techniques to study the aging of PVC under different conditions thus highlighted the strengths and limits of each one. Finally, the relative mass loss speed was similar for both plasticizers but strongly dependent on the wrapping material. Whereas silk paper and LDPE slowed down the plasticizer loss, acceleration was evidenced in presence of PET.