Patricia Schossler
Abstract
Due to its economical and technical importance, poly vinyl chloride (PVC) is one of the most produced and consumed plastics since the 1950s. Recent surveys pointed out the consequent increasing presence of soft-PVC in museums collections, as well as the fast and remarkable degradation of objects made from or containing soft-PVC. The degradation of plasticized PVC is directly related to dehydrochlorination accompanied by diffusion of the plasticizer through the polymer matrix, deposit at the surface of the object and further emission in the environment. This results in tacky surface, stiffening, tearing, embrittlement and discoloration of the soft-PVC object. Esters of phtalic acids were widely used as plasticizers until the beginning of the 1980s, when “alternative or non-phthalate plasticizers” were introduced in the market as substitutes for the controversial mutagenic phthalates. In this work the long term emission profile of three alternative plasticizers from soft-PVC samples was measured, in order to verify the quantity of plasticizer emitted over a long period of time as well as to monitor of changes in optical and mechanical properties of the soft-PVC samples under study. Experimental Results: Three soft-PVC samples were provided by artists: sample PVC1 was plasticized with diisononylphthalate (DiNP), sample PVC2 presented 1,2-cyclohexane dicarboxylic acid diisononyl ester (DINCH) as plasticizer and in the sample PVC3, diethyl citrate (DEC) was identified as plasticizer. The plasticizers emission measurements were realized using a Field and Flow Emission Cell (FLEC) with an air exchange rate of 269 h-1. The sampling took place every week during 5 months and was accomplished using glass wool absorption tubes. The measurement of the loaded collecting phase was done by thermal desorption and GC/MS. The plasticizers presented a similar long-term emission profile with an increasing loss of plasticizer during the first 4 weeks, after which the steady-state was reached and the constant plasticizer loss rate observed was in accordance with the vapor pressure of the compounds under study. After accelerated ageing, tacky surfaces and stiffening were observed in all the samples. PVC3 presented the major yellowing among the samples, which could be justified by the presence of DEC as biodegradable plasticizer. At the aesthetic change corresponded a structural degradation, as it was confirmed by an increase in stiffness and a decrease in the strain at break of all the samples. Sample PVC3 was the most degraded, while samples PVC2 and PVC1 presented similar degradation profile after the accelerated thermal ageing. Conclusions The results showed a major and considerable susceptibility to degradation of sample PVC3, if compared to samples PVC2 and PVC1. Considering previous researches related to the emission of the banned plasticizer di-2-ethylhexyl phthalate (DEHP) from soft-PVC samples, only the sample plasticized with DiNP presented a lower emission potential. Consequently, it is to expect a faster degradation and consequent shorter lifetime of PVC objects plasticized with DINCH and DEC. Since the samples under study were provided by artists, they will be advised about the degradation susceptibility of the materials, as well as a valuation of other possible plasticizers will be provided.