Microbial deterioration of Mowilith DMC 2, Mowilith DM5 and Conrayt poly(vinyl acetate) emulsions used as binding media of paintings by pyrolysis-silylation-gas chromatography–mass spectrometry

Evaluation of the deterioration produced by microbiological attack on Mowilith DM5, Mowilith DMC2 and Conrayt poly(vinyl acetate) (PVA) emulsions has been carried out using pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS). The proposed method includes the on-line derivatization of PVA emulsions using hexamethyldisilazane during pyrolysis. Specimens consisting of thin films formed on glass slides from dried PVA emulsions have been used. Py-GC–MS analyses performed on the specimens where the fungi Aspergillus niger, Penicillium chrysogenum, Trichoderma pseudokoningii, Cladosporium cladosporioides, Chaetomium globosum, Rhizopus oryzae, Aureobasidium pullulans, and the bacteria Streptomyces cellulofans, Bacillus amyloliquefaciens, Arthrobacter oxydans and Burkholderia cepacia were inoculated and allowed to grow, enable an evaluation of the effect of these microorganisms on the composition of the PVA emulsion. Decrease in the relative content of external plasticiser of phthalate type used in these PVA emulsions has been the main effect observed. Moreover, a different behavior was observed depending on the plasticiser present in every commercial PVA emulsion studied. Diisobutyl phthalate, used in Conrayt emulsion slightly varied its content in specimens inoculated with bacteria whereas dibutyl phtalate used in Mowilith DMC2 emulsion noticeably decreased its content in the specimens inoculated with fungi, thus suggesting that the effects of the metabolic processes associated to the latter microorganisms on the studied PVA emulsions are more significant than those from bacteria.