Nanothermal Analysis and DSC characterization of glass transition behaviour of PMMA after solvent contact and natural aging

Donald Sale
 
Polymethyl methacrylate is an important plastic in modern art and design collections due to its glossy transparency and structural properties. Naum Gabo, Roy Lichtenstein and Donald Judd mastered the exceptional properties of PMMA, still in use by artists and designers today. PMMA is susceptible, however, to damage from solvents used in conservation cleaning solutions, and adhesives, inks, paints and varnishes. Solvents can cause immediate damage, and also can be absorbed, causing molecular changes not always visible, which effect long term stability.
The aim of this study was to investigate the suitability of xylene for use in the conservation of PMMA, due to the range of perspectives encountered in discussions with conservators, and differences in the conservation and industrial literature. Samples immersed in xylene for one minute or one hour, were compared to control samples and those immersed in acetone and toluene, which are known to dissolve PMMA. As anticipated the samples immersed in acetone for an hour were damaged severely, yet there was no obvious visible damage of most samples, even though there were apparent weight losses (some minute) after solvent immersion in the initial study in 1988.
 
A further aim of the study was to compare surface glass transition temperature (Tg) behaviour from nanothermal analysis (nano-TA), to bulk material Tg with differential scanning calorimetry (DSC) of samples which had been immersed in solvents before natural dark aging for 29 years. Nano-TA of sample surfaces identified a slightly lower Tg of all immersed samples, which suggested polymer chain scission; yet the range of Tg values appear to indicate more complex surface aging mechanisms which warrant further investigation. DSC of the bulk sample material identified Tg values that indicate differences in molecular weight caused by polymer chain scission, and compositional loss which presumably relates to the presence of MMA monomer, or other polymeric fragments.
 
The PMMA samples immersed in xylene in this study, showed no apparent visible damage at either solvent immersion time, however the Tg appeared to be lower on the surface, which could indicate chain scission, and the difference in Tg of bulk material was minimal when compared to the control.
 

Future Talks 017 – updated original submission

Nanothermal Analysis characterization of surface Tg behaviour of plastics in art after solvent contact and natural aging, and synthetic polymer media in aged artificially in different environments

Synthetic polymers found in modern and contemporary art were characterised with nanothermal analysis (nano-TA) to investigate glass transition (Tg) behaviour of samples naturally dark-aged 29 years after immersion in conservation solvents, or artificially aging in a range of environmental conditions including museum lighting.
In one study, nano-TA identified lower surface Tg in samples immersed in solvents known to damage polymethyl methacrylate (PMMA), suggesting polymer chain scission and justifying further investigation. Tg values from bulk thermal analysis using DSC were comparable.
In another study, nano-TA revealed a trend in surface Tg associated with the environmental conditions used to age the synthetic media 1:1 Paraloid B67: Paraloid F10 on PMMA. Tg values from bulk thermal analysis using DL TMA were similar.
Nano-TA is useful when investigating the Tg of thin layered samples such as plastic film, or adhesive, paint and varnish media on a support material. In these studies, 10-40 rapid measurements were taken directly on sample surfaces without destroying them entirely, unlike conventional bulk material characterisation.
Nano-TA appears promising when investigating surface Tg behaviour associated with chain scission and cross linking, which effects the solubility and long-term stability of plastics and synthetic polymer media used in art and conservation.
 
Authors
Donald Sale, Art and Conservation Consultation and Research, London 1
Dr Angelica Bartoletti, Post-Doc, NanoRestArt, Tate Gallery, London
Dr Laurent Bozec, Head Research, Biomaterials & Tissue Engineering Department – Eastman Dental Institute, University College London,
Dr Marianne Odlyha, Birkbeck, University of London