Effect of solvent on PARALOID® B72 and B44 acrylic resins used as adhesives in conservation

Abstract Paraloid® is one of the most frequently used acrylic polymers, employed mainly for its adhesive and consolidating properties in the conservation of a wide range of materials. Appreciated for its reversibility, mechanical characteristics and ease of use, application of the polymer requires it to be simply dissolved in a solvent. Nevertheless, the chemical nature of the relevant solvent must be regarded as an essential parameter, due to its influence on the physico-chemical characteristics of the resulting adhesive film. The aim of this study was to evaluate the effect of the solvents used with Paraloid® acrylic resin on adhesive film properties, and more specifically on their thermophysical characteristics. Two compounds used in conservation (Paraloid® B72 and B44) and six solvents (ethanol, acetone, ethyl acetate, ethyl lactate, butyl acetate and toluene) were used to make adhesive film replicates. Thermogravimetry and differential scanning calorimetry (DSC) analyses allowed us to determine the value of the glass transition temperature (Tg) of solvent/Paraloid® mixtures. Mass monitoring of the films enabled us to correlate Tg values with the quantity of residual solvent. Results showed that all the solvents remained present for a long time in Paraloid® films when drying took place at room temperature. Moreover, DSC analysis highlighted the fact that residual solvent had a considerable impact on the value of film Tg. In fact, residual solvent significantly lowered the Tg value of Paraloid® (by up to 30 °C below its theoretical value). This underlined the importance of taking the impact of solvent on resin properties into account.