Assessing the Impact and Suitability of Dense Carbon Dioxide as a Green Solvent for the Treatment of PMMA of Historical Value

Abstract

Surface cleaning of plastic materials of historical value can be challenging due to the high risk of inducing detrimental effects and visual alterations. As a result, recent studies have focused on researching new approaches that might reduce the associated hazards and, at the same time, minimize the environmental impact by employing biodegradable and green materials. In this context, the present work investigates the effects and potential suitability of dense carbon dioxide (CO2) as an alternative and green solvent for cleaning plastic materials of historical value. The results of extensive trials with CO2 in different phases (supercritical, liquid, and vapor) and under various conditions (pressure, temperature, exposure, and depressurization time) are reported for new, transparent, thick poly(methyl methacrylate) (PMMA) samples. The impact of CO2 on the weight, the appearance of the samples (dimensions, color, gloss, and surface texture), and modifications to their physicochemical and mechanical properties were monitored via a multi-analytical approach that included optical microscopy, Raman and attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopies, and micro-indentation (Vickers hardness). Results showed that CO2 induced undesirable and irreversible changes in PMMA samples (i.e., formation of fractures and stress-induced cracking, drastic decrease in the surface hardness of the samples), independent of the conditions used (i.e., temperature, pressure, CO2 phase, and exposure time).

Proof-of-Concept Study on the Feasibility of Supercritical Carbon Dioxide-Assisted Consolidation Treatment for a Pair of Goalkeeper Gloves on Synthetic Latex-Based Foam Mock-Ups

“…As previously stated, the use of scCO 2 is relatively unexplored in treating plastics of historical value [61,62], with no previous research of application on foams, including synthetic latex-based or the more frequently common PUR ones. Hence, initial tests were performed to assess the safety of the method for the foam samples, i.e., the impact of the scCO 2 and the selected experimental conditions on the samples, and to evaluate potential induced changes, such as visual, morphological or molecular alterations.…”

“…However, there are no examples of consolidation treatments (the equivalent to impregnation as a conservation treatment), except for a study by Tuminello et al on the solubility of fluorinated resins in liquid CO 2 and their application via CO 2 spraying for stone preservation [60]. The use of scCO 2 is also relatively unexplored in treating plastics of historical value [61,62], with no previous investigation of application on synthetic latex-based foam materials or even in more frequently found types of foams, such as polyurethane (PUR).…”

Assessing the Use of Supercritical Carbon Dioxide as a Carrier for Alkoxysilanes to Consolidate Degraded PUR Ester Foams: An Alternative to Traditional Methods

“…By matching the ideal T and p conditions with the material and treatment, scCO2 may be advantageous in various conservation processes including cleaning, decontamination, deacidification, stabilisation, consolidation, and drying [25,27,28]. Recent publications have studied the application of scCO2 to paper [27,29,30], wood [28,31,32], textiles [33][34][35], waterlogged artefacts [36][37][38][39], archaeological heritage [40,41], and poly(methyl methacrylate) of historical value [42]. In the "PlasCO2: Green CO2 Technologies for the Cleaning of Plastics in Museums and Heritage Collections" project, conducted by the authors, scCO2 technology was used for the first time to design a conservation treatment for a pair of heavily degraded goalkeeper gloves from Museum Benfica-Cosme Damião.…”