Anna Comiotto
Abstract
This paper reports on the development of a plasma-pen that opens up new possibilities for overcoming adhesion problems during small-scale conservation and restoration treatments on non-polar plastics in modern and contemporary art. The setup of the developed plasma equipment will be described, as well as today’s state of knowledge concerning the effectiveness of the plasma pre-treatment to enhance the wettability, bondability and coatability of polyethylene, polypropylene, and polystyrene. The extent to which the pre-treatment enhanced the bondability was evaluated by performing tensile shear tests on untreated and plasma pre-treated adhesive bonds. These bonds were made on polyethylene and polypropylene with the acrylic resin Paraloid B-72. Improvements in coatability were examined in pull-off tests carried out on gouache-painted polyethylene and polystyrene.
In the case of all plasma pre-treated, non-polar plastics, the plasma pre-treatment resulted in a significant improvement of adhesive qualities. The breaking forces necessary to separate all tested adhesive bonds were significantly increased, and the tested gouache coatings gained a considerable mechanical resilience. This has interesting implications for conservation practice: adhesive bonds and retouchings with high mechanical resilience can be applied on the plasma pre-treated surfaces, helping to prolong the expected lifespan of conservation measures. Furthermore, the application of mechanically resilient, water-based and water-removable gouache retouchings on hydrophobic plastic surfaces becomes feasible. An essential chemical mechanism during plasma treatment is surface oxidation. This was proved on plasma pre-treated polypropylene by using infrared spectroscopy in attenuated total reflection. Little is known about whether or not this surface oxidation negatively affects the oxidation stability of the pre-treated materials. Chemiluminescence analysis was used to expand the knowledge about this issue.