Lecture 015.008


The widespread use of plastic materials as supports of artworks and design objects, urges for an ever deeper knowledge of their behavior in order to be able to ensure their preservation into the future. Restoration practices already standardized for works created by more traditional materials should be carefully tested to be transferred or excluded from the practice of conservation of plastics. In the field of cleaning to expand the knowledge already known after the research on the compatibility of the organic solvents, an experimental application has been focused on specimens of certain types of synthetic polymers to test the threshold level of risk to the use of lasers at different wavelengths, in order to provide additional operational tools for conservators.
The samples selected are polyethylene, polystyrene, polyurethane (polyether), polymethacrylate used as such and with a layer of alkyd paint, known to be highly resistant to organic solvents.
The tested laser cleaning regimes involved three wavelengths of various pulse durations: UV (QS Nd:YAG laser,  355 nm, 15ns), IR (QS Nd:YAG laser,  1064 nm, 15ns and SFR Nd:YAG laser,  1064 nm, 130μs ), and visible (QS Nd:YAG laser,  532 nm, 8ns). The application of different types of lasers at different energy levels indicated the potential applicability of laser ablation for cleaning successfully plastics. Specifically this research pointed out its limitations (the energy thresholds in order to avoid damage to the media and elimination of the overlaid foreign material) in close relation to the laser wavelength and energy used. The application of an alkyd enamel has provided a further example of the laser cleaning methodology; to test the feasibility of removing a layer particularly tenacious, which would be very difficult or even impossible to be removed with organic solvents.
A table of the combined solubility of industrial paints to organic solvents and sensitivity to different types of lasers has been resulted, in addition to various plastics, in order to complete the observation overview of the state of knowledge on synthetic polymers such as paints and/or plastic substrates.

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