Lights out! The conservation of polypropylene wall tapestries

Polypropylene (PP) as a manmade fibre shows excellent properties in constituents of fabrics, upholstery and carpets. Many industrial uses involve ropes, woven and non-woven fabrics and reinforcements. Like many plastics, PP has virtually endless uses, and its development has not slowed since its discovery. However, this polymer is prone to degradation by photo-oxidation, especially by UV radiation. Earlier studies confirmed the rather fast degradation of PP to be less than 40 years in the work of modern arts. Two wall tapestries, Fête I (1969) and Fête II (1969), woven by the Dutch artist Wil Fruytier, consist of PP ropes. These works of art have been exposed to daylight and UV radiation for more than 30 years, resulting in degraded, brittle fibres. Due to the fact that the objects will remain exposed under non-museum conditions, conservation treatment is necessary to preserve these important elements of cultural heritage. The aim of this study was to investigate the application of a light-stabilising system on PP. Moreover, the effectiveness in preventing photodegradation of this consolidant containing UV absorbers, heat stabilisers and light absorbers, was studied. PP is an inert polymer with a low surface tension that makes the adhesion of other substances very difficult; hence, a method to activate its surfaces was researched first. Corona treatment and atmospheric plasma pretreatment were used to investigate the increase in PP surface activity through electrical discharge. To apply consolidants on activated PP surfaces, nebuliser and airbrush spraying systems were compared to establish the most useful method. To verify the strength of the adhesion of the applied consolidants on PP, cross-cut tests according to ASTM D3359 were performed. An Atlas Xenotest Alpha chamber was used to artificially light-age PP test samples. Fourier transform infrared (FTIR) spectroscopy was used to follow photo-oxidation by measuring the carbonyl absorption during ageing. Burst tests on textile PP were performed to establish the effectiveness of the consolidant in protecting the PP surface from photo-oxidation. Atmospheric air plasma proved to be the best surface activation pretreatment for PP and Plextol D 498, an acrylic emulsion, combined with Tinuvin B72 was confirmed as the best applicable consolidant with the airbrush being the most useful application method. Six hundred hours of artificial ageing of a consolidated PP surface in the Xenotest did not show any photodegradation; 600 hours of ageing is comparable to 150 years of museum conditions (at 200 lux). Before implementing the above-described conservation treatment on the two wall tapestries, it will be tested on mock-up tapestries made from PP ropes. This investigation is currently ongoing.