Museums across the world are facing a pressing issue: the plastic artefacts in their collections are deteriorating. With time artefacts all over the world including sculptures, iconic designs, and historical films made from plastics may decay beyond the point of repair. European researchers are investigating exactly how synthetic materials age, which will hopefully give rise to new techniques for their preservation.
Plastics became a popular material with designers in the post-war years. Housed within the Victoria & Albert Museum in London is the Colombo chair made from ABS plastic, the first chair moulded from a single material. Originally white, the chair has begun to yellow. This happens as the chemical structure of the chair absorbs energy, for example in the form of light or heat, which changes the structure of the material, causing it to darken.
Films, cartoons and photographs are also at risk. As a film degrades it becomes sticky and smells strongly of acetic acid, or vinegar. Celluloids, which are used to produce animations, also degrade and retract, making the colours break off from the plastic surface.
The way plastics decay is quite different to other materials. The rate of decay is very abrupt; an artefact may seem fine for many years and then rapidly decay within months. After this point the plastic artefact can no longer be saved.
Brenda Keneghan is a polymer scientist working at the Victoria & Albert Museum and is studying plastic artefacts, including some from the 1950s, to gain insight as to how different polymers degrade, discolour and distort. One type of rubber material oxidises (reacts with the air), destroying the surface leaving it brittle and flaky. Objects made of PVC, on the other hand, are sensitive to light and their colour may become very dark with time. Once the materials have become unstable even excellent storage conditions will not stop the degrading process.
Plastics from the same family of polymers can differ in their rate of degradation. Why this is so is not yet properly understood. POPART is a European research project aiming to understand how different polymers degrade. Bertrand Lav�drine, the project coordinator, is running a series of experiments at the CRCC (Centre de recherche sur la conservation des collections) in Paris. Light and heat are used to accelerate the ageing of plastics to better understand how their chemical structures change. For example, a foam object is kept in a large oven at 90 degrees Celsius and 50% humidity, becoming yellow and fragile. It is hoped to be able to identify the processes that lead to the changes in chemical structure and to slow them down.
There has already been research conducted in the degradation of plastics in the building industry. However, in such an industry the plastics can simply be replaced, which is not an option for the artefacts in museum collections. Here the ageing process must be stopped or at least slowed down. The actual preservation of plastics is in fact a relatively new science.
This problem poses a great threat on an extensive portion of our cultural heritage. The films and photographs are also of large historical importance. Although plastics are the most typical of disposable products, some plastic artefacts should be preserved for as many future generations as possible.