Malignant Plastics
Malignant plastics consist of various groups or types of plastic that release corrosive or toxic substances as they break down.
This can lead to the loss of the affected item and damage to nearby exhibits.
By what other names are malignant plastics known?
Malignant plastics were used to make a host of products from dolls and Lego to “false ivory” dice, billiard balls, jewelery, and tortoise shell brushes, combs, and trays. It is difficult to think of some of these objects as “plastics”.
These plastics are made from cellulose esters, of which there are four main types:
- Cellulose nitrate was an early type of plastic from the late 19th century. It was often used to fashion 'false ivory' brush handles.
- Cellulose acetate, sometimes called celluloid, can be used to make film and three-dimensional Lego-type shapes.
- PVC or poly-vinyl-chloride can be either flexible like a raincoat or solid like a plastic milk container or car soft top.
- Polyurethane is usually associated with gutters and pipes but can also be used to make clothes and shoes, as can vulcanised rubber, which is one of the earliest “plastics” and mostly associated with tyres.
Why are malignant plastics a hazard we need to think about?
Plastics such as PVC and polyurethane break down over time, especially in UV light, and degrade to form acids and corrosive gases. These can damage items stored nearby. They do not present a hazard to staff or the public, only to other museum or gallery items.
How can we confirm that we have malignant plastics?
Unless you have the original packaging for the item, it will be difficult to know with certainty what type of plastic you have. Some of the early Bakelite plastics from the late 19th and early 20th centuries do not look like plastic at all. If you wish to seek advice on how to test and identify your plastic items, contact the Physical Evidence Division of the Institute of Environmental Science and Research. The testing may be destructive, so seek clarification. They are based at Mount Albert in Auckland, and you can find their contact details here: https://www.esr.cri.nz/home/contact-us/
How can institutions manage malignant plastics in their collections?
Like many museum artefacts, plastics do not do well when exposed to constant light, heat, or high humidity. They can shrink and become brittle, developing cracks. This applies to most plastics, not just the malignant ones.
Identify your plastic items and note any degradation. Ensure they are stored/displayed correctly and separately where possible. Storing some plastics in a cold environment, or in a reduced oxygen environment can halt or delay further degradation. For further information see Sources and References.
PVCs: are corrosive when they break down. This is usually caused by heat and UV light. To prevent them breaking down, manufacturers add heat and light stabilizers, but these are used up as they work. Objects will appear fine for years then suddenly start degrading. Soft car tops are a great example of this.
Polyurethane: can either crumble or hydrolyse. Polyurethane was used as storage foam for museum items, but the foam crumbled and damaged them.
Vulcanised rubber (inlcuding ebonite and vulcanite): develops a film of sulphuric acid over time. Added stabilisers often leach their colour.
You can learn more about health and safety plans by going to H&S Management Plan
If museums wish to dispose of malignant plastics, how can they do this safely?
Plastics can be disposed with regular domestic waste or recycling.
Sources and references
