Many people believe that plastic items are indestructible and will last forever. But what if you learnt this wasn’t the case?
Conservator, Nirmala Balram, gives us an insight into the science of plastic deterioration and how you should look after your prized plastic possessions.
So much plastic
The world of plastics is huge. Plastics are everywhere. Your computer, work materials, nail polish, house paint, and even your clothes have a plastic component.
Have you ever wondered why your polyester dress doesn’t crease easily? It’s because fine strands of polyester, a stable type of plastic, are woven in between the cotton, linen, or wool fibres keeping the surrounding fibres straight.
The invention of plastic
Plastic has always occurred naturally, but in 1856 the first man-made plastic called ‘Parkesine’ was invented in the UK by Alexander Parkes.
Since then, hundreds of new forms of plastic have been developed, and more continue to be made today.
Collecting plastics at Te Papa
At Te Papa we have approximately 5,500 objects made of plastics.
Their bright colours and shapes are common in our Pacific collection because migrant communities have found it difficult to source original organic materials, so have substituted these with easily available plastics.
Plasticisers: what are they?
Plastics are made with a polymer which are like tiny molecules joined together just like flour grains in bread dough.
To be able to shape this, an oil like material called a ‘plasticiser’ is added.
The plasticiser has strengthening agents and preservatives, but also makes the plastic pliable, allowing the manufacturer to mould into shapes.
Good and bad plastics
Part of my work at Te Papa is identifying the different types of plastics in our collections and assessing how best to store them to ensure they last as long as possible.
There are good and weak plastics – meaning those that are stable and those that are unstable.
Heat, pollutants, and some chemicals draw the plasticisers to the surface of weak plastics making it look ‘sticky’.
This loss of the plasticiser makes the plastic brittle meaning that eventually the structure will crumble and break down.
You can see in the image below that the hat made from plastic bags has become brittle and degraded.
Plastic fumes
Depending on what plasticiser is added, the fumes that can potentially come off plastic can be damaging to other materials around it.
For example, the plasticiser in PVC will release acidic products from chemical reactions with the atmosphere which will cause materials like metals to corrode.
Today there is biodegradable plastic which helps keep the environment clean. Some of the plasticiser is made of starch molecules that are attacked by everyday bacteria.
Loss of colour
Coloured dyes and pigments are added to the plastic ‘dough’ during the manufacturing process.
You can see that these 1970s Barbie’s heads are a completely different colour to their bodies.
A different composition of plastic ‘dough’ has been used for their heads to make them softer and more pliable.
This is achieved through adding more plasticisers, which migrate to the surface when left exposed to heat and sunlight. The plasticisers diminish along with other additives like colour pigments leaving behind a discoloured and hardened material – and a lovely yellowy/green hue!
PVC degradation has also caused their bodies to turn more pink than they should be.
Ideal storage for plastics
In museums, decisions around the storage of plastic are becoming more and more important as we learn about the agents of deterioration for plastics and how they can affect the objects around them.
Plastics should be stored and displayed in low temperatures preferably between 13-18 degrees Celsius, low UV-limited light, and a chemical-free environment.
If you want the toys in your house to have a much longer life keep them in a clean, dry environment, away from direct sunlight and don’t wash them in harsh chemicals.
Even better, keep your favourite Barbie in a moisture-proof bag in the fridge – ensuring she stays forever young!
Very interesting thank you!