Beware of crispy bra syndrome

As the 20th century draws to a close, the material which has characterised the century more than any other - plastic - is coming under increasing scrutiny. Some kinds of plastic have survived well, losing little of their colour or texture. Others are fading, becoming brittle, shedding acidic tears, even crumbling away.

The rate of decay, and what form it takes, can be predicted, says Anita Quye, conservation scientist at the National Museum of Scotland. Early film stock made from cellulose nitrate (or celluloid) is very susceptible to decay: most of the material owned by the British National Film Archive made before the 1950s has already disintegrated. Electric guitars made from cellulose acetate, on the other hand, are more robust, but not as sturdy as Barbie dolls, made from polyvinyl chloride (PVC). All three types are polymers, with long linear chains which break down in similar ways.

Plastics can break down as a result of being in sunlight, getting wet or hot, or being contaminated somehow. Dolls made of cellulose acetate in the 1940s have begun to weep acetic acid, or vinegar, since the acetate has broken off from the cellulose and has reacted with moisture in the air. Barbie dolls, if they do break down, shed tears of hydrochloric acid.

Even plastics made in the 1960s are vulnerable: a sixties bra kept at the National Museum of Scotland has become decidedly crispy. The better lasting plastics are sometimes those which have complex internal arrangements of molecular chains, which interlink to provide extra strength. Bakelite, for example, has lasted better than most: 1930s Bakelite radios are now highly prized, selling for as much as £20,000 each ($32,000).

But in a material like polyurethane, used for its flexibility in objects such as furniture, will react with oxygen over time and turn brittle, then crumble. So, if you’re investing in some kitsch modern plastic objects, it is as well to understand the potential life span before you spend, in case your treasures turn to dust.

Footnote: Researchers at Purdue University in the US have developed a hand-held probe which can differentiate between different kinds of plastics, identifying more than 100 pieces of plastic per second. This allows them to be separated before being recycled, since different polymers will not melt down properly.

The device works by shining a laser beam at the plastic and collecting the scattered light. Ford cars and the US Environmental Protection Agency helped to finance the research.