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PLASTICS were once regarded as wonder-materials.
They are still ubiquitous, but find less favour than they used to because of the very stability and persistence that won them plaudits in the first place. Persistence is not a quality to be desired in something that gets thrown away, and so much plastic is used in packaging, and in articles that are disposable, that many people now see conventional petrochemical plastics as a nuisance and a threat.
The search is on, then, for biodegradable alternatives. One possibility has recently been explored by David Schiraldi of Case Western Reserve University, in Ohio, and his colleagues. They propose to reach back into history and revive the use of a feedstock that was used to make some of the first plastics invented: milk.
What they actually suggest is using casein, the principal protein found in milk. The curds (of “curds and whey”) are mostly made of this protein. In 1889 a French chemist called Jean-Jacques Trillat discovered that if casein is treated with formaldehyde the result is a hard, shiny substance that does well as a substitute for materials like ivory and tortoiseshell. So widespread was the enthusiasm for the new material that Queen Mary herself ordered several pieces of jewellery made from it. However, casein-based plastic of this sort is too brittle for general use. It was eventually superseded by the modern, petrochemical variety, and manufacture stopped altogether by the 1970s.
The thought of reviving it, though, has never quite gone away, and these days the fact that it is made mostly of protein, and could thus be chewed up by bacteria, is regarded as a virtue—if only the structural weakness could be overcome. Dr Schiraldi’s approach does this by using a silicate clay called sodium montmorillonite as a skeleton that holds the plastic together.
