The plastic is made from corn starch, which is modified to make it thermoplastic and to give it other mechanical properties. No details of the process have been made public, pending formal approval of a patent.
The Michigan institute said that the resulting corn polymer, when applied with existing techniques, could be used to construct many products now made of non-biodegradable plastics. The institute has been working with injection moulding companies to show that the corn polymer can be processed in exactly the same way as petroleum-based plastics. Because it is biodegradable, the polymer is being recommended for use in such throw-away products as plastic razors and cutlery.
However, Ramani Narayan, director of the biomaterials programme at the Michigan institute, said the corn polymer could also be modified for use in plastic products that need to be more durable, such as signs or garden furniture.
Its key property is that it does not pick up moisture in air - which means hot tea will not break down a plastic cup while you are drinking it - but does pick up moisture when disposed of through composting.
The institute is also working with several fast-food restaurants to develop a system for the use, collection and disposal of food packaging made from the polymer.
There are already several biodegradable plastics on the market, including Biopol, made by Zeneca. But most are more expensive than petroleum- based plastics and cannot just be thrown out with the rest of the rubbish. They will break down by composting, but landfills often do not have enough microbial activity to make them thoroughly biodegradable.