Ironically, this material is chemically similar to polyethylene, one of the most widely used and persistent types of plastic in the environment, but it does not accumulate around bee colonies despite thousands of new nests being built year after year.
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Jonathan Cote, an assistant professor in the Department of Chemical Engineering and Materials Science at the University of Minnesota and the lead author of the study, says the problem the team is trying to solve is not a lack of alternative plastics, but rather the difficulty of creating a material that behaves like polyethylene during use and then breaks down easily when it reaches the environment.
Scientists have known for over 45 years that cellophane bees line their nests with a mixture of silk threads and a polymer secreted from a gland in their abdomen, but this has largely remained a biological curiosity that has not been studied in detail. Jonathan explains to Al Jazeera Net that these bees sometimes live in colonies containing more than 10,000 nests, and new generations return to the same locations for decades, yet no accumulated layers of this material appear in the soil.
Therefore, the researchers collected modern nest linings from a bee colony in the US state of Tennessee, then returned to the same site after four months, then seven, and eleven months, and compared the composition, shape, and properties of the material over time.
The team used a series of tests to determine the composition of the material, its hardness, the arrangement of its molecules, and how it changes over time. One of the surprises was that the bee polymer did not dissolve even when placed in strong solvents and heated to 150 degrees Celsius for two days.
This indicates, according to the researcher, that its chains are not completely separate, but rather are linked together in a network that helps them maintain their shape—a property called "crosslinking." At the same time, the researchers found that about 60% of the material is arranged in cohesive crystalline regions similar in structure to polyethylene crystals, a high percentage that would normally be expected to make its decomposition more difficult, not faster.
But monitoring the nests in the soil yielded the most significant result: the newly formed lining consisted of approximately 73% polymer and 27% silk, but the polymer content dropped to only about 40% after four months. By the seventh month, noticeable cracks appeared in the material, and after 11 months, it had lost most of its elasticity and become more prone to crumbling.
The researchers describe this result as remarkable because chemically similar synthetic materials do not decompose this quickly even when placed in harsher conditions, such as industrial fertilization at high temperatures or exposure to acids and enzymes.
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