Sugar turns plastics biodegradable
Bacteria make a meal of sweetened polythene and polystyrene.
Chemists in India are lacing plastics with sugar to make them palatable to soil bacteria1. The plastics, which normally survive for decades in landfills, start to biodegrade within days.
The tweaked plastics are polythene, polystyrene and polypropylene. These make up around a fifth of urban waste by volume. Bottles, bags and sacks are made of polyethylene, food packaging is made of polypropylene, and drinking cups, fast-food cartons and the hard casing of electronic equipment are fashioned from polystyrene.
Digambar Gokhale and colleagues at the National Chemical Laboratory in Pune mix the styrene subunits of polystyrene with small amounts of another substance that provides a chemical hook for sucrose or glucose pieces. They then add sugars to the styrene chains like pendants on a necklace.
By weight, less than 3% of the final polymer is sugar, so the material is more or less the same. But bacteria such as Pseudomonas and Bacillus break open the chains when they chomp on these sugary snacks, kicking off decay.
It remains to be seen whether the polymer biodegrades into entirely non-toxic substances. Fully broken down, the end products are carbon dioxide and water. But along the way, all sorts of other compounds are produced, such as organic acids and aldehydes.
Indeed, it is not yet clear how far, or how quickly, the plastic will break down in the real world. And adding the sugar would require significant manufacturing changes, which could be costly.
Other additives that make polythene, polystyrene and polypropylene biodegradable have been toxic and can leach out of garbage. Another approach is to initiate the breakdown process using heat, ultraviolet light or exposure to oxygen, but this is cumbersome and expensive.
Galgali, P., Varma, A. J., Puntambekar, U. S. & Gokhale, D. V. Towards biodegradable polyolefins: strategy of anchoring minute quantities of monosaccharides and disaccharides onto functionalized polystyrene, and their effect on facilitating polymer biodegradation. Chemical Communications, 2002, 2884 - 2885, (2002).
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