Sugar renders packaging biodegradable
palatable to soil bacteria. The plastics, which normally survive
for decades in landfills, start to biodegrade within days.
Chemists in India are lacing plastics with sugar to make them palatable to soil bacteria. The plastics, which normally survive for decades in landfills, start to biodegrade within days.
According to the journal Chemical Communications, 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 discovered that mixing the styrene subunits of polystyrene with small amounts of another substance provides a chemical hook for sucrose or glucose pieces. The scientist then added sugars to the styrene chains like pendants on a necklace.
By weight, less than 3 per cent 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. According to the research team, another approach is to initiate the breakdown process using heat, ultraviolet light or exposure to oxygen, but this is cumbersome and expensive.
