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Ask the researchers

Ask the researchers

What is the difference between OXO biodegradable plastic bags and ordinary ones? (José João Lelis Leal de Souza, via e-mail)

ANA PAULA CAMPOS OVER PHOTO BY EDUARDO CESAR“Ordinary” plastic bags are made from polyethylene, a raw material derived from petroleum or sugar cane, and take more than 100 years to decompose. OXO biodegradable bags have a similar composition, with just one difference: they receive an additive that accelerates their degradation, making the bag break up into pieces that are invisible to the naked eye when exposed to light, humidity and the air. The problem is that the minute pieces appear not to be consumed by microorganisms, like fungi and bacteria, the necessary condition for a material to be biodegradable. In addition to the petrochemical compounds continuing in the environment, the additives themselves may be toxic.

A bag made from cornstarch, the most heavily quoted to substitute the polyethylene bag that so far has been distributed in supermarkets, also contains petroleum derivative, but to a lesser extent. There is already a type of polyester that is 100% biodegradable, which is produced by microorganisms during their digestion of sugar, but it is dearer to make than conventional plastic and this means that it is not very feasible for use in the large scale production of supermarket bags.

It is worth highlighting that a biodegradable product is not necessarily made from renewable sources. Compounds of a petrochemical origin may be biodegradable and others coming from sugarcane may not be.

Marco-Aurelio De Paoli,
Chemistry Institute – Unicamp