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What makes biodegradable plastic degrade?

by Green Plastics


There is one question that we hear over and over again from people who are interested in using home-made bioplastic in their products and designs.  Whether they are students making a bowl or a decoration for a class project, or a young entrepreneur looking to invent a new type of jewelry or fishing lure, people always want to know:

What will actually make my biodegradable product degrade?

How can I make sure that it doesn’t degrade too soon?

composting-bottle_largeMaterials can be “degradable” but still last for a long time. Degradation has certain environmental requirements; a material may degrade readily in one environment and be long-lasting in another. ¬†Degradation requires, for example, some level of moisture (to allow the process of “hydrolytic” degradation). For example, old newspapers have been found in landfills where they had not come into contact with any water, and as a result they have not degraded. Temperature also plays a role. Animal remains have been found trapped in ice for hundreds of years.

Exposure to microorganisms is also necessary. Plants and animals, inherently biodegradable, will not biodegrade if they are kept in a sterile environment.

So what about your home-made bioplastics?

A gelatin or starch bioplastic product can last for years sitting on a shelf; however, when placed in soil, or a landfill, or an ocean, it can biodegrade in days. The applications you have to be careful about are those which put it in contact with heat and moisture. For example, jewelry that is worn close to the skin for long periods of time will show signs of wear much faster than an ornament that hangs on a wall. Alternatively, a bowl that you wipe clean by hand under warm water will show signs of wear much faster than a desk lamp that simply sits, dry, on the table.

There are many commercially-produced bioplastics that are specifically designed to be programmed-degradable. These materials have already been used commercially to produce bowls and trash bags that are stable through the periods of shelf-life and use and then biodegrade in several disposal environments. You can learn more about the idea of “programmed-degradable plastics”, plastics that are made to be stable for some period of time (depending on the application) and then degrade when placed in some defined disposal environment, in the Green Plastics book.

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