What makes biodegradable plastic degrade?

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?

Materials 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.

What can i mix with my bioplastic product?

Dina is a product design student who is working on using bioplastic to make new products. At one point she asks:

Is it possible to mix the plastic with additional material, crushed egg shell for instance or Carob tree fruit (we have this one widely available) to make an interesting texture?

There are a lot of things that you can add to your home-made bioplastic during the mixing process, to make it more interesting or more visually appealing.  The thing people use most often is food coloring, to affect the color of the end result. One American designer even used food flavoring, in his BITE ME product: an edible bioplastic lamp!

But you can also add solids, like you were suggesting. If you added something like crushed egg shell, the end result would be called a “composite” – a solid consisting of a binding material (“matrix”) and a fibrous or particulate reinforcement.

One commercial biodegradable plastic that is actually out on the market right now consists of a polymer matrix mixed with calcium carbonate, from crushed limestone. Your crushed egg shell idea is very similar.

As I’m sure you can imagine, there are very many possible combinations, and they would all have to be tested separately (for example, your carob fruit idea). You would probably want to experiment with small batches at first, where you try out different materials, possibly also in different amounts or concentration, to make sure that you get both the texture and visual properties that you want, but that the end result is still strong and hard and will not come apart or crumble.

Please feel free to send us pictures of your final product, with composite egg shells or any other material, and we will add them here to this article as illustration!

Will my bioplastic be dishwasher safe?

Dina, a product design student, wants to use bioplastics for a school project that involves making two products a fruit bowl and a wastebasket. She asks:

How heat resistant is the bioplastic? If I use the gelatin recipe or the algae one, can I make the product dishwasher safe?

First of all, thank you very much for your question! I think home-made bioplastics are exactly the right kind of material for projects like this.  However, I also think that you might have more success using bioplastics for a wastebasket than a fruit bowl. I will explain why.

Bioplastics cast from water solutions are not water resistant and if the water is hot, they are even more vulnerable. Heat resistance is limited. Products made with this method would not be dishwasher safe, both because of the temperature but also because of the water.

Water-proofing coatings have been used to improve water resistance. Shellac, for instance, has been used. But the coating would have to be tested for good bonding to the particular material.

Although a bowl made from home-made bioplastic would probably not be safe to put in a dishwasher, it might survive careful hand-washing in warm water, especially if it has a coating. You would have to test it out, depending on what you used for the base plastic and what kind of coating (e.g. shellac) you used.

Good luck, and happy experimenting!


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