Firstly, we could define what a polymer is. It is a molecule with a high molecular mass, made up with monomers linked with covalent bondings. They are mainly organic molecules. "Biopolymers" refer to a kind of polymers obtained with only natural and renewable resources, and not toxic to produce. Starch*, found in many vegetables, is one of them.

They can be produced by biological systems (such as micro-organisms, plants and animals), or chemically synthesized from biological starting materials (like sugars, starch, natural fats or oils).

Biopolymers are an alternative to petroleum-based polymers which are the most marketed plastics nowadays. Biopolymers are also, for the current time, more expensive then 'classic" plastics.

Now, we will present the most common biodegradable plastics which are biopolymers (Careful: not all such called "bioplastics" are biodegradable, and some petroleum-based plastics are).

It is a biodegradable plastic derived from lactic acid. This acid can be obtained using starch from corn, wheat or sugar beat. It is widely used in the whole world.

Its decomposition is complete in 3 or 4 weeks in a proper compost system. It is insoluble in water, and does not support heat.

It looks like clear polystyrene, but it needs to be modified for nearly every of its application (especially to increase its flexibility). We can use it to make compost bags, plant pots and packaging. It also can be used for medical purpose, as it degrades itself in the body.

This photo shows biodegradable plastic cups made in PLA in a restaurant.

This plastic is like an enhanced version of PLA. It is a mixture of lactide and aliphatic polyesters. It can be either a hard plastic or a soft flexible one depending on the amount of aliphatic polyester present in the mixture.  CPLA is made by fermenting cornstarch or cheese whey and mixing it with aliphatic polyester, made from fermentation of glycerol*. All are renewable resources.

Its principal feature is that, unlike PLA, this plastic supports heat up to 200°C. Its complete decomposition occurs after 12 months in a natural environment.

This photo shows some cutlery made in CPLA found on the biofutura website.

Plastarch Material is a biodegradable, thermoplastic resin. It is composed of starch combined with several other biodegradable materials. It has the same properties as PLA, except that it is resistant to heats up to 120°C. It is widely used to make food packaging, ustensils or plastic bags.

Below, here is an example of cutlery made in PSM.

Indeed, all those plastics are made in industrially with a very complex process which we cannot reproduce by our own means. 

Here is a diagram from Toyota corporation explaining the whole process of making PLA.

Recipes for making this type of plastic can be found easily on internet. We found a protocol made by the Dijon academy which seemed reliable to us.

The concept is to use starch to make a biopolymer, to add water to it, and glycerol in order to obtain a certain flexibility and to make the plastic more resistant. Glycerol is a "plasticizer", making the mobility between molecules easier. Moreover, it gives a specific texture to the transparent matter. This will be our basic recipe around which we will experiment.

Notice: We chose not to include in our recipe any unnatural/toxic ingredient, in order to have the most simple and safe plastic. It is eatable, and not toxic for humans.

Equipment list :
 
- 100 mL beakers
- Heater
- Pipette and propipette
- Graduated cylinder
- Potato starch
- 50% glycerol solution
- Distilled water
- Food coloring
- Balance
- Pan and whisk
- Glass stirrer
- Spatula
- Cup
- Ceramic plate

Protocol:

- Put 100 mL of water in a pan.
- Add 2 mL of glycerin and stir with the whisk.
- Next, gradually add 5 g of potato starch while continuing to stir, adding food coloring (optional).
- Heat this mixture until it becomes translucent. When it becomes translucent , continue to heat over low heat while stirring for 10 minutes.
- Pour this mixture (still warm and liquid) on a plastic support (or glass) on which it can easily peel off by spreading a thin layer on its surface.
- Make the plastic dry at room temperature for about a week.
- Once dry, the plastic can be taken off.

http://padlet.com/CillyKarma/prodfin1S2

http://padlet.com/CillyKarma/prodfin1S2part2

Enjoy your reading!