Steps in Making Biodegradable Plastic

Fermentation and Polymerization

In the production process of the starch-based plastic, PLA, or polylactic acid, corn is milled to separate the starch; the starch is then broken down into sugars, which are fermented by microorganisms to produce lactic acid. Through condensation, lactic acid becomes a lactide, which is then polymerized, or made into the long chains characteristic of plastic. Alternately, in the case of fermentation where bacteria produce polymers directly, there may be no need for an extra polymerization step. The final product can then be used for packaging material, tableware and potted plant containers.

In a different type of manufacturing process to produce biodegradable plastic, polymers such as poly-B-hydroxyalkanoate (PHA) and poly-B-hydroxybutyrate (PHB) are created inside certain types of bacteria, which produce the polymers in response to emergency situations as a reserve source of energy. Scientists can induce the bacteria to create PHAs under different conditions. During this type of polymerization, producers can customize the properties of the polymer by changing the substrate on which it is grown to make a stronger plastic, or one with a different proportion of polymers.

Strides in genetic engineering are allowing plants to create bioplastic. Scientists isolate the gene that codes for the enzyme that bacteria need to produce plastic. They then place this gene inside the plant, which then produces plastic as part of its normal activities. The plants are treated with a solvent to extract the plastic and the result is distilled to eliminate the solvent.

Rather than making bioplastics "from scratch," a technology has been developed that takes regular plastic such as polyethylene, polypropylene and polystyrene resins and includes a chemical additive to assist in their degradation. The advantages of the plastic are retained, while at the same time the plastic can now decompose by several orders of magnitude. Manufacturers suspend the additive, which contains a catalyst that hastens the oxidative degradation of plastics, in a polymeric matrix. After this, it is added to standard plastic resin at a specified percentage, depending on the intended use of the plastic.