Biodegradable plastics can be categorized into several major families, which will be discussed following.

PHAs

One of the earliest truly biodegradable non-cellulose-based plastics was polyhydroxybutyrate/valerate (PHBV), a bacterially grown polyester with properties similar to polypropylene. PHBV was first produced commercially by Imperial Chemical Industries (ICI) in Britain, sold under the name Biopol. Since then, other bacterially grown polyesters and copolyesters belonging to the general family of polyhydroxyalkanoates (PHAs) have also been produced. High costs have been an ongoing problem. ICI spun off the Biopol unit to Zeneca, which then sold it to Monsanto. In late 1998, Monsanto decided to discontinue Biopol production and research. Later researchers at the Massachusetts Institute of Technology began to work on PHAs, and Metabolix, a spin-off company from this effort, began commercializing these resins.

Polylactides

Biodegradable plastics based on lactic acid have been available on a small scale for many years. They have been used in applications such as medical implants, but their high price was a deterrent to widespread use in lower value applications such as packaging. However, new technologies for the production of lactide monomers greatly lowered costs, making the polymers much more competitive. Generally, the lactic acid is obtained from corn or other biobased materials by a fermentation process, and then chemical synthesis is used to produce the polymer from the lactic acid or lactide monomers.

Cargill was one of the first companies to develop biodegradable polylactides (PLA) for applications such as packaging. Cargill and Dow Chemical partnered to form Cargill Dow LLC, which began operating a full-scale production facility in Blair, Nebraska, with a capacity of 140,000 metric tons (300 million lbs) per year. Dow is no longer part of the venture. Lactides are produced from cornstarch by fermentation and then converted to PLA through a ring-opening polymerization process. Cargill’s NatureWorks PLA is produced in a variety of grades, including film, sheet for thermoforming, and injection molding resins. It has applications outside packaging, such as fiber for clothing, as well as packaging applications such as food containers, drink cups, blister packs, etc., and related applications such as food service ware. The transparency of the materials is generally excellent. Mechanical and barrier properties depend on the grade.

Other producers of PLA resins and related copolymers have included Mitsui Toatsu, Shimatsu, CornCard International, Chronopol, Dainippon, and Neste Oy, but Cargill is by far the largest producer.

Other polyesters

Polycaprolactone is a synthetic polyester that has been available for a number of years. Union Carbide is the major supplier and sells the resins under the Tone brand name. DuPont sells a family of synthetic biodegradable polyesters under the Biomax name. The degradation mechanism is a combination of microbial action and hydrolysis. Costs are reported to be only marginally higher than PET. Eastman has also developed a synthetic biodegradable and compostable polyester, with properties comparable to low-density polyethylene. Other companies manufacturing biodegradable polyesters include Showa Highpolymer, Bayer, and BASF.

Starch-based plastics

Several companies have developed starch-based plastics. By using carefully selected starch feedstocks, and water as a plasticizer, they produce thermoplastics from nearly 100% starch, or from blends of starch with other biodegradable components. Many of these materials are water-soluble in addition to being biodegradable. The major target application has been as a replacement for polystyrene foam, including both molded cushions and loosefill.

Warner-Lambert was the first major producer of starch-based plastics, which is sold under the Novon name, beginning in about 1990. It discontinued manufacture in 1993 and sold the operation to EcoStar International, which was shortly thereafter acquired by Churchill Technology, which then declared bankruptcy. Other suppliers of biodegradable starch-based plastics include StarchTech Inc. of Minnesota, FP International, Biotec in Germany, Mellita, and Novamont, among others.

Other biodegradable plastics

There are a number of other families of biodegradable plastics, most at an earlier stage of development than those discussed above. Examples include protein-based plastics, polysaccharides, and wood-derived plastics. Two water-soluble plastics have a much longer history.

Polyvinyl alcohol is a synthetic polymer manufactured by Air Products, ChrisCraft, Nippon Gohsei, and Italway, among others. It is biodegradable once it is dissolved in water. A major limitation to its use is that it generally not melts processable unless modified. It is also relatively high in cost.

Polyoxyethylene is another water-soluble plastic that has been known for a number of years but has seen little use. There are conflicting reports about its biodegradability. Mitsubishi is the major supplier.

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