Biodegradable material is the chemical breakdown of materials by a physiological environment. The term is often used in relation to ecology, waste management and environmental remediation (bioremediation). Organic material can be degraded aerobically with oxygen, or anaerobically, without oxygen. A term related to biodegradation is biomineralisation, in which organic matter is converted into minerals. Biosurfactant, an extracellular surfactant secreted by microorganisms, enhances the biodegradation process.

Biodegradable matter is generally organic material such as plant and animal matter and other substances originating from living organisms, or artificial materials that are similar enough to plant and animal matter to be put to use by microorganisms. Some microorganisms have the astonishing, naturally occurring, microbial catabolic diversity to degrade, transform or accumulate a huge range of compounds including hydrocarbons (e.g. oil), polychlorinated biphenyls (PCBs), polyaromatic hydrocarbons (PAHs), pharmaceutical substances, radionuclides and metals. Major methodological breakthroughs in microbial biodegradation have enabled detailed genomic, metagenomic, proteomic, bioinformatic and other high-throughput analyses of environmentally relevant microorganisms providing unprecedented insights into key biodegradative pathways and the ability of microorganisms to adapt to changing environmental conditions.

In the past five years, a broad range of synthetic biodegradable resins based on aliphatic polyesters and aliphatic-aromatic copolyesters have been commercialized by global suppliers. Demand for biodegradable polyesters is said to be growing by about 30%/yr, though from a relatively small base, and North America is belatedly catching up with other regions in finding packaging applications for biodegradable material.

Synthetic biodegradable polyesters are made in modified PET polymerization facilities from petrochemical feedstocks. Unlike other petrochemical-based polymers that take centuries to degrade after disposal, these polyesters break down rapidly to CO2 and water in appropriate conditions where they are exposed to the combined attack of water and microbes. These products meet U.S., European, and Japanese composting standards, typically breaking down in 12 weeks under aerobic conditions.

Synthetic biodegradable polyesters fall into two broad categories. One is highly amorphous, imparting flexibility and clarity comparable to a conventional LDPE copolymer. A second group of semicrystalline polyesters is more rigid, with properties similar to PET, PP, or PS.

There are also biodegradable polymers that fall loosely within the definition of polyesters. However, these resins—Cargill Dow’s polylactic acid (see PT, March ’02, p. 50) and Novamont’s thermoplastic starch-based polymer—are true biopolymers obtained from renewable (plant-derived) resources.

Cost is a stumbling block for synthetic biodegradable polyesters, whose densities are in the range of 1.22 to 1.35 g/cc and prices run $1.50 to $2.00/lb. That puts them at a disadvantage relative to paper, LDPE, PP, PS, and PET. Initially, suppliers hoped that degradable polyesters would gain value from the rise of compostable material, avoidance of disposal taxes, and the marketability of “green” packaging. The benefit of low-cost disposal has paid off in some film markets. But in North America, the infrastructure for sorting and composting organic waste is developing far more slowly than had been anticipated, and the value of being “green” is often trumped by higher cost.