Biodegradable polyesters include a range of microbiologically produced polymers with tuneable mechanical and physical properties, as well as petrochemical polymers produced by conventional methods. Suitable for packaging, product, medical and textile applications, they have gained a lot of interest as potentially more sustainable alternatives to non-biodegradable plastic. There are a growing number of commercially available solutions, especially in packaging. For example, Tipa packaging films are based on a mix of bio-based and petroleum based compostable plastic. The quantity of bio-based ingredients ranges from 20-80% depending on the requirements of the application. They are certified compostable, but not always at home.

End of life is a very important consideration for biodegradable plastics. If they end up in landfill, deprived of oxygen, they may release methane, which is much more harmful than carbon dioxide emissions.

The most common biodegradable polyester is polylactic acid (PLA), which makes up nearly half of all bioplastic production. Like several biodegradable polyesters it is derived from the fermentation of renewable biomaterials such as sugar cane and maize. It is relatively strong and rigid and has good processing characteristics using conventional mass-production techniques. Degradation is slow under normal conditions. However, at elevated temperatures (>60 degC) and humidity the process is quite rapid. First of all, the polymer chains are reduced by hydrolysis, and then completely broken down by microorganisms.

To be certified as compostable, the product must breakdown into water, CO2 and biomass at a rate consistent with other biomaterials. Also, there must be no negative chemical effects on the final compost, which is ensured through eco-toxicity testing. To achieve this target, biodegradable polyesters tend to be limited to parts less than 1 mm thick, which mainly consists of packaging films, thin-wall containers and single-use cutlery. Parts with thicker wall sections, like injection moulded, thermoformed and blow moulded packaging, take longer to biodegrade even in industrial composting conditions. So for example, while a thin-walled deli pot may breakdown within a month or so, a blow moulded bottle may still leave residue after 30 days and take longer than the permissible time to fully compost, even at 60 degC. This means that products intended to have a longer shelf life may not be able to be packaged in certified compostable materials. Because while the material is biodegradable, it is not certified compostable due to the length of time taken to breakdown at the wall thickness required for the application.

Purely aliphatic polyesters, characterised by a straight or branched polymer structure, have the best biodegradable properties. The ester bonds are particularly susceptible to hydrolysis (water can break the bond). However, these plastics are have relatively poor mechanical properties. Plastics with an aromatic structure (closed rings of atoms) have improved resistance to heat, chemicals and water. The properties depend on the proportion of aromatic to aliphatic content. Typical thermoplastic polyesters, such as PET and PBT, which have an aliphatic-aromatic structure, have excellent chemical resistance including high resistance to water, which makes them non-biodegradable. By adjusting the proportion of aliphatic to aromatic content, a balance can be met between biodegradability and suitable properties for a range of applications. For demanding situations, such as water and oil contact at 100 degC, it may not be 100% bio-based, but blended with oil-based plastic to enhance performance while maintaining biodegradability.

These materials are often combined with natural fillers, such as wood fibre, wood powder, agricultural by-products, kenaf and hemp. The use of fillers reduces the price of the material and helps with mechanical properties. Other waste products may also be suitable as filler to reduce cost, even if they do not contribute to improvements in properties, such as coffee grounds, cork powder, crushed nut shells and cereal grain.

The source of biomass is critical, because the impact of growing the crops may outweigh the benefits, such as deforestation, monoculture crops, genetic modification (GM), petroleum-powered machinery, transportation and shipping, and displacing food production.