There are three different types of plastic: conventional plastics, biodegradable plastics and bioplastics.
Conventional plastics are made from petroleum-based products derived from oil and take hundreds of years to break down.
Biodegradable plastics are made of similar materials to conventional plastics with the addition of some chemicals that make the plastic more likely to decompose when exposed to water and light.
Bioplastics are made from natural materials such as corn starch. For example, the company NatureWorks uses Polylactide acid (PLA) to manufacture their bioplastics, because it looks and behaves like polyethylene and polypropylene (two polymers commonly used to produce plastics) but they claim it saves two-thirds of the energy that would be used to make traditional plastics.
Although biodegradable and bioplastics seem like a good alternative to conventional plastics, this is not always the case.
Some biodegradable plastics can be composted, but many require specialist facilities to break them down. Many also contain a manganese additive that prevents them from breaking down when in compost. Of the kinds that can be composted, many leave a chemical residue in the soil or release large quantities of greenhouse gases like methane or carbon dioxide. Some biodegradable plastics fragment rather than break down, leaving small pieces of plastic in the soil, which can also be harmful. Biodegradable plastics will never break down in landfill, as they require generally require water or light to decompose, so they are only effective if properly disposed of. It is usually ok to put them in food waste bins for collection, but this facility is not available in many areas and is often unknown.
Bioplastics are generally better than biodegradable plastics, although they are not ideal. Ones made from starch are common but not suitable for all uses, as they often break down when wet. The environmental impact of growing crops like maize just to produce plastic must also be considered as this land could be used to grow food.
Traditional plastics are not quite as bad as they may seem. Many petrochemicals used to make them are a by-product of the oil refining process, and while we are so dependent on oil, it seems less wasteful to use these. Good recycling facilities for these plastics are also more widely available and well-known.
I am not advocating the use of single-use plastics, but biodegradable and bioplastics are not perfect either! The best solution is to reduce our use of plastics altogether, and to improve education on ‘environmentally-friendly’ plastics.