A quick overview of some important (and highly confusing!) terms:
“Bioplastic” is a confusing term that can refer to bio-based, biodegradable, and/or compostable plastic.
Bio-based plastic = partly or entirely made from plants (e.g. corn or potato starch), but often still contains fossil fuels. Functionally or even chemically identical to conventional plastic. They can be non-biodegradable or biodegradable.
Biodegradable plastic = under certain conditions, these plastics can be broken down by microorganisms into water, carbon dioxide, and naturally occurring materials in various time frames. Made from biological materials, fossil fuels, or both.
Different biodegradable plastics require different conditions and take different time frames to biodegrade. Therefore claiming biodegradability without outlining the conditions it requires and the time-frame is greenwashing and may led to more littering, as people believe they'll breakdown in the open environment. In fact, California has criminalised the use of misleading terms like “biodegradable” or “degradable" on plastic products due to their ambiguity. Also many studies show they do not biodegrade in real world environments and can contribute to microplastics.
Compostable plastic = a subset of biodegradable plastic that only biodegrades in the specific conditions of an industrial composting facility or home compost heap within 3-6 months. Made from biological materials, fossil fuels, or both. Does not breakdown in open environment and therefore can contribute to microplastics (same as other biodegradable plastics).
So all compostable plastic is biodegradable' but not all biodegradable plastic is compostable.... (don't worry, you're not the only one with a sore head!).
Degradable plastic = degradable simply means to 'breakdown'. So everything is degradable, even conventional plastic! Indeed many degradable poo bags are simply plastic bags but described as degradable as greenwashing. There's no guarantee how long degradable products will take to breakdown and there are no independent standards or certifications to verify or prove claims of 'degradability' and they likely contribute to microplastics. Can be made from fossil fuels, plants, or both.
Oxo-degradable plastic = fossil fuel based plastic with certain additives that allow it to fragment into microplastics in the presence of UV light.
Often used interchangeably with oxo-biodegradable plastic = a fossil fuel based plastic that supposedly biodegrades in the presence of UV light into harmless biomass, water and CO2. Both types of 'oxo' plastics have been banned in the EU.
The above 'Oxo'-plastics are very controversial. The claims of oxo-biodegradability have been widely disputed by the EU and wider scientific community, with many people arguing they don't truly biodegrade but fragment into microplastics. Both are currently banned in the EU. More research is needed to understand the true implications and uses of this type of plastic.