Biodegradable plastic

A biodegradable plastic is a plastic designed so that it can be broken down by microorganisms such as bacteria and fungi. Because it decays instead of piling up, it reduces the build-up of plastic waste. Malay: plastik terbiodegradasi · Chinese: 可生物降解塑料.

Ordinary synthetic plastics are non-biodegradable, so scientists design biodegradable plastics with structures that microorganisms can attack, for example by building in groups that soil microbes can break, or by basing the plastic on natural materials such as starch. When such a plastic is thrown away, microorganisms digest it over time into simpler, harmless substances, so it does not linger in the environment. Biodegradable plastics are one of several responses to the plastic-waste problem, alongside photodegradable plastics that break down in sunlight, and the practices of reducing, reusing and recycling.

Example. A biodegradable food container made partly from starch will be broken down by microorganisms in soil after it is discarded, unlike an ordinary polythene container, which would remain intact for a very long time.

Confusion to avoid. Do not confuse biodegradable with photodegradable. A biodegradable plastic is broken down by microorganisms, while a photodegradable plastic is broken down by light, especially sunlight. Both reduce waste, but by different agents, living organisms in one case, light energy in the other. Also remember that “biodegradable” is the opposite of “non-biodegradable”.

When you evaluate biodegradable plastics in an answer, note both sides: they cut down long-lasting waste, but they can cost more to produce, may need particular conditions to break down, and are not a reason to use more plastic overall. Balancing the benefit against the limitations is exactly what the extended-response mark scheme rewards.

Biodegradable plastics are part of the solutions section of the chapter, so they connect the problem of non-biodegradable waste to the responses that SPM Chemistry asks you to suggest and evaluate.