What is bioplastic?

The term "bioplastics" denotes plastic substances based (in whole or in part) on organic biomass rather than petroleum. Many bioplastics are biodegradable, which in theory is one of their greatest advantages (more on this later). However, some of the common terms in use are confusing; although they sound similar, many of the terms used regarding bioplastics are not interchangeable. The following are three different descriptors.

 

What does bio-based plastic mean? It is a very broad term that basically means that a substance is derived from plant material, either in whole or in part. Starch and cellulose are the two most common renewable raw materials used to make bioplastics. These usually come from corn and sugar cane. Bio-based plastics are distinct from the more common petroleum-based polymers. While many would assume that any "bio-based" is biodegradable, this is not the case.

What does it mean to be a biodegradable plastic? Whether a plastic is biomass-based or petroleum-based is a different question than whether it biodegrades (the process by which microorganisms break down a material if the conditions are right). Technically, all materials are biodegradable, but for practical purposes, only those materials that degrade in a relatively short period of time (usually weeks to months) are considered biodegradable. As mentioned earlier, not all biobased plastics are biodegradable; bioplastics that do not degrade within months or years are sometimes referred to as "durable". Conversely, some petroleum-based plastics degrade faster than their organic biomass counterparts under optimal conditions.

What does it mean to be a compostable plastic? According to ASTM, compostable plastics are those that "are capable of biodegrading in a compost pile as part of an available process so that the plastic is visually indistinguishable and breaks down into carbon dioxide, water, inorganic compounds and biomass (e.g., cellulose) at a rate consistent with that of known compostable materials, and leaves no toxic residue. " The requirement of no toxic residues is one of the distinguishing features between compostable and biodegradable. It is also worth noting that some plastics can be composted in home gardens, while others require commercial composting (the temperature becomes higher and the composting process occurs more quickly).