Bioplastics are increasingly seen as a viable alternative to fossil fuel-based virgin plastics and are a vital tool to deliver more sustainable plastic end-use applications. Important terms to understand in the sustainability lexicon are recyclable, biodegradable and compostable:
A recyclable item can be reused and converted into new materials and items/parts instead of being dumped into a landfill.
A biodegradable item will break down in the natural environment into carbon dioxide, biomass and water within a reasonable time.
A compostable item will biodegrade and leave no toxicity in the soil. In addition, it releases valuable nutrients into the soil and degrades within three to six months in an industrial composting facility.
Important distinctions and facts surrounding bioplastics help clarify the differences between these categories. First, bio-based plastics are made wholly or partially from renewable biological resources. For example, sugar cane is processed to produce ethylene, which can then be used to manufacture polyethylene. “Bio-based” means it is sourced from organic renewable materials but does not mean it is biodegradable. An example is polyethylene furanoate (PEF), which is 100% bio-based but not biodegradable.
Biodegradable does not mean compostable. Composting refers to a set environment and time in which a material will biodegrade. A material that biodegrades may not be compostable. Recyclers resist biodegradable and compostable materials for fear of contamination of high-valued streams such as PET. Biodegradable and compostable materials require consumer education to succeed and avoid contamination of composting facilities.
Bioplastics finding commercial success today include PLA, polyhydroxyalkanoate (PHA) and cellulose acetate (CA). PLA is a thermoplastic aliphatic polyester derived from renewable resources, such as corn starch, tapioca roots, chips, starch and sugarcane. PLA is one of the world’s most widely used bioplastic. However, the name “poly (lactic acid)” does not comply with IUPAC standard nomenclature. In addition, it is potentially ambiguous or confusing because PLA is not a polyacid (polyelectrolyte) but a polyester.
PHAs are polyesters that are produced in nature by numerous microorganisms. This conversion can occur through the bacterial fermentation process of sugar or lipids. When produced by bacteria, these materials serve as a source of energy and a carbon store. More than 150 different monomers can be combined within this family to create materials with significantly different properties. In addition, these plastics are biodegradable and used in the production of bioplastics.
Finally, CAs are bioplastics consisting of cellulose esters (including CA and nitrocellulose) and their derivatives, including celluloid. Cellulose can become thermoplastic when extensively modified. An example is CA, which is expensive and rarely used for packaging. However, cellulosic fibers added to starches can improve mechanical properties and gas permeability while enhancing water resistance by being less hydrophilic than starch.