BIODEGRADABLE POLYMERS | BIOPLASTICS


Carmine Di Fiore provides some insight into the complex area of biodegradable polymers


Explaining the basics of biodegradable plastics


The durability of today’s plastics makes them ideal for so many applications, ranging from packaging and hygiene products to automotive parts and building materials. However, that durability can present challenges at end-of-life with careless disposal and poor waste management resulting in the accumulation of plastics in the environment. Biodegradable polymers, both synthetic and natural, are often presented as the sustainable alternative. However, there is confusion — at both consumer and industry level — around what these materials are and what environmental benefits they offer. Biodegradation of plastics, as for any material, occurs through the action of enzymes and/or living organisms. It is a two-step process: first the polymer is converted to lower molecular mass species by abiotic reactions such as oxidation, photodegradation or hydrolysis; then the polymer fragments are bio-assimilated and mineralised by micro-organisms. The biodegradability of a polymer depends on its chemical structure and environmental condi- tions, not on its origin. Essentially, the polymer


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must contain one or more hydrolysable elements — such as an ester, amide, or urethane group in its main chain. Chemical composition — together with production, storage, processing, aging and environmental exposure — also determines mechanical characteristics. Most of the main biodegradable polymers available today include an ester group on the main polymer chain. Polyhydroxyalkanoates (PHA) are thermoplas- tic polymers synthesised by various bacteria — Ba- cillus, Rhodococcus, Pseudomonas, etc — through fermentation of sugars or lipids under particular cultivation conditions, such as the absence of certain nutrients. The PHA polymer accumulates in the form of granules inside the bacterium itself and can compose up to 90% of the dry weight of the bacterial mass. The products are 100% biodegradable and


produced from 100% renewable sources. PHA is characterised by considerable variation in the length of side and main chains so it displays quite variable physical and chemical properties. Melting points range between 40-180°C.


Main image: Polylactic acid polymer — this image shows Natureworks’ Ingeo pellets — is perhaps the best known and most widely-used biodegradable plastic


� September 2021 | COMPOUNDING WORLD 41


IMAGE: NATUREWORKS


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