Bio-sourced plastics vs biodegradable plastics

There is a confusion between bio-sourced plastics and biodegradable plastics. Many people think that bio-sourced plastics are biodegradable simply because they originate from plants.

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A typical example is PLA, which comes from corn starch. However, the fact is that bio-sourced plastic is not always biodegradable. For example, bio-sourced PE is non-biodegradable. On the contrary, some fossil-sourced plastic, such as PBAT, is biodegradable.

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Except the polymers made through fermentation (actually made by bacteria, such as PHAs), synthetic polymers are made from monomers (the basic repeating units of the polymer chain) through chemical reactions, also known as polymerisations.

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Monomers can be either fossil-sourced or bio-sourced. No matter where the monomers come from, they are identical both chemically and physically. As a result, the polymers made from the same monomers, regardless of their origins, must be exactly same. In other words, whether the polymers are biodegradable or not is solely determined by their chemical and physical structures, without any relationship to the origin of the monomers.

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Bioplastics, also known as “bio-based plastics”, are commonly defined as the polymers that are either bio-sourced, biodegradable or both. Since “Bioplastic” has a broad meaning in terms of its origin and biodegradability, in order to avoid any confusion it has to specify whether it is bio-sourced and whether it is biodegradable, when this word is used each time.