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Is it possible to manufacture biodegradable plastic?

In fact, we not only already have the production technology of biodegradable plastics, but also the research and development process of this technology has a long history.

Polyhydroxyalkanoate (PHA) was first observed in bacteria in 1888 by Martinus Beijerinck. In 1926, French microbiologist Maurice Lemoigne chemically identified the polymer after extracting it from Bacillus megaterium. It was not until the early 1960s that the groundwork for scaled production was laid. Several patents for the production and isolation of PHB, the simplest PHA, were administered to W.R. Grace & Co., but as a result of low yields, tainted product and high extraction costs, the operation was dissolved. When OPEC halted oil exports to the US to boost global oil prices in 1973, more plastic and chemical companies began making significant investment in the biosynthesis of sustainable plastics. As a result, Imperial Chemical Industries (ICI UK) successfully produced PHB at a yield of 70% using the strain Alcaligenes latus. The specific PHA produced in this instance was a scl-PHA. Production efforts slowed dramatically due to the undesirable properties of the PHA produced and the diminishing threat of rising oil prices soon thereafter.

In 1983, ICI received venture capital funding and founded Marlborough Biopolymers to manufacture the first broad-application biodegradable plastic, PHBV, named Biopol. Biopol is a copolymer composed of PHB and PHV, but was still too costly to produce to disrupt the market. In 1996, Monsanto discovered a method of producing one of the two polymers in plants and acquired Biopol from Zeneca, a spinout of ICI, as a result of the potential for cheaper production.

As a result of the steep increase in oil prices in the early 2000s (to nearly $140/barrel US$ in 2008), the plastic-production industry finally sought to implement these alternatives to petroleum-based plastics. Since then, countless alternatives, produced chemically or by other bacteria, plants, seaweed and plant waste have sprung up as solutions. Geopolitical factors also impact their use.

After decades of development, biodegradable plastics have now developed into a large family, which contains hundreds of plastic products such as films, bags, bottles, etc.

Basically, all biodegradable plastics are divided into two categories.

One is bio-based plastics: the raw materials of the products are derived from biomass resources (such as plant fibers, starch, etc.).

One is petrochemical-based plastics: the raw materials of the products are derived from petrochemical resources such as oil and natural gas.

Bio-based biodegradable plastics can be mainly divided into four categories: the first category is plastics directly processed from natural materials; the second category is polymers obtained by microbial fermentation and chemical synthesis; the third category is polymers directly synthesized by microorganisms The fourth category is the biodegradable plastics obtained by blending the above materials or by blending these materials with other chemically synthesized biodegradable plastics.

Petrochemical-based biodegradable plastics refer to plastics obtained by polymerizing petrochemical monomers by chemical synthesis, such as PBAT, polybutylene succinate (PBS), carbon dioxide copolymer (PPC), etc.

It should be noted that whether plastic is biodegradable or not has nothing to do with which raw material the plastic is made of. Not all bio-based plastics are biodegradable plastics, and bio-based plastics are also non-degradable.

According to the classification of biodegradation process, biodegradable plastics can be divided into two types: completely biodegradable plastics and destructive biodegradable plastics. Destructive biodegradable plastics currently mainly include starch modified (or filled) polyethylene PE, polypropylene PP, polyvinyl chloride PVC, polystyrene PS, etc.

Completely biodegradable plastics are mainly made from natural polymers (such as starch, cellulose, chitin) or agricultural and sideline products through microbial fermentation or synthesis of biodegradable polymers, such as thermoplastic starch plastics, aliphatic polyesters, polylactic acid , starch/polyvinyl alcohol, etc. belong to this type of plastic.

Biodegradable plastics based on natural substances such as starch currently mainly include the following products: polylactic acid (PLA), polyhydroxyalkanoate (PHA), starch plastics, bioengineering plastics, bio-universal plastics (polyolefin and polychlorinated ethylene) .

Depending on the raw material, common biodegradable plastics are at least the following:

Polycaprolactone (PCL)

This plastic has good biodegradability with a melting point of 62°C. Microorganisms that decompose it are widely distributed under festive or anaerobic conditions. As a biodegradable material, it can be mixed with starch, cellulose materials, or polymerized with lactic acid.

Polybutylene succinate (PBS) and its copolymers

The technology of manufacturing various high molecular weight polyesters based on PBS (melting point is 114°C) has reached the level of industrial production.

Polylactic acid (PLA)

The American company Natureworks has done active and effective work in improving the production process of polylactic acid, and has developed the production of polylactic acid by fermenting glucose from corn, with an annual production capacity of 14,000 tons. Japan's UNITIKA company has developed and produced many kinds of products, among which canvas, trays, tableware, etc. are widely used in the Aichi World Expo in Japan.

Polyhydroxyalkanoate (PHA)

Using biodegradable plastics obtained from renewable resources, aliphatic polyester and starch are mixed together, and the technology of producing degradable plastics has also been successfully studied.

Aliphatic Aromatic Copolyester

The aliphatic aromatic random copolyester (Ecoflex) manufactured by German BASF company, its monomers are: adipic acid, terephthalic acid, 1,4-butanediol.

Polyvinyl alcohol (PVA) biodegradable plastic

Adding PVA to starch, it can blow film and process other products. Polyvinyl alcohol materials have good biodegradability after certain modification.

Poly-β-hydroxybutyrate (PHB) & PHBV

It is a kind of biological material produced by using starch as raw material and using fermentation engineering technology. is a biopolyester that is produced by bacteria, digested by bacteria, and completely decomposed into carbon dioxide, water and biomass under soil or composting conditions.

Others such as chitin, polyamide, polyaspartic acid, polysaccharide, cellulose, etc. are under research and development.

From a worldwide perspective, PHB and PHBV are recognized as one of the most promising biodegradable plastics, and are also new products under development.

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