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What is biodegradable polymer?

In our daily life, we are exposed to more and more degradable and recyclable products, in the promotion of these products, a phrase is repeatedly mentioned, "made from biodegradable polymers", so, what is "polymer" ", what is "biodegradable"?

polymer, any of a class of natural or synthetic substances composed of very large molecules, called macromolecules, that are multiples of simpler chemical units called monomers. Polymers make up many of the materials in living organisms, for example, proteins, cellulose, and nucleic acids. Moreover, they constitute the basis of such minerals as diamond, quartz, and feldspar and such man-made materials as concrete, glass, paper, plastics, and rubbers.

"Plastic", you may have noticed that in the definition of polymer, the word "plastic" is mentioned, in fact, all plastics are polymers, whether it is hand guard on your hammer, or the Shopping bags brought back from the supermarket, they are all plastic, In fact, plastic is the most common type of human creation, your house is full of plastic, half of your car is made of plastic, the clothes you wear contain plastic, And your shoes, at least the soles are made of plastic, one can say we live in a pile of plastic.

What if, I mean, What if so much plastic turns out to be harmful? It's very sad that plastic has proven to be bad for the environment, it turns out, at least until the 1970s, plastic is quite harmful, it pollutes oceans and land, it causes biological harm and species extinction, so, Why didn't plastic hurt that much by the 1970s?

"Biodegradable" is a technology proposed to solve the problem of plastic pollution. It refers to a certain polymer that can be degraded into harmless gases or solids(carbon dioxide, water, or other ingredients) at a specific time by specific methods such as sunlight, oxygen, and microorganisms.Yes, the technology was mature and applied in the 70s.

Now we can talk about what a "biodegradable polymer" actually is.

Biodegradable polymers can be divided into two categories: natural and synthetic. Natural degradable polymers include starch, cellulose, polysaccharide, chitin, chitosan and its derivatives; synthetic degradable polymers are divided into two categories: artificial and bacterial synthesis. Alkyl alcohol esters (PHAs), poly (malate), synthetic degradable polymers include poly base esters, polycaprolactone (PCL), polycyanoacrylate (PACA) and so on.

We now know that a large part of "polymer" is plastic or the raw materials used to make plastic. Therefore, you can simply understand that "biodegradable polymer" refers to biodegradable plastic. Of course, this generalization Not completely accurate, for example "paper" is a typical biodegradable polymer, but it is not plastic.

According to the source of raw materials, biodegradable plastics can be divided into two categories: bio-based biodegradable plastics and petrochemical-based biodegradable plastics.

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.

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.

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).

If we explore further, the common synthetic and large-scale applied biodegradable polymers are as follows:

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)

A new type of biodegradable material made from starch raw materials proposed by renewable plant resources such as corn. It has good biodegradability and can be completely degraded by microorganisms in nature after use, and finally generates carbon dioxide and water, which does not pollute the environment, which is very beneficial to protect the environment and is recognized as an environmentally friendly material.

Polyhydroxyalkanoate (PHA)

The biodegradable plastic obtained from renewable resources is mixed with aliphatic polyester and starch. It can be degraded in various ways. For example, in the soil environment, a 1 mm film can be completely degraded and disappeared within 6 weeks.

Polyvinyl Alcohol (PVA)

It is a synthetic polymer, starch is added to PVA, and the film-forming property of PVA is used to make plastic products. It can be degraded by water and biological degradation, and finally degraded into CO2 and H2O

Due to the high production cost of natural biodegradable polymers, the current application scenarios are relatively small, and they are mainly used in the medical industry. The common ones are as follows: chitin, polyamide, polyaspartic acid, polysaccharide, cellulose, etc.

Now there are quite a few categories of daily necessities made of biodegradable plastics, including but not limited to disposable tableware, garbage bags, compost bags, thermal insulation mulch, mobile phone cases, sport shoes, buckets, kitchenware, toys, diapers using superabsorbent polymers, toothbrushes, Cosmetics, shampoo, condoms, etc. Maybe the next time you go shopping, you can take a look at the ingredient list and let's make a personal contribution to protecting the environment.

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