The past, present, and afterlife of biodegradable plastics (middle): the mirror image of biodegradable materials

In addition to the above-mentioned components, plants and animals are also rich in many other organic small molecule compounds. Their structure and performance are exactly the same as those extracted from petroleum. Used to synthesize polymer materials. In order to distinguish it from petroleum-based chemical raw materials, we refer to small organic molecules derived from living organisms as bio-based raw materials.

So using bio-based raw materials to synthesize polymers, can the degradation of plastics be achieved ? That's what everyone thought at the beginning, so synthetic bio-based polymer materials were given a great mission from birth, wearing the degradable "cosmic halo". Thousands of people have studied its degradability day and night and published tens of thousands of papers. As a result, everyone found that this was another scene in the mirror. Most of the polymers synthesized with natural bio-based materials have forgotten where their ancestral graves are. So much corn, soybeans and other grains were wasted in vain, but the glorious degradable traditions of our ancestors did not inherit a little bit of it. Of course, we must also admit that products produced directly from natural bio-based polymers, such as the four-piece Tencel set made of bamboo fiber, have very good performance, especially women's underwear made of tencel , The comfort is very commendable.

Bio-based polymer material is a very important conceptual material. Some of the degradable plastics of are produced with synthetic bio-based polymers, and some are produced with petroleum-based polymers. Having said that, some friends may ask, you said earlier that petroleum-based plastics and synthetic bio-based plastics cannot be degraded.Isn't it a contradiction?

Let’s talk about nature’s biological code first. We all know the four seasons of the year, spring, summer, autumn and winter. In spring, all things begin to recover, and nature is thriving and vigorous; in summer, plants grow the most luxuriant and bloom and bear fruit; autumn is the season when fruits mature and leaves begin to wither; leaves and fruits that fall from the earth will rot in winter , Will turn into spring mud in the spring of the following year, providing sufficient nutrients for the revival of all things. Repeatedly, endlessly.

All plants in nature have a unique genetic code , which is passed on from generation to generation, so we never have to worry that the fallen leaves on the ground will pile up like mountains and destroy the earth. Even tree roots that are difficult to rot will slowly decay under the action of microorganisms until they disappear. The same goes for animals. Except for bones (mainly inorganic substances), other parts will be completely decomposed by bacteria after death.

So natural polymer materials made of cotton, hemp, silk, animal fur, or their extracts, such as cellulose, lignin, chitin, etc. They still remember this code, so they can quickly natural degradation.

However, most of the synthetic bio-based polymer materials, like ordinary plastics, cannot be degraded. For example, two monomers, pentanediamine and adipic acid, the petrochemical raw materials, can be polymerized to prepare nylon 56. This is a petroleum-based polymer material, which is not degradable, but the current chemical preparation method of pentanediamine is still under development. ; If nylon 56 polymer is obtained directly from animals and plants, this is a natural polymer, which is naturally degradable. Unfortunately, this is an assumption, because this polymer does not exist in nature; if it is directly extracted from animals and plants (carcasses or corn) Diamine, use vegetable sugar and vegetable oil to prepare adipic acid, this pentane diamine and adipic acid are bio-based raw materials, and then use them to prepare nylon 56 through the same polymerization method, which is a synthetic bio-based polymer material. However, this synthetic bio-based polymer material forgets who the ancestors are.It does not degrade like nylon 56 polymerized with petroleum-based pentanediamine and adipic acid. That is to say, they are either not assigned the degraded code, or they become silly during the aggregation process and forget the degraded code.

Why should we develop bio-based polymer materials?

The development of bio-based polymer materials is due to the lack of petroleum resources. Everyone is always worried that one day petroleum resources will be exhausted and all the chemical raw materials will be gone by then. You have to prepare in advance. Since there are so many plants in nature that are rich in natural macromolecules, or are rich in raw materials for preparing natural macromolecules, why not directly use them to prepare macromolecular materials to achieve rapid degradation? Natural green environmental protection, how good!

I admit that the original intention is good, but I just don’t like it. They never tell you the truth behind it: most bio-based polymers are derived from trees and food, for example The bamboo and trees used to prepare Tencel not only have requirements for growth time, but also have very high requirements on the place of origin. Generally, they can only be produced from imported bamboo and trees, which are very expensive. The most abominable thing is the eucalyptus used for papermaking. This is a disaster. , Growth rate is fast, water absorption capacity is strong, wherever they go, it can be said that no grass is left. It’s even more troublesome if the biomass component is derived from grain. For example, if you can extract pentylenediamine from corn stalks, it will be waste utilization and be of immense merit, but if you extract it from corn, it will compete with the people for food. It will not allow you to cross the red line of food control and develop arbitrarily. In fact, we now have many bio-based polymers and raw materials that are directly extracted from food. But they will tell you seriously that it is extracted from straw, straw..., it is a real waste utilization and resource recycling. Even if it is food, they will emphasize that it is bought from the neighboring house, such as corn 50 cents per catty, as if the neighboring house’s food is not valuable and inexhaustible.

If a person tells a lie for a long time, he will believe that what he is telling is the truth. If you point out that he is lying, he will be anxious with you and swear by heaven. Therefore, if even the people who set the rules of the game forget the truth, how can ordinary people know the truth?

The most interesting thing is that the concept of bio-based polymer is the same as various nano-lithium batteries hydrogen energy perovskite solar wind energy tidal energy ,Has been played into tricks. Don't think that bio-based polymer materials are all made of natural bio-based polymer materials or synthetic bio-based polymer materials. Some are processed with a mixture of natural polymer materials and petroleum-based polymer materials, and some are processed with polymers synthesized from part of petroleum-based raw materials and part of bio-based raw materials. Later, as long as the content of natural bio-based polymer materials or bio-based raw materials exceeds a certain percentage, such as 10%, this material can be called "bio-based materials" or bio-based modified materials.

Everyone can think about it, even if your natural bio-based components can be quickly and naturally degraded, the remaining petroleum-based components still cannot be degraded. In fact, in order to achieve degradation, countless Chinese people, led by countless foreigners, have almost used all the methods that can be thought of in the world, all kinds of mud, bacteria, biological mold, bought online, and cultivated by themselves. Was played as a flower. The original intention was to realize a great degradation dream, and in the end it became a paper. He even came up with the concept of "pre-control degradation" (good pre-treatment), using photosensitizer blending or grafting starch to achieve degradation. is that useful? Of course it works. The starch is completely degraded, and other polymers seem to be degraded, but this degradation component is uncontrollable, and the harm to nature has been under debate?

But they don't say that. At first, they said that it was completely degraded into carbon dioxide and water. Later, the Internet developed and people became smarter, and found that they were not very good at flickering, so they were said to be completely degraded under certain conditions.

So I specifically turned out the degradable international standards (International Standard Organization, ISO) and national standards (People's Republic of China standard, Guo Jia Biao Zhun, GB). (hereinafter The content comes from the web and has not been modified) .

International standard "ISO 472:2013 Plastics-Vocabulary", "ISO 472:2013/AMD1:2018 Plastics-Vocabulary-Amendment 1: Additional items", national standard "GB/T 2035-2008 Plastic Terms and Definitions", "GB /T 20197-2006 Definition, Classification, Labeling and Degradability Requirements of Degradable Plastics" and "GB/T 32163.2-2015 Eco-design Product Evaluation Specification Part 2: Degradable Plastics" are defined as follows:

1, degradation ：

irreversible process leading to a significant change in the structure of a material, typically characterized by a change of properties (eg integrity, molecular mass or structure, mechanical strength) and/or by fragmentation, affected by environmental conditions, proceeding over a period of time and comprising one or more steps

2, degradable plastic:

plastic designed to undergo a significant change in its chemical structure under specific environmental conditions, resulting in the loss in some properties, as measured by standard test methods appropriate to the plastic and the application, in a given period of time that determines whether the plastic can be classified as biodegradable or not

3. Degradation: Affected by environmental conditions, after a certain period of time and including one or more steps, the structure changes significantly and performance is lost (such as: integrity, relative molecular mass, structure or mechanical strength) the process of.

4. Degradable plastic (degradable plastic): Under specified environmental conditions, after a period of time and containing one or more steps, it will cause significant changes in the chemical structure of the material and loss of certain properties (such as integrity, molecular mass, structure) Or mechanical strength) and/or broken plastic.

The classification of degradable plastics is based on the degradation of degradable plastics:

1. Biodegradable plastic (biodegradable plastic): It is often said that biodegradable plastics.

Biodegradation: Degradation caused by biological activities, especially the significant changes in the chemical structure of materials caused by the action of enzymes. As the material is gradually degraded by microorganisms or certain organisms as a source of nutrients, it causes quality loss, performance such as physical properties, etc., and ultimately causes the material to be decomposed into simpler compounds or elements, such as carbon dioxide (CO2) or/and methane CH4), water (H2O) and mineralized inorganic salts of the elements contained therein, and new biomass.

2. Heat-and/oroxide-degradable plastic (eat-and/oroxide-degradable plastic):

refers to plastic that is degraded by heat and/or oxidation.

3. Photo-degradable plastic:

Degradable plastic caused by natural sunlight.

4. Compostable plastic:

is a kind of plastic that can be degraded and disintegrated under composting conditions due to the biological reaction process, and finally completely decomposed into carbon dioxide, water and its elements The mineralized inorganic salt and the new biomass, and the final compostable heavy metal content, toxicity test, residual debris, etc. should meet the requirements of relevant standards. For details, refer to the standard "GB/T 28206-2011 Technical Requirements for Compostable Plastics".

emphasized that only 1 (biodegradable plastic) and 4 (compostable plastic) can be completely degraded into carbon dioxide and water. What we call degradable plastics is basically degradable under composting conditions.

Let’s take a look at the current biodegradable plastics .Current degradable plastics include polylactic acid (PLA), polycaprolactone (PCL), polybutylene succinate (PBS), polyhydroxyalkanoate (PHA), and succinate adipate Copolymer of alcohol ester and butylene terephthalate (PBAT) . Among them, PLA, PBS and PHA are bio-based degradable plastics, and PCL and PBAT are petroleum-based degradable plastics. Of course, there is also a polyethylene furandiformate (PEF) , which is used to replace polyester to prepare fully degradable cola bottles. There are reports on the Internet that a subsidiary of the Netherlands Avantium has signed a contract with Eastman. The patent license agreement, obtained the right to operate the FDCA related patent portfolio in Eastman, will have products coming out in 2023. In view of the fact that furandicarboxylic acid has been studied all over the world for more than 100 years, this matter needs to be tracked to see the results before making a conclusion.

Among the biodegradable plastics, the greatest and most legendary is PLA, is the first member of the biodegradable plastics family, stood in the pyramid as soon as it was born At the top, the natural degradability is said to be as fast as a cup of tea, that is to say, the cup you use it to pour tea, it is estimated that the tea may be spilled on the ground before it is delivered to the customer. In fact, it is not that its degradation rate is fast, but that its mechanical properties are really bad, and the aging rate is fast under the conditions of light and heating, and the product will be broken when it is gently broken by hand.

degradable plastics need to be printed with a special mark when they are sold : This mark is a circular circle with arrows, double "j" (degradable pinyin initials) Abbreviations (such as PBAT, PLA, PBS, etc.), six types of degradation environment names (optional), national standards and product names are a combination of green smiley pattern ,Its meaning is that through the use of degradable plastics, the goal of completely degrading under corresponding conditions without polluting the environment is finally achieved.

Example of pictorial label:

Label 1: PBAT

>PBAT<>

Mark 2: PLA

>PLA

Mark 3: PBAT/PL blend _strong p18

40 >P2

It’s just that the picture below is that you’re serious, if you believe it, you lose. Dare to say that it is safe to enter the soil, and it will be completely degraded in 4-6 months? Because they see through human nature, knowing that you would not test it like this.