Abstract: At present, the production and use of polymer materials in China have jumped to the forefront of the world, producing millions of tons of waste every year. Therefore, many polymers urgently need to be biodegradable to reduce the pollution to human beings and the environment. This paper discusses the development and application of biodegradable polymer materials at present.
[Keywords:] biodegradable polymer materials
At present, the production and use of polymer materials in China have jumped to the forefront of the world, producing millions of tons of waste every year. Therefore, many polymers urgently need to be biodegradable to reduce the pollution to human beings and the environment. Biodegradable materials refer to materials that can be completely degraded into low molecular weight under the action of natural microorganisms, such as bacteria, molds and algae. This material is convenient to store, as long as it is kept dry, it does not need to be protected from light, and it is widely used, and can be used in plastic films, packaging bags, medicines and other fields. There are three mechanisms of biodegradation: the growth of biological cells causes mechanical destruction of substances; Microorganisms act on polymers to produce new substances; The direct action of enzymes, that is, microorganisms erode the polymer, leading to cracking. According to the above mechanism, several main biodegradable polymer materials currently studied are introduced as follows.
1, the concept and degradation mechanism of biodegradable polymer materials
Biodegradable polymer materials refer to polymer materials that can be degraded by microorganisms or their secretions under certain conditions and within a certain period of time under the action of enzymes or chemical decomposition.
There are three mechanisms of biodegradation: the growth of biological cells causes mechanical destruction of substances; Microorganisms act on polymers to produce new substances; The direct action of enzymes, that is, microorganisms erode the polymer, leading to cracking. It is generally believed that the biodegradation of polymer materials goes through two processes. Firstly, microorganisms secrete hydrolases in vitro to combine with the surface of the material, and the polymer chain is cut off by hydrolysis to generate small molecular weight compounds with molecular weight less than 500; Then, the degradation products are ingested by microorganisms, and through various metabolic pathways, they are synthesized into microbial substances or converted into energy of microbial activities, and finally converted into water and carbon dioxide.
Therefore, biodegradation is not a single mechanism, but a complex physical and chemical process in which biophysics and biochemistry cooperate and promote each other. So far, the mechanism of biodegradation has not been fully clarified. In addition to biodegradation, the degradation of polymer materials in vivo is also described as biological absorption, biological erosion and biological degradation. The degradation of biodegradable polymer materials is not only related to the properties of the materials themselves, but also related to the external environment such as temperature, enzymes, PH value and microorganisms.
2. Types of biodegradable polymer materials
According to the source, biodegradable polymer materials can be divided into natural polymers and synthetic polymers. According to the classification of uses, biodegradable polymer materials can be divided into medical and non-medical categories. According to the synthesis method, it can be divided into the following categories.
2. 1 microbial yield
Polymers synthesized by microorganisms. This kind of polymer mainly includes microbial polyester and microbial polysaccharide, which is biodegradable and can be used to make biodegradable plastics that do not pollute the environment. Such as "Biopol" products produced by ICI company in the UK.
2.2 Synthetic polymer types
Aliphatic polyester has good biodegradability. But its melting point is low, its strength and heat resistance are poor, so it can't be used. Aromatic polyester (PET) and polyamide are engineering plastics with high application value because of their high melting point and good strength, but they are not biodegradable. Aliphatic and aromatic polyesters (or polyamides) are made into polymers with certain structures, which have good properties and certain biodegradability.
2.3 Natural polymer types
Cellulose, chitin and lignin existing in nature belong to degradable natural polymers and can be completely degraded by microorganisms. However, due to the insufficient physical properties of cellulose, the water resistance and strength of the membrane made of cellulose alone can not meet the requirements. Therefore, most of them are mixed with other polymers, such as chitosan. 2.4 Mixed types
In non-biodegradable polymer materials, a certain amount of biodegradable polymer compounds are mixed, which makes the products have considerable biodegradability, which makes the blended biodegradable polymer materials, but this material is not completely biodegradable.
3. Development of biodegradable polymer materials.
3. 1 Traditional methods for developing biodegradable polymer materials
Traditional methods to develop biodegradable polymer materials include modification of natural polymers, chemical synthesis and microbial fermentation.
3. 1. 1 Modification method of natural polymer
Through chemical modification and * * * mixing, a large number of polysaccharide polymers existing in nature, such as starch, cellulose, chitin and other biodegradable natural polymers can be modified to synthesize biodegradable polymer materials. Although this method has sufficient raw materials, it is generally not easy to form and process, and its output is small, which limits their application.
3. 1.2 chemical synthesis method
By simulating the chemical structure of natural polymers, polymers containing ester groups, amide groups and peptide groups in molecular chains were prepared from simple small molecules. These polymer compounds contain biodegradable chemical structures or biodegradable fragments embedded in polymer chains. Chemical synthesis method has harsh reaction conditions, many by-products, complex process and high cost.
3. 1.3 Microbial fermentation method
Many organisms can use some organic substances as carbon sources to secrete polyester or polysaccharide polymers through metabolism. However, it is difficult to separate synthetic products by microbial fermentation, and there are still some by-products.
3.2 A new method to develop biodegradable polymer materials-enzymatic synthesis
Enzymatic synthesis of biodegradable polymer materials, thanks to the development of non-aqueous enzymology, shows different properties in organic media and has the ability to catalyze some special reactions, thus showing many characteristics that water phase does not have.
3.3 Combination of enzymatic synthesis and chemical synthesis.
Enzymatic synthesis has a high degree of positional and stereoselectivity, while chemical polymerization can effectively improve the molecular weight of polymers. Therefore, in order to improve the polymerization efficiency, many researchers began to use enzymatic synthesis and chemical synthesis to synthesize biodegradable polymer materials.
4. Application of biodegradable polymer materials
At present, biodegradable polymer materials have two main uses: (1) to solve the environmental pollution problem and ensure the sustainable development of human living environment. There are usually three methods to treat polymer materials, such as landfill, incineration and recycling, but these methods all have their shortcomings. (2) Due to its biodegradability, it can be used as biomedical materials. At present, China produces more than 300 billion tablets and controlled-release capsules every year, of which more than 70% are coated epidermis, more than 80% are traditional sugar-coated tablets, and more than 80% in developed countries use water-soluble polymer materials as film-coated tablets. Therefore, China's tablet computer manufacturing level is far from the international advanced level. Overseas tablets and film-coated tablets mostly use hydroxypropyl methylcellulose, hydroxypropyl cellulose, acrylic resin, polyvinylpyrrolidone, cellulose acetate, cellulose acetate phthalate, sodium hydroxymethylcellulose, microcrystalline cellulose, sodium hydroxymethyl starch and so on.
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Zhai Meiyu, Peng Qian. Biodegradable polymer materials [J]. Chemistry and Adhesion, 2008, (05).