The most comprehensive knowledge of degradable materials in history!

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In recent years, with the rapid development of the economy, people's pursuit of material and spirituality has become higher and higher, and they have correspondingly higher requirements for product packaging. When people buy products, they not only look at the aesthetics of the outer packaging, but also the Consider a variety of other features. It is precisely because people's pursuit of product packaging continues to improve that many new packaging materials are constantly being applied to product packaging.

Synthetic polymer materials have the advantages of light weight, high strength, good chemical stability and low price. Together with steel, wood and cement, they have become the four pillars of the national economy and are widely used in product packaging. However, a large amount of waste after its use is also increasing day by day, becoming a source of white pollution, seriously harming the environment, causing sewage and soil pollution, endangering human survival and health, and causing a negative impact that cannot be ignored on the environment on which humans live. In addition, petroleum, the raw material for the production of synthetic polymer materials, will eventually be used up. Therefore, it is urgent to find new environmentally friendly materials and develop non-petroleum-based polymers, and biodegradable materials are the solution to this problem. Effective Ways.

Definition of biodegradable materials and degradation mechanism Biodegradable materials, also known as "green ecological materials", refer to materials that can be degraded under the action of soil microorganisms and enzymes. Specifically, it refers to polymer materials that can biodegrade under certain conditions under the action of natural microorganisms such as bacteria, mold, and algae.

An ideal biodegradable material is a polymer material that has excellent performance, can be completely decomposed by environmental microorganisms after being discarded, and is ultimately converted into CO2 and H2O to become an integral part of the carbon cycle in nature.

The decomposition of biodegradable materials is mainly through the action of microorganisms. Therefore, the degradation mechanism of biodegradable materials is the process of digestion and absorption of materials by bacteria, molds, etc. First, microorganisms secrete hydrolase outside the body and bind to the surface of the material, cutting off the polymer chains on the surface through hydrolysis to generate small molecular weight compounds. Then the degraded products are taken into the body by the microorganisms, and through various metabolic routes, they are synthesized or transformed into microbial substances. The energy for microbial activities is eventually converted into water and carbon dioxide. According to the chemical nature of its degradation, it is divided into two types: hydrolysis and enzymatic hydrolysis.

01Hydrolysis mechanism

The degradation of a material is essentially a process in which its internal polymer chain segments are broken into low molecular weight oligomers under specific conditions, and finally decomposed into monomers. The "corrosion" of materials refers to the process in which the water-soluble small molecular substances formed leave the polymer material due to the breakage of the molecular chain, resulting in a reduction in the mechanical properties of the material and the final complete disappearance of the material. Dissolution can also be surface corrosion or overall corrosion.

If the degradation rate of molecular chain segments is faster than the diffusion rate of water molecules in the material, the hydrolysis of the chain segments is limited to the surface of the material, and it is difficult to enter the interior of the material. This method belongs to surface corrosion or heterogeneous corrosion. If water molecules When the diffusion rate of the material is faster than the hydrolysis rate of the polymer chain segments, then the degradation of the surface and interior of the material proceeds at the same time, so it belongs to overall dissolution.

02 Enzymatic hydrolysis mechanism

Enzymatic hydrolysis mechanism

For easily hydrolyzable polymers, both simple hydrolysis and enzymatic hydrolysis may occur simultaneously in the body. Lipase can promote the decomposition of polyester, while hydrolase can promote the degradation of easily hydrolyzable polymers. Lipase R.delemer lipase, Rhizopus arrhizus lipase, and Pseudomnas lipase are specific degrading enzymes for PCL. In the presence of these enzymes, the degradation rate of PCL is accelerated. Under normal circumstances, complete degradation takes 2-3 years. In the presence of enzymes, Complete degradation time is reduced to a few days.

Enzymatic oxidation mechanism

For some non-hydrolyzable polymers, the possible degradation mechanism is enzymatic oxidation. Immunohistological studies have confirmed that the material is ultimately absorbed and metabolized through endocytosis of phagocytes in the body. After polymer biomaterials are implanted into the body, they will cause acute inflammatory reactions of varying degrees locally. When the tissue is damaged, the permeability of surrounding blood vessels changes. Multinucleated leukocytes quickly move to the inflammatory site, and activated neutrophils Can differentiate monocytes into macrophages. The metabolism of polymorphonuclear leukocytes and macrophages produces large amounts of peroxide anion (O2), which is an unstable intermediate and is then converted into the stronger oxidant hydrogen peroxide. Reduced coenzyme (NADPH) and oxidase in the body are involved in this conversion reaction, while superoxide dismutase (SOD) accelerates the conversion. Hydrogen peroxide may cause the polymer to decompose itself at the implantation site; at the same time, hydrogen peroxide can be further converted into hypochlorous acid under the action of myoperoxidase (MPO). Hypochlorous acid is also a strong oxidant for biological materials. It can oxidize the amino groups in polyamide, polyurea, and polyurethane, breaking the polymer chains, thereby achieving degradation.

PLA

Among biodegradable materials, microorganisms such as bacteria, molds, fungi, and actinomycetes play a major role in degradation. They can be divided into three types according to their forms of degradation:

1. The physical effects of organisms cause mechanical damage to materials due to the growth of biological cells;

2. Biochemical effects of organisms, microorganisms act on materials to produce new substances;

3. Through the direct action of enzymes, microorganisms corrode some components of the material products, causing the materials to decompose or oxidize and collapse.

Characteristics of biodegradable materials

Biodegradable materials have the following characteristics:

1. It can be disposed with garbage or made into compost and returned to nature;

2. The volume is reduced due to degradation and the service life of the landfill is extended;

3. There is no problem that ordinary plastics need to be burned, and the emission of harmful gases such as dioxins can be suppressed;

4. It can reduce the harm caused to wild animals and plants by random discarding;

5. It is easy to store and transport, as long as it is kept dry and does not need to be protected from light;

6. It has a wide range of applications, not only in agriculture and packaging industries, but also in the medical industry.

Classification of biodegradable materials

Biodegradable materials can be divided into two types: completely biodegradable and biodestructive materials according to their degradation mechanism and destruction mode:

01Completely biodegradable material

Completely biodegradable materials refer to biodegradable materials that can be completely decomposed by microorganisms such as bacteria, fungi, and actinomycetes. It can eventually decompose into carbon dioxide, water and other substances and return to nature under the action of bacteria or their hydrolases, so it is called "green material". The preparation methods can be divided into three types: microbial fermentation, chemical synthesis and natural polymer blending.

02Biodestructive materials

Biodestructive materials are at the material level, mainly degradable materials made by blending or copolymerizing natural polymers and general-purpose synthetic polymers. The combination methods are as follows:

1. Use melt and solution blending methods;

2. Disperse one polymer material in an aqueous solution of another polymer to form a suspension system, and finally make various composites;

3. Disperse or dissolve natural polymer materials in a system that can perform polymerization reactions, perform homopolymerization and copolymerization reactions, polymerize monomers in the system, and obtain composite materials containing natural polymers;

4. Properly degrade natural polymers under appropriate conditions (such as acidic or alkaline, etc.), and polymerize the degraded molecular segments with other monomers to prepare new copolymers with biodegradable properties.

Application of biodegradable materials

Biodegradable materials are new materials developed after the 1980s as the contradictions between environment and energy became prominent. They can partially replace general-purpose plastics. At present, biodegradable materials are mainly used in environmental protection and medical fields.

Problems faced in the development of biodegradable materials

In recent years, biodegradable materials have been rapidly developed at home and abroad. In particular, disposable material products, such as degradable food packaging bags, beverage bottles, agricultural films, etc., have achieved industrial production. However, there are still some problems in the current development and application of biodegradable materials:

1. Market application: Due to the high cost of producing degradable materials, their prices in the market are relatively high, which has a great impact on the promotion of degradable materials.

2. Technology and technology: Compared with traditional plastics, degradable materials have problems with poor water resistance, poor mechanical properties and poor processing performance, making it difficult to meet the requirements of industrial production. In addition, degradable materials have accurate degradation time control, and after use Rapid degradability, complete degradability and scrap recycling technology need to be further improved and perfected.

3. Standards and experimental evaluation methods for biodegradable materials: For biodegradable materials, there is no unified experimental evaluation method, identification mark and product testing technology in the world, resulting in a lack of correct and unified understanding and accurate evaluation. The product market is relatively chaotic and really It’s hard to argue with fakeness.

The future of biodegradable materials

In recent years, with the advancement of raw material production and product processing technology, biodegradable materials have attracted much attention and become the focus of sustainable and circular economic development. It is of great significance whether it is from energy substitution, carbon dioxide reduction, environmental protection and solving the "agriculture, rural areas and farmers" issues. At present, in the field of development and application of biodegradable materials in my country, the research and development capabilities and investment in independent intellectual property rights and innovative products need to be improved, and the recycling and processing system of biodegradable materials needs to be improved.

3D printing of magnesium-containing biodegradable bone repair materials

In order to better realize the industrialization of biodegradable materials, efforts should be made in the following aspects in the future:

1. Establish a quick and simple biodegradability evaluation method to reflect the actual biodegradation of degradable materials in nature;

2. Further study the decomposition rate, completeness of decomposition, degradation process and mechanism of biodegradable materials, and develop technologies that can control the degradation rate;

3. Develop new means of regulating material properties through structure and composition optimization, processing technology and morphological structure control;

4. In order to improve the competitiveness with other materials, it is necessary to research and develop new methods, new processes and new technologies with independent intellectual property rights, simplify synthesis routes, reduce production costs, and participate in international competition.