Biodegradable Polymer Materials (Continued)

3.3 Cellulose-based biodegradable materials Cellulosic-based biodegradable materials are a new direction developed in China in recent years. Like starch, cellulose has abundant resources and low prices. Compared with synthetic biodegradable materials, cellulosic materials have many advantages: First, there are many hydroxyl groups on cellulose macromolecular chains, which have a strong ability to react.

Therefore, the processing technology of this type of material is relatively simple, low cost, and no pollution during the processing; Second, the material can be completely degraded by microorganisms; Third, the cellulose material itself is non-toxic. Therefore, taking into account the "white pollution" faced by humans and the increasing shortage of petroleum resources, the development of biodegradable composite materials based on cellulosic materials in China will create ecological balance, protect the environment, save resources, develop the economy, and participate in international markets. Competition is of great significance. However, due to the weakness of cellulose itself, the film made of it alone, its water resistance, strength can not meet the requirements of PE film, therefore, it is mostly mixed with other natural polymers, the material is currently not available.

Jinjing Key Industrial Co., Ltd.19 uses natural fibers such as cotton fiber as the main raw material, and uses a blend of cellulose and chitosan as binder to obtain a dry non-woven fabric with high water resistance, which can be produced using existing equipment. Moreover, the amount of adhesive is only 5 to 10, and the cost of the product is increased little. This kind of biodegradable non-woven fabric can be used as agricultural material, packaging material and so on. Ni Xiuyuan et al studied the copolymerization of hydroxyethyl cellulose (HEC) with methyl methacrylate (MMA) and acrylic acid (AA) under ultrasonic irradiation, and studied the degradation of the copolymer by cellulase. The results showed that: Within the concentration range of MMA studied, the copolymerization yield and the MMA content of the copolymer increased with increasing MMA concentration. Under certain conditions of the enzyme, HEC degrades for a period of time and an extreme molecular weight appears. The higher the enzyme concentration is, the lower the molecular weight is. Even if the enzyme concentration is very low, the molecular weight of HEC decreases greatly after about 2 minutes of enzyme action.

Light-biodegradable material is a kind of material made by a combination of photodegradation and biodegradation, and it is an ideal material for degradation. This method not only overcomes the defects that are not easily degraded and incompletely degraded due to lack of light or lack of illumination, but also overcomes the disadvantages of the biodegradable materials being complicated in processing, high in cost, and difficult to be promoted, and is thus rapidly developed in the application field in recent years. A technology. Our country's technology in this area is relatively advanced. The degradable plastic film has basically met the requirements of various parties and is developing other application fields. However, at present, the main problem of the photo-biodegradable materials is that the organic combination of both light and biodegradation is not ideal and needs further development.

Sun Yi et al. (2003) found through several years of research that a double-film containing 15 starch can support microbial growth under un-lighted conditions. After 124 days of culture, the C02-C conversion rate was comparable to PE film and ordinary photo-degradable film. 6.8, decrease in molecular weight 21.7 The higher the starch content, the easier it is to be degraded. The double solution film directly buried in the soil has a relatively small impact on the crops, so the use of the double solution membrane can overcome the defect that the pure photodegradation film does not degrade in the soil. Lin Yichao studied ultra-fine starches and iron stearate (FeSt) or iron N,N-di-n-butyldithiocarbamate/nickel N,N-di-n-butyldithiocarbamate (FeDBC/NiDBC) The photooxidative degradation of LDPE films of photosensitizers changes the carbonyl index, viscosity average molecular weight and fungal erosion. The results showed that adding 5%-15% starch and 0.1-0.3% FeSt or 0.5%-0.2% FeDBC/NiDBC photosensitizer in LDPE film can control the service life of LDPE film. Zhang Huaji 231 in the starch by adding 2 aluminate, can change its hydrophobic properties; adding OPE compatibilizer, can increase the binding force between LDPE and starch, improve the tensile properties of the film, OPE dosage control 10 ~1 is appropriate. In LDPE/starch films containing 0.4% carboxylic acid guanidine, the length of photodegradation induction period can be adjusted by changing the ratio of starch and light stabilizer A, and a biodegradable LDPE packaging film with different induction periods can be prepared; containing 2% starch, 0.4 The mechanical properties and hygienic properties of the barium stearate LDPE packaging film meet the requirements of national standards. After being discarded, it is naturally exposed for 3 months, and the viscosity average molecular weight is reduced to 3600. The garbage yard is buried for 6 months and the elongation at break decreases by 88.5%. , Loss of weight 23. Into; piled la, the degradation of less than 25cm2 fragments, gradually assimilated by the soil. Zhou Yifeng et al.241 used photosensitizers (iron alkylthiocarbamate and nickel alkyl thiocarbamate) and added modified starch to prepare a photodegradable and biodegradable polyethylene film. .

4. Problems and suggestions in the research and development of degradable materials No matter from the perspective of foreign or domestic markets, the degradable materials market has never experienced the phenomena of vigorous development. There are various reasons among them. The following are the main points: Costs High, high prices The starch-filled biodegradable materials, despite being questioned by people, still have a large market. The main reason is that the raw materials are cheap, the production process is simple, the cost is low, and the relative prices are low. The PCL, PLA and other biodegradable materials, in spite of their excellent biodegradability, have greatly limited their application because of their high price, and they are mainly used in medical and other fields with high added value.

The immature degradation technology at home and abroad focuses on the improvement of the degradability of materials and the commercialization of degradable materials. The study on the degradation mechanism, the intermediate process of degradation, the kinetics, and the thermodynamic factors is not thorough enough, and it is to some extent blocked. The pace of research and development of degradable materials.

Degradability standards and evaluation methods are not perfect enough, not detailed, making people lack the necessary basis in research and development.

Judging from the domestic research situation, the gap between domestic and foreign countries lies in the following points: It is impossible to harmonize scientific research with product commercialization and industrialization. Although the State emphasizes the combination of production, education, and research, most domestic research institutions cooperate with enterprises. Not close enough, thus causing a strange phenomenon, we use the product is eliminated abroad, and some of the scientific research unit is the world's leading technology.

The awareness of sustainable development is not strong. From the point of foreign company research and development and product launch, they have a certain long-term ideological preparation when developing products. Although these products cannot be produced on a large scale at present, they can do research and development in light of the development of the existing market and the prediction of market development. Therefore, foreign countries always have corresponding products launched at appropriate moments. Domestic companies do not consider enough long-term interests and are only looking at the current market trends and are reluctant to carry out excessive risk investment. This is why the market is relatively weak after the degradable materials swarmed in 1993.

Market development of degradable materials is not sufficient. The market for degradable materials in China is mainly used for plastic film, packaging film, garbage bags, disposable tableware, etc., while other areas are less involved. We should take joint ventures and cooperation in the form of joint ventures and cooperation with relevant companies and research institutions in the United States and Japan to develop and produce degradative polymers in high-tech fields such as medicine and optoelectronics. This will enable us to work in line with international standards and move quickly into high-level fields. .

There are certain defects in the degradable material. Domestic products are always degradable when they recommend their own products, but the extent to which they will be degraded will require little time to mention. In fact, most starch-filled polyethylenes and other resins produced by domestic companies are not biodegradable materials, but bio-destructive materials. Starch can be decomposed by microorganisms, but the molecular skeleton of the resin can not be decomposed for a long time. Instead, Difficulties have arisen in the recovery of waste materials. Photodegradable materials are constrained by the geographical environment and climate, and it is difficult to accurately control the degradation time, and they cannot be degraded after they are buried in the landfill and into the landfill system.

Poor use performance. Starch-containing degradable plastics have poor water resistance, and their mechanical properties are greatly reduced upon water contact. Therefore, it is not suitable to be processed into a shed film; the usefulness of the processed lunch box is also poor, the texture is soft, and the hot-packed food is easily deformed; the performance into a packaging bag is also poor and easily torn.

In order to open up the market for degradable materials, the main problems that people will solve in the future are: (1) There are two methods to reduce the cost of degradable materials: First, to improve production technology, optimize production processes, and develop efficient degradative material production processes; second, expand Yield. (2) Improve people's awareness of environmental protection and make people consciously use degradable materials. (3) The state and the government shall make corresponding policy support to promote the improvement of the market for the application of degradative materials. (4) The development of biodegradable plastics must go hand in hand with the establishment of post-use treatment and regeneration technologies.

The future development direction of biodegradation research work is estimated as follows: The use of natural polymer materials such as cellulose, starch, chitin and other biodegradable materials to further develop and improve the function and technology of natural polymers. In addition to copolymerization modification, a variety of biodegradable polymer materials are blended and modified to prepare a biodegradable polymer material with good overall performance, which is still an important technical approach.

Biodegradable materials are synthesized using molecular design and fine synthesis techniques. Emphasis is placed on the controllability of material degradation, and after treatment, the material decomposes rapidly. Through biodegradation of biodegradable synthetic polymer biodegradation mechanism to obtain biodegradable materials; at the same time, this kind of polymer and existing general polymer, natural polymer, microbial polymer block copolymer research and development .

Biodegradable materials are obtained by the cultivation of microorganisms. The production of genetically modified organisms is an important aspect of degradable polymer materials that cannot be ignored. Looking for microorganisms that can produce polymer materials, discovering new macromolecules, and analyzing their synthesis mechanism, at the same time, improve their productivity through existing methods and genetic engineering methods, and study efficient methods for culturing microorganisms.

U) Light-biodegradable materials, due to their dual photo- and biodegradable functions, have a good application prospect. Therefore, the research and development of light and bio-degradable materials that can accurately control the degradation time will be one of the future development directions.

4.4 Several proposals for the development of domestic degradable materials Based on China's national conditions, China's research and development of biodegradable materials should mainly proceed from the following aspects: Due to the restrictions on the use of foreign membranes, therefore, foreign countries in the degradation of film technology progress is slow, The point of mature application has not yet been reached. From this point of view, the development of degradable plastic film is an advantage area in China. Therefore, research and development of degradable plastic film, especially controllable light-biodegradable plastic film, deserves great attention.

As far as China's technology is concerned, starch-filled biodegradable materials do not have the ability to be widely used. Therefore, China should vigorously carry out research on environmentally-friendly biodegradable materials technology, increase the human resources in this area, invest in people, focus on low-cost development, the market is in urgent need of popular biodegradable materials, and do a good job of high-tech reserves.

China is rich in resources, starch, cellulose, lactic acid and other resources are sufficient, the price is low, and oil resources are increasingly lacking. Therefore, thermoplastic starch and cellulose-based materials can be fully biodegradable, and PLA and PHB have good prospects for development. We should learn from foreign technologies, strengthen self-innovation, and seize the market for degradable materials.

With the development of society and economy, the improvement of people’s living standards, the enhancement of people’s environmental awareness, the continuous improvement of national legislation, and the continuous improvement of degradation technologies, degradation of materials will surely have a bright future.