Development and application of the hottest biodegr

Development and application of biodegradable plastics (Part 2)

2.2.1.2 hydrogen bonding method

hydrogen bonding method is to mix starch with other synthetic polymers [such as polyvinyl alcohol (PVA), polyacrylic acid or polyacrylate] that can form hydrogen bonding groups with hydroxyl groups on starch macromolecular glucose residues to form starch plastic raw materials, and then produce plastic products as usual

oteyd and others have been studying the blending of ethylene acrylic acid copolymer (EAA) and starch for 20 years. EAA has good compatibility with starch and polyethylene (PE). They compared the design and brought some limitations. Comparing different blending methods, they found that the samples obtained by water dispersion and CO concentration method were better than dry mixing; In the dry mixing method, the blending effect of pretreated starch (such as dianfen containing xanthic acid) is better than that of raw starch. Since then, research has been devoted to improving physical properties and reducing costs. The methods adopted include: dry mixing EAA containing ammonium salt with starch, and the blend can be blown into a film; Add a certain amount of ammonia to the dispersed blend to prepare a semi dry starch EAA blend, then repeatedly extrude and dry it on the extruder, and then add a certain amount of LDPE to prepare PE blow molding film; Using NaOH instead of ammonia as blending accelerator, the blend blown film obtained is better than ammonia in strength and light transmittance. Later, oteyd et al. Proposed the semi dry mixing method, using ammonia and urea as blending accelerators to obtain starch PE blown film, and the mass fraction of starch and LDPE should not exceed 40%

pva can also form hydrogen bond association with starch. In order to improve the compatibility of the two polymers during mixing and the light transmittance of products, PVA is often modified. First, PVA was block copolymerized with propene phthalide amine and acrylic acid under the condition of ph3.o and adding potassium thiosulfate, and then the block copolymer was mixed with starch in the ratio of 3:7 to form a solution with a solid content of 10% (mass fraction). After stirring at 90 ~ 95 ℃ for 1 h, the starch was completely gelatinized into a homogeneous solution and cast into a film

2.2.1.3 blending method

blending method is to add starch or modified starch directly to ordinary synthetic resin. The first two methods are chemical combination, while the mixing law is physical combination. Separate phases can also be seen under the microscope. In order to improve the compatibility between starch and resin, compatibilizers or modification of starch can be used. This method has been used in PE, polyvinyl chloride (PVC), polypropylene (PP) and polystyrene (PS). When used as an admixture of PE and PP, in order to improve its compatibility, the starch can be pretreated with lubricating oil or paraffin. For example, if corn starch with water content of 1% (mass fraction) is mixed with paraffin and then mixed with PE, 50% can be obtained μ M. The biodegradation test showed that the degradation rate was proportional to the starch content. The addition of trace elements is more conducive to degradation. When used as an admixture of PS, starch needs to be modified. For example, the blending product of corn starch modified with transition metal octenylsuccinate and PS will significantly retain mechanical strength, and the transition metal hemiester has good photosensitive properties, realizing a combination of good biodegradation and photodegradation properties. The optimum technological conditions are stirring speed 40R/min, temperature 185 ℃, starch content 7% ~ 15%

2.2.2 chitin

chitin, also known as chitin, is the main component of the shell and fungal cell wall of crustaceans or insects such as shrimp and crab. It is very abundant in nature, and its output is second only to cellulose. Chitin is insoluble in water and ordinary organic solvents. As a biodegradable material, chitin is deacetylated under alkaline conditions to produce chitosan. Chitosan is easily soluble in organic acids such as formic acid and acetic acid, and is easy to modify and process. Chitosan can be blended with other polymer materials to make biodegradable materials. For example, the acetic acid aqueous solution, PVA aqueous solution and glycerol of chitosan are mixed in a certain proportion and streamed onto the flat mold. After drying and removing the solvent, the biodegradable plastic film is obtained, which is expected to be used in food packaging and so on

2.2.3 cellulose

cellulose plastic mainly refers to the blending of cellulose with other materials that should detect the output and then feed back the pressure and flow of the hydraulic system, such as cellulose derivatives, chitosan, protein, polyvinyl alcohol, etc. The crushed micro cellulose, chitosan acetic acid aqueous solution, plasticizer, etc. are stirred evenly within a certain tolerance range by Shikoku Institute of technology in Japan, and then cast on the glass plate, dried and formed a film. Its air tightness is 10 ~ 100 times that of PE, its tensile strength is 10 times that of PE, and its tear strength is similar to that of cellophane. This kind of material has complete biodegradability and good air permeability, but it is a non thermoplastic material, which is not easy to be processed by blow molding and other molding methods. Its performance needs to be improved and its use needs to be developed

2.3 microbial synthesis

microbial synthesis, which uses organic compounds as carbon source food, many bacteria, algae and other microorganisms have the ability to synthesize biodegradable aliphatic polyester. The representative products of this kind of synthetic materials are 3-hydroxybutyric acid and 3-hydroxyvaleric acid copolymer (PHBV) developed by ICI company in the UK. Among them, 3-hydroxyvaleric acid accounts for 0 ~ 30% (mass fraction), and the trade name is biopol. Biopol has good mechanical properties, excellent heat resistance, water resistance, oil resistance and gas barrier. It shows good biodegradability under aerobic and anaerobic conditions, and finally decomposes into carbon dioxide and water; It will not degrade in air and purified water, so it is safe and stable. At present, the main problem of this material is that it is expensive, which is 4 ~ 5 times the price of commonly used plastics, so its use is greatly limited

3 problems of biodegradable plastics

problems of Biodegradable Plastics: (1) the price is high, and the price of biodegradable plastics is 2 ~ 15 times higher than that of ordinary plastics, which is difficult to popularize and apply. As jimstoppert, President of DuPont company, said: the most important thing is to be competitive in price and performance. Only when the price and performance exceed that of traditional plastics, the status of biodegradable plastics will be recognized. Fortunately, scientists have used transgenic plants to produce PHB (polyhydroxybutyrate), which can greatly reduce the cost of biodegradable plastics. (2) The degradation control of biodegradable plastics needs to be solved. For example, as a packaging material, it is required to have a certain service life, while medical materials require rapid degradation. (3) Biodegradability evaluation is an important topic for popularizing biodegradable materials. Biodegradability evaluation and test methods require that biodegradable plastics can be evaluated in line with the definition of biodegradability. At present, there is no unified national standard, ministerial standard and industrial standard in China, so that the subject of degradable plastics can be launched. Chengte is now urgently recruiting workshop technicians, after-sales personnel, and marketing department network optimization, network implementation specialists The identification and technology transfer of several famous fruits lack the necessary basis and criteria

4 development direction of biodegradable plastics

(1) biodegradable plastics are made from natural polymer materials such as cellulose, starch and chitin, and the functions and technologies of improving natural polymer wine are further developed. The National Natural Science Foundation of China (NSFC) has listed the preparation of environmentally degradable polymer materials from natural polysaccharide macromolecules (cellulose, starch, etc.) as a key project in 1999 (environmentally friendly materials). (2) Biodegradable plastics are synthesized by polymer design and fine synthesis technology. Biodegradable plastics are prepared by analyzing the biodegradation mechanism of synthetic polymers with biodegradability; At the same time, the block copolymerization of this kind of polymer with existing general polymers, natural polymers, microbial polymers and so on was studied and developed. (3) Biodegradable plastics are obtained through the cultivation of microorganisms. Find microorganisms that can produce polymer plastics, find new polymers, analyze their synthesis mechanism, improve their productivity through existing methods and genetic engineering, and study efficient methods of cultivating microorganisms. (4) Improve the biodegradability and reduce the cost of biodegradable plastics, and expand their applications. (5) Enrich, improve and continue to research and develop evaluation methods of biodegradation, and clarify the degradation mechanism. (6) Study on the control of degradation rate. In a word, with the increasing voice of people for environmental protection, the research and application of biodegradable plastics will be paid more and more attention by countries all over the world. Biodegradable plastics will become a major research topic in the future

5 conclusion

internationally, in order to promote the use and promotion of degradable plastics, while increasing the research on biodegradable plastics, many developed countries have successively legislated or banned "short-term use" ordinary plastics. In China, the State Economic and Trade Commission also issued Order No. 6 of 1999, which stipulates that the elimination period of disposable non degradable foamed plastic tableware is before the end of 2000. In addition, oil resources are increasingly exhausted, the development of non petroleum based biodegradable plastics has an extremely broad development prospect