Application analysis of the hottest biodegradable

2022-08-13
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Application analysis of biodegradable polymers (I)

at the end of 2000, the global output of synthetic resins reached 130 million tons, of which plastic packaging materials developed the fastest. Since 1975, plastic has occupied the third place in packaging materials after glass, paper and paperboard. Packaging materials account for 41% of the total plastic output, and food packaging accounts for 47% of the packaging materials. Lamb packaging, which is convenient, non-toxic, cheap and beautiful, has become the first choice for people. Glass packaging continues to be used. Paper packaging will decompose naturally after processing. Plastic packaging materials account for 41% of household waste, which is actually "permanent" and cannot be degraded. How to face and deal with plastic waste has become a worldwide environmental problem. The solution of plastic waste will largely determine the world's ecological environment and the development speed and trend of synthetic resins in the 21st century. Otherwise, human beings will be surrounded by plastic garbage

in order to purify the surrounding environment and eliminate plastic waste, people strive to do the following work to reduce pollution: first, sanitary landfill (burying garbage with soil), and second, waste utilization. Although sanitary landfill can significantly alleviate environmental pollution, it will put the heavy responsibility of environmental protection on the next generation; Waste utilization is a more feasible method, which can be divided into incineration, high-temperature degradation and recycling. Neither incineration nor high-temperature degradation of plastic packaging waste can fundamentally improve the ecological environment. Although secondary processing can improve the environment to a certain extent, it will cost huge human and material resources. First of all, plastic containers and packaging materials should be picked out from the garbage, then classified according to the type of plastic, washed, dried, crushed, and finally processed into products. In terms of recycling and secondary processing, many countries have formulated strict laws and regulations to guide people to actively use plastic waste, especially containers and packaging materials. European laws stipulate that recycled plastics account for 15% of the production of plastic packaging materials, while Germany stipulates that recycled plastics account for 50% and will be expanded to 60%. For food hygiene reasons, experts believe that this is not feasible. For transportation and non food packaging materials, it is possible to use 25% recycled plastics, but it is never suitable for food packaging

it should be noted that the recycling and secondary processing of plastic containers and packaging materials will lead to the rise in the price of packaging raw materials, and the quality of recycled containers is low, not to mention that not every consumer agrees to use recycled packaging materials. If allowed, a large number of containers and packaging materials will be reused. People can't help asking how many containers and packaging materials are allowed to be processed, and how long it takes to bury and burn them. Whether buried or incinerated, it can only aggravate the deterioration of the surrounding environment. Experts suggested that a large number of biodegradable and harmless plastics should be developed and produced, which is the fundamental solution to the problem of "plastic waste"

the life degradation of polymer compounds is the focus of research because it can eliminate a large amount of "data garbage" composed of waste plastic containers and products. According to the research and development status of biodegradable plastics, the current exploration and application work in this field mainly includes the following three aspects:

first, hydroxyl acid polyester

Second, natural polymer plastics

Third Biodegradable polyester of industrialized polymer synthetic materials

biodegradable polyester

in recent years, the literature on the research of biodegradable polymers shows that the production of hydroxy carboxylic acid polymers is showing a positive upward trend. Since the discovery in 1925 that Polyhydroxybutyric acid is the nutrient source and medium of various microorganisms, human beings have paid special attention to this group of compounds. Under the action of microorganisms, hydroxybutyric acid is decomposed into CO2 and H2O. Other hydroxy carboxylic acid polyesters such as hydroxyacetic acid, polylactic acid, polyhydroxyvalerate, polyhydroxy, but in recent years, with the country vigorously promoting the development and transformation of plastic recycling granulator industry, caproate has similar characteristics

polylactide is a biodegradable plastic that can be used as packaging material in recent years, and has broad application prospects. The raw material of polylactide is lactic acid, which has hydroxyl and carboxyl functional groups at the same time. It has high reaction activity and is easy to dehydrate and shrink to synthesize polylactic acid under appropriate conditions. There are two methods for the synthesis of lactide: direct polycondensation and ring opening polymerization of lactide. The ring opening polymerization process is divided into two steps: first, lactide is prepared by dehydration and cyclization of lactic acid; Then lactide is prepared by ring opening polymerization. Whether synthetic polylactide or fermented glucose, maltose, sweet cereal juice or potato starch can be used to prepare biodegradable materials. The composted polylactide is degraded by cleaning the inside of the oil pipe with clean kerosene for about a month, and can be absorbed by microorganisms in seawater. Polylactide is a colorless and transparent thermoplastic polymer, which can be processed by general thermoplastic. The plates are made into pallets by extrusion molding, and can also be made into films, fibers, food packaging materials, and medical import tubes. The toughened polylactide becomes elastic and may replace polyethylene, toughened polyvinyl chloride and polypropylene. When the composition of polylactide monomer decreases and is removed, the elastic modulus and thermal stability of polylactide will be improved, and its service life will also be extended. Although polylactide has the above advantages, it cannot be widely used in daily life because of its complex production process, long process and low output, resulting in high product cost. Improving production efficiency and reducing the cost of biodegradable materials have become the focus of polyester researchers. Cargill Inc. of the United States has done active and effective work in improving the production process of polylactic acid and developed a biodegradable polymer with the trade name of ecopla. Compared with polystyrene, the impact strength of extruded ecopla sheet is higher than 200 ℃. The coating materials and films have the characteristics of high strength, transparency, good gloss and low friction coefficient. The film has good adhesion and can be degraded in compost. Cargill chose Electronic Universal Experimental Machine Model Technology Inc. the research result of the company is to ferment glucose in corn to produce polylactide, with an annual production capacity of 6000 tons. The company plans to continue to expand production, expand the annual production capacity to 50000 ~ 150000 tons, and reduce the cost of polylactide from 250 $/kg to 2.2 $/kg

CSMN in the Netherlands has built a lactic acid plant with an annual output of 34000 tons, and will double its production capacity if possible. Purac-grape joint company has developed and patented the manufacturing process of lactic acid. The brand of lactic acid sold by the company in the international market is PURAC. In order to reduce the cost of lactic acid polymer, Mitsui toatsu in Japan built an industrial pilot production plant and developed a direct polycondensation process of polylactide. The thermal stability of the product is better than that of lactide ring opening polymerization (two-step process), and the price of direct polycondensation of lactide is 4.95 $/kg. The polylactide film developed by Dai Nippon company can be compared with polystyrene in toughness and polyethylene in elasticity. Neste company of Finland began to study the manufacturing process of polylactic acid polymer in 1991. The scientific researchers of the company systematically studied the physical and mechanical properties and application fields of polylactide with molecular weight of 5000 ~ 10000. Zeneca bioproducts PLC in the UK not only produces biodegradable polylactide, but also produces polyhydroxycarboxylic acid blends with a wide range of applications, such as poly-3-hydroxybutyl ester and copolymers, poly-2-hydroxybutyric acid and poly-3-hydroxyvaleric acid. In 1995, the company produced 75 tons of biodegradable polymers with the brand name of biopol at a price of 13.5dm/kg, which is 5 ~ 7 times more expensive than polyethylene, polypropylene, polystyrene and polyvinyl chloride, and 1.5 ~ 2 times more expensive than polylactide

obviously, compared with a large number of synthetic resins, the price of existing biodegradable plastics is indeed high, and reducing the cost has become an urgent problem to be solved. If it also promotes the demand for connectors and wants to increase the output of biodegradable plastics, we should actively look for effective bacteria from a large number of bacteria to accelerate degradation. It was found that 1m3 of enzyme could degrade 50 ~ 60kg of polymer in one day. The cost of biodegradable polymers is expected to be reduced to 3dm/kg by adopting the best fermentation process, the best molding process and equipment, and the use of low-cost culture medium

the widely used fermentation medium includes sugar, organic fermentation and ethanol. People not only study the safe degradation properties of hydroxy carboxylic acid monomer polymers or hydroxy carboxylic acid copolymers, but also actively study the blending of polyhydroxycarbonyl acid with various synthetic materials and natural polymers as biodegradable initiators for composites. Hydroxycarbonyl acid blends as initiators can make products have good biodegradability, reduce costs and ensure the physical and mechanical properties of products. Researchers have done a lot of work in the preparation of biodegradable packaging materials, films, fibers, fruit baskets and vegetable baskets with biodegradable polymers, polydicarboxylate and ethylene glycol esters as raw materials. The main problem to be solved is how to adjust the proportion of raw material formula so that the products can meet the demand and degrade in compost. Because the composition, quantity, physical properties and proportion of fillers largely determine the decomposition rate of enzymes in polylactide blends, it is necessary to carefully study all the above factors. This can be clearly seen from the extruded film samples of polylactide and vinyl polyester blends (the ratio of polylactide and vinyl polyester in the film varies from 100 to 0,0 to 100). When the content of polyvinyl acetate increased, the degradation ability of the film decreased significantly. If the polylactide film degrades 52% in 10 hours, after adding 5% - 10% vinyl polyester, the film degrades only 8% in 60 hours, and 30% vinyl polyester in the blend does not actually degrade. The relationship between degradation rate and film preparation method is expressed as follows: degradation rate of soft film orientation film, extrusion film fixation quenching film quenching film at 90 ℃ for 9 minutes. Due to the high crystallinity, the polyvinyl polyester on the film surface moves during quenching, which changes the degradation performance

it should be pointed out that biodegradable polymers studied in recent years include not only packaging containers, packaging materials, medical materials, but also polymer materials with specific uses, such as glue, paint, engine lubricating oil, fishing, building materials, agricultural plastics. Pure polylactide, lactic acid copolymer and polyhydroxycarboxylic acid polymer are used

to sum up, acid polyester has great potential in occupying packaging materials, containers, disposable tableware, health care products and agricultural markets because of its self degradation characteristics. If the price of biodegradable plastics can be reduced, relevant laws and regulations can be formulated, and the application of non biodegradable plastics can be restricted, then everything will become a reality, and the purpose of protecting the environment and reducing "plastic waste" can be achieved

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