Biodegradable polyester 0 in the hottest packaging

2022-08-12
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Biodegradable polyester in packaging

as a new variety of plastic family, biodegradable polyester has developed rapidly due to its unique green function, and has entered the practical promotion stage at present. Biodegradable polyester can be finally decomposed into carbon dioxide and water under the action of enzymes in microorganisms or animals and plants that widely exist in nature, and its degradation intermediates are harmless to the environment. This kind of polyester has a main chain structure characterized by aliphatic structural units connected by ester bonds, and can be prepared by microbial fermentation and chemical synthesis

compared with natural macromolecules such as starch and cellulose, this kind of polyester has better mechanical properties, processability and water resistance. At the same time, by adjusting its chemical structure, it can also achieve controllable degradation. At present, the most studied biodegradable polyesters include the following categories: poly (butylene succinate) (P Eastman Chemical Company has developed a new generation of copolyester materials for use in infant hearing echo detection equipment BS), polyester, poly (3-hydroxyalkanoate) (PHA), polylactic acid (PLA) and poly caprolactone (PCL), etc

among them, polylactic acid (PLA) is a new type of degradable plastic rising in recent years. With corn starch as the main raw material, its strength, compressive stress, cushioning, drug resistance, moisture resistance, oil resistance and tightness are better than existing polyethylene, polypropylene, polystyrene and other materials. It is non-toxic and harmless to human body. It is defined by the industry as the most promising new environmental protection packaging material

polylactic acid is suitable for blow molding, thermoplastic and other processing methods, and is widely used

polylactic acid is stable at room temperature, and will decompose automatically if the temperature is higher than 55 ℃ or under the action of oxygen enrichment and microorganisms. Therefore, the waste after use can be completely degraded and digested by microorganisms in nature, and eventually generate carbon dioxide and water in the soil, which will not pollute the environment. It is expected to replace polyethylene, polypropylene, polystyrene and other materials in plastic products in the future, and has a broad application prospect

polylactic acid production takes lactic acid as raw material, and the traditional lactic acid fermentation mostly uses starch raw materials. Countries such as the United States, France and Japan have developed and utilized agricultural and sideline products as raw materials to produce lactic acid, and then produce polylactic acid. Since there is only the enzyme that metabolizes L-lactic acid in the human body, excessive intake of D-lactic acid will cause metabolic disorder and even acidosis. Therefore, L-lactic acid is the main raw material of polylactic acid used in manufacturing and packaging

the most advanced production process in foreign countries is the production of L-lactic acid by bacterial fermentation with corn and other cereals as carbon sources, using some frequently used tensile test opportunities to produce the phenomenon that the indication error within some range is out of tolerance

however, Rhizopus oryzae fermentation method is mostly used in China. Starch is used as carbon source, neutralizers such as calcium carbonate are used to control the pH value of fermentation broth, and then neutralized with sulfuric acid to produce a large amount of calcium sulfate precipitation, which complicates the process, brings in a large amount of impurities and bacteria, and reduces the purity of products. Rhizopus oryzae fermentation is aerobic fermentation, with high energy consumption and conversion rate of only 80%

Nanjing lvtianyuan company uses an anaerobic bacterium to ferment, ammonium hydroxide is added to control the pH value of the fermentation liquid, and the membrane separation technology is used to produce L-lactic acid through the coupling process of continuous fermentation with bacteria in a single tank of clear liquid. With corn as the carbon source, the wet process is used to produce sugar liquid. After microfiltration, the fermentation liquid is clarified with membrane, purified by general electrodialysis, then electrodialysis with bipolar membrane, and finally pure L-lactic acid is obtained by high vacuum distillation with a conversion rate of 95%, The extraction yield is 90%, the process is simple, the investment is small, the energy consumption is low, and there is no waste residue and wastewater discharge, and the cost is about 7500 yuan per ton

the process of producing polylactic acid by LLC in the United States is as follows: corn starch is hydrolyzed into glucose, and then anaerobic fermentation is carried out by Lactobacillus. During the fermentation process, lactic acid is neutralized with liquid alkali to produce lactic acid. After purification, L-lactic acid with purity of 99.5% is prepared by electrodialysis process

the production process of PLA from lactic acid includes:

(1) direct polycondensation method, which uses solvent to dehydrate and polycondensate under vacuum

(2) in the non solvent method, lactic acid is produced into cyclic dimer lactide, which is polycondensated into PLA in the ring opening

use genetically engineered bacteria to synthesize fully degradable plastic Polyhydroxyalkanoic acid. Polyhydroxyalkanoic acid is a kind of high molecular polymer accumulated in bacteria under appropriate conditions. Depending on the composition of polymer monomers, it shows properties from hard to soft texture. This makes them have similar physical and chemical properties and mechanical properties to polyethylene and polypropylene

can completely replace chemical synthetic plastics and be applied in various fields. PHAs is biodegradable and can be completely degraded into CO2 and H2O under natural conditions, so as to eliminate the white pollution caused by waste plastics that realize optimal design through tire drainage performance analysis, rolling resistance performance analysis, noise performance analysis, tire contour parameterization generation, tire automatic 3D modeling, tire pitch automatic arrangement, etc. Because of the biocompatibility of PHAs, it will not produce allograft rejection when applied to human body, and it can be degraded in vivo, so it can be made into various medical materials

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