Polylactic acid: a rookie in the field of degradable films

The domestic research and development of degradative films has covered several major categories: photodegradation, photobiodegradation, high-starch content biodegradation, high-calcium carbonate-filled photo-oxygen degradation, and total biodegradation. The application of degradable plastic products in packaging has covered ordinary packaging films, shrink films, shopping bags, garbage bags, etc., and has played an active role in improving the environment. Material characteristics of polylactic acid Polylactic acid (PLA) is a new type of degradable plastic that has emerged in recent years. Corn starch is used as the main raw material, and its strength, compressive stress, cushioning, drug resistance, moisture resistance, grease resistance and airtightness are all It is better than the existing materials such as polyethylene, polypropylene and polystyrene, and it is non-toxic and harmless to the human body. It is defined by the industry as the most promising new type of environmental protection packaging material. Polylactic acid is suitable for various processing methods such as blow molding, thermoplastics and so on. It is widely used.

It can be processed into various downstream products such as films and packaging bags like thermoplastics. Polylactic acid is stable at room temperature. If the temperature is higher than 55 degrees Celsius, it will be decomposed automatically under the influence of oxygen and microorganisms. Therefore, wastes after use can be completely degraded and digested by microorganisms in the natural world, eventually generating carbon dioxide and water in the soil, and will not cause pollution to the environment. In the future, it will be expected to replace polyethylene, polypropylene, polystyrene and other materials for plastic products. Wide application prospects.

Environmental protection production process Polylactic acid production is based on lactic acid as the raw material, traditional lactic acid fermentation mostly uses starchy raw materials. At present, the United States, France, Japan and other countries have developed and used agricultural and sideline products as raw materials to ferment and produce lactic acid, and then produce polylactic acid. Since only the enzyme that metabolizes L-lactic acid exists in the human body, excessive D-lactic acid intake can cause metabolic disorders and even acidosis. Therefore, in the production of polylactic acid for packaging applications, L-lactic acid is mainly used as a raw material.

At present, the most advanced production technology in foreign countries is corn and other cereals as carbon sources, and bacterial fermentation is used to produce L-lactic acid. Most of the domestic use of Rhizopus fermentation method, using starch as a carbon source, using calcium carbonate and other neutralizing agents to control the pH of the fermentation broth, and then use sulfuric acid to neutralize, produce a large number of calcium sulfate precipitation, so that the process is complicated and brought into A lot of impurities and bacteria, so that the product purity. Rhizopus oryzae fermentation is aerobic fermentation, high energy consumption, conversion rate is only 80%.

Nanjing Lutianyuan used an anaerobic fermentation, ammonium hydroxide was used to control the pH of the fermentation broth, and membrane separation technology was used to produce L-lactic acid in a single-batch bacterial continuous fermentation coupled process. Corn was used as a carbon source and used wet The process of making sugar, fermentation broth microfiltration after removal of mycelium, using membrane clarification, general electrodialysis purification, and then bipolar membrane electrodialysis, and finally high vacuum distillation to obtain pure L-lactic acid, the conversion rate of ≥ 95% , extraction yield ≥

90%, simple process, low investment, low energy consumption, no waste residue discharge, cost about 7500 per ton

yuan. The American company LLC produces polylactic acid as follows: corn starch is hydrolyzed to glucose and then anaerobicly fermented with lactobacillus. During the fermentation process, lactic acid is neutralized with liquid caustic soda. The fermentation broth is purified and electrodialyzed to achieve a purity of 99.5. % of L-lactic acid. The PLA production process from lactic acid includes:

(1) Direct polycondensation, and dehydration polycondensation using a solvent under vacuum.

(2) The non-solvent method produces lactic acid as a cyclic dimer lactide, which is polycondensed in open loop to PLA.

Greening, the ultimate trend of packaging film has broad prospects in the domestic market

In 2001, the world's total output of lactic acid was 130,000 tons, and in 2002 it exceeded 200,000 tons, and it has been rising year by year. At present, the demand for lactic acid in Japan and the United States alone reaches 35,000 tons. It is estimated that the total global demand for lactic acid is about 150,000 to 200,000 tons. The lactic acid fermentation industry in China began in the period of the War of Resistance against Japan. After 60 years of development, it has now formed a production capacity of about 40,000 tons, but the annual output is only about 20,000 tons.

In China, Qingdao Fuso Chemical Company is the largest refined (fermented) lactic acid export company in China. As early as 1998, the Haizheng Group in Taizhou learned that it was developing and producing PLA abroad. They immediately contacted the Chinese Academy of Sciences and other relevant scientific research institutes, and transferred strength to form a scientific research group within the company to start research. In September 2002, the research and development work of Hisun PLA also achieved a breakthrough. At present, the company has mastered key technologies such as fermentation, extraction, and polymerization of lactic acid that are in the leading position in China, and fully embodies the requirements for environmental protection and clean production in process design.

In June 2004, Polylactic acid (PLA) developed by Hisun Group entered the industrialization stage. Polylactic acid film production effect is remarkable

In March 2004, Asahi Kasei Corporation was made from corn sugar and biodegradable polylactic acid. After using this polylactide as a film, it can still maintain a good softness.

In April 2004, American CollegeFarm brand candy began to use biodegradable resin PLA (Poly) lactic acid NatureWorks natural material packaging film. The appearance and performance of this film is the same as that of traditional candy packaging film (glassine or biaxially oriented polypropylene film). Crystal clearness, excellent kink retention, printability and strength, and high barrier properties, can better preserve the aroma of the candy.

In July 2004, Toray China announced the world's first successful development of a polylactic acid film made from plants. This film has the flexibility and heat resistance inherent in polylactic acid, and also has flexibility that can be rolled up. A research institute in the United States has successfully converted the processed potatoes to dextrose syrup and fermented with bacteria into lactic acid fermentation liquor. By electrodialysis separation, heating to evaporate the water to obtain a film and coating can be made of polylactic acid, as a fresh bag can replace polyethylene and waterproof wax packaging material.

Reprinted from: Global Flexible Packaging Industry