Biodegradable material looks promising

The high-molecular-weight microbial polysaccharide pullulan produced by fermentation of starchy raw materials has good film forming ability, can be used as an edible packaging for foods and medicines, can be metabolized, and is produced by microbial fermentation. Polyethylene and polypropylene are similar in nature, capable of drawing, molding, and injection molding. It is a biodegradable material that can replace plastic packaging materials. The above two materials that can replace plastic films produced with starchy raw materials have all achieved scientific research results, but due to the high cost, no commercial products have been produced so far.

According to foreign reports, the world's real biodegradable material production in 2002 was only 40,000 tons. The China Biodegradable Materials Working Group (BMG) announced that only 10,000 tons of biodegradable materials were produced in China in 2003. There are dozens of domestic starch-based degradable plastics with an annual output of about 100,000 tons. A large number of starch-based disintegrable materials are composited with polyethylene and starch (approximately 50% of starch raw materials), and are not fully degradable materials. Therefore, the use of renewable starchy raw materials, through the denaturation or fermentation to obtain new composites, is the focus of research and development of biodegradable materials at home and abroad. Among them, polylactic acid PLA is worth noting because of its unique superior performance compared with chemical compositions.

In terms of medical equipment, PLA has unique biocompatibility and biodegradability, so it can be used as artificial fracture internal fixation (instead of metal fixation, exempt from secondary operations), sustained-release materials, surgical sutures, and tissue repair materials. The high added value of PLA technology is currently the main market for polylactic acid, and it is also a promising polymer material for the medical industry.

The biodegradable fiber made of polylactic acid has a heat resistance of 175°C. It can be made into filaments and short filaments like polyester fibers, used for clothing and non-clothing fabrics. It has the hygroscopicity of natural fibers, has a good feel, has smooth synthetic fibers, and is comfortable and stiff. Japan's Bell spinning company's original hundreds of tons of PLA fiber production capacity in 2001 and CDP (the United States Cargill and Tao chemical joint venture), plans to expand to 10,000 tons. In 2002, the company exhibited a PLA fiber with a melting point of 175°C, an elongation of 25%-35%, and a strength of 4.5-5.5 g/d at the Swiss Nonwovens Trade Fair under the trade name Cornfiber (corn fiber). . In addition, Japan's Unicornka and Kuraray also cooperate with CDP to produce PLA fibers.

Biodegradable plastics countries have many patents. CDP, a joint venture between Cargill and Tao Chemicals, completed a PLA 6000-ton pilot test for polylactic acid in 2001 and a project to produce 140,000 tons of products per year in 2002. It now has a production capacity. The current production cost per ton drops to 1,500 US dollars. The CDP has used it for mineral water bottles. The United States Collegefarm Candy Company began using CDP's PLA as an environmentally friendly packaging material. One set of high-speed kink packaging equipment uses this material with a capacity of 1300 bpm. The candy packaged with PLA has good transparency, kink, and printability, and has good barrier properties to maintain the aroma of the candy. The Shimadzu, Mitsui and Ink companies all have 500-1000t/a units and both plan to expand. Germany's EmsInventa-Fischer builds a 3000-ton-per-year PLA demonstration plant in eastern Germany at a cost of 2.2 euros/kg for food packaging and packaging. It plans to expand to 25,000 tons, with a construction period of 18 month. The next step is to build a plant with an annual capacity of 100,000 tons of PLA, and the expected cost is reduced to 1.25 euros/kg. Germany's Treofan has developed a polylactic acid metallized film with high barrier properties, suitable for packaging a variety of flavored cream, cheese and high oil foods. Its oxygen transmission rate is only 1/12 of uncoated metal, which is higher than metal coated cellophane.

It should be pointed out that in China, polylactic acid PLA is currently produced from lactic acid because of the high raw material cost, which is about 1,000 US dollars per ton of DL-lactic acid, and the price of L-lactic acid per ton is 2000 US dollars. Therefore, domestic trials of polylactic acid PLA, which can be used for degradable fibers and biodegradable plastics, will be expensive. Therefore, the use of low-cost starch (1800 yuan per ton) as the initial raw material, the development of biodegradable packaging materials, has attracted much attention at home and abroad. The degradable materials that were modified with starch in the domestic market a few years ago can be used in agricultural breeding cups, industrially used in lunch boxes and small packaging boxes, and domestically produced in small batches. The corn starch tableware recently produced by Shanghai Greenclean Packaging Co., Ltd. does not deform, wrinkle or leak at -30-120°C, and is moderately priced. Appraisal by the Shanghai Technical Supervision Department, its degradability, appearance, health and health protection and other aspects are in line with national regulations. At present, the consumption of expanded polystyrene lunch boxes is more than 10 billion yuan per year, and starch raw materials are used to develop food lunch boxes and packaging materials, which have broad prospects for development.