At present, there are more than a thousand patents on the production and processing of polylactic acid at home and abroad. According to Li Liman et al.'s patent analysis of polylactic acid in the field of domestic and foreign fields, before March 2005, he searched in the Chinese patent database with polylactic acid as the key word, and found that patents related to the preparation and application of polylactic acid were 154. In this paper, 96 articles published by domestic applicants, followed by medical, preparation, packaging and fiber, were 56, 26, 6 and 4 respectively, and 58 were published by foreign applicants. In the DERWENT patent database, "TS=(polylacticacid or polylactide) notpn=cn'' was used as a strategy to retrieve nearly 1,740 foreign patents, including 542 medical patents, 517 patents for preparation, and 293 patents for packaging. Patented 419 patents on fiber. Statistical analysis of patent families published by foreign DERWENT found that the main applications for polylactic acid patents are Japan, the United States, Germany, France and the United Kingdom. In the DERWENT patent database, the application of polylactic acid in packaging is relevant. There are 293 patent reports and 419 patents related to polylactic acid fiber, the largest number of which are Japan, the United States and Germany. According to the Chinese patent database, the patent applications for domestic polylactic acid are mainly universities, among which universities applying for polylactic acid related patents. Mainly: Zhejiang University, Tianjin University, Wuhan University, East China University of Science and Technology, Tsinghua University, Nankai University, Southeast University, Shanghai Jiaotong University, Chongqing University, Jinan University, Chinese Academy of Sciences Changchun Institute of Applied Chemistry, etc.; enterprises also have a certain amount of applications, But in contrast, the company's patent application for polylactic acid is far less than that of colleges and universities. From DER double Nr The database can be found that most of the foreign applicants for polylactic acid patents are enterprises, and many of them are internationally renowned large enterprises. 
BRUSSELS BIOTECH (BE) World Patent WO 2004 014889, published February 13, 2004, discloses the preparation of polylactic acid, the independent rights of which include the following: (1) Preparation of lactic acid by: (a) evaporation of lactic acid or lactic acid derivatives The solution has a molecular weight of 400-2000, an equivalent acidity of 119-124.5% of total lactic acid, an optical purity equivalent to an oligomer of 90-100% L-polylactic acid, and (b) an oligomer and a depolymerization catalyst added to the depolymerization reaction. a lactic acid-rich gas phase and an oligomer-rich liquid phase; (c) condensing the gas phase to obtain liquid crude lactic acid; (d) extracting and crystallization of the crude lactic acid; (e) separating and discharging the crystal to obtain a rich a wet cake of lactic acid crystals; (f) drying the wet cake to obtain pre-purified lactic acid; and (g) crystallization pre-purified lactic acid to obtain a residual acidity of less than 10 meq/kg, a water content of less than 200 ppm, and a meso-lactic acid content of less than 1%. Purifying lactic acid; (2) Polymerizing the lactic acid obtained above to obtain polylactic acid.
A method for preparing polylactic acid which can be used for a confectionery packaging material is reported by BOTELHO T et al., 2004, WO 2004 057008-A1, which is mainly obtained by a fermentation method, and the specific method reported in the examples is: a culture solution ( 451) (including whey, milk protein and other nutrients such as inorganic salts and semi-glyceric acid) was heated to 70 ° C for 45 minutes and then cooled to 45 ° C. Lactobacillus helveticus (9 g) and Flavourzyme (RTM) (A) (26.5 g) were added. Batch fermentation was carried out for 9 hours, supplemented with fresh broth containing whey, lactose and Flavourzyme (RTM). The pH was adjusted to 5.75 with ammonia gas, the biological density was controlled at 7-8%, and continuous ventilation was performed during the fermentation, and the aeration was 1 liter/min. The dilution rate during the 34-day fermentation period was 0.15-0.3/hour. The lactate in the effluent was 4%, and the yield was 12 g/L. at a dilution rate of 0.3/hr. The lactic acid effluent is separated by an ion exchange resin and a chelating agent, and after two consecutive electrodialysis, the recovery rate is 85-90%.
US Patent No. 2003 158360, published on Aug. 21, 2003, to the disclosure of a method for preparing a polylactic acid, the steps are as follows: fermenting starchy agricultural products to obtain lactic acid, ultrafiltration through ultrafiltration, nanofiltration and/or electrodialysis Lactic acid, concentrated lactic acid, preparation of prepolymer, cyclization depolymerization into dilactic acid, purification of dilactic acid, ring-opening dilactic acid polymer and de-monomerization of polylactic acid.
JP 2002 300898, published on October 15, 2002, to SHIMADZU, discloses a process for producing lactic acid and polylactic acid. The specific method is: (1) synthesizing lactic acid ester by using ammonium lactate; (2) polycondensing lactate in the presence of a catalyst other than butyl tin, synthesizing an average molecular weight of less than 15000 mol. wt polylactic acid (lactic acid prepolymer); (3) depolymerizing polylactic acid to obtain lactic acid; The method further includes preparing a polylactic acid by ring-opening the lactic acid polymer.
SHIMADZU CORP, OHARA H, TOYOTA JIDOSHA KK, ITO M and SAWA S WO 2002 60891-A, published on August 8, 2002, discloses a preparation method of lactic acid and polylactic acid for producing biodegradable plastics, the patent One of the examples is reported as follows: the L-lactate obtained by fermentation is reacted with ethanol at 90-100 ° C to separate and collect ethanol; the water in the reaction is removed at 120 ° C; and the ethyl lactate obtained by distillation is purified. The ethyl lactate was polycondensed at 160 ° C in the presence of octyl tin and the ethanol was removed. The obtained reaction liquid was distilled at 200 ° C to obtain lactic acid, and the yield was 99.2%. Lactic acid is obtained by polymerizing lactic acid in the presence of octyltin. NATL INST OF ADVANCED INDUSTRIAL SCIENCE TECHNOLOGY METI, KONAN KAKO KK, and TOKIWA YUTAKA Japanese Patent JP 2001 224392, published on Aug. 21, 2001, discloses the preparation of polylactic acid using a hydrolase instead of an organometallic catalyst.