Method for preparing polylactic acid from lactic acid under catalysis of titanium composite catalyst

Abstract

The invention relates to a method for preparing polylactic acid from lactic acid under catalysis of a titanium composite catalyst, belonging to the technical field of polymer materials. The method comprises the steps of: removing water from a raw material under normal pressure by an inert gas blowing method; gradually reducing pressure for pre-polycondensing: pre-polycondensing under low vacuum degree of 1000-10000Pa and high vacuum degree of 20-1000Pa at the temperature of 60-160 DEG C for 1-10h to obtain a lactic acid prepolymer; and carrying out melt polycondensation on the lactic acid prepolymer as a raw material in the presence of the titanium composite catalyst to finally prepare polylactic acid. The method has the advantages that any organic solvent is not used, the production equipment is simple, operation is convenient, industrialized continuous production is easy to realize, and the obtained product namely polylactic acid has higher molecular weight.

Description

technical field [0001] The invention belongs to the technical field of polymer materials, and in particular relates to a preparation method of polylactic acid materials. Background technique [0002] In recent years, there are fewer and fewer new products developed by chemical synthesis methods, and people have shifted their attention to the development of safety, non-toxic, renewable, and environmental protection. Today, the advocacy of "low-carbon" life reflects human concerns about the future due to climate change. Synthesizing new materials from natural materials has become a new development direction of material science, the most representative of which is new biodegradation Materials—Research on polylactic acid [Liu Jia, Zhang Wei. A review of new biodegradable materials polylactic acid [J]. Guizhou Chemical Industry, 2008, 33(3): 18-20]. [0003] Polylactic acid (Polylactic acid, PLA) is an important lactic acid derivative. It is a kind of polymer material obtained b...

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Problems solved by technology

[0007] As a green material, the catalyst used in its synthesis should be non-toxic and compatible with the application field. According to the previous research results, we concluded that the catalyst selection in the lactic acid synthesis method is mainly divided into two categories: one is the transition Metal compounds; the other is the complex system of transition metal compounds and protonic acid, but there are very few studies on this type of complex catalytic system[Mai H Z, Yang F, Yan B. Erythromycin poly lactic acid microspheres for lung-targeting[J]. Reactive Polymers (English Edition), 2002, 11(1): 11-16; Moon S L, Lee C W, Taniguchi.Melt / solid poly condensation of L-lactic acid: an alternative route to poly(L-lactic acid) with high molecular weight. Polymer. 2001, 42: 5059-5062; Sung II Moon and Yoshiharu Kimura. Melt poly condensation of L-lactic acid to poly(L-lactic acid) with Sn(II)catalysts combined with various metal alkoxides. Polymer International.2003, 52: 299-303] in these two kinds of catalysts, it is recognized that the best catalytic effect is tin compounds. In addition, the predecessors tried to synthesize new catalysts (such as metal-Salen Schiff base complex ), and a lot of research on the catalysis of lactic acid has been done, and some good results have been obtained, but this type of research is limited to the ring-opening polymerization of lactide (two-step method), so far, no relevant research has been found. Catalyzed lactic acid polycondensation (one-step method) report, therefore, the key to research lactic acid polycondensation is to find a cheap and non-toxic catalytic system

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