Biodegradable plastic materials, which are eventually decomposed into water and carbon dioxide by microorganisms, are used in a wide variety of applications such as food containers and agricultural materials.
At present, such polyesters are produced by polycondensation of a material derived from a fossil fuel resource; however, in view of recent environmental problems at a global scale such as concerns for depletion of fossil fuel resources and increase in the atmospheric carbon dioxide level, attention has been drawn upon a method of deriving a starting materials of these polymers from a biomass resource.
So far, there have been disclosed technologies for producing a dicarboxylic acid used as a starting material of a polyester, such as succinic acid or adipic acid, from glucose, sucrose or the like of a biomass resource origin by a fermentation method (see Patent Documents 1 and 2 and Non-patent Document 1).
In cases where a dicarboxylic acid is used as a starting material of a polymer, in order to maintain the polymerization activity and to thereby obtain a high-quality polymer with less coloration, a highly pure dicarboxylic acid is required. As a method of purifying a dicarboxylic acid produced by a fermentation method, there are disclosed, for example, a method in which an ion-exchange resin is used and a method in which electrodialysis is used (Patent Documents 3 and 4). Examples of a substance which causes coloration of a polymer include those impurities that exhibit absorption in the ultraviolet region of 250 to 300 nm, and it is described to be useful that such impurities be reduced to not higher than a specific amount (Patent Document 5).