Showing papers by "Yoshiharu Kimura published in 2004"

Production of D-lactic acid by bacterial fermentation of rice starch.

Abstract: D-Lactic acid was synthesized by the fermentation of rice starch using microorganisms. Two species: Lactobacillus delbrueckii and Sporolactobacillus inulinus were found to be active in producing D-lactic acid of high optical purity after an intensive screening test for D-lactic acid bacteria using glucose as substrate. Rice powder used as the starch source was hydrolyzed with a combination of enzymes: alpha-amylase, beta-amylase, and pullulanase to obtain rice saccharificate consisting of maltose as the main component. Its average gross yield was 82.5%. Of the discovered D-lactic acid bacteria, only Lactobacillus delbrueckii could ferment both maltose and the rice saccharificate. After optimizing the fermentation of the rice saccharificate using this bacterium, pilot scale fermentation was conducted to convert the rice saccharificate into D-lactic acid with a D-content higher than 97.5% in a yield of 70%. With this yield, the total yield of D-lactic acid from brown rice was estimated to be 47%, which is almost equal to the L-lactic acid yield from corn. The efficient synthesis of D-lactic acid can open a way to the large scale application of high-melting poly(lactic acid) that is a stereocomplex of poly(L-lactide) and poly(D-lactide). Schematic representation of the production of D-lactic acid starting from brown rice as described here.

Hydrogel Formation between Enantiomeric B‐A‐B‐Type Block Copolymers of Polylactides (PLLA or PDLA: A) and Polyoxyethylene (PEG: B); PEG‐PLLA‐PEG and PEG‐PDLA‐PEG

Abstract: A mixed suspension of the enantiomeric B-A-B triblock copolymers, polyoxyethylene-block-poly(L-lactide)-block-polyoxyethylene (PEG-PLLA-PEG) and polyoxyethylene-block-poly(D-lactide)-block-polyoxyethylene (PEG-PDLA-PEG), was found to induce reversible gel-to-sol transition depending on the polymer concentration and temperature. The storage and loss moduli of the gel formed at lower temperature were much higher than those of the gel prepared from the corresponding ABA-type triblock copolymers because of the higher polymer concentration in the former. Although the stereo-complexation of the PLLA and PDLA blocks occurred at higher temperature also in the B-A-B copolymers, it was not responsible for the gelation of the mixed suspension. The PEG chains, involved in the helix formation of the PLLA and PDLA, should form helices with opposite helical senses to aggregate and lead the gelation of the system.

Effect of steric hindrance on hydrogen‐bonding interaction between polyesters and natural polyphenol catechin

Abstract: The phase behaviors for the blends of poly(3-hydroxypropionate) (PHP), poly(L-lactide) (PLLA), poly(D-lactide) (PDLA), and poly(D,L-lactide) (PDLLA) with catechin were investigated by differential scanning calorimetry. In PLLA/catechin, PDLA/catechin, and PDLLA/catechin blends, two glass transitions were detected when the catechin content was ≥40 wt %, whereas in PHP/catechin blends only one glass transition was observed over the whole range of blend compositions. The former and the latter results should reflect the inhomogeneous and the homogeneous nature of the blends, respectively, in the amorphous phase. These different phase behaviors should arise from the differences in the chemical structures between PHP and PLLA/PDLA/PDLLA, which dominates the strength and the number of intermolecular hydrogen-bonding interactions between the ester carbonyl groups of polyesters and the phenol groups of catechin. As detected by FTIR spectroscopy, in comparison with PHP, the steric hindrance of side-chain methyl groups of PLLA, PDLA, and PDLLA might restrain the formation of hydrogen bonds between their ester carbonyl groups and the phenol hydroxyl groups of catechin, even weakening the strength of such hydrogen bonds. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 91: 3565–3573, 2004

X-Ray and Electron Diffraction Study of Poly(p-dioxanone)

Abstract: Solution-grown lamellar crystals of poly(p-dioxanone) (PPDX) have been crystallized isothermally from butane-1,4-diol at 100°C The crystal structure of PPDX has been determined by interpretation of X-ray fiber diagrams of PPDX fibers and electron diffraction diagrams of lozenge-shaped chain-folder lamellar crystals The unit cell of PPDX is orthorbombic with space group P2 1 2 1 2 1 and parameters: a=0970 nm, b=074 mm, and c (chain axis) = 0682 nm There are two chains per unit cell, which exist in an anti parallel arrangement

Synthesis of polyglactin by melt/solid polycondensation of glycolic/L-lactic acids

Abstract: Polyglactin was successfully synthesized by the melt/solid polycondensation of a mixture of glycolic acid (GA) and L-lactic acid (LA) mostly at a GA to LA monomer ratio of 90/10. In the polymerization procedure, a solid polycondensate was first prepared by melt-polycondensation at 150–190 °C, mechanically crushed into particles of various sizes (150–180, 180–210, 210–250, 250–300 and 300–355 µm), and subjected to solid-state post-polycondensation at 170 °C for 10–20 h. The polyglactin finally obtained was a colourless solid. Catalyst screening revealed that the single use of methanesulfonic acid gave the highest molecular weight of the product. Starting from the crushed melt-polycondensate with a diameter range of 180–250 µm, the highest number-average molecular weight of attained was 80 000 Da. This process can afford a facile route to large-scale synthesis of polyglactin with high molecular weight. Copyright © 2004 Society of Chemical Industry

Polyester block copolymer and process for preparing the same

Abstract: PROBLEM TO BE SOLVED: To provide a process for preparing a high-molecular weight polyester block copolymer having a high degree of tendency to form blocks linked through an ester bond without using any harmful bonding agent. SOLUTION: The process for preparing the polyester block copolymer comprises subjecting two or more polyesters each of which has different repeating units to a transesterification reaction at a temperature less than the melting point of the polyester having the highest melting point among the two or more polyesters to thereby produce a polyester block copolymer having a high Pr (persistence ratio) value. COPYRIGHT: (C)2004,JPO&NCIPI

Microorganism capable of degrading aromatic polyester and method of degrading aromatic polyester using the same

Abstract: A microorganism which belongs to the genus Rhizobium and has the ability of degrading an aromatic polyester, and a method of degrading an aromatic polyester by using the microorganism. According to this method, the aromatic polyester can be degraded safely and relatively swiftly at a low cost.