Yasumitsu Uraki

Preparation of carbon fibers from softwood lignin by atmospheric acetic acid pulping

Infusible softwood acetic acid lignin (SAL) was converted to a fusible one as a raw material for carbon fibers by removing the infusible high molecular mass fraction. The resulting low molecular mass fraction (SAL-L) was spun by fusion spinning after thermal treatment to remove volatile materials. Carbon fibers (CFs) were prepared from these fibers by direct carbonization without thermostabilization, leading to reduction of the production costs. The tensile strength of SAL-L CFs increased with decreasing diameter, and those of the fine SAL-L CFs were comparable to those of other lignin based CFs such as phenolated exploded lignin. Therefore, SAL-L CFs were classified into general performance grade.

Preparation of carbon fibers from Organosolv lignin obtained by aqueous acetic acid pulping

Lignin fibers as precursors for carbon fibers were prepared by melt spinning from organosolv lignin (AWL), which was obtained from birch wood by aqueous acetic acid pulping at atmospheric pressure and used without any chemical modification. The spinnability of AWL was attributable to polydispersity of the lignin and to partial acetylation of hydroxyl groups during the pulping. Production of satisfactory lignin fibers was achieved by simple thermal treatment of lignin, followed by continuous spinning at a rate of more than 400m/min. The thermostabilization of thin (less than 30μm in diameter) and thick threads was achieved by heating to 250°C at a rate of 0.5°C/min in air and under oxygen stream, respectively. Carbonization of thermostable fibers was achieved by heating to 1,000°C under nitrogen stream. The mechanical strength of the carbon fibers was found to be related to the diameter of fibers. Typical mechanical properties of carbon fibers from AWL were as follows : fiber diameter 14 ± 1.0 μm ; elongation, 0.98 ± 0.25% ; tensile strength, 355 ± 53 MPa ; modulus of elasticity, 39.1 ± 13.3 GPa. The carbon fibers derived from AWL can be classified as fibers of general performance grade.

Preparation of activated carbon fibers with large specific surface area from softwood acetic acid lignin

Softwood acetic acid lignin (SAL) free from a high-molecular-mass fraction could be spun at 220°C by a spinning machine equipped with an extruder. Although the resulting fibers required thermostabilization, this step could be conducted with a faster heating rate than that for fibers obtained from hardwood acetic acid lignin (HAL). The thermostabilized SAL fibers were converted to activated carbon fibers (ACF) by carbonization in a stream of nitrogen at 1000°C, followed by steam activation at 900°C. At an activation time of 40 min, the SAL-ACF had a larger specific surface area than the corresponding HAL-ACF. When the activation time for SAL carbon fibers was prolonged to 80 min, the adsorption capacities of resulting ACF against iodine and methylene blue were markedly increased, as was the surface area of the ACF. It was found that SAL-ACF had adsorption properties comparable to those of high-performance commercial ACF. Also, it had a tensile strength equal to that of a pitch-derived ACF.

Thermomechanical analysis of isolated lignins

The thermal behavior of kraft lignin (KRL), periodate lignin (PIL), steam-exploded lignin (SEL) and acetic acid lignin (AAL), with emphasis on changes in volume upon heating, was investigated by thermomechanical analysis (TMA) in an attempt to evaluate the fusibility of lignin. All lignins underwent a glass transition but, with the exception of AAL, they all had infusible characteristics. The TMA curve for birch AAL(B-AAL) revealed two clear inflection points, assigned to the glass transition point (Tg) and the softening point (Ts) for transformation into a fluid liquid. Thus, only B-AAL among the lignins examined in this study had a fusion state. A fraction of B-AAL with almost the same weight-average relative molecular mass (Mw) as original B-AAL but with less polydispersity was found not to be transformed into a fused state. By contrast, fractions with lower relative molecular mass, namely, with Mw of less than 1,000, which accounted for 30% of AAL, had good fusibility. Therefore, the low-Mw fractions were responsible for the fusibility of B-AAL. Thermostable fusion states of acetylated KRL could not be confirmed by results of TMA and visual inspection. Thus, lignins could not be converted to fusible materials solely by the introduction of acetyl groups. Furthermore, from the results of TMA of fir AAL (F-AAL), which did not have a clear fusion state, it appeared that the fusibility of lignins was related to their molecular structures, for example, the extent of condensation of aromatic nuclei.

Influence of syringyl to guaiacyl ratio on the structure of natural and synthetic lignins.

Several kinds of natural woods and isolated lignins with various syringyl to guaiacyl (S/G) ratios were subjected to thioacidolysis followed by Raney nickel desulfuration to elucidate the relationships between the S/G ratio and the interunit linkage types of lignin. Furthermore, enzymatic dehydrogenation polymers (DHP) were produced by the Zutropf (gradual monolignol addition) method from mixtures of various ratios of coniferyl alcohol and sinapyl alcohol. The analysis of DHPs and natural wood lignins exhibited basically a similar tendency. The existence of both syringyl and guaiacyl units is effective for producing higher amounts of beta-O-4 and 4-O-5 structures, but it lowers the total amount of cinnamyl alcohol and aldehyde end groups. The relative frequency of the beta-beta structure increased, whereas that of beta-5 and 5-5 structures decreased with increasing syringyl units.

Easy synthesis of β-O-4 type lignin related polymers

The β-O-4 structure is the most abundant substructure in lignin. Lignin related polymers composed of only the β-O-4 structure were prepared using simple aromatic compounds as starting materials. Acetophenone derivatives were brominated, polymerized in the presence of K2CO3 and reduced with NaBH4 to give the lignin related polymers. These are linear polymers which resemble natural lignins in their structures, although they do not have a γ-hydroxymethyl group. The number average degree of polymerization (DPn) was determined with peracetate of the polymers by gel permeation chromatography. The DPn of guaiacyl type polymers ranged from 15.2–21.4, where the value for the syringyl type was 11.3 and for the p-hydroxyphenyl type 16.9. The Guaiacyl type polymer was very soluble in usual lignin solvents such as 1, 4-dioxane–water (96 : 4, v/v) and DMSO, but only slightly soluble in acetone–water (9 : 1, v/v).

Activated Carbon Fibers from Acetic Acid Lignin

Activated carbon fibers (ACFs) were prepared from acetic acid lignin-based carbon fibers by steam activation. The ACF had excellent properties, such as more rapid adsorption rate and higher iodine and methylene blue adsorption capacities, as compared to a commercially available activated carbon. The adsorption mechanism of ACF was quite different from that of activated carbon (AC). as supported by the micropore distribution profiles.

Lignin gel with unique swelling property.

Lignin gels were prepared from acetic acid lignin by use of polyethylene glycol diglycidyl ether as cross-linker. The gels were found to swell in aqueous ethanol solution, in particular 50% (v/v) solution. In addition, they also swelled in alkaline solution and shrank upon heating. A literature search showed that investigation on gel swelling in aqueous ethanol has not been reported so far. Gels prepared from the cross-linker alone and its analogues did not show such swelling characteristics in aqueous ethanol. Therefore, the unique swelling property must be attributable to an intrinsic property of lignin.

Carboxymethyl-chitin as a drug carrier of sustained release

Abstract Methamphetamine-bound carboxymethyl-chitin (CM-chitin) was found to induce hapten-specific antibodies through subcutaneous injection only in the presence of Freunds complete adjuvant in spite of its highly biodegradable property. CM-Chitin was employed as a sustained-release drug carrier for the subcutaneous injection. The induced specific antibody was applied to the titration of methamphetamine secreted into the blood of rabbits. The methamphetamine concentration in blood serum was maintained for 120 h at fairly high levels. Methamphetamine was also excreted into urine at high levels with a similar time course to that in blood serum.

Preparation and Characterization of Amphiphilic Lignin Derivatives as Surfactants

Abstract Acetic acid lignin (AL), one of the organosolv lignins, was modified by polyoxyethylation using commercially available polyethylene glycol diglycidylethers (PEGDE) having various chain lengths in order to generate novel nonionic polymeric surfactants. AL could be converted to the amphiphile by modifying with PEGDE (PEGDE-AL) having more than 9 of the ethylene oxide (EO) repeating units. Although the surface activities of PEG and AL were very limited, PEGDE-AL did strongly depress surface tension of water, and showed clear critical micelle concentrations (CMC). The CMC value of PEGDE-AL could be comparable to a commercial anionic lignin surfactant, lignosulfonate. The surface activity of AL amphiphile was further improved by modification with monoepoxides, ethoxy-(2-hydroxy)-propoxy-polyethylene glycol glycidylether (EPEGGE). The surface tension of water was depressed by the addition of the EPEGGE-AL to the same level as Triton® X-100, which is a commercial PEG-based nonionic surfactant, although there is still room for improvement in CMC value. The hydrophile–lipophile balance (HLB) of these AL amphiphiles was in the range of 11–14, and significant biodegradation was observed. These results suggest that the AL amphiphiles can be used as emulsifier and detergent.