Satoshi Kubo

Lignin-based carbon fibers for composite fiber applications

Abstract Carbon fibers have been produced for the first time from a commercially available kraft lignin, without any chemical modification, by thermal spinning followed by carbonization. A fusible lignin with excellent spinnability to form a fine filament was produced with a thermal pretreatment under vacuum. Blending the lignin with poly(ethylene oxide) (PEO) further facilitated fiber spinning, but at PEO levels greater than 5%, the blends could not be stabilized without the individual fibers fusing together. Carbon fibers produced had an over-all yield of 45%. The tensile strength and modulus increased with decreasing fiber diameter, and are comparable to those of much smaller diameter carbon fibers produced from phenolated exploded lignins. In view of the mechanical properties, tensile 400–550 MPa and modulus 30–60 GPa, kraft lignin should be further investigated as a precursor for general grade carbon fibers.

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.

Thermal Decomposition Study of Isolated Lignin Using Temperature Modulated TGA

Abstract Temperature modulated TGA (MTGA) was utilized to study the kinetics of lignin pyrolysis. Three industrial lignin preparations were investigated: softwood kraft lignin, hardwood kraft lignin, and Alcell lignin. Unlike conventional TGA, MTGA provides apparent activation energy (E a ) distribution curve using a single experimental run in a relatively short experimental time. Under Hi-Res conditions using a dynamic heating rate, the activation energies were higher than those determined using a constant heating rate. Likewise, small sample masses provided higher activation energies than those run with large sample mass. These effects can be eliminated by using a relatively large sample mass, > 10 mg. In this study, we discuss the effect of MTGA conditions on calculating E a distribution curves for lignin pyrolysis.

Chemical analysis of the product in acid-catalyzed solvolysis of cellulose using polyethylene glycol and ethylene carbonate

Degradation and decomposition of cellulose were studied in an acid-catalyzed solvolysis treatment of biomass using polyethylene glycol (PEG) and ethylene carbonate (EC). The solvolysis reaction was followed by a typical reaction system of wood liquefaction that uses sulfuric acid catalyst at 140° or 150°C at atmospheric pressure. The methods of fractionation and chemical analysis of the degraded cellulose in the solvolyzed product are discussed. The solvolyzed product was separated into several fractions, and they were hydrolyzed to release glucose and levulinic acid to determine the quantity of glucosides and levulinates in the solvolysis product. The data clearly showed that the solvolysis reaction had the same mechanism when using PEG or EC. Degradation of cellulose leads to the formation of glucosides, which then decompose, resulting in a levulinic acid structure, and producing a water-insoluble fraction. The conversion rates of both glucosides and levulinates strongly depend on the reaction conditions of the solvolysis. In particular, EC promotes faster conversion of the reactions. The method discussed here is a chemical analytical technique for characterization of the products of wood liquefaction.

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.

Lignin-Based Carbon Fibers

Carbon fibers are one of the most important engineering materials in advanced composites. They are lightweight, fatigue resistant materials that possess high strength and high stiffness. These unique properties result from their flawless structure and the development of highly anisotropic graphic crystallites orientated along the fiber axis during the production process.1 Carbon fibers are manufactured by thermally treating fibers at 1000-2000 ℃ in an inert atmosphere while maintaining the fibrous structure. This is aided by a stabilization stage in which the precursor fibers are heated under tension at 200-300 ℃ in the presence of air. This causes crosslinking on the fiber surfaces, among other reactions, and prevents shrinking, melting and fusing.

A Characteristic Reaction of Lignin in Ionic Liquids; Glycelol Type Enol-Ether as the Primary Decomposition Product of β-O-4 Model Compound

Abstract Guaiacylglycerol-β-guaiacyl ether (GG), which contains a predominant inter-unit linkage of lignin, could be converted into a corresponding glycerol type enol-ether (EE), 3-(4-hydroxy-3-methoxyphenyl)-2-(2-methoxyphenoxy)-2-propenol, by the heat treatment in ionic liquids. EE is believed to be the unstable intermediate of the lignin decomposition process under acidic and alkaline conditions. By contrast, EE could be isolated as a relatively stable compound from the reaction mixture of ionic liquids. EE was formed as a primary reaction product in all ionic liquids used in this research under the temperature conditions of 120°C, although the decomposition rate and secondary decomposition products of GG varied with the ionic liquid used. NMR data suggested that dehydration reaction of GG progressed stereospecifically and [Z] isomer was predominantly formed (stereoselectivety of [Z] is higher than 90%).

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.

Surface Porosity of Lignin/PP Blend Carbon Fibers

Abstract The surface porosities of carbon fibers derived from the polymer blend fibers of hardwood kraft lignin, HKL and polypropylene, PP, were discussed using thermal analyses, FTIR, and nitrogen adsorption. HKL/PP carbon fibers were prepared by two‐step thermal processing, thermostabilization, and carbonization. During the thermostabilization process, pores are created by oxidative degradation of the PP component. After thermostabilization some crystalline and highly oxidized PP components remained in the blend fiber. These residual PP components were subsequently pyrolyzed during carbonization, and effectively created a porous structure in the resulting carbon fibers. N2 adsorption tests of the porous carbon fibers revealed the same type of adsorption/desorption isotherms as for activated carbon fiber. The internal surface area of the HKL/PP = 62.5/37.5 carbon fibers was calculated to be 499 m2 g−1. This value was lower than that for commercial activated carbon, 745 m2 g−1. However, these porous lignin‐based carbon fibers were not activated carbon fibers, which could be relatively easily done through steam activation. Thus, the HKL/PP blend carbon fibers appear to be promising precursors for activated carbon fibers.

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.