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A novel solvent system, lithium chloride/dimethyl sulfoxide (LiCl/DMSO), was developed for dissolving milled wood. This system completely dissolved beech and spruce milled woods prepared from the Wiley woods (coarse wood meals prepared by a Wiley mill) by 2 h planetary ball-milling under the milling conditions employed. The dependence of the structural change of lignin on the degree of milling was examined to evaluate the correlation between the dissolution and lignin structure. The nitrobenzene oxidation analyses showed that the 2 h milling caused almost no structural change in the aromatic part of lignin in the milled woods. The ozonation analyses suggested that the decrease of the erythro ratio [erythro/(erythro + threo)] obtained from beta-O-4 structure in lignin is only 0.35% after the 2 h milling. Although the yield decrease of the ozonation products was 9.8% after the 2 h milling, this value was fairly smaller than that after a longer time milling. When it is taken into consideration that the other solvent systems for dissolution of wood meal, which are proposed by Lu and Ralph, require 5 h of milling under the same milling conditions to dissolve the milled woods, it is safely stated that the LiCl/DMSO solvent system completely dissolves milled wood, the lignin of which is structurally less altered and, thus, is expected to provide an improved method for structural analysis of the entire lignin fraction in wood cell wall.

The reactivity of lignin during alkaline delignification was quantitatively investigated focusing on the effect of the structural differences between syringyl and guaiacyl aromatic nuclei and between erythro and threo in the side chain of β-O-4 type lignin substructure on the β-O-4 bond cleavage rate. It was known that the ratio of this reaction rate of the erythro to threo isomers of the dimeric β-O-4 type lignin model compound with two guaiacyl aromatic nuclei was ca. 4. However, the presence of a syringyl nucleus strongly influenced the rate, and the ratio of the syringyl type analogue was in the range between 2.7 and 8.0 depending on the reaction temperature. The effect of syringyl nucleus on the enhancement of the reaction rate appeared to be greater when the syringyl nucleus consists of the cleaving ether bond rather than being a member of the carbon framework.

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Microanalytical techniques were developed which allow the rapid characterization of fiber components and morphology of loblolly pine in a large number of samples. These techniques consist of extractives removal, holocellulose preparation, alpha-cellulose and lignin content determination, and fiber length and coarseness analyses. Greater than 95% of the nonvolatile extractives from an increment core sample of loblolly pine was removed by four successive two-day acetone extractions. Fiber morphology and alpha-cellulose content was determined from holocellulose prepared from only 100 mg of wood. Similarly, a microanalytical acetyl bromide method was developed that enabled the accurate determination of lignin content from less than 50 mg of wood. Through the development of these microanlytical methods, it is possible to accurately and rapidly analyze fiber morphology and chemical components in a large number of increment core samples.

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The reaction route of a dimeric non-phenolic C6-C2 type lignin model compound, 2-(2-methoxyphenoxy)-1-(3,4-dimethoxyphenyl)ethanol (VIII), was kinetically examined under acidolysis conditions (0.2 mol l-1 HBr in 82% aqueous 1,4-dioxane at 85°C). The disappearance of (VIII) followed the pseudo-first-order rate law, and the rate constant k (VIII) was 0.00854. In the course of the reactions, the following compounds were produced quantitatively at any time: an enol ether, 1-(2-methoxyphenoxy)-2-(3,4-dimethoxyphenyl)ethylene (IX), 2-methoxyphenol (X), and a Hibbert's ketone, 3,4-dimethoxyphenylacetaldehyde (XI). The substances (X) and (XI) are the result of the β-O-4 bond cleavage and their amounts were always equal during the whole reaction. When (IX) was subjected to the acidolysis under the identical conditions, its disappearance followed the pseudo-first-order rate law, and the rate constant k (IX) was 0.00825. Furthermore, (VIII) was not observed at all, and (X) was produced quantitatively at any time. Based on these results, the formation rate of (IX) during the acidolysis of (VIII) is expressed by the equation: d[(IX)]/dt=A·k (VIII)[(VIII)]-k (IX)[(IX)], where A is the proportion of (VIII) that converted into (IX) when (VIII) degraded. It was confirmed by solving this differential equation that the formation and disappearance of (IX) is best simulated when A was assumed to be 1.00. Therefore, it was proven in this paper for the first time that (VIII) primarily converts into (IX), and subsequently the β-O-4 bond cleavage occurs and (X) and (XI) are yielded.