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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.

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 polydispcrsity 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 30μηι 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. Topical mechanical properties of carbon fibers from AWL were as follows: fiber diameter 14± Ι.Ομιη; elongation, 0.98 ±0.25%; tensile strength, 355±53MPa; modulus of elasticity, 39.1 ± !3.3GPa. The carbon fibers derived from AWL can be classified as fibers of general performance grade.

The beta-O-4 structure is the most abundant substructure in lignin. Lignin related polymers composed of only the beta-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 gamma-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).

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