Lignin in hardwoods

Woods B and Calnan CD (1976) Toxic woods. British Journal of Dermatology, 95 (suppl 13) Wu J, Fukazawa K and Ohtani J (1992) Distribution of syringyl and guaiacyl lignins in hardwoods in relation to habitat and porosity form in wood. Flolirforschung, 46 181-5 Wu Q (1989) An investigation of some problems in drying of Tasmanian eucalypt timbers. 

Table 3.2 Distribution of lignin in softwoods and hardwoods in the various morphological zones.

Lignin in the true middle lamella of wood is a random three-dimensional network polymer comprised of phenylpropane monomers linked together in different ways. Lignin in the secondary wall is a nonrandom two-dimensional network polymer. The chemical structure of the monomers and linkages which constitute these networks differ in different morphological regions (middle lamella vs. secondary wall), different types of cell (vessels vs. fibers), and different types of wood (softwoods vs. hardwoods). When wood is delignified, the properties of the macromolecules made soluble reflect the properties of the network from which they are derived. 

This study describes the application of differential vis-cometry as a GPC detector to the problem of determining molecular weight distributions of acetylated hardwood lignins in tetrahydrofuran. Molecular weight distributions of ball-milled, organosolv, alkali-extracted/mild acid hydrolyzed, and alkali-extracted/steam exploded aspen lignins were estimated using universal calibration. 

Recent work has concentrated on the use of ALCELL lignin as a substitute for phenol-formaldehyde resins in wood adhesives, particularly wafer-board. Some of the results obtained when a PF resin (Bakelite 9111) was replaced with different levels of hardwood ALCELL lignin in waferboard manufacture will be briefly discussed below. Table III shows the conditions used for waferboard manufacture. 

Figure 1. Absorption characteristics of lignins in the visible region of the electromagnetic spectrum hardwood kraft lignin (A), HPL (B), and a typical bleached HPL (C).

The only very slight photochromic behaviour obtained upon irradiation of bleached aspen CTMP may be due to the presence of syringyl instead of guaiacyl units in hardwood lignin. These structures are less able to form orr/to-quinones during irradiation than softwood pulps (8). 

Very interesting results have been obtained with very similar model compounds, representing hardwood and softwood non-phenolic lignin. In the case of the... 

Musha Y, Goring DAI (1975) Distribution of synngyl and guaiacyl moieties in hardwoods as indicated by ultraviolet microscopy Wood Sci Technol 9 45-58 Nimz HH (1974) Beech lignin - proposal of a constitutional scheme Angew Chem Int Ed 13 313-321... 

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