Wood, constituents

Brower, H.E. 1966. Gas chromatographic sugar analysis in hydrolyzates of wood constituents. Anal. Chem. 38 362. 

This research was undertaken to study aqueous alkaline reactions of monomeric structures, similar to polymeric wood constituents, from which color would be formed. Since hardwood pulps were of the greatest immediate interest, the reaction of syringyl alcohol, representing the hardwood lignin structure, in aqueous alkaline solution at room temperature has been studied extensively up to the present time, but the reactions of vanillyl alcohol and a-methylvanillyl alcohol, representing the softwood lignin structure, have also been studied to some extent under the same reaction conditions. 

Generally, no cellulose is lost in the acid sulfite process. The losses of hemicelluloses are higher for hardwood than for softwood. Typical yield values for various wood constituents have been collected in Table 7-3 in which comparative data for the kraft process are also shown. 

Th is book attempts to discuss various aspects of wood chemistry in relation to applications. It is believed that the book might be useful not only for students and teachers but generally for chemists, biochemists, and others working either in the laboratory as researchers or in production and planning. Chapter 1 describes the structure and anatomy of wood. Carbohydrate chemistry belongs to the fundamentals in wood chemistry because two thirds of the wood constituents are polysac-... 

A classical strategy makes use of odor thresholds calculated in matrix as similar as possible to the wine subject of the study. This strategy, for instance, demonstrated its usefulness for assessing the importance of wood constituents on wine aroma (Boidron et al. 1988) or for establishing the maximum limits beyond which some odorants exert a negative effect on wine aroma (Chatonnet et al. 1993). However, this strategy is quite limited in scope and can only be applied to those compounds that really play the role of impact compounds and to those cases in which is possible to find wines free from such substances. It is, therefore, very well suited to characterize taints and off-flavors. 

Apparent kinetic parameters have been obtained for mass-loss and noncondensable gas evolution. The activation energy, above an ambient temperature of 370 "C, was found to be about 30 kJmol under the present circumstances. The activation energy for the imss-loss below 370 C agrees with those found in the literature for the kinetics of the main wood constituents. 

Cu / lignin complexes physically adsorbed on wood constituents Cu / cellulose complexes... 

There are several errors involved in gravimetric moisture measurements. One error is the assumption that h is zero in an ordinary oven. This effect can be minimized by using a vacuum oven or a strong desiccant such as phosphorus pentoxide. Another problem is the evaporation of volatile wood constituents, if present, to give a higher apparent moisture content in the wood. A third problem in accurate moisture measurement is the effect of sample moisture history (8). 

Effect of Wood Species and Extractives. The sorption isotherms of all woods are generally similar in shape. However, there may be considerable variations among them with respect to the absolute values of hygroscopicity. This variation may be because of differences in the proportion of the primary wood constituents, such as cellulose, hemicellulose, and lignin in different woods or more importantly, because of differences in the kind and quantity of ex-... 

Cu -lignin complexes Physically adsorbed on wood constituents... 

The first law of photochemistry [the Grotthus-Drapper principle (30)] states that for a photochemical reaction to occur, some component of the system must first absorb light. The second law of photochemistry [the Stark-Einstein principle (3J)j states that a molecule can only absorb one quantum of radiation. The absorbed energy causes the dissociation of bonds in the molecules of the wood constituents. This homolytic process produces free radicals as the primary photochemical products. This event, with or without the participation of oxygen and water, can lead to depolymerization and to formation of chromophoric groups such as carbonyls, carboxyls, qui-nones, peroxides, hydroperoxides, and conjugated double bonds. 

Supercritical fluids display attractive solvent characteristics which can be manipulated by either the pressure or temperature. Using supercritical fluids as reaction media, simultaneous reaction and separation are also achievable. This methodology has recently been applied to the reactive separation of wood constituents, especially lignin, by supercritical fluids (1-4). Delignification processes using supercritical fluids are of potential Industrial Importance (5,6) and there Is a need for the development of kinetic models which could permit a priori prediction of the rate of lignin removal. The present paper discusses such a model. 

Any treatment of wood must take account of the differing accessibilities and reactivities of the principal wood constituents. Further, any chemical or microbial method of breaking down wood has to devise conversion pathways for cellulose, the hemicelluloses and lignin, and if necessary consider ways of isolating the individual reaction products so that they can be processed separately. Hydrolysis has proved to be a most effective method of opening up the wood structure for subsequent treatments. The expression hydrolysis of wood is used rather loosely. It is not technically correct since the reactions affect primarily the carbohydrate fraction of wood. Lignin is largely unaffected. 

T Ona, T Sonoda, M Shibata, T Kato, and Y Ootake. Non-destructive Determination of Wood Constituents by Fourier Transform Raman Spectroscopy. J. Wood Chem. Technol. 17 399 17, 1997. 

Sorvari, J., Sjdstrom, E., Klemola, A., and Lanine, J. E. (1986) Chemical characterization of wood constituents, especiaUy hgnin, in fractions separated from middle lamella and secondary wall of Norway spruce Picea abies). Wood Sci. Technol. 20, 35-51. 

In the future, more attention will undoubtedly be devoted to the molecular architecture of wood, including the exact physical state of the hemicelluloses in the cell wall and their relation to other wood constituents, especially cellulose and lignin. Little is currently known concerning the bios3mthesis of cellulose and hemicelluloses, and their role in cell development. The numerous hemicelluloses occurring in the phloem have only recently attracted attention. It is probable that, in many species, some of them differ considerably from those present in the xylem. 

The objective of this chapter is to follow the process of abiotic chemical degradation as it takes place within a piece of wood by examination of a series of tissues taken at increasing distances from the wood surface. Chemical analysis of the tissues under investigation is indispensable for interpretation of the optical evidence. Standard analyses for the main wood constituents were made of the respective tissues to supplement the micro-... 

Figure 1. Cross sections of waterlogged archaeological woods showing zones of slight and heavy degradation, and the composition of the main wood constituents. Squares indicate where samples were taken for microscopy.

The different main polymers in wood appear to have structural roles that are related to this microarchitecture. Cellulose, an intrinsically rigid crystalline material, provides the reinforcing framework of the cell walls. Theoretical treatments of stress-strain relationships in wood under load indicate that the stiflhess of the material is imparted primarily by cellulose fibrils 10). The main function of hemicellulose and lignin is to buttress the fibrils. Degradation of any of these wood constituents results in a decrease in the strength of the material. 

The spectrum of aspen wood (Figure 7.1) shows the presence of the three fundamental wood constituents. A band for cellulose is at 895 cm (g-anomer in pyranose ring) <22). xhe band at 1740 cm" is due to uronic acid and acetyl groups in hemicellulose. The bands from 1235 to 1605 cm, specially the one at 1505 cm", are representative of lignin while those from 950-1100 cm" are due, in part, to carbohydrates (C-0 bonds in alcohols). 

Wilkins K, Larsen K, Simkus M, 2003. Volatile metabolites from indoor molds grown on media containing wood constituents. Environmental Science and Pollution Research 10,206-8. 

The coating of wood is strongly influenced by its structure and properties (elasticity, hardness, strength, shrinking tendency). Some wood constituents (e.g., pigments, resins, or tanning acids) can interfere with the coating process. 

Rule 2 High temperature. A high value of temperature is most often a positive factor. This accelerates the internal moisture transfer and activates the viscoelastic creep. However, care should be taken with sensitive species high temperature levels can increase the risk of collapse, problems of color, or even thermal degradation of the wood constituents. 

The use of gypsum binders with improved water resistance is indicated in applications in which limited exposure of the hardened material to liquid water is to be expected. As the setting and hardening of the binder are not impeded by soluble wood constituents, binders of this kind are also suitable for use in the production of particle boards (Deng et al., 1998). 

S. Jeamtrakull, A. Kositchaiyong, T. Marlqjin, V. Rosarpitak, and N. Sombatsompop, Effects of wood constituents and content, and glass fiber reinforcement on wear behavior of wood/ PVC composites. Compos. B 43,2721-2729 (2012). 

In case a worker has to change his job, retraining should not include occupations that bear the risk of recurrent allergic contact dermatitis. Cross reactions might occur in wood workers sensitive to quinonoid wood constituents. After changing job to that of a gardener, florist, nursery worker or even pharmacy assistant, relapses may occur resulting from related quinones in ornamental plants or extracts handled occupationally. 

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