Wood structure

Wood cell walls have an outer primary and an inner secondary wall layer. The thin primary wall is formed first and is flexible to accommodate changes to the shape of the cell as it grows and develops. The secondary wall is thicker and more complex and is laid down when the cell shape is established. In addition, the secondary wall is composed of three layers - the outermost Sh adjacent to the primary wall, the S2 and the innermost S3, which are adjacent to the cell lumen. Cells are held together by the middle lamella that cements the outer surface of primary wall layers of one cell to the primary walls of adjacent cells. 

In contrast to the two-dimensional nature of the wood polysaccharides, lignin is described as a three-dimensional polymer composed of phenyl 

1 Archaeological Wood Recovered from the Marine Environment 

The marine environment presents a hostile and seemingly unlikely situation for the survival of archaeological wood, yet it does survive. Normally, wood does not survive long enough in marine environments to enter the archaeological record because of the activities of wood-boring animals and aerobic microbes. However, studies have shown that rapid burial in the anoxic sediments of the seabed will protect ships timbers and wooden artefacts from the physical, chemical and biological processes that influence the deterioration of exposed wood. 

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R. L. Whisder and C.-C. Chen, iu M. Lewiu and I. S. Goldsteiu, eds.. Wood Structure and Composition, Vol. 11, International Eiber Science and Technology Series, Marcel Dekker, Inc., New York, 1991, Chapt. 7. 

In hardwoods, morphological structural elements in longitudinal series comprise the segmented structure termed vessel . Vessels, which are exposed in transverse section, constitute about 10-46% of the stem volume in deciduous hardwoods and are cells of relatively large diameters (50-300 p.m). Vessels have in short the appearance of open vertical tubes within the wood structure because their end walls have partially dissolved. By comparison, the hardwood vessel diameter can be as much a 10 times the diameter of a softwood fiber. 

Wood structure before pressing, size and shape of particles... 

There are known to be about 30,000 disease-causing agents (fungi, viruses, nematodes, bacteria) in 3,000 types of cultivated plants. More than 10,000 species of arthropods (insects, ticks, arachnids) affect agricultural plants and animals. Along with agriculture, pesticides are also widely used in forestry and fisheries, in energy and railroads (to clear plants), in construction (to protect wood structures), etc. 

Lignin comprises about 17-33% of the dry weight of wood. It is a complex aromatic polymer which appears to function both as a strengthening agent in the composite wood structure and also as a component which assists in the resistance of the wood towards attack by micro-organisms and decay. 

Lignin and carbohydrates exist in close association in the wood structure and there is now strong evidence to suggest that formal covalent links exist between the lignin macromolecule and carbo-... 

Richard J.T., "Wood Formation and Morphology" in Wood Structure and Composition, Ed. Lewin M och Goldstein I. S., Marcel Dekker (New York), Int. fiber science and technology series v. 11, (1991). 

Stamm has made a thorough examination of the effect of sucrose and invert sugar on the relevant physical properties of wood and has found that shrinkage is definitely retarded by the deposition of the sugar in the wood structure. Invert sugar seems superior in this effect to sucrose itself. 

Housing and construction (wood structures, flooring, furniture, laminates, composites, displays, wiring and cables, and optical fibers)... 

Data concerning the elemental composition and methods for isolating lignin from the wood structure, as well as the mean molar masses and distributions of the obtained fragments, are given in Table II (1,5). 

Substantial arsenic may leach into adjacent soils from wooden structures with CCA or other arsenic-bearing preservatives. Townsend et al. (2003) has shown that 65 surface soil samples from underneath nine CCA-treated wood structures in Florida, USA, contain 1.18-217 mg kg-1 of arsenic when compared with control soils that average only 1.36 mg kg-1 (Table 3.20). In a study involving ammoniacal copper zinc arsenate wood preservatives, arsenic concentrations generally fell to background levels within 150-300 mm away from 19 utility poles in Virginia, New York, and Florida, USA ((Morrell, Keefe and Baileys, 2003) Table 3.20). The environmental effects of arsenic-bearing wood preservatives are further discussed in Chapters 5 and 7. 

Townsend, T Solo-Gabriele, H., Tolaymat, T. et al. (2003) Chromium, copper, and arsenic concentrations in soil underneath CCA-treated wood structures. Soil and Sediment Contamination, 12(6), 779-98. 

D. Plastic Composites. Many different woods have been treated with organic monomers and the monomers catalytically polymerized within the wood structure. The subject of treating wood to form plastic composites is covered by Dr. John Meyer in another section of this publication. For the most part, these composites have been prepared and studied for their use in dimensional-stabilized products (for example, see 13-17). 

Alcohols also promote wettability and penetration of the wood surface. This may easily be shown by the following simple experiment. When equal sized drops of distilled water were placed on the surface of a freshly planed piece of southern yellow pine, the times for the drops to completely soak into the wood were observed. On the early wood it took 65 seconds and on the latewood 179 seconds. When similar drops of 50% ethanol solution were used instead of pure water, it required only six seconds to disappear into the earlywood and 26 seconds into the latewood. However, if a small drop of adhesive syrup, with no hardener added, was placed on the wood surface, no adsorption took place at all. It was surmised that the viscosity prevented its permeation. When the adhesive was diluted with 50% alcohol it was readily absorbed and produced a red stained spot on either earlywood or latewood areas. This showed that the low molecular weight adhesive molecules could readily permeate the wood structure before condensation with the curing agent. 

Since most vinyl monomers are non-polar, there is little if any interaction with the hydroxyl groups attached to the cellulose molecule. In general, vinyl polymers simply bulk the wood structure by filling the capillaries, vessels and other void spaces in the wood structure. 

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