Reaction wood, chemical composition

In Roman times tar and pitch from Pinaceae resinous wood were used to treat the inner surface of amphorae to store fluids such as wine [ 145,149] and to seal ship planks [89,144], Heating treatments applied to natural resins and resinous wood profoundly modify the chemical composition of the original material. Diterpenoid compounds undergo aromati-zation, demethylation and decarboxylation reactions, with the formation of new compounds of a lower molecular weight that show a high degree of aromatisation [87,88]. In tar and pitch produced from Pinaceae resin and woods, retene is considered as a stable end product of these reaction pathways and nor-abietatrienes, simonellite and tetrahydroretene represent the intermediates of these reactions [87,89,150]. 

Now the assumption is dropped that the chemical reaction is a rate-controlled conversion to an invariant product composition, and the composition is permitted to vary with local thermodynamic state. Zel dovich, Brinkley Si Richardson, and Kirkwood Wood pointed out that since in a chemically reactive wave, pressure is a function not only of density and entropy but also of chemical composition, the sound speed for a reacting material should be defined as the frozen sound speed... 

Morohoshi N, Sakakibara A (1971) The chemical composition of reaction wood Mokuzai Gakkaishi 17 393-399... 

Moisture content of wood appears to be the most important physical parameter to take into account in wood carbonization. An increasing moisture content decreases the production of pyrolytic liquids and increases the production of non condensable gases by enhancing secondary reactions of pyrolysis inside the solid matrix. This effect is increased by the shape of wood samples wet blocks of 4 4 16 cm produce less pyrolytic liquids and more non condensable gases than other wood samples. However, moisture content does not influence the chemical composition of carbonization products. This confirms the fact that water present in wood acts physically and not chemically in the carbonization of wood at low temperature and heating rate. 

There are definite changes in the chemical composition of reaction wood. Compression wood has a significant increase in lignin and a corresponding decrease in polysaccharides as compared to normal softwood. Tension wood has just the opposite relationship. Since juvenile wood tends to contain a high level of reaction wood, its chemical composition should differ from that of mature wood. 

Chemical modification of wood. Corona and plasma treatment. Wood estaification. Wood etherification. Reactions between wood and isocyanates. Reactions of wood with siloxanes. Reactions of wood with furfuryl alcohol. Wood-based composites... 

Wood structure within a given tree species is not uniform but varies depending on the conditions under which the tree is growing. For example, trees compensate for exposure to wind or other types of bending pressure by the production of reaction wood. In softwood, the formation of reaction wood is induced on the compressed side of a bending trunk (compression wood), whereas in hardwood, reaction wood is formed on the elongated side of the trunk (tension wood). Reaction wood cells are morphologically similar to normal wood cells but differ in their cell wall structure and chemical composition. 

Chemical charge, Hquor composition, time of heatup, and time at temperature of reaction are all functions of the wood species or species mix being digested and the intended use of the pulp. A typical set of conditions for southern pine chips in the production of bleachable-grade pulp for fine papers is active alkaH, 18% sulfidity, 25% and Hquor-to-wood ratio, 4 1. Time of heatup is 90 min to 170°C time at temperature of reaction, 90 min at 170°C. Hardwoods require less vigorous conditions primarily because of the lower initial lignin content. 

Gould, R. F., ed., Lignin Structure and Reactions, Advances in Chemistry Series, No. 59, American Chemical Society, Washington, D.C., 1966 and Rebello, A., "Composition of Wood", in Environmental Biogeochemistry, Nriagu, J., 2 vol., 1975, Ann Arbor Science Publishers, Ann Arbor, Michigan. 

During the early 1960 s a new class of chemicals containing one or more double bonds was used to treat wood vinyl type monomers that could be polymerized into the solid polymer by means of free radicals (2). This vinyl polymerization was an improvement over the condensation polymerization reaction because the free radical catalyst was neither acidic nor basic, nor does the reaction leave behind a reaction product that must be removed from the final composite, such as water. The acid and base catalysts used with the other treatments degrade the cellulose chain and cause brittleness of the composite. Vinyl polymers have a large range of properties from soft rubber to hard brittle solids depending upon the groups attached to the carbon-carbon backbone. 

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