Hardwood Extractives

M. Caude, D. Thiebaut, ed.. Practical Supercritical-Fluid Chromatography and Extraction, Hardwood, Amsterdam, 397 (1999). 

Wood also contains 3—10% of extraceUulat, low molecular weight constituents, many of which can be extracted from the wood using neutral solvents and therefore ate commonly caUed extractives. These include the food reserves, the fats and their esters in parenchyma ceUs, the terpenes and resin acids in epitheUal ceUs and resin ducts, and phenoUc materials in the heartwood. Resin materials occur in the vessels of some hardwood heartwood. 

Xylose is obtained from sulfite Hquors, particularly from hardwoods, such as birch, by methanol extraction of concentrates or dried sulfite lyes, ultrafiltration (qv) and reverse osmosis (qv), ion exchange, ion exclusion, or combinations of these treatments (201). Hydrogenation of xylose is carried out in aqueous solution, usually at basic pH. The Raney nickel catalyst has a loading of 2% at 125°C and 3.5 MPa (515 psi) (202,203). 

Softwoods are generally more resistant to acids than are hardwoods because they have high lignin and low hemiceUulose contents. In general, heartwood is more resistant to acids than sapwood, probably because of heartwood s higher extractive content and slower movement of Hquid into the heartwood. For these reasons, the heartwood of certain conifers has been widely used in the chemical industry. 

Similar studies were conducted by Kudzin and Nord (64) on the hardwoods oak, birch and maple. The fungus employed to bring about the decay of these wood samples was Daedalea quercina. The results of the periodic analyses of the decayed wood and the chemical compositions of the alcohol extractable lignins are outlined in Tables 6 and 7 respectively. 

Fungi. I. Metabolic Products otLentinus lepideus. Biochem. J. 34. 82 (1940). 7a. Black, R. A., A. A. Rosen and S. L. Adams The Chromatographic Separation of Hardwood Extractive Components Giving Color Reactions with Phloroglucinol. J. Amer. chem. Soc. 75, 5344 (1953). 

Wood contains a small proportion (usually less than 5%) of components which are extractable by organic solvents such as ethanol or dichloromethane. The proportion of these extractives varies in hardwoods and softwoods and also between species. Although many of these substances are removed during the chemical pulping process, some may still be retained in the final sheet of paper. Their chemical composition is very varied, and they include alkanes, fatty alcohols and acids (both saturated and unsaturated), glycerol esters, waxes, resin acids, terpene and phenolic components. The proportion which remains in pulp and paper depends upon the pulping process used. In general, acidic components such as the resin and fatty acids are relatively easily removed by alkali by conversion to their soluble... 

The basic structure of all wood and woody biomass consists of cellnlose, hemicelluloses, lignin and extractives. Their relative composition is shown in Table 2.4. Softwoods and hardwoods differ greatly in wood stmctnie and composition. Hardwoods contain a greater fraction of vessels and parenchyma cells. Hardwoods have a higher proportion of cellulose, hemicelluloses and extractives than softwoods, but softwoods have a higher proportion of lignin. Hardwoods ate denser than softwoods. 

Hemicelluloses are quite difficult to extract from cell walls of softwoods (9,10) and are usually destroyed or depolymerized during the chemical pulping of these raw materials. However, other hemicelluloses, primarily xylans, can be extracted by cold, dilute sodium hydroxide from grasses and many hardwoods in very high yields (9,77). These xylans are deacetylated in an alkaline medium and are for the most part insoluble (hemicellulose A). A partially water soluble fraction (hemicellulose B) has also been... 

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. 

This study reports the first application of universal calibration via HPSEC-DV to four acetylated hardwood lignins obtained from aspen (Pop-ulus tremuloides) wood meal by ball milling and solvent extraction steam explosion followed by alkaline extraction organosolv pulping followed by water extraction of the associated sugars and dilute sulfuric acid hydrolysis followed by sodium hydroxide extraction. 

In the ALCELL process, conventional hardwood chips are cooked in batch extractors with an aqueous ethanol liquor at appropriate temperatures, pH, and time. In the process lignin, hemicellulose and other various components of wood are extracted from the chips into the aqueous ethanol forming a black liquor. 

General Procedures. Optical brightness pads of hardwood BCTMP and cellulose were prepared following TAPPI procedures (IS). All handsheets were extracted with methanol followed by dichloromethane, vacuum dried, and stored at below 0° C prior to use. Cotton linter handsheets had an average Tappi brightness value of 86.5 0.1 and the BCTMP... 

The most recent publication reviewed was by Einspahr and Harder (63), who discuss the basic properties of hardwood barks that could be important in the manufacture of any fibrous product. This was a progress report showing results for 16 pulpwood species work is in progress on 16 additional species. Measured were such bark factors as specific gravity, extractives content, strength, toughness, reaction to hammermilling, and ash content. 

After the veneer has been properly unitized and dried, it is transported to the gluing operation. It is here that the greatest proportion of chemicals other than water are involved in the plywood process. To better understand the adhesive resins involved, perhaps it is best to review the quantities of softwood and hardwood plywood manufactured in relation to the adhesive needs required. The 1972 - 1973 era were years of peak production in the United States for plywood. Data will be extracted from various reports for presentation purposes. Hardwood and softwood plywood production is normally reported in different manners and it is difficult to compare. While the values reported are not intended to be exactly accurate, they will give some comparison, relatively speaking, and should give some concept of the volume of plywood produced and in turn the volume of adhesives used. 

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