Pretreatment of Wood

Properly graded sanding with appropriate sandpapers is a prerequisite for a satisfactory wood surface. Industrially, sanding is performed on cylindrical abrasive-belt machines or automatic grinders, followed by brushing and suction to remove abrasive dust. 

1) Removal of resins, e.g., by hydrolysis (wood soaps or soda solution) or dissolution (e.g., alcohol, acetone) 

3) Rectification (filling, patching) of processing and growth defects in the wood 

4) Structuring by brushing, burning, sandblasting, embossing, or leaching 

5) Staining with dyes dissolved in water or solvents, or with pigment dispersions 

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Pretreatment of wood with pectinolytic enzymes facilitates the debarking. The energy consumption during debarking of spruce in a laboratory scale debarker is clearly decreased after treatment with Pectinex Ultra (Table 1). Several hours is needed for effective preteatment (Table 2). 

Kiguchi, M., Karaoke, Y., Evans, P.D., Kadegaru, Y. and Imamura, Y. (2001). Pretreatments of wood surfaces for improving weatherabUity of clear finishing. International Research Group on Wood Preservation, Doc. No. IRGAVP 01-40196. 

Ozone has recently become industrially available at low cost. From the point of view of the development of complete wood utilization, the pretreatment of wood with ozone enhances the yield of glucose by enzymatic saccharification. Ozonized lignin is thereby obtained as a by-product. 

Almost any substrate that will be powder coated, whether metal, medium-density fiberboard (MDF) or some other material, requires some kind of surface treatment. Surface preparation ( pretreatment ) of wood and, more specifically, of MDF preparation, consists of sanding, removal of contaminants and board conditioning. MDF boards that will be coated by UV-curable powders should have moisture content of 4 to 9%. It is also a common practice to preheat MDF boards prior to application of the UV powder.37... 

The adverse effects of weather on wood and wood finishes and resultant chemical and physical changes on wood surface will be reviewed and discussed in this work. In addition, recent research findings on surface pretreatment of wood for enhancing durability of applied finishes will be presented. 

The technology actually employed in treating a given waste depends upon waste characteristics primarily, but it is also influenced by such other factors as available land area, volume of discharge, and disposition of treated waste. Oil separation, for example, is necessary only for oily wastewater and, among timber products industries, is employed only in the pretreatment of wood preserving wastes. Adjustment of pH is required only if the pH value falls outside the range of 6.0 to 9.0. 

Of the reducing methods, the pretreatment of wood chips with hydrogen sulfide (140°C, pH 7) might be technically feasible. During such a treatment the aldehyde end groups are reduced to thioalditols according to the following equation ... 

Enzymatic Hydrolysis. Saccharification of wood polysaccharides to sugars can be accomplished by enzymatic techniques instead of acid hydrolysis. The U.S. Army Natick Laboratories developed a method for conversion of cellulose to glucose with a cellulose enzyme from an active strain of the fungus Trichoderma viride. However, extensive pretreatment of wood is necessary before sufficient enzymatic hydrolysis will take place. 

Chemical modification reactions continue to play a dominant role in improving the overall utilization of lignocellulosic materials [1,2]. The nature of modification may vary from mild pretreatment of wood with alkali or sulfite as used in the production of mechanical pulp fibers [3] to a variety of etherification, esterification, or copolymerization processes applied in the preparation of wood- [4], cellulose- [5] or lignin- [6] based materials. Since the modification of wood polymers is generally conducted in a heterogeneous system, the apparent reactivity would be influenced by both the chemical and the physical nature of the substrate as well as of the reactant molecules involved. 

Surface oxidation processes have also been used as pretreatments for improving the bonding strength of adhesives. Brink et al. [9] reported that the wet bonding strength of plywoods or particleboards manufactured using phenol formaldehyde increased after pretreatment of wood with nitric acid. Mari et al. [10] also reported that nitric acid oxidation reduced the amount of isocyanate resin adhesive required to manufacture particleboard and improved the mechanical properties and biological resistance of boards. 

GM Scott, M Akhtar, Ml Lentz, RE Swaney. Engineering, scale-up, and economic aspects of fungal pretreatment of wood chips. In RA Young, M Akhtar, eds. Environmentally Friendly Technologies for the Pulp and Paper Industry. New York John WUey Sons, Inc., 1998, pp. 341-383. 

K Messner, S Masek, E Srebotnik, G Techt. Fungal pretreatment of wood chips for chemical pulping. In M Kuwahara, M Shimada, eds. Biotechnology in Pulp and Paper Industry. Tokyo UNI Publishers, 1992, pp. 9-13. 

Bihani, B. Sanuelson, O. Consumption of nitrogen oxides during pretreatment of wood with nitrogen dioxide and dioxide oxygen. Wood Sci. Technol. 1984, 18, 295-306. 

Acidic pretreatments of wood chips have also been investigated under varying conditions mainly to recover hemiceUuloses. ° The integration of pretreatment with kraft pulping, mainly with respect to pulping performance and pulp properties have also been studied.In addition, the lignin fragments in hydrolysates have been characterized.The main chemical utilization of hemicelluloses includes films, surface modifiers, and various derivatives. 

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