Etherification of wood

Propylene oxide is a useful chemical intermediate. Additionally, it has found use for etherification of wood (qv) to provide dimensional stabiUty (255,256), for purification of mixtures of organosiUcon compounds (257), for disinfection of cmde oil and petroleum products (258), for steriliza tion of medical equipment and disinfection of foods (259,260), and for stabilization of halogenated organics (261—263). 

Etherification of wood can be conducted by reacting wood with alkyl halides, acrylonitrile (AN), epoxides, P-propiolactone (acid conditions), aldehydes, and dimethyl sulfate [2]. Preparation of the following etherified woods has recently been studied actively. 

Etherification of Wood. Etherification of wood involves the derivatization of hydroxyl groups to other functional groups. In general, etherification of wood produces more stable bonding and generates lower heat of reaction than esterification. Swelling of wood and formation of sodium salt are commonly applied as a pretreatment prior to etherification. Benzylation, cyanoethylation, allylation, and/or hydroxyethylation are commonly used in the etherification of wood. Some methods of etherification of cellulose may also be applied to wood. 

Etherification of wood (PO) was done using propylene oxide and 5%... 

Partial etherification of the beech wood MGX with p-carboxybenzyl bromide in aqueous alkali yielded fully water-soluble xylan ethers with DS up to 0.25 without significant depolymerization the Mw determined by sedimentation velocity was 27 000 g/mol [400,401]. By combination of endo- 6-xylanase digestion and various ID- and 2D-NMR techniques, the distribution of the substituents was suggested to be blockwise rather than uniform. The derivatives exhibited remarkable emulsifying and protein foam-stabilizing activi-... 

Kiguchi, M. (1990a). Chemical modification of wood surfaces by etherification. I. Manufacture of surface hot-melted wood by etherification. Mokuzai Gakkaishi, 36(8), 651-658. 

Matsuda, H., Dohi, H. and Ueda, M. (1987). Catalysts for the etherification reaction of wood with an epoxy compound. Mokuzai Gakkaishi, 33(11), 884—891. 

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. 

This chapter deals with the chemical modification of wood by such methods as etherification, esterification, and thermoplasticization of wood, with emphasis on recent and new research in these fields. 

More recently, Kiguchi reported benzylation of wood particles with the solvent dilution and vapor phase methods for reducing the amount of benzyl chloride in the etherification agent [12]. In the vapor phase benzylation below the boiling point of benzyl chloride, greatly thermoplasticized particles could be produced after 2-4 h at 140°C. However, in the solvent dilution method, higher reaction temperatures and longer reaction times than those in the ordinary liquid phase method were found to be necessary to obtain the thermoplasticized particles. 

On the other hand, Matsuda et al. [47] recently conducted systematic studies on catalysts for etherification reaction of wood with phenylglycidyl ether (PGE) [47]. It was found that, among various basic catalysts, the K salts of fatty acids accelerate the reaction remarkably, and a high WG indicating a high degree of polyetherification could be obtained. As shown in Table 1,... 

Table 1 Effect of Carbon Number of Fatty Acid on Yield and Weight Gain of Etherified Wood Meal for Etherification Reaction of Wood Meal (3 g) with PGE (30 g) at 140°C for 3 h in the Presence of Various K Salts of Fatty Acids as Catalyst (2 mol % Based on PGE)...

Kiguchi [ 10] reported that hot-melted wood surfaces treated by benzylation and allylation lost surface glossiness by weathering because of the benzyl or allyl groups induced by the etherification of the surfaces. These groups can absorb ultraviolet rays and degrade the surfaces. As a result of ESC A, the... 

Rgure 10 Etherification treatments for surface thermoplasticization of wood. 

Various chemical modifications of wood have been tried to improve native properties such as swelling and shrinking and to apply new properties such as thermoplasticity, solubility, and so on [1-5]. These treatments will increase the use of wood as an important renewable resource. Several kinds of treatments have been applied to cellulose alone, whose properties have been studied by many scientists [6-9], e.g., esterification, etherification, and cya-noethylation. As for wood, the introduced side chains with these reactions are combined with OH groups of its several components, especially those of cellulose chains. The treatments give new properties due to the introduced side chains and to the change of the conditions around the side chains, so that the interaction between wood components molecular main chains is remarkably varied. Thus, new physical and chemical properties are applied to wood with such chemical modifications. 

Some chemical reactions of the wood components involve functional groups that do not form part of the polymer chain and may have only a slight effect on some wood properties and may enhance some. For example, esterification or etherification of free hydroxyl groups in carbohydrates or lignin may reduce hygroscopicity, increase dimensional stability, and actually increase wood strength by reducing the equilibrium moisture content. 

Abstract Cellulose is the most important biopolymer in Nature and is used in preparation of new compounds. Molecular structure of cellulose is a repeating unit of p-D-glucopyranose molecules forming a linear chain that can have a crystallographic or an amorphous form. Cellulose is insoluble in water, but can dissolve in ionic liquids. Hemicelluloses are the second most abundant polysaccharides in Nature, in which xylan is one of the major constituents of this polymer. There are several sources of cellulose and hemicelluloses, but the most important source is wood. Typical chemical modifications are esterifications and etherifications of hydroxyl groups. TEMPO-mediated oxidation is a good method to promote oxidation of primary hydroxyl groups to aldehyde and carboxylic acids, selectively. Modified cellulose can be used in the pharmaceutical industry as a metal adsorbent. It is used in the preparation of cellulosic fibers and biocomposites such as nanofibrils and as biofuels. 

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... 

Cellulosics. CeUulosic adhesives are obtained by modification of cellulose [9004-34-6] (qv) which comes from cotton linters and wood pulp. Cellulose can be nitrated to provide cellulose nitrate [9004-70-0] which is soluble in organic solvents. When cellulose nitrate is dissolved in amyl acetate [628-63-7] for example, a general purpose solvent-based adhesive which is both waterproof and flexible is formed. Cellulose esterification leads to materials such as cellulose acetate [9004-35-7], which has been used as a pressure-sensitive adhesive tape backing. Cellulose can also be ethoxylated, providing hydroxyethylceUulose which is useful as a thickening agent for poly(vinyl acetate) emulsion adhesives. Etherification leads to materials such as methylceUulose [9004-67-5] which are soluble in water and can be modified with glyceral [56-81-5] to produce adhesives used as wallpaper paste (see Cellulose esters Cellulose ethers). 

Etherification to produce cyanoethyolated, benzylated or allylated wood surfaces does not result in an improvement in UV resistance, but the latter two treatments have been found to improve the performance of clear coatings on the modified substrate (Kiguchi, 1990b). Kalnins (1984) methylated wood by pre-treating with concentrated aqueous... 

Lukowsky, D. and Peek, R.D. (1998). Time dependent over-uptake of etherificated melamine resins. International Research Group on Wood Preservation, Doc. No. IRGAVP 98-40109. 

On the other hand, it has recently been demonstrated that untreated wood and/or wood modified by, for example, esterification or etherification can be dissolved in several organic solvents including phenols (3-10). Characterization of the resulting wood tars has revealed a high reactivity and the products can be converted readily into adhesives, moldable resins, etc. 

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