Epoxide reactions with wood

Figure 4.3 Reaction of wood with maleic anhydride, followed by oligomerization of the activated wood with epoxide and maleic anhydride.

Epoxides can react with alcohols via acidic or basic catalysed reaction mechanisms. However, since both strong acids and bases will degrade the cell wall polymers of wood, the reaction is usually catalysed via the use of amines, which are more strongly nucleophilic than the OH group. For example, whereas the production of epoxy-phenolic resins requires temperatures in the region of 180-205 °C, reaction between epoxides and primary or secondary amines takes place at 15 °C (Turner, 1967). Reaction of epoxides with wood often involves the use of tertiary amines as catalysts (Sherman etal., 1980). The sapwood is more reactive towards epoxides than heartwood (Ahmad and Harun, 1992). 

The first reported study of a reaction of wood with an epoxide appears to be that of McMillan (1963). This involved the use of gaseous ethylene oxide (Figure 4.9, R=H) at a temperature of 93 °C and a pressure of 3 atmospheres (0.3 MPa). In some cases, the wood was diffusion pre-treated with trimethylamine vapour as the catalyst. A 65 % ASE at 20 % WPG was obtained, attributed to a bulking effect due to in situ polymerization of the epoxide. There was no effect on the static bending strength of samples, and the modified wood became distinctly brown at higher levels of treatment. 

Qetin, N.S. and Hill, C.A.S. (1999). An investigation of the reaction of epoxides with wood. Journal of Wood Chemistry and Technology, 19(3), 247-264. 

Rowell, R. M. Ellis, W. D. Reaction of Epoxides with Wood. 

The carboxyl groups introduced into wood by Reaction (13) are reactive with epoxy groups. Mastuda et al. 181,82] obtained epoxide-adducted esterified woods by the addition reaction of the carboxyl group-bearing esterified wood meal with epoxides as follows [Reaction (14)] ... 

When the epoxide-adducted esterified wood meals were further allowed to react with the anhydride and the epoxide at high temperatures, alternately adding esterification reactions occurred, to produce oligoesterified woods [81]. 

Polymerizable oligoester chains have been introduced into wood by the oligoesterification reaction of wood meal with the anhydrides and the epoxides such as AGE or GMA as follows [Reaction (15)] [83-85] ... 

Bonding of chemicals to wood cell wall components--cellulose, hemicellulose and lignin—can change the physical and chemical properties of the wood. For example, reaction of southern pine with simple epoxides results in a modified wood which is resistant to attack by subterranean termites in laboratory tests (1). Wood modified with acetic anhydride, dimethyl sulfate, 0-propiolactone and epoxides are highly resistant to attack by microorganisms in standard soil block laboratory tests (2,3). Southern pine modified by reaction with acetic anhydride and propylene and butylene oxides has a reduced tendency to swell in the presence of water (4). 

Conjugate addition of hydroperoxide to unsaturated carbonyl compounds generates epoxide in the presence of superbases. Wood et al. conducted the epoxidation reaction of 183 by treatment with ferf-butyl-hydroperoxide, using a catalytic amount of DBU [55]. The resulting epoxide 184 was converted to ( )-epoxysorbicillinol (185) (Scheme 7.41). 

In similar conditions Rosu et al. [52] conducted controlled photo-aging experiments of chemically modified surface of Abies alba L. softwood species. Chemical modification was undertaken in two stages (Scheme 6—reproduced with kind permission from Elsevier— License No. 3723031483298). The former stage consisted in the reaction of wood components with succinic anhydride (SA) to yield monoester entities with final carboxyl groups, followed by crosslinking with epoxidized soybean oil (ESO) in the latter stage. Success of flie chemical modification reactions was confirmed by FTIR. 

Of several anhydrides studied, acetic anhydride reacted the most readily. Reactions were carried out by refluxing the wood in a xylene/acetic anhydride solution or with acetic anhydride vapors alone at 120°C. With this system, for each mole of acetate bonded onto the wood a mole of acetic acid is generated as a by-product. Although this by-product generation is a disadvantage of the process, the chemical system does penetrate and react quickly with wood, without a catalyst. It is not so sensitive to moisture as are the epoxide and isocyanate systems. 

Matsuda, H. and Ueda, M. (1985c). Preparation and ntilisation of esterified woods bearing carboxyl gronps. V. Addition reaction of esterified woods with epoxide and oligoesterification of the addncts obtained. Mokuzai Gakkaishi, 31(4), 267-273. 

The epoxide is also formed from the reaction of C60 with dimethyldioxirane, and the 1,3-dioxolane (figure 9) is also obtained (Elemes et al. 1992). Photochemical irradiation of C60 in hexane had previously been shown to result in the addition of 2-5 oxygens, and also various methylene groups (the results depend upon the fullerene purity) (Wood et al. 1991). In this work, two oxygens were found to add to C70. 

When wood is treated with epoxides, etherification occurs as follows [Reaction... 

Epoxides. The reaction between epoxides and hydroxyl groups is an acid- or base-catalyzed reaction however, all work in the wood field has been with base-catalyzed reactions ... 

Epoxy resins are polymers with tremendous adhesive properties and are used to bind glass, porcelain, metal, and wood. The production involves a ring opening reaction on the epoxide epichlorohydrin as it reacts with bisphenol A. 

Several epoxides have been used the past decades for fiber modification purposes. They include ethylene oxide, propylene oxide and butylene oxide [39]. Usually the reaction is catalyzed under mild basic conditions. In most experiments, triethylamine is used as a catalyst. Decay resistance of wood treated with propylene oxide was ineffective towards G. trabeum decay. 

Starch xanthate and alkyl diepoxides formed gels in concentrated (6—8%) solutions or in turbid suspensions in dilute (0.1—1.0%) solutions, the degree of gelling varying with the nature of the epoxide. When wood pulp was added to dispersions or suspensions of the gel, the paper produced therefrom possessed improved strength. These improvements were unrelated to the degree of xanthation, but depended on the reaction times and on the order in which the diepoxide and xanthate were added. 

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