Vapor-phase treatment acetylation

A large number of catalysts and swelling agents have been studied for the acetylation reaction. The best acetylation conditions have been reported in vapor phase treatment with uncatalysed acetic anhydride in xylene solutions at 100-130 C (28). Acetylation reaction between wood and acetic anhydride proceeds as follows 0... 

The fibrous acetylation process is performed in the presence of a suitable liquid, such as benzene, in which the reaction product is insoluble and which thereby retains the fiber form. For fibrous acetylation vapor-phase treatment with acetic anhydride can also be used. Besides sulfuric acid, perchloric acid and zinc chloride have been used as catalysts. 

The reaction with acetic anhydride can be conducted in a liquid or vapor phase. However, the vapor phase treatment results in a product with poorer properties than the liquid phase [51]. Therefore, the treatment has been carried out usually in liquid phase. Goldstein et al. [49] reported that uncatalyzed acetylation in xylene at 100-130°C is the best condition. 

Acetylation can also be done by vapor-phase treatments, but the diffusion rate varies inversely as the square of the thickness (37, 56). Because of this effect, vapor-phase treatment has been applied only to thin veneers. 

Treatment of acetone with uranium(VI) fluoride in the vapor phase at room temperature gives13 some acetyl fluoride, along with much polymeric material. Under the same conditions, cyclohexanone also produces an unidentified acid fluoride initially, but this is then consumed to give polymeric material. 

Two species, chir (Pinus roxburghii Sargent.) size 7.5 x 2.75 x 1.25 cm3and mango (Mangifera indica Linn.) size 7.5 x 1.25 x 1.25 cm3 were studied to establish different reaction variables. Four replicates were taken for each treatment and experiments were carried out with oven-dried samples except in case of those where effect of moisture content was studied. Samples were placed in a reaction chamber and reaction was carried out under reflux conditions at 93+1 C, the boiling point of thioacetic acid. Experimental set-up for vapor phase acetylation is shown in Figure 1. 

Treatment r 1 Vapor phase acetylation 1 1 Vapor phase acetylation... 

Figure 2 Creep-recovery tests of chemically treated woods. U, untreated wood Fs, vapor phase formalization F, liquid phase formalization A, acetylation PO, etherification with propylene oxide MG, treatment with maleic acid and glycerol PFl, impregnation with low molecular weight phenol-formaldehyde resin PEG-ICP, impregnation with polyethylene glycol (PEG-IOOO) WPC, formation of a wood- polymer composite (PMMA) WIC, formation of a wood-inorganic material composite.

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