100 THE PLANT CELL WALL 



Acid hydrolysis, like thermal decomposition is a method for 

 overall degradation that has long occupied the interest of wood 

 technologists. Particular attention has been given to the sacchari- 

 fication process. A variety of acid treatments have been studied, 

 ranging from high acid-low temperature processes to vigorous 

 thermal procedures with dilute acid. The most successful sacchari- 

 fication processes use the technique of percolation. Wood chips or 

 sawdust are treated with dilute sulfuric acid (0.2-1.0 per cent) 

 at temperatures of 170-1 80°C. One hundred kilograms of dry 

 coniferous wood yields about 400 kg of fermentable sugars, which 

 in turn yield 20-24 1. of 100 per cent ethanol. The residue, princi- 

 pally lignin, is used as a fuel. Other methods have been developed 

 to separate products including pentoses and furfural formed by 

 differential hydrolysis. Residual lignocelluloses are used for plastic 

 molding. 



Alkaline hydrolysis, alkali fusion, oxidation, and hydrogenation 

 represent other chemical treatments applied to wood and other 

 cell wall materials. Of some interest have been the methods for 

 production of liquid hydrocarbon fuels by pressure hydrogenation. 



Wood plastics have been prepared by thermal hydrolysis and 

 acid hydrolysis. These treatments yield residues which may be 

 molded into figures or board. Molding compositions may be pre- 

 pared by condensation of aniline, phenols, or aldehydes with 

 sawdust and agricultural waste. 



The most important chemical process in wood technology is 

 undoubtedly pulping of wood to yield celluloses for paper manufac- 

 ture and preparation of derivatives. In its essentials, chemical 

 pulping is directed toward retention of a maximum of highly poly- 

 merized cellulose while removing substantially all of the hemi- 

 cellulose and lignin. It is largely a delignification process. A multitude 

 of pulping treatments have been developed, and have found applica- 

 tion in the preparation of various desired grades of pulp from 

 the specific raw materials available. 



The important delignification processes include treatment with: 

 acid bisulfites chlorine 

 alkali nitric acid 



sodium sulfite organic solvents 



