PROPERTIES AND USES OF CELL WALLS 101 



The chemistry of these processes is extremelly complex and 

 cannot be treated here. It is, in fact, far from understood in detail. 



In sulfite pulping, the fundamental reactions are sulfonation 

 of the lignin, and, secondarily, acid hydrolysis of hemicelluloses. 

 An average analysis of commercial unbleached, sulfite pulp 

 yields about 79 per cent a-cellulose, 15 per cent cellulosons 

 associated with cellulose, and less than 2 per cent lignin. The 

 yield of sulfite pulp is about 50 per cent of the initial 

 wood. 



Alkaline pulping involves solubilization of lignin by release 

 of free hydroxyl groups and hydrolysis and degradation of poly- 

 uronide hemicelluloses. Two variants are soda pulping with 

 caustic soda, and sulfate (kraft) pulping, which is the soda process 

 modified by addition of sodium sulfide. The unbleached pulps 

 obtained are similar in analysis to sulfite pulps, but run to higher 

 percentages of non-cellulosic constituents. 



Bleaching with chlorine or other oxidants follows pulping and 

 yields materials higher in a-cellulose and lower in lignins and 

 other non-cellulosic constituents. 



The spent sulfite liquors represent a major by-product of the 

 pulping operation, and are as yet unsolved problems in industrial 

 by-product utilization. Many millions of tons of potentially useful 

 chemical materials representing half of the starting wood are 

 available in sulfite and other waste liquors. The high carbohydrate 

 content has led to the use of neutralized waste for production of 

 alcohol and yeasts. 



Alkaline hydrolysis of sulfite liquor yields vanillin and vigorous 

 oxidation yields vanillic and protocatechuic acids. The former 

 finds limited use as a flavoring, the latter have been proposed as 

 acid components for polyester fibers. The possible uses for ligno- 

 sulphonic acids are legion. Aside from their fuel value these sub- 

 stances have been proposed for: drilling mud components; fillers 

 and extenders in furfural plastics; latex stabilizers; soil condition- 

 ers; air entrainment agents in concrete; binders; tanning; agents; asp- 

 halt modifiers ; emulsifying agents; dye intermediates; etc. At present, 

 the productive utilization of lignin sulfonates is insignificant relative 

 to the supply, and in addition to the wastefulness itself is added 



