3140 Chapter 25 



25-8 DISSOLVING PULP 



The art of converting native cellulose fibers into solutions from which other 

 cellulose forms are regenerated has been known since the late 1800s; large-scale 

 use of wood cellulose for man-made fibers began in 1916, 1919, and 1921 by 

 application of the acetate, cupr ammonium, and viscose processes, respective- 

 ly. From these beginnings, uses for dissolving pulp, the dry, loosely matted 

 sheets of refined fibers used for chemical processing (also termed chemical 

 cellulose) have grown along with other uses for wood fiber. Four southern mills 

 manufacture dissolving pulp — at least one of which uses southern hardwoods — 

 and in 1969 they produced about 40 percent of all market pulp made in North 

 America, that is, pulp manufactured by one organization and used by another. 



The technology of dissolving pulp manufacture and its conversion into regen- 

 erated cellulose products such as fiber and film (cellophane) by the viscose 

 process, and fiber, film and tow (in cigarette filters) by the acetate process is 

 complex. For a summary the reader is referred to Durso (1969), reproduced with 

 minor revisions in Koch (1972, p. 1454-1463). 



Rayon is produced by dissolving cellulose and then reprecipitating it under 

 conditions favoring orientation and crystallization. Rayon, like cotton, can have 

 moisture absorbent properties that make it highly desirable for certain textiles 

 and non- woven fabrics, a characteristic not shared by other synthetic fibers such 

 as polyester and nylon. Limited world cotton supplies at economic prices may 

 afford a market for expanded production of improved rayon if new methods for 

 its manufacture were invented to reduce capital costs to a range commensurate 

 with plant costs required for synthetic fibers, and to reduce pollution problems. 

 Hergert et al. (1978) reviewed technology for rayon manufacture, and concluded 

 that the ideal system is yet to be discovered, but that a major new system will 

 likely be developed. 



Most southern dissolving pulp is made from southern pine by the prehydroly- 

 sis kraft process, but hardwoods are also used (Logan 1952, Simmonds et al. 

 1955; Makukha et al. 1976; and Kosaya et al. 1978). Literature specific to 

 conversion of dense pine-site hardwoods to dissolving pulp is scarce. 



CELLULOSE ETHER DERIVATIVES 



Cellulose ether derivatives are traditionally made from chemical cellulose 

 (mostly from wood), pulped and bleached by conventional operations that 

 chemically remove lignin and hemicelluloses, then dried at high temperature. 

 These operations, particularly drying, alter molecular structure and significantly 

 reduce accessibility of cellulose to etherifying reactions. Carboxy methyl cellu- 

 lose (CMC) is produced when chloroacetic acid is the etherifying reagent. 



To increase accessibility of the cellulose during etherifying reactions, to 

 simplify the process, and to broaden the potential raw material source for 

 cellulose derivatives, Durso (1976, 1978, 1981) invented a system of producing 



