Pulp and Paper 3093 



increased from 7.0 percent in 1972 to 11.2 percent in 1979 of the value of 

 shipments from pulp mills in the United States (Slinn^^). 



If bark from pulpwood is dry and it is burned efficiently, and energy conserva- 

 tion is practiced, it is estimated that kraft pulp mills can be about 68 percent self 

 sufficient in energy without resorting to additional residues available from forest 

 operations (Personal correspondence with H. A. Schroeder, December 1981). 



25-2 TYPES OF WOOD PULP, PAPER, 

 AND PAPERBOARD' 



There are dozens of pulping procedures and perhaps thousands of different 

 kinds of construction paper and boards, paper, and paperboards; a summary of 

 definitions provided by the American Paper Institute (1978) is helpful in classi- 

 fying the most important of these pulps, papers, and boards. The few major 

 procedures for pulping southern hardwoods are further described in sections 25- 

 3 and 25-5 through 25-8. 



WOOD PULP, MECHANICAL FOR PAPER AND PAPERBOARD 



Mechanical pulps are produced by stone grinding or disk defibration. For use 

 in paper and paperboard pulps are fine-textured and usually bright. 



Stone groundwood pulp is produced by grinding wood logs or bolts (usually 

 4 feet in length) into relatively short fibers. In general, this process is not 

 practical for pine-site hardwoods. 



Refiner pulp is produced by subjecting wood chips and/or residues to atmos- 

 pheric or open-discharge refining (sections 18-27 and 23-6). 



Thermomechanical pulp is a high-yield pulp produced from wood chips and/ 

 or residues softened by preheating before defibrating in pressurized (or non- 

 pressurized) refiners (sections 18-27 and 23-6, and fig. 25-21). It is used to 

 replace or reduce the chemical pulp component in newsprint or groundwood 

 papers. 



Slinn, R. J. 1980. Energy in the pulp and paper industry. Paper presented to the 1980 Ann. 

 Meet., Amer. Pulpw. Assoc, Atlanta, Ga., March 18. 6 p. 



^Definitions in this section are from American Paper Institute (1978). 



