3130 



Chapter 25 



INLET 

 ROTARY VALVE 



LIQUOR 

 EXTRACTION 



BROWN- STOCK WASHERS 



DE-SHIVE REFINER 



^ 



PULP TO 

 STORAGE 



STEAM- PRESSURIZED 

 DOUBLE- REVOLVING DISK 

 REFINER 



THICK-STOCK PUMPS 



Figure 25-22. — Continuous digester system for NSSC pulping of hardwood chips. (Dia- 

 gram from the Bauer Bros. Co.) 



Unbleached NSSC pulps. — Individual species of southern hardwoods that 

 are commonly found on southern pine sites produce unbleached NSSC pulps 

 with different pulp properties (table 25-14). Sweetgum, black tupelo, and yel- 

 low-poplar made stronger pulps than other southern hardwoods; they were lower 

 in bursting and tensile strengths, but higher in tearing resistance than quaking 

 aspen {Populus tremuloides Michx.). Data on properties of bleached NSSC pulp 

 are given in table 25- 1 5 , but not in units that permit direct comparison with those 

 of table 25-14. 



A tendency for chip quality to decrease under stress of procurement has led to 

 the introduction of chip cleaning systems in mills employing continuous digest- 

 ers. Most southern mills using the NSSC process have both. Whole-tree chips 

 have been used extensively in the manufacture of unbleached NSSC pulps, a 

 development that has greatly increased utilization of southern hardwoods. 



Table 25-14. — Yield, strength properties, and sheet density^ of neutral sulfite 



semichemical (NSSC) pulps of six southern hardwoods and Populus tremuloides Michx. 



(McGovern and Auchter 1976) 



Species 



Yield 



Burst 



Tear 



Tensile 

 strength 



Sheet 

 density 



Aspen 



Ash, white 



Oak, southern red' 



Oak, white^ 



Sweetgum 



Tupelo, black 



Yellow-poplar 



'Data from Keller and Fahey (1956) 

 ^Data from Keller et al. (1959) 



Percent 



78 

 77 

 73 

 74 

 11 

 80 

 78 



Points/lb 



per ream 



0.61 



.41 



.41 



.31 



.40 



.40 



.48 



g/lb 



per ream 



0.90 



.80 



.75 



.75 

 1.07 

 1.14 



.98 



lb/in width 



22 

 17 

 15 

 9 

 15 

 16 

 19 



g/cm- 



.44 

 .54 

 .46 

 .47 

 .39 

 .49 



