Pulp and Paper 3083 



Some properties of typical pulps made from southern hardwoods are given in 

 table 25-1 . The lower strength of hardwood pulps has traditionally limited their 

 use in papers where high strength is the primary requirement. For the majority of 

 white papers, however, hardwood pulps offer special properties — particularly 

 when they are optimally blended with softwood fibers and non-fibrous additives 

 during papermaking. Recent developments in press drying hardwood pulps 

 (Setterholm 1979) will likely increase the use of hardwood kraft pulps for 

 linerboard (see section 25-4). 



Table 25-2 lists some paper grades and the percentages of hardwood pulps 

 used in them, as produced in southern paper mills. 



Table 25- 1 . — Some properties of hardwood pulps at three freeness values' (Reeves 



1979b) 



Freeness, °SR- 



Property 15-^ 25 40 



Tear factor — 100 91 



Burst factor — 32 46 



Breaking length — 5,400 7,200 



Fold — 80 250 



Bulk 2.14 1.68 1.55 



Opacity 78.5 74.7 70.1 



'Data based on 51 samples of pulps from 17 southern mills in the United States. 



^Schopper-Riegler (°SR). 



^Unbeaten. 



Table 25-2. — Percentages of hardwoods typically used by southern paper mills in 17 

 grades of white papers (Reeves 1 979b) 



Paper grade Hardwood content 



Percent 



Bond 40-95 



Continuous stationery 40-75 



Ledger 60-85 



Tissue, facial 35-60 



Tissue, sanitary 25-70 



Light weight coated 20-50 



Offset, uncoated 50-70 



Offset, coated 40-70 



Litho, coated one site 40-70 



Litho, cast coated 25-50 



Publication, mechanical 50-65 



Envelope 50-75 



Tablet 40-70 



Milk container 25-40 



Tag 30-55 



Glassine 10-40 



Cover, coated 50-80 



