Pulp and Paper 3 1 1 9 



The short, thick-walled fibers (tables 5-4 and 5-7), large proportions of 

 vessels and parenchyma (table 5-3), high-density (table 7-7) and excessive color 

 (figs. 5-16 and 5-4 through 5-15) of most pine-site hardwoods reduce their 

 suitability for thegroundwood process, and they are little used for paper-grade 

 mechanical pulp. 



Schafer and Pew (1942, 1943) found that green ash and hackberry, both light 

 in color, have some potential for the groundwood component of newsprint. 

 American elm yielded a groundwood pulp that is both short fibered and dark 

 colored, which would appear to limit its application to filler stock for dark 

 colored boards and papers. 



McGovern and Auchter (1976) tabulated data (table 25-10) on experimental 

 groundwoods produced in 1947 from sweetgum, black tupelo, and yellow- 

 poplar — all medium- and low-density hardwoods comprising about one-third of 

 the volume of hardwoods on southern pine sites; these groundwood pulps were 

 relatively low in strength and required much power to grind. Yellow-poplar 

 approached southern pine in freeness, burst, and tensile strength; tear strength of 

 yellow-poplar pulp, however, was only about one-tenth that of the pine pulp. 



Schafer and Hyttinen (1949) stone-ground yellow birch, red maple, American 

 beech, and white oak on a 3-pocket grinder equipped with a 53-inch diameter 

 aluminum oxide pulpstone. They found that red maple produced the strongest 

 pulps and beech the weakest. They concluded that the best use of these hard- 

 wood pulps would be as filler pulps in the softer bulkier grades of paper, and that 

 with the possible exception of white ash, the hardwood pulps would need to be 

 bleached before they could be used in appreciable quantities in white papers. 

 Groundwood pulps containing up to 35 percent of these hardwoods, with stone- 

 ground eastern white pine {Pinus strobus L.) had strength and brightness suitable 

 for newsprint. 



Table 25-10. — Specific energy requirements and properties of experimental pulps ob- 

 tained by stone grinding southern woods (McGovem and Auchter 1976)' 



Wood 



density Specific Fiber 



(oven-dry grinding Free- length 



Species basis) energy^ ness-^ index'* 



Hp days/ton ml 



Sweetgum 0.51 69 50 0.072 



Tupelo, black 51 75 95 .075 



Yellow-poplar 40 83 120 .089 



Southern pine 45 60 115 .090 



'Based on data from U.S. Forest Products Laboratory files, 1947. 

 ^Per ovendry ton of wood 

 ^Canadian Standard 



'^Proportional to fiber length 



