3120 Chapter 25 



CHEMIGROUNDWOOD 



Libby and O'Neil (1950) reviewed potential pretreatments of hardwoods prior 

 to grinding and described their development of a chemigroundwood process by 

 which 2- to 4-foot lengths of hardwood were pretreated in a digester. Optimum 

 strengths and brightness with Poplus sp., Betula sp., and Fagus sp. were ob- 

 tained with neutral sulfite liquors of sodium sulfite (Na2S03) and sodium bicar- 

 bonate (NaHCO,) in water. The sodium bicarbonate partially neutralized 

 organic acids formed during the cook and prevented wood darkening. Liquors 

 containing 1 to X-Vi pounds chemical per gallon and having a chemical ratio of 

 6: 1 (sodium sulfite:sodium bicarbonate) were optimum for pulp strength. About 

 10 percent of the chemical was consumed during digestion. Wood was subjected 

 to a vacuum for 30 minutes before the liquor was admitted and cooking contin- 

 ued at a temperature of 150°C and a pressure of 200 psi for 6 hours. In their 

 experiment they used a stone peripheral speed of 3,300 fpm, grinding pressure 

 of 40 psi, and grinder pit consistency of 5 percent with temperature of 130°F. 

 Strength values of pulp from beech and birch were further improved about 20 

 percent and power consumption was lowered 5 hp days/ton if the pretreated 

 wood was stored for 16 hours before grinding. Pulp yields were 85 to 90 percent 

 of the weight of the original wood. The slightly dark pulps could be successfully 

 bleached with sodium peroxide or hydrogen peroxide. The pretreatment in- 

 creased burst strength of birch groundwood pulp about 10-fold; effect of the 

 pretreatment on tear strength of birch and beech was not reported, but on aspen 

 the improvement was significant. 



Hyttinen and Schafer (1955) treated 2- and 4-foot lengths of sweetgum, black 

 tupelo, red oak sp., and other hardwoods with neutral sulfite solutions for 1 to 

 5.5 hours at temperatures from 125° to 155°C, pressures from 100 to 150 psi, 

 and with liquor concentrations of 0.5 to 1 .5 pounds of chemical per gallon. The 

 ratio of sodium sulfite to sodium bicarbonate was 6:1 (4:1 in one test), and the 

 ratio of liquor to wood was about 2.5:1. Mild treatments before grinding in- 

 creased freeness and the long-fiber fraction of the pulps; strength, brightness, 

 and density were only slightly affected. Increasing the severity of the pretreat- 

 ment increased the strength and density of the pulps and decreased the brightness 

 and opacity of the papers in which they were used. Chemigroundwood pulps 

 were made that approached neutral sulfite semichemical pulps in strength and 

 could probably be used for the same purposes. The darker chemigroundwood 

 pulps were easily brightened with a single-stage hypochlorite treatment. Hyt- 

 tinen and Schafer concluded that it might be possible to substitute chemiground- 

 wood pulps entirely, or in part, for softwood groundwood in newsprint, book, 

 and toweling papers. Severely treated sweetgum yielded chemigroundwood 

 equal or superior to spruce groundwood in burst, tear, and tensile strength. A 

 newsprint furnish made with 40 percent black tupelo chemigroundwood along 

 with semibleached southern pine sulfate and southern pine groundwood pulps 

 was comparable in strength and brightness to standard newsprint paper, but was 

 somewhat stiffer; book paper of good quality was made using 60 percent black 

 tupelo chemigroundwood and 40 percent semibleached pine sulfate pulp. The 

 red oak sp. from Arkansas yielded pulp of high strength with low fines content 



