High-yield pulping of switchgrass.

Application: Switchgrass pulp might be useful to reinforce newsprint furnis or as a potential replacement component in higher quality printing grades.

Switchgrass (Panicum virgatum L.) is a warm-season grass that shows excellent growth performance. The seasonal yield of the "Cave-in-Rock" variety ranges from about 13 to 25 oven dry metric tons/hectare/year. Due to its high yield biomass, switehgrass represents a good source of fiber for papermaking in North America. The present work concentrates on making a wide range of high-yield pulps from switchgrass to be used as a potential replacement or reinforcement component in some grades of lower quality, such as newsprint and specialties. This may help alleviate some of the pressure on softwood supply for mechanical pulping. The results obtained indicate that the papermaking characteristics of switchgrass mainly depend on its pulp yield regardless of the chemicals used. Pulp yield of 65% appeared to be the upper limit for producing pulps with useful papermaking properties; above this limit, the pulps exhibit unacceptable quality for printing grades. Switchgrass pulps in a yield range of about 55%-60% showed good mechanical strengths but poor optical properties and drainage.

We used vapor phase cooking to produce the pulps. Prior to digestion the material was impregnated with a solution made up with 26.7 g sodium sulphite per litre of water with or without a second agent such as sodium carbonate, sodium bicarbonate, magnesium carbonate, lithium carbonate and zinc carbonate. The concentration of the second agent was 3.3 g/1 of water. The uptake of sodium sulphite was 4.8% (on oven dry basis) while that of the second agent was 0.6%. Pulps with various yields were obtained by steaming the impregnated material at different temperatures and times. The yield ranged from about 60% to 80%. Among the second treatment agents, lithium carbonate had the most significant influence on some of the pulp properties.

The study shows that switchgrass pulp at about 60% yield has a good potential for use as one of the components in newsprint or liner manufacture. Various other studies are still needed. The relatively low drainage of switchgrass pulp may mean that in application it has to be incorporated into other furnish components having a higher freeness.

Law is senior research associate, Kokta is professor, Szczesiul is a graduate student, and Ruzinsky is a postdoctoral fellow, now with UBC, Vancouver, Canada, Pulp and Paper Research Center, University of Quebec in Trois-Rivieres, 3351 Blvd. des Forges, P.O. Box 500, Trois-Rivieres, QC, Canada G9A 5H7; email [e-mail].