Characterization of kenaf by chemimechanical pulping.

Application: High-yield CMP from the bast may be used as a reinforcement component in newsprint making to maintain a relatively high freeness in TMP from wood, reducing the refining energy cost. CMP from the core may be used in products requiring high bulk.

Kenaf (Hibiscus cannabinus) is a fast growing tropical and subtropical plant that can grow to 5 m in height and yield about 14 tons/ha of biomass. The bast (bark) of kenaf has been used as a jute substitute. In view of the increased interest and potential use of kenaf in paper and board manufacture, we conducted a series of chemimechanical pulping trials on the bast and woody core of kenaf and evaluated their papermaking properties.

We used sodium hydroxide (NaOH) and sodium sulfite ([Na.sub.2]S[O.sub.3]) to cook the two components of kenaf, resulting in pulp yields of 55%-85%. The bast fibers were longer than many hardwood fibers, having an average length of 1.55 mm, while the core fibers were only half as long (0.68 mm). Under similar conditions, the bast gave higher pulp yield than the core. The former produced sheets with significantly greater density, tensile, and tear indices, but a lower light scattering coefficient, when compared to the core pulp. The tensile index of the bast pulp is relatively yield-independent, while that of the core pulp is yield-dependent, in a yield-range of 65%-85%. Further, the bast pulp was more responsive to PFI beating than was the core pulp in terms of tear index. Conversely, the core pulp is more responsive to the beating than the bast as far as tensile index is concerned. Replacing one-third of the core by bast in chemimechanical pulping improved only marginally the tensile and tear indices when compared to 100% core pulp. Due to their differences in chemical and physical nature, it is desirable to process the two components separately. S!

Law is senior research associate, Lanouette is professor, and Mama Sarr is a graduate student at the Pulp and Paper Research Centre, Universite du Quebec a Trois-Rivieres, P.O. Box 500, Trois-Rivieres, Quebec, Canada G9A 5H7. Email Law at [e-mail].