Abstract
It has been well-known that the heart wood of larch (Larix leptolepsis Murray) contains much taxifolin and epsilon-galactan, and that its pulping by the conventional Ca-base sulphite process is very difficult.The heart wood chip used in this study produced screenings of ca. 20% of dry chip by a Ca-base cooking. Addition of a nonionic surface active reagent (nonyl-phenol polyethylen glycol ether) to cooking liquor made little effect on reduction of screenings. Screenings was reduced to 9.4% by a Mg-base cooking, and much reduction was found in NH4- or Na-base pulping, especially having an adequate penetration period (2-2.5 hrs. at ca. 105°), in which screenings was 1% or below of dry chip. It has been from pulping results and quality of purified pulps (rayon grade) that adequate content of combined acid is 1% or near in the case of NH4-base and 1 : 6 of wood to liquor ratio. In NH4- or Na-base process, rayon pulps of good quality (in the content of alpha-, beta-cellulose and resin, and filtrability of viscose) were obtained by a conventional three steps purification (chlorination-alkali digestion-NaOCl bleaching) of the screened unbleached pulps of the heart wood as well as the whole.
