Influence of the chemical composition of kenaf bast and core on the alkaline pulping response

The bast and core of kenaf, Hibiscus cannabinus L., have markedly different chemical components and alkaline cooking responses. The bast had about dou ble the hot-water extractives content and only about half the lignin conten t of the core. The core contained a large amount of hemicellulose, mostly c omposed of xylan. The lignin structures of bast and core were also quite di fferent. The former had a significant abundance of syringyl structures, Evi dence showed that the bast was much more easily delignified than the core. When the bast and core were cooked together in alkaline condition, the pulp yields at the same kappa number were higher than those of the individual p ulpings of bast and core. The bast-core pulping gave a positive effect on t he yield of bast pulp in the soda-anthraquinone and kraft pulpings. On the other hand, kenaf was abundant in the hot water extractives. These extracti ves consumed alkali during cooking to a relatively large extent but acted a s a protector of hemicellulose and slightly increased the pulp yields.