Pulping of Mitsumata by using Twin Screw Extruder

Abstract

he bast fiber of Mitsumata （Edgeworthia papyrifera Sieb. et Zucc.） has traditionally been used as a raw material of paper. Mitsumata belongs to Thymelaeaceae family, and the paper made from its bark is known to have hue of egg yolk color and unique texture. Mitsumata pulp for paper making is manufactured as follows. Mitsumata branches are steamed and barks are taken off, from which its epidermis and cuticle are removed. Then, the residual white bark is cooked with an aqueous alkaline solution in the digester. Compared to the chemical composition of wood, the white bark contains more amount of pectin and less amount of lignin. So, pulping of Mitsumata primarily aims to remove pectin that works as a binder among cells, and pectin in the white bark can be removed by alkaline solution under heated.In this research, we used twin screw extruder to produce Mitsumata pulp from its white bark. Twin screw extruder consists of two co-rotating screws in a cylinder barrel, and it is widely used in the manufacturing industry for material processing such as shearing, kneading, heating and mixing. The white bark is impregnated with an aqueous solution of sodium hydroxide before defiberizing by twin screw extruder. The process of twin screw extruder is continuous and its processing time is short compared to normal cooking process.The effect of processing temperature and addition rate of sodium hydroxide on defiberizing of Mitsumata fiber was investigated. We found that Mitsumata fibers could be defiberized by twin screw extruder at lower temperature than cooking process.Handsheets were made from the pulp produced by twin screw extruder, and their optical and physical properties were studied. The ISO brightness of the handsheet produced by twin screw extruder was high compared to the handsheet produced by normal cooking process. The pulp yield produced by twin screw extruder was also higher than the yield by cooking process. The side chemical reaction is considered to be suppressed during the extrusion process because of the low processing temperature and the short processing time.