[in Japanese]

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The behavior of the crack tip region under in-plane fracture toughness testing was observed by means of CCD camera with enlarging lens system, and was quantitatively analyzed as “crack opening”. From the relationship between “crack opening“ and displacement, the start point of the crack propagation can be clearly determined. It varies with specimen direction and size. Smaller specimens tend to start at the maximum load point, while larger specimens start earlier. Generally, the start point of MD** specimens are not so far from the maximum load point as in the case of CD*** specimens. Specimens with small ligament length were confirmed to satisfy the prerequisite of “Essential Work of Fracture“ method to obtain the fracture toughness of paper. **Mn (machine direction) is the direction of the flow at paper making. ***CD (cross machine direction) is the direction at right angles to MD.

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[in Japanese]

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Using a retted Chinese kenaf bast fiber (CBF) as raw material, various pulps were prepared by using three cooking methods, i.e. soda-AQ pulping, kraft pulping and non-pressurized soda pulping. The capabilities of these pulps, as substitutes for manila hemp pulp which is used mainly as specialty paper applications, were investigated. The soda-AQ and kraft pulps of retted CBF had lower Kappa number and ash content with greater pulp yield than those of unretted Japanese kenaf bast fiber (JBF). The CBF pulps prepared by the three cooking methods were bleached to about 80% Hunter brightness, by a two-stage hypochlorite process, and the relationship between strength properties and CSF was studied. Tensile index and burst index of those pulps at CSF 400ml were in the following order: non-pressurized soda＆ｇｔ； soda-AQ＆ｌｔ； kraft. The strengths of the non-pressurized soda pulp were superior to those of commercial manila hemp pulp. The folding endurance of the three pulps were lower than that of manila hemp pulp, while, that of the non-pressurized soda pulp became equal by 300ml CSF. Therefore, the non-pressurized soda pulp from retted CBF was found to be hopeful as substitute for manila hemp pulp.

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