Strenght characteristics of chemi-mechanical pulp from rapeseed straw

The objective of this work was to determine the potential application of rapeseed straw in the chemi-mechanical pulping process. Stalks of rapeseed straw (species Brassica napus L. convar. napus) were used for the pulping process. The chemi-mechanical pulping comprises four main operations, viz. chipping, grinding, leaching, and beating. For chemi-mechanical pulps, the influence of caustic soda charge applied in the leaching process upon the bending stiffness and bending modulus of elasticity in the region of reversible deformation was investigated by using a three-point loading method. The preliminary results revealed that the bending modulus of elasticity increases with increasing caustic soda charge from 0.22 to 1.11 kN.mm−2 for both basis weights of the handsheets (approx. 260 g.m−2 and 520 g.m−2). Similarly, the bending stiffness of handsheets having lower basis weight slightly increases with increasing alkaline charge, whereas, for higher basis weight, the effect of alkaline charge on the bending stiffness is ambiguous. Of course, the tensile strength of chemi-mechanical pulps was much lower than that published for kraft pulp or waste paper. The results obtained for rapeseed straw were compared with those measured for unbleached spruce groundwood and for moulded fibre products, which were published earlier. The bending stiffness and bending modulus of elasticity were much greater than those for moulded fibre products made from waste paper. Besides the strength characteristics, the degree of polymerization and bonding properties of rapeseed straw pulp were investigated. Owing to the presence of low molecular substances, the degree of polymerization of chemi-mechanical pulp was found to be within the limits of 96 to 224, depending on caustic soda charge applied in the leaching process.