Neutral sulfite semi-chemical pulping of rapeseed residues

Neutral sulfite semi-chemical (NSSC) pulping of rapeseed residues from Karadj rapeseed growing fields was investigated. Rapeseed residue was collected from the research field at the Agriculture and Natural Resources Campus, University of Tehran located in Karadj. Cellulose, lignin, holocellulose, extractives soluble in alcohol acetone, 1% NaOH solubility, and ash were determined as 42 ± 2%, 17 ± 1%, 77.5 ± 2%, 2.2 ± 0.1%, 50.3 ± 1.6%, and 6%, respectively. Fiber length, width, and cell wall thickness were measured as 1.190 mm, 32 μm, and 4 μm. Three pulping durations of 20, 40, and 60 min and 5 chemical charges of 8%, 10%, 12%, 14%, and 16% active alkali were used. Cooking temperature at 175 °C, Na2SO3 to Na2CO3 ratio of 3:1, and liquor to residue ratio of 8:1 were kept constant. The highest yield (72%) was obtained applying the treatment combination of 20 min pulping time and 8% active alkali and the lowest yield (58.7%) was observed with 60 min pulping time and 16% chemical. After the pulping study, selected pulps were refined to 375 ± 5 mL CSF and 60 gm^–2 handsheets were made. The results of pulping and handsheet evaluation indicated that 12% active alkali, 60 min pulping at 175 °C can be considered as the optimum pulping condition for rapeseed residues. Tear, tensile, and burst indices and breaking length of this pulp were measured as 7.5 mN m²g^–1, 66.5 N mg^–1, 2.57 kPa m²g^–1, and 6.78 km, respectively.