Eucalyptus wood chips from Tasmania were cooked by the neutral sodium sulphite (NS) method, fiberized, and then cooked by the oxygen-alkali (OA) method to prepare the sodium sulphite-oxygen-alkali pulp (NS-OAP).
To make easy-bleaching NS-OAP, kappa number of which is 10 or below 10, the adequate pulping conditions were : Na
2SO
3/chip 2030%, cooking temperature 180°C, and cooking time 34hr for the NS pulping stage ; and NaOH/NS-pulp 48%, initial oxygen pressure 6kg/cm
2 on gage, cooking temperature 120°C, and cooking time 2hr for the OA pulping stage.
On equivalent kappa number level, the yield of NS-OAP was 45% higher than that of sulphate pulp (KP). The brightness of unbleached NS-OAP was 47.375.5% and much higher than that of unbleached KP.
NS-OAP, which kappa number is about 10, could be bleached to brightness of 80% by the one stage bleaching with NaClO and to brightness of 85% by the two stage bleaching with NaClOClO
2. The bleached NS-OAP was higher in yield and less in the brightness reversion than was the bleached KP.
The strengths of NS-OAP were somewhat weaker than those of KP.
The results show that the NS-OA pulping is an èxcellent method for making an easy-bleaching pulp.
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