Oxygen Delignification of Bamboo Kraft Pulp and Bleaching Effects Using Totally-chlorine-free Bleaching Sequences

Bamboo kraft pulp with a Kappa number 25.6 was sampled, and oxygen delignification and totally-chlorine-free bleaching sequences were applied to bleach these bamboo pulp samples. By investigating pulp yield, Kappa number, viscosity, brightness of pulp, and delignification-selectivity, ithas been proven that caustic soda dosage and reaction temperature were major factors for oxygen delignification. The optimal conditions for oxygen delignification were proposed as follows:alkali dosage of 3.5% on o.d. pulp-mass, reaction temperature 85℃, oxygen pressure 0.6 MPa, and temperature retention time 80 min. Two stages of oxygen delignification were used and no washing was required between each stage. It was found that delignification efficiency and selectivity to lignin-removal were improved significantly. In addition, addinghydroquinone compounds (Oq) during oxygen delignification can improved greatly the qualities of delignified pulps such ashigher viscosity and better selectivity of delignification. The brightness levels of all bleached pulps, using OQ(PO), (O1O2)Q(PO), OQ(PO)1(PO)2 and OqQ(PO) bleaching sequences, individually, were increased up to more than 80%(ISO). Strength properties of bleached pulps using OQ(PO), (O1O2)Q(PO) or OQ(PO)1(PO)2 bleaching sequence, show insignificant differences, while tensile, tearing and burst indices of bleached pulp using OqQ(PO) bleaching sequence were remarkablyhigher than other three sequences.