Study On Low-polluting Bleaching Process Of Small-and-middle Diameter Bamboo Kraft Pulp

With good environmental emotion, Elemental Chlorine Free (ECF) bleaching and Totally Chlorine Free (TCF) bleaching have being trend of pulp bleaching, and taking over the traditional pulp bleaching processes.It was studied technology of ECF bleaching on bamboo kraft pulp, such as oxygen delignification, chlorine dioxide bleaching, boosted alkaline extraction, and xylanase boosted bleaching, then low-polluting bleaching process of bamboo kraft pulp was put forward. It was also analyzed the mechanism of each stage of the bleaching process by IR.Known that oxygen has better oxidizing power, it can delignify, but oxidize carbohydrate at the same time. Adding MgSO₄ is to complex -OH on carbohydrate and defend carbohydrate from dehydrogenation by OH.The result of two-stage oxygen delignification (OO) is much better than one-stage oxygen dilignification (O). Declining rate of Kappa was 60.5% in two-stage oxygen delignification while 46.7% in one-stage oxygen delignification. The optimal conditions of two-stage oxygen delignification were non-washed in between, added chemicals twice, NaOH dosage 2.0%/0.5%, oxygen pressure 0.9Mpa/0.4Mpa, temperature 70℃/100℃, time 40min/60min, pulp consistency 10%/10% and MgSO₄ dosage 0.5%/0.5%.As ClO₂ has great oxidizing power, it can choose to oxidizing lignin and coloring matter, but be less to carbohydrate. The optimal conditions of first chlorine dioxide bleaching (D₁) were ClO₂ dosage 1.90%, NaOH dosage 0.95%, temperature 75℃, time 120min and pulp consistency 10%. Properties of bleached pulp showed on declining rates of 56.2% in Kappa and 5.5% in viscosity, increasing rate of 73.8% in brightness.O₂ and H₂O₂ together can boost the result of alkaline extraction. The optimal conditions of boosted alkaline extraction (Eop) were NaOH dosage 2.5%, oxygen pressure 0.4Mpa, H₂O₂ dosage 0.5%, temperature 75℃, time 60min, and pulp consistency 10%. Properties of bleached pulp showed on declining rates of 66.0% in Kappa and 9.3% in viscosity, increasing rate of 25.4% in brightness.The optimal conditions of second chlorine dioxide bleaching (D₂) were ClO₂ dosage...