| Fast-grown poplar was used as the raw material and three novel xylanase was selected to pretreated KP and NaOH-AQ pulp in this thesis. The influence of xylanase treatment on oxygen delignification, ECF and TCF bleaching was investigated. Furthermore, the mechanism of lignin dissolution, fiber properties of bleached pulp, beating performance and physical properties of paper sheet was analyzed. In summary, the results above would provide technical support and theoretical basis for clean production of fast-grown poplar chemical pulp.The impact of three kinds of xylanases treatment on oxygen delignification of fast-grown poplar KP pulp was studied. Based on the results of oxygen delignification by varying key parameters (including time, pH, temperature, enzyme dosage), the optimal condition was proposed as followed: X1:enzyme dosage8IU/L, temperature50-55℃, pH8, time120min; X2:enzyme dosage6IU/L, temperature55-60℃, pH8-9, time120min; X3:enzyme dosage8IU/L, temperature50℃, pH8-9, time120min.The impact of three kinds of xylanases treatment on oxygen delignification of fast-grown poplar NaOH-AQ pulp was studied. Based on the results of oxygen delignification by varying key parameters (including time, pH, temperature, enzyme dosage), the optimal condition was proposed as followed: X1:enzyme dosage10IU/L, temperature50-55℃, pH8-9, time90-120min; X2:enzyme dosage8IU/L, temperature55-60℃, pH8-9, time90-120min; X3:enzyme dosage10IU/L, temperature50-55℃, pH8-9, time120min.The influence of three kinds of xylanases on the ECF bleaching of KP pulp was studied, and the results as followed:The XODED bleaching sequence can provide the highest brightness of88.1%ISO. ODED can provide brightness of85.1%ISO, which can higher2.5-3%ISO when employed xylanases pretreatment. XODQP bleaching sequence can provide the highest brightness of87.0%ISO. ODQP can provide brightness of84.5%ISO, which can higher2.0-2.5%ISO when employed xylanases pretreatment. The XOpDQP bleaching sequence can provide the highest brightness of89.7%ISO. OpDQP can provide brightness of87.2%ISO, which can higher2.1-2.5%ISO when employed xylanases pretreatment. The XO1O2pDQP bleaching sequence can provide the highest brightness of89.6%ISO. O1O2pDQP can provide brightness of87.1%ISO, which can higher2.1-2.5%ISO when employed xylanases pretreatment. The viscosity, Kappa Number, p.c. Number, and physical properties could get improved by xylanases pretreatment.The influence of three kinds of xylanases on the TCF bleaching of KP pulp was studied, and the results as followed:The XOPQP bleaching sequence can provide the highest brightness of83.3%ISO. OPQP can provide brightness of81.2%ISO, which can higher1.9-2.1%ISO when employed xylanases pretreatment. XO1O2pQP bleaching sequence can provide the highest brightness of82.7%ISO. O1O2pQP can provide brightness of80.6%ISO, which can higher1.8-2.1%ISO when employed xylanases pretreatment. The XO1pO2pQP bleaching sequence can provide the highest brightness of83.5%ISO. O1pO2pQP can provide brightness of81.6%ISO, which can higher1.8-2.1%ISO when employed xylanases pretreatment. The viscosity, Kappa Number, p.c. Number, and physical properties could get improved by xylanases pretreatment.The influence of three kinds of xylanases on the ECF bleaching of NaOH-AQ pulp was studied, and the results as followed:The XODED bleaching sequence can provide the highest brightness of88.6%ISO. ODED can provide brightness of85.3%ISO, which can higher2.9-3.3%ISO when employed xylanases pretreatment. XODQP bleaching sequence can provide the highest brightness of87.7%ISO. ODQP can provide brightness of84.7%ISO, which can higher2.5-3.0%ISO when employed xylanases pretreatment. The XOPDQP bleaching sequence can provide the highest brightness of88.5%ISO. OpDQP can provide brightness of85.3%ISO, which can higher2.8-3.2%ISO when employed xylanases pretreatment. The XO1O2pDQP bleaching sequence can provide the highest brightness of88.2%ISO.0,02pDQP can provide brightness of85.0%ISO, which can higher2.8-3.2%ISO when employed xylanases pretreatment. The viscosity, Kappa Number, p.c. Number, and physical properties could get improved by xylanases pretreatment.The influence of three xylanases on the TCF bleaching of NaOH-AQ pulp was studied, and the results as followed:The XOpQP bleaching sequence can provide the highest brightness of83.5%ISO. OpQP can provide brightness of81.0%ISO, which can higher2.2-2.5%ISO when employed xylanases pretreatment. XO1O2pQP bleaching sequence can provide the highest brightness of83.3%ISO. O1O2pQP can provide brightness of80.8%ISO, which can higher2.2-2.5%ISO when employed xylanases pretreatment. The XO1pO2pQP bleaching sequence can provide the highest brightness of84.0%ISO. OlpO2pQP can provide brightness of81.8%ISO, which can higher1.8-2.2%ISO when employed xylanases pretreatment. The viscosity, Kappa Number, p.c. Number, and physical properties could get improved by xylanases pretreatment.The results of FT-IR showed that:xylanase treatment does not change the structure of lignin fundamentally, but can degraded part of the xylan to promote the lignin dissolution. The lignin can get further removed and lead to decreased Kappa number and improved brightness.The alkali-soluble lignin of oxygen delignification after xylanase treatment of KP and NaOH-AQ pulp has less absorption at280nm, which may caused by part of xylan degradation. The LCC structure was destroyed and low molecular weight and hydrophilic lignin was dissolved during xylanase treatment. The results showed the treatment benefit the delignification.The comparison of residual lignin between pretreated and un-pretreated pulp was carried out, the results showed that:aliphatic hydroxyl group, condensation phenolic hydroxyl group, phenolic hydroxyl and carboxyl in syringyl were decreased, while phenolic hydroxyl increased. The changing tendency of hydroxyl group and carboxyl group of lignin in oxygen delignification was consistent in pretreatment and un-pretreated pulp. The results indicated xylanase pretreatment can improve delignification, despite the different mechanism of varied xylanase.SEM showed:fiber voids was increased, and became softer, and surface fibrillation phenomenon was more obvious with xylanase pretreatment. AFM showed:the single fiber surface has numerous soft fine fiber groups, the unevenness of the surface was obvious, fiber surface was more porous, and surface area was greater after xylanase pretreatment.In conclusion, the xylanase has obviously and effectively effect on bleaching process. |
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