Process of Kraft Pulping of Fast-Growing Poplar and Defibration Point

The process of kraft pulping of Fast-growing Poplar was studied,by determining the lignin contents including Klason lignin and acid soluble lignin, the yield of pulping, the rate of carbohydtare degradation and delignification rate. Results indicated that the delignificaton of Fast-growing Poplar in kraft pulping can be divided into three distinguishable stages. (a)The initial delignification stage before 140°C,the rate of delignification reaches to 35.76%; (b)The bulk delignification stage, the rate of delignification reaches to 90.50%，in the period from 140°C to 170°C and for 30 min; (c)The residual delignification stage,the rate of delignification exceeds 95.56%. The defibration point was reached when cooking temperature raised to 170°C and for 30 min with 52.22% pulping yield ,17.83 kappa number.