Strength Improvement of Wheat Straw Chemi-mechanical Pulp by the NaOH-urea Pretreatment

The NaOH-urea pretreatment system under mild temperatures was used to modify mechanical pulp properties of wheat straw, and the effects of alkali impregnation time and treatment temperature time were evaluated through single factor tests. The results showed that the optimal conditions were chosen as NaOH and urea concentrations of 5% and 3.5%, impregnation time of 10 min, treatment temperature of 50 ºC and treatment time of 60 min. Compared with the results of the NaOH-pretreated chemi-mechanical pulp production, the refining energy consumption of the mechanical pulp prepared by the NaOH-urea system was decreased by 14%, while screened yield and brightness of the pulp were increased by 1.5% and 4.2% （point） and sheet density, tensile index and burst index were increased by 3.5%, 20% and 17%, respectively.