Study On The Fluid Transmission Characteristics Of Aspen During NaOH Impregnating Process

The wood fluid transmission characteristics research is always playing a significant role in the basic theory research of wood application. In the field of pulp and paper industry, the wood fluid transmission characteristics of impregnating liquid and cooking liquid has a significant influence on the pulping process of chemical pulp and high yield pulp including pulp properties, cooking time and refining energy. Based on the importance of fluid transmission characteristics, the chemical composition and physical structure of raw material of aspen were analyzed comprehensively. And then the diffusion and penetration of NaOH impregnating were studied with the self-made equipments. Meantime, the effects of main factors, which included temperature, concentration of NaOH, thickness of sample and moisture of sample, the diversity of sapwood and heartwood, the diversity of transverse impregnating and longitudinal impregnating, were investigated.Through the analysis of chemical composition and fiber morphology of the raw material, the aspen used in this research has typical characteristics of hardwood. Although there were some differences between the raw materal in the research and other enumerative hardwood species, the differences were within a reasonable range. Meanwhile, the analysis of raw materal showed that the fluid transmission performance of sapwood was better than the heartwood. Furthermore, the subsequent studies of diffusion process and penetration process showed that the difference of fluid transmission between sapwood and heartwood in longitudinal impregnating process was more significant than that in transverse impregnating process.The study of diffusion process showed that there were three stages in the process of the NaOH impregnating diffusion of aspen, namely reaction-driven stage, reaction and diffusion coexistence stage and diffusion-driven stage. Meantime, the effects of main factors, which included temperature, concentration of NaOH, thickness of sample and moisture of sample, were investigated. The results showed that temperature and thickness of sample had significant effects on the NaOH impregnating diffusion process, but thickness of sample did almost not influence diffusion coefficient of longitudinal impregnating diffusion process. The concentration of NaOH influenced the inflection point mainly which had close link with reaction rate in the impregnating process.The study of penetration process showed that transverse penetration of NaOH impregnation was layer-by-layer penetration process, and there was a linear relationship between the unit penetration volume flow rate and the penetration time. The longitudinal penetration process could be divided into two stages, namely the rapid penetration stage (the first stage) and the slow penetration stage (the second stage). Besides, with conditions of this research, the temperature and the concentration of NaOH had positive effects on the penetration process, while, the thickness of sample and moisture of sample had negative effects on the penetration process.