Study On The Relationship Between The Chemical Chracteristics Of Wood Fiber And Paper Sheet Strength

From the view of traditional papermaking sentific theory, the theory of sheet strength has not been so perfect. Although it was understood that chemical characteristics of fiber surface and fiber morphology have a great impact on hydrogen bonding between the fibers, the sheet strength theory can not quantitatively express the relationship between fiber surface chemical characteristics and sheet strength. This paper tries to determine the quantitative relationship between surface chemical characteristics and sheet strength so as to guide the modification of fiber surface. It will be helpful to guide the extent of lignin removal during the pulping process, achieve fiber orientation design and manufacturing according to the physical parameters of sheet and promote the development of the scientific system in pulp and papermaking industry.This paper used surface analysis instruments including atomic force microscope (AFM) and X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FT-IR) to analyze the fiber morphology and chemical characteristics of aspen CTMP (CTMP), bleached softwood kraft pulp (SBKP) and bleached hardwood kraft pup(HBKP) and determine the varation of chemical characteristics of fiber surface with different furnish ration of CTMP by means of chemical pulp furnishing with mechanical pulp. The results showed that CTMP fiber surface was covered with granular lignin and extractives, the diameter of the granule was between 50~109 nm. Wood species and pulping methods have significant impacts on chemical charateristics of fiber surface. The lignin coverage of CTMP, SBKP and HBKP were respectively 48.72%, 5.18% and 13.14%. Refining had an impact on chemical properties of the fiber surface, with an increase of refining degree, lignin coverage at fiber surface decreased. A linear relationship existed between lignin coverage of mixed fibers and furnished ratio.Besides the chemical componets, sheet RBA and fiber mophological factor also had impacts on sheet strength. This paper analyzed relative bonded area (RBA) of sheet by the methods of light scattering coefficients and nitrogen adsorption, tested the mophorlogical factors of the fiber by FS-300 Fiber Analyzer. The relationship between fiber surface chemistry, sheet relative bonded area, fiber mophological factors and sheet strength were investigated. The quantitive relationship between fiber surface chemical characteristics, tensile strength and the internal bond strength of the sheet were established by multiple regression analysis and the relationship between fiber surface chemical characteristics and the sheet strength was focused on. The results showed that fiber surface chemical characteristics had a great impact on the sheet tensile index and the internal bond strength, 1% increase in lignin coverage at fiber surface would lead to approximate 0.5 Nm/g decease in tensile and 0.67J/m~2 decaeae in internal bonded strength within this experiment. There was no correlation between zero tensile strength of sheet, lignin coverage and RBA. RBA decreases with an increase of suface lignin coverage.In order to verify above conclusions, this paper performed the surface modification of CTMP and SBKP pulp by plasma and plasma grafting acrylamide. The results showed that 1% increase in tensile index would cause a 0.22N.m/g decrease in tensile strength. With the plasma treatment, the group of–OH and -COOH could be presented at surface of CTMP and SBKP fiber, the fiber surface would be more hydrophilic, and tensile index of the sheet was improved, mealwhile, C-C bond and–CONH- were envolved, by which a linked network formed with the fibers, and wet strength of sheet was improved.With an increase in sheet bulkness, the tensile index and wet tensile index increased significantly.