Search

Xylan is primarily found in the secondary cell wall of plants providing strength and integrity. To take advantage of the reinforcing effect of xylan in papermaking, it is crucial to understand its role in pulp fibers, as it undergoes substantial changes during pulping. However, the contributions of xylan that is added afterwards (extrinsic) and xylan present after pulping (intrinsic) remain largely unexplored. Here, we partially degraded xylan from refined bleached softwood kraft pulp (BSKP) and adsorbed xylan onto BSKP. Enzymatic degradation of 1 % xylan resulted in an open hand sheet structure, while adsorption of 3 % xylan created a denser fiber network. The mechanical properties improved with adsorbed xylan, but decreased more significantly after enzymatic treatment. We propose that the enhancement in mechanical properties by adsorbed extrinsic xylan is due to increased fiber-fiber bonds and sheet density, while the deterioration in mechanical properties of the enzyme treated pulp is caused by the opposite effect. These findings suggest that xylan is decisive for fiber network strength. However, intrinsic xylan is more critical, and the same properties cannot be achieved by readsorbing xylan onto the fibers. Therefore, pulping parameters should be selected to preserve intrinsic xylan within the fibers to maintain paper strength. [Display omitted] [ABSTRACT FROM AUTHOR]

Tensile testing was used to measure the mechanical properties of paper at various orientations relative to the fiber alignment of paper. New, artificially aged, and naturally aged paper were shown to behave as orthotropic materials, as shown by the orientation dependence of the Young's modulus, E. The Young's modulus data could be fit to a simplified equation, indicating the shear modulus is relatively insensitive to the specific orientation. The shear modulus as measured by ultrasonic measurements was similar to that measured by fitting the modulus vs orientation data obtained by tensile testing to the orthotropic equation. The inelastic tensile strength could also be described by a simple non-linear equation, and there was more deviation of the data from this prediction for brittle papers than for non-brittle papers. The extent of fiber orientation (E x /E y) could be inferred by either the Young's modulus or the tensile strength, TS, i.e. E x /E y ≈ TS x /TS y. The measured strains were lowest for brittle paper. All brittle papers gave a strain to failure <1% whereas the non-brittle papers gave a strain to failure >1%. • Paper was shown to behave as an orthotropic material for new, artificially aged, and naturally aged papers. • The Young's modulus versus fiber orientation data could be fit to a simplified equation. • The shear modulus is relatively insensitive to the fiber orientation. • The Ramberg-Osgood equation can be used to describe the stress-strain measurements. • All brittle papers gave a strain to failure <1% whereas the non-brittle papers gave a strain to failure >1%. [ABSTRACT FROM AUTHOR]