为何纸张强度上不去？

Refining affects fibers in many ways, with the most important effects being as follows：

— Cutting and shortening of fibers
— Fines production and complete removal of parts from fiber walls, creating debris in suspension
— External fibrillation, the partial removal of the fiber wall, leaving it still attached to the fiber
— Internal changes in the wall structure, variously described as delamination, internal fibrillation, or swelling
— Curlingthe fiber or straightening the fiber
— Creating nodes, kinks, slip planes, microcompressions in the cell wall, or removing those from cell wall
— Dissolving or leaching outcolloidal material into the external liquor
— Redistribution of hemicelluloses from the interior of the fiber to the exterior
—  Abrasion of the surface at the molecular level to produce a more gelatinous  surface.

As a result of the above effects, fibers after refining are collapsed (flattened) and made more flexible, and their bonding surface area is increased. The measurable fiber and sheet properties, when refining chemical pulps, can be seen as follows：

— Drainage resistance (water removal resistance) increases.
— Tensile strength, tensile stiffness, burst strength, internal bonding strength, and fracture toughness increases.  
— Tear strength of softwood fibers might slightly improve at first, but then decreases, whereas that of hardwood fibers at first significantly increases but then decreases after prolonged refining.
— Air permeability, bulk, absorbency, opacity, and light scattering decreases.
— Brightness slightly decreases.