Wood Fibre Preparation
Grinding logs against rotating stones creates mechanical pulp by physical abrasion rather than chemical dissolution. This production method retains nearly all components of the original log, including lignin, which binds cellulose fibres together. Because the fibres remain stiff and bulky, finished sheets exhibit high opacity and bulk that benefit printing substrates.
The process lacks the selectivity of chemical digestion, however, so the resulting fibres are shorter and physically damaged by the grinding action. This damage reduces the inherent bonding strength of the paper web, which limits the potential grammage and durability of the finished product.
Physical Property
Mechanical pulp influences the printability of paper through its specific surface area and scattering coefficient. High lignin content prevents the collapse of fibres during the drying process, allowing the structure to maintain a porous and light-reflecting network. Manufacturers adjust the sharpness of the grindstone surface to alter the ratio of long fibres to fines, where an abundance of fines fills gaps in the web to improve surface smoothness.
Achieving this balance governs the ink holdout and prevents show-through on lightweight newsprint or groundwood-containing papers. Printers recognize that these sheets demand careful moisture control because the wood components remain sensitive to humidity fluctuations within the facility.
Conversion Tolerance
Finished stock utilizing this fibre composition requires adjustment during mechanical processing and printing. Because the fibres exhibit low tensile strength, web tension must remain stable to prevent breaks during high-speed runs on rotary presses. Press operators reduce the pressure applied to the sheet to preserve the inherent bulk, as over-compression removes the air pockets that define the optical quality of the paper.
Consistency in the grind process creates a predictable foundation for subsequent coatings or calender treatments. The mechanical fibre structure dictates the failure threshold for tearing and folding operations throughout the supply chain.
