Fiber Length
Chemical pulping of coniferous wood species yields long cellulosic fibres with thick structural cell walls. Alkaline sulphate cooking dissolves wood lignin while preserving long, resilient cellulose strands. Incorporating softwood kraft pulp provides structural reinforcement and tear strength in heavy paper and packaging grades.
Pine, spruce, and fir trees serve as primary raw material sources for long-fibre chemical pulps.
Tensile Reinforcement
Fiber lengths averaging two point five to four point five millimetres form strong interlocking networks within paper webs. Long softwood fibres absorb mechanical stresses, resisting tearing, bursting, and tensile failures under physical loading. Packaging grades like linerboard and folding boxboard require high softwood content to sustain stacking loads and converting forces.
Mechanical refining hydrates long fibres, raising inter-fibre bonding surface area and enhancing burst resistance. Adding softwood pulp to short-fibre hardwood furnish improves web runnability on high-speed papermaking machines. Structural packaging substrates depend on long-fibre networks to prevent score-line cracking during high-speed folding box conversion.
Refining Limit
Excessive refining of long softwood fibres reduces drainage speed on Fourdrinier forming wires, slowing paper machine production rates. High softwood content increases sheet surface roughness, impairing smooth ink transfer during high-resolution offset printing. Unbleached softwood pulps limit achievable paper sheet brightness levels.
