Fibre Integrity
Fibre bond density defines the physical state of a cellulose suspension as it moves through the refining stages of paper production. Pulp viscosity functions as an index of the average degree of polymerization of the cellulose chains within the wood fibres. Shorter molecular chains lead to lower values, which signal a reduction in the intrinsic strength of the resulting paper sheet.
This metric dictates the degree of mechanical work applied to the stock before it reaches the headbox.
Refining Constraints
Mechanical refiners shear the stock to fibrillate the outer walls of the fibres, an action that relies upon the fluid resistance of the slurry. Lower readings indicate higher degradation of the cellulose polymers, which necessitates a reduction in the plate load to prevent excessive fibre cutting. High shear intensity applied to degraded fibres produces fine particles that decrease the drainage rate on the wire and disrupt the formation of the web.
Operators monitor this variable to keep the tear and tensile properties of the finished stock within the limits of the grade specifications.
Performance Consequences
The final physical properties of the printed substrate depend on the degree to which the fibres retain their length and structural cohesion during the processing phase. High values correlate with better resistance to stress during the printing process, especially for webs subjected to high tension in offset lithography. Papers derived from pulps with deficient chain length exhibit increased dust formation and poor surface pick resistance during the transfer of ink.
Strict control of the cooking and bleaching chemistry ensures that the fibre network retains sufficient mechanical stamina to perform under the load of high speed conversion equipment.
