Structural Ratio
Interfiber bonding parameters govern the fraction of internal fiber surface area participating in molecular contact within a paperboard sheet. Relative bonded area expresses the proportion of total fiber surface area involved in hydrogen bonding relative to total unbonded fiber surface area. Higher bonding ratios increase mechanical strength properties while reducing optical opacity and sheet porosity.
Light Absorption
Sheet formation compresses wet cellulose fibers into intimate contact, enabling hydroxyl groups to form hydrogen bonds during water evaporation. Relative bonded area is determined experimentally by comparing light scattering coefficients of bonded sheets against unbonded sheets prepared by solvent exchange drying. Increased refining and wet pressing force fibers to collapse into flattened ribbons, expanding contact surface area between adjacent fibers.
High relative bonded area values correlate with elevated tensile strength and elastic modulus in paperboard grades. However, extensive fiber bonding reduces void spaces inside the sheet, decreasing opacity and liquid absorption capacity. Papermakers adjust mechanical refining energy to optimize structural strength while maintaining required light scattering levels.
Fiber Boundary
Optical scattering metrics estimate interfiber contact within cellulosic web structures. Relative bonded area calculations do not apply to synthetic nonwoven sheets or non-porous extruded polymer films. Evaluation stops once maximum fiber consolidation occurs at ultimate pressing limits.
Calculations lose precision when light-absorbing dyes or heavy mineral fillers alter light scattering properties.
