SUPERHEATED STEAM DRYING OF PAPER FROM CHEMITHERMOMECHANICAL PULP

The effect on paper properties of superheated steam drying of chemithe rmomechanical paper is reported. Strength properties, such as Scott in ternal bond, burst index, and tensile index, were up to 32% higher for steam-dried paper than for paper dried in air under the same conditio ns. Lower scattering coefficients for the steam-dried sheets are consi stent with increased relative bonded area being the mechanism for the increased strength. The proposed mechanism accounts for the changes in physical and optical properties through softening of lignin and hemic elluloses within the fibers, rendering the fibers more flexible, allow ing better interfiber contact and better bonding, thereby providing a stronger sheet. This softening is a consequence of the sheet temperatu re from the onset of drying being significantly higher for drying in s uperheated steam in the air.