Fibre characteristics of some mechanical pulp grades

Based on optical and electron micrographs, studied by image analysis, the f ibre fractions of some commercial mechanical pulps were compared and relate d to differences in paper surface smoothness. Fibres from SGW and PGW-pulp were found to be much more split and damaged than fibres from TMP-pulp. Mod el studies using hand sheets from some typical GW and TMP grades were under taken. Intact groundwood fibres had thicker walls than intact TMP-fibres fr om pulps with the same freeness. Intact groundwood fibres (in sheet cross-s ections) had larger lumen openings than TMP-fibres at the same freeness. St ill, super calendered laboratory sheets made from GW-fibres were less rough ened by moistening than were TMP-based sheets. The increase in roughness up on moistening increased with larger degrees of fibre splitting. Both wall t hickness, fibre splitting and fibrillation appear to affect moisture-induce d roughening. Crushing TMP-fibres while maintaining fibre length could give a pulp with better surface smoothness properties without losing strength.