Irreversible long fibre collapse at high temperature TMP reject refining – Effects on fibre surface properties

Effects on fibre and sheet properties of preheating to temperature well above the softening temperature of lignin in refining of spruce TMP reject were evaluated. This study indicates that an improved surface smoothness can be attained on TMP-based wood-containing papers through high-temperature reject refining. Under these conditions the degree of irreversible fibre collapse increased. Results from tests of the fibre-wall, fibre surface characteristics, pulp yield and sheet brightness show only marginal differences at high temperatures compared to standard reject refining. Experiments in which laboratory sheets were moistened showed that a high degree of irreversible fibre collapse correlates with surface smoothness.