Influence of Recycling on Wood Pulp Fibres II.

Changes in Pore Volume of Pulp Fibres by Recycling

Abstract

Commercial hardwood and softwood sulphate pulp sheets, which were deaten to about 350 ml C. s. f., were subjected to recycling of a sequence of defibration, bewatering at 80°C for 6 days as flake upto five times.
Inaccessible water or pore volume by Scallan's solute exclusion method was measured on recycled fibres, as well as the water retention value by centrifugal force., Following results were obtained.
(1) The fibre saturation point, which was defined as the amount of inaccessible water measured by dextran corresponding to 560 Å molecular diameter, of pulp fibres before beating, beaten, and recycled for one and five times were 1.14, 1.39, 0.90 and 0.86 ml/g for the hardwood pulp and 1.12, 1.59, 1.16, and 0.86 ml/g for the softwood pulp.
(2) Smaller pores less than 50Å in the hardwood pulp fibres seemed unaffected by recycling. However, such smaller pores in the softwood pulp fibres diminished after the first recycling.
(3) The magnitude of centrifugal force necessary to expel absorbed water from cell walls to reach the fibre saturation point increased with recycling times. This means pore diameters in cell walls of pulp fibres decreased with recycling.