EFFECT OF REFINING ON THE OPTICAL-PROPERTIES OF SOFTWOOD THERMOMECHANICAL AND CHEMITHERMOMECHANICAL PULPS

The effect of refining on the brightness of softwood chemithermo-mecha nical and thermomechanical pulps (CTMP and TMP) has been investigated. Refining seems to increase both the absorption and scattering coeffic ients of unbleached pulps. However, the extent of increase in scatteri ng coefficient depends on the nature of the raw material ; when an inc rease in the scattering coefficient outweighs the increase in absorpti on coefficient, there is a resultant increase in brightness. It was he nce found that pine TMP increases in brightness with increased refinin g, while CTMP and TMP of spruce and a mixture of softwoods does not be have similarly. Also, the bleached CTMP behaves more like a chemical p ulp in that brightness decreases with refining. However, opacity and t ensile strength generally increased with refining.