THE BIREFRINGENCE OF SOFTWOOD MECHANICAL PULP FINES

Mechanical pulp fines which originate from the cell wall are birefring ent while fines originating from the middle lamella are mostly compose d of lignin and are not birefringent. A simple microscopic procedure h as been developed to measure the fraction by number of birefringent ma terial in a fines population. This proportion can vary by almost a fac tor of two between white water samples from various newsprint mills an d can vary by the same amount with energy in RMP fines. Since fibre le ngth analyzers like those of the Kajaani FS series detect particles by their birefringence, a large and variable proportion of mechanical pu lp fines will not be detected by these instruments.