Evaluation of a laser-optical resin particle counter.

Application: A new instrument should soon be able to measure on-line the concentrations of resin particles in white water and help mill personnel assess the impact of process changes on pitch control.

Scientists at Paprican evaluated a new instrument for pitch control. Made by BASF, this instrument counts the particles of dispersed pitch, or suspended wood resin, in pulps and white waters by measuring the fluorescent intensities of dyed resin particles as they pass through a laser beam in a tiny stream. The results were compared with those from a microscope and hemacytometer, which is an instrument for counting blood cells.

The laser-optical particle counter gave reproducible results for pulp filtrates after the researchers changed the procedure for dyeing particles to reduce the concentration of dye. The instrument could reliably detect only resin particles with diameters greater titan about 0.8 [micro]m, whereas most of the resin particles in pulp filtrates are in the range of 0.2-2.0 [micro]m, with a peak at 0.75 [micro]m. However, this segment of particles accounts for most of the volume of dispersed resin.

The new instrument usually gave a higher particle concentration than that given by the hemacytometer. Fines are usually coated with wood extractives, and the staining is not entirely selective. The concentrations were higher for the new instrument because some stained fines were indistinguishable from resin particles. In pulp and paper mills, however, it is probably appropriate to count the resinous fines since they are found in pitch deposits.

Yu and Allen are with Paprican, 570 St. John's Blvd., Points-Claire, Quebec, Canada H9R 3J9. Esser is with BASF Aktiengesellsehaft, Ludwigshafen, Germany. Email Allen at [e-mail]