Characterization of the flocculation dynamics in a papermaking system by non-imaging reflectance scanning laser microscopy (SLM)

Non-imaging reflectance scanning laser microscopy (SLM) was used to charact erize fiber-filler slurries and the flocculation processes in paper furnish es typical of those used for alkaline fine papermaking. The measurement pro duced a distribution of chord lengths characteristic of the size and shape of the furnish fiber and filler particles. Flocculation induced by a cation ic polyacrylamide (C-PAM) flocculant resulted in significant changes in the chord length distribution which was monitored as a function of time. Upon addition of C-PAM to the furnish, the mean chord length increased to a maxi mum value followed by a decay in magnitude at longer times. The SLM data wa s compared to dynamic drainage jar first pass retention data obtained at eq uivalent polymer dosages. At longer times, the shear instability of the flo cs caused the subsequent decrease in the mean chord length. The time depend ent decay of the percentage of chord lengths greater than 40 mu m was fit t o an exponential decay, yielding a decay time constant, tau. tau increased slightly with C-PAM dosage, but decreased dramatically with increased mixin g intensity due to more rapid flee degradation under the more turbulent she ar conditions. The advantages and limitations of the SLM technique in compa rison with conventional flocculation analyzers are also discussed.