The interactions between hydrophobic colloidal substances (HCS) and cationic polymers in pulp suspension were investigated by means of conforcal laser scanning microscopy (CLSM). In this experiment, four types of cationic polymers, Poly (allylamine hydrochloride) (PAH), poly (vinylamine) (PVAm), Poly (diallyldimethylammonium chloride) ⁄acrylamide copolymer (DADMAC⁄AM) and polyacrylamide (PAM), were used. PAH and PVAm were labeled with fluorescein-4-isothiocyanate (FITC). The HCS in the filtrate of a deinked pulp from a mixture of ONP⁄OMG were also dyed with a fluorescent hydrophobic probe, Nile Red. The dyed HCS were added to hardwood bleached kraft pulp (HBKP), and then these cationic polymers were added individually. The suspension after the polymer addition was divided into long fibers, fiber fines and colloid fractions. The state of the dyed HCS in each fraction was observed as fluorescence by CLSM.
In the case of the addition of only dyed HCS to HBKP, the pulp after washing showed no fluorescence. Therefore, no interaction between the HCS and the fiber could be observed. Conversely, when 0.5% of the labeled PAH were added, patches of fluorescence were observed on the surface of the fiber. The addition of HCS to HBKP followed by 5% of the labeled PVAm revealed that most of the fluorescent patches caused by dyed HCS were located on the external fibrils of fibers, and some of dyed HCS formed large agglomerates. By adding PAM and DADMAC⁄AM, the turbidities of colloid fractions were low, but the HCS formed large agglomerates and fixed to the external fibrils of fibers. The smaller polymers, PVAm and PAH, formed the smaller HCS agglomerates although the turbidities of colloid fractions were high. Observations from the fraction of fiber fines revealed that PAM and DADMAC⁄AM caused large agglomerate of fines with the HCS whereas PVAm and PAH gave no agglomeration.
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