Fibre performs the role of an effective and abundant de-tackifier, preventing collisions between free pitch particles. The introduction of such a pre-tower fixation point for TMP stream, eliminated both pitch-related breaks and holes in a southern US LWC mill after it was converted to neutral pH and switched pitch control program from alum to HYBRID polymer. A typical dosage of HYBRID polymer for early fixation is 1-2 lbs./t based on the solids of the treated pulp stream. Polishing treatment: Final polishing application to thick stock, preferably to the suction side of the machine chest pump or stuff box, is accepted prior to the final dilution with white water. Typical recommended dosage from this feeding point is 0.5-2.0 lbs./t. Additional benefits observed from this dosage point (such as a reduction of retention program dosage and increased colloidal retention of additives added upstream) compensate for some of the cost of the polishing application of HYBRID. In few cases, due to the reduction of a high molecular weight flocculant dosage closer to the HB, formation improvement was observed. Equipment: To provide appropriate mixing with the stock, the polymer should be added through an injection point equipped with Pareto nozzle with a large amount of dilution water. This is an absolute requirement in order to achieve uniform treatment. Preparation of initial polymer solution: this is done at the 0.5-1.5% concentration level by mixing the neat polymer with water using simple on-line systems, equipped with a high shear pump or mixing jet / static mixer combination. UNIQUE PERFORMANCE BENEFITS OF HYBRID FIXATIVES Effectiveness of fixation: The effectiveness of fixation is best measured through filtered turbidity reduction as a function of dosage of the polymer. When compared with a typical coagulants dosage, the HYBRID polymer required to meet a 70% reduction in filtered turbidity is typically reduced at least 2-4 times, but in some cases even higher reduction of dosage was observed (Figure 4). The mixed, charge neutralisation – bridging flocculation mechanism of operation – allows the fixing of small particles to the fibre without a need for significant charge neutralisation. Fixation vs. Agglomeration: Recent work by Vahasalla6 using flowcytometry measurement indicated that, in the case of high charge / low molecular weight coagulants, the desired fixation of coated broke latexes used as model hydrophobic contaminants was accompanied by the significant amount of their homo- agglomeration. The author concluded that this agglomeration was especially pronounced in the case of “aggressive and fast” fixation. The recommendation was made to perform fixation in a moderate fashion by splitting the required dosage between two to three dosage points, or targeting lower total turbidity reduction levels. Figure 5 shows a patch-assisted fixation mechanism. Richardson11 studied fixation of Pine Radiata TMP pitch in newsprint production using several different types of fixatives. High charge coagulants were found to cause the significant amount of deposition onto non- cellulosic surfaces that could, in real applications, represent deposits on the Figure 4. Performance of HYBRID polymers and typical coagulants in terms of filtered turbidity reduction for TMP furnish. The mixed charge neutralisation – bridging flocculation mechanism of operation – allows the fixing of small particles to the fibre without a need for significant charge neutralisation. WORLD PULP&PAPER 96 DEPOSIT CONTROL IN PAPERMAKING SYSTEMS