Reference
J. P. Sisk, A. D. Harrison, P. W. Steenbeek - As presented to the 7th International Symposium for the Paper Machine Clothing Industry
Abstract
As paper machine operators and service chemical suppliers are moving towards increased use of Hypohalous acids utilized as industrial biocides these actives have undergone severe scrutiny in the microbiological control of paper machines. Although these biocides are becoming the preferred choice for control of biofouling in the pulp and paper industry, one must consider the effect of long term use on paper machine clothing. The expendable items on a paper machine such as wires and felts are quite costly, and can be affected by many chemicals they encounter during their life cycle. The machine down time caused by the time needed to replace the felts effects the runnability of the machine. The effective life cycle of these wires and felts may be reduced by incorrectly feeding a particular treatment program or by poor treatment selection. This paper examines the two main oxidizing biocides currently used on paper machines, BromiCide and bleach (NaOCl), and how they affect the life cycle of polyamide fiber based paper machine clothing.
Conclusion
Historically paper manufacturers have been reluctant to use chlorine as paper machine slimicide for many reasons. One of these reasons is that chlorine is known to damage polyamide machine clothing. While it can be a good slimicide, provided that the water does not become alkaline, and provided that the local safety and handling as well as eco-toxicity is not a problem, it of course becomes a too costly to replace felts and wires. An ideal situation would be an environmentally acceptable and cost effective oxidizing biocide which does not damage polyamide. During several years of experience it has been found that BCDMH is an excellent paper machine slimicide, but paper machine operators have been cautious because of the unknown potential to harm polyamide. In these investigations, BCDMH has been compared to NaOCl using various measurements of their effect on polyamide material. All of the measurements (tensile strength, % elongation, modulus surface incorporation of Br of Cl, abrasion resistance, and relative viscosity) made on polyamide exposed to BCDMH or NaOCl have consistently shown that BCDMH is significantly less harmful to the polyamide materials use to make machine clothing. This translates into a considerably longer life span for clothing treated with BCDMH than clothing treated with chlorine based biocides.
Theoretically these results are not surprising. It is well know that bromine biocides, especially bromine derived from BCDMH, is less chemically aggressive than chlorine based biocides without showing any decreased efficacy as biocides. A measurement of the Oxidation Reduction Potential (ORP) quickly shows that halogen from BCDMH is much less aggressive than halogen from NaOCl or Cl2. The cooling and process water industries have long seen the results of this in the lower tendency of BCDMH to cause corrosion, or induce other side reactions when compared to chlorine.
The demonstration of this with polyamide felt materials should allow paper machine operators to confidently use BCDMH as their paper machine biocide without undue fears about the reduced life times of their paper machine clothing.