Pulp and Paper Canada

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Giving machine clothing a long life


September 1, 2008
By Pulp & Paper Canada
Machine clothing plays a vital role in the final project

PPC was interested in learning how chemicals used in the papermaking process interact with paper machine clothing. BWA Additives, a provider of specialty water solutions for industrial and process wat…

PPC was interested in learning how chemicals used in the papermaking process interact with paper machine clothing. BWA Additives, a provider of specialty water solutions for industrial and process water treatment, desalination, pulp and paper, oilfield and other industries, provided details on this interaction, as well as steps papermakers can take in order to prolong the life of paper machine clothing.

PPC: What sorts of papermaking applications are the most susceptible to paper machine clothing damage from biocides?

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BWA Additives: The most susceptible types of papermaking applications are those which require a higher usage of biocides due to the nature of the process and/or the quality of the stock in use (virgin versus recycled). For example, fine papermaking and tissue making – where a relatively delicate and highly uniform sheet is required -generally demands a more robust biocide treatment program, since the end product is more susceptible to biofouling-induced breaks due to the accumulation of slime on the wet end of the machine. Food grade paper products also require minimal microbiological content in the finished paper and, as such, necessitate a higher-level biocide treatment.

PPC: Can improvements to biocides increase the lifespan of machine clothing? If so, how?

BWA Additives: Yes. Choosing organic biocides or selecting less harmful oxidizing biocides that are bromine-based, such as BCDMH (Bromo-Chloro- 5.5-Dimethylhydantoin) rather than chlorine-based products, will extend the clothing lifespan. Chlorine-based biocides are good slimicides under neutral or acidic pH conditions, and they are known to damage polyamide machine clothing. BCDMH is an excellent paper machine slimicide, but its use has been cautioned in the past due to the unknown potential to harm polyamide. In the last decade, extensive comparison analyses, including tensile strength, percentage of elongation, modulus, surface incorporation of Br or 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 used to make machine clothing. This translates into a considerably longer lifespan for clothing treated with BCDMH than clothing treated with chlorine-based biocides. 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 lifetimes of their paper machine clothing.

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