Biostability of waterborne paints and coatings is a complex and multi-faceted subject, but is often broken down into three general areas :
- Viscosity loss due to cellulase enzyme attack on cellulosic thickeners
- Resistance of the finished paint to growth of microorganisms (including bacteria and mold)
- Resistance of the dried paint film to surface growth of mold & mildew
Items 2 & 3 above are generally mitigated through the use of biocides in the paint formulation. Aqualon does not offer biocides, but they are at times used in Aquaflow nonionic synthetic associative thickeners for storage stability.
Enzyme production is a by-product of bacterial activity. Enzymes can be found in process water and finished paint, even after bacterial activity has been killed through the use of biocides. In particular, cellulase enzymes can be introduced in to the paint making operation through untreated water and raw materials. Over time, the presence of cellulase enzymes will break the bonds between adjacent unsubstituted anhydroglucose units in the cellulose backbone. This reduces the molecular weight leading to significant viscosity loss in paint.
Ashland Aqualon Functional Ingredients offers superior biostable cellulosic thickeners in our Natrosol® B-series HEC and Natrosol® Plus modified HEC thickeners. These high performance workhorse thickeners for latex are manufactured in a way so as to protect the backbone from enzyme attack. The end result is 95% viscosity retention over time, even when paint is intentionally dosed with cellulase enzyme (at 1.0 ppm).
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