Thermal conservation instead of using biocides?
In-can preservatives are biocidal products that are used to protect products from microbial damage during storage, e.g. paints and varnishes in containers. Due to potential health risks, they are currently under strong pressure from prohibitions and regulatory restrictions.
At the Fraunhofer Institute for Manufacturing Engineering and Automation IPA, department Coating Systems and Painting Technology a research project on the thermal preservation of architectural paints and corresponding binder dispersions is currently being prepared.
|Interior wall paint||Binder emulsion|
|125-130 °C, 30 min||125-130 °C, 60 min||140-144 °C, 15 min||125-130 °C, 30 min||125-130 °C, 60 min||140-144 °C, 15 min|
|Airtight closure||yes||yes||yes||yes||no (“boiled over”)||yes|
|Status||OK or stirrable||OK or stirrable||OK or stirrable||OK||small gel content, bulk OK||small gel content, bulk OK|
|Minimum film-forming temperature||–||–||–||unchanged||unchanged||unchanged|
|almost unchanged||almost unchanged||almost unchanged||partially slightly increased||almost unchanged||almost unchanged|
|Fig. 1: Test results in the sterilizer. All details are compared to the thermally unstressed initial sample.|
Positive results in first tests
Preliminary tests with a commercially available white interior wall paint and a corresponding styrene-acrylate copolymer dispersion using an autoclave, a so-called sterilizer, showed surprisingly positive results. In contrast, correspondent experiments using microwaves (125 ° C, 300 W, 15 min) were unsuccessful; both colour and dispersion coagulated completely.
|Fig. 2: Examples of the practically unchanged minimum film-forming temperature of the binder emulsion with and without thermal stress (0 = unstressed, 1 h / 125 ° C (applied twice) and 15 min / 140 ° C).|
These preliminary tests showed that the thermal preservation of emulsion paints and corresponding binders is promising: at least for small container sizes, this could be an alternative to the use of in-can preservatives in the future.
|Fig. 3: Examples of the almost unchanged flow curves of the emulsion paint after thermal stress (samples from different preserving jars; each 125 ° C, 30 min) and without thermal stress (blue curve).|
Further investigations, now, should also include the limits of the thermal resistance (depending on the chemical composition), the biological durability of thermally preserved, biocide-free emulsion paints and the application properties of the thermally preserved materials compared to their untreated counterparts.
A corresponding cooperation project, for which partners are still being sought, is being prepared at Fraunhofer IPA. Interested parties may contact Dr. Norbert Pietschmann (firstname.lastname@example.org).
The technical book “Microbicides in Coatings” gives readers a comprehensive insight into the mode of action and areas of application of biocides in surface technology. The book deals with both chemical and biological aspects.