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Wednesday, 30 September 2020
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Raw materials & technologies, Technologies

Thermal conservation instead of using biocides?

Monday, 3 August 2020

Fraunhofer IPA has carried out promising preliminary tests to preserve emulsion paints thermally. Partners are being sought to participate in a research project.

The Fraunhofer IPA wants to make emulsion paints thermally durable by heating to avoid usage of biocides. (Picture: Julia - stock.adobe.com)

The Fraunhofer IPA wants to make emulsion paints thermally durable by heating to avoid usage of biocides. (Picture: Julia - stock.adobe.com)

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
paintability yes yes yes - - -
Minimum film-forming temperature - - - unchanged unchanged unchanged
Viscosity/
 flow curve
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.

MFF Bindemittel
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.

Fließkurve Bindemmitel
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).

Thermal resistance

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 (norbert.pietschmann@ipa.fraunhofer.de).

Book tip

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.

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