Elimination of mudcracking in latex paints by microfibrillated cellulose additives

The application of thick layer water based latex paints is generally seldom made on purpose. Typically wet film thicknesses of 25 – 50 µm (1 – 2 mils) are applied and generally very little is exceeded when wet film is exceeded 100 µm (4 mils) per wet film application. Of course, specially selected latex paints with high film building capacity in thick layers are also present, however, similarly to putties, they are formulated for such application.

Mudcracking on latex paint coating applied on plasterboard panel

What if, during application, on a substrate with an uneven structure, there are places where, as a result of application or not quite good sagging resistance, thickenings will form, which significantly exceed the typical thickness of the wet layer applied, or if drying in layers of non-nominal thickness will be greatly accelerated, e.g. by elevated temperature?

Then there is a risk of cracks appearing on the coating in the form of mudcracking.

In accordance with ASTM D16 defining terminology in the paint and coating industry:
mud-cracking – an irregular broken network of cracks in the film, which occurs due to volatile loss while drying or curing.

Mudcracking is caused by the inability to evaporate water from deeper layers of coatings when the surface layer is already largely dry. This process is intensified as the thickness of the coatings increases, where it is more and more difficult to evaporate water from the lower layers.

A way to eliminate mudcracking during the drying of thick layers of latex paints, especially at elevated temperatures, can be the use of functional additives in the form of MFC – microfbrillated cellulose. The fibrous structure, small size of the fibers and excellent water retention create a spatial network in the coating that allows for slow evaporation of water from the lower layers to the upper, thicker ones, by water migration through the fibers. This phenomenon causes a significantly reduced shrinkage of the coating during drying and elimination of mudcracking.

Schematic formation of mudcracking and coating shrinkage

The mudcracking test is carried out in the Spektrochem Paint Laboratory in accordance with the Australian Standard AS 1580.409.1-2002. In accordance with this test method, case studies of paint were carried out to determine the effectiveness of mudracking elimination by the addition of microfibrillated cellulose.

Case studies samples of latex paint formulation: control – left side and with 5 % and 10 % of MFC gel in the formulation

The test was carried out at an elevated temperature of 50 °C (122 °F) and the coating was applied in a 500 µm wet layer to the plasterboard.
The photos above show the coatings of paints after the tests performed. The left-hand latex paint coating (controlna) shows very significant mudcrakcing. Subsequent coatings were obtained from paints, the formulation of which was formulated with 5 % and 10 % microfibrillated cellulose gel. The photos clearly show a significant improvement and elimination of mudcracking. The addition of 5 % MFC gel eliminated mudcracking to such an extent that shrinkage cracks can be noticed only at the edges of the coating. The addition of 10 % MFC gel allowed to completely eliminate mudracking in the prepared formulation.

Microfibrillated cellulose is an additive agent that allows you to modify the formulation of latex paints in terms of improving many parameters of both liquid paints and coatings. The Spektrochem laboratory conducts research and case studies for manufacturers of this type of additive in order to maximize their performance in latex paint formulations, from interior paints, through facade paints, to acrylic liquid roof coatings.

Published by Artur Palasz

Scientist, paint formulator and testing expert.

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