An emulsion is a two-phase system of immiscible liquids. Depending on the composition of the continuous and dispersed phase, an oil-in-water emulsion or water-in-oil emulsions could be obtained. The addition of a surfactant is essential for the stability of all emulsions, serving to reduce the interfacial tension between the two liquids. Whereas other additives might be used to increase this stability.

Wax emulsions provide a useful means of delivering wax to a product, as they are easily incorporated into waterborne coatings and paints formulations by simple mixing due to their liquid form. Waxes are typical additives that significantly influence the surface properties of any coating to improve and protect its appearance.

Due to the chemical structure of waxes, one of the most remarkable improvements attained with these additives is water repellency. As the name implies, this characteristic is the protection of a surface against water penetration, source of mould problems (which are unhealthy and unattractive) or even irreversible structural damage.

Usually, paraffin waxes perform very well, particularly on porous surfaces, because they are mainly composed of straight alkane chains and have good crystalline structure, giving excellent barrier effects against water.

The range of EMULTROL wax emulsions wraps a variety of waxes like paraffin, polyethylene, lignite, carnauba, etc. that in combination with different emulsifiers covers most of the requirements of our customers. Among all, we can pinpoint EMULTROL CM-2469 SPL and CM-2655 E as the most appropriate candidates for improving water repellency in waterborne paints. Both, paraffin wax emulsions, exhibit white appearance, low particle size (< 1 µm), low viscosity and alkaline pH (see Figure 1 and Table 1).

Figure 1 – EMULTROL CM-2469 SPL and CM-2655 E appearance and their corresponding particle size distribution.

Table 1EMULTROL CM-2469 SPL and CM-2655 E properties. 

Study 

The examination of the interaction of a liquid with a surface can provide a simple but effective evidence about the surface’s characteristics and how it will perform in other related environments. Water droplet contact angle can provide an insightful information of a surface that has been tailored to exhibit desirable functions by the addition of coatings.

A droplet that remains round, exhibiting a high contact angle (see Figure 2, left), reveals a hydrophobic or water repelling surface. On the other hand, when a droplet lies flat and wets the surface (see Figure 2, right) disclosing a low water droplet contact angle, indicates a hydrophilic surface.

 

Figure 2 – Coated (left) and uncoated (right) surfaces to improve hydrophobicity.

For the evaluation of the hydrophobic behaviour of each product, a layer of each of the emulsions was applied (30 μm wet) on paper and allowed to dry completely (minimum 12 h at room temperature). Then, a droplet of water was carefully placed on top of this layer, in order to observe its shape.

Furthermore, to demonstrate the beneficial effect of using wax emulsions as additives in paints, a 2 and 3 % of each emulsion have been added to two different commercially available styrene-acrylic and acrylic resins used for paints and coatings. The characteristics of those resins are shown in table 2. Then, the same procedure mentioned above was performed using the modulated resins as coating.

 

Table 1 – Resins properties.

Results 

It is well known that an uncoated paper will immediately get soaked by water when its poured on it. However, when using the appropriate coating, a hydrophobic surface can be obtained. From Figure 3, we can observe how the water droplets behave on top of coated paper. As mentioned above, the hydrophobic character is emphasized with wax emulsions (a), when compared to the purely acrylic resins (b), as a more spherical shape is attained (implying a higher contact angle).

 

Figure 3 – Water droplets on top of coated paper with a) EMULTROL CM-2469 SPL and CM-2655 E wax emulsions and b) resin 1 and resin 2.

Moreover, in Figure 4, we can perceive an improvement in the hydrophobicity of the coating when using wax emulsions as additives in acrylic resins. This effect is more accentuated when using resin 2 (b), exhibiting a more round-like shape on the water droplet.  As expected, when the dosage is increased from 2 to 3% the hydrophobicity of the surface is enhanced (Figure 5).

 

Therefore, we can conclude that EMULTROL CM-2469 SPL and EMULTROL CM-2655 E are good candidates to use as wax emulsion additives for waterborne paints, especially those based on polymeric dispersions.

Figure 4 – Water droplets on top of coated paper with a) purely and additivated resin 1 b) purely and additivated resin 2 with 2% of wax emulsions.

Figure 5 – Water droplets on top of coated paper with a) resin 1 b) resin 2 with 2 and 3% of wax emulsions respectively.

Conclusions 

EMULTROL CM-2469 SPL and EMULTROL CM-2655 E are paraffin wax emulsions, especially developed for waterborne coatings. Designed with two different emulsifying systems to increase the compatibility with typically aqueous resins used for this purpose. The main benefit of using those wax emulsions in water-based coatings is to increase the film hydrophobicity. The effectiveness of these wax emulsions is demonstrated in this study.

Keep in mind that every formulation is unique and may require compatibility tests to ensure optimal results.

AUTHOR: Carlota Clarasó