Designing Effective Defoamers and Deaerators Using Design of Experiments

In our daily lives, we have a high probability of encountering foamy materials such as beverages (coffee, carbonated drinks, etc.), soaps, and insulation materials (polyurethane foam). For these materials we have mentioned, foam is a desired property. Foamed Turkish coffee in particular is indispensable and has become part of our daily life. For paint manufacturers and applicators, the situation is the exact opposite. Obtaining paint with a quality and smooth appearance and ensuring foam control during its application is a mandatory task. Therefore, the use of high-performance antifoaming or defoaming additives is required to prevent and eliminate foam formation in paints and coatings. Antifoaming and defoaming agents; prevent foam formation during the production, application and transportation of paints, ensuring that paint performance remains at the desired level. Particularly in industrial applications such as dispersion processes, pumping of liquids, and mixing processes, and during paint application, foam formation is definitely an unwanted situation. This foam that forms; causes production processes to take longer than necessary (for example, dispersion time), prevents effective and efficient filling during packaging, loss of efficiency in operations requiring high mixing speeds, and leads to various paint defects on the surfaces of applied paint such as blistering, cratering, fish-eye, and "pinhole." Foam, in the simplest terms, is gas bubbles dispersed in liquid (air, carbon dioxide gas, etc.). Foam formed in pure liquids such as water is not thermodynamically stable; foam rapidly forming in liquid quickly rises to the liquid surface and disappears by bursting [Figure 1(a)]. However, as everyone has experienced before, when water is mixed with soap, the soap stabilizes the foam, creating tremendous persistent foam. Similarly, in water-based paints, inks, and adhesive formulations, wetting agents and emulsifiers present are surfactants like soap and cause the foam formed to remain stable. Surfactants surround the air created in the liquid, preventing it from merging with other air bubbles, and this situation slows down the rate at which air bubbles reach the surface, stabilizing micro foams.** Air bubbles that manage to reach the surface form macro foams [Figure 1(b)]. [caption id="attachment_136387" align="aligncenter"] Figure 1. Schematic representation of foam behavior in pure water (a), macro and micro foam representation (b)[/caption] Since antifoaming and defoaming agents function according to the type of foam they are effective against, they can be qualified as different products from each other. Antifoaming agents are more effective on stable foams formed on the liquid surface (liquid-air interface) (macro foam), while defoaming agents play an active role in eliminating small air bubbles trapped in the liquid (micro foam). Since micro foams are very small particles, visual identification of them is not always possible. However, they can be identified by methods such as the paint formulation's density coming out lower than expected. The air release mechanism works on the principle of bringing small micro foams together so they can leave the paint faster as larger foams. From the moment micro foams are created, they rise in the liquid attempting to reach the surface. According to Stoke's Law;*** the foam's rising speed depends on foam diameter and liquid viscosity. The lower the liquid's viscosity, the faster they rise toward the surface. According to Stoke's Law, the foam's rising speed is directly proportional to the square of its radius. Therefore, foam diameter is more effective on rising speed than liquid viscosity. Defoaming agents allow micro foams to merge, increasing their diameter and enabling them to reach the surface faster. In doing this, they disrupt the stabilization of surfactants surrounding the micro foams and allow the air in the foam to diffuse into the paint. Thus micro foams merge to form larger diameter foams and reach the surface faster (Air release) (Figure 2). [caption id="attachment_136389" align="aligncenter"] Figure 2. Air release mechanism[/caption] Effective defoaming agent design depends on many variables and processes. Careful and meticulous work must be done considering factors such as the defoaming agent's compatibility with the system, defoaming effectiveness, cost, and particularly ensuring it does not cause haze in clear coatings. The 6 Sigma**** methodology allows results that would be obtained through hundreds of trials to be achieved with far fewer experiments through effective experimental design, and enables optimal time management. Design of Experiments (DOE) is a useful 6 Sigma tool that helps project teams understand the effects of all possible process inputs on the final product. Denge Kimya is a company that adopts and prioritizes the 6 Sigma philosophy in all projects it undertakes. A new study conducted at Denge Kimya with this philosophy is the project of producing effective defoaming agents developed for clear coatings. The process of obtaining the best-performing defoaming agent for clear coatings was initiated with the creation of an effective experimental design (Table 1). In two-component (2K) clear coatings, generally a high viscosity is observed. Air bubbles (micro foams) mechanically drawn into the system (by mixing) are in combat with viscosity to reach the surface. The high viscosity extremely slows the rising speed of the micro foams formed. Since curing is fast in these systems, micro foams do not find sufficient time to reach the surface and become trapped within the system. Defoaming agents come into play to overcome this problem. Defoaming agents allow micro foams to reach the surface before curing occurs and to burst and disappear on the surface. The defoaming agents used are expected not only to rapidly release air in the resin system but also to not cause haze. Products obtained from the experimental design specified in Table 1 were tested according to the method specified below: First, 0.5% defoaming agent was added to the A and B component mixture of high-viscosity (11000-14000 mPas) solvent-free epoxy resin. After the defoaming agents were added, mixing speed and time were kept equal in all samples. Coatings created at 5 cm thickness were applied entirely by pouring method without applying any shear force. After 1 hour, foam quantities and turbidity were checked visually. Following the tests performed, the visual analysis of the work producing the best result was compared with the competing product and blank sample (without defoaming agent) and is given in Figure 3. In the image, while the text under the blank sample without defoaming agent reading "Densurf" was unreadable, the text under the coating containing the defoaming agent coded "RD-Safe 80001-31" could be easily read. The readability in the competing product was better than the blank sample but insufficient. [caption id="attachment_136391" align="aligncenter"] Figure 3. Top view of 5 cm thick clear coatings; blank sample, RD-Safe 80001-31, competitor.[/caption] References: 1. Béla Márton Somosvári, PhD Thesis, Foam evolution and stability at various gravity conditions, University of Miskolc, Faculty of Materials Science Department of Polymer Engineering, Miskolc, 2012. 2. Garrett, P.R. (Ed.). (1992). Defoaming: Theory and Industrial Applications (1st ed.). CRC Press. https://doi.org/10.1201/9781315140827. 3. Web: http://www.kansaialtan.com/icerik/pinhol-ve-gaz-hapsi_274 Footnote: *"Pinhole defect is a paint film defect that occurs when gas bubbles created in wet paint, as the film dries, leave the film and, due to its rising viscosity, the tears created during bubble exit are not filled by flow, resulting in permanent holes." ** Micro foam: Air bubbles trapped in liquid, generally having a round appearance. Macro foam: Air bubbles found on the liquid surface, generally having a polyhedral appearance. *** ν=r²η (Stoke's Law) ν: Foam rising speed r: Foam radius η: Liquid viscosity **** 6 Sigma is a project-oriented working methodology that aims to systematize improvements by using scientific approaches on all available and obtainable data.

Aylin Aydemir Senior Application Specialist Densurf

Dr. İlker Yatı Senior R&D Specialist Denge Kimya