Slow-Release Encapsulated Biocides

Turkchem 23 Aug 2021 57 4 dk okuma

TURKCHEM

The purpose of slow-release biocide technology is to slow down biocide release within a certain timeframe so that biocide concentrations found in the dry film can be retained in the system for a longer duration. The principle of slow-release (SR) technology is to keep biocidal actives effective for a longer period by demonstrating resistance to washing with water, high temperatures, high alkalinity, precipitation and UV radiation. Biological fouling is defined as the adhesion and growth of organisms on surfaces in contact with water. Depending on external factors, algae and fungal formation are observed over time in exterior facade paint films. Various efforts have been made to combat and prevent biological fouling. The most common way to prevent biological fouling is to add biocides to paint formulations. Biocides (preservatives) are used in recipes to prevent unwanted effects of bacterial and fungal growth. The most innovative approach in this field is the emergence of Tributyltin-based paints (TBT) in the 1960s. However, due to the slow degradation of these paints, it has been shown that they are extremely harmful to the ecosystem. As a result, the use of TBT in toxic paints was banned in 2008 [1]. Another biocide used in dry film protection systems is diuron. Diuron becomes active when exposed to external factors and separates from the system. Diuron (3-(3,4-dichlorophenyl)-1,1-dimethylurea), used as a dry film protectant in decorative paints, belongs to the halogenated-phenylurea family, which represents an important herbicide class [2]. It is wettable in the form of powder and liquid suspension. Diuron is resistant to hydrolysis at pH 5, 7 and 9 [3]. However, diuron loses its effectiveness quickly in exterior facade paints due to its chemical structure, meaning it provides only short-term protection. For this reason, the painted surface easily deteriorates because it has low activity. To solve this problem, alternative work has been carried out with encapsulated biocides that release biocides as they are exposed to external factors and provide longer dry film protection. It allows the development of durable formulations by holding a component within a polymer capsule that can be designed to respond to various release triggers (such as pH, temperature, pressure or dilution). The release of active substances from the capsule occurs through diffusion and the rates are a function of their water solubility. Depending on the activity in question, there will be different water solubility rates. This can be controlled by varying the level of the encapsulation process – sufficient material must be released to protect the film, but excessive release will cause washing from the surface. With this method, the release rate of biocides produced is slowed down in a controlled manner. By using encapsulated biocides in exterior facade products, the aim is to protect the environment and human health by reducing the amount of harmful substances leaching from the facade to the ground. Additionally, color change problems are reduced by increasing UV resistance. By reducing water solubility, the amounts of parasites mixing into soil and water sources are reduced and resistance to exterior facade conditions is increased. The appearance of encapsulated biocide is as shown in Figure 1. [caption id="attachment_127399" align="aligncenter"] Figure 1. Encapsulated Biocide Image [4][/caption]

3. Experimental

In this study, coating samples were produced using encapsulated biocides in exterior facade products. Three different biocide-containing exterior paint formulations were studied. The biocide packages used in the scope of this study are given in Table 1. The paint formulations tested with these biocide packages are given in Table 2. UV effects in exterior facade paints were evaluated using QUV and natural weathering tests. [caption id="attachment_127400" align="aligncenter"] Table 1. Biocide packages used in the scope of this study[/caption] [caption id="attachment_127401" align="aligncenter"] Table 2. Products tested within the scope of this study[/caption]

4. Results and Discussion

Paints were prepared using different biocide types and at different concentrations in the film. These paints were applied to panels in two coats. Panels were positioned facing south at a 45° angle. Samples were evaluated every 6 months according to ASTM D3274-09 (2013) standard test method for the determination of mold or fungal formation or surface deterioration of paint films due to soil and dirt accumulation. The results stated below are the evaluation results after 12 months of exterior facade weathering. Images of pure acrylic low PVC natural weathering samples are provided in Figure 2. It was observed that paint containing 1% by weight encapsulated (slow-release) biocide showed better performance than paint containing 0.7% by weight non-encapsulated standard biocide. Additionally, the paint film without biocide also appears good after weathering. [caption id="attachment_127402" align="aligncenter"] Figure 2. Pure Acrylic Low PVC Natural Weathering Samples (1A-Control; 1B-Standard; 1C-Encapsulated)[/caption] Images of low Tg pure acrylic natural weathering samples are provided in Figure 3. It was observed that the paint film without biocide appeared worse than paint with biocide. Additionally, it was observed that paint containing 1% by weight encapsulated (slow-release) biocide showed better performance than paint containing 0.7% by weight non-encapsulated standard biocide. [caption id="attachment_127403" align="aligncenter"] Figure 3. Low Tg Pure Acrylic Natural Weathering Samples (2A-Control; 2B-Standard; 2C-Encapsulated)[/caption] Styrene acrylic high PVC siloxane natural weathering images are provided in Figure 4. In-film biocide improved paint film appearance for the high PVC siloxane product. Additionally, it was observed that paint containing 1% by weight encapsulated (slow-release) biocide showed better performance than paint containing 0.7% by weight non-encapsulated standard biocide. [caption id="attachment_127404" align="aligncenter"] Figure 4. Styrene Acrylic High PVC Siloxane Natural Weathering Samples (3A-Control; 3B-Standard; 3C-Encapsulated)[/caption] 5. Conclusion The use of encapsulated biocides in paint recipes is beneficial for extending service life and reducing environmental impacts of coatings exposed to the outdoors. In this study, an improvement in ΔE was determined after accelerated 2000-hour QUV and 12 months of natural weathering. It was also observed that chalking that develops over time (depending on external factors) was improved with the use of slow-release encapsulated biocides.