Slow Release Encapsulated Biocide

Turkchem 02 Sep 2021 44 5 dk okuma

TURKCHEM

1. Summary

Slow-release biocide technology is designed to delay the release of biocides over a specified period so that the designed concentrations from the dry film can be maintained within the system for an extended duration. The principle of slow-release (SR) technology is to keep biocidal actives effective for longer by resisting water leaching, elevated temperatures, high alkalinity, precipitation, and UV irradiation.

2. Introduction

Biofouling is defined as the adhesion and growth of organisms on surfaces in contact with water. Algae and fungal growth are observed on exterior paint films due to external factors over time. Various efforts have been made to combat and prevent biological contamination. The most common method to prevent biofouling is by adding biocides to paint formulations. Biocides (preservatives) are used in formulations to prevent the formation of these undesirable effects such as bacterial and fungal growth. The most revolutionary generation emerged around 1960 with the introduction of Tributyltin-based paints (TBT) due to their high antifouling effectiveness and versatility. However, they proved extremely harmful to the ecosystem due to slow degradation and toxicity persistence. As a result, the use of TBT in antifouling paints was banned in 2008 [1]. Another biocide in use is diuron in dry film protection systems. Diuron becomes active and is released from the system when it encounters external factors. Diuron (3-(3,4-dichlorophenyl)-1,1-dimethylurea), which is used as a dry film preservative in decorative paints, belongs to the family of halogeno-phenylurea compounds and represents an important herbicide class [2]. It is available in wettable powder and liquid suspension forms. Diuron is resistant to hydrolysis at pH 5, 7, and 9 [3]. However, diuron loses its effectiveness quickly in exterior paints due to its chemical structure, meaning it provides only short-term protection. As a result, painted surfaces degrade easily due to its low residual activity. Alternative studies are being conducted with encapsulated biocides that release biocides in response to external factors and provide longer-lasting dry film protection to address this issue. In encapsulation technology, the encapsulation process enables the development of durable formulations by housing a component within a polymer capsule that can be designed to respond to various release triggers (such as pH, temperature, pressure, or dilution) using normally incompatible components. The release of active substances through the capsule occurs via diffusion, and release rates are a function of water solubility. Different release rates occur depending on the specific active substance in question. This can be controlled by varying the level of encapsulation – enough active material must be released from the capsule to be available for film protection, but excessive release would cause leaching. The use of encapsulated biocides in exterior products aims to protect the environment and human health by reducing the amount of harmful substances leaching from facades to the ground. Additionally, colour-difference problems are reduced through improved UV resistance. By reducing water solubility, the risk of biocides flowing into groundwater or water sources through rain is also reduced, and outdoor weathering resistance is improved. An encapsulated biocide image can be seen in Figure 1. [caption id="attachment_127773" align="aligncenter"] Figure 1. Encapsulated Biocide Image [4][/caption]

3. Experimental

In this study, coating samples were produced using encapsulated biocide in exterior products. Three different biocide-containing exterior paint formulations were studied. The biocide packages used in this study are listed in Table 1. The tested paint formulations with these biocide packages are given in Table 2. UV effects were evaluated using QUV accelerated testing and natural weathering tests on exterior wall paints. [caption id="attachment_127774" align="aligncenter"] Table 1. The biocide packages used in this study.[/caption] [caption id="attachment_127775" align="aligncenter"] Table 2. Paint formulations tested in this study.[/caption]

4. Results and Discussion

Paints were prepared using different biocide types at different concentrations in the film. These paints were applied to panels in two coats. The panels were exposed facing south at a 45° angle. Samples were evaluated every 6 months in accordance with ASTM D3274-09 (2013), the standard test method for evaluating the degree of surface disfigurement of paint films by fungal or algal growth, or soil and dirt accumulation. The results presented below represent 12-month post-exposure evaluation findings. Visual results for pure acrylic low PVC natural weathering samples are shown in Figure 2. The paint formulation containing 1 wt% slow-release encapsulated biocide performed better than the paint containing 0.7 wt% non-encapsulated standard biocide. The paint film without in-film biocide also appeared well preserved. [caption id="attachment_127776" align="aligncenter"] Figure 2. Pure Acrylic Low PVC Natural Weathering Samples (1A-Control; 1B-Standard; 1C-Encapsulated)[/caption] Visual results for low Tg pure acrylic natural weathering samples are shown in Figure 3. The paint film without biocide showed worse performance than with biocide. Additionally, the 1 wt% slow-release encapsulated formulation performed better than the 0.7 wt% non-encapsulated biocide. [caption id="attachment_127777" align="aligncenter"] Figure 3. Low Tg Pure Acrylic Natural Weathering Samples (2A-Control; 2B-Standard; 2C-Encapsulated)[/caption] Visual results for styrene acrylic high PVC siloxane natural weathering samples are shown in Figure 4. In-film biocide improved paint film appearance in the high PVC siloxane product. Additionally, the paint containing 1.0 wt% slow-release biocide performed better than the 0.7 wt% standard non-encapsulated formulation. [caption id="attachment_127778" 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 formulations is beneficial for extending service life and reducing the environmental impact of coatings exposed to outdoor conditions. Improvements in ΔE were determined after 2000 hours of accelerated QUV testing and 12 months of natural weathering in this study. It was also observed that chalking, which occurs over time due to external factors, is reduced with the use of slow-release encapsulated biocides.