In-can preservation of water-based paints and coatings free of labeling

September 2021.
By Anna García, Manager of the Paints and Coatings Business Unit, and Eduard Broto.  

A change in the mindset is underway. When in 1992 at the Earth Summit in Rio de Janeiro the European Union promoted the idea of asserting the Globe as the base of the resources that are available for life, setting “sustainability” as a beacon of an efficient economy, started to emerge among industrialized countries and free market economies a consciousness about ecology, appealing to address environmental problems through the environmentalist practices and sustainable development.

Today, when we select a paint, besides expecting that it will accomplish with its function, it is probable that we will ask ourselves if we are going to harm the environment when making use of it and how will affect health of people around. Sustainability practices are gradually spreading through the market, changing the industrial practices, and crystallizing in new regulations. One of the challenges that arise during the process of formulating water-based paints and coatings, is the selection of the in-can preservative that enables to protect the coating in wet state from microbial spoilage while, at the same time, also meets the marketing requirements and regulatory at the suitable cost. In this context, the industry manufacturer of biocides for paints and coatings has the focus on developing in-can preservatives with low toxicity and that do not compromise safety of the people who enter in contact with such.

Protection of a water-based system from undesired microbial growth is determined by three factors. First, are the hygienic conditions of the entire product manufacturing, storage, distribution, and handling processes. Practices that minimize microbial intrusion into the system during the manufacturing process allow products to reach the market with less microorganism load and, therefore, with fewer possibilities for their properties to be altered. Also, the in-can preservative added will persist longer time because it will not be spent by reducing the initial contamination. The next factor that determines the preservation of the coating is the selection of a biocide that has the chemical composition suitable for the physicochemical characteristics for the system to protect. It is necessary to determine parameters of temperature and pH, and the characteristics of the manufacturing process and product storage, to be able to select a biocide compatible with the formulation and stable in the system, as well as to determine the right moment for its addition into the production. The third factor that determines the preservation of water-based paints and coatings is the optimal use dosage of the biocide. If it were the case that the amount of in-can preservative was not sufficient, even if the biocide chosen is the right one, it will not be capable to reduce the number of microorganisms that are normally present during the manufacturing process or product handling and contamination will end up proliferating until it will alter the coating properties and parameters.

No Hazard labels

The labeling of a final coating is determined by the classification of each raw material it is made of and their concentration. The in-can preservative is one among all the components of the coating formula and as such contributes with its hazard classification to the calculation of the final product labeling. With the objective to avoid the biocide increase the danger classification of the coating, one could be tempted to decrease its use dosage or use a milder preservative only. Both decisions would leave the coating unprotected, more over if they were taken without the guarantee of keeping optimal hygienic conditions throughout the life cycle of the products, and if the coating was not formulated with the parameters that could somehow compensate for the lack of biocide, which presents other challenges.

Biocides for paints work when they enter in contact with the microorganism. When the biocidal substances reach the cell membrane, an enzymatic disruption occurs, preventing metabolic function of respiration from taking place, what disturbs the homeostasis (the internal balance the cell needs for functioning) preventing the cell from its development or getting it to decomposition.

The food and cosmetic industries they have experience, since long time ago, considering the preservation system at the beginning of the development of new formulations and it is usual that, in addition to the preservative itself, they include other ingredients such as chelating and sequestering agents that makes a hostile environment for microorganisms to grow (“hurdle effect”), or incorporating surfactants and emulsifiers that help the action of preservatives (“enhancing effect”). Combining in the same formulation the appropriate preservative together with other components that boost its efficacy and create a barrier effect to microbial growth, is achieved the optimal level preservation using a minimum quantity of biocidal substances.

Although the manufacturing practices of decorative and industrial water-based paints and coatings are not comparable to the production of food or cosmetic products, it is feasible to include ingredients in the formulation of in-can preservatives that enhance its efficacy controlling microorganisms development. The new generation of biocides for water-based paints already include biocidal active substances in their composition together with efficacy boosters. This solution makes possible an optimal control microbiological contamination by using biocidal active substances of milder toxicity, and thus reduce associated undesired side effects such as skin sensitization, toxicity and hazard classification, which can be a problem when handling the biocides and also for the labelling of final coatings ready for the market.

Booster technology to enhance efficacy

Biocides for paints and coatings with enhanced efficacy, are active on the cell’s shell and solubilize parts of the membrane, making it easier for the biocidal substances to enter in contact with the cell and accelerating the enzyme disruption process that triggers the instability of the homeostasis and the consequent cellular deactivation. When homeostasis is broken, microorganisms enter a dormant phase, they lose the ability to reproduce and, at the appropriate use concentration of biocide, all cellular functions are disrupted, and the microorganisms die.

Efficacy tests (Table 1) carried out in parallel with traditional in-can preservatives and biocides with booster technology, show that the total amount of active substance required to control microbial growth is higher in samples using traditional preservatives compared to those samples protected with formulations containing efficacy boosters. The biocide enhancer compound reduces the surface tension of the cell membrane so that the action of the biocide is more efficient, and indeed does not interfere with the chemistry of the biocidal active substance. Thus, the use of biocides formulated with booster technology provides optimal protection adding lower amount of biocidal active substances into the coating and, at the same time, the booster itself allows the use of biocidal active ingredients with a milder environmental and health hazard classification. Therefore, the use of biocides with efficacy enhancer technology reduces the effects associated with the toxicity of active ingredients and does not worsen the hazard labeling of the final products to protect.

Biocides with booster technology

The different variations that are possible in the formulation of boosted efficacy biocides makes possible to obtain balanced combinations for protecting many different types of water-based paints and coatings. BIOPOL BI is an in-can preservative based on three biocidal active substances combined with an efficacy booster compound derived from glycerin and lauric acid, effective against Gram-positive and Gram-negative bacteria, fungi and yeasts. By its formulation it is the optimal biocide to protect many types of aqueous systems in wet state, without increasing the hazard classification of the final product and not adding labeling to it. The boosting surfactant that has been included in BIOPOL BI acts on the surface tension of the cell membrane of microorganisms and increases the antimicrobial efficacy of the biocidal actives themselves.

The use of biocides with built-in efficacy booster also enables the formulation of water-based paints and coatings with eco-label. The enhancing compound makes the biocide to be more efficient than traditional ones: they deliver optimal protection with fewer biocidal active substances and, moreover, these can be selected with a gentler toxicological classification. In this way the unwanted effects associated with the concentration of biocidal active substances in the final product are minimized.

During the paint formulation, additionally to the use of the booster technology, also can be included other ingredients that create a hurdle to the microorganisms development. In this direction, the inclusion of pH buffers, water scavengers, chelating agents, lithium salts, as well as maintaining up to date plant hygiene protocols and system disinfection, help to keep paints long term protected.

Conclusion

The use of biocides with booster technology will allow to protect water-based paints and coatings in wet state during the in-can storage phase. In the first place, the development of microorganisms in the system will be controlled, keeping the product protected and its characteristics unaltered. Second, they are neutral with respect to the coating’s hazard classification, allowing final products without labeling. Additionally, they are suitable for coatings with ecological certifications. While the amount of in-can preservative included in a formulation is small, the throughput of the work that is devoted to its selection provides excellent benefits.