At every stage of their service lives, paints and coatings are susceptible to contamination and degradation by a variety of microorganisms. Further, the presence of water makes these paints very susceptible to microbial attack - both in the wet state and as dry film.
● Bacteria can spoil emulsions and paint in the storage container
● After paint has been applied to a substrate and dried, it becomes vulnerable to attack by the fungi that cause mildew
To protect against the microorganisms that can cause problems, paint manufacturers must customarily use Biocides Antimicrobial Agents.
What is biocide? Antimicrobial additives (also called Biocides) are used in formulations to keep bacteria from spoiling paint during storage, or to keep fungi, algae and other micro-organisms from growing on the applied paint.
What is biocide used for? The two main applications of biocides are:
● In-can protection to prevent spoilage of the wet-state product during storage and transportation
● Dry-film protection to ensure long-term performance of the coating
Microbial Growth in Coatings - Why and How?
Microbial growth in the wet state is usually manifested by a loss of product functionality and may include gas formation, offensive odors and changes in pH, viscosity and color. Microbial contaminants can be introduced:● With water (process water, wash water),
● With raw materials (latex, fillers, pigments, etc.) and
● By poor plant hygiene
Bacteria are the most common spoilage organisms, but fungi and yeasts are sometimes responsible for product deterioration. Spoilage of the waterborne products, which may go unnoticed until the product reaches the consumer, can result in significant economic loss.
Upon drying, both water- and solventborne coatings are susceptible to colonization by fungi and/or algae.
● Fungi can penetrate coatings, resulting in cracking, blistering and loss of adhesion, leading to decay or corrosion of the underlying substrate.
● Algae colonies, which seem to grow more rapidly on porous substrates such as stucco, cement and bricks, can occlude water.
The freezing and thawing of this entrapped water may induce cracking or increase the permeation properties of the coating, leading to failure
The presence of water may also encourage colonization by other microorganisms, which in turn may cause bio-deterioration.
The type of microorganism that can colonize the coating will depend on several factors, including:
● Moisture content of the surface - Surface moisture content is affected by climatic conditions (amount of rainfall, dew, humidity, temperature and time of the year) as well as by local conditions (surfaces sheltered from winds and shaded areas will contain higher moisture content)
● Presence of nutrients - Nutrient sources include constituents of the coating itself (such as polymers, thickeners, etc.), partially biodegraded substances produced by other microorganisms, or simply material deposited on the coating from the atmosphere, such as dirt
● Substrate - The composition of the substrate may affect the pH of the surface, making it suitable for microbe colonization. For example, fungi favor more acidic conditions, such as those provided by wood. Some species of wood are more susceptible to colonization by fungi than others (e.g., pine is more susceptible than cedar). Algae, on the other hand, favor alkaline conditions, such as those provided by masonry.
● Coating composition - the coating composition and properties (polymer type, water repellency, porosity, hardness, chalking and roughness) determine the type of microbial community that will colonize the coating
The use of biocides is recommended to maintain the microbiological quality of a product and to protect it against contamination
There exists a criterion for selecting antimicrobial additives depending on the coating type and end-use application of your product. To learn the same, it is important to know about the types of antimicrobial additives available in the market, their chemistries and purpose of addition.
