Need for Preservatives / Biocides
Microorganisms can breakdown adhesive or sealant products before their service life is complete or, in some cases, even before their service life has even begun. These microorganisms include bacteria, fungi, yeast, and mold.
Microorganisms exist everywhere especially where water and appropriate nutrients are available for their growth and survival
. They thrive primarily at 20°-30°C and high humidity
Given their relatively simple needs for life, microorganisms can attach and grow in many adhesive and sealant products that contain water or naturally-based ingredients. Good source of food include:
- Animal fats, and
- Vegetable oils
- Polymers that contain aliphatic hydroxyl and ester groups
- Polyester-based urethanes, and
Synthetic polymer water emulsions
that are especially susceptible to microbial contamination
include polyvinyl acetate, polyvinyl alcohol, and ethylene / vinyl acetate.
Even RTV silicone sealants
, that do not inherently support microbe growth, are subject to microbial degradation
. External chemicals, commonly found near construction sealants, can migrate into the sealant and these chemicals may support microbial growth.
The base polymer in an adhesive formulation is not the only component that the formulator needs to worry about when fighting microbial growth. Formulation additives are also often an excellent nutrition source and become a primary focus of biological attack. These include:
Microbial contamination can manifest itself in a number of ways
- Ester plasticizers
- Cellulosic rheology modifiers, and
- Epoxy ester stabilizers among others
. There are primarily two stages
in which microbial infection can become dominant:
- When the adhesive or sealant is in liquid form. The microbes can feed off the moist environment and nutrients supplied by additives and raw materials.
- After the adhesive or sealant is applied and cured. Microbial attack can occur on the finished surfaces of the polymer film.
Microbial Growth in Polymer Emulsions
Microbial growth on polymer emulsions could lead to costly customer quality issues and down time for factory decontamination. Bacterial growth can also contribute to a decrease in indoor air quality and lead to human health problems. The effects of microbial growth in polymer emulsions are listed in the table below.