Prevention and control of microorganisms in polymer dispersions

The previous sections of this chapter have emphasised the susceptibility of synthetic polymer dispersions, the ease with which they can be spoiled by microorganisms and some of the effects of contamination both in the dispersions themselves and the formulated products in which they may be used. To prevent microbial spoilage and so retain their beneficial properties, it is essential that biodeterioration be prevented. The two ways of doing so are  

It is also very important to ensure that the biocide used is stable in the product for the period over which protection is required. The two main means of preventing infection are equally applicable to the end user of the dispersion, e.g. the paint, adhesive or ink manufacturer to ensure that they too get trouble-free performance from the product. 

Biocides are designed to protect uncontaminated products from occasional microbial contamination and, at typical use concentrations, most preservatives are not able to withstand continual repeated challenges of high levels of microorganisms. In such situations, the biocide may be consumed and the product will no longer be protected from subsequent microbial infection. 

Very few biocides have a high enough vapour pressure to diffuse into the headspace of mixing vessels, storage tanks and containers, giving some degree of protection to those areas of potential microbial infection foci. Formaldehyde is one of the few preservatives that can fulfil this requirement but, as will be seen later, the use 

Unlike formaldehyde, most other preservatives have very low vapour pressures, which result in little or no preservative present in the storage tank headspaces. As has already been mentioned, microorganisms introduced into the headspace of a storage tank can often proliferate in the condensation on the walls and ceiling of the tank and on the agitator shaft. When new material is added to the tank, all of the preservative can be consumed in eradicating these microorganisms. 

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