Past, Present, and Future Options for Preservatives in Coatings
March 2017 www.coatingsworld.com Coatings World | 79
BIT blends with either zinc or sodium
pyrithione represent options to provide
robust in-can preservation in many applications without the requirement to declare an EU H208 or EU H317 phrase on
the packaging.
In our laboratory we conducted testing to evaluate three potential blend
formulations of this type. Formulation
#1 was prepared as a solution and
it contained 8% sodium pyrithione
(NaPT) and 2% benzisothiazolinone
(BIT). Formulation 2 was prepared as
a dispersion and it contained 5.5% zinc
pyrithione (ZnPT) and 5.5% benzisothiazolinone (BIT). Formulation #3
was prepared as a solution and it contained 4% sodium pyrithione (NaPT)
and 2% benzisothiazolinone (BIT).
Note that an in-can preservative with a
BIT concentration of 2% can be used
up to a dosage of 0.25% without causing the preserved product to attract
the EU H208 allergen phrase. Since
both formulation #1 and formulation
#3 contain 2% BIT, they both have
the same 0.25% dosage level trigger
for EU H208. Given their higher trigger threshold, these two formulations
were evaluated in our challenge tests
by preparing a ladder of samples with
increasing preservative levels, for example: 0.10%, 0.15%, 0.20%, 0.25%,
etc. In contrast, an in-can preservative
with a BIT concentration of 5.5% can
only be used up to a dosage of 0.09%
without causing the preserved product
to attract the EU H208 allergen phrase.
Therefore, given its higher BIT level,
formulation #2 was evaluated in our
challenge tests at only the single 0.09%
dosage level.
The three preservative formulations
were evaluated using an industry-standard
repeat insult antimicrobial challenge test.
Challenge testing was conducted in a variety of industrial substrates. In setting up
these tests, consideration was given to the
type of organism most likely to thrive in
the individual preserved product. Acidic-preserved products were challenged with
yeast and fungi, and alkaline-preserved
products were challenged with bacteria. For each type of inoculum, we used
a mixture of microbial strains, and the
individual strains in the mixture were
selected to represent the common spoilage organisms for that type of industrial
substrate. The intent in testing a range of
substrates was to determine if these three
formulations could consistently pass challenge tests at concentrations below their
hazard communication trigger concentrations. As shown in Tables 1-3, these three
formulations did in fact meet that criterion. Summary results for formulation #1
are shown in Table 1. Summary results
for formulation #2 are shown in Table 2.
Summary results for formulation #3 are
shown in Table 3.
Conclusion
Regulatory trends for preservatives are
significantly limiting the options for in-can protection of coatings. When it is desired to create a coating formulation that
has relevance for multiple regions, the
preservative selection challenge for the
formulator becomes particularly acute.
In some regions coatings formulations
that would otherwise be non-hazardous may attract hazard communication
phrases based on their in-can preservative content. This situation already poses
a considerable challenge for formulators
of water-based coatings and, as additional hazard communication requirements
come into force, the difficulty will only
increase. In this environment, preservative blends where the pyrithione active
agents are used as co-biocides can be welcome new preservation tools for the coating formulator’s toolbox. CW
Table 1. Summary results for Formulation #1, EU H208 trigger concentration 0.25%.
Table 2. Summary results for Formulation #2, EU H208 trigger concentration 0.09%.
Table 3. Summary results for Formulation #3, EU H208 trigger concentration 0.25%.
