Specialty Fabrics Review February 2020 - 55

MICROBIAL CONTAMINATION ON
FLEXIBLE VINYL SURFACES
Fungi and bacteria feed on phthalate esterbased plasticizers in flexible vinyl, thus
accelerating the plasticizer migration as it
passes from a higher concentration within
the vinyl to a lower concentration on the
surface. This biological activity on the surface
of flexible vinyl causes both physical and
cosmetic damage.
Physical damage results when the loss
of plasticizers changes the flexibility of the
vinyl to a brittle surface prone to cracking.
Cosmetic damage occurs when bacteria use
their secondary metabolism to produce
chemicals designed to defend themselves
against other organisms. Those chemicals
diffuse into the flexible vinyl product, causing
stains and unpleasant odors.
Pink stain bacteria (Streptoverticillium
reticulum) is a perfect example and widely
prevalent. It produces a secondary metabolite
called prodigiosin, a red liquid that diffuses
into flexible vinyl, creating pink stains that
cannot be cleaned. Pink staining is a typical
problem on boat seats; outdoor fabrics such as
pillows, umbrellas and sun shades; and vinyl
flooring used around pool and boat decks.
There is no conventional way to remove the
stain because the visible pink dye created by
the bacteria's metabolic processes is absorbed
into the vinyl substrate and is no longer on the
surface. It essentially diffuses into the vinyl
in the same way the plasticizer migrates out
of the vinyl. Prevention of pink staining can
only be accomplished with barrier coatings,
biocides or both to prevent the bacteria from
blooming on the vinyl, which is why original
equipment manufacturers (OEMs) are seeking
out antimicrobial solutions.
TOPCOAT BARRIERS
Some vinyl manufacturers incorporate biocides
and fungicides into the plastisol formulation
during the compounding process, before it's
cast on paper, extruded or calendared. This
offers great initial protection against microbes.
Like plasticizers, these additives are prone
to migration, ultimately losing their ability
to inhibit microbe growth within a year or
two of outdoor exposure, depending on
conditions. AM topcoats provide an extra layer
of protection against the elements and block

this diffusion process. Having antimicrobial
protection in a concentrated finish on the
surface is critical, as this is the primary point of
contact for bacteria, fungi, UV rays, humidity
and moisture.
AM agents work by either inhibiting the
organic cell from reproducing or reacting with
the organic cell, essentially destroying it. More
specifically, they damage cell walls, extracting
the DNA, which upsets reproduction and
kills the cell. Some AM additives also work
by damaging the cell's flagella and pili, which
interferes with the organism's ability to move
and attach itself to a host surface.
Because AM additives can be expensive
to incorporate into the vinyl formulation
at an effective concentration, AM topcoats
have become an alternative solution to the
problem. For materials where bacterial and
fungal growth is a significant nuisance,
manufacturers often incorporate both AM
additives and topcoats for the ultimate
protection and life cycle. As mentioned,
finishes offer a highly concentrated and
thin bacteria-fighting layer directly on the
surface of the vinyl or fabric. The surface
layer concentration is important because it
is the area subjected to direct skin contact,
such as human hands. Think about the
contamination on the surface of medical
bedding and mass transit seating.
DETERMINING THE RIGHT
ANTIMICROBIAL TOPCOAT
When researching the appropriate AM
topcoat for a flexible vinyl product, OEMs
should identify the following:
* Broad spectrum activity. An effective
concentration of the antimicrobial is
essential, but it is also important to identify
which types of microbes the coating must
withstand. For flexible vinyl and fabrics, a
broad spectrum of protection is essential.
The coating manufacturer should conduct
a variety of ASTM tests on the specific
substrate with prototype coatings containing
a range of AM concentrations, then provide
data regarding microbe growth and the zone
of inhibition.
* Service life. In studying the data from
ASTM test standards and OEM specified
tests, positive initial readings are ideal,
but learning how long the antimicrobial

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