Originally, the vinyl materials were
defined to include any polymeric composition that incorporated ethylene (-CH=CH-) in its synthesis. Later
these came to include any of the double-bonded, alkene monomers like propylene, vinyl chloride, styrene, vinyl acetate,
acrylonitrile, butadiene, and others. These are reactive molecules and are the feedstocks for polyethylene, polypropylene,
styrofoam, and many other very useful plastics. Each of these materials are made via free-radical polymerizations
that require reaction initiators like persulfates, peroxides, or UV light that act to stimulate addition of an electron
to the alkene monomer. This destabilizes the double bond and renders the monomer into the activated,
free-radical form. This, in turn, activates the next monomer, allowing the original residue to be incorporated
as a single-bonded, stable residue. But now there is a free-radical dimer that will activate a third
monomer molecule and so on.
|Free radical polymerization of ethylene
These reactions are often highly exothermic and require built in controls to keep them on track
toward the desired product. There are invariably residuals of unreacted monomers left in the product, often along
with other additives like catalysts and initiators. These can be removed via extra purification steps, but often the
residuals are left in, at least to some extent, owing to the extra effort and costs of producing highly purified products.
In the biopolymer field, there have been major efforts and continue to be major efforts to enter the mega-markets
of plastics, foams, and fibers. Although at Aquero Company we have participated in projects like this from time-to-time,
the vinyl molecules and materials that interest us the most are the anionic and cationic polymers, having principally
acrylic acid and acrylamide as the building blocks.
Acrylic and Acrylamide Polymers
|Copolymer of acrylic and acrylamide residues
The polyacrylates, polyacrylamides, and the copolymers of acrylate and acrylamide
and related polymers are used in many applications that generally call for water-soluble additives. There are three very
large markets that are serviced by these polymers: detergent additives, water treatment chemicals, and superabsorbents.
Polyacrylate is an additive in detergents, with billions of pounds of annual use. It serves as a dispersant
and also a cleansing agent by helping to lift the soil and stains from surfaces such as cloth fibers or dishes and to keep
these substances dispersed in the water so that they are removed in the rinse.
Copolymers of acrylate and acrylamide are also commoditized
for use in water-treatment and sewage treatment, again with billions of pounds of annual use worldwide. In these applications,
the copolymers act as water-clarification agents that interact with unwanted solids and emulsified materials in
the water, cause them to flocculate into larger agglomerations that can be removed, restoring the water to a clear fluid.
There are other designations for these kinds of polymers; some comprise large markets such as thickening agents
and "viscosifiers," but water and
sewage treatment are the main ones.
The third of the commodity markets service by polyacrylates is the superabsorbent
market, in particular components of disposable baby diapers. In this application,
crosslinked networks of polyacrylates were formulated as small granules,
added in an amount of 20 to 30 grams in a typical diaper during its construction, and sold under the familiar brand names in the beginning like Pampers and Huggies, and
now including many other brands. The global market for this is also measured in the billions of pounds of annual use.