Polyester is only one compound in a class of
petroleum-derived substances known as polymers. Thus, polyester (in common with
most polymers) begins its life in our time as crude oil. Crude oil is a
cocktail of components that can be separated by industrial distillation.
Polymers are made by chemically reacting a lot of little
molecules together to make one long molecule. The little molecules are called
monomers and the long molecules are called polymers.
Like this:
O + O + O + . . . makes OOOOOOOOOOOOOOOO
Depending on which polymer is required, different monomers
are chosen. Ethylene, the monomer for polyethylene, is obtained directly from
the distillation of crude oil; other monomers have to be synthesized from more
complex petroleum derivatives, and the path to these monomers can be several
steps long. The process for polyester is made by reacting ethylene glycol and
terephthalic acid.
The polymers themselves are theoretically quite unreactive and therefore not particularly harmful, but this is most certainly not true of
the monomers. Chemical companies usually make a big deal of how stable and nonreactive the polymers are, but that’s not what we should be interested in. We
need to ask, what about the monomers? How unreactive are they?
We need to ask these questions because a small proportion of
the monomer will never be converted into polymer. It just gets trapped in
between the polymer chains. Over time this unreacted monomer can escape, either
into the atmosphere if the initial monomers were volatile, or by dissolving
into water if the monomers were soluble. Because these monomers are so toxic,
it takes very small quantities to be harmful to humans, so it is important to
know about the monomers before you put the polymers next to your skin. Since
your skin is usually moist, any water-borne monomers will find an easy route
into your body.
Polyester is the terminal product in a chain of very
reactive and toxic precursors. Most are carcinogens; all are poisonous. And
even if none of these chemicals remain entrapped in the final polyester
structure (which they most likely do), the manufacturing process requires
workers and our environment to be exposed to some or all of the chemicals.
There is no doubt that the manufacture of polyester is an environmental and
public health burden that we would be better off without.
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