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Polyesters
are condensation polymers formed when an alcohol reacts with an acid as
shown in the diagram. The condensation product (green box) is water. For
the polyester to be formed the resulting ester must be bifunctional, which
requires that both the acid and the alcohol must be bifunctional.
The
lower diagram is for the commercially important polyester, PET, polyethylene
terphthalate, formed from the condensation reaction between ethylene glycol
and terephthalic acid. In fiber form this material is known by the Dacron
trademark. It is also used in the form of sheets with the Mylar trademark.
PET
has a density of about 1.3 Mg/m3,
a Young's modulus of 3 GPa, Yield stress of 60 MPa, a UTS of 60 MPa, and
an elongation to fracture of 30%. |
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