Polyester fiber
Polyester
fiber occupies a leading position among all chemical fibers. The unique
properties of these fibers are due to the presence of aliphatic and aromatic
moieties in the macromolecular chain and regular molecular structure. Polyethylene
terephthalate (PET) is the main polyester used for fiber production, not only
because of its good end-use properties and economy of production but
especially because of the ease of physical and chemical modification, negative
suppression, and positive enhancement properties. Although PET and modified PET
fibers have been extensively investigated, there is still no fully described
phenomenon to predict mechanical behavior and tensile failure based on
structure or manufacturing parameters. One of the main reasons is the complex
nature of changes during fiber production and changes in structure during the
influence of pressure fields, temperature, time, and environmental factors.
Properties of polyester
The properties of polyester are as below-
A. Physical properties of polyester
i. Tenacity: Tenacity is the term that is used to
measure the strength of fiber/yarn. It is usually defined as the ultimate or
breaking force of the fiber (in gram-force units) divided by the linear density
(denier). The tenacity of Polyester is 5-7 gm/den.
ii. Elongation at break: Elongation at break is also known as
fracture strain. It is the ratio between the changed length after breaking the
test specimen and the initial length. It expresses the fiber's ability to
resist shape change without forming cracks. Elongation at the break of polyester is
15 – 30%.
iii. Elastic modulus: The modulus of elasticity, or Young's
modulus, is an essential property of polymers. It is the ratio of stress to
elastic strain and it depends on temperature and strain rate. The elastic modulus of
polyester is 90.
iv. Elasticity: Most of today's polyester fibers are
composed of terephthalic acid and ethylene glycol. Yarns and fabrics made from
this type of polyester are strong and very elastic.
v. Moisture Regain (MR %): It has only 0.4% moisture regain at 65%
RH which causes static electrical charges to easily build up.
vi. Specific Gravity: Specific Gravity is the ratio of the
density of a substance at a given temperature to the density of an equal volume
of water at the same temperature. The Specific Gravity of polyester is 1.38.
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vii. Melting point: Polyesters have a high melt temperature
(250–265°C).
viii. Volumetric Swelling: None
ix. Ability to protest
friction: The ability to
protest friction of polyester is excellent.
x. Color: White
xi. Light reflection
ability: It is very good.
xii. Lusture: The luster of polyester is bright.
B. Chemical properties of Polyester
i. Effect of Acids: Polyester has good resistance to acids in
cold conditions. But polyester degrades by H2SO4 at high temperatures.
ii. Effects of Basic: Polyester has good resistance to basic in
cold conditions but strong NaOH dissolves polyester in boiling.
iii. Effect of bleaching: Polyester does not affect by the bleaching processes like H2O2 or Chlorine bleach.
iv. Organic solvent: Organic solvent does not affect polyester.
v. Protection ability
against mildew: Good
vi. Protection ability
against insects: Good
vii. Affinity to Dyes: Polyester could be dyed with dispersed,
azoic color, and some pigments.
viii. Solvents of
polyester: Following
are the solvents of polyester:
a. Chlorinated hydrocarbon,
b. CF3COOH
c. Phenol (in hot condition)
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