This is a sample polyester fiber from a sample of polyester thread. The interference color is high order white as
can be seen by the multiple interference orders evident where the fibers cross at right angles.
Transmitted Crossed Linear Polarized Light
Polyester fiber is derived from terephthalic acid. It is formed into a fiber by extruding the heated polymer through a
spinneret. This results in the fiber taking the cross-section of the spinneret. Polyester fiber can be round or any other
desirable extruded shape.
Significance in the Environment:
This is a common clothing fiber.
Polyester fiber has a refractive index along its length of about 1.71 to 1.73 and perpendicular to its length of about 1.53
to 1.54. It has a birefringence of about 0.18 and a positive sign of elongation. It tends to exhibit a smooth, regular
surface along its length depending on its cross-section of the fiber. Extreme shapes, such as heptalobate types, can
result in an irregular appearance along the length as the fiber twists or bends.
DuPont Company Techinical Bulletin X-156: IDENTIFICATION OF FIBERS IN TEXTILE MATERIALS, December 1961.