Most polyesters are made from petroleum from which the constituent acids and alcohols are derived. The types of processes that manufacturers use vary, and little is known about specific manufacturing processes, because the companies want to keep them a secret in order to remain competitive. Here is a general description of how polyester is synthesized:
1) Polymerization
Condensation polymerization occurs when the acid and alcohol are reacted in a vacuum at high temperatures. The polymerized material is extruded in the form of a ribbon onto a casting trough or cooling wheel. After the ribbon hardens, it is cut into chips.
The chips are dried and then put into hopper resevoirs for melting. Polyester is a "melt spun" fiber, which means that it is heated, extruded through the spinnerets, and cools upon hitting the air. From there it is loosely wound around cylinders.
3)Drawing
The fibers are then hot stretched until they are about five times their original length in order to decrease their width. The fiber is then wound onto cones as filaments or is crimped and then is cut into staple lengths.
Variations on the Basic Polyester
Different fibers can be created by doing one or more of the following:
1) Adding a delusterant--Polyester is a naturally bright fiber, but can be made dull or semi-dull by the addition of a delusterant.
2) Changing the shape of the spinneret--The simplest and most common shape is a circle, but by changing ths shape of the spinneret, square, oval, and bean-shaped fibers can be formed. One can even create a hollow fiber. The different shapes affect the hand and strength of the fiber.
3) Drawing it out more--Drawing out the fiber to five times its orginal length is normal, but polyester can be stretched even further to create the now-popular microfiber. Drawing it out may also affect the strength, elasticity, and dyeability.
4) Adding dye--In its natural state, polyester is a slightly transparent off-white. Adding dye at the manufacturing stage can create brilliant colors like electric blue and atomic red.
5) Crimping--When the fiber is drawn out it is long and smooth. Crimping can give the fiber more texture and bulk and can increase its insulation properties, as well as its elasticity.
Making Yarns
After the fiber itself is created, it is made into a yarn. There are two types of polyester yarns: filament and spun. Filament yarns are made by taking the long polyester filaments, grouping them together, and then twisting them to make them thicker and stronger. A monofilament yarn has just one, long polyester fiber that is not twisted.
Spun yarns are produced in much the same way that a cotton or wool yarn is produced. The long filaments are fist cut into short pieces called staples (see photograph.) These are then combined together and spun to create a yarn made up of thousands of short filaments.
Blends
At this stage, polyester can also be combined with other fibers to produce a variety of effects.
Polyester and cotton is probaby the most famous and popular blend. The polyester helps the fabric retain its shape and resist stains and wrinkles. The cotton makes the fabric more absorbent and comfortable.
Polyester is combined with wool to give it wrinkle-resistance and shape retention in all kinds of weather. Since polyester is stronger than wool, it increases the durability and life of the fabric. The wool contributes good draping characteristics and elasticity.
Polyester and rayon is another popular blend fabric. Here again the polyester makes the fabric more resilient and durable, and helps it keep its shape. The rayon adds a different texture, has a good hand, is good for draping, and is absorbent.
Polyester and nylon produce a strong fabric because of nylon's strength and abrasion resistance and polyester's wrinkle-free properties. This combination produces a yarn that is strong, durable, stable, easy to launder, and resistant to mildew and insects. Problems with this blend, however, are that pilling may occur, and it does not have a very good hand. Furthermore, since neither nylon nor polyester is very absorbent, the fabric may feel wet and clammy in warm or humid weather.
Weaving
After the yarns are made, they are shipped out to textile mills to be woven into fabric. Polyester can be made into both woven and knitted fabrics (such as the infamous double-knit!)
Finishing Processes
Finally, after the fabric is made, one or more of the following finishing processes is often used to improve the quality of the fabric:
- Heat setting--creates a permanent shape
- Singeing--improves the hand, reduces pilling, and increases smoothness
- Anti-static finish--reduces static electricity
- Water and stain repellency--increases comfort and makes it easier to clean; also used for rainwear
- Resin finishes--increases ease of care
- Calendering--increases smoothness and reduces pilling
- Embossing--creates a design and/or luster
Trademarked Fabrics
Polyester is the generic name for the fiber which encompasses several fiber variations with different structures and shapes. E.I. du Pont de Nemours Co., Inc.(go to their homepage), Hoescht Celanese (go to their homepage), and BASF (go to their homepage) are three of the major producers of polyester; each has several trademarked names.
Go to a page that lists several different polyesters with the companies that produce them.
