Polyester, Industry Sector TEXTILE

POLYESTER 

Polyester is one of the major synthetic fibres. Its name must be familiar to most shoppers; 100% polyester is seen often on the labels of ladies and men’s outerwear, while the blend polyester/cotton is very common in shirts and bed sheets. Another very common blend, polyester/wool is popular in dress fabrics and men’s suits. There are a number of reasons for this wide use of polyester. Most important are its properties of easy care and toughness, while its relatively low price obviously has a marked influence on its universal acceptance.

HISTORY

Polyester began as a group of polymers in W.H. Carothers' laboratory, the inventor of nylon fibres. Carothers was working for DuPont at the time when he discovered that alcohols and carboxyl acids could be successfully merged to create fibres.
Polyester was put on the back shelf once Carothers discovered nylon. In 1939, his work was resumed by a group of British scientists, J.R. Whinfield, J.T. Dickson, W.K. Birtwhistle, and C.G. Ritchie. In 1941, they successfully created the first polyester fibre called Terylene. In 1946, DuPont bought all legal rights from them and came up with another polyester fibre which they named Dacron.

In 1951 Polyester was first introduced to Americans ans was advertised as a miracle fibre that could be worn for 68 days without ironing and still would not wrinkle.

Ever since, the polyester market has been growing. Since it is an inexpensive and durable fibre, small textile mills emerged all over US. Polyester reached a constant growth until the 1970s when sales drastically fell down due to the negative public image that came up during the late 60s as a result of the infamous polyester double-knit fabric! Today, polyester is still widely regarded as a "cheap, uncomfortable" fibre, but even now this image is slowly beginning to change with the emergence of polyester luxury fibres such as polyester microfibre.

CHEMISTRY

Polyester is currently defined as “Long-chaim polymers chemically compose of at least 85% by weight of an ester and a di-hydric alcohol and a terephthalic acid” The name polyester refers to the linkage of several monomers(esters) within the fibre. Esters are former when alcohol reacts with carboxylic acid.

The polymer usually used for textile fibres is poly(ethylene terephthalate), or PET, which is formed by reacting ethylene glycol with either terephthalic acid or dimethyl terephthalate. Antimony oxide is usually added as a catalyst, and high vacuum is used to remove the water or methanol by-products. High temperature (>250^oC) is necessary to provide the energy for the reaction, and to keep the resultant polymer in a molten state.

PET molecules are regular and straight, so their inter-chain forces are strong — but not strong enough to prevent melting. Thus, PET is a “thermoplastic” material; that is, it can be melted and then solidified to form specific products. Since its melting point is high, it does not soften or melt at temperatures normally encountered in laundering or drying.

The ability of polyester fabrics, after heat setting, to retain a flat shape by shedding accidental creases but also to retain pleats and fashion creases set into the fabric is a major advantage.

Because of its high melting point polyester has good thermal stability. It softens at about 200C and will not easily burn. Unless supported in a fabric by another fibre it will melt away from heat rather than burst into flame. At a temperature of 150C it retains about 50% of its tenacity and has good long term resistance to heat in the absence of strong chemicals.

Polyester’s easy care properties are helped by a very low value of moisture absorption. Under normal atmospheric conditions it absorbs only about 0.4% water compared with 4% for nylon and 7% for cotton. Its strength is little affected when wet and it also has the added advantage of drying very quickly.

MANUFACTURING

The chemical process creates bulk polyester (PET) which is delivered to the melt spinning machines in the form of chopped up plastic pellets. Fibres are created by “extrusion” — forcing a thick, viscous liquid (about the consistency of cold honey) through the tiny holes of a device called a spinneret to form continuous filaments of semi-solid polymer.

Melt spun fibres can be extruded from the spinneret in different cross-sectional shapes (round, trilobal, pentagonal, octagonal, and others). Trilobal-shaped fibres reflect more light and give an attractive sparkle to textiles.

Pentagonal-shaped and hollow fibres, when used in carpet, show less soil and dirt. Octagonal-shaped fibres offer glitter-free effects. Hollow fibres trap air, creating insulation and provide characteristics equal to, or better than, down.

While extruded fibres are solidifying, or in some cases even after they have hardened, the filaments may be drawn to impart strength. Drawing pulls the molecular chains together and orients them along the fibre axis, creating a considerably stronger yarn.

FIBRE USERS

• Apparel: Every form of clothing
• Home Furnishings: Carpets, curtains, draperies, sheets and pillow cases, wall coverings, and upholstery
• Other Uses: hoses, power belting, ropes and nets, thread, tire cord, auto upholstery, sails,  and fibrefill for various products including pillows and furniture

World production figures illustrate the dominance of polyester as the current main synthetic fibre. In 1970 nylon had the highest production value of all synthetics, at a level of 40%, with polyester second at 34%. Since 1975, however, when nylon had fallen to 33% and polyester had passed it to a level of 45%, polyester continued to grow on a percentage basis so that in 1998 it had reached 58% of world synthetic fibre production, mainly at the expense of nylon, which had fallen to less than 15% (acrylics account for most of the remaining production).

Crazy Facts Corner

• Three tiny polyester cords placed in the floppy tissue near the back of the roof of the mouth have been proven to curb snoring .The Pillar Palatal Implant System – was approved by the US Food and Drug Administration in December 2002.
• Polyester from the grocery store to your closet? May sound like and odd idea but it is true! It takes about 26 recycled plastic bottles to make a polyester suite.
• Next time you put on a polyester shirt just remember that what you are really wearing is coal tar and anti-freeze.
• In 1981 the legendary combination of director John Waters and star Divine produced a film called “Polyester” premiered in Odorama which allowed the audience to smell the film!

Links:

http://www.teonline.com/fiber-history.html#polyester

http://www.e4s.org.uk/textilesonline/content/6library/report1/textile_fibres/polyester.htm

http://www.news-medical.net/?id=5262

http://www.fibersource.com/f-tutor/techpag.htm

Researched by Dynamic Dave