Polyester

Polyester Fibers Prepared by: MUHAMMAD FIAZ 06-NTU-122 (C)

Definition The name "polyester" refers to the linkage of several monomers (esters) within the fiber. Esters are formed when alcohol reacts with a carboxylic acid.

Definition Polyester fiber is a " manufactured fiber in which the fiber forming substance is any long chain synthetic polymer composed at least 85% by weight of an ester of a dihydric alcohol (HOROH) and terephthalic acid (p-HOOC-C6H4COOH)“.

Introduction The first polyester fiber was Terylene. In 1946 second polyester fiber prepared was Dacron. In 1958 another polyester fiber called Kodel was developed by Eastman.

Introduction Today, polyester is still widely regarded as a "cheap, uncomfortable" fiber, but even now this image is slowly beginning to change with the emergence of polyester luxury fibers such as polyester micro fiber.

Process 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.

Process 1) Polymerization Polyethylene Teraphthalate (PET) is a condensation polymer and is industrially produced by either terephthalic acid or dimethyl terephthalate with ethylene glycol. A. Terephthalic Acid (PTA), produced directly from p-xylene with bromidecontrolled oxidation.

Process 1) Polymerization B. Dimethyl Terephthalate (DMT), made in the early stages by esterification of terephthalic acid. However, a different process involving two oxidation and esterification stages now accounts for most DMT. C. Ethylene Glycol (EG) initially generated as an intermediate product by oxidation of ethylene. Further ethylene glycol is obtained by reaction of ethylene oxide with water.

Process 2) Spinning 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 wound around cylinders.

Process 3) Drawing To produce uniform PET, the drawing process is carried out at temperature above the glass transition temperature (8090oC) with draw ratios (3:1-6:1)

PROCESS

Variations on the Basic Polyester Different fibers can be created by doing one or more of the following: Adding a delusterant (dulling agent) Polyester is a naturally bright fiber, but can be made dull or semi-dull by the addition of a TiO2. Changing the shape of the holes in the spinneret The simplest and most common shape is a circle, but by changing the 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.

Variations on the Basic Polyester Drawing out the fiber to five times its original length is normal, but polyester can be stretched even further. Drawing it out more than normal may also affect the strength, elasticity, and dye-ability. Adding dye stuffs In its natural state, polyester is a slightly transparent off-white. Adding dye stuffs at the manufacturing stage can create brilliant colors like electric blue and atomic red.

Variations on the Basic Polyester 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. Another word for this is texturizing.

STRUCTURAL COMPOSITION OF PET PET is attributed to the benzene rings in the polymer chain. The aromatic character leads to chain stiffness. Polyester fibers may be considered to be composed of crystalline, oriented semi crystalline and noncrystalline (amorphous) regions. Stabilization distances between atoms in neighboring molecules are usually van der Waals contact distances.

STRUCTURAL COMPOSITION OF PET The cohesion of PET chains is a result of van der Waals interactions, caused by induced dipole interaction and dispersion forces among the chains The unusually high melting point of PET (compared to aliphatic polyesters) is not the result of any unusual intermolecular forces, but is attributed to ester linkages.

STRUCTURAL COMPOSITION OF PET The interactive forces create inflexible tight packing among macromolecules, but the limited flexibility in the macromolecule is mainly due to the ethylene group. A number of basic structural models are required to represent the different states of the fiber: amorphous (no orientation) after extrusion, amorphous (no orientation) after cold drawing, crystalline orientation after thermal treatment and after hot drawing, stretching and annealing.

Crystallinity of Polyester Fiber Density Gradient

DSC Measurements

Fiber Type Base Fibers

Density (g/cc) Crystallinity (%)

Tg(oC)

Tm (oC)

∆H (Cal/g)

Crystallinity (%)

A

1.3803

41.22

154.3

251.3

17.19

51.38

B

1.3584

45.80

161.7

254.6

16.61

49.65

C

1.3809

41.73

152.9

255.8

15.29

45.73

D

1.3871

47.34

161.0

255.5

15.40

46.03

E

1.3825

43.71

175.9

257.4

16.41

49.05

Physical properties strong resistant to stretching and shrinking resistant to most chemicals quick drying crisp and resilient when wet or dry wrinkle resistant mildew resistant abrasion resistant able to retain heat-set pleats and creases easily washed

Mechanical Properties An increase of molecular weight further increases the tensile properties, modulus, and elongation. High tenacity filament and staple fiber curve (A and B) have very high breaking strengths and moduli, but relatively low elongations. Partially oriented yarn (POY) and spun filament yarns, exhibit low strength but very high elongation (curve E).

Mechanical Properties Typical stress strain curve for PET fibers. A-High tenacity filament B-High tenacity staple C-regular tenacity filament D-regular tenacity staple

Mechanical Properties When exposing PET fiber to repeated compression (for example, repeated bending), so-called kink bands start to form, finally resulting in breakage of the kink band into a crack. If relaxation of stress and strain in the oriented fiber is allowed to occur through shrinkage during fiber manufacture, then shrinkage at the textile processing stage is reduced and initial modulus is lowered.

Mechanical Properties It recovers well from stretch, compression, bending, and shear because of its relatively high initial modulus Reducing the molecular weight, which affects the abrasion resistance; flex life, and breaking strength, results in a decrease in pilling tendency of PET fiber. The tighter the packing of molecular chains, the stiffer and more mechanically resistant the fiber is.

Physical Properties of Polyester Fibers Filament yarn

Staple and tow

Property

Regular tenacitya

High tenacityb

Regular tenacityc

High tenacityd

breaking tenacity,e N/tex

0.35-0.5

0.62-0.85

0.35-0.47

0.48-0.61

breaking elongation

24-50

10-20

35-60

17-40

elastic recovery at 88-93 5% elongation, %

90

75-85

75-85

initial modulus, N/texf

6.6-8.8

10.2-10.6

2.2-3.5

4.0-4.9

specific gravity

1.38

1.39

1.38

1.38

Moisture regian, %

0.4

0.4

0.4

0.4

Melting temperature, oC

258-263

258-263

258-263

258-263

Mechanical Properties Crimp stability of the fiber can be improved with an increase in heating temperature crimp compression of the fiber can be decreased by increasing draw ratio when the fiber is produced.

CHEMICAL PROPERTIES Polyester fibers have good resistance to weak mineral acids, even at boiling temperature, and to most strong acids at room temperature. Hydrolysis is highly dependent on temperature. Thus conventional PET fibers soaked in water at 70oC for several weeks do not show a measurable loss in strength, but after one week at 100oC, the strength is reduced by approximately 20%.

CHEMICAL PROPERTIES Polyesters are highly sensitive to bases such as sodium hydroxide and methylamine, which serve as catalysts in the hydrolysis reaction. alkaline attack is sometimes used to modify the fabric aesthetics during the finishing process. The porous structures produced on the fiber surface by this technique contribute to higher wettability and better wear properties

CHEMICAL PROPERTIES Polyester displays excellent resistance to oxidizing agents, such as conventional textile bleaches, and is resistant to cleaning solvents and surfactants. Concentrated solutions of benzoic acid and ophenylphenol have a swelling effect. PET is both hydrophobic and oleophilic. The hydrophobic nature imparts water repellency and rapid drying. But because of the oleophilic property, removal of oil stains is difficult.

CHEMICAL PROPERTIES polyester fibers have a low moisture regain of around 0.4%, which contributes to good electrical insulating properties even at high temperatures. The tensile properties of the wet fiber are similar to those of dry fiber. The low moisture content, however, can lead to static problems that affect fabric processing and soiling.

OPTICAL PROPERTIES PET has optical characteristics of many thermoplastics, providing bright, shiny effects desirable for some end uses, such as silk-like apparel. Recently developed polyester microfiber with a linear density of less than 1.0 denier per filament (dpf), achieves the feel and luster of natural silk.

DYEING PROPERTIES Because of its rigid structure, welldeveloped crystallinity and lack of reactive dyesites, PET absorbs very little dye in conventional dye systems. Polyester fibers are therefore dyed almost exclusively with disperse dyes.

DYEING PROPERTIES Third monomer Polymerizing a third monomer, such as dimethyl ester, has successfully produced a cationic dyeable polyester fiber into the macro-molecular chain. The third monomer make the structure of cationic dyeable polyester less compact than that of normal PET fibers. The disturbed structure is good for the penetration of dyes into the fiber. The disadvantage of adding a third monomer is the decrease of the tensile strength.

DYEING PROPERTIES Low temperature (40C) process This method employs a disperse dye in a microemulsion of a small proportion of alkyl halogen and phosphoglyceride. The main advantage of this method is low temperature processing. The environmental problem that is produced by using toxic carriers.

DYEING PROPERTIES Plasma technique Spun bond PET nonwoven webs have been treated by (SO2+O2) plasma and (N2+H2+He) plasma. Results show that spun bond PET nonwovens web can be colored by conventional water-soluble acid dyes. Plasma techniques open new avenues for coloring PET fabrics and are sure to be more evident in the coloring of polyester fibers in the future.

Other Properties Polyester fibers display good resistance to sunlight but long-term degradation appears to be initiated by ultraviolet radiation. Although PET is flammable, the fabric usually melts and drops away instead of spreading the flame. Polyester has good oxidative and thermal resistance.

Other Properties the resistance of polyester fibers to mildew, aging and abrasion is excellent. Molds, mildew and fungus may grow on some of the lubricants or finishes, but do not attack the fiber.

Applications Because of their many desirable qualities, polyester fibers and fabrics have many uses. 1)

Polyester is often used in outerwear because of its high tenacity and durability. It is a strong fiber and consequently can withstand strong and repetitive movements.

2)

Its hydrophobic property makes it ideal for garments and jackets that are to be used in wet or damp environments - coating the fabric with a water-resistant finish intensifies this effect.

Applications 3) Since polyester can be molded into almost any shape, certain insulating properties can be built-in to the fiber. One method is to create hollow fibers. 4)

One method is to create hollow fibers, This process traps air inside the fiber which is then heated by the body. The warm air stays inside and helps warm the body in cool weather.

Applications 5) A second method is to use crimped polyester in a fiberfill product. The crimp helps to keep in warm air. 6) Polyester is used in pants, shirts, suits, and bed sheets either by itself or as a blend, because of its wrinkle-resistant property and its ability to retain its shape. Since these garments are frequently worn and washed, its stain-resistance and durability are also desirable.

Applications 7) Polyester also has industrial uses as well, such as carpets, filters, synthetic artery replacements, ropes, and films.

Applications Apparel For every form of clothing Home furnishing carpets, curtains, draperies, sheets and pillow cases, wall coverings and upholstery Other fiberfill for various products; automobile upholstery, fire hose, power belting, ropes and nets, sewing thread, tire cord, sails, vbelts, floppy disk liners

Grades POY yarns flat yarn textured yarn airtextured yarn high tenacity monofilament staple fibers cut flock tow spun yarns

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 single polyester filaments, grouping them together and then twisting or air-entangling them to make them workable. A monofilament yarn has just one, single polyester fiber that is usually not twisted

Making Yarns Spun yarns are produced in much the same way as a cotton or wool yarn is produced. The long filaments are fist cut into short pieces called staple. 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 probably 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.

Blends 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 more absorbent.

Blends 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 nice 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

Finishing Processes Water and stain repellency--increases comfort and makes it easier to clean; also used for rainwear Resin finishes--increases ease of care Calendaring--increases smoothness and reduces pilling Embossing--creates a design and/or luster