A-level Applied Science/Colour Chemistry/Fibres/Synthetics

Nylon is a form of synthetic fibre. See under Polyamides and protein fibres.

Cellulose fibres such as cellulose acetate are chemically-modified. See under Cellulose fibres.

Acrylic

Acrylic fibres are synthetic fibres made from a polymer with a weight average molecular weight of ~100,000. To be called acrylic in the U.S., the polymer must contain at least 85% acrylonitrile monomer. Typical comonomers are vinyl acetate or methyl acrylate.

Methyl acrylate (methyl propenoate).

Acrylonitrile (cyanoethylene, cyanoethene, vinyl cyanide or 2-propenenitrile).

Vinyl acetate (1-acetoxyethylene, acetic acid ethenyl ester or ethenyl ethanoate).

Polyacrylonitrile.

Properties

Acrylic fibre don't dye very well but have excellent colourfastness. Because acrylic fibres form anions in solution, they are very suitable for use with basic dyes. It is resilient, retains its shape, and resists shrinkage and wrinkles. It is quite varied in form and sometimes has an appearance similar to wool or cotton.

The disadvantages of acrylic is that it tends to fuzz (or pill) easily and that it does not insulate the wearer as well as cashmere. Many products like pashmina or cashmina use this material to create the illusion and deception of cashmere to the consumer.

Acrylic is resistant to moths, oils, and chemicals, and is very resistant to deterioration from sunlight exposure. However, static and pilling can be a problem.

Aesthetic Qualities

Acrylic is lightweight, soft, and warm, with a wool-like feel.

Uses

End uses include sweaters, hand-knitting yarns, rugs, awnings, boat covers, and as a precursor for carbon fibre. Production of acrylic fibres is centered in the Far East, declining in Europe and now shut down (except for precursor) in the U.S.

Acrylic has recently been used in clothing as a cheaper alternative to cashmere, due to the similar feeling of the materials.

Synthesis

The polymer is formed by free radical polymerisation. The fibre is produced by dissolving the polymer in a solvent, metering it through a multi-hole spinnerette and coagulating the resultant filaments in an aqueous solution of the same solvent. Washing, stretching, drying and crimping complete the processing.

Polyester

Scanning electron microscope picture of a bend in a high surface area polyester fibre.

Polyester is a category of polymers, or, more specifically condensation polymers, which contain the ester functional group in their main chain. Although polyesters do exist in nature, polyester generally refers to the large family of synthetic polyesters (plastics) which includes polycarbonate and above all polyethylene terephthalate (Terylene, Dacron, PET or PETE). PET is one of the most important thermoplastic polyesters. Extreme care with fire around polyester should be exercised, as polyester is extremely flammable and flames can leap from a match to polyester at a range of at least three inches.

Polyethylene terephthalate (PET or PETE).

History of polyester

Terylene was the first polyester fibre and was produced in England. It was brought to the U.S. in 1951 by Dupont under the trade name Dacron.

Properties

Polyester has excellent durability, abrasion resistance, tenacity and high elongation. The fibre also has high appearance retention, dimensional stability, elastic recovery and excellent resiliency. It remains very strong when it is wet.

Aesthetic Qualities

The fibre blends well with other fibres and maintains a natural look. Polyester can be engineered to be very similar in appearance and feel to wool, linen and silk.

Polyester clothing is generally considered to have a "less natural" feeling to it compared to natural fibres. The low absorbency causes the fabric to be very uncomfortable. This can be improved through blending it with other fibres. Polyester fibres are often spun together with fibres of cotton, producing a cloth (sometimes called 'polycotton') with some of the better properties of each.

Static can be controlled through additives and changes in the compound.

Environmental impact

The impact is very similar to that of nylon. Polyester is extensively recycled, and less pollution is created when the recycled fibres are reengineered than when new ones are created.

Uses

Polyester is the most widely used manufactured fibre in the U.S. Woven fabrics are used for apparel and home furnishings. These include bed sheets, bedspreads, curtains and draperies. Polyester used in knitted fabrics include shirts and blouses. Fiberfill is also used to stuff pillows, comforters and cushion padding.

The first synthetic polyester, glycerine phthalate, was used in the First World War for waterproofing. Natural polyesters have been known since around 1830.

• Fibres (and microfibres) for fabric
• Bottles
• Films such as biaxially oriented PET film, often aluminised
• Photographic film (after cellulose triacetate, polyester is the most important substrate film base)
• A common matrix for glass-reinforced plastic (commonly called "fibreglass") and other composite materials.
• Liquid crystal displays
• Holograms
• Filters
• Dielectric film for capacitors and film insulation for wire, and insulating tapes
• Carpet

Liquid crystalline polyesters are among the first industrially used liquid crystalline polymers. In general they have extremely good mechanical properties and are extremely heat resistant. For that reason, they can be used as an abradable seal in jet engines.

Synthesis

Synthesis of polyesters is generally achieved by a polycondensation reaction.

Azeotrope esterification

In this classical method an alcohol and a carboxylic acid react to form a carboxylic ester. To assemble a polymer, the water formed by the reaction must be continually removed by azeotrope distillation.

Alcoholic transesterification

O \\ C - OCH3 + OH[Oligomer2] / [Oligomer1]	$\leftrightarrow$	O \\ C – O[Oligomer2] + CH3OH / [Oligomer1]
(ester-terminated oligomer + alcohol-terminated oligomer)		(larger oligomer + methanol)

Acylation (HCl method)

The acid begins as an acid chloride, and thus the polycondensation proceeds with emission of hydrochloric acid (HCl) instead of water.

Silyl method

In this variant of the HCl method, the carboxylic acid chloride is converted with the trimethyl silyl ether of the alcohol component; trimethyl silyl chloride is produced.

Acetate method (esterification)

Silyl acetate method

Ring-opening polymerisation

Aliphatic polyesters can be assembled from lactones under very mild conditions.

References

• Kadolph, S & Langford, A (1998) Textiles, 8th Edition.
• Aspland, JR (1993) Chapter 12: The application of basic dye cations to anionic fibers: Dyeing acrylic and other fibers with basic dyes. Textile Chemist and Colorist Vol 25, No 6 June 1993 21-26.