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Nylon
Density	1.15 g/cm3
Electrical conductivity (σ)	10−12 S/m
Thermal conductivity	0.25 W/(m·K)
Melting point	463–624 K 190–350 °C 374–663 °F

Nylon is a generic designation for a family of synthetic polymers known generically as polyamides, first produced on February 28, 1935, by Wallace Carothers at DuPont's research facility at the DuPont Experimental Station. Nylon is one of the most commonly used polymers.

Overview[link]

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Wallace Carothers

Nylon is a thermoplastic, silky material, first used commercially in a nylon-bristled toothbrush (1938), followed more famously by women's stockings ("nylons"; 1940). Nylon is made of repeating units linked by amide bonds and is frequently referred to as polyamide (PA). Nylon was the first commercially successful synthetic polymer. There are two common methods of making nylon for fiber applications. In one approach, molecules with an acid (-COOH) group on each end are reacted with molecules containing amine (-NH₂) groups on each end. The resulting nylon is named on the basis of the number of carbon atoms separating the two acid groups and the two amines. These are formed into monomers of intermediate molecular weight, which are then reacted to form long polymer chains.

Nylon was intended to be a synthetic replacement for silk and substituted for it in many different products after silk became scarce during World War II. It replaced silk in military applications such as parachutes and flak vests, and was used in many types of vehicle tires.

Nylon fibers are used in many applications, including fabrics, bridal veils, carpets, musical strings, and rope.

Solid nylon is used for mechanical parts such as machine screws, gears and other low- to medium-stress components previously cast in metal. Engineering-grade nylon is processed by extrusion, casting, and injection molding. Solid nylon is used in hair combs. Type 6,6 Nylon 101 is the most common commercial grade of nylon, and Nylon 6 is the most common commercial grade of molded nylon. For use in tools such as the spudger, a nylon is available in glass-filled variants which increase structural and impact strength and rigidity, and molybdenum sulfide-filled variants which increase lubricity.

Aramids are another type of polyamide with quite different chain structures which include aromatic groups in the main chain. Such polymers make excellent ballistic fibers.

Chemistry[link]

Nylons are condensation copolymers formed by reacting equal parts of a diamine and a dicarboxylic acid, so that amides are formed at both ends of each monomer in a process analogous to polypeptide biopolymers. Chemical elements included are carbon, hydrogen, nitrogen, and oxygen. The numerical suffix specifies the numbers of carbons donated by the monomers; the diamine first and the diacid second. The most common variant is nylon 6-6 which refers to the fact that the diamine (hexamethylene diamine, IUPAC name: hexane-1,6-diamine) and the diacid (adipic acid, IUPAC name: hexanedioic acid) each donate 6 carbons to the polymer chain. As with other regular copolymers like polyesters and polyurethanes, the "repeating unit" consists of one of each monomer, so that they alternate in the chain. Since each monomer in this copolymer has the same reactive group on both ends, the direction of the amide bond reverses between each monomer, unlike natural polyamide proteins which have overall directionality: C terminal → N terminal. In the laboratory, nylon 6-6 can also be made using adipoyl chloride instead of adipic.

It is difficult to get the proportions exactly correct, and deviations can lead to chain termination at molecular weights less than a desirable 10,000 daltons (u). To overcome this problem, a crystalline, solid "nylon salt" can be formed at room temperature, using an exact 1:1 ratio of the acid and the base to neutralize each other. Heated to 285 °C (545 °F), the salt reacts to form nylon polymer. Above 20,000 daltons, it is impossible to spin the chains into yarn, so to combat this, some acetic acid is added to react with a free amine end group during polymer elongation to limit the molecular weight. In practice, and especially for 6,6, the monomers are often combined in a water solution. The water used to make the solution is evaporated under controlled conditions, and the increasing concentration of "salt" is polymerized to the final molecular weight.

DuPont patented^[1] nylon 6,6, so in order to compete, other companies (particularly the German BASF) developed the homopolymer nylon 6, or polycaprolactam — not a condensation polymer, but formed by a ring-opening polymerization (alternatively made by polymerizing aminocaproic acid). The peptide bond within the caprolactam is broken with the exposed active groups on each side being incorporated into two new bonds as the monomer becomes part of the polymer backbone. In this case, all amide bonds lie in the same direction, but the properties of nylon 6 are sometimes indistinguishable from those of nylon 6,6 — except for melt temperature and some fiber properties in products like carpets and textiles. There is also nylon 9.

The 428 °F (220 °C) melting point of nylon 6 is lower than the 509 °F (265 °C) melting point of nylon 6,6.^[2]

Nylon 5,10, made from pentamethylene diamine and sebacic acid, was studied by Carothers even before nylon 6,6 and has superior properties, but is more expensive to make. In keeping with this naming convention, "nylon 6,12" (N-6,12) or "PA-6,12" is a copolymer of a 6C diamine and a 12C diacid. Similarly for N-5,10 N-6,11; N-10,12, etc. Other nylons include copolymerized dicarboxylic acid/diamine products that are not based upon the monomers listed above. For example, some aromatic nylons are polymerized with the addition of diacids like terephthalic acid (→ Kevlar, Twaron) or isophthalic acid (→ Nomex), more commonly associated with polyesters. There are copolymers of N-6,6/N6; copolymers of N-6,6/N-6/N-12; and others. Because of the way polyamides are formed, nylon would seem to be limited to unbranched, straight chains. But "star" branched nylon can be produced by the condensation of dicarboxylic acids with polyamines having three or more amino groups.

The general reaction is:

A molecule of water is given off and the nylon is formed. Its properties are determined by the R and R' groups in the monomers. In nylon 6,6, R = 4C and R' = 6C alkanes, but one also has to include the two carboxyl carbons in the diacid to get the number it donates to the chain. In Kevlar, both R and R' are benzene rings.

Concepts of nylon production[link]

The first approach: combining molecules with an acid (COOH) group on each end are reacted with two chemicals that contain amine (NH₂) groups on each end. This process creates nylon 6,6, made of hexamethylene diamine with six carbon atoms and adipic acid.

The second approach: a compound has an acid at one end and an amine at the other and is polymerized to form a chain with repeating units of (-NH-[CH₂]_n-CO-)_x. In other words, nylon 6 is made from a single six-carbon substance called caprolactam. In this equation, if n = 5, then nylon 6 is the assigned name (may also be referred to as polymer).

The characteristic features of nylon 6,6 include:

• Pleats and creases can be heat-set at higher temperatures
• More compact molecular structure
• Better weathering properties; better sunlight resistance
• Softer "Hand"
• Higher melting point (256 °C/492.8 °F)
• Superior colorfastness
• Excellent abrasion resistance

On the other hand, nylon 6 is easy to dye, more readily fades; it has a higher impact resistance, a more rapid moisture absorption, greater elasticity and elastic recovery.

Characteristics[link]

• Variation of luster: nylon has the ability to be very lustrous, semilustrous or dull.
• Durability: its high tenacity fibers are used for seatbelts, tire cords, ballistic cloth and other uses.
• High elongation
• Excellent abrasion resistance
• Highly resilient (nylon fabrics are heat-set)
• Paved the way for easy-care garments
• High resistance to insects, fungi, animals, as well as molds, mildew, rot and many chemicals
• Used in carpets and nylon stockings
• Melts instead of burning
• Used in many military applications
• Good specific strength
• Transparent to infrared light (−12dB)^[3]

Bulk properties[link]

Above their melting temperatures, T_m, thermoplastics like nylon are amorphous solids or viscous fluids in which the chains approximate random coils. Below T_m, amorphous regions alternate with regions which are lamellar crystals.^[4] The amorphous regions contribute elasticity and the crystalline regions contribute strength and rigidity. The planar amide (-CO-NH-) groups are very polar, so nylon forms multiple hydrogen bonds among adjacent strands. Because the nylon backbone is so regular and symmetrical, especially if all the amide bonds are in the trans configuration, nylons often have high crystallinity and make excellent fibers. The amount of crystallinity depends on the details of formation, as well as on the kind of nylon. Apparently it can never be quenched from a melt as a completely amorphous solid.

Hydrogen bonding in Nylon 6,6 (in mauve).

Nylon 6,6 can have multiple parallel strands aligned with their neighboring peptide bonds at coordinated separations of exactly 6 and 4 carbons for considerable lengths, so the carbonyl oxygens and amide hydrogens can line up to form interchain hydrogen bonds repeatedly, without interruption (see the figure opposite). Nylon 5,10 can have coordinated runs of 5 and 8 carbons. Thus parallel (but not antiparallel) strands can participate in extended, unbroken, multi-chain β-pleated sheets, a strong and tough supermolecular structure similar to that found in natural silk fibroin and the β-keratins in feathers. (Proteins have only an amino acid α-carbon separating sequential -CO-NH- groups.) Nylon 6 will form uninterrupted H-bonded sheets with mixed directionalities, but the β-sheet wrinkling is somewhat different. The three-dimensional disposition of each alkane hydrocarbon chain depends on rotations about the 109.47° tetrahedral bonds of singly bonded carbon atoms.

When extruded into fibers through pores in an industrial spinneret, the individual polymer chains tend to align because of viscous flow. If subjected to cold drawing afterwards, the fibers align further, increasing their crystallinity, and the material acquires additional tensile strength.^[5] In practice, nylon fibers are most often drawn using heated rolls at high speeds.

Block nylon tends to be less crystalline, except near the surfaces due to shearing stresses during formation. Nylon is clear and colorless, or milky, but is easily dyed. Multistranded nylon cord and rope is slippery and tends to unravel. The ends can be melted and fused with a heat source such as a flame or electrode to prevent this.

When dry, polyamide is a good electrical insulator. However, polyamide is hygroscopic. The absorption of water will change some of the material's properties such as its electrical resistance. Nylon is less absorbent than wool or cotton.

Historical uses[link]

The worn out nylon stockings will be reprocessed and made into parachutes for army fliers c. 1942

Bill Pittendreigh, DuPont, and other individuals and corporations worked diligently during the first few months of World War II to find a way to replace Asian silk and hemp with nylon in parachutes. It was also used to make tires, tents, ropes, ponchos, and other military supplies. It was even used in the production of a high-grade paper for U.S. currency. At the outset of the war, cotton accounted for more than 80% of all fibers used and manufactured, and wool fibers accounted for nearly all of the rest. By August 1945, manufactured fibers had taken a market share of 25%, at the expense of cotton.

Some of the terpolymers based upon nylon are used every day in packaging. Nylon has been used for meat wrappings and sausage sheaths.

Use in composites[link]

Nylon can be used as the matrix material in composite materials, with reinforcing fibers like glass or carbon fiber; such a composite has a higher density than pure nylon. Such thermoplastic composites (25% glass fiber) are frequently used in car components next to the engine, such as intake manifolds, where the good heat resistance of such materials makes them feasible competitors to metals.

Hydrolysis and degradation[link]

All nylons are susceptible to hydrolysis, especially by strong acids, a reaction essentially the reverse of the synthetic reaction shown above. The molecular weight of nylon products so attacked drops fast, and cracks form quickly at the affected zones. Lower members of the nylons (such as nylon 6) are affected more than higher members such as nylon 12. This means that nylon parts cannot be used in contact with sulfuric acid for example, such as the electrolyte used in lead-acid batteries. When being molded, nylon must be dried to prevent hydrolysis in the molding machine barrel since water at high temperatures can also degrade the polymer. The reaction is of the type:

Incineration and recycling[link]

Various nylons break down in fire and form hazardous smoke, and toxic fumes or ash, typically containing hydrogen cyanide. Incinerating nylons to recover the high energy used to create them is usually expensive, so most nylons reach the garbage dumps, decaying very slowly.^[6] Some recycling is done on nylon, usually creating pellets for reuse in the industry.^[7]

Etymology[link]

In 1940, John W. Eckelberry of DuPont stated that the letters "nyl" were arbitrary and the "on" was copied from the suffixes of other fibers such as cotton and rayon. A later publication by DuPont explained that the name was originally intended to be "No-Run" ("run" meaning "unravel"), but was modified to avoid making such an unjustified claim and to make the word sound better.^[8] An apocryphal explanation is that Nylon is a conflation of "New York" and "London". A humorous backronym is "Now You've Lost, Old Nippon" referring to the supposed loss of demand for Japanese silk.

See also[link]

References[link]

Further reading[link]

• Textiles by Sara J. Kadolph, ISBN 0-13-118769-4

External links[link]

For historical perspectives on nylon, see the Documents List of "The Stocking Story: You Be The Historian" at the Smithsonian website, by The Lemelson Center for the Study of Invention and Innovation, National Museum of American History, Smithsonian Institution.

Wikimedia Commons has media related to: Nylon

• A chemical demonstration of the synthesis of nylon in Carleton University's CHEM 1000 course. (Video)
• Typical properties of Nylon / Polyamide
• Polyamide material description
• Discussion of nylon synthesis and properties
• "How Nylon Yarn Is Made", January 1946, Popular Science from raw material to shipment article with drawings and illustrations

v t e Fibers Natural Animal Alpaca Angora Byssus Camel hair Cashmere Catgut Chiengora Guanaco Llama Mohair Pashmina Qiviut Rabbit Silk Sinew Spider silk Wool Vicuña Yak Vegetable Abacá Bagasse Bamboo Coir Cotton Flax Linen Hemp Jute Kapok Kenaf Piña Raffia Ramie Sisal Wood Mineral Asbestos Synthetic Cellulose Acetate Triacetate Art silk Bamboo Lyocell Rayon Modal Rayon Rayon Mineral Glass Carbon Tenax Basalt Metallic Polymer Acrylic Aramid Twaron Kevlar Technora Nomex Microfiber Modacrylic Nylon Olefin Polyester Polyethylene Dyneema Spectra Spandex Vinylon Vinyon Zylon

Nina Dobrev
Dobrev at PaleyFest 2010's The Vampire Diaries night at the Saban Theatre in 2010
Born	Nina Constantinova Dobreva[1] (1989-01-09) January 9, 1989 (age 23)[1] Sofia, Bulgaria
Nationality	Bulgarian-Canadian
Occupation	Actress, model
Years active	2006–present

Nina Dobrev (born Nina Constantinova Dobreva; January 9, 1989)^[1] is a Bulgarian-born Canadian actress and model. She played the role of Mia Jones, the single teenage mother, on Degrassi: The Next Generation, from the show's sixth to ninth season. She currently stars as Elena Gilbert and Katherine Pierce on The CW television teen drama, The Vampire Diaries.

Personal life[link]

Dobrev at the 2008 Toronto Film Festival

Nina Dobrev was born in Sofia, Bulgaria, and moved to Canada at the age of two, where she was raised in Toronto, Ontario. She speaks fluent French, English, and Bulgarian. She has an older brother, Alexander; her father is a computer specialist and her mother is an artist.^[1]

Dobrev attended J. B. Tyrrell Sr. Public School, where she started ballet and jazz classes, and competed in rhythmic gymnastic.^[1] Then, she attended and Wexford Collegiate School for the Arts in Scarborough, Ontario and Ryerson University in Toronto, majoring in sociology. She left in 2008 to pursue her acting career.^[2]

While working on the show, she began dating her Vampire Diaries co-star Ian Somerhalder.^[3][4]

Career[link]

Modeling jobs led to commercials, which then turned into film auditions. Shortly thereafter, she booked roles in feature films, including Fugitive Pieces, Away from Her, Never Cry Werewolf, and the television series Degrassi: The Next Generation. She starred in a number of Lifetime original movies. She also was in an MTV movie called The American Mall on CTV. She is currently starring in The CW's drama The Vampire Diaries, playing the dual role of Katherine Pierce, a vampire loved by two human brothers during the American Civil War, and Katherine's doppelgänger Elena Gilbert, a human who is caught between the same two brothers, now vampires, Damon and Stefan Salvatore.^[5]

She also had a minor role in the erotic thriller Chloe, theatrically released by Sony Pictures Classics on March 26, 2010.^[6] The film had enjoyed commercial success and became director Atom Egoyan's biggest moneymaker ever.^[7]

In April 2011, she was cast as Candace in the film adaptation of The Perks of Being a Wallflower, alongside Logan Lerman, Emma Watson and Paul Rudd.^[8] Shooting began in May of that year in Pittsburgh, Pennsylvania and she completed her scenes on June 27, 2011.^[9]

Philanthropy[link]

In September 2011, Dobrev co-hosted We Day alongside Joe Jonas.^[10] We Day is organized by Free the Children. Dobrev also designed a T-Shirt^[11] with Me to We Style, which gives 50% of its profits to Free the Children.^[12]

Filmography[link]

Dobrev at the 2011 San Diego Comic-Con.

Accolades[link]

Dobrev at the 2011 MuchMusic Video Awards