Editing Nylon (section)

== Properties ==

Above their [[glass transition temperature|melting temperatures]], ''T''<sub>m</sub>, [[thermoplastic]]s like nylon are [[amorphous solid]]s or viscous [[fluid]]s in which the chains approximate [[random coil]]s. Below ''T''<sub>m</sub>, amorphous regions alternate with regions which are [[lamellae (materials)|lamellar]] [[crystal]]s.<ref>[https://web.archive.org/web/20041230231859/http://www.aml.arizona.edu/classes/mse222/1998/nylon66/mse222.htm Valerie Menzer's Nylon 66 Webpage]. Arizona University</ref> The amorphous regions contribute elasticity, and the crystalline regions contribute strength and rigidity. The [[Plane (geometry)|planar]] amide (-CO-NH-) groups are very [[chemical polarity|polar]], so nylon forms multiple [[hydrogen bond]]s among adjacent strands. Because the nylon backbone is so regular and symmetrical, especially if all the amide bonds are in the [[geometric isomerism|''trans'' configuration]], nylons often have high crystallinity and make excellent fibres. The amount of crystallinity depends on the details of formation, as well as on the kind of nylon.

[[File:Nylon-3D-h bond.png|thumb|upright=1.2|Hydrogen bonding in Nylon&nbsp;66 (in mauve)]]

Nylon&nbsp;66 can have multiple parallel strands aligned with their neighboring peptide bonds at coordinated separations of exactly six and four carbons for considerable lengths, so the [[carbonyl]] [[oxygen]]s and amide [[hydrogen]]s can line up to form interchain hydrogen bonds repeatedly, without interruption (see the figure opposite). Nylon&nbsp;510 can have coordinated runs of five and eight carbons. Thus parallel (but not antiparallel) strands can participate in extended, unbroken, multi-chain [[beta sheet|β-pleated sheets]], a strong and tough supermolecular structure similar to that found in natural [[keratin#Molecular biology and biochemistry|silk fibroin]] and the [[keratin|β-keratins]] in [[feather]]s. (Proteins have only an amino acid α-carbon separating sequential -CO-NH- groups.) Nylon&nbsp;6 will form uninterrupted [[hydrogen bond|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 [[rotation]]s about the 109.47° [[alkane#Molecular geometry|tetrahedral]] bonds of singly bonded carbon atoms.

When [[extrusion|extruded]] into fibres through pores in an industry [[Spinneret (polymers)|spinneret]], the individual polymer chains tend to align because of [[viscosity|viscous]] [[rheology|flow]]. If subjected to [[cold drawing]] afterwards, the fibres align further, increasing their crystallinity, and the material acquires additional [[tensile strength]]. In practice, nylon fibres are most often drawn using heated rolls at high speeds.<ref name=Campbell>{{cite book|last1=Campbell|first1=Ian M.|title=Introduction to synthetic polymers|date=2000|publisher=Oxford Univ. Press|location=Oxford|isbn=978-0198564706}}</ref>

Block nylon tends to be less crystalline, except near the surfaces due to [[Shear (fluid)|shearing]] [[stress (physics)|stresses]] during formation. Nylon is clear and [[color|colourless]], or milky, but is easily [[dye]]d. Multistranded nylon cord and rope is slippery and tends to unravel. The ends can be [[melting|melted]] and fused with a heat source such as a [[flame]] or [[electrode]] to prevent this.

Nylons are hygroscopic and will absorb or desorb moisture as a function of the ambient humidity. Variations in moisture content have several effects on the polymer. Firstly, the dimensions will change, but more importantly moisture acts as a plasticiser, lowering the [[glass transition temperature]] (''T''<sub>g</sub>), and consequently the elastic modulus at temperatures below the ''T''<sub>g</sub><ref>{{cite web|title=Measurement of Moisture Effects on the Mechanical Properties of 66 Nylon - TA Instruments Thermal Analysis Application Brief TA-133|url=http://www.tainstruments.com/pdf/literature/TA133.pdf|website=TA Instruments|access-date=19 June 2017}}</ref>

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.

The characteristic features of nylon 66 include:
* Pleats and creases can be heat-set at higher temperatures
* More compact molecular structure
* Better weathering properties; better sunlight resistance
* Softer "Hand"
* High melting point ({{cvt|256|C}})
* Superior colourfastness
* 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.
* Variation of luster: nylon has the ability to be very lustrous, semi-lustrous, or dull.
* Durability: its high tenacity fibres 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 (−12&nbsp;dB)<ref>{{cite journal|doi=10.1063/1.1771814|title=Millimeter-wave, terahertz, and mid-infrared transmission through common clothing|year=2004|last1=Bjarnason|first1=J. E.|last2=Chan|first2=T. L. J.|last3=Lee|first3=A. W. M.|last4=Celis|first4=M. A.|last5=Brown|first5=E. R.|journal=Applied Physics Letters|volume=85|issue=4|pages=519|bibcode=2004ApPhL..85..519B|doi-access=free}}</ref>{{clarify|reason=-12&nbsp;dB of which quantity?|date=August 2014}}

Nylon clothing tends to be less flammable than cotton and rayon, but nylon fibres may melt and stick to skin.<ref>{{cite web|url=https://kidshealth.schn.health.nsw.gov.au/flammable-clothing|title=Flammable clothing|website=The Children's Hospital at Westmead|date=24 February 2016 |access-date=5 July 2017}}</ref><ref name="Phillips">{{cite book|url=https://books.google.com/books?id=sDQrAAAAYAAJ&pg=PA30|title=Mass burns : proceeding of a workshop, 13-14 March 1968 / sponsored by the Committee on Fire Research, Division of Engineering, National Research Council and the Office of Civil Defense, Dept. of the Army|author=Workshop on Mass Burns (1968 : Washington, D.C.)|date=1969|publisher=National Academy of Sciences ; Springfield, Va. : reproduced by the Clearinghouse for Federal Scientific & Technical Information|editor-last1=Phillips|editor-first1=Anne W.|location=Washington, D.C.|page=30|access-date=5 July 2017|editor-last2=Walter|editor-first2=Carl W.}}</ref>