Preparation, properties and uses of nylon

Apr 27 • Engineering Notes • 270 Views • No Comments

HIGH POLYMER

Preparation, properties and uses of nylon

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.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.

 The general reaction is -:

 Two molecules of water are 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.

Types of Nylon-:

The naming scheme for unsubstituted nylon is as follows. If polymerized from the monoacid [NH2(CH2)n-1-C(O)(OH)] to form (1), it is designated as nylon-n.If made from the condensation of the diamine [H2N-(CH2)m-NH2] and the diacid [C(O)(OH)-(CH2)n-2-C(O)(OH)] to form (2), it is denoted as nylon-m,n. Commercially, the mostimportant nylons are nylon-6,6 and nylon-6, which are used in carpet fibers and textiles.

Concepts of nylon production

    1. 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.
    2. 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).
    3. The third method:Nylon 6 is synthesized by ring opening polymerization of caprolactam. Caprolactam has 6 carbons, hence ‘Nylon 6′. When caprolactam is heated at about 533 K in an inert atmosphere of nitrogen for about 4-5 hours, the ring breaks and undergoes polymerization. Then the molten mass is passed through spinnerets to form fibres of Nylon 6. 

Properties of nylon-:

  1.  MELTING POINT :-                                                 485 DEG. F
  2.  MAX. WORKING TEMPERATURE UNDER LOAD:- 250 DEG. F
  3.  TEMPERATURE RANGE: -                                     70 TO +250 DEG. F
  4.  THERMAL CONDUCTIVITY:-                                  1.2 BTU/hr/sq.ft/Deg. F.in
  5.  TENSILE STRENGTH (@ -70 F):-                          15,700 PSI.
  6.  TENSILE STRENGTH (@+73 F):-                          12,500 PSI.
  7.  COMPRESSIVE STRENGTH:-                                1% OFFSET: 9,700 PSI.
  8.  DIELECTRIC CONSTANT :-                                    60HZ.: 4.1
  9.  POWER FACTOR :-                                               60HZ.: 0.014
  10.  DEFLECTION TEMP.:-                                           66 PSI: 360 F.
  11.  DEFLECTION TEMP:-.                                           264 PSI 155-160 F.
  12.  SHRINKAGE:-                                                         0.12 TO 0.20 IN/IN.
  13.  HARDNESS (ROCKWELL):-                                   R118…R120
  14.  VOLUME RESISTIVITY:-                                         4.5X10E13 OHM CM.

Uses of nylon-:

Historical uses

·         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 is also used to make tires, tents, ropes, ponchos, and other military supplies.

·         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% to 30% 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.

·         It is used as elastomers

·         It is used as plastics

·         It is used in toys.

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. Some recycling is done on nylon, usually creating pellets for reuse in the industry.

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