Download - Nylon 6
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NYLON 6
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Nylon 6
•Nylon 6 or polycaprolactam unlike most other nylons, not a condensation polymer, but formed by ring-opening polymerization
•It was given the trademark Perlon in the year 1952
•It is a semi crystalline polyamide
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Repeating Unit
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Application
• Thread in bristles for toothbrushes
• Surgical sutures
• Strings for acoustic (Guitars, Violins, Violas)
• Variety of threads, ropes, filaments & nets
• Tire cords
• Hosiery and Knitted garments
• Gun frames
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Properties
• Glass transition temperature: 47oC
• Melting temperature: 220oC
• Amorphous density at 25oC: 1.084 g/cm3
• Crystalline density at 25oC: 1.23 g/cm3
• Molecular weight of repeat unit: 113.16 g/mol
• Degraded by light as natural fibers
• Permanent set by heat and steam
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Properties
• Tenacity-elongation at break ranges from 8.8g/d-18% to 4.3 g/d-45%. – Its tensile strength is higher than that of wool, silk,
rayon, or cotton.
• 100% elastic under 8% of extension
• Specific gravity of 1.14
• Extremely chemically stable
• No mildew or bacterial effects
• 4 - 4.5% of moisture regain
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Properties
• Abrasion resistant • Lustrous- Nylon fibers have the luster of silk • Easy to wash • Can be pre colored or dyed in wide range of
colors; dyes are applied to the molten mass of nylon or to the yarn or finished fabric.
• Resilient • Filament yarn provides smooth, soft, long
lasting fabrics • Spun yarn lend fabrics light weight and warmth
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Synthesis of Nylon 6
Nylon 6 is only made from one kind of monomer, a monomer called caprolactam whereas Nylon 6,6 is made from two monomers, adipoyl chloride and hexamethylene diamine
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Caprolactam is firstly heated to about 250oC with about 5-10%
water thrown in. The carbonyl oxygen looks around, and sees
a water molecule & steal one of the water's hydrogen atoms
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The carbonyl oxygen donates a pair of electrons to the hydrogen atom of water results in protonated carbonyl, and a free hydroxyl group. Carbonyl oxygen having positive charge, swipes a pair of electrons from the carbonyl double bond, leaving the positive charge on the carbonyl carbon atom
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Carbocation in a molecule allows nucleophile to come along and attack it. Hydroxide ion whose proton was stolen by caprolactam attacks the carbocation
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An unstable gem diol is formed. The nitrogen atom donates a pair of electrons to a hydrogen atom on one of the hydroxyl groups, stealing it away. The electrons that the hydrogen shared with its oxygen shift to form a double bond between the oxygen and the carbon atom. And lastly, the electrons shared by the carbon and the nitrogen shift completely to the nitrogen, severing the carbon-nitrogen bond
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Caprolactam circle brakes & makes it linear amino acid which react with other caprolactam molecule. Caprolactam molecule will steal the acid hydrogen form the linear amino acid. The carbonyl oxygen donates a pair of electrons to that hydrogen, stealing it away from the amino acid
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The electrons rearrange to form the carbocation
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This carbocation is still an open invitation to any nucleophile around, but this time, there's a new nucleophile on the block. That's the amino acid that just lost its acid hydrogen
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Very unstable ammonium species are formed. Ring nitrogen steals a hydrogen from the ammonium nitrogen. In addition, the bond joining the carbon and the nitrogen disengaged, opening the ring
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Carboxylate group at the end of the molecule is going to sweep around and steal the alcohol hydrogen
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This makes a new carbonyl group in the middle of the
molecule, and regenerates the carboxylic acid. As an acid , it is
sure to react again with another caprolactam molecule, and
then another, and another, until we get long chains of nylon 6
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Pre-Treatment Flow Process
• Padding
• Heat-setting
• Preliminary scouring with non-ionic detergent
• Bleaching
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SCOURING
• Before heat-setting and dyeing it is advisable to remove the finishing oil from the polyamide yarn
• Scouring in a solvent with perchloroethylene in continuous scouring machines.This is the best method of removing finishes from nylon yarns with a silicone oil base
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HEAT - SETTING
• This process is required for fixing the final dimensions of the fabrics
• Heat-setting is normally carried out before dyeing, but can also be performed at the end of the process. The setting times and temperatures are as
• 180°C-190°C for 20-40 sec
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BLEACHING
• Polyamide yarns tend to yellow when heat-set
• In nylon multifilament fabrics, a protection agent may have to be used to reduce the possibility of yellowing during heat-setting e.g. – Spanscour GR
– Sybron Tanatex
• Conditions for Bleaching are – stabilised sodium hydrosulphite - 2-3 g/l
– pH = 4,5 – 5
– Temperature:....90°C - 95°C
– Time:..............30-45 minutes
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DYEABILITY
• Nylon is a synthetic fiber, but its unique chemistry
means that it can be dyed, easily and well, using
the same acid dyes that are commonly used on
wool and other animal fibers.
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DYEABILITY
• The dyeing efficiency of nylon fibers is enhanced due to the end groups -COOH and -NH2, which exhibit polar and hydrophilic characteristics.
• Dye diffusion into fibers is closely related to the rate of dyeing, level of dyeing through dye migration, wet fastness properties of dyes, etc.
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DYEABILITY
• Earlier studies were made about the diffusion of disperse dyes on nylon 6 and found that the actual diffusivity on nylon 6 fibers is not always independent on dye concentration
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DYEABILITY
• It was further reported that both dyeing rate and dye saturation of 1,4 -diaminoanthraquinone (1,4-DAA) were improved considerably in the presence of didodecyldimethlammonium bromide (DDDMAB).
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DYEABILITY
• This suggests that there might be fairly strong interaction between DDDMAB and the fiber by virtue of electrostatic and hydrophobic interactions.
• There have been many attempts to improve nylon's dyeability or at least to point out the factors and mechanisms acting in nylon dyeing.
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DYEABILITY
• It has been shown that acrylonitrile and styrene radiation grafting on the polymer could improve the dye ability of nylon .
• Another approach to higher dye ability of nylon 6 is by copolymerization.
• In this case, the dye ability can be improved at the expense of a decrease of specific viscosity and of heat and hydrolysis resistance.
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DYEABILITY
• Other treatments, such as plasma etching and superheated steaming have proved to decrease nylon dye ability.
• Superheated steaming of the fibers leads to higher shrinkage and to higher crystallinity and crystal size, which contribute to decrease dye ability.
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