nylon 6

NYLON 6

Imrananwar_112ntu@yahoo.com

NATIONAL TEXTILE UNIVERSITY

FAISALABAD

PAKISTAN

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

Repeating Unit

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

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

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

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

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

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

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

Carbocation in a molecule allows nucleophile to come along and attack it. Hydroxide ion whose proton was stolen by caprolactam attacks the carbocation

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

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

The electrons rearrange to form the carbocation

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

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

Carboxylate group at the end of the molecule is going to sweep around and steal the alcohol hydrogen

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

Pre-Treatment Flow Process

• Padding

• Heat-setting

• Preliminary scouring with non-ionic detergent

• Bleaching

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

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

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

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.

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.

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

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).

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.

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.

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.