Manufacturing Process of Nylon 6

Manufacturing Process of Nylon 6

Nylon Manufactured in India at present is of this type. This is made from Caprolactum which is made by a series of reactions using products obtained from coal tar

Coal Tar--> Benzene--Chlorine--> Chlorobenzene--> Sodium Phenate--HCL--> Phenol--H2 (Nickel)-->Cyclohexanol--Oxidation Air Fe, Zn Catalyst--> Cyclohexanone--> Cyclohexanone Oxime--H2SO4--> Caprolectum

Polymerisation

Caprolectum is a white flaky solid, melting at 68 deg C and is soluble in water. the polymerisation is carried out in stainless steel cylinders.

Hot Caprolectum is mixed with a suspension of pigment, acid promotor and acid chain stopper. The extent of polymerisation depends upon the temperature of polymerisation. The purpose of acid chain stopper is to stop furthur polymerisation so that a desired density of molten polymer may be obtained.

The molten polymer is extruded into ribbons and cut into chips. These chips are used for the production of continuous filaments.

Melt Spinning

Continuous filaments are made by melt spinning. Dry polymer chips are fed to a melt spinning apparatus, wherein one section of the chips fall, into a melting region where they are heated electrically to 250-260 deg C. The molten polymer flows into a conical section to form a pool, which feeds a spinning pump and spinnerette. The pool is kept under an atmosphere of nitrogen to prevent decomposition by air.

The molten polymer leaving the pump is filtered before entering the spinnerette which is a stainless steel disc having a number of holes, the number and diameter of which determine the type of yarn formed. Before reaching the machine in which cheese is build up, the filaments are moistened with water to ensure dimensional stability of the final packages.

The yarn thus formed is not strong enough and has a very high extensibility. the yarn contains a large number of macro molecules which are unoriented and these must be oriented so as to lie parallel to the length of the fibre to develop full strength. This is done by stretching the yarn to 3-4 times its original length.

Properties of Nylon 6,6

Properties of Nylon 6,6

Strength

The most outstanding property of nylon is its strength and elasticity. The tenacity varies from 8.8-4.3 gpd while corresponding elongation at break varies from 18-45%. The wet strength of nylon is 80-90% of its dry strength and the elongation at break increases by 5-30% on wetting.

Density: 1.14 g/cc

Elastic Recovery

When nylon yarn is stretched 1,2 and 4% with a load of 0.25 gpd for 30 seconds and then released the recovery after 60 seconds is 38, 63 and 73% respectively.

Moisture Regain

Nylon has a moisture regain of about 4% at 65% RH and 70 deg F.

Action of Light

Like other fibres, nylon undergoes degradation and weakens when exposed to lights.

Appearance

Nylon is dull and semi opaque before cold drawing, but on orientation its lustre is greatly incresed. Delustering is done by adding TiO2 in the polymerisation mixture.

Action of Heat

Nylon melts at 262 deg C in an atmosphere of Nitrogen and at 250 deg C in air. When a very hot iron is used for ironing nylon garments, sticking or even fusion may take place. Therefore ironing should not be done above 180 deg C. Permanent set may be applied to Nylon by heat setting with 25 psi pressure with saturated steam. The pleats thus set remian on wearing and washing even in hot water.

Chemical Properties

Nylon is extremely stable chemically. For example dry cleaning solvents, alcohols, aldehydes, ketones, ethers, hydrocarbons, chlorinated hydrocarbons, soaps and synthetic detergents and water including sea water do not affect Nylon.

Also it has got a remarkable stability towards alkali.

Biological Properties

Nylon is not a nutrient for Mildew or bacteria and is not eaten up by moth larvae. But they bite their way up when imprisoned in nylon cloth. It is harmless to human skin.

Manufacturing Process of Nylon 6,6

Manufacturing Process of Nylon 6,6

Nylon 6,6 is made from Hexamethylene diamine and adipic acid as shown in the figure below.



Spinning of Nylon 6,6



The chips of nylon polymer are fed through a hopper A, into a spinning vessel B, on an electrically heated grid ( perforated plate) C. The perforations are so small that the chips do not pass through, but when melted, the liquid can pass.

The molten nylon collects as a pool D, at the bottom of the vessel. This liquid should not come into contact with oxygen or air and hence nitrogen is introduced into the vessel. The molten polymer is kept at a temperature of about 288 deg C and sucked by a pump F, into a spinnerette E. The molten polymer solidifies as soon as it emerges out of the spinnerette. The filament thus formed pass through a colloing zone, in which cold air G circulates directed towards the filaments. The filaments are then passed through a steam chamber H, to wet them before winding on the bobbin L.

Drawing

Nylon filaments as obtained are not very strong. They have to tbe drawn 4-7 times their original length. This is done by cold drawing. The yarn in pulled off from bobbin L through guides M and N, between a pair of rollers O. The speed of rotation of these rollers determines the initial speed. The yarn then goes over a deflector P, and two to three times around roller Q, running at five times the speed than that of O. The yarn subsequently courses through another guide R, and wound on another bobbin which rotates at very high speed, to impart twist in the yarn before being wound.

Properties of Acetate Rayon

Properties of Acetate Rayon

55/20/3s means 55 denier yarn, 20 filament and 3 TPI S side.

Moisture content of sec. Cellulose acetate is 6.5% at 70 deg F and 65% RH.
( Moisture Content= Wt of water in a material /Total wt of material) ( Moisture Regain= wt of water in a material/ oven dry wt of material)
( RH= actual humidity/ humidity of air saturated in water).

Tenacity of Acetate rayon is 1.4 gpd at dry state and 0.9 gpd at wet state.

Elongation at break is 25% in dry state and 35% in wet state

Acetate Rayon is more sensitive to heat. It begins to weaken at 93 deg C. At 175 deg C it becomes sticky and melts at 260 deg C. Like nylon and polyester it is thermoplastic. Thus permanent crimp, pleats and creases can be imparted to the garment under carefully controlled conditions.

Acetate rayon is soluble in acetone, methyl ethyle ketone etc.

Some degeneration takes place when this fiber is exposed to light but not very serious.

It is stable to hot water.

It can also withstand treatment with soap or alkali solution having a pH of not more than 9.5 at temp upto 100 deg C. Therefore it can undergo normal scouring and dyeing operations without affecting the lustre.

It is unaffected by dilute solutions of weak acids but attacked by strong acids. Concentrated organic acids cause swelling

It is resistant to attack by bacteria and fungi. Its low moisture content contributes to resistance to mildew.

It is non toxic and non irritating to skin

Only a few striations ( 2-3) are present in the fibre as can be seen from the longitudinal view. The cross section of the fiber have individual lobes and are round and smooth. It is the smaller number of lobes or serrations of acetate fibres that distinguish the fibre from more numerous serrations of viscose rayon.