Nylon

Nylon The word “Nylon” is a generic term Used for a group of chemical compounds classified as “polyamides” Nylon is known as “polyamide” as it contains 85% amide linkages

Types of Nylon: 1. Naylon 6,6 2. Nylon 6 3. Nylon 11 4. Nylon 6, 10

Nylon 6,6 Raw Materials: Hexa Methylene Diamine -H₂N(CH₂)₆NH₂- Adipic Acid C6 H10 O4

Nylon 6,6 Production of Polymer: Hexamethylene adipamide which subsequently polymerizes with further elimination of water to produce nylon polymer The reaction is carried out in an inert atmosphere (nitrogen gas) at 280 degree centigrade for 4 hours

The water formed in the reaction is removed from the mixture When required viscosity is obtained, the polymer reaction is stopped The molten polymer is extruded from the autoclave on to water-cooled casting wheel in the form of ribbons The polymer ribbons are solidified on casting wheel

Cool Casting Wheel

These ribbons are cut into chips by dicing machine The chips are collected in storage bins The wet chips are dried in air in rotary dryers The chips obtained from different lots are mixed to ensure uniformity of final product The chips are transferred to spinning section for the manufacture of filaments

Polmer chips

Spinning: Nylon is spun after melting and the process is called “melt spinning” The chips of nylon polymer are fed through a hopper of spinning vessel the chips are dropped on an electrically heated grid (perforated metal plate) the perforations of heated grid are so small that chips do not pass but melted into liquid

The molten polymer passes through holes of the grid and collected at the bottom of spinning vessel The nitrogen gas is introduced into spinning vessel to exclude air or oxygen The molten polymer is kept at temp about 280 degree centigrade and sucked by pump into spinneret through filter, which consists of several layers of metal gauze

The filter removes any solid impurity present in molten polymer The spinneret consist of steel plate of 0.25” thick and 2-3” in diameter having fine holes of 0.01” diameter in it The molten polymer in the form of filaments solidifies as soon as it emerges out of spinneret The filaments formed pass through a cooling chamber in which cold air is circulated

The temperature of filaments is dropped to about 70 degree centigrade in the cooling chamber The filaments are passed through steam chamber to wet them before winding on a bobbin The filaments are spun at speed of about 1200 m/min

Stretching and drawing: Nylon filaments obtained after spinning are not very strong these filaments are drawn 4-7 times to their original lengths these filaments are taken on to guide rollers and then to draw rollers the speed of draw rollers is 4-7 times faster than guide rollers

Structure of Nylon Nylon 6,6 can be produced with circular cross section and trilobal section The physical and chemical properties of trilobal cross section are quite similar to normal cross section fibers but trilobal cross section resulted in fabrics with increased covering power and greater bulk The length wise view is straight cylindrical rods

Properties of Nylon 6,6 Tenacity: regular filament----- 4.6-5.8 g / denier High tenacity nylon---- 9.0 g/ denier Staple ---------- 4.1-4.5 g/ denier Tensile strength: Regular filament------ 65000-85000 lb/sq inch High tenacity ----- 90,000-130000 lb/sq inch staple---------------- 60000-66000 lbs/sq inch

Elongation: Regular filament: 26-32 % High tenacity filament: 19-24% Staple: 37-40% Elastic recovery: Highly elastic fiber and standard filament has 100 % recovery till 8% extension High tenacity filament has 100 % recovery till 4 %

Has resemblance to rubber but does not recover as quickly as rubber If nylon is allowed to stretch for several days and then allowed to relax, it will cover 50% of its stretch almost immediately but rest of recovery takes place very slowly

Abrasion resistance: Excellent Specific gravity: 1 Abrasion resistance: Excellent Specific gravity: 1.14 Effect of moisture: Nylon absorbs only a small amount of moisture as compared with most of natural fibers. Its moisture regain of 4-4.5 %

The tenacity of thoroughly wet nylon is 80-90% of its dry tenacity The elongation of wet nylon is 5-30% Melting: Approximately 250 degree centigrade Effect of low temperature: Nylon retains its strength well at low temperatures. After several hrs at -40 degree centigrade, a nylon rope does not lose

strength and this strength is retained after the rope is reconditioned at normal temperature Flammability: Nylon is less flammable than cotton, rayon, wool or silk. If a flame is applied to a nylon fabric, the material melts Effect of age: Negligible

Effect of sunlight: Nylon is affected by prolonged exposure to light there is gradual loss of strength but little or no discolouration Effect of acid : Dilute acids have little effect on nylon Hot acids like HCl and H2SO4however decompose nylon

Alkalies: It has excellent resistance to alkalis Alkalies: It has excellent resistance to alkalis. It can be boiled in strong caustic soda solutions without damage Effect of Insects: It is not affected by insects Effect of microorganisms: It is not weakened by moulds or bacteria

Electrical properties: The low moisture absorption of nylon encourages the accumulation of static electricity but the effects may be overcome by use of antistatic finishes and static eliminators End uses: used for sports wear, swimwear and hosiery, socks and gloves Used in tire cord and conveyor belt

Nylon 6 Nylon 6 is known as “Perlon” Made by self condensation of caprolactm Raw Material: Caprolactam Catalyst: Benzoic Acid Acid chain stopper: Acetic acid

Nylon 6 Production of Polymer: Caprolactam is available in white solid flakes its melting point is 68 degree centigrade It is soluble in water Polymerization is carried out in autoclave Autoclave is heated at 240-270 degree centigrade The autoclave is fed continuously with hot caprolactam mixed with acid promoter and acid chain stopper from its top

Caprolactam Flakes

Chemical Structure of Nylon 6

Acid chain stopper is acetic acid, this acid prevent further polymerization by replacing end groups Polymerization is stopped when desired viscosity is reached During the down flow, polymerization takes place and at bottom of autoclave, a highly viscous molten polymer solution is collected The yield of polymer is extruded into ribbons, solidified by water, dried and chips are made by dicing machine

The chips are washed with water at 80 degree centigrade to remove caprolactam, then dried under reduced pressure at a temperature not exceeding 85 degree centigrade in tumble dryers These chips are used for the production of continuous filaments

Spinning Production of Filament Yarn: Continuous filaments are made by melt spinning Dry polymer are fed to melt spinning vessel Spinning vessel is made of stainless steel and insulated to prevent loss of heat Chips fall on a grid electrically heated to 250-260 degree centigrade The molten polymer is collected into conical section and then is fed to spinning pump

The molten polymer is kept in nitrogen atmosphere to prevent decomposition by air Passing through packs of graded gauze filters to remove solid impurities before entering the spinneret filters the molten polymer The molten polymer emerges from spinneret in the form of filaments in a cooling chamber in which cold air is circulated The filaments are solidified by cold air

These filaments are moisturized with water to make them dimensionally stable The spinning of filaments is carried out in a spinning room maintained at temperature 20 degree centigrade and relative humidity 45 – 55 %

Stretching and Drawing: The filaments emerged from spinneret are not strong enough and therefore subjected to treatment of stretching to produce the desired textile properties The filaments are stretched to 3-4 times to their original lengths on stretching rollers to orient a large number of un-oriented macromolecules These filaments pass through the stretching device

The filaments are wound on bobbins The hosiery yarn is given twist about 3 tpi and 7 tpi for a woven cloth The winding room is maintained at temperature 20 degree centigrade and relative humidity at 55-65 %

Properties Tenacity: It can be varied by adjustment of manufacturing conditions Standard tenacity: 4.5-5.8 g/denier High tenacity: 7.5- 8.3 g/denier Staple : 3.8-5.5 g/denier the greater the degree of stretch during drawing, the greater will be tenacity

Tensile strength: Standard: 73000-84000 lbs/sq inch High tenacity: 110, 000-120000 lb/sq inch Elongation: Standard: 23-42.5 % High tenacity: 16-19 % Staple: 23-50 %

Elastic recovery: Like nylon 6,6 nylon 6 is highly elastic fiber Its recovery is 100% when extension is 6-8% Its recovery is 85% when extension is 8.5% Resistance to abrasion: It has excellent resistance to abrasion

Effect of moisture: 4-4.5 % Melting point: 215 degree centigrade Effect of low temperature: The nylon 6 regain its original strength when returned to its room temperature Effect of High temperature: It loses strength with increase in temperature the effect is a condition of thermoplastic nature of fiber

Effect of High temperature: It loses strength with increase in temperature the effect is a condition of thermoplastic nature of fiber Flammability: It melts when heated above 215 degree centigrade and it does not support combustion on its own Effect of Age: Negligible Effect of sunlight: It suffer some loss of strength when exposed to sunlight

Acids: Dilute acids have little effect on nylon 6 Acids: Dilute acids have little effect on nylon 6. However conc H2SO4, HCl and HNO3 can create damage Alkalis: It has excellent resistance to alkalis. Resistance to microorganisms: Not attacked by moulds or bacteria

Insects: It cannot be serve as food for moths or beetles