textiel technology study notes about polymers

textile

1. Introduction Polymer – It is a substance made up of a large number of smaller molecules that link together to form larger molecules.

2. Degree of Polymerization The degree of polymerization (DP or X n ) is defined as the number of monomer units in the polymer. It is calculated as the ratio of molecular weight of a polymer and molecular weight of the repeat unit.

3. Fiber physics (Structural arrangement) Fiber physics is the study of the structure and physical properties of fibers. Basically three types of structural arrangement are shown on the fiber- ❶ Orientation ❷ Crystallinity ❸ Amorphousness

4. Amorphous and crystalline polymers the polymers that contain molecules are arranged Amorphous polymers are amorphous regions where randomly. C r y s t all i n e p o l y me r s are the polymers with crystalline regions where molecules are arranged in a partial pattern.

5. Difference between Amorphous and Crystalline

6. Filament Spinning

7. Melt spinning is the simplest method of fibre manufacturing mainly because it does not involve problems associated with the use of solvents . The polymer chips are dried and then melted in the extruder. The homogenized and filtered melt is squirted through narrow channels into a quench chamber where the solidification of fluid bundle is achieved. Finally spin finish is applied before the filament bundles are wound on the tube roller. Melt Spinning

8. Melt Spinning Polymer is melted in the extruders to get homogeneous melt. Then the melt is transported under pressure to spinning blocks where an exact metering pump (gear pump) maintains even delivering of the melt. The polymer is then forced through a fine filter (20 – 80μm sized wire mesh) to eliminate semisolids, gels, bubbles. Efficient filteration reduces the end breakage during spinning process. After filteration, the melt is forced through capillaries in a plate called spinneret through which fine stream of fluid is formed. The filaments are then quenched and solidified in the quench chamber while being drawn off from the bottom. The filament diameter reduces and a number of these filaments are then made to converge into a bundle with the help of two guides.

9. Melt Spinning

10. Conventional process – spinning at 600 – 1500 mts / min then drawing of spun yarn at 400 – 100 m/min. Direct spin-draw process with spinning speed at 4000 m/min and winding speed at 6000 m/min High speed spinning process – spinning at 3000 – 4000 m/min to get partially oriented yarn (POY) which is drawn further. Super High speed spinning – spinning at 4000 – 6000 m/min and above.

11. MELT SPINNING When the winding speeds are high, the filaments are directly wound on to the winder without the godets. When the polymer chips form the starting material, chips from several polymerization reactors are mixed to minimize the batch-to-batch variation. The chips are dried and then melted. Polymer Residual Moisture Nylon < 0.05% by weight Polyester < 0.005% by weight

12. Solution Spinning

13. First step in dry spinning is the preparation of the spinning solution or dope. The dissolving power of the solvent must be relatively good and be volatile. It should be cheap and precautions need to be against flammability , explosion and toxicity. Dry Spinning Polymer Solvent Boiling Point ( o C) Cellulose Acetate Acetone 56 Cellulose Triacetate Met h ylen e chlor id e , methanol, ethanol, 40/78 PVC Acetone + CS 2 mixture. 39 PAN, Spandex DMF 153 PVA Water 100

14. Dry Spinning Spinning process: ❶ In dry spinning, a volatile solvent is used to dissolve the raw materials and form a salutation . ❷ Then the solution is purified by filter . ❸ The solution is extruded through a spinneret into a warm air chamber where the solvent evaporates, solidifying the fine filaments . ❹ Finally the filament yarn either is immediately wound onto bobbins or is further treated for certain desired characteristics or end use.

15. Example:  Dry spinning is used in the production of acetate, triacetate, and some acrylic, modacrylic , spandex, and vinyon (PVC,PVA) fibers . Advantages: ►Yarn does not require purification Disadvantages: ►Flammable solvent hazards ►Solvent recovery ►Slow (200-400 yds /min)

16. Solution Preparation and Transport The methods of solution preparation and transport for wet spinning are similar to those used in dry spinning. The polymer is mixed and dissolved in vessel provided with a stirring device . The concentration of polymer is limited by polymer solubility , spinning pressure. Since the solution is spun at relatively lower temperatures , a lower percentage of solids (polymer) are used in wet spinning with viscosity of several hundred poises. Wet Spinning

17. Solution Preparation and Transport The degassed solution is filtered to remove any physical impurities and after filteration, it is homogenized . The solution is then sent through the metering pump to spinning machine with a spinneret having 200-600 holes, the diameter of the hole can range between 0.005 – 0.025 cm. ] Spinnerets with 2000 to 50000 holes are also used and spinnerets are submerged in the coagulation bath. Wet Spinning

18. WET SPINNING The wet spinning process falls into two broad classes namely Full y s y n t h e t ic f i br e s li k e acr y lics and m o d acrylics emp lo yi n g a solvent-nonsolvent system . Regenerated natural fibres like viscose rayon employing a chemical reaction to dissolve and precipitate the polymer.

19. Wet spinning This is the oldest, most complex and also the most expensive method of man-made yarn manufacture. This type of spinning is applied to polymers which do not melt and dissolve only in non-volatile or thermal unstable solvents.

20. Spinning process: ❶ In wet spinning, a non-volatile solvent is used to convert the raw material into a solution. ❷ The solvent is extruded through the spinneret either by simply washing it out or by a chemical reaction between the polymer solution and a reagent in the spinning bath. ❸ After extrusion, the solvent is removed in a liquid coagulation medium. ❹ Finally the filament yarn either is immediately wound onto bobbins or is further treated for certain desired characteristics or end use. Example:  Wet spinning is used in the production of aramid, Lyocell , PVC, Vinyon (PVA), viscose rayon, spandex, acrylic and modacrylic fibers.

21. Advantages: ►Large tows can be handled Disadvantages: ►Slow (70-150 yds /min) ►Washing to remove impurities ►Solvent and chemical recovery

22. Gel Spinning Process Gel spinning is defined as a  spinning method  for high strength fibers through a gel-like state as intermediate substance. The industrially prosperous spinning method called “gel spinning ”. Gel spinning, also known as semi  melt spinning , is a method that prepares high-strength and high-elastic modules fiber in the gel state. After the extrusion of the polymer solution or plasticised gel from the spinnerets, it is cooled in solvent or water before being stretched into gel fiber by ultra-high extension. Gel spinning can promote the polymer of fiber’s molecular weight, degree of orientation, crystallinity and fiber density effectively, and that contributes to increasing the fiber’s strength and modules

23. Gel spinning

24. Steps in Gel Spinning Process Dissolution:  The dissolution of polymer in solvent. The molecular chains of the solid polymers may be entangled, and the entanglements will affect the molecular chain stretching. The dissolution of polymers in solvent can disentangle these entanglements to aid the gel fiber stretching . Spinning and formation:  Extruding the solvent from the spinnerets by gear pump, and cooling it rapidly by air or water. The rapid cooling process can lead to the formation of crystals and retain the disentangled state of polymers to aid the formation of high-strength and high- elasticmodulus fiber.

25. Steps in Gel Spinning Process Remove solvent:  The most commonly used methods to remove solvent in gel spinning include the natural drying method and the use of extractant , which mainly aims to remove the solvent residuals in gel fiber. The extractant can displace the gel fiber solvent based on diffusion and penetration principles. In gel spinning, the selection of solvent and extractant directly affect the stretching stability, and is key to the gel spinning method . Stretching:  The high magnification stretching of the gel fibre. High magnification stretching can change the folded polymer molecular chains to straight chains, and improve polymer crystallinity and orientation. This is a unique feature of gel spinning, and is the key to enhancing gel fiber performance.

26. Types of Fibers Produced Using Gel Spinning Gel spinning is usually applied in the processing of high molecular weight or ultra-high molecular weight polymers. The entanglement of long chain polymers is fully stretched by appropriate solvent and temperature. After spinning, high magnification stretching can further stretch the polymer molecular chain to get the high strength of the fiber. Gel spinning is most widely applied in production of UHMWPE, Polyvinylalochol (PVA) polymer and polyacrylonitrile (PAN) fiber.

27. Drawing/Stretching Drawing is a process in which a group of slivers or filaments is elongated by passing them through a semi-series pair of rollers/ godet pairs, each pair of roller moving faster than the previous one After extrusion of the fiber, its chainlike molecules are in an amorphous or disordered arrangement. The filament fiber must be drawn to develop the desirable strength, pliability, toughness, and elasticity properties. Some fibers are cold-drawn; others must be hot-drawn. Drawing aligns the molecules in a more parallel arrangement and brings them closer together so they are more crystalline and oriented. The amount of draw (draw ratio) varies with intended use, determines the decrease in fiber size and controls the increase in strength.

28. Object – Drawing process  To increase strength  To increase orientation & crystallinity  To decrease elongation at break (EB).

29. Drawing process

30. The drawing process can be done in a single process step to a fully oriented yarn (FOY) directly after spinning (as it is shown in Figure) or in two process steps. In the latter case the fibers are only partly drawn to a partially oriented yarn (POY) and the final drawing process to fully oriented yarn (FOY) is done at the next process step (e.g. texturizing). Depending on the degree of orientation filament yarns have different names : LOY        Low Oriented Yarn   MOY    Medium Oriented Yarn   POY      Partially Oriented Yarn   HOY     High Oriented Yarn   FOY     Fully Oriented Yarn

31. Texturing   Texturing is a treatment in which flat filaments are distorted to have loops, coils, curl or crimps along their length to gain increased bulkiness, porosity, softness and elasticity in some situations. Object:  To gain increased bulkiness, porosity, softness and elasticity in some situations

32. Principle of texturing After drawing, drawn filaments are wound with or without twist into a package. For many applications. flat filament yarns are textured in order to gain increased bulkiness, porosity, softness and elasticity in some situations. Thermoplastic filament yarns are used in most texturing processes. The inter-fiber bonds break and reform during the texturing process. A filament yarn is generally textured through  three steps .  

33. The  first step  is to distort the filament in the yarn so that the inter-fiber bond is broken. Twisting or other means are used to distort the filaments within a yarn .  The  second   step  is to heat the yarn, which breaks bonds between polymers, allowing the filaments to stay crimped .  The  last step  is to cool the yarn in the distorted state to enable new bonds to form between the polymers. When the yarn is untwisted or otherwise released from its distorted slate, the filaments remain in a coiled or crimped condition.

34. Advantages Higher bulk Greater water absorption Increased warmth Good draping capacity Better air permeability Better dimensional stability Higher covering power Higher hygienic characteristics Pleasing hand and appearance Disadvantages: Increased hairiness Reduced strength and abrasion resistance

35. Methods of texturization Textured yarns can be produced by following methods: ❶ False-twist coiling method ❷ Stuffer-box crimping method ❸ Air-jet texturing method ❹ Knit-de-knit crinkling method ❺ Gear crimping method

36. Heat setting Heat setting is a process of imparting dimensional stability of fibers or yarns with successive heating and cooling in dry and most condition.   In the heat setting operation, the fiber is heated to its glass transition temperature. At this temperature, lateral bonds within the fiber are disturbed and the polymer chains can shift their positions. The fabric is kept under tension until it is cool, to lock this shape into the fiber’s molecular structure. After cooling, the fabric or yarn will be stable to any heat lower than that at which it was set. Higher temperatures may cause shrinkage or other changes. Heat setting may be done at any stage of finishing, depending on the fiber’s heat resistance and end use.

37. Objects of heat setting  To impact dimensional stability.  To remove shrinkage of fabric.  To decrees crease resistance.  To increase elasticity and resiliency . Disadvantages of heat setting  Fiber become very stiff.  Crystallinity increase but dye takes decrease.  Fiber color may be change.

38. Spin finish Spin finish are the lubricants which provides surface lubricating, plasticizing and static protection to man-made fiber. A package, bobbin, or bale cannot be made without application of a spin finish.  It is applied to the yarn in fluid form just before winding. Objects:  To lubricate the filament to control friction  To increase cohesion of the yarn  To reduce static electricity  To plasticize the fabric

39. Glass transition temperature ( Tg ) Glass transition temperature ( Tg ) is an important characteristic that determines the response of the polymer to changes in temperature. The polymers which a glass transition temperature below room temperature are Tg polymers making them elastic in surrounding conditions. At this temperature hard, glassy state converts into a rubbery state . Polymers can be classified into amorphous or crystalline based on their molecular structure. Amorphous polymers have a randomized arrangement of repetitive units while crystalline polymers have an orderly form. At glass transition temperature amorphous go from being hard and brittle to be softer and more flexible. The Tg of a polymer depends on various factors, including the chemical structure of the polymer, the presence of chemical groups, flexibility, etc. The Tg determines the applications of the polymer, including coatings and stretchy materials called elastomers.

40. Glass transition temperature ( Tg )

41. Tm polymer Tm polymer is the temperature at which a solid plastic material changes into a softer, flexible form or a solid amorphous form. The conversion occurs because the bond holding the plastic due to intermolecular force becomes loose or breaks down. The intermolecular forces in Tm polymers are very strong which helps them withstand high temperatures, and resist chemicals, wear, and tear. They are used in a variety of industries because of these properties The value of Tm polymer depends on several factors, including molecular structure, the chemical structure of the polymer, and the crystallinity of the polymer. For example, polymers with long chains and a high degree of crystallinity have higher Tm values because of stronger intermolecular forces and ordered arrangement of molecules in the crystal lattice. They are classified into two categories based on their Tg values i.e. Amorphous Tm polymers ( low Tg values and do not exhibit any crystalline structure) and Semi-Crystalline (high Tg values and exhibit crystalline structure) Tm polymers.

42. Tm polymer

43. Comparison Between Tg and Tm Polymers

44. Factors affecting Tg and Tm Tg is influenced by molecular weight, cross-linking, and degree of crystallinity. This is because due to cross-links the polymer becomes rigid and ordered in structure, hence making it more difficult to convert into a rubbery state. The Tm is also influenced by molecular weight and melting behavior.

45. Polymerisation of Nylon 6 Polymerisation : Nylon 6 is produced by  “ring opening polymerization”  of caprolactam, which has six carbon atoms.  When caprolactam gets heated at about  533 Kelvin temperature  in an inert atmosphere of nitrogen for  4-5 hours, the ring of caprolactum starts to break . The ring opening gets started by water through hydrolysis process. The  growth of the molecular chains gets continued in a nitrogen atmosphere at low pressure. The viscosity of the caprolactum begins to change from fluid to a honey-like state. Thus  hot molten polymer is obtained.

46. Quenching in water: Quenching in water : This molten polymer is  pressed through a type of spinnerets into a water quench, where the polymer gets cooled down and gets a shape of a solid forming a strand. In the granules making machine, these strands of polymer are cut and “granulates of polymer of nylon 6 is manufactured”. The whole reaction follows below chemical equation:

47. Melt-spinning: The spinning of nylon 6 is done by using the “melt spinning”  process. In this process, the polymer gets melted under exclusion of air at a temperature of 250 °C- 270 °C ( 30 °C-50 °C more than the melting point ). For a very homogenous melting process, the polymer is melted in an extruder. The hot and molten polymer is fed to the spinnerets with the help of a feeding pump and extruder. This molten polymer passes through very small holes of spinnerets. “Thus the nylon 6 filament is formed”. On the lower part of the spinneret, the filaments are entered the quench duct. This is a part of 2-4 metres where the still hot filaments are quenched with air. It is very important to keep the airflow very gentle and stable to avoid the filaments sticking together.

48. Drawing During the drawing process, “the filaments are drawn 4 – 5 times of their original length”.  The macromolecules are oriented themselves in the best way during this process. It is the orientation of the highest parallelism which provides the required yarn properties like good tensile strength and tenacity. The drawing is performed on godets , which are heated rotating cylinders, running at different speeds so that the filaments are drawn between the different duos . After this drawing, the filaments (normally between 140 and 280) are intermingled with a continuous air jet. This intermingling tangles the filaments together and allows the customer to work with the yarn easily . The now finished yarn is directly wound on spools. The size of such a spool is about 9.0 kg of yarn. The winding speed in the spin-draw process varies from 2000 to 4000 metres /minute. The fully automatic winders change within seconds from a full to an empty tube to start a new bobbin.

49. Polymerisation of Nylon 6,6 Nylon-66 is a polyamide fibre which is manufactured by a process that involves step growth polymerization and condensation polymerization. The generic term used to define long chain synthetic polyamides is Nylon. One of the key members from the group of poly-condensation products of acids and diamines , Nylon-66 has great abrasion resistance, strength andresistance towards heat, water and chemicals . Manufacturing Process The ingredients i.e. Hexamethylenediamine and adipic acid are combined with water in a reactor. The outcome of this process is the nylon salt which is sent for evaporation which removes any excess water. The nylon salt is then passed through a reaction vessel where a continuous polymerization process makes molten Nylon 6,6. The molten nylon is then passed through a spinning process, with Nylon-66 extruded and sent via spinneret. Once the nylon is air cooled to form filaments.

50. Polymerisation of Nylon 6,6

51. Polymerisation of Polyethylene terephthalate “Polyethylene terephthalate is a condensation polymer of ethylene glycol and terephthalic acid.” The by-product of the reaction is water so it is an example of condensation or step-growth polymerization. On the basis of mechanism, there are two types of polymerization; step-growth and chain-growth polymerization .

52. Polymerisation of Polyacrilonitrile ( Acrylic) Polyacrilonitrile ( Acrylic ) Vinyl Cyanide, more commonly known as acrylonitrile, can under go addition polymerisation to form polyacrylonitrile . Polyacrylonitrile  ( PAN ) :-   Polyacrylonitrile (PAN) is a synthetic, semicrystalline organic polymer resin, with the linear formula (C3H3N)n. Though it is thermoplastic, it does not melt under normal conditions. It degrades before melting. It melts above 300 y if the heating rates are 50 degrees per minute or above.