CONDITIONS OF OBTAINING THE CHEMICAL FIBER
The polymer used must be liquid or must be liquefied. The liquid polymer must be sprayed through the fine holes under constant pressure. There must be an environment where the liquid polymer coming out of the holes can solidify into filaments.
WET SHOOTING METHOD
In the wet spinning method, a solution of the polymer in a suitable solvent is prepared. The prepared solution is conveyed to the spinneret head in a coagulation bath under constant pressure with the help of a suitable pump. The bath with the nozzle head (chemical mixture that solidifies the polymer) is called a coagulation bath. The reason for this is that the polymer coagulates in this bath. polymer solution; It coagulates and precipitates in the same way as it emerges from thin holes in the form of filaments.
The structure of the coagulation bath is prepared in such a way that it turns the polymer from solution to solid. For example, a basic solution of a polymer substance is prepared that is soluble in basic solutions but insoluble in acids. An acidic solution in which the polymer is not dissolved is chosen as the coagulation bath.
DRY SHOOTING METHOD
In order to obtain yarn with the dry spinning method, first of all, a substance with a low boiling point should be selected in the polymer solution, which is easily volatile of the solvent to be used. When this prepared solution is sprayed from the nozzles under constant pressure and into the chambers through which the air flow is flowing, the solvent evaporates quickly. What remains is a filamentous polymer material.
In this method, the solvent to be used is easily volatile, and the economical, easily available, non-flammable type is preferred. If the polymer coming out of the nozzle is affected by hot air, hot saturated steam or hot nitrogen gas is used instead of hot air.
SOFT DRAWING METHOD
Polymers, which have thermoplastic properties and are insoluble in any solvent, are turned into filaments by the soft spinning method. Polyamide, polyester and polypropylene fibers are turned into yarn by soft drawing method.
The molten polymer chips are conveyed to the spinneret with the help of a pump and turned into filament wires. When the filaments come out of the closed area at high temperature, they encounter cold air and solidify. Solidifying fibers do not stick to each other due to this hardness. It is then wrapped together in thick bundles. However, the number of filaments in the bundle varies according to the number of nozzles and the diameter of the nozzle holes. In this process, it is necessary to control the filament diameters. It should be ensured that each nozzle hole of the arrangement is fed properly, and that the filaments coming out of the holes of equal diameter solidify under the same cooling condition. The solidification of the soft filaments coming out of the nozzle should be completed at the end of the first one meter, then they should be collected in bundles with the help of a winding mechanism.
Since the cooling and solidification of the filaments is carried out in a short time and quickly, even if the fiber structures are sufficiently crystallized or even partially elongated during this time, the proportion of amorphous regions does not decrease much. For this reason, since the orientation of the filaments is not strong, the fiber strength is not high either. The necessary physical properties are imparted by subjecting the macromolecules to the stretching process.
Nozzle heads (spinnerets) are heads with one or more holes as large as the diameter of the filament to be obtained. A single filament called “monofilament” or simply “monofil” from a single hole nozzle; A filament called "multifilament" or "multifil" is obtained from a multi-hole nozzle.
TENSION-DRAWN PROCESS
The yarn, which has taken the form of filament, is not yet suitable for use in textiles in terms of its properties. The sudden transition of the polymer from the liquid state to the solid state causes complex arrangement of molecular chains. Stretching is applied to increase the crystalline (regular) regions in the fiber structure and, as a result, to give the filament some necessary properties. As a result of stretching, filaments are elongated 3-10 times (300–1000%) of their length. When the longitudinal sections of the two fibers that have not been stretched-drawn are examined under the microscope, it is observed that the polymer chains in the inner structure are complex and amorphous at first, and that crystalline areas oriented along the fiber are formed after the stretching-drawing process. After this application, the strength of the filament also increases.
MAKING THE TENSION-STRING PROCESS
The stretching process is done by passing the filament between two rollers with different speeds. The filament is placed on both cylinders by wrapping it several times to prevent slipping. The speed (v1) of the roller it is wrapped should be less than the speed (v2) of the second roller. Thus, due to the fact that the second roller is faster, the filament length is drawn in the region between the rollers. This region is called the gravitational zone. The higher the speed of the second cylinder than the first, the greater the elongation. The stretching-drawing process can be done in the cold, as well as in the hot by heating the cylinders or the drawing area.
PROCESS STEPS OF MANUFACTURING AND SYNTHETIC FIBER
In order to manufacture artificial and synthetic fibers, it must go through a certain sequence of processing steps.
EXTRUSION
The extrusion process can be examined in three stages.
1-Transmission of raw material
The raw material chips are fed into the extruder inlet by the conveying system. From here it is poured into the hopper. The level sensor present in the hopper controls the raw material level. The chips transport system is adjusted to keep the amount of raw material at the desired level.
2-Dosing
Before the extrusion process, dye and additives are mixed with the raw material. It is possible to produce yarn in the desired color and tone by measuring both the raw material and the dye at the same time and mixing them in a synchronous manner at a certain rate.
3-Extruder
The granular raw material is transferred to the feeding section by the vacuum system and mixed with the dye in the desired amount and ratio by the dosing unit and given to the extruder. Extruder is the most important part of filament yarn production. This part ensures that the primary polymer chips and additives are melted and reach the viscosity that can pass through the nozzles. The temperature required to melt the polymer chips in the extruder may vary depending on the fiber type used. In the extruder section; hive, funnel, screw in the hive, motor and heaters that provide screw movement. The funnel is connected to the feeding zone of the screw. The granular raw material coming to the funnel is taken from the feeding area of the screw by the rotation of the screw and pushed towards the level.
The melting process in the extruder is done in several stages. The polymer is melted first, then cooled a little by means of fans, if necessary, to adjust the temperature and viscosity, and in the last step, the polymer reaches a viscosity that can pass through the nozzles. It is ensured in the extruder that the melt of a certain viscosity can enter the nozzles and that this viscosity is stable. In order to obtain the desired quality melt from the extruder, it is possible to keep the temperature of the molten polymer in the desired range.
METAL DYEING
Colorant and necessary additives are mixed with polymer chips into the extruder. This mixture should be in a certain proportion. The filament obtained at the exit of the extruder is dyed. In this way, the dyeing process when it is in the form of granules is called dyeing in the melt. If dyeing is not done in the melt, the fiber is produced as transparent (colorless). If it needs to be colored, it is painted later. Melt dyeing is an optional process. However, some polymers (such as polypropylene) can only be dyed in a melt state. Polypropylene cannot be dyed into yarn or fabric. While the polymer is in melt, some additive chemicals are added to help both the dyestuff and the end use of the yarn. This mixture is called masterbatch. Dosage adjustment takes place between this masterbatch material and raw material chips.
FILTRATION
Before the molten polymer reaches the level, it is passed through a series of filters. Thus, foreign substances (all kinds of particles, gels, etc.) that may be present in the molten polymer are separated before they reach the level.
If these impurities pass through the filters without being sieved, they will either clog the nozzle holes or settle into the fiber and reduce the performance of the fiber in later processes. Therefore, the melt passing through the extruder is separated from foreign materials by passing through filters before it reaches the nozzles.
FLAMENT FINISH AND FLOATS
The most sensitive step in the filament production system is the passing of the molten polymer through the nozzles. In this part, which is the last stage of filament production, the polymer melt that has passed through the extruder is sent to the filament production heads (nozzle blocks) at a certain temperature and pressure. The polymer coming out of the nozzle is a liquid mass that has not yet acquired the quality of a yarn and flows at a very high temperature. This liquid is sprayed into a medium where it can solidify. Looking at the nozzle plate, it is seen that there are many holes in its structure. The number of holes in the nozzle plate is one for mono filament production. The number of holes in the nozzle for filament yarns is usually between 10 and 150. In tow production, which is the beginning of staple fiber production, there are tens of thousands of holes in the nozzles. Usually nozzle holes are round holes. In this way, a round fiber cross-section is formed. However, specially shaped nozzle holes are also used.
COAGULATION ( SOLIDING )
The polymer melt sprayed at a certain temperature and pressure in the nozzles is transmitted to an environment where it solidifies. Solidification is done in various ways. These; hot steam, cold air or coagulation bath methods. The liquid mass that comes out of the nozzles by flowing at a very high temperature is solidified in this section and turned into a filament. The solidification process of this liquid mass critically affects the strength and elongation properties that the yarn will gain.
TENSION-TOUCH
After filament production; It was observed that the ratio of unoriented amorphous regions in the fiber was high. Stretching is performed to increase the crystalline regions in the fiber structure and, as a result, to provide some necessary properties to the filament. With the stretching-drawing process, the ratio of the amorphous region decreases and the ratio of the crystalline region increases. Thus, the brightness, tensile strength and flexibility properties of the fiber increase. In addition, a certain number of yarn is obtained.
Stretching – pulling process is carried out between the rollers rotating in the same direction. While the filament taken from the nozzles is conveyed to the texturing area, stretching - drawing is done by means of rollers (godet). The filament is passed between rollers of different speeds. These cylinders are at a certain distance from each other and the speed of the 2nd cylinder is higher than the 1st cylinder. In this way, draft occurs due to the speed difference between the two cylinders. The drawing process can be done hot (such as polypropylene) or cold (such as polyamide 6,6). Thanks to the speed difference between the rollers and the heat given to the rollers, the stretching - pulling process of the filament is completed. The stretching - stretching zone can consist of 2 or 3 zones depending on the machine structure used.
LUBRICATION AND ANTI-STATIC TREATMENT
During the processing of the fiber; Lubrication is required in order to prevent fiber abrasion by reducing fiber-to-metal friction and providing a smooth and low tension. The filaments are lubricated just after the point where they meet to form yarn. The lubrication process is carried out with spin-finish oil. Spin-finish oil consists of a special mixture of antistatic, bactericidal and anti-corrosion substances. Spin – finish oil; It can also be defined under names such as preparation oil, finishing oil, protection oil, spin finish. Spin-finish oil can be given in pure form or by forming an emulsion with water. It can be applied by contacting the film layer formed on the surface of a rotating roller with the yarn, or by contacting the yarn with the oil dosed to the guide while passing through a guide. filaments; After it is first converted into yarn and then into fabric, the task of the spin-finish oil is completed. It is often washed away just before the yarn or fabric is dyed.
The properties gained by lubrication can be listed as follows.
1-It increases the adhesion of filaments to each other.
2-It prevents the fibers from being damaged by reducing friction.
3-Reduces static electricity.
4-It reduces the number of yarn breaks.
5-Improves the dye distribution on the yarn.
6-By preventing bacterial growth, it ensures the longevity of the filament.
7- It works more efficiently at high shooting speeds.
MATTING
It is the process of reducing the natural shine of chemical fibers on demand. For this, white pigments such as titanium dioxide are used. By adding these substances to the polymer solution, it turns dull. It has a very high wet fastness in contrast to post matting.
CURVING
The filament cable, which goes through the drawing process and is lubricated, comes to the texturing process. This process is the curling process in order to give the yarn the necessary volume and flexibility. Texturized with the process of breaking; It is applied to synthetic fiber by many methods. In filament yarn production; Stacking box and air-jet texturing methods are generally used in one-step systems available on the machine and applied after stretching. In the texturing process with the stacking box, the yarn is conveyed to the texturing chamber heated by steam or hot air. In this part, the yarn is curled and ejected with compressed air. The crimped yarn comes to the cooling drum and is properly cooled. It must provide a constant inlet tension to the filament in the texturing unit, keep the temperature constant during the process, and curl each filament individually. In addition, the yarn should be taken from the texturing unit with a certain tension and this yarn should be cooled.
In the polypropylene yarn production technique called BCF (bulked continuous filament), an air-jet texturing unit is used. The yarn is brought to the required heat by air and texturized.
Air is delivered to each texturing jet through a separate channel. With the help of thermostats located at the entrance of each jet, it is ensured that the air temperature is kept constant at all times. With an additional second heater, thermal continuity of all jets is ensured during the texturing process. This makes it possible to texturize high-quality yarn instantly after a production interruption.
FIXING
Fixation can be applied to the yarn during filament production as well as after yarn production. Fixing; It is the process of gaining dimensional stability with moist or dry heat. Fixation can be applied to all kinds of textile materials. However, it has a special importance in the processing of synthetic fibers. Because processes such as bending and drawing applied to thermoplastic fibers during production cause deformation in intermolecular bonds. Deformation of the bonds creates strain resistance on the bent filament. However, if this resistance is removed, the filament tends to return to its original state. The most crucial point of the texturing process is fixation. During this process, the yarn should be heated to the softening point, the tensions between the filaments should be allowed to be reduced and relaxation should be ensured. The internal tensions of the fibers made of thermoplastic materials by fixation are relieved by heat. The textured filaments are wound on bobbins after the fixation process. However, in some filament production systems, centering, winding and twisting processes are performed before fixation. After these processes, the fixation takes place in a separate machine. First of all, the processes of centering, winding and twisting applied before the fixation process will be explained only in the production of yarn from polypropylene (BCF) polymer, and then the fixation methods used in the fixation process of all synthetic yarns will be explained.
STITCHING
A little twist should be given so that the filaments, which have gained the necessary volume and softness by texturing, can come to a full yarn form. In BCF (PP) yarn production technique, the required cohesion is gained to the filaments by centering instead of this twisting. The purpose of centering is to intertwine a filament bundle at certain points and in this way to obtain a collective yarn structure.
WINDING
The yarn coming out of the centering is now ready to be wound. The last part of the BCF yarn manufacturing machine is the yarn winding process. The winding speed is also the production speed. The yarn winding process should create a perfect package without changing the textile properties of the yarn. Fully automatic winders are used in BCF yarn production technique. Errors are minimized by making the winding fully automatic. The efficiency of the bobbin winding part determines the efficiency of the BCF spinning machine. Since modern filament yarn production systems operate at ever-increasing speeds, bobbin change times must be short and bobbin changes must be carried out at more frequent intervals. This requires very fast manual replacement or as advanced automation as possible.
TWIST
If the yarn coming out of the BCF yarn production machine as a bobbin will be used as carpet yarn, the twisting process should be applied. Generally, centering of the yarn on the BCF machine is not sufficient to give the yarn the necessary cohesion. Two – for – one twisting machines are generally used for polypropylene BCF carpet yarn. Depending on the fineness of the yarn (tex-denier), it is given a twist of 80 or 150 twists/meter. Two or more yarns produced can be twisted together here.
FIXING METHODS
After the yarn is twisted, it is requested that the yarn maintain this twist. This can only be achieved by the fixation process. The fixation process is generally applied in two different ways.
SATURATED STEAM TECHNIQUE
With the saturated steam technique, the filament is safely brought to the softening temperature. The working principle of the machine that fixes with the saturated steam technique is as follows. The yarns are taken from the creel and laid on an endless conveyor belt made of perforated stainless steel without tension by the spreader head. As a result of this process, the filaments will pull freely and proper and regular crimp will be obtained on the yarn. Then the yarn passes through the cooling unit and enters the fixing tunnel. In the fixing tunnel, the yarn is treated with pure saturated steam and high temperature (150oC). It is subjected to a thermal shock that completely fixes the twist of the yarn and affects its twist and molecular structure. The fixed yarn layer passes through the cooling device and accumulates on the accumulator before winding. The yarns are separated from each other and wound into conical or cylindrical bobbins in the winding machine. Thus, waiting times during yarn breakage or doffing are eliminated.
HOT AIR TECHNIQUE
In this method, which is the second method, hot air or superheated steam is used for the fixation process. When hot air or hot steam is used, the temperature required for the fiber is exceeded. Since the softening point of polypropylene is extremely low (130oC), it is extremely sensitive to high temperatures. In the use of hot air, temperature fluctuations of the air should not exceed 5oC. Because the working temperature is close to the decomposition point (140oC). The usage area of PP is based on carpet yarn. With the fixation process, the abrasion resistance, dimensional stability, paint adhesion and surface unevenness of the carpet are improved.
POLYMERIZATION REACTIONS
Polymer; It is a large molecular chain that occurs as a result of the combination of individual molecules. Each of the molecules that come together to form a polymer is called a monomer. The degree of polymerization refers to the number of repeating units or monomers in a polymer chain. In order to determine the molecular size of the polymer material, the degree of polymerization must be known. Fiber is the result of a polymerization reaction and is formed by the synthesis of various chemical substances. First, a polymer is formed by one of the polymerization reactions, and then fiber is obtained from these polymers. Fiber is produced from synthetic polymers. Synthetic polymers are obtained as a result of three reactions. Examples of polymerization reactions that provide synthetic polymers and fibers produced from polymers obtained by these reactions are given. This table can also form the basis for the grouping of man-made fibers.
POLYMERIZATION
It is a reaction that occurs by the formation of active centers that are not present in the monomer. Polymers are obtained by combining monomers from the active centers formed. Polyacrylonitrile, polyvinylchloride, polyvinylidenechloride, polyvinylalcohol, polyolefin, polytetrafluorethylene etc. It is used to obtain the polymers from which the fiber is produced.
POLYADITION
It is a polymerization reaction in which a molecule containing a double bond is added to another molecule. Polyurethane etc. It is used to obtain the polymers from which the fiber is produced.
POLYCONDENSATION
These are reactions in which monomers have at least two reactive groups and as a result, a low molecular weight compound (water, ammonia, etc.) is released. Polyester, polyamide 6,6 polyurethane etc. It is used to obtain polymers from which fibers are produced.
