With the development of synthetic fibers, the production of very fine fibers has become possible today. The importance of microfibers, which are much finer than conventionally produced fibers, is increasing with the physical and comfort properties they provide. The production methods of microfibers, which are mostly produced from polyester, nylon, polypropylene, acrylic and viscose, have been developed and have found many uses.
The development of microfibers started in Japan in the 60s. The first microfiber was created by Toray Industries, a chemist in the Textile Research Laboratory of Dr. It was introduced by Miyoshi Okamoto in the mid-1960s in the form of a suede-like leather material.
Microfiber production is carried out by companies such as Asahi, Kanebo, Kuraray, Mitsubishi, Rayon, Toray, Teijin, Du Pont, Lenzing.
The most produced man-made microfibers consist of polyester, nylon, polypropylene, acrylic and viscose. Depending on the purpose of use, microfibers are produced in the form of continuous filaments or staple staples. Compared with conventional fibers, microfibers provide fabrics with a luxurious appearance, improved physical and handling properties, and a high level of wearing comfort. Therefore, there has been an increasing trend towards microfibers in recent years. Microfibers are widely used in many areas such as high quality clothes, evening dresses, sportswear, home textiles, industrial products.
In defining the term microfiber, the fiber diameter or filament number in dtex or denier is generally taken into account. Accordingly, fibers in the range of 0,1-1,0 dtex are defined as microfibers. Fibers thinner than 0,1 dtex are called super microfibers.
Microfiber is 40 times finer than wool, 30 times finer than cotton, and 10 times finer than silk.
Microfiber production is divided into two as continuous filament and staple fiber.
1-CONTINUOUS FLAMENT (CONTINUOUS) PRODUCTION
Continuous filament production method;
- A-Direct fiber spinning (conventional fiber spinning)
- B-Bicomponent shooting method
It is carried out in 2 ways.
A-Direct fiber spinning method (conventional method)
As is known in conventional fiber spinning, the polymer is pressed into either gas (often air) or solution and then drawn. Before the polymers are passed through the nozzles, they are either melted or turned into solutions. Sending the polymers to the nozzles by melting is defined as pulling fiber from the melt, and using the polymer solution is defined as pulling fiber from the solution. In the production of microfibers, the method of drawing fiber from the melt is generally used. When the conventional drafting system is applied for microfiber production, problems such as fiber breakage, change in filament thickness, nozzle clogging and denier variability between filaments in the yarn arise..
Therefore, in order to eliminate these problems, researchers named Mukhopadhyay and Nakajima considered the following issues for microfiber production.
Optimizing polymer viscosity (high shrinkage temperature reduces viscosity)
Optimizing the nozzle design (arranging the nozzle holes to give homogeneous cooling)
Optimizing the ambient temperature under the nozzle (controlling the cooling rate)
Proper splicing of filaments (assembly closest to level)
Optimizing the fiber draw (controlling the spinning tension)
Low speed shooting (smooth polymer delivery)
Ensuring that the polymer is pure (high degree of filtration)
- shooting head
- nozzle system
- polymer melt
- spinning head insulation
- thermal insulation plate
8.thermal solidification zone
- shooting line
- pull column
- lubricating roller
- delivery cylinder
- heat insulation plate
- air vent plate
Unica Co. It is the first company to produce microfibers in the 0,3-0,5 denier range. Asahi Chemical Industry Co. The firm then developed a finer micro polyester fiber in the 0,1-0,3 denier range by optimizing the polymer melt viscosity, the nozzle design, the ambient temperature under the nozzle, and the way the filaments are brought together. Unica Co. In order to produce microfibers finer than 0,3 denier, the company brought the polymer melt viscosity to 950 poise, the cross-sectional area of the nozzle holes to 3,5 10 cm, and the ambient temperature 1-3 cm below the layout to 200 ºC, and the drawn filaments were 10-20 cm below the layout. gathered together. Asahi Chemical Industry Co. To produce polyester microfiber finer than 0,15 denier, the company uses the polymer melt viscosity as 480 poise, ( poise: absolute unit of viscosity )
It brought the cross-sectional area of the nozzle holes to 1,0 10 cm, the ambient temperature 1-3 cm below the arrangement to 150 ºC, and gathered the drawn filaments 20-70 cm below the arrangement. The direct spinning method is advantageous in that it is simple, easy to control, and does not require complex post-drawing processes such as separation of two components or removal of the second component.
B-Bicomponent shooting method
Bicomponent shooting method;
- island in the sea,
- Multi layered
It is carried out in 3 ways.
1-Island method at sea
The island type in the sea is formed by drawing fibers using the bicomponent method of two components that cannot be mixed with each other.
As one polymer creates a sea, the other polymer is fed into it. In this case, part of the fibers is the island component and the other is the marine component. Micro-denier filaments are formed by dissolving the marine polymer after the fibers are turned into fabric. Therefore, the spinning and fabric forming processes are the same as for standard single polymer fibers.
As can be seen from the figure, the polymer stream consisting of two components is combined to form a single stream.
Polymer streams consisting of two components determine the thickness of the obtained filaments. The number of filaments after drawing varies between 2-5 denier (12-20 micron). After the marine polymer is removed, the remaining island polymer fibers have a diameter of 100-800 nanometers. The island component usually consists of polyester. Nylon, polypropylene and polyethylene are also other polymers used in island components. Marine polymer, on the other hand, consists of water-soluble polymers such as PVA or copolyester. Although the island-in-the-sea method requires additional costs, it is successfully applied in the production of suede type synthetic leather products. This method is also used in fine filters and cleaning cloths. The number of islands in the very fine multifilament yarn depends on the nozzle design. The ratio of the island component to the sea component is determined by the gravity of each component. In previous years, 24 and 32 island fibers were produced and these fibers were used in products such as ultra suede and artificial leather. Today, mostly 64 island fibers are used commercially. Hills Inc. His firm later increased the number of islands in the fibers up to 600 and 900.
Above Hills Inc. The cross sections of 25, 37, 64 and 600 island fibers produced by the firm are shown. The island makes up about 80% of the fiber, and the sea makes up about 20% of the fiber. Island filaments become square if they exceed 65% of the mass of the island polymer.
2- Separation method
It is one of the oldest methods used in microfiber production. In this method, two different polymer fibers that do not mix with each other are arranged in the form of cake slices or triangular prisms. The difference of the separation method from the island method in the sea is that instead of removing the second component by thawing, the second component is included in the fiber like the first component. Fibers are generally produced from PET and nylon. Recently, copolyester fiber has replaced nylon fiber. Polyamide/polyester or polyester/polyolefin are also preferred combinations. Fibers produced according to the separation method are used in artificial leathers, cleaning cloths, silk-like fabrics and the production of water-proof fabrics with high air permeability due to their good drape, softness, bulkiness, smoothness, aesthetic and comfort properties when compared with conventional polyester fibers. According to the separation method, fiber formation takes place by various methods. Generally, in these methods, the polymer components are streamlined. Then, the fibers are divided into sections in the form of cake slices by various mechanical or chemical processes to form the microfiber. Since polymers have different properties, they are divided into two components by swelling, shrinkage and mechanical stresses that occur after shrinkage and solidification.
Methods applied according to this principle
In the first method, composite fibers with two separable polymers are first formed, then the fiber is treated with benzyl alcohol or phenyl ethyl alcohol to separate these combined fibers.
In the second method, splittable composite fiber is formed again, the separation process is carried out mechanically with hot aqueous solution or in dry condition.
Hills Inc. Using this technique, his firm produced yarn with 2-4 denier filaments. In fabric form, a moderate caustic (NaOH) solution was applied to the fabric to separate the fibers.
In the third method, the combined fibers are needled hydraulically or mechanically to separate their cross-sections. Very fine fibers are made with specially designed nozzles in the form of “*” and “+”. Components are divided into 3 sections with a “+” shaped nozzle. The number of sections has been increased with the "*" shaped nozzle. The "*" shaped cross section of the fiber produced according to the separation method is shown below.
As can be seen in the figure, the fiber is divided into 8 triangular sections in the form of a pie slice. The fibers can be divided into various numbers of triangular segments. 16 and 32 slices are commonly used slice numbers. After separation, most of the filaments have a size of less than 0,1 denier. Fibers consisting of nylon and polyester are commonly made in 16 parts. Nylon is used at a rate of 10-15% and polyester at a rate of 80-85% due to cost.
3-Multilayer type (Side-by-side bicomponent fibers)
Two incompatible polymers are sprayed simultaneously from a bicomponent nozzle, forming different layers side by side parallel to each other. The appearance, handling and physical properties of textile products produced from these fibers vary according to the appropriate choice of polymer type, cross-section and proportions of the two components. Polyester and nylon are commonly used. Composite fiber consisting of polyester and nylon 6 is then split into 0,2-0,3 denier filaments.
2- PRODUCTION IN STAP FIBER
The production of microfibers in the form of staple fibers is made using nonwoven surface production methods.
C- Endless fiber spreading (spunbond)
D-Polymer blended spinning (polymer blend spinning)
It is carried out in 4 ways, including methods.
A-Method of melt spraying
The most important feature of the melt spray method is that the melted polymer is drawn with a high speed hot air flow for the formation of microfiber web..
In this method, the polymer is first melted in the extruder, passes through the filtration steps and then comes to the fiber spinning heads with a pump. Here, the molten polymer ejected from the nozzle is directly exposed to the high velocity hot air at the nozzle of the nozzle.
In this way, fiber-air mixture is formed. Depending on the melting conditions, fiber shape and temperature, fiber spinning is carried out with air at a speed of 6000-30000 m/min.
To draw fibers at high temperature, the air temperature is adjusted according to the melting temperature of the fibers. In the next step, cold air is applied. The cold air mixes with the hot air and the polymer solidifies. The thinned fibers eventually fall on the collector located at the bottom and form a cheesecloth. Fine fiber construction requires a very low viscosity of the polymer melt at the exit of the spinning head. Therefore, the viscosity of the molten polymer is lower than that of the conventional polyester used in the melt drawing method. High melting temperature causes low viscosity. Air velocity and air temperature largely determine fiber properties and web quality.. Today, the melt spraying method is widely used in the production of microfibers. Its biggest advantage is to produce very fine fiber at high speed without the need for a very fine nozzle. It is widely used in products that require filtration, hygiene and absorbency. With this method, it is possible to produce fibers with diameters less than 1-5 nanometers. The strength of the fibers produced is low. Fiber diameters vary greatly along and between fibers. Another disadvantage of this method, which can provide the opportunity to create a textile surface directly from the polymer, is that the production equipment costs are very high.
B-Flash Spinning Method
In this method, the polymer is first dissolved in a solvent under high temperature and pressure. The temperature here must be above the boiling point of the solvent. The polymer solution is then sprayed into an area under lower atmospheric pressure. In this way, the solvent evaporates, leaving a pile of fibers. The resulting fibers consist of fine fibrils that are connected to each other in the form of a 3-dimensional network.
The fiber fineness to be obtained with this technology varies between 0,01-10 denier. It is generally produced with an average of 0,1-0,15 denier. The filament cross-section is not circular and the fibers formed have a microbubble structure. This process also provides the production of fine fibers ranging from 0,5 to 10 nanometers. This technology was discovered accidentally by Du Pont while investigating the explosive behavior of organic solvents.
C-Endless Fiber Laying Method
The general endless fiber laying method is based on the principle of forming a web consisting of continuous filaments and then bonding the fibers by mechanical, thermal and chemical means.
The endless fiber laying method is generally similar to the melt spraying method. In the endless fiber laying method, the filaments are drawn with an air jet. It is also possible to draw the filaments with rollers instead of an air jet. With the conventional endless fiber laying method with normal denier value, microfiber formation is also possible. The fineness of filaments composed of microfibers is 0,5 denier or finer. Various types of polymers can be used to form the filaments. These polymers include polyethylene terephthalate (PET), polyolefin, polyphenylsulfide (PPS), and polyamide. Polymer combinations are also used for various purposes.
Ç-Polymer Blended Spinning Method
In this method, bicomponent fiber is produced by mixing and drawing two polymer melts. Dispersed and non-dispersed (matrix) components are determined by looking at the mixing ratios of the components and their melt viscosities.
Conventional fiber spinning system can be converted to polymer blended fiber spinning system by adding a mixer. Although the fiber spinning stability is completely dependent on the polymer components, the fiber fineness produced by this method cannot be controlled and the fibers are easily broken during production. It is not possible to produce a continuous filament type with this fiber spinning method, since the polymer is drawn in the form of microfibers at the disperse stage.
PROPERTIES OF MICROFILES
1-Microfibers are finer than many natural fibers. For this reason, the fine structure of microfibers greatly affects the properties of the yarn and fabrics obtained.
2-Due to its fine fiber structure, products made from microfiber contain more fiber or filament compared to products made from standard fiber. For this reason, the products made of microfiber show soft, smooth and voluminous properties.
3-Due to the high number of fibers, the products with microfibers have a higher surface area. The high surface area makes the fabrics obtained from microfiber brighter.
(The tensile strength and bending stiffness of a fiber are highly dependent on the fiber diameter. Therefore, the small diameter of the microfiber greatly influences the tensile strength and bending stiffness properties of the microfibers).
4-Microfibers have low resistance to bending due to their small diameters. As the fiber diameter gets smaller, the moment of inertia, which varies in direct proportion to the fiber diameter, decreases, and as a result, the bending deformation increases, the bending resistance of the microfibers decreases.
5-Low bending strength of microfibers ensures better draping of fabrics produced from microfiber.
6-The strength of yarn and fabrics obtained from microfiber is high.
7-The fact that microfiber fabrics contain more fibers reduces the gaps between the fibers, thus ensuring that the resulting fabric structure is tighter.
While the tight fabric structure prevents the wind from entering, it prevents body heat from coming out of the clothing.
8- Fabrics made from microfibers have cold, wind, rain and waterproof properties.
9-Microfiber fabrics allow the passage of water vapor although they are water repellent.
10- The water vapor permeability feature ensures that the microfiber fabrics are hygienic. Therefore, microfiber fabrics have antimicrobial properties. At the same time, microfiber fabrics absorb more water than 7 times their own weight.
11-Microfiber fabrics are prone to form mixtures with other materials.
12- They have the features of being easy to wash and dry clean.
13-Thermal conductivity of microfiber fabrics is higher.
In the study examining the properties of knitted fabrics obtained by using microfiber modal viscose and conventional modal viscose, microfiber modal knitted fabrics showed higher thermal conductivity values than conventional modal knitted fabrics. The reason for this is that fabrics containing microfibers contain less air and more fiber. As is known, the thermal conductivity of air is lower than the thermal conductivity of fiber.
USAGE AREAS OF MICROFIBER FABRICS
Cleaning cloths that do not contain microfibers generally carry dirt and dust from one place to another without taking them in. On the other hand, microfiber fabrics take the dirt from the surface and keep the dirt in the fabric structure until they are washed. In addition, they can be cleaned with just water without the need for any chemicals.
The surface area of the microfibers is 10 times higher than the fiber with normal fineness. In addition, the small diameter of the fabric provides a high degree of absorbency.
Microfiber fabrics attract the liquid as well as the microbes and particles in the liquid. For this reason, the increased surface area and absorption properties allow the microfibers to absorb liquid up to many times their own weight. Since the thinner fiber provides more fibers per square centimeter, more fibers come into contact with the surface to be cleaned. In this way, faster and more efficient results are obtained. In particular, the microfibers obtained according to the separation method hold the dirt on it more easily.
When polyamide is used in microfiber production, microfiber gains a positively charged feature. Most dirt and dust particles, bacteria, pollen, rust on metal etc. is negatively charged. This feature allows the microfiber to attract negatively charged particles.
High fluid transfer, high elasticity and body fluidsDue to its ability to camouflage the undesirable odors of cotton, microfibers are used in the manufacture of sick diapers, sanitary pads and baby diapers.
Fabrics made of microfibers are used in wound care as they have very good breathability. The cross-section of the microfibers is mostly triangular, with sharp edges and diameters close to nanometers. The diameter of any bacteria is 2-5 nanometers. Therefore, the small size and structure of the microfiber allows the fiber to penetrate under bacteria or microbes smaller than the fiber and largely removes them from the surface. In addition, to increase performance, microfibers are mixed with polyester fibers at a ratio of 50/50 in woven fabrics and 70/30 in knitted fabrics.
Especially non-woven surfaces are used in medical textiles. Microfiber nonwovens have lower cost, easier use, safer and disposable properties compared to other textile surfaces. For this reason, microfiber nonwovens are used in protective masks, surgical gowns, gloves and bedding.
Microfiber fabrics are mostly used in high quality evening dresses due to their thin structure, draping, soft and silk-like handle.
Natural leathers are very popular with their beautiful appearance, softness and high water absorption and porous structure that allows water vapor to pass through. On the other hand, they are found in small quantities in the market due to limited resources, excessive cost and awareness of animal protection.
With the discovery of synthetic fibers, very thin filaments produced by the Japanese were first used in synthetic leather and nonwoven fabrics, upon the request of obtaining very fine fibers. In particular, microfibers produced according to the island method in the sea are widely used in the production of artificial leather..
Today, synthetic leather production is produced by impregnating microfiber nonwoven surfaces with PET, PA or PAN with polyurethane (PU) material.
Synthetic leather is better than natural leather in terms of soft handle, resistance to wrinkles, elongation at break and strength, air permeability, water absorption and easy maintenance. Synthetic leather has low dye fastness due to the high surface area of microfiber.
Thanks to its fineness and tight structure, microfibers offer an excellent filtering effect for air and liquid filtration.
Regardless of the known microfibres, products made from ultrafine microfibres, for example nonwovens made of 0,05 dtex polypropylene, attract and absorb charged dust particles together with a high electrical voltage that ensures permanent polarization.
Microfiber liquid filters have features such as high liquid passage rate, high filtration performance that keeps micro-sized particles and easy cleaning of micro-particles from the filter.
Separable synthetic microfibres increase the performance of the filtration material. In particular, the selection of two different polymers in split fibers creates turbo-electric properties under current conditions. The two polymers can be electrostatically charged in the first step to increase their filtration properties.
Heat exchangers produced using metal-coated microfibers provide radical savings in energy consumption. This is due to the heat conduction property of microfibers. As the number of metal-coated microfibers increases, heat transfer increases. In addition, the pressure drop increases with the number of metal-coated microfibres. The heat transfer feature of the heat exchangers has been improved by using metal-coated microfibre inside the heat exchanger tubes.
Composites are multi-layer materials formed by combining layers with different properties. Composites are obtained in order to provide a better use of these different layers. Polypropylene and bicomponent microfibers are very important components for fiber reinforced composites. Because they are used not only as a reinforcement element, but also as a binder. Various composites such as polypropylene and bicomponent microfiber reinforced concretes (for reinforcement and prevention of cracking), insulation materials (to prevent the use of chemical binders), multifunctional liquid transport materials (layer acquisition and distribution), woven fabrics (as a dimensional stability net) and coating products. are used in materials.
Polypropylene and bicomponent (PP/PE) microfibers have the ability to impart structural performance and functionality to composite materials and provide the following advantages in fiber-reinforced composites:
They allow the formation of low-weight structures.
They enable the production of thermoplastic structures that are easy to process and environmentally friendly.
They show high mechanical properties, hardness and impact resistance. They provide stability in solid environments.
They give the composite material size and softness.