13. The Non-woven Fabrics.pdf

Textile Institute of Pakistan, Karachi. TEXT202 (Fabric Technology) What are Non-woven Fabrics? Non-wovens are produced directly from fibres without the need for making yarn. Non-woven fabrics can be produced at a very rapid rate of production. Bec...

Textile Institute of Pakistan, Karachi. TEXT202 (Fabric Technology) What are Non-woven Fabrics? Non-wovens are produced directly from fibres without the need for making yarn. Non-woven fabrics can be produced at a very rapid rate of production. Because of a short and simple process and a high rate of production, non-wovens can be produced very economically. Fibres which cannot be used for a yarn formation can be utilized to make non-woven fabrics. Layered composite non-woven fabrics can also be formed. Formation of Non-woven Fabrics To create a non-woven fabric: o First, a web is made either from staple fibres or continuous filaments using the following web formation techniques: Wet-laid Dry-laid ▪ Parallel-laid ▪ Cross-laid ▪ Air-laid or random-laid Melt blown o Then the web is strengthened by using one of the four following bonding techniques: Adhesive bonding ▪ Saturation bonding ❖ Nip padding ❖ Lick-up padding ▪ Spray bonding ▪ Print bonding Mechanical bonding ▪ Pressed felts ▪ Needle felts Thermal bonding Stitch bonding Classification of Non-woven Fabrics Prepared By: Shakeel Ahmad Paracha Page 1 of 7  Textile Institute of Pakistan, Karachi. TEXT202 (Fabric Technology) Web Formation Techniques Wet-laid The wet-laid technology of making non-woven fabrics is based on paper making. In this method, the fibres are suspended in water to create a slurry. The suspension is then filtered on a screen to form a mat or web on the screen. The water is then removed by suction or squeezing, and the mat of fibres is dried. The mat of fibres is then compacted and bonded together using different bonding techniques. Dry-laid In the dry-laid web forming technique, the fibres are opened, blended and cleaned and are then taken into a web form. The machine line used for dry-laid webs is similar to a typical short staple spinning system and includes a series of opening machines and a carding machine. Depending upon the required thickness of the non-woven fabric, several webs produced by carding machine are laid on top of one another and are bound together by some means to form a fabric. Depending upon the way the dry-laid webs are formed and combined, the dry-laid web forming technique is further classified as: o Parallel-laid o Cross-laid o Air-laid or random-laid Parallel-laid Prepared By: Shakeel Ahmad Paracha Page 2 of 7  Textile Institute of Pakistan, Karachi. TEXT202 (Fabric Technology) Cross-laid Air-laid or random-laid Melt Blown In this method, the polymer is extruded through the spinneret and is then sprayed using hot gas or air on to a vacuum belt. The fibres are then bonded together to form a sheet of fabric employing thermal bonding using calendar rollers. The fibres can also be deposited on a web formed by the dry-laid process to form a composite material. This method can give a very fine non-woven fabric suitable for filtration and absorbent purposes. Bonding Techniques Adhesive Bonding In this method, the textile material composed of a web or batt of fibres is bonded together by means of some adhesive materials. Prepared By: Shakeel Ahmad Paracha Page 3 of 7  Textile Institute of Pakistan, Karachi. TEXT202 (Fabric Technology) After applying the adhesives to the web, it is necessary to cure the adhesives by heating or blowing air. Adhesive bonding is further classified as: o Saturation bonding o Spray bonding o Print bonding Saturation Bonding In saturation bonding, the web of fibres is passed through a trough containing adhesive. The excess of the adhesive solution is squeezed off between rollers nip. Saturation bonding can be applied in the following two ways: o Nip padding o Lick-up padding Spray Bonding In spray bonding, the adhesive is applied to the web in the form of droplets being sprayed from spraying nozzles. The adhesive is showered on the sheet in a separate spraying chamber with the help of air. The spraying nozzles are reciprocated in the machine direction to prevent any streaking on the fabric. Suction can also be applied beneath the web to help the drops of adhesive to penetrate the web sheet. Print Bonding In print bonding, just like regular colour printing of fabrics, the binding agent is applied intermittently over the surface of the web in the form of some design. Prepared By: Shakeel Ahmad Paracha Page 4 of 7  Textile Institute of Pakistan, Karachi. TEXT202 (Fabric Technology) Since, the print bonding technique does not entirely cover the surface of the fabric, it leaves the fabric softer and more flexible as compared to saturation or spray bonding. The adhesive or the binder is applied to the web either from a rotary screen or engraved print roll. Colour binders can also be used to print designs along with the binding of the fibres. Mechanical Bonding In mechanical bonding, the web of fibres is bound with each other by the entanglement of protruding fibres present on the surface of the webs using mechanical techniques. Mechanically bonded fabrics are usually given an additional thermal bonding treatment. Two main types of mechanical bonding techniques are: o Pressure felting o Needle felting Pressed Felts The fabric simply known as felt was produced about 4000 years ago by the Chinese by the process of pressure felting. In this method, conventionally wool fibres are used which are treated with moisture, heat and mechanical pressure. This causes the fibres to get entangled with each, and the individual fibres cannot slip back forming a fabric. Man-made fibres cannot be used to form pressed felts. However, a blend of wool and man- made fibres can be used to create such a fabric. Prepared By: Shakeel Ahmad Paracha Page 5 of 7  Textile Institute of Pakistan, Karachi. TEXT202 (Fabric Technology) Needle Felts Fibres other than wool can be converted into a felted fabric by mechanical entanglement of the fibres using barbed needles. Such a fabric is called as needle felt. A series of needles are mounted on a board or frame called as needle board. The needles are driven down into the web of fibres and are withdrawn. In this way, each barbed needle punches the fibre, entangling them together to form a needle felt fabric. Barbed Needle Needle Loom Thermal Bonding In thermal bonding, a web of fibres is created by mixing it with a melt-able material. Thermal bonding is achieved by heating the fibre web until the material melts down and becomes adhesive and then the web is cooled down to hold the fibres together. For bonding material either adhesive is mixed with the fibre web in the form of powder or thermoplastic textile fibres can also be used. During thermal bonding, pressure can also be applied. For heating the fibre web, various techniques can be used as shown below: Powder thermal bonding Prepared By: Shakeel Ahmad Paracha Page 6 of 7  Textile Institute of Pakistan, Karachi. TEXT202 (Fabric Technology) Stitch Bonding In stitch bonding, the webs of fibres are held together as fabric by means of stitched loops. Stitches through the fibre web are formed using the row of needles, and the process resembles to warp knitting. Stitch bonding using a latch needle Microscope image of stitch bonded fabric Uses of Non-woven Fabrics Prepared By: Shakeel Ahmad Paracha Page 7 of 7