19 Non-woven – II

B. A. Muralidhar

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In web bonding, the fibres are consolidated to produce felts. Bonding of the nonwoven web is the primary factor determining the nonwoven fabric strength, integrity, flexibility, porosity, density and softness. Fibre characteristics such as fibre type, shape, geometry, location within the felt mass influence the degree of bonding. Nonwoven web consolidation / bonding can be brought about by mechanical, chemical, solvent and thermal means. Bonding is generally carried out as a sequential operation in tandem with web formation, however, it may also be carried out as a separate and distinct operation. In choosing the web consolidation method, the desired product properties, followed by economy, versatility, strength, softness and primary absorbency needs to be taken into account.


In web bonding, the conversion of a fibrous batt to fabric is effected by either a physical, chemical or thermal process. In the physical process, the physical entanglement between the fibres is brought about either due to friction, adhesion or cohesion. In the chemical process, the bonds between fibres transpire only when the softened fibre surfaces meet each other. However, in the thermal process the bonding requires fibres (or) powders with thermoplastic characteristics.


Through combination of bonding processes, a variety of special effects can be obtained. The techniques available for web bonding are largely classified as follows:


1) Mechanical Bonding Processes:

  •  Needle-punching
  •  Hydro-entanglement

2) Thermal Bonding Processes:

  •  Hot calendaring
  •  Belt calendaring
  •  Through-air bonding
  • Ultrasonic bonding
  • Radiant-heat bonding

    3)  Chemical Bonding Processes:

  • Saturating
  • Spraying
  • Printing
  • Foaming techniques

   2.  Mechanical bonding


2.1Needle punching:


Needle punching industry around the world is an exciting and diverse trade and enjoys one of the greatest success. In this method web bonding/consolidation is brought about by repeated insertion of barbed needles into the preformed dry fibrous web (batt), which is unbounded, thick and voluminous either from one side or both sides Figure 2. This consolidation of initially arranged staple fibres in different orientation (Cross or parallel) is brought about by interlocking of fibres in the z-direction. Needle punching is carried out on needle looms. The barbed felting needles are repeatedly passed in and out of the web. The web passes through two plates namely the web plate on the bottom and the stripper plate on the top. Holes are located in each plate and it is through these holes, the needles carry bundles of fibres through the bed plate holes. The stripper plate, strips the fibres from the needle so that the material can advance through the needle.


During the needle punching process the fibres or filaments are reoriented into the vertical planeby the barbed needles. The fibre movement takes place in the fibrous batt as the fibres caught by the needle slide down and change their position. The fibre movement, results in the change in fibre mass, along the length and width. Majority of the fibres remain in the horizontal position.


The performance characteristics of the needle punched non-woven largely depend on parameters such as fibre, areal density of web, penetration depth of needle, needle density and number of passages. Needle is the heart of needle punching machine. Selection of suitable needle is very essential for getting good quality non-woven fabrics. Needles are generally triangular in cross-section and carry barbs, and the dimensions of the barbs and their relative arrangement depend on non-woven application and machine operation. Needle gauge is defined as number of needles that can be fitted in a square inch area, thus finer the needle, higher the gauge of needles whereas coarser fibres use lower needle gauge. The more the needles penetrate the web, more dense and stronger the web generally becomes. Needle punched non-woven find extensive application in civil engineering, railways and geotextiles etc.

Figure 2. Needle Punching (Courtesy NPTEL)




The mechanical process of entangling fibrous webs by water jets has gained attention for almost three decades. In this method web bonding/consolidation is brought about by subjecting the web (batt) of loose fibres (both natural and synthetic fibres) supported by a conveyor belt to high pressure fine water jets. Here fluid forces  or currents with the required energy is used to reorient the fibres by entanglements, knotting or intertwining the fibres together. As the water jet strikes the fibrous web, the fibres get deflected and the agitation within the web brings about fibre entanglement. The basic elements of the machine are shown in Figure 3. This process is accomplished in a hydro entanglement or spun lace machine.


Important fibre characteristics essential for this process is fibre hydrophilicity and flexural rigidity of fibres. Course fibres with higher flexural rigidity compared to finer fibres would require more hydro-entangling energy to have similar bonding.


The fibrous web is supported on a surface with randomly distributed holes, and the high velocity water jets are directed towards it. As a result of the high pressure jets, entanglements among the fibres are introduced by the combined effect of incident water jets and the turbulent water created in the web which twists fibres around each other forming an integrated structure.


One problem associated with hydro-entangled non-woven quality is related to the jet marks, which spoils its aesthetic appearance and also reduces the mechanical performance. Most of the de-energized water is drawn through the permeable membrane for reuse. The consolidated web is further dried to remove the water.


The performance characteristics of the hydro entangled non-woven largely depend on parameters such as fibre properties, web properties and jet and forming wire geometry. Hydro entangled non-woven have wide range of applications such as medical dressing, automotive fabrics, lining, clothes, personal care, household wipes etc.


Nonwovens fabrics manufactured by the hydro-entanglement method process the following distinct characteristics such as:

  1. The non-woven are free from additive’s such as binding agents, impurities and other foreign matters and are especially best suited for sanitary, medical and other hygienic applications.
  1. Hydro entangled non-woven, are generally soft, absorbent and drape able, as such these non-woven find application as cleaning cloth, wipes, polishing and for other clean room requirements.

Figure 3. Hydro entanglement(Courtesy NPTEL)


3 Thermal bonding Process


In the past few years, the growth of thermally bonded webs have steadily increased. The viability of this process is rooted to its price advantage and ability to address demanding quality requirements. Better web formation technologies have made this process more viable for both disposable and durable nonwovens.


The main requirements of the binder polymer are:

  • Good melt flow characteristics
  • Good adhesion characteristics
  • Lower melting point w.r.t. carrier fibre

Binders for thermally bonded nonwovens may be in the form of – binding fibres both single and bi-component fibres are mostly used as binder fibres in thermal bonding nonwovens.


Binding powder sometimes powdered polymers are also used when a light weight, soft and open structure fabric is required.


Binding web – an open structured, thermoplastic fabric with low melting point is positioned in between two layers of the web and when passed through the calendar rolls the fabric melts bonding the webs together.


3.1 Hot calendaring:


There are three types of hot calendaring namely:

  • Area
  • Point and
  • Embossing

Area Bonding – In this process, 2, 3 or 4 roll hot metal calendars, opposed by special composition roll can be used depending on the degree of bonding required and the weight of the batt. In this process as heat is applied from the outside, the inner area is less bonded and becomes more pronounced w.r.t. bulky fibrous web. This process is best suited for low-to-medium weight product requiring light to medium bonding. Major factors influencing this process are roller heat, pressure, roller speed, roll combination and cooling rolls.


Point Bonding – this process is mainly used in bonding sanitary napkins, medical products, diapers etc. It involves use of two roller nips which may or may not be heated depending on the requirements. The web is fed to the calendar nip, fibres caught between the engraved points and the smooth roll get adhered together. The degree of bonding depends on the engraved pattern. Bonded areas are tightly compressed and compacted. Embossing – in this process, the heat able metal calendar roll has a male patterned (figured or sculptured) roll matching with a female felt roll.

  3.2 Belt calendering: this process consists of a heated roll and a rubber blanket. Pressure is applied by varying the blanket tension. The products are less bulky compared to hot roll calendar. This process facilitates the use of binders with sharp flowing and melting characteristics.


3.3 Through-Air bonding: this process involves the application of hot air through holes positioned below the nonwovens. Vacuum created pulls the air through the open conveyor apron that supports the nonwoven as it passes through the oven. Products are generally open, bulky, strong, absorbent and extensible.


3.4 Ultrasound bonding: this method is frequently used for patterned or spot bonding. The process involves application of quickly altering compressive forces to localized areas of the web, the compressive force is converted to thermal energy, which softens the fibres, and upon removal the softened fibres solidify forming the bonding. The ultrasound technology for web bonding requires a constant, amplitude across the entire web width. Further, the stable mounting of the ultrasound heads accompanied by the high precision roller maintain the constant gap. This method is used to make patterned quilts, outdoor jackets etc.


3.5 Radian heat bonding: in this process, the fibrous web is exposed toa source of radiant energy from infrared range, which increases its temperature and melts the binder fibre. Upon removal of the radiant heat source bonding occurs.

  1. Chemical bonding process

Bonding a web by means of a chemicals, followed by curing is one of the most common methods of bonding. Chemical binders, adhesive materials are applied to the non-woven fibrous web in different way; these chemical binders form an adhesive film between the fibre intersections, thereby holding the fibres together. The chemical composition of the binder material determines the strength, stiffness/softness properties, elasticity, water affinity, aging and durability. The type and nature of side group determines solvent resistance, cross-linking nature and adhesive characteristics.


Chemical binders are applied in the range from 5% to 60% on the weight of the web. Vinyl polymers, acrylic esters, natural and synthetic rubber, starch are usually used polymer binders applied in aqueous dispersions. Latex are extensively used because they are versatile, economical, easily applied and effective adhesives.


Some of the common techniques of applying binder to fibrous web are by saturation, foam, spray, and print methods.


4.1 Saturation process:


Saturation bonding can be carried out in three ways – Screen, dip/squeeze and size-press.


Screen saturation is used for intermediate weight nonwovens such as interlinings. Dip/Squeeze saturation involves complete immersion of the fibrous non-woven web in a trough containing binder and the excess removed by a pair of nip rollers, the binder pick up by the non-woven depends on the weight of nonwoven, dwell time, nip pressure and fibre wet ability. This method provides higher binder/fibre bonding throughout, and is more suitable for light weight highly permeable nonwovens. Size-press saturation is used in high speed process such as wet-laid nonwovens


4.2 Foam binding process:


In this process mechanically generated foam is used to carry the dilute binder to remain at the surface or made to penetrate through the fabric cross-section. Main advantage of the process is more efficient drying, higher production rates, less waste to dispose of, improved drape, more uniform binder distribution, greater bulk, softness and higher air permeability. The concept employed involves applying binder at low water level and high binder solid concentrations. The solids content is about 40-50% with 15% liquor impregnation. Foam bonded nonwovens require less energy to dry the web. Foam bonded nonwovens exhibit enhanced loft, resilience and hand. Some of the disadvantages of this process are additional cost involved in foam generation, irregular binder distribution in thick webs and reproducibility difficulties on account of foam stability and variable formability.


4.3 Spray bonding process:


In this process, the binder in the form of small droplets is sprayed onto the moving web through a system of nozzles, strategically mounted on the machine. The depth of penetration of binder depends on the permeability of the web; fibre wet ability and amount of binder. In certain cases to assist binder migration suction is applied to the lower side of the web. Further, where both higher strength and bulk are desirable both sides of the web can also be sprayed one after the other. The binder is atomized by air pressure, centrifugal pressure or hydraulic pressure and applied on the upper surface of the web as fine droplets. After each spraying the web is passed through the dryer to remove water. This process is best suited to produce bulky, porous non-woven, as the fibrous web is not compressed. The applications of spray bonded nonwoven include upholstery, filters, insulating, wadding and stuffing.


4.4 Print bonding process:


In this process, the binder is applied to the fibrous web only in predetermined areas as per the print pattern. The binder is transferred from the feed roller to the engraved roller and as the web passes the engraved roller, it is against the surface of the engraved roller by a rubber roller transferring the binder to the fibrous web. The excess binder is removed by doctor blade. The web is further cured for cross linking the binder. This method is suitable for applying low levels of binder to produce nonwovens suitable for applications that require a part of the fabric to remain binder free. The main advantages of this process is the outstanding softness with adequate strength.


4.5 Powder Bonding:


Powder bonding have established as an alternative to binder fibres and binder fluids in web bonding. Though regarded as an expensive process, there has been a steady increase in its acceptance because of its high production, low energy costs, non-residual and contactless application. In this method, the adhesive powder is mixed with the web in the early production stage or the powder is spread over the web later on. This permits uniform powder distribution across the thick web. Following this the web consolidation is carried out by heat and pressure. Low glass transition  temperature and molecular weight polyesters and polyolefin are used as powder binders. Bulky and dense nonwovens are produced by this method. Applications:


Chemical bonding process developed nonwovens find application in footwear, automotive, home furnishing, wipes, interlinings, medical products, towels, filter media, coating substrates, bedding products, furniture applications, apparel, pillows etc.

  1. Finishing

Finishing treatments for the non-woven fabrics are carried out to control the fabric width and the possible shrinkage of materials through other treatment processes. Non-woven fabrics like the regular woven and knitted fabrics, can also be given some special finished to develop certain advantageous properties depending on their end use applications. Mechanical, chemical or both finishing techniques can be incorporated to impart certain aesthetic and functional characteristics to the non-woven.

  1. Conclusions

In this module, we have covered the web bonding techniques– mechanical, thermal and the chemical bonding used in the manufacture of non-woven fabrics. The characteristic features of the non-woven fabric produced by each method and their intended application areas have also been touched upon.

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  1. Gupta, V.B. and Kothari, V.K. (Eds.). 1997. Manufactured Fibre Technology. (Gupta, A.K. Chapter 10 Characterization of Polymers and Fibres. Pp. 203-247). Chapman & Hall. London.
  2. Kothari, V.K. (Ed.) Quality Control. (Sen, K. Chapter 4 Textile Fibres: Classification and Identification, Pp.46-54.) Textile Dept. IIT, New Delhi.
  3. Sreenivasa Murthy, H.V. 1987. Introduction to Textile Fibres. The Textile Association (India), Mumbai.


Web links


  • http://nptel.ac.in/courses/116102014/6