Friction in Textile Fibers and Its Effect in Fiber Processing

FRICTIONAL PROPERTIES OF TEXTILE FIBER
Ali Rayhan Sarkar 
B.Sc. in Textile Engineering
Daffodil International University
Email: alirayhansarkar3268@diu.edu.bd



Introduction:
Friction is the force that resists the movement of a surface over another surface during sliding. When the textile materials are processed, then friction is developed between the fibers. The properties which are shown by a textile material during friction is known as frictional property. This properties are shown during processing. Too high friction and too low friction is not good for yarn. Therefore it is an important property when yarn manufacturing and processing. 
 
There are two types of friction.
  1. Static friction: The force that must be overcome in order to start sliding is called static friction.
  2. Kinetic friction: The force that resists continued sliding is known as kinetic friction.
Frictional properties depend on:
  1. Composition of the material
  2. State of the surface of the material
  3. Pressure between the surfaces
  4. Temperature
  5. Relative humidity %
  6. Area of contact
  7. Water absorption of fiber
Co-efficient of friction:
Frictional force is proportional to the normal or perpendicular of a material due to its own weight. 
 
That is, F ∞ N Or, F = μ N Or, μ = F/N 
 
Where, F = Frictional force, N = Normal / perpendicular force. Here, μ is the proportional constant known as “co-efficient of friction”. So, co-efficient of friction can be defined as the ratio of frictional force and perpendicular force.

Methods of measuring co-efficient of friction:

Capstan method is most commonly used to measure co-efficient of fraction. Capstan method can be classified into two classes-
  1. Static capstan method
  2. Dynamic capstan method
Other methods-
  1. Buckle & Pollitt’s method
  2. Abboh & Grasberg method
  3. Gutheric & Olivers method
Frictional properties influences:
In fiber stage
  1. The behavior of fiber during drafting.
  2. The frictional force holds together the fiber in yarn, i.e, frictional force helps to spun the fiber to yarn.
In yarn stage
  1. If the frictional force is too low, yarn strength will be low.
  2. Friction increases the luster and smoothness of yarn.
  3. Friction makes more clean yarn.
  4. Friction increases hairiness.
  5. Friction occurs nep formation.
In fabric stage
  1. Fabric feelings varied for difference between static and kinetic friction.
  2. Fabric will be slippery if µs >µk is high. Fabric will be harsh if µs >µk is low.
    Here, µs= Co- efficient of static friction, µk= Co-efficient of kinetic friction.
  3. If the frictional force is high the handle properties of fabric quality will be low.
  4. High static friction causes high breakage of yarn in weaving.
Factors affecting frictional intensity:
  1. Load: If load increases frictional intensity will also increase.
  2. Area of contact or angle of contact: Frictional intensity increases with the increasing of angle of contact.
  3. Speed of sliding: More speed of sliding causes more frictional intensity.
  4. The state of surface: The frictional force is changed if the surface is lubricated either naturally or artificially or has been contaminated by dirt or impurities. The frictional force increases both as the oil content is increased and as the viscosity of the oil increases.
  5. Effect of absorbed water: The frictional force usually increases as the regain of the fibre is raised.
Importance of friction in Textile Industry:
  1. Friction holds the fibre in a sliver and hence material does not break due to self weight.
  2. Friction helps in drafting and drawing process.
  3. Uniform tension can be maintained in winding and warping because of friction.
  4. Friction helps in twisting during spinning.
  5. Friction modifies the luster and appearance of a cloth.
  6. Friction makes more clean yarn.
Demerits of friction on textile material:
  • Friction causes nap formation. 
  • High static friction causes high breakage of yarn during weaving.
  • If the frictional force is high, the handle properties of fabric will be low.
  • Friction generates temperature and therefore static electricity is developed which attracts dust, dirt etc. and the materials become dirty.
  • Sometimes due to over friction materials may be elongated.
  • Friction increases yarn hairiness. 
  • Friction worn out parts of machine.
Friction in textile material
Friction in textile material
Minimization of friction intensity:

1. By processing with lubricates:
Lubricating material as emulsion is used before jute spinning. Sizing is done during weaving preparation process. It also reduces yarn damage. Emulsion, oil, lubricants are applied specially on jute fibre to reduce friction.

2. By chemical treatment:

By using acid or alkali. Acid or alkali is done on wool fibre to reduce scale sharpness and thus frictional intensity.

3. By finishing process:
  • Mechanical finishing: Ironing of calendaring.
  • Chemical finishing: By using resin. Resin is one typed anti-crease agent because it prevents fibre from creasing by blocking hydroxyl groups.
  • By using softener we can minimize frictional intensity.
Theories of friction in textiles:
In this section, the various theories proposed for friction in textiles are reviewed. Kragelskii divided friction theories into four groups, as follows: friction is a result of (i) lifting asperities over one another (ii) overcoming the forces of molecular interaction; (iii) displacing a volume of material (ploughing); and (iv) at least two components contributing to friction, i.e. composite theories.

The adhesion theory of friction has been the basis of explanation for friction in fibrous materials.

Arrows are vectors indicating directions and magnitudes of forces (Figure 1). W is the force of weight, N is the normal force, F is an applied force, and Ff is the force of kinetic friction, which is equal to the coefficient of kinetic friction times the normal force. Since the magnitude of the applied force is greater than the magnitude of the force of kinetic friction opposing it, the block is accelerating to the left.

Yarn friction

Factors affecting yarn friction Overview:
Yarn friction is related to both surface properties and bulk properties of yarns. There are four main groups of factors: (i) Fibre parameters; (ii) Yarn structural and bulk parameters; (iii) Operational parameters; and (iv) Finishes. Fibre parameters include fibre structural and bulk parameters. Yarn structural and bulk parameters include yarn twist, spinning method, yarn denier, etc. Operational parameters consist of normal load, frictional speed, humidity, temperature, sliding speed, measuring method, contact geometry, and the like. The effect of finishes depends on the nature, the viscosity, and the content of lubricant, etc.

Yarn friction has been investigated in relation to fibre parameters; yarn structural parameters, operational parameters, and finishes, including lubricants.

Effects of fibre parameters:
Fibre Surface Roughness: It has been observed that with an increase in roughness of the fibre surface, final tension and hence friction in the yarn increases (Table 1).

Table 1: Effect of fibre surface roughness on yarn friction
Continuous filament yarn sample tested
Initial tension (gm)
Final tension (gm)


Smooth
Rough
Yarn to metal test
25
60
40
Yarn to yarn test
15
41
31
 

Molecular Orientation:
Gupta and El Mogahzy investigated the effect of molecular orientation on the friction of acrylic yarns. Inter-fibre friction and molecular orientation at the fibre surface, characterised by a sonic modulus orientation factor, increased with draw ratio. They found a strong correlation between molecular orientation of the fibre and inter-fibre friction. More intimate or greater area of contact by smoothing out of the surface for a more highly oriented fibre may be responsible for this finding.

Table 2: Orientation factor and Coefficient of Friction (µ) of acrylic yarns at different values of cascade stretch (Xc.s)
Sample no
Xc.s
Orientation factor
µ, Point contact
µ, Line contact
1
2.0
0.6949
0.135
0.186
2
3.0
0.7316
0.136
0.221
3
4.0
0.7556
0.134
0.230
4
5.0
0.7725
0.138
0.235
5
6.0
0.7847
0.138
0.238
6
7.0
0.7918
0.141
0.243










Effects of yarn structural and bulk parameters:
Yarn denier: The fineness (denier) has an increasing effect on friction due to an increase in the area of contact. Kalyanaraman observed that the coefficient of friction of yarn increased with increasing yarn linear density, due to the larger contact area, using the SITRA friction measuring device.

Yarn twist: Chattopadhyay and Banerjee found that, with increasing yarn twist of ring and rotor spun yarns, friction decreased for cotton, viscose rayon, and polyester yarns. In this study, the material and processing parameters selected were Yarn linear density = 59 tex, Relative Speed = 40 m/min., Input Tension = 11 cN. and Number of wraps = 2. Higher twist decreases compressibility, resulting in a smaller area of contact and thus lower frictional force. Higher twist showed greater friction for cotton ring spun yarns. Subramaniam and Natarajan found that the coefficient of friction of siro spun yarns increased with increasing strand spacing and twist. This result was attributed to the nature of the yarn surfaces.

Spinning method: Chattopadhyay and Banerjee studied the effects of spinning method on yarn-to-yarn and yarn-to-guide friction, using ring, rotor and friction spun yarns for cotton, polyester and viscose rayon. The effects of spinning method on yarn to-guide friction depend on the frictional speed and material type. Yarn surface structural characteristics, eg, belt fibres of rotor yarns, and compressibility were considered as important factors affecting yarn friction.

From the results, it may be observed that. For both cotton and viscose fibres, ring spun yarn shows the maximum frictional force and tension ratio, followed by rotor and friction spun yarns, which are close to each other. The results are therefore just the reverse of what was observed for friction between yarns. The order in which the magnitude of the friction changes for cotton and viscose fibre is therefore different in two cases and shown below:

Between yarns: friction-spun > rotor-spun > ring-spun
Between yarn and guide: ring-spun > rotor-spun > friction-spun
 
In above study, the material and processing parameters selected were Yarn linear density = 98.4 tex. Input Tension = 12 cN. In case of polyester fibre, friction spun yarn shows the highest value, followed by rotor- and ring-spun yarns. The order in which the friction changes is therefore just the reverse of what is observed for cotton and viscose fibres.

Yarn surface roughness: Yarn roughness was increased by insertion of twist in a multifilament yarn and by incorporation of titanium dioxide. The yarn friction decreased with increased roughness of the yarn surface. However, for a very rough yarn surface, the yarn friction tended to increase owing to the Coulomb component.

Unevenness: Unevenness of yarn tends to influence the frictional forces. As yarn unevenness increases, frictional force becomes greater.
 
Effects of operational parameters:
Pretension: An increase in pretension results in an increase in friction. This may be because the increase in pressure with pretension causes an increase in the area of contact and thus an increase in friction. 
 
The coefficient of friction between silk filaments and steel is reduced from 0.44 to 0.27 (along the fibre) and 0.34 and 0.23 (across the fibre) with increasing yarn tension from 5 to 20 cN at a specified angle of wrap. 
 
Sliding Speed: The increase in the friction of spun yarns with increasing speed may be attributed to the fact that, at high-speeds, the hairs may bend down owing to the pull of the yarn, leading to an increase in the contact area.

With increase in speed, the friction coefficient of cotton, rayon, and silk yarns increases when measured by the capstan method.

The friction of ring, rotor and friction spun yarn decreases with increasing frictional speed from 40 to 200 m/min. In this study, the material and processing parameters selected were Yarn linear density = 98.4 tex. Input Tension = 11 cN. Number of wraps = 2.

Temperature: The effects of temperature on yarn friction have been related to the thermal conductivity of guide materials.

The effect of guide temperature on friction should be considered along with speed. Thermally stable lubricants are required to prevent melting of fibres at the fibre-to-metal surface, due to high temperature. For the effect of temperature, the initial decrease in friction with increasing temperature may be attributed to the decrease in lubricant viscosity, and subsequent increase in friction to volatilisation and/or thermal decomposition of lubricant causing softening of the polymer surface.

Humidity: The effects of relative humidity and moisture content of yarns on friction affect yarn breakage rates and the quality of products. The coefficient of friction of yarn was reported to increase with increase in humidity and sharply increase above 80% relative humidity.

Effects of Finishes:

General: In this section, the effects of finishes including lubricants and softeners, and finishing such as mercerization, plasma etching and laser irradiation are discussed.

Lubricants: The action of a lubricant is to (a) reduce the abrasion of fibres, yarns and machine parts, (b) reduce static electrification during textile processing, and (c) ensure adequate strength of spun yarns and their final products. A lubricant has been found to have a pronounced effect on both yarn-to-metal and yarn-to-yarn friction. Under boundary lubrication, friction is governed by the chemical nature of lubricants and the sliding surfaces, the shear strength of the lubricants, the rigidity of the substrates, and the pressure at the areas of contact.

Lubricants reduced friction of spun yarns by reduction in friction index a. The index n remained constant either with the type or concentration of lubricants. Lubrication of the yarn gradually reduced the coefficient of friction. This trend was more pronounced when the lubricant or the surface active agent was deposited at the interface, as in dry treatment studies, rather than when it was present in solution, as in the case of submerged experiments.

Softeners: Sebastian, et al reported that treatment with cationic softening agents reduced inter-yarn sliding friction.

Mercerization: The effects of slack mercerization, using zinc chloride, on yarn properties of ring and open-end spun cotton yarns have been investigated. The coefficient of friction of yarns increased after mercerization.

Plasma etching: The effect of plasma etching on frictional properties of polyester filaments has been investigated. Plasma treatment increased the roughness of fibre surface and caused an increase in inter-fibre friction and fibre cohesion.

Laser Irradiation: By laser irradiation of polyester yarn surfaces during a continuous winding process, the friction between the yarns and the guiding elements was reduced. 
 
Lubrication of yarns:
Purpose: Lubrication of yarn is critical to knitting yarns and sewing threads for their processing performance-to provide low levels of friction (Table 7), and for protection from heat generated by the needle. Fabric and garment manufacturing require good yarn lubrication.

Lubricants can modify both the surface and the bulk of yarn. For yarn, depending on its molecular size and charge, the lubricating agent may deposit itself on the yarn surface, or penetrate the yarn and deposit on the surface of the individual fibre.

Applications:
Friction is an important factor in many engineering disciplines. 
 
Transportation:
  1. Rail adhesion refers to the grip wheels of a train have on the rails, see Frictional contact mechanics.
  2. Road slipperiness is an important design and safety factor for automobiles
  3. Split friction is a particularly dangerous condition arising due to varying friction on either side of a car.
  4. Road texture affects the interaction of tires and the driving surface.
Laws of friction:
  1. The frictional force is independent of the area of contact between two surfaces.
  2. The frictional force “F” is proportional to the normal reaction “RN”.
  3. This law is known as Coulomb’s law and friction’s third law. Kinetic force is independent of the speed of sliding.
Measurement of friction:
Methods of friction measurement can be divided into two classes. They are – 
 
1. Frictional at only one point of contact.
  • Between two different fibres.
  • Between two different fibres.
  • Between a fibre and non-fibre materials such as metal, plastic and ceramic.
2. Average friction at a great number of contacts.

Conclusions :
Friction is the resistance to movement of one body over body. The word comes to us from the Latin verb fricare, which means to rub. The bodies in question may be a gas and a solid (aerodynamic friction), or a liquid and a solid (liquid friction); or the friction may be due to internal energy dissipation processes within one body (internal friction). In this article, the discussion will be limited to the effects of solid friction. Two of the most significant inventions of early man are friction-related: He learned to use frictional heating to start his cooking fires, and he discovered that rolling friction is much less than sliding friction (that is, it is easier to move heavy objects if are on rollers than it is to drag them along). This second discovery would eventually lead to the invention of the wheel. 
 
Friction plays an important role in a significant number of our daily activities and in most industrial processes. It aids in starting the motion of a body, changing its direction, and subsequently stopping it. Without friction, we could not readily move about, grip objects, light a match, or perform a multitude of other common daily tasks. Without friction, most threaded joints would not hold, rolling mills could not operate, and friction welding would obviously not exist. Without friction, we would hear neither the song of the violin nor the squeal of the brake. In moving machinery, friction is responsible for dissipation and loss of much energy. It has been estimated, for example, that 10% of oil consumption in the United States is used simply to overcome friction. The energy lost to friction is an energy input that must continually be provided in order to maintain the sliding motion. This energy is dissipated in the system, primarily as heat—which may have to be removed by cooling to avoid damage and may limit the conditions under which the machinery can be operated. Some of the energy is dissipated in various deformation processes, which result in wear of the sliding surfaces and their eventual degradation to the point where replacement of whole components becomes necessary.

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