FRICTIONAL
PROPERTIES OF TEXTILE FIBRES
Friction
is the force that resists the movement of a surface over another surface during
sliding. When fibres are processed in textile industry, friction is developed
between them. Due to the friction, the properties shown by textile fibres are
called as frictional properties.
Fibre Friction
It is the surface property of the fibre when
two solid surfaces slide against each other. When we talk about fiber friction
then it is very necessary because it is the the force that holds together the
fibre in a spun yarn and the interlacing threads in a fabric. For example, if we rub silk fabric with itself or
any other type of material then static
charge and heat energy is produced due to fiber
friction.
There may be two kinds of fiber frictions-
Fiber to Fiber friction that is in between two same
or different fibers.
Fiber to Solid friction that is present in between
fiber and solid particle or surface.
Types of Friction
There are two types of frictions-
Static Friction:
It is the force that must be overcome to begin
sliding of two objects or fibers in contact. It is independent of area of
contact.
Kinetic or Dynamic friction:
It is the force that must be overcome to continue
sliding. It is independent of sliding speed, however in case of some semi
crystalline polymers this behavior is very complex. Kinetic friction is always less than that of static
friction.
Factors Affecting
the Frictional Intensity of Textile Materials
v Composition
of the material (natural/synthetic)
v The
state of the surface (slippery/rough surface)
v Weight
of the fibre
v Pressure between two surfaces
v Area
of contact or angle of contact
v Speed
of sliding of one surface over another
v Temperature
& Relative humidity (%)
v Water
absorption of fibre
v Cross-sectional
area of fibre
Directional Frictional
Effect (DFE)
The friction of the
wool fibre depends on the direction in which it is pulled. The resistance is
greater when it is pulled against the scales than when it is pulled with the
scales. This is known as the directional frictional effect. So, in case of wool
fibre it can be said that, less friction takes place between the fibres with
the direction of scales and the friction becomes higher between the fibres
against the scales.
Wool has greater friction for having scales
in its surface. But, cotton also has more friction due to its convolution
(natural crimp) and has more friction than wool.
Co-Efficient
of Friction
Frictional
intensity of textile fibres can be determined by measuring co-efficient of
friction. According to Amonton’s basic law (2nd
law) of friction, frictional force is proportional to the normal
force between surfaces in contact that is frictional force
is proportional to the perpendicular force of a material due to its own weight.
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So, F∞ N; where F=
Frictional force & N= Normal or perpendicular force
Or,
F= µ N
Or, µ= F/N
Here, µ is the
proportionate constant known as co-efficient of friction. Thus, co-efficient of
friction can also be defined as the ratio between frictional force and
perpendicular force of a material.
Frictional
intensity of textile fibres depends on the difference between µs and µs
(µs-µk), where µs is always higher than µk. If the difference is high, then the
fabric becomes slippery and if the difference is less, then the fabric becomes
rough.
Some typical values
of µs and µk
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Friction between
fibre on fibre
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µs
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µk
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Rayon
on rayon
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0.35
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0.26
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Nylon
on nylon
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0.47
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0.40
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Polyester
on polyester
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0.15
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0.12
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Cotton on cotton
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0.51
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0.26
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Wool on wool
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with scale
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0.13
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0.11
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against scale
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0.61
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0.38
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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-
v Static
capstan method
v Dynamic
capstan method
v Other
methods-
v Buckle
& Pollitt’s method
v Abboh
& Grasberg method
v Gutheric
& Olivers method
Importance of
friction in Textile Industry
v Friction
holds the fibre in a sliver and hence material does not break due to self
weight.
v Friction
helps in drafting and drawing process.
v Uniform
tension can be maintained in winding and warping because of friction.
v Friction
helps in twisting during spinning.
v Friction
modifies the lustre and appearance of a cloth
v Friction
makes more clean yarn.
Problems of
friction in Textile Industry
v Fiber friction can lead to damage of fiber surface;
it weakens the fibers, even causes breakage of
fibers.
v Friction
causes neps formation.
v Over
friction causes high breakage of yarn in weaving.
v Due
to friction handle properties of fabric will be changed.
v Sometimes,
due to friction textile materials may be elongated.
v Friction
causes yarn and fabric hairiness.
v Friction
causes static charge formation in textile material and therefore, dust, dirt
etc. are attracted by the textile material and it becomes dirty.
v Friction
worns out different parts of a machine.
Minimization of
frictional intensity of textile materials
The
following steps may be taken to reduce the frictional intensity in textile
materials-
v Sizing
is done on warp yarn before weaving to reduce friction between adjacent yarns;
as a result ends breakage rate during weaving becomes minimized.
v Emulsion,
oil, lubricants etc. are applied specially on jute in batching section to
reduce the stiffness of fibre and thus fibre damage is reduced in processing.
Thus, lubrication reduces the effect of friction.
v Chemical
treatment is applied on wool fibre to reduce scale sharpness and thus frictional
intensity of fibre is minimized.
v By
calendaring it is possible to minimize the frictional intensity of cloth.
v Sometimes
resin finish or anti-crease finish can be applied on cloth to reduce the
frictional intensity.
v Softener can also be applied on textile material to reduce its frictional intensity.
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