SWELLING
PROPERTIES OF TEXTILE FIBRES
When
textile fibres absorb water, they change in dimensionally (axially &
transversely). Swelling occurs in the transverse direction (width-wise) and
axial direction (length-wise) of fibre. It may be expressed in terms of the
increase in diameter, area, length or volume of a fibre. The changes in dimension due to absorbing
moisture or water by any textile fibre are termed as swelling properties.
Swelling
phenomenon of textile fibres
The
molecular chains are laying roughly parallel to the fibre axis, as a result
fibre has lower space between the adjacent chains and swelling will be lower.
When the fibres are immersed into water, the water molecules enter into the
fibre and occupy the molecular space of fibre and thus push the fibre chains.
As a result, there will be a considerable increase in diameter of the fibre but
very little increases in length.
Types
of Swelling
1)
Transverse diameter swelling
The fractional
increase in diameter of a fibre after swelling is known as transverse diameter
swelling. Transverse diameter swelling of a fibre is denoted by SD.
So, SD= ΔD/D, where ΔD= increase
diameter of fibre & D= original diameter of fibre
2)
Transverse area swelling
The fractional
increase in area of a fibre after swelling is known as transverse area
swelling. Transverse area swelling of a fibre is denoted by SA.
So, SA= ΔA/A, where ΔA= increase
area of fibre & A= original area of fibre
3)
Axial swelling
The fractional
increase in length of a fibre after swelling is known as axial swelling. Axial
swelling of a fibre is denoted by SL.
So, SL= ΔL/L, where ΔL= increase
length of fibre & L= original length of fibre
4)
Volume swelling
The fractional
increase in volume of a fibre after swelling is known as volume swelling.
Volume swelling of a fibre is denoted by SV.
So, SV= ΔV/V, where ΔV= increase
volume of fibre & V= original volume of fibre
Relationship
between SA & SD
We
know that,
Transverse
area swelling, SA = ∆A / A
Transverse
dia. swelling, SD = ∆D / D
For
a circular fiber, area A = (Ï€/4) D2
For
a swollen fiber, we get, A+∆A = (Ï€/4) (D+∆D)2
= (Ï€/4) (D2 + 2D. ∆D
+ ∆D2)
Now,
SA = ∆A / A
= (A+∆A-A) / A
= {(Ï€/4) (D2
+ 2D. ∆D + ∆D2) - (Ï€/4) D2}/ (Ï€/4) D2
= (Ï€/4) (D2
+ 2D. ∆D + ∆D2 - D2) /
(Ï€/4) D2
= (2D. ∆D + ∆D2)
/ D2
= (2D. ∆D / D2)
+ (∆D2/ D2)
= 2(∆D / D) + (∆D2/
D2)
= 2 SD +
SD2
So,
SA = 2 SD + SD2.
Relationship
between SA, SV and SL
We
know that,
Transverse
area swelling, SA = ∆A / A
Volume swelling, SV = ∆V / V
Axial swelling, SL = ∆L / L
For
a circular fiber, volume, V=AL
For
a swollen fiber, we get, V +∆V = (A +∆A) (L +∆L)
= AL + A∆L + ∆AL + ∆A ∆L
Now,
SV = ∆V / V
= (V+ ∆V - V) / V
= (AL + A∆L + ∆AL +
∆A ∆L - AL)/AL
= ∆L / L+ ∆A/ A +
∆A/ A. ∆L / L
= SL + SA
+ SL. SA
So,
SV = SL + SA + SL. SA.
Factors
influencing swelling properties of textile fibres
v Composition
of the material (such as cotton, polyester, acrylic, nylon etc.)
v Size
and form of the sample (such as fiber, yarn, fabric etc.)
v External
condition (temperature, humidity)
v Chemical
content (such as oil, wax and other
impurities)
Effects
of swelling on textile fibres
v Swelling
improves the absorption of dyes and chemicals in fibre.
v Due to
swelling the pores of closely interlaced woven fabric will be completely
blocked and thus it may act as water proof fabric.
v Swelling
changes the dimensional stability of fabric.
v Swelling
changes the electric and tensile properties of fibre.
v Swelling
minimizes static charge formation.
Swelling
(%) of different fibres:
|
Fibre
|
Transverse
diameter
swelling
% (SD)
|
Transverse
area swelling % (SA)
|
Axial
swelling % (SL)
|
Volume
swelling % (SV)
|
|
Cotton
|
20
|
40
|
-
|
-
|
|
Flax
|
20
|
47
|
0.1
|
-
|
|
Jute
|
20
|
40
|
-
|
-
|
|
Viscose
rayon
|
35
|
67
|
3.7
|
119
|
|
Wool
|
14.8
|
25
|
-
|
37
|
|
Silk
|
16.5
|
19
|
1.6
|
30
|
|
Nylon
|
1.9
|
1.6
|
2.7
|
8.1
|
