5 Yarn and woven fabric properties
5.3 Permeability and pore size
The air permeability of a fabric is affected by the open area, the pores in the fabric. It is measured as airflow through the fabric at the standard pressure drop, in cubic meter of air per square meter of fabric. For example higher level of yarn twist increases the open area, and thus increases the air permeability (Adanur 2000, p. 361-373; Hatch 2006, p.
287-299). The weave pattern affects the density of fabric and thus the permeability. The air permeability is smaller with patterns with few interlacing points. (Hatch 2006, p.
317-370) Void volume is the volume of empty space inside the fabric. The fabric thickness and the weave pattern have an effect on the void volume. (Adanur 2000, p.
361-373) It can be calculated from the following equation (12):
(12) where Voltotal = total volume of the sample
m = mass of the sample = density of the material
Water vapour permeability is the ability of water vapour to pass through (diffuse) the fabric via yarns and between the fibres. The yarn twist affects the water absorbance.
Higher twist decreases the yarn’s surface area, and thus decreases the water absorbance.
The more the yarn is twisted the higher is the water vapour permeability. (Hatch 2006, p. 287-299) Hydrophobic and hydrophilic fibres act differently due to the water repelling nature of hydrophobic fibres. Water repellency causes water to form droplets on the fabric surface rather than absorbing the water into the fabric. Different types of fabrics and materials act differently and the water repellency can be estimated by the contact angle between the water droplet and the fabric surface. The surface energy of the fabric inflicts the water drop behaviour. If the surface energy of the fabric is lower than of the water, water forms drops on the surface. If the fabric’s surface energy is higher than of the water, water spreads and wets the fabric. (Hatch 2006, p. 14-43)
There are several theories to calculate the pore sizes of woven fabrics. The most accurate method to know the pore sizes is to use a microscope, but that is very time-consuming. Thus, different mathematical models have been developed. The pores of a fabric are rarely the same size or shape or distributed evenly on the fabric surface. This complicates the calculation of porosity or permeability of the fabric. Darcy’s equation (13) can be used to determine the effective pore size of a multifilament woven fabric, if the measured permeability, porosity and pressure drop data are known. Unfortunately
Vtotal
Voltotal m
Voltotal
29 this equation does not compare the measured and the calculated effective pore sizes.
(Järvinen, 2005)
dp,eff 32K 32cL
p (13)
where K = Kozeny constant (dimensionless) = porosity (dimensionless)
L = thickness of the fabric (m)
c = effective concentration of solids in the feed, % w/w or kg/m3 = fluid viscosity (Pa s)
p = pressure difference (Pa)
According to Järvinen Brasquet and Cloirec determined effective pore sizes using equation (14).
dp,eff 2 4LA
NN0
4 (14)
where L = thickness of the fabric (m)
A = cross sectional area of the fabric (m2) = fluid viscosity (Pa s)
N = viscous energy loss coefficient, dimensionless N0 =number of opening per unit area
The bubble point measurement can be used to determine the pore size of a woven fabric. The fabric is wetted, in the case of very tightly woven multifilament fabric by using vacuum impregnation to eliminate any possible air pockets. Then the airflow is increased and the pore diameter (assumed as cylindrical) can be calculated from the first air bubbles going through the fabric (liquid film break-through pressure, p), which depends on the contact angle between the liquid and the pore (zero for totally wetted fabrics) and the surface tension of the liquid. (Järvinen, 2005) The equation (15) is used to calculate the pore diameter:
d 4
p (15)
where = surface tension of fluid
p = liquid film break-through pressure
However, these equations are not the be sizes, since
equations assume the pores being cylindrical pore are seldom cylindrical in woven f
pores: pores between the yarns, i.e. macroporosity, and pores between the fibres, i.e.
intra-yarn microporosity.
dimensions, which results in errors 5.4 Crimp
Crimp is caused by
completely straight when it is interlacing with
length of the forming fabric is not as long as the initial warp on that length.
applies for the weft
i.e. plain weave has the highest crimp of wea much lower crimp due to the
yarn has no crimp tension in weaving or
Increasing the tension of the yarn the crimp can be reduced, but this will result in an increase of tension in the other yarn system. The increase of crimp in one direction affects also the modulus and elongat
increasing the elongation on that directi thickness, cover
and has higher mass per unit area a Figure 19
warp yarn is pulled straight making the filling yarn crimp.
parameters to the crimp calculation.
Figure 19
and warp straight
However, these equations are not the be
sizes, since all the pores are not in same shape or size.
equations assume the pores being cylindrical pore are seldom cylindrical in woven f
pores: pores between the yarns, i.e. macroporosity, and pores between the fibres, i.e.
yarn microporosity.
dimensions, which results in errors Crimp and
Crimp is caused by
completely straight when it is interlacing with
length of the forming fabric is not as long as the initial warp on that length.
applies for the weft yarns. The crimp is the higher the more there are interlacing points, i.e. plain weave has the highest crimp of wea
much lower crimp due to the
yarn has no crimp. The crimp can be controlled to a certain extent by changing the yarn tension in weaving or
Increasing the tension of the yarn the crimp can be reduced, but this will result in an increase of tension in the other yarn system. The increase of crimp in one direction affects also the modulus and elongat
increasing the elongation on that directi thickness, cover and flexibility of the fabric.
and has higher mass per unit area a
19a the warp is crimped and the filling can stay straight, and in warp yarn is pulled straight making the filling yarn crimp.
parameters to the crimp calculation.
19 Variation of crimp and warp straight (modified from:
However, these equations are not the be
all the pores are not in same shape or size.
equations assume the pores being cylindrical pore are seldom cylindrical in woven f
pores: pores between the yarns, i.e. macroporosity, and pores between the fibres, i.e.
yarn microporosity. Also the compression of yarns as woven affects the pore dimensions, which results in errors
and fabric yield
the interlacing of wa completely straight when it is interlacing with
length of the forming fabric is not as long as the initial warp on that length.
yarns. The crimp is the higher the more there are interlacing points, i.e. plain weave has the highest crimp of wea
much lower crimp due to the long yarn floatings
. The crimp can be controlled to a certain extent by changing the yarn tension in weaving or for example
Increasing the tension of the yarn the crimp can be reduced, but this will result in an increase of tension in the other yarn system. The increase of crimp in one direction affects also the modulus and elongat
increasing the elongation on that directi and flexibility of the fabric.
and has higher mass per unit area a
the warp is crimped and the filling can stay straight, and in warp yarn is pulled straight making the filling yarn crimp.
parameters to the crimp calculation.
Variation of crimp, a) warp is crimped and weft straight, b) weft is crimped modified from:
However, these equations are not the be
all the pores are not in same shape or size.
equations assume the pores being cylindrical pore are seldom cylindrical in woven fabrics.
pores: pores between the yarns, i.e. macroporosity, and pores between the fibres, i.e.
Also the compression of yarns as woven affects the pore dimensions, which results in errors in the calculated values. (Järvinen, 2005)
fabric yield
the interlacing of wa completely straight when it is interlacing with
length of the forming fabric is not as long as the initial warp on that length.
yarns. The crimp is the higher the more there are interlacing points, i.e. plain weave has the highest crimp of wea
long yarn floatings
. The crimp can be controlled to a certain extent by changing the yarn for example by heat setting in case of thermoplastic polymers.
Increasing the tension of the yarn the crimp can be reduced, but this will result in an increase of tension in the other yarn system. The increase of crimp in one direction affects also the modulus and elongation of the fabric by decreasing the modulus and increasing the elongation on that direction.
and flexibility of the fabric.
and has higher mass per unit area and greater thickness.
the warp is crimped and the filling can stay straight, and in warp yarn is pulled straight making the filling yarn crimp.
parameters to the crimp calculation.
, a) warp is crimped and weft straight, b) weft is crimped modified from: Adanur 2000, p.
However, these equations are not the best way to determine the pore diameters and all the pores are not in same shape or size.
equations assume the pores being cylindrical and straight,
abrics. In addition, there are always two types of pores: pores between the yarns, i.e. macroporosity, and pores between the fibres, i.e.
Also the compression of yarns as woven affects the pore in the calculated values. (Järvinen, 2005)
the interlacing of warp and weft completely straight when it is interlacing with the weft
length of the forming fabric is not as long as the initial warp on that length.
yarns. The crimp is the higher the more there are interlacing points, i.e. plain weave has the highest crimp of weave patterns, and in the contras
long yarn floatings of the weave pattern
. The crimp can be controlled to a certain extent by changing the yarn eat setting in case of thermoplastic polymers.
Increasing the tension of the yarn the crimp can be reduced, but this will result in an increase of tension in the other yarn system. The increase of crimp in one direction ion of the fabric by decreasing the modulus and on. The crimp affects further the weight, and flexibility of the fabric. The fabric with more crimp stretches more
nd greater thickness.
the warp is crimped and the filling can stay straight, and in warp yarn is pulled straight making the filling yarn crimp.
, a) warp is crimped and weft straight, b) weft is crimped Adanur 2000, p. 361
st way to determine the pore diameters and all the pores are not in same shape or size. The fact that many of the
and straight, distorts the results, since the In addition, there are always two types of pores: pores between the yarns, i.e. macroporosity, and pores between the fibres, i.e.
Also the compression of yarns as woven affects the pore in the calculated values. (Järvinen, 2005)
rp and weft. The warp
weft yarn. As a result of the crimp the length of the forming fabric is not as long as the initial warp on that length.
yarns. The crimp is the higher the more there are interlacing points, ve patterns, and in the contras
of the weave pattern
. The crimp can be controlled to a certain extent by changing the yarn eat setting in case of thermoplastic polymers.
Increasing the tension of the yarn the crimp can be reduced, but this will result in an increase of tension in the other yarn system. The increase of crimp in one direction ion of the fabric by decreasing the modulus and The crimp affects further the weight, The fabric with more crimp stretches more nd greater thickness. (Adanur 2000, p.
the warp is crimped and the filling can stay straight, and in warp yarn is pulled straight making the filling yarn crimp.
, a) warp is crimped and weft straight, b) weft is crimped 361-373).
st way to determine the pore diameters and The fact that many of the distorts the results, since the In addition, there are always two types of pores: pores between the yarns, i.e. macroporosity, and pores between the fibres, i.e.
Also the compression of yarns as woven affects the pore in the calculated values. (Järvinen, 2005)
warp yarn cannot flow . As a result of the crimp the length of the forming fabric is not as long as the initial warp on that length.
yarns. The crimp is the higher the more there are interlacing points, ve patterns, and in the contras
of the weave pattern, during which the . The crimp can be controlled to a certain extent by changing the yarn eat setting in case of thermoplastic polymers.
Increasing the tension of the yarn the crimp can be reduced, but this will result in an increase of tension in the other yarn system. The increase of crimp in one direction ion of the fabric by decreasing the modulus and The crimp affects further the weight, The fabric with more crimp stretches more
(Adanur 2000, p. 361 the warp is crimped and the filling can stay straight, and in Figure
Figure 20
, a) warp is crimped and weft straight, b) weft is crimped 30 st way to determine the pore diameters and
The fact that many of the distorts the results, since the In addition, there are always two types of pores: pores between the yarns, i.e. macroporosity, and pores between the fibres, i.e.
Also the compression of yarns as woven affects the pore
yarn cannot flow . As a result of the crimp the length of the forming fabric is not as long as the initial warp on that length. The same yarns. The crimp is the higher the more there are interlacing points, ve patterns, and in the contrast satin has during which the . The crimp can be controlled to a certain extent by changing the yarn eat setting in case of thermoplastic polymers.
Increasing the tension of the yarn the crimp can be reduced, but this will result in an increase of tension in the other yarn system. The increase of crimp in one direction ion of the fabric by decreasing the modulus and The crimp affects further the weight, The fabric with more crimp stretches more
361-373) In Figure 19b the Figure 20 gives the
, a) warp is crimped and weft straight, b) weft is crimped 30 st way to determine the pore diameters and The fact that many of the distorts the results, since the In addition, there are always two types of pores: pores between the yarns, i.e. macroporosity, and pores between the fibres, i.e.
Also the compression of yarns as woven affects the pore
yarn cannot flow . As a result of the crimp the The same yarns. The crimp is the higher the more there are interlacing points, t satin has during which the . The crimp can be controlled to a certain extent by changing the yarn eat setting in case of thermoplastic polymers.
Increasing the tension of the yarn the crimp can be reduced, but this will result in an increase of tension in the other yarn system. The increase of crimp in one direction ion of the fabric by decreasing the modulus and The crimp affects further the weight, The fabric with more crimp stretches more
In the gives the
, a) warp is crimped and weft straight, b) weft is crimped
The crimp factor
where
Figure 20
Another very similar term is yield, which can be defined as the ratio of length of woven fabric to the warp length. Yield is
warp yarn is needed to weave a certain length of fabric and it affects the fabric modulus thickness, air permeability, width, filling density and overall appearance
the yield must be kept uniform during the weaving. ( 5.5 Mechanical properties
For woven fabrics, t It is important to measure
break, rupture or develop holes too easily tensile strength and elongation at
quality of the fabric longitudinal pulling force.
withstand without breaking.
with few interlacing points in the weave pattern weave, but when th
instance, twill weaves have higher 370). Elongation
breaking or tearing
elongation just before the fabric breaking. In addition, that the fab
373; Hatch 2006 Tear strength
lateral direction, and when the tear strength exceeds the fabric tears progressively along one line
greatly the magnitude of tear strength. In the case of low yarn density the yarns are able The crimp factor,
Crim
where L = length of the yarn X = length of
20 Parameters to yarn crimp calculations (Adanur 2000, p.
Another very similar term is yield, which can be defined as the ratio of length of woven fabric to the warp length. Yield is
warp yarn is needed to weave a certain length of fabric and it affects the fabric modulus thickness, air permeability, width, filling density and overall appearance
the yield must be kept uniform during the weaving. ( Mechanical properties
For woven fabrics, there are several important mechanical factors that can be measured.
is important to measure
break, rupture or develop holes too easily tensile strength and elongation at
of the fabric longitudinal pulling force.
withstand without breaking.
with few interlacing points in the weave pattern , but when the yarn packing becomes too high instance, twill weaves have higher
Elongation describes the fabric’s abilit breaking or tearing
elongation just before the fabric breaking. In addition, that the fabric can still
; Hatch 2006, p.14
ear strength describes the
lateral direction, and when the tear strength exceeds the fabric progressively along one line
greatly the magnitude of tear strength. In the case of low yarn density the yarns are able i.e. percent crimp can be calculat
mp % L
X
= length of the yarn
X = length of the woven fabric
Parameters to yarn crimp calculations (Adanur 2000, p.
Another very similar term is yield, which can be defined as the ratio of length of woven fabric to the warp length. Yield is
warp yarn is needed to weave a certain length of fabric and it affects the fabric modulus thickness, air permeability, width, filling density and overall appearance
the yield must be kept uniform during the weaving. ( Mechanical properties
here are several important mechanical factors that can be measured.
is important to measure durability
break, rupture or develop holes too easily tensile strength and elongation at
of the fabric. Tensile strength
longitudinal pulling force. Thus, the tensile strength is the greatest force the fabric can withstand without breaking. (Adanur 2000, p.
with few interlacing points in the weave pattern e yarn packing becomes too high instance, twill weaves have higher
describes the fabric’s abilit (Hatch 2006, p.14
elongation just before the fabric breaking. In addition, can still recover when it is no
, p.14-43) describes the
lateral direction, and when the tear strength exceeds the fabric progressively along one line
greatly the magnitude of tear strength. In the case of low yarn density the yarns are able i.e. percent crimp can be calculat
greatly the magnitude of tear strength. In the case of low yarn density the yarns are able i.e. percent crimp can be calculat