Journal of Analytical Sciences, Methods and Instrumentation, 2012, 2, 92-97
http://dx.doi.org/10.4236/jasmi.2012.22017 Published Online June 2012 (http://www.SciRP.org/journal/jasmi)
Textile Environmental Conditioning: Effect of Relative
Humidity Variation on the Tensile Properties of Different
Fabrics
Mansoor Iqbal, Munazza Sohail, Aleem Ahmed, Kamran Ahmed, Arsheen Moiz, Khalil Ahmed*
Applied Chemistry Research Centre, PCSIR Laboratories Complex, Karachi, Pakistan.
Received December 25th, 2011; revised January 7th, 2012; accepted January 31st, 2012
ABSTRACT
With the aim that to confirm the n eed for humidity control in the environment in wh ich textile sample are visually and
instrumentally analyzed, three different pre-conditioned fabrics sample of cotton, p ol yester and silk were treated at a fix
temperature of 21˚C. The relative humidity adjusted to four levels: 55%, 65%, 75% and 85% RH for a conditioning
time of 24 hour s as specified in ASTM D-1776-98. It h a s been observed that as the r e lative humidity increase from 55%
to 85% cotton increase its tensile strength, silk losses its strength and there was no significant change observed in the
tensile strength of polyester fabric.
Keywords: Tensile Properties; Relative Humidity; Temperature; Fiber; Silk; Polyester; Cotton
1. Introduction
The properties of textile fibers are in many cases strongly
affected by the atmospheric moisture content. Many fi-
bers, particularly the natural ones are hygroscopic in the
sense that they are able to absorb water vapour from a
moist atmosphere and to give up water to a dry atmos-
phere. If sufficient time is allowed, equilibrium will be
reached. The amount of moisture that such fiber contains
strongly affects many of their most important physical
properties [1]. Many physical properties of a fiber are
affected by the amount of water absorbed such as dimen-
sions, tensile strength, elastic recovery, electrical resis-
tance, rigidity and so on. When in fabric from the mois-
ture relationships of a fiber play a major part in deciding
whether the fabric is unsuitable for a particular purpose.
The importance of this point is appreciated when fabrics
for clothing, both outerwear and underwear, are consid-
ered additional factors arise in these cases since the
structural details of the can modify the apparent behavior
of the fiber [2]. In an orderly array of molecules the side
chain will be linked, but in a random arrangement a
number of free links or hooks will be available, and if
they are of a polar character i.e. possess an attraction of
polar chemical groups such as hydroxyl OH, carboxyl
COOH, carbonyl CO etc, th en water molecule can attach
themselves. Orderly arrays of molecules occur in the
crystalline region of the fiber structure and random ar-
rays in the amorphous region. For a first approximation
we could conclude that the absorption of water takes
place in the amorphous region [3]. An alternative defini-
tion for Relative Humidity (RH) is the ab solute humidity
of the air to that of air saturated with water vapour at the
same temperature and pressure. This ratio may then be
expressed as a percentage. At ordinary temperatures such
as those at which processing and testing are carried out
the two ratios are almost identical. It is convenient to
describe a given atmosphere in term of relative humidity
rather than absolute humidity because the region of tex-
tile materials appears depends upon the relative hu midity
rather than the actual amount of water vapour present.
Since the relative humidity affect the region of textile
materials and since the properties of textile materials
influenced by the region. It is necessary to specify the
atmospheric condition in which testing should be carried
out [4]. Because of the important changes that occur in
textile properties as the moisture content changes, it is
necessary to specify atmospheric condition in which any
testing carried out. Therefore a standard atmosphere has
been agreed for testing purposes and is defined as a rela-
tive humidity of 65% and a temperature of 20˚C. For
practical purposes certain tolerances in these values are
allowed so that for testing atmosphere the RH is 65% ±
2%, 20˚C ± 2˚C. In tropical region a temperature of 27˚C
± 2C may be used [5]. Even though a testing laboratory
may have a controlled atmosphere, it is not good practice
*Corresponding author.

Textile Environmental Conditioning: Effect of Relative Humidity Variation on the Tensile Properties of Different Fabrics 93
to take in samples and immediately start to test them.
Sufficient time should be allowed for the sample to reach
equilibrium conditions before the test are made. A pre-
conditioning is therefore required specially before tensile
testing at 50˚C and 25% RH for 4 hours. Breaking
strength or tensile strength is the maximum force re-
corded in extending a test piece to breaking point. It is
the figure that is generally referred to as strength. The
force at which a specimen breaks is directly proportional
to its cross-sectional area, therefore when comparing the
strength of different fibers, fabrics allowances have to be
made for this. The tensile force recorded at the moment
of rupture is sometimes referred to as the tensile strength
at break [6]. In the present study we are trying to evalu-
ate the effect of RH at different levels on tensile strength
of polyester, cotton and silk fibers.
2. Materials & Methods
2.1. Material
Scoured and bleached, optical brightener free plain weave
cotton, silk and polyester fabric were used as given in
Table 1.
2.2. Equipments
To obtain the required relative humidity & temperature,
Conditioning Chamber (Denco, England) was used. For
pre-conditioning of fabrics, Associated Environmental
System (SDL Atlas, England) was used. Tensile strength
of the fabric was carried out on CRE Tensile Testing
Machine (LRX Plus, LLOYD). Fabric weight was de-
termined on G.S.M Cutter (Hans Schmidt & Co. Ger-
many). End & Picks were determined by Pick Glass
(Waltex 6X pick glass).
2.3. Procedure
 Pre-conditioning of all the fabrics were carried out in
Associated Environmental System of SDL Atlas at
50˚C and 25% RH for 4 hrs [5].
 Conditioning of samples was done in Conditioning
Chamber of DENCO England at 55%, 65%, 75% and
85% RH and 21˚C for 24 h rs [5].
 For Tensile Strength determination take two sets of
test specimen one in warp and other in weft direction.
Threads should be removed in approximately equal
numbers from each of the long edges of the cut strip
until the width of the test specimen is achieved. Each
set consist of at least 5-test specimen each should be
50 mm in width and 200 mm length. Tensile Strength
of fabric was determined according to standard test
procedure ISO 13934-1 (1999). [7]
 Fabric Weight was determined according to standard
test procedure ISO 3801 (1977)-E [8].
 Ends & Picks were determined by ISO 7211-2 (1984) [9]
3. Results and Discussion
To determine that how different levels of relative humid-
ity can affect on the tensile properties of fabrics, three
different fabrics cotton, polyester and silk were first pre-
conditioned at 50˚C at 25% R.H, then they again under-
goes to conditioning at 55%, 65%, 75% and 85% for
different levels of RH and at 21˚C temperature. It has
been observed that different fibers shows different be-
havior in terms of tensile strength under the same condi-
tions of RH and temperature. Shown in Table 2 and
Figure 1, as we passes from 55% to 85% RH, cotton
Table 1. Fabric weight and construc tion.
Fabric GSM (g/m2) Construction
Cotton 132 g/m2 22*22/80*58
Polyester 110.92 g/m2 60*30/140*72
Silk 70.01 g/m2 102*102/187*69
Table 2. For 100% cotton (tensile strength both in warp &
weft direction at different RH value s).
RH 55% 65% 75% 85%
Temperature 21˚C 21˚C 21˚C 21˚C
S #
Time 24 hrs 24 hrs 24 hrs 24 hrs
1 Warp 772N 810N 845N 910N
2 Warp 772N 810N 845N 910N
3 Warp 772N 810N 846N 912N
4 Warp 771N 811N 840N 908N
5 Warp 771N 809N 846N 910N
Mean warp 771.60N 810N 844.40N 910N
1 Weft 680N 730N 760N 819N
2 Weft 682N 731N 765N 825N
3 Weft 679N 729N 761N 820N
4 Weft 678N 727N 755N 817N
5 Weft 683N 733N 758N 816N
Mean Weft 679.8N 730N 759.8N 819.4N
Figure 1. Tensile strength of cotton in warp and weft direc-
tion at different RH values.

Textile Environmental Conditioning: Effect of Relative Humidity Variation on the Tensile Properties of Different Fabrics
94
increases its strength. Fundamentally, it is due to the de-
crease in cohesive force between the chain molecules due
to swelling and the release of internal strain by swelling.
Thus in the native cellulosic fiber, such as cotton, the
release of internal strain between the long chain mole-
cules predominant and this increase the fiber strength
because of a more uniform internal distribution of stress.
Also the av er age cha in leng th (DP) in co tton is fiv e ti mes
greater than regenerated cellulose, so that the individual
molecules in cotton may be expected to have more point
of adhesion and so to process greater internal strain [10].
In its mature dried form, nearly 90 per cent by weight of
the cotton fibre is cellulose. In fact the cellulose found in
cotton fibres is the purest form of cellulose found in all
plants. The cellulose in cotton fibres is mostly (88 - 96.5
per cent). The non-cellulose components (4 - 12 per cent)
are located either on the outer layers of the cotton fibre in
the cuticle and primary cell wall or inside the residual
protoplasm called the lumen. The secondary wall of ma-
ture fibres is primarily cellulose in its most highly crys-
talline and oriented form Figure 2 show s the structure of
the cellulose molecules in cotton. From a physical view-
point the molecule is a ribbon-like structure of linked
six-member rings each with three hydroxyl groups (OH)
on the C2, C3 and C6 atoms projecting out of the plane
of the ribbon. As well as providing structural stability the
hydroxyl groups allow extensive intermolecular hydro-
gen bonding with many molecules, including water. The
accessibility of water to these hydroxyl groups depends
on the spacing between crystal lattice planes. From a
completely dry state, water molecules will form hydro-
gen bonds with hydroxyl groups that are not already
linked within crystalline regions [11].
Figure 2. Assembly of cellulose molecules in a sheet. Hy-
drogen bonds are shown by dotted lines. Circled carbon
atoms; C2, C3 and C6, show location of hydroxyl (-OH)
groups.
As indicated from Table 3 and Figure 3, the silk fab-
ric shows a reverse result as compared to cotton, as we
move from 55% towards 85% R.H, the tensile strength
determined were gradually decreased. The silk fiber are
linear, fibroin polymer that forms a chemical point of
view, differ from wool fiber due to their different amino
acid composition. More precisely, silk fiber does not
contain disulphide bonds. This Chemical difference may
affect the morphology of the crystal, producing only the
β-configuration, which together with the high degree of
crystallinity is responsible for high tens ile strength of silk
fiber. In wet conditions the tensile strength of silk fiber
decreases because water molecules hydrolyze a signifi-
cant number of hydrogen bond [12]. Silk is a natural fi-
ber secreted as a continuous filament by the silk worm,
Table 3. For silk (tensile strength both in warp & weft direc-
tion at different RH values).
RH 55% 65% 75% 85%
Temperature 21˚C 21˚C 21˚C 21˚C S #
Time 24 hrs 24 hrs 24 hrs 24 hrs
1Warp 512N 480N 452N 407N
2Warp 510N 480N 450N 410N
3Warp 508N 478N 449N 409N
4Warp 514N 483N 453N 405N
5Warp 512N 480N 452N 403N
Mean Warp511.20N480.20N 451.20N406.8N
1Weft 463N 441N 414N 368N
2Weft 465N 444N 416N 370N
3Weft 462N 445N 418N 371N
4Weft 466N 438N 412N 365N
5Weft 460N 440N 413N 367N
Mean Weft 463.20N441.6N 414.6N368.2N
Figure 3. Tensile strength of silk in warp and weft direction
at different RH values.

Textile Environmental Conditioning: Effect of Relative Humidity Variation on the Tensile Properties of Different Fabrics 95
Bombyx mori. Silk consists essentially fibroin polymer
and in the raw state coated with a gum Sericin that is
usually removed before spinning. The silk polymer is
composed of 16 different amino acids linked with pep-
tide bonds. The important chemical groups of the silk
polymer are the peptide groups which gives rise to hy-
drogen bonds, and the carboxyl and amine groups which
gives rise to the salt linkag es. The silk filament is strong.
This strength is due to its linear, β-configuration polymer
and very crystalline polymer system. These two factors
permit more hydrogen bonds to be formed in a much
regular manner. When wet silk losses its strength. This is
due to water molecules hydrolyzing a significant number
of hydrogen bonds and in the pro cess weakening the silk
polymer. The greater crystalline of silk polymer system
allows fewer molecules enter into the polymer system of
silk [13].
-NH-CH-CO-NH-CH-CO-NH-CH-CO-
H- n
- OH
RR1R2
The general formula for the polypeptide polymer. De-
pending upon the type of radical R, R1, R2, the polypep-
tide polymer would be identical either as being a silk
fibroin polymer or a wool keratin polymer.
The results obtained from Table 4 and Figure 4, poly-
ester fabric shows that it is strong to very strong fabric
because of their extremely crystalline polymer system.
This allows the formation of very effective Van der
Waals forces as well as the very weak hydrogen bond,
resulting in very good tensile properties one associated
with polyester polymer. The tensile strength of polyester
fiber remains unaltered when we passes from 55% to
85% RH. This occurs because of the completely hydro-
phobic and extremely crystalline polyester polymer sys-
tem, which resists the entry of water molecules to any
significant extant [14].
Polyester fiber is the condensation polymerization
product of ethylene glycol and terepthalic acid. The word
ester is the name given to salt formed from the reaction
between an alcohol and an acid. Ester is organic salt and
polyester means many organic salts. Chemically it is a
polymer of polyethylene glycol terphlate. The important
chemical groups in the polyester polymer are the ethyl-
ene group, - CH2-, the sligh tly polar carb onyl group, -CO-,
and the ester group, -O CO- group. The one of the distin-
guishing characteristics of polyester is attributed to the
benzene rings in the polymer chain. The aromatic char-
acter leads to chain stiffness, preventing the deformation
of disordered regions, which results in weak Van der
Waals interaction forces between chains. The aromatic,
carboxyl and aliphatic molecular groups are nearly planar
in configuration and exist in a side-by-side arrangement.
The cohesion of polyester chains is a result of hydrogen
bonds and van der Waals interactions, caused by dipole
interaction, induction and dispersion forces among the
chains. The insignificant amount of moisture, which may
be present in polyester textile materials, exists as a mo-
lecular film of water on the surface of filaments of staple
fiber [15].
OOCCOO CH22n
Polyet hylene Terpthlate
Table 4. For polyester (Tensile Strength both in warp &
weft direction at different RH value s).
RH 55% 65% 75%85%
Temperature 21˚C 21˚C 21˚C21˚C
S #
Time 24 hrs 24 hrs 24 hrs24 hrs
1 Warp 935N 942N 937N939N
2 Warp 936N 945N 939N937N
3 Warp 938N 944N 940N936N
4 Warp 933N 939N 934N940N
5 Warp 934N 941N 935N942N
Mean warp 935.2N 942.2N 937N938.8N
1 Weft 860N 864N 862N863N
2 Weft 861N 866N 866N864N
3 Weft 857N 864N 868N867N
4 Weft 859N 867N 857N859N
5 Weft 863N 858N 858N861N
Mean Weft 860N 863.8N 862.2N862.8N
Figure 4. Tensile strength of polyester in warp and weft
direction at different RH values.

Textile Environmental Conditioning: Effect of Relative Humidity Variation on the Tensile Properties of Different Fabrics
96
Figures 5(a) and (b) indicates the combined effect of
Tensile Strength both in Warp and Weft direction of silk,
cotton and polyester at different RH values. It has been
also observed that the tensile strength calculated in weft
direction for each cotton, polyester and silk fiber comes
out to be minimum as compared to the warp direction,
furthermore fluctuation in the RH have no significant
effect on tensile results of polyester fabric and a pro-
nounced effect were found in case of cotton and silk fi-
ber.
All fibers, whether hydrophilic or hydrophobic, absorb
some water from an atmosphere having a relative humid-
ity above 0%. The amount of moisture contained by a
fiber when its own relative humidity is equal to that of
the surrounding atmosphere, and the point at which fiber
will neither gain nor lose moisture to the atmosphere is
called equilibrium moisture co ntent. The equilibrium mois-
ture content will remain unchanged unless the relative
(a)
(b)
Figure 4. (a) Combined effect of Tensile Strength in Warp
direction at different RH values; (b) Combined effect of
Tensile Strength in Weft direction at different RH values.
humidity is changed; lowering the relative humidity of
the environment will result in the fiber losing moisture
until new equilibrium moisture content is reached. Simi-
larly, increasing the relative humidity of the environment
will result in the fiber gaining moisture until new equi-
librium moisture content is reached.
Relative humidity (RH) governs the amount of mois-
ture contained in materials at equilibrium with the envi-
ronment. This is almost independent of temperature. As
relative humidity changes, the object’s water content
adjusts to the new relative humidity level, creating a new
equilibrium. At higher RH, there is more water in fiber
[16].
Silk and cotton are hydrophilic fibers, meaning that
their surface has bonding sites for water molecules. There-
fore, water tends to be retained in the hydrophilic fibers,
which have poor moisture transportation and release;
they have the ability to absorb moisture from the sur-
roundings. At equilibrium the moisture content of silk is
about 11% and that of cotton is about 8%. Polyester is a
hydrophobic fiber; meaning that their surface has few
bonding sites for water molecules. Hence, they tend not
to get wet and have good moisture transportation and
release. Its moisture content is low as 0.4%, it absorbs
moisture very slowly and dries quickly. Cotton and silk
absorbs moisture very quickly but dries slowly. As the
relative humidity (RH) of the surrounding increases, the
moisture absorption also increases and as the relative
humidity decreases the drying of fibers or “Desorption”
takes place [17].
If two identical samples of fibre, one wet and one dry,
are placed in a standard atmosphere of 65% RH, it might
be expected that they would both eventually reach the
same value of regain. However, this is not the case as the
one that was originally wet is found to have a higher re-
gain than the one that was originally dry; this difference
is due to hysteresis between moisture uptake and mois-
ture loss [18].
Exposure to moisture for prolonged period of time
may cause to degradate the textile fibes. Under higher
humid conditions for prolonged period of time may cause
to change the dimension, texture and shape of the textile
fibers. As the relative humidity decreases, desorption or
drying of textile fibers takes place. It is not reversible
under drying conditions, because under lower humidity
conditions some textile fibers may losses and some in-
creases their strength. Controlled humid conditions are
required for partic u la r f abric [19].
4. Conclusion
The present research work has demonstrated that textile
samples exhibits often significant change in tensile
strength testing as relative humidity fluctu ates around the
recommended standard condition of 65% RH. In case of

Textile Environmental Conditioning: Effect of Relative Humidity Variation on the Tensile Properties of Different Fabrics
97
synthetic fiber polyester, we found no significant differ-
ence in tensile properties due to the hydrophobic charac-
ter of this fiber. In natural fiber cotton we found a pro-
nounced effect in tensile properties by fluctuate the rela-
tive humidity from 65% to 85%. In cotton the tensile
strength gradually increases. The silk fiber shows a re-
verse result as compared to cotton, the tensile strength
decreases as we passes from 65% to 85% RH. It is rec-
ommended that environmental conditions must be speci-
fied and continually controlled so as to minimize tensile
strength results variation for all samples to be evaluated.
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