Impact of Artificial Weathering on Swimwear Fabric

Abstract

Lately, being physically active has become a priority of daily life. Despite that outdoor sports boost an individual’s mental and physical health, it also generates the problem of ultraviolet light exposure. Clothes provide the wearer protection from the sun, but they are also damaged while completing this task. Therefore, the impact of ultraviolet aging on swimwear fabric, which is the most exposed type of garment to the sunrays, was investigated in this study. Changes in breaking force, elongation at break, air permeability, fabric elasticity and stiffness, and dimensional characteristics were examined after 120 and 240 h of artificial weathering, together with scanning electron microscope (SEM) images and Fourier-Transform Infrared (FTIR) spectroscopy. The influence of seawater treatment was explored as well. The results presented that breaking force, elongation at break, fabric elasticity and stiffness, and air permeability were dramatically influenced by ultraviolet exposure. No chemical destruction was observed in FTIR spectra, while micro-damages were detected in SEM images. Furthermore, it was concluded that the main detrimental parameter was UV radiation, and the effect of seawater treatment was usually found to be minimal or not distinctive. Due to the limited number of research on the impact of UV aging on warp-knitted swimwear, this study is expected to contribute to the related literature.

Full text

Vol.:(0123456789)
Fibers and Polymers
https://doi.org/10.1007/s12221-024-00579-4
REGULAR ARTICLE
Impact ofArtificial Weathering onSwimwear Fabric
BernaCüreklibatırEncan1
Received: 9 February 2024 / Revised: 20 April 2024 / Accepted: 3 May 2024
© The Author(s) 2024
Abstract
Lately, being physically active has become a priority of daily life. Despite that outdoor sports boost an individual’s mental
and physical health, it also generates the problem of ultraviolet light exposure. Clothes provide the wearer protection from
the sun, but they are also damaged while completing this task. Therefore, the impact of ultraviolet aging on swimwear
fabric, which is the most exposed type of garment to the sunrays, was investigated in this study. Changes in breaking force,
elongation at break, air permeability, fabric elasticity and stiffness, and dimensional characteristics were examined after 120
and 240h of artificial weathering, together with scanning electron microscope (SEM) images and Fourier-Transform Infrared
(FTIR) spectroscopy. The influence of seawater treatment was explored as well. The results presented that breaking force,
elongation at break, fabric elasticity and stiffness, and air permeability were dramatically influenced by ultraviolet exposure.
No chemical destruction was observed in FTIR spectra, while micro-damages were detected in SEM images. Furthermore,
it was concluded that the main detrimental parameter was UV radiation, and the effect of seawater treatment was usually
found to be minimal or not distinctive. Due to the limited number of research on the impact of UV aging on warp-knitted
swimwear, this study is expected to contribute to the related literature.
Keywords Warp-knitted fabric· Swimwear· Ultraviolet aging· Artificial aging· Seawater
1 Introduction
Exercising, especially outdoors, is a mostly preferred means
of maintaining a state of physical and mental health. Moreo-
ver, physical activity has become a necessity for an indi-
vidual’s social life. Swimming is quite a beneficial sport as
it actuates the whole body and also provides refreshment in
the summer heat. For this reason, swimwear constitutes an
important part of sportswear. Similar to other types of gar-
ments, swimwear is also expected to maintain its properties
during use. However, due to its nature, swimwear is exposed
to heavy detrimental factors that lead to aging whether it is
used for sports or refreshment. Polymer aging is the combi-
nation of several irrevocable changes in polymer properties
due to the effects of light, oxygen, heat, chemicals, etc. [1].
Public awareness regarding the risks of prolonged skin
exposure to sunlight has increased during the last decades.
Since clothing is the easiest way of guarding the body
against UV radiation, market demand for garments providing
ultraviolet (UV) protection is growing rapidly [2]. A study
comparing the defensive effect of four sun-protective textiles
and two broad-spectrum organic sunscreens was conducted
by Berry etal. [3]. Each fabric was found superior to both
sunscreens. Besides, research has presented that long-term
use of sunscreens may result in neurological, endocrine, and
developmental complications [4]. Although clothes are the
most suitable way of protecting the human body from UV
radiation, the radiation itself is one of the major causes of
the degradation of textile materials [5]. Photodegradation
substantially impacts the overall lifetime of materials [6].
The detrimental effect of UV radiation on fabric depends
on several parameters, such as mass per unit area, fiber type,
yarn properties, duration of UV exposure, finishing, and col-
oration process [7].
The literature search presented that the related literature
can be divided into three main aspects. In the first aspect,
various parameters that affect the UV protection factor
(UPF) of fabrics have been studied by researchers. Numer-
ous work was presented in this aspect. Therefore, only the
ones that included knitted fabrics were mentioned in this
research. In the second and third aspect, the influence of
Online ISSN 1875-0052
Print ISSN 1229-9197
* Berna Cüreklibatır Encan
berna.encan@ege.edu.tr
1 Ege University Emel Akın Vocational Training School,
İzmir, Turkey

Fibers and Polymers
natural and artificial weathering on fabrics was examined
respectively.
Stankovic etal. [8] examined the UPF of gray fabrics
knitted in single jersey structure. Samples were knitted
with three cotton yarns differing in twist level. Yarn twist
level was found as a major factor affecting a fabric’s UPF
value due to its influence on yarn compactness and surface
properties, such as porosity and stitch density. Wong etal.
[9] investigated the effect of various knit structures and
fabric parameters on the UPF of greige and bleached knitted
fabrics. It was concluded that fabrics with miss stitches
provide higher UPF than fabrics with tuck stitches. Besides,
double-layer fabrics were found to have superior UV
protection than single-layer fabrics. Bleaching was observed
to have different impacts on the UPF of single and double-
layer fabrics. It was expressed that fabric porosity can be a
good indicator of UV protection. Kan [10] investigated the
impact of fabric parameters on UPF of 100% cotton-knitted
fabrics. UPF of various fabric structures (plain, pineapple,
piquet, half Milano, full Milano, half cardigan, full cardigan,
1 × 1rib, and interlock) was analyzed in terms of weight,
thickness, and stitch density. Data presented that weight was
the most influential parameter on UPF. The effect of yarn and
knitting parameters on ultraviolet radiation protection was
analyzed by Mal etal. [11] with Taguchi design methods.
The influence of loop length, knitting speed, yarn input
tension, and yarn count of single jersey and 1 × 1 rib samples
knitted with 100% cotton yarn was investigated. Yarn count
and loop length were reported as significantly effective on
UPF for both knitted structures. The ultraviolet protection
factor of several weft-knitted fabrics was investigated by
Wong etal. [12]. It was concluded that stitch types (knit,
tuck, and miss) and their ratios within the structure vastly
affect UPF. Tuck stitches were reported to decrease UPF due
to the more porous structure they created. Miss stitches were
suggested to be preferred in both single and double-jersey
fabrics to enhance UPF as they formed a more compact
structure. Moreover, interlock gaiting was recommended to
achieve a higher UPF in double-jersey fabrics. UV resistance
of polyester interlock derivatives (plain interlock, pique,
half cardigan, half Milano, and cross-miss) was studied by
Jamshaid etal. [5]. It was observed that fabric structure and
stitch type play key roles in UPF. In addition, half Milano
was noted as the structure with the highest UPF among the
others. Louris etal. [2] studied the UPF of various knitted
fabrics. 27 fabric samples were knitted with 2-ply and 3-ply
100% organic cotton yarns on a flat knitting machine. It was
concluded that fabric structure had a great effect on the UPF.
The existence of miss stitches was associated with higher
UV-blocking performance. On the other hand, the influence
of tuck stitches on UPF may be both positive and negative
depending on the combination and repetition in the knit
structure. It was revealed that closer and tighter structures
offer higher UV protection, as expected. Abdel-Megied etal.
[13] investigated the effect of various fabric parameters on
the UPF of single jersey structure. The influence of two raw
materials (cotton and microfiber polyester), three machine
gages (E20, E24, E28), two yarn counts (Ne 30/1 for cotton
and 150/288 denier for polyester), and three yarn tension
levels (high, medium, low) on UPF was examined. It was
concluded that higher machine gage and yarn tension
resulted in enhanced UPF values. Microfiber polyester
provided better protection than cotton, and thicker yarns
presented superior UPF. Kamal etal. [14] researched the
impact of some construction parameters on the UV radiation
resistance of bi-layer knitted fabrics. Samples of the study
were produced on a circular knitting machine with polyester
yarn in the inner layer and various yarns (cotton, modal,
and cotton-bamboo blends) in the outer layer. Mass per
unit area, fabric thickness, sun-protective factor, bursting
strength, water vapor permeability, and air permeability
of the samples were measured. It was determined that
the sample with tuck stitches had the lowest rate of UV
protection due to its more porous structure. Samples with
cotton yarn exhibited the highest UV protection factor
for back materials, while bamboo–cotton (70/30%) had
the lowest value. For face materials, the polyester–viscon
blend provided superior UV protection. Fabrics containing
bamboo yarn were found to have better UV protection than
cotton and modal yarns. The knit structure of the samples
was spotted as the most significant parameter regarding UV
protection.
The impact of photodegradation on fabrics was
investigated by various researchers via natural and artificial
weathering.
Bhat etal. [15] studied the effect of sunlight on cot-
ton woven fabrics. Samples were kept under sunlight with
and without artificial perspiration for 6h daily constitut-
ing a total of 336h from February to June. Fabrics were
removed for testing every 84h. After sunlight exposure,
changes in tensile strength, surface morphology, and X-ray
diffraction were evaluated. A significant strength loss was
observed in both samples; however, the loss was larger for
the samples kept without perspiration. More fibrillation was
observed as the aging duration extended. Dierickx and Van
Den Berghe [16] observed the changes in several proper-
ties of five agrotextiles during a five-year period of natural
aging. The results presented that the effect of weathering
depended on the material type. PVC-coated woven samples
showed a significant decrease in tensile strength especially
after one year of exposure, while UV-stabilized polyeth-
ylene samples (woven and knitted) presented only a slight
decrease. Mass loss was observed in PVC-coated samples.
On the other hand, no loss was measured in UV-stabilized
samples. Fabric thickness was not influenced by weathering.
Cubric etal. [17] investigated the changes in knitted fabric

Fibers and Polymers
properties after exposure to outdoor natural weathering.
Single jersey fabrics made of cotton, cotton/modal, viscose,
lyocell, and polyester were produced. Samples’ heat resist-
ance, structural, and tensile properties were measured after
exposure to summer weather conditions for three months.
Results presented a decrease in breaking force and heat
resistance, whereas an increase in vertical density and mass
per unit area. Cubric etal. [18] studied the changes in water
vapor resistance of polyurethane (PU)-coated knitted fabrics.
Totally nine different warp and weft-knitted samples made
out of polyester and polyamide were coated with the same
process. All samples were exposed to natural weathering
in the summer and winter seasons. A loss was observed in
water vapor resistance for all samples after outdoor expo-
sure. Fabric shrinkage was more evident after summer aging.
Besides, SEM images revealed a more severe PU degrada-
tion in summer. Additionally, the thermal resistance of these
samples after the same aging procedure was examined in the
study by Matkovic etal. [19]. The analysis presented a drop
of 13% and 25% after aging in the summer and winter sea-
sons respectively. Matkovic and Skenderi [20] researched the
changes in various properties of polyurethane-coated warp
and weft-knitted fabrics made out of polyester and polyam-
ide after natural weathering. Solar radiation was reported
to have a considerable effect on the decrease of breaking
force. Additionally, samples were reported to shrink, and
had lower values of elongation (in both wale and course
directions) and thickness after exposure. The performance
of paragliding fabrics after natural aging was evaluated by
Süpüren Mengüç etal. [21]. Five different paragliding fab-
rics with various colors, densities, yarn counts, and coating
materials were chosen for this study. After 150h of natural
aging, significant loss was observed in mechanical proper-
ties, such as tearing and breaking strength. Yet, no change
was observed in air permeability values. Cubric etal. [22]
aimed to develop an aging protocol for swimwear materials
for athletes training in swimming pools. They also evaluated
the change in some comfort and durability characteristics
after sunlight exposure. Four weft-knitted materials contain-
ing polyester, polyamide, and their blends with elastane were
aged in swimming pool water both indoors and outdoors.
Samples were aged for 21, 42, and 63h simulating the mate-
rial use for 6,12, and 18weeks respectively.
Ming etal. [23] aimed to establish a correlation between
natural and artificial UV aging using B. mori silk fabric.
Samples were aged naturally for six months and artificially
for 160h. Various tests to determine the changes in fabric
parameters (whiteness, mechanical property, ultraviolet
protection factor) and Fourier-Transform Infrared (FTIR)
Spectroscopy were applied. Whiteness index and breaking
strength declined as the duration of aging extended. On the
contrary, UPF values of the samples exhibited higher values
after both types of aging. Temel etal. [7] artificially aged
emergency tent fabrics (100% cotton, woven, ammonium
dihydrogen phosphate (ADP)-coated) for 250, 500, and
750h, afterward various tests were conducted. Results
showed that a considerable loss of tensile strength (40%)
and tear strength (70%) was observed after 500h of aging.
No significant loss of tear and tensile strength was observed
later on. Furthermore, a change in air permeability was not
observed. Gohar and Mazari [6] investigated the changes in
comfort and physical properties of six abaya clothing (three
woven and three knitted) after artificial UV weathering.
Samples were tested for drapeability, air permeability,
water vapor, and thermal resistance after UV weathering.
A significant loss was observed in drapeability for all
samples, the loss was higher for knitted samples though.
The air permeability of both types of samples also decreased
substantially. On the other hand, UV weathering enhanced
both water vapor and thermal resistance. Saceviciene etal.
[24] examined the changes in the physical properties of
architectural PES/PVC-coated membranes after different
artificial aging conditions. Two commercially available
membranes were tested for various physical properties.
The results demonstrated that SEM images presented initial
cracks after aging. However, the mechanical performance
of the PES/PVC membranes did not change. The impact
of weathering on PVC-coated fabrics’ tear strength was
also studied by Dobilaite etal. [25]. Three PES/PVC-
coated architectural membranes used as building envelopes
were exposed to accelerated aging conditions. The effect
of abrasion, high temperature, and humidity on tearing
properties was determined. After exposure to artificial
weathering, the tear strength of architectural membranes
changed within limits. The dominant factor in the aging
of these membranes was expressed as high temperature.
Mazari etal. [26] investigated the impact of ultraviolet
radiation on thermal protective performance and comfort
properties of firefighter protective clothing. They tested
two firefighter clothing with outer shells made of different
fiber blends. Samples were exposed to UV radiation in an
artificially accelerated weathering chamber for 13days. It
was concluded that tensile strength, bending moment, and
air permeability values declined. On the other hand, water
vapor resistance values enhanced after UV radiation for both
outer shell samples.
The majority of the studies in the literature focused on
the UPF, which defines how well a fabric protects the human
body from UV radiation. Parameters affecting the UPF,
such as yarn properties, fabric structure, and production
parameters, were investigated comprehensively. The changes
occurring due to natural and artificial UV radiation have
become the subject of various, yet relatively fewer, studies
as well. Cubric etal. [22] also stated that research about
the effects of UV aging on the comfort and durability of
textiles is quite rare in the literature. Since fabrics provide a

Fibers and Polymers
shielding layer against the destructive effects of UV rays, it
is important to distinguish how UV radiation affects them.
Swimwear can be recognized as the garment which is the
most prone to photodegradation. Nevertheless, studies about
swimwear and UV radiation are quite limited. Polyamide
warp-knitted fabrics are generally preferred in swimwear.
Literature regarding UV aging mostly consists of studies
with woven or weft-knitted fabrics usually made of cotton
or coated fabrics for technical purposes. To address this gap,
this study investigates the effect of UV radiation on a warp-
knitted swimwear fabric made of polyamide. In the case of
swimwear fabrics, maintaining the fit of the garment along
with its durability during its lifetime is crucial. Therefore, a
swimwear fabric was exposed to artificial weathering with
and without seawater treatment in this study. Change in
mass per unit area, fabric thickness, course and wale per
cm, breaking force, elongation at break, fabric stiffness, air
permeability, and fabric elasticity were evaluated after the
procedures. Besides, the change in the chemical structure
and surface morphology of the fabric was analyzed by
Fourier-Transform Infrared (FTIR) spectroscopy and
scanning electron microscope (SEM) respectively.
2 Materials andMethods
Characteristics of the warp-knitted swimwear fabric are
given in Table1. Test samples were kept in standard atmos-
phere conditions (20 ± 2ºC temperature, 65% ± 2 relative
humidity) for at least 24h prior to testing.
Artificial UV aging of the swimwear fabric was con-
ducted on a Prowhite UV Test Box under 35 W/m2 radia-
tion intensity for 120 and 240h of continuous exposure to
fluorescent ultraviolet light. Since seawater is considered
a detrimental factor for swimwear, an additional seawater
treatment was applied to half of the 120 and 240-h-aged
fabrics as shown in Table2. The seawater treatment was
conducted as per ISO 105-E02 Textiles – Tests for color
fastness – Part E02: Color fastness to seawater. Seawater
treatment was applied at the beginning of the aging proce-
dure and repeated every 60h until either a 120- or 240-h
procedure was completed. Samples treated with seawater
were rinsed with tap water before testing. Sample codes and
applied procedures are given in Table2.
Tested parameters of the samples and followed test
standards are shown in Table3.
The bursting strength test was applied to the samples
on two different test instruments operating according to
pneumatic and hydraulic test principles. However, neither of
the instruments could burst the fabric due to its high elastane
content. Therefore, the breaking force and the elongation
values of the samples were measured to compare the changes
in tensile properties after UV aging, as in the research of
Cubric etal. [17] and Jamshaid etal. [5].
The determination of elasticity properties of the fabrics
was performed on a test apparatus with hangers as shown
in Fig.1. Test samples of 10cm × 40cm in size were folded
in two and sewn from their short side to form a ring. Two
lines with a 13cm distance (l1) were drawn on the samples
before they were located on two hangers. A dynamometer
was hung on the bottom hanger to apply a 5kPa force four
times. During the fifth application of the 5kPa force, the
distance between the drawn lines (l2) was measured. Fabric
elasticity was calculated as per the below Eq.(1).
The surface morphology of fabric samples was analyzed
by a Thermo Scientific Apreo S scanning electron
microscope (SEM) with a magnification of 150 × to 10000x.
Prior to imaging, the specimens were metalized using gold
sputtering.
The effects of artificial weathering and seawater treat-
ment on the chemical structure of swimwear fabric were
(1)
Elasticity
(%)=
l
2
−l
1
l
1
x
100
Table 1 Fabric characteristics
Material
Course
per cm
(cm-1)
Wale
per cm
(cm-1)
Mass per
unit area
(gm-2)
Thickness
(mm)
Microscopic image
(250x)
80% polyamide –
20% elastane
28 22 190 0.673
Table 2 Sample codes and applied procedures
Sample code Procedure
S1 Unaged
S2 120h of aging
S3 120h of aging and seawater treatment
S4 240h of aging
S5 240h of aging and seawater treatment

Fibers and Polymers
determined by Fourier-Transform Infrared (FTIR) spec-
troscopy equipped with a deuterated triglycine sulfate
detector (DTGS). FTIR spectra were acquired using a Per-
kin Elmer Spectrum Two Spectrometer. Four scans were
performed for each sample with a resolution of 4 cm−1 in
the range of 600–4000 cm−1. Peak height was expressed
in terms of absorbance.
Test results were evaluated using the software PASW
Statistics 18 with a 95% confidence interval. The statistical
method analysis of variance (ANOVA) was applied to
determine the statistical importance of the variations. The
probability values or p values were examined to determine
whether the parameters were significant or not. If the p
value of a parameter is greater than 0.05 (p > 0.05), the
parameter was accepted as insignificant and was ignored.
When the p value was stated as lower than 0.05 (p < 0.05),
then the Student–Newman–Keuls (S–N–K) post hoc test
was used for homogeneous variance and Tamhane’s T2
post hoc test was used for heterogeneous variance.
3 Results andDiscussion
Test results of the samples are given in Table4. The mean
values are marked with letters from “a” to “d” where
“a” and “d” represent the lowest and the highest values,
respectively. If the mean values were not significantly
different, then they were marked with the same letter.
3.1 Dimensional Characteristics
The results presented that UV aging of the samples led to
a 9% shrinkage in the number of wales per cm, as observed
in the research of Cubric etal. [17]. The samples, even
after the first 120h of aging, shrunk widthwise. On the
other hand, no change was observed in the course per
cm value. The higher number of wales in the unit area
resulted in a higher stitch density which is defined as the
multiplication of wale and course per cm values. Elevated
stitch density values after UV exposure created minor
escalations in mass per unit area values. However, these
changes were found statistically insignificant.
Fabric thickness decreased 1 and 2% after 120 and 240h
of UV exposure, respectively. However, the mentioned
reductions were found statistically insignificant. The
influence of seawater treatment was not distinctive as well.
Similarly, a decrease in fabric thickness after UV aging
was observed in the research of Cubric etal. [17] and
Matkovic and Skenderi [20].
The results presented minimal increases in mass per
unit area and the number of wales in unit area, while
minor reductions in fabric thickness. These changes
can be associated with the combined impact of fabric
wear causing a reduction in mass and fabric shrinkage
increasing the weight, as explained by Matkovic and
Skenderi [20].
Table 3 Tested parameters and
followed test standards Parameter Related standard Test devices Repetition
Mass per unit area EN 12127:1999 Digital scale with .000 accuracy 3 times
Fabric thickness TS 3374 ISO 1765: 2004 Wira Digital Thickness Gage (2kPa
presser foot)
5 times
Course per cm TS EN 14971: 2006 Magnifying glass 5 times
Wale per cm TS EN 14971: 2006 Magnifying glass 5 times
Breaking force EN ISO 13934–1 Zwick Roell Z010 5 times
Elongation at break EN ISO 13934–1 Zwick Roell Z010 5 times
Fabric stiffness BS 3356:1990 Shirley Bending Length Tester 4 times
Air permeability ISO 9237:1995 Textest FX 3300 (100Pa pressure
and sample area of 20 cm2)
10 times
Fabric elasticity TS 10985 Test apparatus with hangers 3 times
Fig. 1 Fabric elasticity test
apparatus

Fibers and Polymers
3.2 Breaking Force andElongation atBreak
Breaking force and elongation at break defines a fabric’s
strength and extensibility [27]. A 68% breaking force reduc-
tion was observed lengthwise after 120h of UV exposure
(Fig.2). Although an additional 27% decrease was measured
after the second 120-h procedure, the main strength loss
occurred in the first round of aging (120h) in accordance
with the work of Davis etal. [28]. The effect of seawater
treatment was marked as minimal and statistically insignifi-
cant for breaking force in the wale direction. A substantial
fall of 39% in lengthwise elongation capability was identi-
fied after the first 120-h procedure (Fig.3). Yet, the elonga-
tion value did not change much as the aging process was car-
ried on until 240h. However, the negative effect of seawater
on elongation was evident after 240h of exposure.
In course direction, considerable deterioration of breaking
force (77%) was obtained after 120h of exposure (Fig.2).
An improvement was observed in the widthwise breaking
force after the second 120-h procedure surprisingly. The
influence of seawater treatment was not clear on this fabric
Table 4 Test results of the samples
Parameters p value Mean value
Mass per unit area (gm−2) S1 0.021* 190.26 a
S2 199.38 a
S3 197.61 a
S4 191.44 a
S5 199.38 a
Fabric thickness (mm) S1 0.000* 0.673 a
S2 0.666 a
S3 0.663 a
S4 0.658 a
S5 0.666 a
Course per cm (cm−1) S1 – 28
S2 28
S3 28
S4 28
S5 28
Wale per cm (cm−1) S1 – 22
S2 24
S3 24
S4 24
S5 24
Breaking force–lengthwise (N) S1 0.000* 434 c
S2 141 b
S3 136 b
S4 103 a
S5 96 a
Elongation at break–lengthwise (%) S1 0.000* 276 c
S2 169 b
S3 182 b
S4 178 b
S5 145 a
Breaking force–widthwise (N) S1 0.000* 305 d
S2 71 a
S3 116 c
S4 104 b
S5 80 a
Elongation at break–widthwise (%) S1 0.000* 578 d
S2 274 a
S3 366 c
S4 344 b
S5 291 a
Fabric stiffness S1 – 5.92
S2 14.63
S3 11.43
S4 7.96
S5 11.13
Fabric elasticity–lengthwise (%) S1 0.000* 54 a
S2 58 a
S3 58 a
S4 65 b
S5 69 b
Table 4 (continued)
Parameters p value Mean value
Fabric elasticity–widthwise (%) S1 0.000* 39 a
S2 54 c
S3 48 bc
S4 46 b
S5 69 d
Air permeability (l/m2s) S1 0.000* 753 b
S2 674 a
S3 703 a
S4 690 a
S5 679 a
*Statistically significant (p < 0,05)
0
50
100
150
200
250
300
350
400
450
S1 S2 S3 S4 S5 S1 S2 S3 S4 S5
LengthwiseWidthwise
Breaking Force (N)
Fig. 2 The breaking force values of the samples

Fibers and Polymers
parameter as it affected breaking force positively after
120h and negatively after 240h of exposure. Widthwise
elongation at break unexpectedly followed the same trend
as the breaking force of the same direction (Fig.3). A
significant drop (53%) was noticed after the first round of
aging (120h). Afterward, fluctuations in elongation were
encountered. The influence of seawater treatment was not
definite as in the case of breaking force in course direction.
Nevertheless, it could be determined that the durability of
the fabric was intensely affected by UV irradiation as in the
studies of Mazari etal. [26], Cubric etal. [22], Matkovic
and Skenderi [20], and Das [29]. Similarly, UV irradiation
substantially deteriorated the elongation capability in
accordance with the study of Davis etal. [28]. The results
presented that elongation loss in the course direction was
more pronounced than the loss in the wale direction as
supported by the research of Cubric etal. [17].
3.3 Fabric Elasticity
The change in fabric elasticity was measured in both course
and wale directions. Walewise elasticity increased as the UV
aging progressed (Fig.4). The increase in elasticity meant
that the fabric deteriorated and could not maintain its stabil-
ity. Cubric etal. [22] also stated that the material structure
changes and the material relaxes with the effect of UV irradi-
ation. Elasticity in the wale direction increased by 7 and 20%
after 120 and 240h of UV exposure respectively. Although a
gradual increase following the exposure time was observed
in fabric elasticity, only the increase after 240h was found
statistically significant. Moreover, seawater treatment was
not found as influential on lengthwise elasticity.
Fabric elasticity in course direction also increased due
to the applied aging procedures. It could be interpreted
that UV aging and seawater treatment damaged the fabric’s
stability. Yet, the effect of the procedures was unexpected.
It was observed that widthwise elasticity was affected quite
negatively after 120h of exposure. However, it improved
at the end of 240h. When seawater treatment was taken
into consideration, its strong negative effect after 240h
of irradiation was quite distinctive. Although enhanced
elasticity could improve the comfort of swimwear, it should
be noted that this increase was caused by the deterioration
and relaxation of the material due to aging. This could be
considered as an issue for the longevity of the garment.
3.4 Fabric Stiffness
Stiffness is described as the opposing force of a material to
an applied force to bend it [30]. A higher number presents a
stiffer fabric in Table4. As a fabric becomes more stiff, its fit
to the body and the comfort it provides worsens. The results
demonstrated that applied procedures resulted in stiffening
of the samples (Fig.5). Fabric stiffness increased dramati-
cally after the first round of aging (120h), whereas dropped
quite substantially at the end of the 240-h procedure. It
could be expressed that at the end of 240h fabric structure
deteriorated and therefore relaxed, as compatible with the
fabric elasticity results. On the other hand, the impact of
seawater on stiffness was obscure. Fabric stiffness values
0
100
200
300
400
500
600
S1 S2 S3 S4 S5 S1 S2 S3 S4 S5
LengthwiseWidthwise
Elongation at Break (%)
Fig. 3 The elongation at break values of the samples
0
10
20
30
40
50
60
70
80
90
100
S1 S2 S3 S4 S5 S1 S2 S3 S4 S5
Lengthwise Widthwise
Fabric Elasticity (%)
Fig. 4 The fabric elasticity values of the samples
0
2
4
6
8
10
12
14
16
S1 S2 S3 S4 S5
Fabric Stiffness
Fig. 5 The fabric stiffness values of the samples

Fibers and Polymers
of seawater-treated samples’ (S3 and S5) after both 120
and 240h were quite the same. Yet, the seawater treatment
caused a decrease in stiffness after 120-h exposure when
compared with sample S2, while an increase after 240h
of aging when compared with sample S4. An interesting
finding to be noted was that this pattern was also viable for
the breaking force, elongation at break, and fabric elasticity
values in the course direction. These results together with
the fabric stiffness were all positively affected from seawa-
ter treatment after 120h, however, negatively affected after
240h.
3.5 Air Permeability
The air permeability of a fabric is the measure of how well
it allows the passage of air through it[31]. Results presented
a substantial loss in air permeability after the applied pro-
cedures (Fig.6). A 10% decline was observed at the end of
120h of exposure. Yet, statistical analysis demonstrated that
the air permeability values after each procedure were insig-
nificantly different. Therefore, it could be interpreted that
the main damage already occurred at the end of 120h. The
loss in air permeability could be caused by the combined
effect of structural and surface deterioration of the fabric
which is defined as fibrillation. The protruding fibers from
the surface closed the air gaps and led to diminished poros-
ity, as expressed by Mazari etal. [26], Cubric etal. [22], and
Gohar and Mazari [6].
3.6 Surface Morphology
Scanning electron microscope (SEM) images with 250 × and
1000 × magnifications were given in Table5.
The SEM images exhibited the changes in the surface
morphology of the samples after UV aging. As can be seen,
noticeable fibrillation and cracks occurred on the surface of
the samples. These fibrillations and cracks are expected to
have a significant influence, especially on the breaking force,
elongation at break, elasticity, stiffness, and air permeability.
As swimwear is directly in contact with the body and the fit
of the garment is crucial, these changes will have a massive
impact on the garment’s durability, comfort, and useful life.
3.7 Fourier‑Transform Infrared (FTIR) Spectroscopy
FTIR spectra of the unaged and aged samples were given
in Fig.7. As can be seen from the figure, no peaks were
identified. This indicated that neither broken nor newly
formed chemical bonds were observed after UV irradiation.
Hence, it was concluded that the UV aging process did not
have an impact on the chemical structure of the samples, as
observed in the research of Cubric etal. [22]. A chemical
deformation may be observed with an extended irradiation
period. Although a molecular deformation was not detected
with FTIR spectra, micro deformations were visible in SEM
images (Table5).
4 Conclusion
Exercise is an inseparable element of maintaining a healthy
life. Being outdoors and receiving enough sunlight is
beneficial for both physical and mental well-being. However,
protection from the unwanted effects of the sun is also a
must. Although clothes provide the body protection from
UV radiation, they are also prone to the destructive impacts
of sunlight. Swimwear is the type of clothing that is most
exposed to UV radiation. Polyamide warp-knitted fabric is
generally preferred in swimwear. However, most research
on the effects of UV radiation focuses on woven or weft-
knitted fabrics. UV radiation’s impact on technical textiles
is quite investigated as well. Therefore, to focus on this
gap and contribute to the lack in the literature, this study
comprehensively investigated the consequences of sunlight
exposure on polyamide warp-knitted swimwear fabric. Since
seawater is considered a major destructive factor besides UV
radiation in the case of swimwear, the impact of seawater
treatment is also examined.
Analyses presented a minor escalation in the number
of wales in the unit area. On the contrary, no change was
observed in the course per cm value. Due to the increase
in wale count, the amount of yarn in the unit area also
increased leading to a rise in mass per unit area. However,
this change in mass per unit area was not statistically
significant and was associated with the combined impact
of fabric wear causing a reduction in mass, and fabric
shrinkage increasing the weight. The fabric thickness was
observed to decrease after UV aging, but this change was
statistically insignificant as well. UV exposure led to a
dramatic fall in breaking force and elongation at break
in both course and wale directions. The significant losses
620
640
660
680
700
720
740
760
S1 S2 S3 S4 S5
Air Permeability (lt/m2s)
Fig. 6 The air permeability values of the samples

Fibers and Polymers
Table 5 Microscopic images of the samples
Sample
Code x0001x051
S1
S2
S3
S4
S5

Fibers and Polymers
in both breaking force and elongation at break values
occurred after the first round of aging (120h). The results
presented that elongation loss in the course direction was
more pronounced than the loss in the wale direction. Fabric
elasticity enhanced in both wale and course directions.
This could be due to the deterioration and the stability
loss of the samples. The materials relaxed with the effect
of UV irradiation and could not regain their original
shape. Although enhanced elasticity could improve the
comfort of swimwear, it should be noted that this increase
was caused by the deterioration and relaxation of the
material due to aging. This could be considered as an
issue for the longevity of the garment. Fabric stiffness
increased dramatically after the first round of aging
(120h), whereas dropped quite substantially at the end
of the 240-h procedure. It could be expressed that at the
end of 240h, fabric structure deteriorated and therefore
relaxed, as compatible with the fabric elasticity results. A
substantial drop in air permeability was observed after the
procedures. The main loss in air permeability was detected
at the end of 120h of exposure similar to the results of
breaking strength and elongation at break. The loss in air
permeability was associated with the combined effect of
structural and surface deterioration of the fabric which is
defined as fibrillation. Chemical destruction due to UV
irradiation was not observed with FTIR spectroscopy after
any of the procedures. However, SEM images presented
changes in surface morphology. Noticeable fibrillation and
cracks occurred on the surface of the samples which was
associated with the significant changes in the breaking
force, elongation at break, elasticity, stiffness, and air
permeability.
The destructive effect of UV radiation was quite obvious
on various measured characteristics. On the other hand, the
impact of seawater treatment was obscure. The analyses
of seawater treatment presented minimal or indistinctive
impacts. Therefore, the results led to the conclusion that
UV radiation was the main detrimental effect in this study.
Funding Open access funding provided by the Scientific and Techno-
logical Research Council of Türkiye (TÜBİTAK).
Data Availability All data generated or analyzed during this study are
included in this published article.
Declarations
Conflict of Interest The authors declare that they have no known com-
peting financial interests or personal relationships that could have ap-
peared to influence the work reported in this paper.
Open Access This article is licensed under a Creative Commons Attri-
bution 4.0 International License, which permits use, sharing, adapta-
tion, distribution and reproduction in any medium or format, as long
as you give appropriate credit to the original author(s) and the source,
provide a link to the Creative Commons licence, and indicate if changes
were made. The images or other third party material in this article are
included in the article’s Creative Commons licence, unless indicated
otherwise in a credit line to the material. If material is not included in
the article’s Creative Commons licence and your intended use is not
permitted by statutory regulation or exceeds the permitted use, you will
need to obtain permission directly from the copyright holder. To view a
copy of this licence, visit http://creativecommons.org/licenses/by/4.0/.
Fig. 7 FTIR spectra of the samples

Fibers and Polymers
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