coatings

Article
Washing Durability and Photo-Stability of
NanoTiO2-SiO2 Coatings Exhausted onto Cotton and
Cotton/Polyester Fabrics
Alenka Ojstršek 1,2, * and Darinka Fakin 1
1 Institute of Engineering Materials and Design, Faculty of Mechanical Engineering, University of Maribor,
2000 Maribor, Slovenia
2 Institute of Automation, Faculty of Electrical Engineering and Computer Science, University of Maribor,
2000 Maribor, Slovenia
* Correspondence: alenka.ojstrsek@um.si; Tel.: +386-2-220-7935




Received: 1 August 2019; Accepted: 23 August 2019; Published: 25 August 2019


Abstract: The purpose of this study was to assess and compare the durability of TiO2 -SiO2 coatings
applied in three concentrations onto two lightweight cellulose-based fabrics diverse in the composition
against two external factors, repeated washings and prolonged intensive UV irradiation, by observing
the changes in surface morphology, investigation of optical properties, and identification of specific
molecular vibrations. The scanning electron microscopy (SEM) micrographs, diffuse reflectance
spectroscopy (DRS) profiles and fourier transform-infrared (FT-IR) spectra implied equal distribution
of TiO2 -SiO2 nanoparticles over the surfaces of both fabrics after exhaustion procedures, regarding
the concentration of colloidal paste and the type of material used, followed by a slight reduction
of nanoparticles after twenty washing cycles. Moreover, the newly gained, good to very good
UV protective functionality proved the suitability of the employed procedure and the sufficient
durability of the selected coatings. Additionally, UV irradiation mainly caused damages to the cotton.
Cotton/polyester became yellower under UV, although the application of TiO2 -SiO2 protected the
material against yellowness.

Keywords: surface functionalization; cotton fabric; cotton/polyester fabric; nanoTiO2 -SiO2 ; washing
durability; photo-stability

1. Introduction
Cellulose fibers are well-known for comprehending imposing characteristics like biocompatibility,
non-toxicity, high water absorbency, being safe and comfortable to wear and easy to dye [1].
Notwithstanding, textile fabrics based on cotton also have some undesirable features such as being
easily soiling, easily wrinkled, having low strength, and an inclination towards microbial attack,
supporting the growth of micro-organisms. This promotes the usage of cotton/polyester blends
(Co/PES) of various ratios (25:75, 35:65, 50:50, etc., depending on the requirements of end-products)
for short-sleeved sport shirts and summer blouses by assuring the required physical properties and
comfort in wear [2]. However, lightweight non-colored or brightly-colored Co/PES garments, which are
very popular for summer shirts, offer only low ultraviolet protection factor (UPF), less than 15; whilst
the sufficient clothing UPF for outdoor wear should be at least 40 [3]. In order to enhance the UV
protection, as well as to improve some other functional properties, numerous researchers have recently
oriented their investigations towards the employment of various nano-sized particles during different
steps of textile finishing [1,4–7]. Moreover, these novel nano-technological accessions seem to be a
good alternative to the conventional harsh chemical treatments, and therefore, should offer desirable
levels of material functionality even after prolonged usage and care.

Coatings 2019, 9, 545; doi:10.3390/coatings9090545 www.mdpi.com/journal/coatings

Coatings 2019, 9, 545 2 of 13

Titanium dioxide (TiO2 ) is among the highly desirable nanoparticles for surface modifications
of numerous textiles, because of its superior chemical stability, non-toxicity, good heat resistance,
excellent transparency for the visible light, and excellent photo-activity under UV radiation [8–10].
Herein, a limited number of studies have focused on both the evaluation of newly gained functional
properties after several washings and the eventual side-effect after prolonged light exposure, like
yellowness, bleaching, polymer degradation, reduction of newly-obtained functionalities, etc. Montazer
et al. [11] studied the photo bleaching of wool using a nanoTiO2 catalyst, in order to decompose the
naturally-occurring pigments. The obtained results confirmed excellent hydrophilicity and reasonable
whiteness even after five washings, regarding the amount of applied TiO2 , although the textile
degradation was not investigated. In contrast, the study realized by Selishchev et al. [6] presented
SEM pictures of the self-destruction of TiO2 functionalized textiles under long-term UV irradiation.
The same paper reported a reduction in material damages when nanoTiO2 was deposited by a silica
(SiO2 ) protective layer. Moreover, SiO2 shell can also be used as a binder between nanoparticles and
the textile surface, providing desired functionalities after laundering or extensive wearing.
The main goal of the presented research was, therefore, to examine the washing durability of
nanoTiO2 -SiO2 coatings, and consecutively, the influence of repeated launderings on the fabrics’
newly obtained UV protective properties. TiO2 -SiO2 core-shell nanoparticles in the form of colloidal
paste were applied in three concentrations onto two industrially bleached non-colored fabrics made
from cotton and cotton/polyester fabric for summer clothes. Emphasis was also given to possible
fabrics’ self-destruction on a micro level under intensive UV-A and UV-B irradiation, as well as to the
visually-perceivable changes in material whiteness/yellowness.

2. Experimental

2.1. Materials
Two woven fabrics in the form of strips (9.5 g) were selected for modification experiments.
One fabric was made from cotton fibers (Co) in plane weave, with a mass of 110 g/m2 , warp density of
41 threads/cm and weft density of 38 threads/cm, and yarn fineness of 20 tex. The other fabric was
made from mixtures of cotton/polyester fibers (Co/PES) in a ratio of 70:30, with a mass of 105 g/m2 ,
warp density of 34 threads/cm and weft density of 30 threads/cm, yarn fineness of 17 tex (from Co) in
warp direction and yarn fineness of 20 tex (from mixture of Co/PES 50/50) in weft direction. Both fabrics
were designed for summer shirts with high transparency, and consecutively, good air permeability.
Moreover, both fabrics underwent the same industrially completed pre-treatment procedures without
optical brighteners (preparation for dyeing). Before the TiO2 -SiO2 modification, the samples were
washed for 20 min at 40 ◦ C by a neutral non-ionic washing agent, in order to remove impurities that
could influence the subsequent modification, and thereafter, thoroughly rinsed with warm and then
cold water, and dried at an ambient temperature.
The commercially-available SiO2 coated TiO2 colloidal dispersion applied during this study was
synthesized by the Cinkarna Inc., Metallurgical and Chemical Industry, Celje, Slovenia, in the form of
paste via the sol-gel process from metatitanium acid, which is a by-product of the sulfate synthesis
process. A detailed description of the surface treated pigmentary TiO2 was disclosed [12]. According to
the producer information, the dispersion contained approximately 20 wt.% of crystalline rutile TiO2
nanoparticles and was precipitated with 3 wt.% of SiO2 .

2.2. TiO2 -SiO2 Application Procedure

The aforementioned nanoTiO2 colloidal dispersion was applied on the two selected fabrics
according to the industrially-acceptable exhaustion procedure, using liquor-to-fabric weight ratio of
20:1 (180 mL of deionized water against 9 g of Co or Co/PES fabric), within a sealed stainless-steel
pot of 200 cm3 capacity, housed within the laboratory apparatus Labomat (W. Mathis AG, Oberhasli,
Switzerland) at a temperature of 60 ◦ C for 110 min. The previously-optimized initial bath was
Coatings 2019, 9, 545 3 of 13

composed of 3%, 6% or 9% owf (of weight of fabric) of TiO2 -SiO2 paste (meaning ca. 0.054 g, 0.108 g or
0.162 g of pure TiO2 ), respectively, 30 g/L of NaCl, 5 g/L of NaHCO3 , 1g/L of leveling agent (Meropan
OFS, CHT Switzerland AG, Montlingen, Switzerland), and 0.8 mL/L of NaOH (32%) for alkaline pH
adjustment. The treated samples were rinsed in warm and then cold deionized water, and dried at
room temperature.

2.3. Washing Procedure

In order to assess the washing durability of TiO2 core-shell nanoparticles bonded onto cotton
and cotton/polyester fabrics, all the samples were washed repeatedly up to 20 times in a Labomat
(W. Mathis AG, Oberhasli, Switzerland), using a solution of 4 g/L of standard reference detergent
without optical brighteners (the formulation is given in EN 20105-CO1:1993; Clause 4.2) at a temperature
of 40 ◦ C for 30 min, and a liquor-to-fabric weight ratio of 50:1. Thereafter, the samples were rinsed
several times in deionized water, and then tap water for 30 min, and finally dried at a room temperature.

2.4. UV Irradiation
For the purpose of the fabrics’ photo-stability evaluation, TiO2 -SiO2 coated samples were irradiated
with an artificial UV source for a prolonged time of up to 720 h. Those samples with an area of
8 cm × 5 cm were placed in a photo-reactor (Luzchem Research Inc., Ottawa, ON, Canada) equipped
with six overhead UV lamps of which three lamps, providing UV-A light within the range of 316–400 nm
and the main peak at 350 nm, and three lamps emitting mainly UV-B light within the range of 281–315 nm
and the main peak at 313 nm. The UV luminance in the reactor was 18,600 Lux measured by a Digital
Light Meter SLM-110, A.W. Sperry Instruments, Inc. (New Berlin, WI, US).

2.5. Characterization Methods

2.5.1. Analysis of Colloidal Dispersion

Three analytical techniques were employed, with the intention of analyzing the selected TiO2 -SiO2
core-shell nanoparticles’ dispersion, i.e., scanning electron microscopy (SEM), transmission electron
microscopy (TEM), and ultraviolet-visible (UV-Vis) spectrophotometry. The sample for SEM analysis
was prepared by drying a drop of water dilution of TiO2 -SiO2 dispersion in a 0.1% concentration on
adhesive carbon tape, which was placed on a brass holder for observation on a scanning electron
microscope FE-SEM-ZEISS Gemini Supra 35 VP (Carl Zeiss NTS GmbH, Oberkochen, Germany).
In addition, morphology analysis of the surface-treated TiO2 was accomplished by dropping a watering
colloidal dispersion of about 1% on the Cu-grid, dried at a temperature of 40 ◦ C and thereafter
observing the using a JEM-2100 transmission electron microscope (Jeol Ltd., Tokyo, Japan) with LaB6
as an electron source. With the aim to establish the particles size distribution and average particle
size, dynamic light scattering (DLS) analysis was accomplished, using a Zetasizer Nano HT (Malvern,
UK), equipped with a light-scattering unit. The measuring temperature was fixed at 25 ◦ C. Finally,
the absorption spectra of TiO2 dispersion (diluted in a deionized water at a concentration of 16 mg/L)
was recorded throughout the UV-Vis spectrum from a wavelength of 200 up to 700 nm, by means of
a Varian Cary 50 UV-Vis spectrophotometer (Agilent Technologies, Santa Clara, CA, USA) using a
10 mm quartz cuvette.

2.5.2. Analysis of TiO2 -SiO2 Coated Fabrics

Various analytical techniques were utilized, with the aim of exploring the washing durability of
coatings (up to 20 washing cycles), as well as the photo-stability of modified fabrics under prolonged
UV irradiation (up to 720 h), i.e., scanning electron microscopy (SEM), diffuse reflectance spectroscopy
(DRS), Attenuated total reflectance-fourier transform infra-red (ATR-FTIR) spectroscopy, and UV
transmittance spectrophotometry.
Coatings 2019, 9, 545 4 of 13

SEM images were obtained by attaching approximately 1 cm2 of fabric samples onto an adhesive
carbon band fixed to a brass holder and observed using a scanning electron microscope FE-SEM-ZEISS
Gemini Supra 35 VP (Carl Zeiss NTS GmbH, Oberkochen, Germany).
Coatings
The 2019, 9,reflectance
diffuse x FOR PEER REVIEW
spectra (DRS) profiles of fabrics in the 220–400 nm wavebands were 4 of 12taken

on a Lambda 900 UV-Vis-NIR spectrophotometer (Perkin Elmer, Waltham, MA, US) with an integrated
SEM images were obtained by attaching approximately 1 cm2 of fabric samples onto an adhesive
sphere at a scanning speed of 450 nm per min. The tested samples were folded three times to obtain
carbon band fixed to a brass holder and observed using a scanning electron microscope FE-SEM-
eight ZEISS
layers,Gemini
so thatSuprathe light
35 VPcould
(Carl not
ZeissbeNTS
transmitted through the
GmbH, Oberkochen, fabric.
Germany).
Measurement
The diffuseof reflectance
reflectance from
spectra wavelengths
(DRS) 400 up
profiles of fabrics to 700
in the nmnm
220–400 was accomplished
wavebands for each
were taken
sampleon ata three
Lambda different locations by
900 UV-Vis-NIR means of a spectrophotometer
spectrophotometer SF 600 Plus
(Perkin Elmer, Waltham, MA,(Datacolor,
US) with Luzern,
an
Switzerland)
integrated under
sphere a standard illuminant/observer
at a scanning speed of 450 nm per D65/10 ◦ (SAV/Spec.
min. The Incl.)
tested samples andfolded
were thereby, the
three average
times
to obtainCommission
International eight layers, so onthat the light could
Illumination notwhiteness
(CIE) be transmitted
(W) andthrough the fabric.
yellowness (YI) indices of samples
Measurement of reflectance from wavelengths
were calculated using Equations (1) and (2), respectively: 400 up to 700 nm was accomplished for each
sample at three different locations by means of a spectrophotometer SF 600 Plus (Datacolor, Luzern,
Switzerland) under a standard W illuminant/observer
= Y + 800(xn − x) +D65/10°
1700(yn (SAV/Spec.
− y) Incl.) and thereby, the (1)
average International Commission on Illumination (CIE) whiteness (W) and yellowness (YI) indices
whereofYsamples were calculated
is the tristimulus using
value; Equations
x and y are the(1)chromaticity
and (2), respectively:
coordinates of the observed white sample;
and xn and yn are chromaticity coordinates
W = Y of the completely
+ 800(x opaque
n – x) + 1700(yn – y) standardized white object.
(1)
where Y is the tristimulus value; x and y are the chromaticity coordinates of the observed white
100 · (1.3013 · X − 1.1498 · Z)
sample; and xn and yn are chromaticity
YI = coordinates of the completely opaque standardized white (2)
object.
Y
where Y, X and Z are tristimulus values YI in =CIE color
∙ . space.
∙ . ∙
(2)
Infrared transmission absorbance spectra of selected samples were obtained using a
where Y, X and Z
spectrophotometer are tristimulus
FTIR values in CIE
System Spectrum GXcolor space.
(Perkin Elmer, Waltham, MA, US) with a Golden
Infrared transmission absorbance spectra of selected samples were obtained using a
Gate ATR attachment and a diamond crystal. The measurements were carried-out within the range of
spectrophotometer FTIR System Spectrum GX (Perkin Elmer, Waltham, MA, US) with a Golden Gate
4000–650 cm−1 , with 32 scans and a resolution of 4 cm−1 .
ATR attachment and a diamond crystal. The measurements were carried-out within the range of
The level of the fabrics’ shielding capability against harmful UV rays is usually expressed by the
4000–650 cm−1, with 32 scans and a resolution of 4 cm−1.
ultravioletThe
protection factor
level of the (UPF).
fabrics’ UPF was
shielding calculated
capability against from the fabrics’
harmful UV raysUV-A andexpressed
is usually UV-B transmittance
by the
values, which were
ultraviolet recordedfactor
protection according
(UPF).to the
UPFAustralian/New
was calculated Zealandfrom the Standard
fabrics’ (AS/NZS
UV-A and 4399-1996)
UV-B [9]
over the ultravioletvalues,
transmittance spectral region
which wereof recorded
280–400 according
nm wavelengths using a solar-screen
to the Australian/New Zealand Varian Cary 50
Standard
(AS/NZS 4399-1996)
spectrophotometer [9] over
(Agilent the ultravioletSanta
Technologies, spectral regionCA,
Clara, of 280–400 nm wavelengths
US), fitted using a solar-
with an integrated sphere
screen Varian Cary 50 spectrophotometer
accessory and a fabric holder accessory. (Agilent Technologies, Santa Clara, CA, US), fitted with an
integrated sphere accessory and a fabric holder accessory.
3. Results and Discussion
3. Results and Discussion
3.1. Colloidal Dispersion Analysis
3.1. Colloidal Dispersion Analysis
In order to study the surface morphology of TiO2 -SiO2 colloidal dispersion for the subsequent
In order to study the surface morphology of TiO2-SiO2 colloidal dispersion for the subsequent
functionalization of Co and Co/PES fabrics, SEM and TEM micrographs were taken, and presented in
functionalization of Co and Co/PES fabrics, SEM and TEM micrographs were taken, and presented
Figure 1. Furthermore, the size distribution of nanoparticles was presented on Figure 2.
in Figure 1. Furthermore, the size distribution of nanoparticles was presented on Figure 2.

(a) (b)
Figure
1. (a)1.SEM
(a) SEM image;
image; andand
(b)(b)
TEMTEMimage
imageof
ofused
used TiO
TiO2-SiO 2 nanoparticles at different magnifications.
Figure 2 -SiO2 nanoparticles at different magnifications.
Coatings 2019, 9, 545 5 of 13
Coatings
Coatings2019,
2019,9,
9,xxFOR
FORPEER
PEERREVIEW
REVIEW 55 of
of 12
12

15
15

(%)
10

Intensity(%)
10

Intensity 55

00
0.1
0.1 11 10
10 100
100 1000
1000 10000
10000
Size (d.nm)
Size (d.nm)

Figure2.2. Size
Figure Size distribution
distribution plot
plot of TiO222-SiO
of TiO -SiO222 colloidal
colloidal dispersion.
colloidal dispersion.
dispersion.

From 1a, non-spherically shaped nanoparticles of ca.

From the
the SEM
SEM image
image in in Figure
Figure 1a, non-spherically shaped nanoparticles of ca. 167 167 nm
nm in
in length
length
and ca. 30 30 nm
nm in in width
width could
could be unequivocally
unequivocally perceived,
perceived, which
which was also confirmed by dynamic
and ca. 30 nm in width could be unequivocally perceived, which was also confirmed by dynamic
light scattering (DLS)measurement
measurement (Figure 2). Further, the isotropic morphology of very small
light scattering
scattering (DLS)
(DLS) measurement (Figure (Figure 2).
2). Further,
Further, the
the isotropic
isotropic morphology
morphology of of very
very small
small non-
non-
non-spherical
spherical TiO2 crystals of >10 nm inand length andnm ca.in4–5 nmwas in width was exposed by TEM
TiO
spherical TiO2 crystals of >10 nm in length and ca. 4–5 nm in width was exposed by TEM (Figure 1b),
2 crystals of >10 nm in length ca. 4–5 width exposed by TEM (Figure 1b),
(Figureaggregated
which 1b), which intoaggregated
an into an(polycrystalline)
individual individual (polycrystalline)
nanoparticle. nanoparticle.
These These nanoparticles
nanoparticles were coated
which aggregated into an individual (polycrystalline) nanoparticle. These nanoparticles were coated
were amorphous
with coated with amorphous SiO2 (white areas). TheSiO formation of SiO2 shell in selected colloidal
with amorphous SiO SiO22 (white
(white areas).
areas). The
The formation
formation of of SiO22 shell
shell in
in selected
selected colloidal
colloidal dispersion
dispersion was
was
dispersion was
depended depended above all on theinvolved
reactions during
involvedindustrial
during industrial synthesis procedure as
depended above all on the reactions involved during industrial synthesis procedure as
above all on the reactions synthesis procedure as well
well
well documented
documented [12].
documented [12].[12].
In absorbance curve of TiO22-SiO22 paste paste dispersed in in water within a
In addition,
addition, thethe UV-Vis
UV-Vis absorbance curve of TiO TiO2-SiO2 paste dispersed
dispersed in water
water within a
concentration
concentration of 16 mg/L was recorded from a wavelength of 200 up to 700 nm, and shown onon Figure 3,
3,
concentration of 16 mg/L was recorded from a wavelength of 200 up to 700 nm, and shown on Figure
of 16 mg/L was recorded from a wavelength of 200 up to 700 nm, and shown Figure 3,
nanoparticles on
in
in order
order to
to elucidate
elucidate thethe role
role of
of TiO nanoparticles on
TiO222 nanoparticles the UV-blocking
onthe UV-blocking properties of modified Co and
the UV-blocking properties of modified Co and
Co/PES fabrics.
Co/PES fabrics.
0.5
0.5 λmax = 291 nm
(a)
(a) 0.5 (b)
(b) λmax = 291 nm
0.5 0.4
0.4
(AU)
Absorbance(AU)

0.4 0.3
0.4 0.3
(AU)

Absorbance

UV-C UV-B UV-A

Absorbance(AU)

0.2 UV-C UV-B UV-A

0.2
0.3
0.3 0.1
Absorbance

0.1
0
0.2
0.2
0
200 220 240 260 280 300 320 340 360 380 400
200 220 240 260 280 300 320 340 360 380 400
Wavelength (nm)
Wavelength (nm)
0.1
0.1

00
200
200 250
250 300
300 350
350 400
400 450
450 500
500 550
550 600
600 650
650 700
700
Wavelength (nm)
Wavelength (nm)
Figure 3. UV-Vis spectrum
spectrum of
of mightily
mightily diluted
diluted colloidal dispersion.
Figure 3. UV-Vis
UV-Vis spectrum of mightily diluted colloidal dispersion.
colloidal dispersion.

It
It could
Itcould
couldbe be concluded
concluded
be concluded fromfrom Figure
Figure
from 3a
3a that
Figure that
3a the the
the employed
employed
that nanoparticles
nanoparticles
employed have
have prominent
have prominent
nanoparticles UV-
UV-shielding
prominent UV-
shielding characteristics
characteristics since they since
absorb they absorb
the the
damaging damaging
UV light UV
withinlighta within
spectral a spectral
range
shielding characteristics since they absorb the damaging UV light within a spectral range of between of range
betweenof between
200 and
200
400 and
andat400
200 nm an nm
400 nm at at an
an exceedingly
exceedingly low
low concentration
low concentration
exceedingly of TiO2 -SiOof
concentration TiO
TiO22-SiO
2 colloidal
of 2 colloidal dispersion,
-SiOdispersion,
2 colloidal with
with
with an
an absorbance
dispersion, an
absorbance
maximum maximum
absorbance(λmaximum (λ max
max ) at a wavelength
) at a
(λmax) at a ofwavelength of
291 nm (Figure
wavelength 291 nm
of 2913b). (Figure
nmIt(Figure 3b).
should3b). It should
alsoItbeshould
mentionedalso be mentioned
that
also be a higher TiO
mentioned that
that
2
acontent
higher inTiO 2 content
dispersion (in in
our dispersion
case was (in our case
approximately was
20% approximately
regarding the 20%
producer
a higher TiO2 content in dispersion (in our case was approximately 20% regarding the producer regarding the
information) producer
indicates
information)
ainformation) indicates
higher absorbance
indicates aa higher
within the UV
higher absorbance
region aswithin
absorbance the
the UV
demonstrated
within UV region as
as demonstrated
by Ojstršek
region et al. [9], which
demonstrated by
by Ojstršek et
et al.
consequently
Ojstršek al.
[9], which
influences
[9], whichtheconsequently
consequently influences
higher UV-protection the
influencesability higher UV-protection
of TiOUV-protection
the higher 2 -modified ability
fabric at
ability theof
of TiO
same
TiO 2-modified
2operational
-modified fabric at
parameters
fabric at the
the
same
same operational
during parameters
the TiO2 application
operational parameters during
during the
procedure. the TiO
TiO22 application
application procedure.
procedure.

3.2.
3.2. Washing
Washing Durability
Durability and
and UV
UV Photo-Stability
Photo-Stability of
of Nano-Modified
Nano-Modified Textiles
Textiles
With
With the
the intention
intention of
of evaluating
evaluating the
the washing
washing durability
durability of
of TiO
TiO22-SiO
-SiO22 coatings,
coatings, and
and therein,
therein, the
the
suitability
suitability of bath composition, as well as the operational parameters of the exhaustion procedure,
of bath composition, as well as the operational parameters of the exhaustion procedure,
Coatings 2019, 9, 545 6 of 13

3.2. Washing Durability and UV Photo-Stability of Nano-Modified Textiles

With the intention of evaluating the washing durability of TiO2 -SiO2 coatings, and therein,
the suitability of bath composition, as well as the operational parameters of the exhaustion procedure,
several approaches/techniques were used on the unwashed reference and the washed coated
samples, including:

• examination of surface morphology by means of SEM;

• investigation of optical properties by measuring the fabrics’ UV transmittance and UV/Vis
reflectance, followed by the calculation of the ultraviolet protection factor (UPF), CIE whiteness
degree and yellowness index, respectively, and
• identification of molecular vibrations through recording the infrared transmission absorbance by
FTIR spectroscopy.

Veronovski et al. [12] explicated that like most organic materials, TiO2 -coated textiles meant
that the outdoor wearer was inclined towards ageing under the influence of external conditions
(sunlight). This can lead to changes in the coatings’ appearances, changes in physical and chemical
properties, as well as to the reduction of materials’ functional properties. Moreover, nano-sized
TiO2 exhibited strong photo-catalytic activity under UV radiation, generating powerful oxidative
intermediates (hydroxyl radicals) that can decompose or degrade various organic compounds [6,8].
Therefore, in order to evaluate the changes in coating appearance, as well as the photo-stability of the
modified fabrics, the above-mentioned analytical techniques were employed on reference and UV
irradiated samples. The results are evidently presented over seven figures in association with adequate
discussions as follow.

3.2.1. Fabric Surface Morphology

With the aim of visually establishing the effect of repeated washings (up to 20 washing cycles)
as well as intensive UV irradiation (up to 30 days) on the durability/stability of TiO2 -SiO2 coatings
and possible fabric damages, the surface morphologies of selected samples at the micrometer level are
disclosed in Figure 4.
Representative SEM images in Figure 4 demonstrated the different coating morphologies regarding
the used material, i.e., cotton (left column) or cotton/polyester (right column) as well as employed
(post)treatment procedure, i.e. untreated, untreated and 30 days UV irradiated samples, modified by
9% owf of TiO2 -SiO2 colloidal dispersion, TiO2 -SiO2 modified and ten times washed, and TiO2 -SiO2
modified and 30 days UV irradiated samples. Co fibers’ morphological structure show regular helical
longitudinal profile in comparison to the PES uniaxial structural symmetry. In the case of TiO2 -SiO2
modified Co, slightly thicker coatings with higher nanoparticle content could be observed over
complete fibers’ surfaces as compared to the Co/PES. This is presumably on account of free hydroxyl
groups on Co surface, which could interact with silanol groups of core-shell nanoparticles, forming
covalent bonds, and thus, ensuring a strong adhesion between the coatings and the fiber surface [13].
On the other hand, PES fibers do not possess hydroxyl groups on the surface, therefore, only a weak
physical adhesion occurs between the PES surface and nanoparticles, causing impaired adhesion of
the coating. After 20 washing cycles, using standard washing procedure at a temperature of 40 ◦ C,
the amount of nanoparticles was reduced on both materials, and less uniform distribution was achieved.
Thus, 720 h of intensive artificial UV-A/UV-B irradiation caused minor injuries and a decrease in the
smoothness, not only on both modified fabrics, but also on unmodified ones; especially cotton fibers
that are prone to the self-degradation under UV rays. Moreover, nanoparticles are agglomerated on
the coated surfaces and in some degree flattened along the fibers. However, in order to evaluate the
decreasing of nanoparticles over the entire fabrics’ surfaces, and consecutively, the deterioration of
materials’ functional properties, further analyses are needed.
Coatings 2019, 9, 545 7 of 13
Coatings 2019, 9, x FOR PEER REVIEW 7 of 12

Co Co/PES

(a) (b)
Co Co/PES

(c) (d)

Co Co/PES

(e) (f)
Co Co/PES

(g) (h)
Co Co/PES

(i) (j)

Figure
Figure 4. 4. SelectedSEM
Selected SEMmicrophotographs
microphotographs of untreated
untreated and
andmodified
modifiedcotton
cotton(Co) and
(Co) cotton/polyester
and cotton/polyester
blend (Co/PES) fabrics further washed and UV irradiated at 5000× magnification. (a,b)
blend (Co/PES) fabrics further washed and UV irradiated at 5000× magnification. (a,b) Reference; Reference; (c,d)
Reference/UV irradiated; (e,f) TiO -SiO modified samples; (g,h) TiO -SiO modified/20×
(c,d) Reference/UV irradiated; (e,f) TiO2 -SiO2 modified samples; (g,h) TiO2 -SiO2 modified/20× washed
2 2 2 2 washed
samples;
samples; (i,j)
(i,j) TiOTiO 2-SiO2 modified/UV irradiated samples.
2 -SiO2 modified/UV irradiated samples.
Coatings 2019, 9, 545 8 of 13
Coatings 2019, 9, x FOR PEER REVIEW 8 of 12

3.2.2. Diffuse
3.2.2. Diffuse Reflectance
Reflectance Spectra
Spectra (DRS)
(DRS)
The DRS
The DRS profiles
profileswithin
withinthe
the
UV UV region
region areare presented
presented andand compared
compared in Figure
in Figure 5 between
5 between TiO2-
TiO -SiO modified
SiO22 modified
2 cotton and cotton/polyester fabrics, with the emphasis on the stability of TiO
cotton and cotton/polyester fabrics, with the emphasis on the stability of TiO22-SiO
-SiO22
nanoparticles application
nanoparticles application after
after 20th
20th washing
washing cycles
cycles and
and after
after long-time
long-time UV
UV exposure.
exposure.

90 90
80 80
70 70
Reflectance (%)

Reflectance (%)
ref. ref.
60 60
ref._UV ref._UV
50 3% 50 3%
40 3%_20x 40 3%_20x
6% 6%
30 30
6%_20x 6%_20x
20 9% 20 9%
10 9%_20x 10 9%_20x
9%_UV 9%_UV
0 0
220 240 260 280 300 320 340 360 380 400 220 240 260 280 300 320 340 360 380 400
Wavelength (nm) Wavelength (nm)

(a) (b)
Figure 5. DRS
DRS profiles
profiles of: (a)
(a) Co;
Co; and
and (b) Co/PES; un-modified (ref.), un-modified/UV irradiated
(ref._UV), nano-TiO22 modified by 3%, 6% or 9% 9% owf
owf of
of TiO
TiO22 paste,
paste, nano-TiO
nano-TiO22 modified/20×
modified/20× washed
fabrics, and 9% owf nano-TiO22 modified/UV irradiated sample.

Figure 5 shows the differences between the DRS curves of the non-modified Co and Co/PES
fabrics as expected
expected on on account
accountofofthe
thehigher
higherUV
UVabsorbance
absorbancecapacity
capacityofof the
thePES
PESfibers
fibersin in
comparison
comparison to
thethe
to CoCofibers. The
fibers. employment
The employment of nano-sized
of nano-sizedTiOTiO2 exceedingly
2 exceedingly diminished
diminished the reflectance
the reflectance curves on
curves
bothboth
on graphs; enlarged
graphs; the UV
enlarged theabsorption ability,ability,
UV absorption as also presented by Zhangbyand
as also presented Zhu [14].
Zhang and Moreover,
Zhu [14].
the higher the
Moreover, the paste
higherconcentration on the fabric,onthe
the paste concentration thelower thethe
fabric, reflectance
lower thevalues were in
reflectance the spectrum’
values were in
UV region,
the spectrum’implying superior
UV region, UV-rays superior
implying blocking properties of the TiOproperties
UV-rays blocking 2 -modified fabrics.
of the The
TiO 2 obtained
-modified
results also
fabrics. Theindicated
obtainedsomewhat increased
results also reflectance
indicated somewhat curves after twenty
increased washing
reflectance cycles,after
curves irrespective
twenty
of the material
washing cycles, used, which of
irrespective was themore explicit
material used,at awhich
lowerwasamount
moreof applied
explicit at TiO 2 -SiOamount
a lower 2 colloidalof
dispersion, i.e., 3% owf. Notwithstanding, we can deduce satisfying durability
applied TiO2-SiO2 colloidal dispersion, i.e., 3% owf. Notwithstanding, we can deduce satisfying of the exhausted
nanoparticles.
durability of theThese resultsnanoparticles.
exhausted were in good agreement
These results with the in
were calculated fabrics’ UPFs.
good agreement with the calculated
Exposure
fabrics’ UPFs. to UV lightness significantly changed the courses of the reflectance curves of the
untreated Co/PES
Exposure sample.
to UV The reflectance
lightness significantlyvalues
changed weretheapproximately
courses of the 20% lower within
reflectance curvesthe of
UV-A
the
region, indicating
untreated Co/PES higher
sample.UV Theabsorption ability,
reflectance values and consecutively,
were approximately a higher
20% UPFlower aswithin
compared to the
the UV-A
non-irradiated
region, indicatingone,higher
whichUV was further proven
absorption byand
ability, transmittance
consecutively,measurement.
a higher UPF as compared to the
non-irradiated one, which was further proven by transmittance measurement.
3.2.3. ATR-FTIR Spectroscopy
3.2.3.The
ATR-FTIR Spectroscopy
FTIR spectra of reference (untreated) and modified Co and Co/PES samples before and
after The
several washings, and after(untreated)
FTIR spectra of reference intensive and UV modified
irradiation Cowere recorded
and Co/PES withinbefore
samples the region of
and after
4000–650 −1
cm and presented in Figure 6, in orderwere to examine the binding
several washings, and after intensive UV irradiation recorded within the efficiency between
region of 4000–650
the fibers and applied
cm and presented in Figure
−1 TiO 2 -SiO 6, colloidal dispersions, and also to study the possible fiber
2 in order to examine the binding efficiency between the fibers and degradation.
All spectra
applied TiOwere normalized at a chosen wavenumber of 1200 cm−1 , which remained unaffected during
2-SiO2 colloidal dispersions, and also to study the possible fiber degradation. All spectra
surface
were modification.
normalized at a chosen wavenumber of 1200 cm−1, which remained unaffected during surface
Figure
modification. 6a depicts a FTIR pattern with typical peak positions for cotton including free hydroxyl
groups at 3500–3200 −1 , water molecules at ~1640 cm−1 , O–H, C–O, C–H and C–O–C vibrations
Figure 6a depictscma FTIR pattern with typical peak positions for cotton including free hydroxyl
within the glucose ring at 1500-800
groups at 3500–3200 cm , water molecules
−1 cm−1 , as also fully cm
at ~1640 interpreted in [3,5].
−1, O–H, C–O, C–HIn Figure 6b, some
and C–O–C typical
vibrations
peaks of polyester were observed, i.e. characteristic stretching vibration band of
within the glucose ring at 1500-800 cm , as also fully interpreted in [3,5]. In Figure 6b, some typical
−1 the ester carbonyl
group of in conjugation withobserved,
an aromatic −1 , asymmetric C–C–O vibrations at 1242 cm−1 ,
peaks polyester were i.e. ring at 1716 cmstretching
characteristic vibration band of the ester carbonyl
and aromatic C–H wagging at 719 cm −1 [15], accompanied by some typical cotton peaks
group in conjugation with an aromatic ring at 1716 cm , asymmetric −1 C–C–O vibrations at 1242ascm
the
−1,

above-named. Although, the absorption peaks of all the obtained spectra

and aromatic C–H wagging at 719 cm−1 [15], accompanied by some typical cotton peaks as the above- are quite similar on an
individual
named. graph, some
Although, characteristic
the absorption peaksabsorption bands are
of all the obtained evidently
spectra recognized
are quite similarfor
on the TiO2 -SiO2
an individual
graph, some characteristic absorption bands are evidently recognized for the TiO2-SiO2 modification
of both Co and Co/PES fabrics, i.e. the peak around 1100 cm−1 corresponded to stretching vibrations
Coatings 2019, 9, 545 9 of 13

Coatings 2019, 9, x FOR PEER REVIEW 9 of 12

modification of both Co and Co/PES fabrics, i.e. the peak around 1100 cm−1 corresponded to stretching
vibrations and around 800 cm to the bending vibration modes of the Si–O–Si bonds, peak at 985 cm−1
−1
and around 800 cm−1 to the bending vibration−1modes of the Si–O–Si bonds, peak at 985 cm−1 related
related to Ti–O–Si linkages, and around 670 cm corresponded to the symmetric stretching vibrations
to Ti–O–Si linkages, and around 670 cm−1 corresponded to the symmetric stretching vibrations of O–
of O–Ti–O bands [3,16]. After repeated washings those peaks were slightly reduced on both diagrams,
Ti–O bands [3,16]. After repeated washings those peaks were slightly reduced on both diagrams, but
but did not disappear, confirming good durability of the selected coatings against washing as could be
did not disappear, confirming good durability of the selected coatings against washing as could be
expected from SEM and DRS results. UV irradiation, on the other hand, caused damage to the material,
expected from SEM and DRS results. UV irradiation, on the other hand, caused damage to the
and consecutively, some peaks became expanded or intensified like peaks at 1716 and 1242 cm−1
material, and consecutively, some peaks became expanded or intensified like peaks at 1716 and 1242
(Co/PES), on account of the larger amount of degradation products on the surface containing –CO
cm−1 (Co/PES), on account of the larger amount of degradation products on the surface containing –
group (ketones, carboxylic acids and esters), and peaks at 3324 and 1633 cm−1 (Co), due to the enlarged
CO group (ketones, carboxylic acids and esters), and peaks at 3324 and 1633 cm−1 (Co), due to the
free hydroxyl groups and water molecules.
enlarged free hydroxyl groups and water molecules.

Ti–O–Si 9%_UV
9%_20x
9%
Si–O–Si reference

O–Ti–O

1450 1350 1250 1150 1050 950 850 750 650

Wavenumber (cm-1)

(a)

3650 3150 2650 2150 1650 1150 650

Wavenumber (cm-1)

Ti–O–Si
9%_UV
Si–O–Si 9%_20x
9%
reference

O–Ti–O

1450 1350 1250 1150 1050 950 850 750 650

Wavenumber (cm-1)

(b)

3650 3150 2650 2150 1650 1150 650

Wavenumber (cm-1)

−1 of: (a) Co; and (b) Co/PES samples modified by 9%

Figure 6. Normalized
Figure 6. Normalized FTIR
FTIR spectra
spectra (at
(at1200
1200cm
cm−1)) of: (a) Co; and (b) Co/PES samples modified by 9%
owf
owf of nano-TiO2-SiO2 before and after 20th launderings, and
of nano-TiO 2 -SiO 2 before and after 20th launderings, and after
after UV
UV irradiation.
irradiation.

3.2.4. CIE Whiteness and Yellowness Index

3.2.4. CIE Whiteness and Yellowness Index
Based on the presumption that TiO2 is a white organic pigment, and thus, applied on the material’s
Based on the presumption that TiO2 is a white organic pigment, and thus, applied on the
surface in an adequate concentration producing a white color, the influence of selected TiO2 -SiO2
material’s surface in an adequate concentration producing a white color, the influence of selected
TiO2-SiO2 coatings and subsequent washing on the changes of the samples’ whiteness degree was
given by CIE whiteness (W) and yellowness index (YI) calculated according to Equations (1) and (2).
The gained results are graphically shown in Figure 7.
Coatings 2019, 9, 545 10 of 13

coatings and subsequent washing on the changes of the samples’ whiteness degree was given by CIE
whiteness (W) and yellowness index (YI) calculated according to Equations (1) and (2). The gained
results 2019,
Coatings are graphically
9, x FOR PEERshown in Figure 7.
REVIEW 10 of 12

85 12

80 10

75
8

Yellowness index
CIE whiteness

70
6
65
4
60

55 2

50 0
ref. 3% 6% 9% ref. 3% 6% 9%
Co Co/PES Sample
zero ten UV zero ten UV

Figure
Figure 7.
7. CIE
CIEwhiteness
whiteness(left axis)
(left and
axis) yellowness
and index
yellowness (right
index axis)axis)
(right of untreated samples
of untreated (ref.),(ref.),
samples and
and2-modified
TiO samples
TiO2 -modified (3%, (3%,
samples 6% and
6% 9%)
and before and after
9%) before 20 washing
and after cycles,
20 washing and and
cycles, afterafter
720 h720
of hUV of
irradiation.
UV irradiation.

The results in Figure 7 revealed higher whiteness of industrially pre-treated Co/PES reference
comparison with
sample (77.8) in comparison with thethe CoCo fabric
fabric (67.2),
(67.2), owing
owing to to the
the major
major brightness
brightness of of PES
PES fibers.
fibers.
The application of TiO22 nanoparticles
nanoparticles slightly
slightly changed
changed the the fabrics’
fabrics’ whiteness
whiteness degree
degree and and thus,
thus,
yellowness index,which
yellowness index, whichdepended
depended upon
upon thethe
type type of material
of material and2 concentration
and TiO TiO2 concentration
used. TiO used. TiO2-
2 -coated
coated
Co/PESCo/PES
were lesswere lessand
white white
moreandyellow
more yellow
compared compared to the reference
to the reference samplesample
and the and the opposite
opposite effect
effect
appeared appeared
on TiO2on TiO2-coated
-coated Co sample;Co sample;
although,although,
the higher the higherofamount
amount TiO2 -SiOof2 colloidal
TiO2-SiOdispersion
2 colloidal

dispersionthe
worsened worsened
whitenessthedegree
whiteness degree
of both of bothSubsequent
materials. materials. washings
Subsequent washings
also somewhat alsochanged
somewhat the
changed
calculatedthe calculated
values, probably values,
due toprobably due relaxation
the fabrics’ to the fabrics’ relaxation
shrinkages shrinkagesuncertainties.
and measuring and measuring
uncertainties.
The biggest and most visually perceivable changes in whiteness originated on both materials
after The biggest 720
continuous andhmost
of UV visually perceivable
irradiation, regarding changes in whiteness
the composition of originated on both
the textile and materials
concentration
after
of thecontinuous 720 hIn
applied paste. ofthe
UVcase
irradiation,
of cotton regarding
fabric, UV therays
composition
influenceofthe theelevated
textile and concentration
whiteness (up to
of the applied
value 78.1), ifpaste. In thewith
compared case of
thecotton fabric,of
whiteness UV rays
the influence the samples.
non-irradiated elevated whiteness
Although, (up to value
Montazer
78.1), if compared
et al. [17] with
studied the the whiteness activity
photo-catalytic of the non-irradiated
of nanoTiO2 causing samples. Although, Montazer
decomposition of someetcotton’s
al. [17]
studied the photo-catalytic activity
naturally-originated/remained of nanoTiO
pigments under 2UV causing decomposition
lightness, our study did of some cotton’s
not prove the naturally-
bleaching
originated/remained
action, probably due to pigments
the silicaunder
coatedUV TiOlightness,
2 . Just theour studyphenomenon
opposite did not prove the be
could bleaching
comprehended action,
probably
from Figure due to the silica
7; namely, coated TiO
the selected 2. Justdispersion
colloidal the opposite phenomenon
prevented couldofbe
yellowness comprehended
Co/PES from
fabric subjected
Figure 7; namely, the
to UV irradiation. Theselected
higher thecolloidal dispersion
concentration the prevented yellownessindex
lower the yellowness of Co/PES fabric
was, i.e., subjected
11.13 for the
to UV irradiation.
reference sample, andThe8.97,
higher the
8.05 andconcentration the lower
7.77 for the samples the yellowness
treated with 3%, 6% index
andwas, i.e., of
9% owf 11.13
TiOfor the2
2 -SiO
reference
dispersion, sample, and 8.97, 8.05 and 7.77 for the samples treated with 3%, 6% and 9% owf of TiO2-
respectively.
SiO2 dispersion, respectively.
3.2.5. UPF Measurement
3.2.5.The
UPFUV-A
Measurement
and UV-B transmittance of samples was spectrophotometrically characterized,
and The
additionally,
UV-A and anUV-B
ultraviolet protective
transmittance factor (UPF)
of samples was calculated regarding
was spectrophotometrically the numberand
characterized, of
washing cycles,
additionally, an in order to protective
ultraviolet evaluate the impact
factor of repeated
(UPF) launderings
was calculated on the
regarding thefabrics’
numberUV-blocking
of washing
functionality, and thus, assessing the durability/bonding ability
cycles, in order to evaluate the impact of repeated launderings on the of TiO 2 -coatings. Furthermore,
fabrics’ UV-blocking
the samples were
functionality, andUV irradiated,
thus, with
assessing thethe aim of studying the
durability/bonding impact
ability ofof a TiO
TiO 2 catalyst
2-coatings. on the materials’
Furthermore, the
newly-obtained
samples were UV functionality. The the
irradiated, with gained
aimresults are shown
of studying in the of
the impact columns of Figureon8.the materials’
a TiO2 catalyst
newly-obtained functionality. The gained results are shown in the columns of Figure 8.
It is evident from Figure 8 that both the untreated fabrics (Co and Co/PES) had almost the same
UPF, i.e., 4.3 and 4.6, indicating a non-ratable UV protection level. After the application of 3%, 6% or
9% owf of TiO2-SiO2 paste, the fabrics’ UPFs exceedingly but non-linearly increased as expected, i.e.,
for Co up to 21.5, 28.6 and 31.6, and for Co/PES 18.6, 20.7 and 22.3, respectively, meaning good to
very good UV protective properties with regard to ASTM guidelines for labeling the sun protective
clothing (ASTM D 6603) [9].
Coatings 2019, 9,
Coatings 2019, 9, 545
x FOR PEER REVIEW 11 of
11 of 13
12

40 40
Rating UPF:
35 Rating UPF: 30 30 25 25 25 35
30 25 25 25 20 20 30
Rating UPF: Rating UPF:
25 25 Rating UPF:
Mean UPF

Mean UPF
20 15 15 10 10 Rating UPF: 20 20 20 15 20
20 15 15 15 15
20 20 15 15 15 10 15
0x 0x
15 5x 15 5x
10 10x 10 Rating UPF: 10x
Rating UPF: 0 0 0 0 5
5 0 0 0 0 0 20x 5
20x
UV UV
0 0
0 3 6 9 0 3 6 9
Concentration of TiO2 dispersion (%) Concentration of TiO2 dispersion (%)

(a) (b)
Figure 8. UPF values nano-TiO2
nano-TiO2 functionalized: (a) Co; and (b) Co/PES fabrics before and after 5, 10
of UV
and 20 washing cycles, and after 720 h of UV irradiation.
irradiation.

It is evident from
Measurements of Figure 8 that both also
UV transmittance the untreated
revealed that fabricsUPF (Co and Co/PES)
values declinedhad withalmost the same
any increase in
UPF, i.e., 4.3
washing and for
cycles 4.6, both
indicating
coateda non-ratable
textiles, as UVwellprotection
as for alllevel. After the application
the concentrations used. ofThe 3%,highest
6% or
9% owf of TiO
reduction -SiO2factor
of 2UV paste,was the fabrics’ UPFsafter
perceived exceedingly
twenty but non-linearly
washings whenincreased
employing as expected,
the lowest i.e.,
for Co up to 21.5, 28.6 and 31.6, and for Co/PES 18.6, 20.7 and 22.3, respectively,
concentration of TiO2 paste, i.e., for 33.5% (Co) and 28% (Co/PES), which is in good analogy with the meaning good to very
good UV protective
above-presented DRS properties with regard
results (Figure to ASTM guidelines
5). Nevertheless, the UPFsfor labeling
after washingthe were
sun protective clothing
higher compared
(ASTM D 6603) [9].
to the initial untreated samples, indicating the sufficient durability/bonding ability of TiO2
Measurements
nanoparticles with the of UV transmittance
cellulose also revealed
fibers. Although that UPF
the reached UPFs values
of alldeclined with any increase
the TiO2-modified/washed
in washing
samples were cycles
lowerfor thanboththecoated
value 55textiles, as well
(declared as UPF as for
50+),allthe
thegained
concentrations used. The
results confirmed that highest
nano-
reduction of UV factor was perceived after twenty washings when employing
sized TiO2 imparts the functionality to both fabrics against transmittance of harmful solar UV rays, the lowest concentration
of TiO2 paste,ati.e.,
particularly for 33.5%
higher (Co) and 28%
concentrations of(Co/PES),
applied which is in good
TiO2. Further analogy withofthe
employment above-presented
dyestuffs/printing
DRS results
pigments and (Figure
finishing 5). agents
Nevertheless, theimprove
could also UPFs after thewashing
UPFs, aswere higher compared
well-documented to the
by Fakin et initial
al. [8]
untreated samples,
and Wong et al. [18]. indicating the sufficient durability/bonding ability of TiO 2 nanoparticles with the
cellulose fibers. Although
In addition, the reached
UV irradiation UPFs ofsamples
of modified all the TiO 2 -modified/washed
contributed to enlarged samples were lower
UPF values than
of Co/PES
the value 55 (declared as UPF 50+), the gained results confirmed
and to a negligible reduction in Co fabrics’ UPF; although UPF rating remained practically that nano-sized TiO 2 imparts
the same,the
functionality to both fabrics against transmittance of harmful solar
thus meaning good photo-stability of applied coatings that were not inclined towards ageing underUV rays, particularly at higher
concentrations
the influence ofof applied
external TiO2 . Further employment of dyestuffs/printing pigments and finishing
conditions.
agents could also improve the UPFs, as well-documented by Fakin et al. [8] and Wong et al. [18].
In addition, UV irradiation of modified samples contributed to enlarged UPF values of Co/PES
4. Conclusions
and to a negligible reduction in Co fabrics’ UPF; although UPF rating remained practically the same,
This paper evaluated the durability of TiO2-SiO2 coatings exhausted in three concentrations onto
thus meaning good photo-stability of applied coatings that were not inclined towards ageing under
two non-colored light-weight cotton and cotton/polyester fabrics against repeated washings and
the influence of external conditions.
prolonged intensive UV irradiation.
The results obtained by surface morphology observation, investigation of optical properties, and
4. Conclusions
identification of specific molecular vibrations of modified textiles demonstrated the equal
This paper
distribution of TiOevaluated the durability of TiO2 -SiO
2-SiO2 core-shell nanoparticles on 2bothcoatings exhausted
fabrics. in threethe
Consecutively, concentrations
fabrics’ UV-
onto two non-colored light-weight cotton and cotton/polyester fabrics against
shielding ability was exceedingly enlarged and, on the other hand, the fabrics’ whiteness degree was repeated washings and
prolonged intensive UV irradiation.
reduced. After repeatedly accomplished standard washings, the amount of nanoparticles was slightly
The results
decreased, and lessobtained
uniform bydistribution
surface morphology
was achieved observation, investigation
on both fabrics. Also, theofnewly
optical properties,
obtained UV
and identification of specific molecular vibrations of modified textiles
protective functionality declined with the increasing of washing cycles. Additionally, 720 h of demonstrated the equal
distribution of TiO2 -SiO
intensive UV-A/UV-B 2 core-shell
irradiation causednanoparticles
minor damage on both and afabrics.
decrease Consecutively,
in the smoothness the onfabrics’
both
UV-shielding ability was exceedingly enlarged and, on the other hand,
materials, as well as visually perceivable changes in whiteness; although TiO2-SiO2 protected the the fabrics’ whiteness degree
was reduced.
Co/PES againstAfter repeatedly accomplished standard washings, the amount of nanoparticles was
yellowness.
slightly decreased,
The newly gained good and less uniform
to very distribution
good fabrics’was achieved
UV-rays on both
shielding fabrics.even
abilities, Also, the twenty
after newly
obtained
washingsUV andprotective
prolongedfunctionality
UV irradiation, declined
proved with
thethe increasing
suitability of washing
of employed cycles. Additionally,
exhaustion procedure,
720 h of intensive UV-A/UV-B irradiation caused minor damage
the sufficient durability/bonding ability of the nanoparticles with the fibers, and good and a decrease in the smoothness
photo-stability on
both materials, as well
of nano-modified fabrics.as visually perceivable changes in whiteness; although TiO2 -SiO2 protected the
Co/PES against yellowness.
Author Contributions: Conceptualization, A.O. and D.F; Methodology, A.O. and D.F.; Formal Analysis, A.O.;
Investigation, A.O.; Data Curation, A.O.; Writing—Original Draft Preparation, A.O.; Writing—Review and
Editing, D.F.; Funding Acquisition, D.F.
Coatings 2019, 9, 545 12 of 13

The newly gained good to very good fabrics’ UV-rays shielding abilities, even after twenty
washings and prolonged UV irradiation, proved the suitability of employed exhaustion procedure,
the sufficient durability/bonding ability of the nanoparticles with the fibers, and good photo-stability
of nano-modified fabrics.

Author Contributions: Conceptualization, A.O. and D.F.; Methodology, A.O. and D.F.; Formal Analysis, A.O.;
Investigation, A.O.; Data Curation, A.O.; Writing—Original Draft Preparation, A.O.; Writing—Review and Editing,
D.F.; Funding Acquisition, D.F.
Funding: The research leading to these results has received funding from the Slovenian Research Agency (ARRS)
under a program group for Textile Chemistry P2-0118.
Acknowledgments: The authors acknowledge Silvo Hribernik, University of Maribor, Slovenia, for his kind effort
to perform SEM analysis.
Conflicts of Interest: The authors declare no conflict of interest.

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