Fundamental and practical aspects concerning [602973]

Fundamental and practical aspects concerning
the characterization of smart textiles
Gianina Broasca1 , Gabriela Borcia2 , Nicoleta Dumitrascu2, Marius Cioca3, Diana
Coman3, Nouredine Ourfelli4 , Narcisa Vrinceanu3*
1”Gheorghe Asachi” Technical University of Iasi, 53 Mangeron Street , Romania
2 “Al.I.Cuza” University of Iasi, 21 Carol I Street, Romania
3 “Lucian Blaga” University of Sibiu, 2 -4 Emil Cioran Street, Roamnia
4 Université de Tunis El Manar, Laboratoire de Biophysique et Technologies Médicales;
Abdulrahman Alfaisal University, Department of Chemistry, College of Science, Saudi Arabia
Abstract. The study proposes a method, based on ZnO impregnation of
polyester textiles, to create inorganic -organic hybrid polymer material,
with enhanced UV -protection properties and high hydrophobicity. Our
approach is based on using ZnO micro particles powder, different of other
methods which are using ZnO nanoparticles. Solutions with differ ent
concentrations of ZnO powder dispersed in methanol are prepared as anti –
UV finishing agent and applied onto polyester fabric. The response of this
hybrid polymer network to UV irradiation, the photo protective
performance and its time stability, also t he hydrophobic character and
mechanical properties are evaluated by different methods. This practical
solution has advantages, as the procedure can be easily standardized, at
lower production cost, ensuring a high homogeneity and dispersion of ZnO
micro pa rticles into the textile polymeric matrix. The coated fabrics show
better photo protective performance, higher hydrophobic character and
control on the surface charge induced by irradiation. This method keeps the
mechanical properties of the material uncha nged, offering enhanced
quality, comfort and time stability of the intelligent/smart garments .

1 Introduction
The textile industry aims to create fabrics adapted to severe environmental conditions,
as to improve the human physiological comfort, by simple and low cost finishing
operations. Usually, the textile industry requires an important number of procedures from
the processing of prime materials to the specific finished products [1 -3].
The properties of textile clothing are depending on the proc essing method. In this
respect, the nanotechnologies gained much interest in the textiles field, allowing to prepare
functional materials with excellent properties, controlled in the 0.1 – 100 nm range. In
recent years, the coating or incorporation of meta l particles (e.g., zinc, gold, silver,
platinum, etc.) was tested, to obtain various novel fabrics [4 ]. Thus, the silver nanoparticles

have been incorporated into the fibers of different fabrics, from clothing to bedding or other
products, mainly to provid e stain -resistance, bactericide properties, or to stop smelly and
odorous vapors [7]. Nonetheless, as these metals often exist in the form of nanoparticles,
these can be harmful to health if absorbed by the human body [ 4]. Such problems require
continuous searching for alternative coating/incorporating materials.
The protection against the UV radiation is one of the practical requirements for the
safety of garments intended for particular service conditions, as prolonged sun exposure
during outdoor activiti es. Zinc oxide (ZnO) powders are semiconductor materials,
occurring in a variety of structures, widely used due to their unique properties, such as
photocatalytic, electrical, optical, d ermatological and antibacterial . Moreover, ZnO is bio –
safe and biocomp atible for applications in medicine . ZnO is known as a UV -blocking
material, especially in the UV -A region . For the applications of ZnO as UV -absorbing
system, it has to be incorporated into different matrices, and various strategies have been
developed to increase the stability of ZnO in different dispersions media and to prevent
particles agglomeration.
Taking this into account, we propose a method, based on ZnO impregnation of polyester
textiles, to create inorganic -organic hybrid polymer material, with enhanced UV -protection
properties and high hydrophobicity. Our approach is based on using ZnO microparticles
powder, different of other methods which are using Z nO nanoparticles. Solutions with
different concentrations of ZnO powder dispersed in methanol are prepared as anti -UV
finishing agent and applied onto polyester fabric. The response of this hybrid polymer
network to UV irradiation, the photoprotective perf ormance and its time stability, also the
hydrophobic character and mechanical properties are evaluated by different methods. This
practical solution has advantages, as the procedure can be easily standardized, at lower
production cost, ensuring a high homo geneity and dispersion of ZnO microparticles into the
textile polymeric matrix.
.
2 Experimental
2.1 Materials and preparation
Woven polyester fabrics (97.5 g/m2) (SC Condor SA, Romania) are selected and prepared
for impregnation in the form of 5 cm – 10 cm strips. ZnO, supplied by Ensait Laboratory,
France, is powder with micrometer -size particles. The particle -size distribution is
determined by laser diffraction, showing that the ZnO powder is 75% composed of 1.7 µm
size particles. The solutions are prepared with ZnO powder dispersed in methanol (99.8%),
at 1%, 3%, 5% and 7% concentration. The solutions are stirred for 15 minutes, adding 4
drops of Vitexol (BASF) to avoid foaming and 80 g/l Apretan (Clariant) to ensure bonding
of ZnO to fibers. The fa brics are impregnated with the ZnO solutions by padding, on a
Wemer Mathis AG Laboratory machine, performed by immersion in solution, followed by
wet-picking, pressing the textile between hydroextraction cylinders, for removal of a part of
liquid/paste fro m the textile surface. The samples are weighted before and after
impregnation. Impregnated samples are dried, for 3 minutes, at 110 °C, in a Vetter
machine. The mixture is then fastened on the fabric, heated at 150 °C for 3 minutes, by
thermal induced cros slinking.

2.2 Characterization methods
Scanning electron microscope (SEM) images of the samples are obtained with a Quanta
200 3D Dual Beam type microscope (FEI Holland), coupled to an energy -dispersive X -ray
spectroscopy (EDS) analysis system (EDAX – AMETEK Holland) equipped with a SDD
(silicon drift detector) type detector. Taking into account the sample type, the analyses are
performed using Low Vacuum working mode, allowing the probes tested in their initial
state, without a previous metallization. B oth for the acquisition of secondary electrons
images and EDS elemental chemical analysis, LFD (Large Field Detector) detector is used,
running at 60 Pa pressure and 30 kV voltage . The wettability of the fabric is evaluated by
contact angle measurement. Th e contact angles are obtained using the sessile drop
technique, under controlled conditions of room temperature and humidity. An automated
system is used to store the drop images, via a Canon A85 camera, with PC -based control,
acquisition and data processi ng. The values of the static contact angle presented are the
average of ten measured values obtained on the imaged sessile liquid drop profile, for 1 µl
drop size. Bidistilled water is used as test liquid. The adhesion work of water on the
surface, which r elates to th e wettability, is calculated as:

) cos1(lv aW (1)
Where Wa is the contact angle and γlv is the surface tension.

3. Results and discussion
SEM microphotographs of polyester fabrics coated with ZnO are shown in Figure 1. The
surface of uncoated polyester fabric is smooth (Figure 1a), showing only some small
isolated particles, probably impurities. Impregnation with ZnO solution conducts to coating
of fibers with a layer, showing different morphology with increasing ZnO concentration of
the finishing agent. A thin layer, with lamellar morphology and good uniformity, develops
on the 1% ZnO sample (Figure 1b). This layer increases in thickness with augmented ZnO
concentration, showing uniform coating of the fibers for 3 -5% ZnO (Figure 1c). For higher
concentration in zinc oxide of the finishing agent, the dispersion of the microparticles is
poorer, and the tendency to agglomerate visibly conducts to non -uniform coating of the
fibers (Figure 1d). Therefor e, the best dispersion of the particles, ensuring uniform coating
of fibers, corresponds to ZnO concentration lower than 5%.
The coating of the fibers is confirmed by EDS measurement, where the Zn content on the
samples shows correlation to the ZnO concent ration of the solutions, in that the content is
the highest for the 7% ZnO sample .

Fig. 1. Figure 1. SEM microphotographs of polyester fabrics coated with ZnO:
a) uncoated, b) 1% ZnO, b) 5% ZnO, d) 7% ZnO .
Wettability
The wettability of the fabric surface controls the material performance in presence of water
or humid environment. The results are presented in Table 2. Importantly, repeated
measurement shows that the contact angle is not affected by macroscopic non -unifo rmity of
the woven materials, as all liquid drops deposited onto the surface show regular, symmetric
profile.
The polyester fabric is hydrophobic, with a water contact angle higher than 90 ˚. This
indicates that the surface is not wetted. Moreover, water is not absorbed in the material,
since the drops deposited onto the surface vanish after long intervals, by evaporation.
The impregnation with ZnO conducts, visibly, to higher hydrophobicity, as the
increase in contact angle relates to the diminution of t he adhesion work, with an average
50%. This confirms that the fibers are coated with an oxide layer, which is more
hydrophobic than the polymer. Interestingly, the lowest wettability is observed for 3% ZnO
impregnated fabric, whereas increased ZnO concentr ation leads to higher wettability, i.e.
reversal of the surface properties. Between the 3% and 7% ZnO samples there is 68%
difference in adhesion work, which is important.
This behavior relates to better dispersion of ZnO particles in the 3% sample, which is
more diluted, allowing more uniform coating of textile fibers, and more hydrophobic
character due to oxide layer. In the samples impregnated at higher oxide concentration, the
agglomeration of ZnO particles conducts to non -uniformity, and therefore the fibers are
irregularly coated with layers of different thickness .

Table 1. Contact ang le and adhesion work of water on polyester fabrics coated with ZnO, before and
after UV irradiation .
Material before UV irradiation after UV irradiation

()
aW (mJ/m2)
 ()
aW (mJ/m2)
polyester 95 66 86 78
polyester + 1% ZnO 121 35 117 40
polyester + 3% ZnO 134 22 130 26
polyester + 5% ZnO 128 28 126 30
polyester + 7% ZnO 119 37 113 44

The UV irradiation of the samples conducts, as expected, to diminution of the contact
angle. The diminution is visible for the polyester fabric, relating to the surface modification
of polymers under exposure to energy sources. The modification is much less important for
the ZnO coated fabrics, thus confirming the UV -protective function of the oxide layer. All
ZnO coated samples retain a pronounced hydrophobicity after UV exposure. The highest
degree of modification is o bserved for the 7% ZnO sample. Here again the better dispersion
of the microparticles and the good uniformity of the surface layer, ensured for 3 -5% ZnO
solutions, relate to enhanced UV -protection

.3 Conclusion
A new technique is proposed, based on ZnO powder impregnation in a polymeric network,
simple and easier to implement in practice, to obtain textile fabrics with combined
properties, as UV protection, water and vapor repellence and stability to UV irradiation.
The method ensures a high homogeneity and dispersion of ZnO particles into the textile
polymeric matrix. The coated fabrics show better photoprotective performance, higher
hydrophobic character and control on the surface charge induced by irradiation. This
method keeps the mechanical properti es of the material unchanged, offering enhanced
quality, comfort and time stability of the garments.

References

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