Fundamental and practical aspects concerning [602701]

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 Sibi u, 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 inorga nic-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 nanopar ticles. Solutions with different
concentrations of ZnO powder disperse d in methanol are prepared as anti-
UV finishing agent and applied onto polye ster fabric. The response of this
hybrid polymer network to UV irradiation, the photo protective
performance and its time stability, also the hydrophobic character and
mechanical properti es are evaluated by differe nt methods. This practical
solution has advantages, as the proce dure can be easily standardized, at
lower production cost, ensuring a high homogeneity and dispersion of ZnO
micro particles 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 mate rial unchanged, 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 processing 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 metal partic les (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

* Corresponding author: [anonimizat]

products, mainly to provide st ain-resistance, bactericide prope rties, or to stop smelly and
odorous vapors [4]. Nonetheless, as these meta ls 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 activities. Zinc oxide (ZnO) powders are semiconductor materials, occurring in a variety of structures, widely used due to their unique properties, such as
photocatalytic, electrical, opti cal, dermatological and antibact erial. Moreover, ZnO is bio-
safe and biocompatible 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 ZnO 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 photoprotec tive performance and its time stability, also the
hydrophobic character an d mechanical properties are evalua ted by different methods. This
practical solution has advantages, as the proc edure can be easily standardized, at lower
production cost, ensuring a high homogeneity 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 Condo r 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 par ticles. 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 ar e prepared with ZnO powder di spersed 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 fabrics are impregnated with the ZnO solutions by padding, on a Wemer Mathis AG Laboratory machine, perfor med by immersion in solution, followed by
wet-picking, pressing the textile between hydroextraction cylinders, for removal of a part of
liquid/paste from 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 th e fabric, heated at 150 °C for 3 minutes, by
thermal induced crosslinking.
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 in to account the sample type, the analyses are
performed using Low Vacuum working mode, a llowing the probes tested in their initial
state, without a previous metallization. Both for the acquisition of secondary electrons
images and EDS elemental chemical analysis, LF D (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. The contact angl es 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 processing. 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 relates to the wettability, is calculated as:

) cos1(θ γ+=lv aW (1)
Where W a is the contact angle and  lv is the surface tension.
3 Results and discussion
SEM microphotographs of polyester fabrics co ated with ZnO are shown in Figure 1. The
surface of uncoated polyester fabric is smoo th (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 lame llar 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). Therefore, the best dispersi on 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 concentration of the solutions, in that the content
is the highest for the 7% ZnO sample.

Fig. 1. SEM microphotographs of polyester fabrics coated with ZnO: a) uncoated, b) 1% ZnO, b) 5%
ZnO, d) 7% ZnO.

3.1 Wettability
The wettability of the fabric su rface controls the material perf ormance in presence of water
or humid environment. The results are pres ented in Table 1. Importantly, repeated
measurement shows that the contact angle is not affected by macroscopic non-uniformity of
the woven materials, as all liquid drops depo sited 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. Moreov er, water is not absorb ed in the material,
since the drops deposited onto the surface vanish after long interval s, by evaporation.
The impregnation with ZnO conducts, visibly, to higher hydrophobi city, as the increase
in contact angle relates to the diminution of th e adhesion work, with an average 50%. This
confirms that the fibers are coated with an oxi de layer, which is more hydrophobic than the
polymer. Interestingly, the lowest wettability is observed for 3% ZnO impregnated fabric,
whereas increased ZnO concentration leads to hi gher 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 ther efore the fibers are
irregularly coated with layers of different thickness.

Table 1. Contact angle and adhesion work of water on polyester fabrics coated with ZnO, before and
after UV irradiation.
Material before UV irradiation after UV irradiation
θ (°) aW (mJ/m2) θ (°) 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 visibl e for the polyester fabric, rela ting 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 observed 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
4 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 su rface charge induced by irradiation. This
method keeps the mechanical properties of the material unchanged, offering enhanced
quality, comfort and time stability of the garments.
References
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