Fundamental and practical aspects concerning [617898]

Fundamental and practical aspects concerning
the characterization of smart textiles
Gianina Broasca1, Gabriela Borcia2, Nicoleta Dumitrascu2, Marius Cioca3, Diana Coman3,
Nouredine Ourfelli4 , Narcisa Vrînceanu3,*
1”Gheorghe Asachi” Technical University of Ia și, 53 Mangeron Street, Romania
2 “Alexandru Ioan Cuza” University of Ia și, 21 Carol I Street, Romania
3 “Lucian Blaga” University of Sibi u, 2-4 Emil Cioran Street, Romania
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 research aims towards a novel methodology of ZnO
impregnation onto polyamide supports , in order to attain a special
inorganic-organic hybrid polymer ma terial, with increased UV-barrier
attributes and high hydrophobicity. The experimental approach employed
ZnO micro particles powder. Solutions with different concentrations of
ZnO powder dispersed in methanol are prepared as anti-UV finishing agent
and applied onto polyamide fabric. Th e responsive behaviour of this
complex polymer network to UV irradiation, the photo protective
performance and its time stability, also the hydrophobic character are
assessed by different characterizati on techniques. The proposed method
has advantages, like: easy standard ization, at lower production cost,
resulting a high homogeneity and disper sion of ZnO micro particles into
the textile polymeric network. The covered polymeric supports show better
photo protective response, higher hydrophobicity and control on the
surface charge induced by irradiation. This method granted enhanced
quality, comfort and long term stability of the intelligent/smart garments.
1 Introduction
The textile area intents to design fabrics accommodated to strict surroundings conditions, as
to promote the human physiological comfort, by facile and reduced cost finishing
procedures. Commonly, the fabrics sector needs relevant procedures from the processing of raw materials to the distinct finished items [1-3].
The attributes of garments are functions of the processing technique. In this regard, the
nanotechnologies polarized much significan ce in the textiles area, granting to realize
multifunctional materials with attractive proper ties, controlled in the 0.1 – 100 nm range.
Recently, the embodiment of metal particles (e .g., zinc, silver, gold, platinum, etc.) was
analysed, in order to attain novel textiles [4 ]. For instance, the silver nanoparticles have
been embodied within different polymeric fibers belonging to various fabrics, primarily to

* Corresponding author: [anonimizat]

provide added value features, lik e: stain-repellence, bactericid al properties, or blocking of
smelly and odorous vapours [4]. Nevertheless, these metals occur in the form of
nanoparticles, meaning that thes e can be destructive to health if absorbed by the human
body [4]. Such issues need extended research efforts for back-up covering/incorporating
polymeric supports.
The barrier against the UV radiation is a pr actical demand for the safety of garments
designed for particular applications, as extended sun exposure during outdoor activities. Due to their unique properties, like: electri cal, photocatalytic, opti cal, dermatological and
antibacterial, zinc oxide (ZnO) powders are widely used semi conductor materials, having
numerous structures. Furthermore, for medical applications ZnO is bio-safe and biocompatible. ZnO is experienced as a UV-blocking system, mainly in the UV-A region.
In order to apply ZnO powder as UV-absorbing system, it has to be assimilated into
different matrices, by means of diverse appr oaches developed to improve the stability of
ZnO in different dispersions media and to block particles clustering.
Considering all these, a novel methodology based on ZnO impregnation of polyamide
supports in order to engineer an inorganic-organic hybrid polymer network, with augmented UV-barrier attributes and high hydrophobicity was nominated. The
experimental component consists of employ ing ZnO microparticles powder. As anti-UV
finishing agent different concentrations of solutions with of ZnO powder dispersed in methanol were prepared and applied onto polyamide fabric. Different characterization
methods were used to evaluate the responsive behaviour of this complex polymer matrix to
UV irradiation, such as: the photoprotective work, long term stability, the hydrophobic
character. As advantages of th is solution we can mention:
• Easy standardization,
• Lower production cost,
• High homogeneity and dispersion of ZnO microparticles into the textile polymeric
network.
2 Experimental
2.1 Materials and preparation
Woven polyamide fabrics (83.5 g/m2) were identified and prepared for immersion in the
form of 3 cm – 7 cm strips. The micromet er-sized ZnO powder was supplied by Ensait
Laboratory, France. Laser diffraction was employed to perform the particle-size
distribution, showing that 75% of the ZnO powder consists of 1.7 μm size particles. The
solutions are based of ZnO powder dispersed in methanol (99.8%), at different concentrations: 1%, 3%, 5% and 7%. The magnetic stirring was used for 15 minutes, in
order to obtain the solutions, adding 4 drops of Vitexol (BASF) to avert foaming and 65 g/l
Apretan (Clariant) to provide the fixation of ZnO to fibers. The studied samples were immersed into ZnO solutions by padding, on a Wemer Mathis AG Laboratory machine,
followed by wet-picking, pressing the textile between hydroextraction cylinders, in order to
eliminate a part of liquid/paste from the polymeric surface. The samples are weighted
before and after impregnation. The immersed specimens were exposed in a Vetter machine
for drying, for 3 minutes, at 110 °C. The mixtur e is then fastened on the 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 wicking of the polymeric support is a ssessed by contact angle measurement. The
sessile drop technique was used in order to obtain the contact angles, under controlled
conditions of room temperature and humidity. An automated system stored the drop images, via a Canon A85 camera, with PC-based control, acquisition and data processing.
Ten measures on the imaged sessile liquid drop profile, for 1 μl drop size were performed.
By averaging these values, the values of the static contact angle were obtained. As test
liquid distilled water was employed. The adhesi on activity of water on the surface, meaning
wicking, is calculated as follows:
) cos1(θ γ+=lv aW (1)
Where Wa is the contact angle and ϒlv is the surface tension.
3 Results and discussion
Figure 1 displays SEM microphotographs of polyamide supports covered with ZnO. The
surface belonging to the reference polyamide fabric is smooth (Figure 1a ), exposing only
tiny detached particles, like im purities. Different co ncentrations of ZnO solutions lead to
different layer covering the polyamide samples, having different morphology based on the
increasing ZnO concentration of the finishing ag ent. For the sample treated with 1% ZnO, a
thin film, with lamellar morphology and good uniformity, was obtained (Figure 1b). The thickness of this layer increments with an increased ZnO concentration, displaying a
uniform coating of the supports for 3-5% ZnO (Figure 1c). In case of higher concentration
in zinc oxide, a lower dispersion of the microparticles was noticed, along with the visible clusters leading to non-uniform covering of the supports (Figure 1d). Consequently, an
uniform covering of fibers is achieved due to the best dispersion of the particles, correlated
to ZnO concentration lower than 5%.
The covering of the supports is sustained by EDS measurement, where the Zn quantity
on the specimens displays correlation to the ZnO concentration of the solutions. It was
demonstrated that the content is the highest for the 7% ZnO sample.
The wicking of the polymeric support surf ace evaluates the material behaviour in
presence of water or humid environment. The values are gathered in Table 1. Moreover,
rerun measurement demonstrates that the contact angle is not altered by macroscopic non-uniformity of the woven materials, since all liquid drops deposited onto the surface show
regular, symmetric profile.

Fig. 1. SEM photos of polyamide supports covered with ZnO: a) reference, b) 1% ZnO, c) 5% ZnO,
d) 7% ZnO.
Generally speaking, the polyamide fabric is hydrophobic, having a water contact angle
higher than 90 ˚. In this case the surface is not wet. In addition, the polymeric support does
not absorb the water, because the drops depo sited onto the surface vanish after long
intervals, by evaporation.
The padding with ZnO pointed out, in a visible manner, a higher hydrophobicity, as the
augmentation of contact angle. This aspect can be regarded as a diminution of the adhesion
activity, with an average 50%. Th is fact certifies that the po lymeric supports are covered
with an oxide layer, which is more hydrophobic than the polymer itself.
Another interesting fact is the lowest wicking noticed for 3% ZnO impregnated
polymeric support, while increm ented ZnO concentration conducts to higher wicking, i.e.
reversal of the surface attributes. Between the 3% and 7% ZnO samples a difference of
68% has been calculated, which is relevant.
This response can be regarded as a function of a better dispersion of ZnO particles in the
3% specimen, which is more diluted, granting more homogenous covering of textile
supports, and more hydrophobic attribute due to oxide film. In case of samples coated with
higher oxide concentration, the cluster of ZnO particles leads to a low levelness, consequently the fibers are irregularly covered with films of different thickness.
Table 1. Contact angle and adhesion responsive attitude of water on polyamide supports covered with
ZnO, before and af ter UV irradiation.
Samples before UV irradiation after UV irradiation
θ (°) aW (mJ/m2) θ (°) aW (mJ/m2)
polyamide 92° 67 88° 75
polyamide + 1% ZnO 120° 32 115° 30
polyamide + 3% ZnO 131° 20 135° 27
polyamide + 5% ZnO 129° 26 124° 32
polyamide + 7% ZnO 113° 33 116° 48

The UV irradiation of the specimens leads, as expected, to the decreasing of the contact
angle. This decreasing is noticeable for the polyamide fabric, in terms of the surface

chemistry modification of polymers under exposure to energy sources. The modification is
important less for the supports covered with Zn O. In this manner the UV-barrier function of
the oxide layer was stressed. It is noteworthy to mention that all the studied ZnO covered
probes show a relevant hydrophobicity after UV irradiation. The 7% ZnO sample showed the highest level of modification. The synergic effect provided by the better dispersion of
the microparticles (3-5% ZnO solutions) and the good levelness of the surface layer,
showed an improved UV-protection.
4 Conclusion
A novel methodology is oriented toward the impregnation of ZnO powder in a polymeric
matrix, applicable, in order to obtain textiles with a multifunctional performance: UV
barrier, high hydrophobicity. The method provides a homogenous dispersion of ZnO particles through the polymeric support. New attr ibutes like higher photoprotection, higher
hydrophobicity and assessment on the irradiat ed surface. This experimental approach
maintains the mechanical features of the material unmodified, providing an improved quality, comfort and long term stability of the clothing.
References
1. Y.W.H. Wong, C.W.M. Yuen, M.Y. S. Leung, S.K.A. Ku, H.L.I. Lam, Autex Research Journal 6
(2006)
2. K.L. Hatch, U. Osterwalder, Dermatologic Clinics 24 (2006)
3. J.M. Menter, K.L. Hatch, in: P. Elsner, K. Hatch, W. Wigger (Eds.), Textiles and the Skin,
Current Problems in Dermatology, vol. 31, Karger, Basel, (2003).
4. C.-H. Xue, W. Yin, S.-T. Jia, J.-Z. Ma, Nanotechnology 22 (2011)