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Научни трудове на Съюза на учените в България-Пловдив. Серия В. Техника и технологии, т. XV, ISSN 1311 -9419 (Print), ISSN 2534-9384 (On- line), 2017. Scientific Works of the Union of Scientists in Bulgaria-Plovdiv, series C. Technics and Technologies, Vol. XV., ISSN 1311 -9419 (Print), ISSN 2534-9384 (On- line), 2017.
ЕЛЕКТРООВЛАКНЕНИ МАТЕРИАЛИ ОТ ФЛУОР-СЪДЪРЖАЩИ ПОЛИМЕРИ,ДЕКОРИРАНИ С НАНОЧАСТИЦИ OTZnO:
ПОКООИСВАНЕ И СВОЙСТВА Мария Георгиев а Спасовв1*, Некеска Емаснило ва Манолова1, Надя Димитр ова IV^^^k^^iïe2, ИлияКлягоев Рашкял1 ^аборатороя Битллгично актявип яолснерт, Индиипут потолимери, Българскаааадедия ла нарират,аПД Софвл, Сългароя ^нетит^т до микри0иология,БлргарикаакадемАд на ндуките,
П(3 СофдЯ( Болгарок
ELECTROSPUN FIBROUS FLUOR-CONTAINING POLYMER MATERAOLS DECOIATDD WDTH ZnO NANOPARTICLES:
PRATARATIOT ANE PROOTETIET Mariya Georgieva Spasova1*, Nevena Emanuilova Manolova1, Nadya Dimitrova Mardova2, IHoo Blaonev Ras hkov1
stit^te ofPolymers, ISi^lgarian Acalemyof Sriencys, BG-IH3 e^fie, Boltaria 2Institute BuegarianAcodome ofSciences,
BGeiei3SO0a, Bulg^ya
Abitaoot
Nooefibaoei motoaioli of fleoa-contoining pelymoai oo° ZoO oooepoatioloi woao paopoaol by olootaeipiooiof on° olootaeipaoyiof toohoiqeoi. Two typoi of fleoa-contoining pelymoai: po(y(viny(i°ono fluoaido) (PVDF) on° po(y(viny(i°ono fluoaido-co-hoxoe(ueaepaepy(ono) (BVDF-HFB) woao ugo°. ZnO woi inooapoaotod in tho fiboai (doiign typo "in") oa woi °opoiito° on tho fiboai' leafooo (doiign typo "on"). Tho paopoaol motoaioli woao ohoaootoaizol by ioonning olootaon mioaoioopy (OBM), taonimiiiion olootaon mioaoioopy (TBM), diffoaontiol ioonning ooloaimotay (DOC), thoamogaovimotaio onolyiii (TGA) and oontoot onglo mooieaomonti. Tho doooaotion of fiboai with ZnO aoieltol in inoaooio of thoia thoamol itobility on° hydaophobioity. Tho mioaobiologiool toiti ihowod tho motoaioli oxhibitol ontibootoaiol ootivity ogoinit tho pothogonio mioaooagoniim Staphylococcus aureus.
Koywoadi: PVDF, ZnO, tlootaoipinning, tlootaoipaoying, ontibootoaiol ootivity Intaoleotion
Recently, increased attention is paid on the self-cleaning effect of natural plant leaves. The excellent water repellent properties of the lotus leaves are due to the combination of a rough structure and the covering waxes on the leaves' surface (Marmur, 2004; Barthlott 1997; Neinhuis 1997).
Inspired by nature, researchers have developed various methods for the preparation of
superhydrophobic surfaces. Recently, electro spinning method was applied to obtain superhydrophobic materials as well (Karim, 2011; Lim, 2010; Cho, 2010). Furthermore, considerable attention has been devoted to fluorine-containing polymers due to their unique characteristics, such as chemical, thermal and oxidative stability, hydrophobicity, excellent mechanical properties and biocompatibility. These characteristics are imparted by the specific properties of fluorine atom (Laroche, 1995). ZnO is nontoxic compound with photochemical and antibacterial activity (Sirelkhatim 2015). Recently, we have reported the possibility to incorporate ZnO nanoparticles in PVDF and PVDF-HFP nanofibers by electro spinning (design type "in") (Spasova 2016). The incorporation of ZnO nanoparticles resulted in an increase of the mean diameter of the composite fibers, improved their thermal stability and increased the hydrophobicity in comparison to the PVDF and PVDF-HFP fibers. When placed on the surface of a material, ZnO nanoparticles may increase the surface roughness and therefore to be used for the preparation of superhydrophobic materials.
The aim of the present study is to prepare nanofibrous mats consisting of PVDF or PVDF-HFP fibers and ZnO nanoparticles and to study the properties of the obtained materials with design type "in" and type "on". Experimental
Materials
Poly(vinylidene fluoride) (PVDF, Aldrich, France) with MW =180,000 g/mol and B=2.53; poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP, Aldrich, USA) with MW
=400,000 g/mol and B=3.07 and commercial nanosized zinc oxide with silanized surface available under the trade mark Zano®20 Plus (Umicore Zinc Chemicals-Belgium) were used. N,N-dimethylformamide (DMF) and acetone were of analytical grade of purity. Nanofibrous mats of PVDF or PVDF-HFP and ZnO with design type "on"
ZnO-on-PVDF and ZnO-on-PVDF-HFP nanofibrous mats were prepared by simultaneous electrospinning and electrospraying. The mats with design type "on" were fabricated by using two syringe pumps NE-300 (New Era Pump Systems, Inc.) for delivering solutions in DMF/acetone (80/20 v/v): (i) PVDF or PVDF-HFP solution (25 wt% and 20 wt% for PVDF and PVDF-HFP, respectively) for the electrospinning and (ii) ZnO suspension (30 % w/v) in solution of PVDF or PVDF-HFP (0.5 wt%) for the electrospraying. The spinning solutions and suspensions were delivered at a constant rate of 0.5 ml/h. Electrospinning and electrospraying were conducted at a constant tip-to-collector distance of 20 cm, rotation speed of the aluminium collector - 1000 rpm and at constant applied voltage of 25 kV provided by custom-made high-voltage power supply. Nanofibrous mats of PVDF or PVDF-HFP and ZnO with design type "in"
PVDF, PVDF-HFP, ZnO-in-PVDF and ZnO-in-PVDF-HFP fibrous mats were prepared according to the procedure described in details elsewhere (Spasova 2016). Characterization of the nanofibrous materials
The morphology of the fibrous materials was evaluated by scanning electron microscopy (SEM) with Jeol JSM-5510 (Jeol Ltd., Japan). TEM observations were carried out by JEM-2100 LaB6 (JEOL Co. Ltd.) operating at 200 kV and equipped with EDS elemental analysis. The thermal behavior of the obtained fibrous materials was evaluated by differential scanning calorimetry (DSC) in the temperature range from 0 to 200 oC at heating rate of 10 oC/min under nitrogen (TA Instruments, DSC Q2000, USA). The thermal stability of the fibrous materials was determined using TA Instruments TGA Q5000, USA under nitrogen flow from r.t. to 800 oC at a heating rate of 10 oC/min. The water contact angles of the fibrous materials were measured using an Easy Drop DSA20E KRUSS GmbH apparatus, Germany. The antibacterial activity of the fibrous materials against S. aureus 749 was evaluated by using the viable cell counting method.
Results
SEM and TEM micrographs are shown in Figure 1 for the ZnO-on-PVDF mat (Figure 1A) and
ZnO-on-PVDF-HFP mat (Figure 1B). As seen from the presented TEM micrographs the Zn particles were distributed in the form of small (ca. 100 nm) or large (1 ^m) spherical particles on the PVDF and PVDF-HFP fibers. ZnO particles were evenly distributed over the entire surface of the nanofibrous mat. The mean fiber diameter of the composite ZnO-zn-PVDF and ZnO-zn-PVDF-
HFP fibers was 228±50 nm and 147±39, respectively (Spasova 2016).
Figure 1. SEM and ТЕМ (inset) micrographs of nanofibrous mats of: А. ZnO-on-PVDF and B.
ZnO-on-PVDF-HFP.
The thermal behaviour and properties of the obtained nanofibrous mats were assessed by differential scanning calorimetry (DSC) and thermogravimetric (TGA) analyses. It was established that the as-spun fibrous mats of PVDF and ZnO-on-PVDF manifest high degree of crystallinity -ca. 42 % and enthalpy of 43 J/g. Similarly the mats of PVDF-HFP and ZnO-on-PVDF-HFP had almost identical values for the crystallinity degree - 18 % and enthalpy of 17 J/g. The incorporation of ZnO nanoparticles in PVDF and PVDF-HFP fibers resulted in decrease in the crystallinity and increase of the amorphous phase of the composite fibers. A possible explanation for the observed decrease in crystallinity is that the addition of the nanofiller in such high concentrations hinders the movement of the polymer chains due to some specific interactions between ZnO and PVDF or PVDF-HFP which hamper the polymer crystallization. The TGA curve for the mats based on PVDF-HFP (Fig. 2B) showed an initiation of degradation at around 350 C. The incorporation of ZnO in PVDF and PVDF-HFP mats increased their thermal stability. Improvement of the thermal stability was observed as well for the mats with design type "on" where ZnO decorated the surface of the PVDF and PVDF-HFP fibers.
50 100 150 200 Temperature (°C)
A.
ZnO-on-PVDF-HFP
ZnO-/n-PVDF-HFP
Temperature (°C)
B.
Figure 2. DSC (A.) and TGA (B.) thermograms of the obtained fibers. The water contact angle values of the obtained nanofibrous materials based on PVDF are shown in
Figure 3. The average values of the water contact angle of PVDF and PVDF-HFP mats were 143±2.3° and 141±2.6°, respectively. The obtaining of novel fibrous mats of PVDF or PVDF-HFP and ZnO nanopraticles with design type "on" resulted in increase of the water contact angle values and in preparation of materials with superhydrophobic properties.
AAA
A. B. C.
Figure 3. Images of distilled water droplet onto mats of: A. PVDF, B. ZnO-in-PVDF and C. ZnO-
on-PVDF,
The antibacterial activity of all nanofibrous mats prepared in this study was tested against S. aureus in liquid medium. The log of the survival cells versus the exposure time for the nanofibrous mats was determined. It was found that the nanofibrous mats of PVDF and PVDF-HFP did not affect the bacterial growth. On the contrary, significant decrease of the number of viable cells was attained after contact of 2 hours with the mats decorated on their surface with ZnO particles (design type "on"). Moreover, all bacterial cells were killed after contact of 24 hours with the ZnO-on-PVDF and ZnO-on-PVDF-HFP mats.
Conclusion
Novel nanofibrous materials based on PVDF and PVDF-HFP decorated with ZnO nanoparticles were prepared. The obtained materials with design type "on" were obtained by using electrospinning and electrospraying techniques. It was found that the decoration of the mats with ZnO resulted in obtaining of materials with improved thermal properties. Moreover, ZnO-on-PVDF mats were superhydrophobic. Furthermore, the mats decorated with ZnO exhibit strong antibacterial activity against S. aureus which makes these fibrous materials suitable for potential application as wound dressing materials.
Acknowledgment.
Financial support from the Program for Career Development of Young Scientists, BAS (Grant DFNP-9/20.04.2016) is acknowledged.
References:
[1] Marmur A., Langmuir, 20, 3517-3519 (2004).
[2] Barthlott W., Neinhuis C., Planta, 202, 1-8 (1997).
[3] Neinhuis C., Barthlott W., Annals of Botany, 79, 667-677 (1997).
[4] Karim M. R., Islam M. S., Journal of Nanomaterials, 2011, 1-7 (2011).
[5] Lim H. S., Baek J. H., Park K., Shin H. S., Kim J., Cho J. H., Advanced Materials, 22, 21382141 (2010).
[6] Cho D., Zhou H., Cho Y., Audus D., Joo Y.L., Polymer, 51, 6005-6012 (2010).
[7] Laroche G., Marois Y., Guidoin R., King M., Martin L., How T., Douville Y., Journal of Biomedical Materials Research, 29, 1525-1536 (1995).
[8] Sirelkhatim A., Mahmud S., Seeni A., Kaus N., Ann L., Bakhori S., Hasan H., Hasan D., Mohamad D., Nano-Micro Letters, 7, 219 (2015).
[9] Spasova M., Manolova N., Markova N., Rashkov I., Applied Surface Science, 363, 363 (2016).
*e-mail: mgspasova@yahoo.com mspasova@polymer.bas.bg
