High
fluorescence emission silver nano particles coated with poly
(styrene-g-soybean oil) graft copolymers: Antibacterial activity and
polymerization kinetics
Baki Hazer
a,⁎
, Özlem A. Kalayc
ı
baBülent Ecevit University, Department of Chemistry, 67100 Zonguldak, Turkey b
Bülent Ecevit University, Department of Physics, 67100 Zonguldak, Turkey
a b s t r a c t
a r t i c l e i n f o
Article history: Received 5 May 2016
Received in revised form 17 November 2016 Accepted 4 December 2016
Available online 7 December 2016
Autoxidation of poly unsaturated fatty acids makes negative effect on foods. In this work, this negative effect was turned to a great advantage using autoxidized soybean oil as a macroperoxide nanocomposite initiator contain-ing silver nano particles in free radical polymerization of vinyl monomers. The synthesis of soybean oil macro peroxide was carried out by exposing soybean oil to air oxygen with the presence of silver nanoparticles (Ag NPs) at room temperature. Autoxidized soybean oil macroperoxide containing silver nanoparticles (Agsbox) suc-cessfully initiated the free radical polymerization of styrene in order to obtain Polystyrene (PS)-g-soybean oil graft copolymer containing Ag NPs. Both autoxidized soybean oil and PS-g-sbox with Ag NPs showed a surface plasmon resonance and highfluorescence emission. Overall rate constant (K) of styrene polymerization initiated by autoxidized soybean oil macroperoxide with Ag NPs was found to be K = 1.95.10−4Lmol−1s−1at 95 °C. An-tibacterial efficiency was observed in the PS-g-soybean oil graft copolymer film samples containing Ag NPs.1H
NMR and GPC techniques were used for the structural analysis of the fractionated polymeric oils.
© 2016 Elsevier B.V. All rights reserved.
Keywords: Soybean oil Autoxidation Ag nano particles Fluorescence emission Polymerization kinetics 1. Introduction
Polyunsaturated fatty acids (PUFA) and poly unsaturated tri glycer-ides (PUTG) are readily susceptible to autoxidation[1–8]. Soybean oil is one of the cheapest and most abundant annually renewable re-sources, and can be converted to polymeric peroxide under atmospheric conditions at room temperature via eco-friendly autoxidation. A chain oxidation is initiated by hydrogen abstraction from allylic or bis-allylic positions leading to formation of peroxyl radicals[9–14]. This peroxyl radical leads to formation of dimers, trimers and oligomers[15–17]. Be-cause of their peroxide groups, they can act as macroinitiators in order to obtain block/graft copolymers[18–22]. In this manner, oxidized poly-unsaturated triglycerides/fatty acids were used as macroperoxide initi-ator in the free radical polymerization of vinyl monomers[23,24]. Water soluble hydroxylated soybean oil polymer was also obtained by the re-action between oxidized soybean oil polymer and diethanol amine[25]. The graft/block copolymers based on polymeric triglyceride/fatty acids were successfully used in biotechnology applications such as
osteogenic activities[26], cell proliferation[27]and protein adsorption
[28]. Allı and Hazer reported the synthesis of thermo responsive conju-gates based on polymeric fatty acid peroxide, poly (N-isopropyl acryl amide)-g-poly (linoleic acid)/poly (linolenic acid) graft copolymers
[29].
In a recent work, the high catalyst efficiency of the gold nano parti-cles on the autoxidation of the double bonds was reported[30]. Stabili-zation of metal nano particles using natural products such as plant oils has also been very important in view of the environmental issue
[30–32]. Antibacterial activity of Ag NPs is well known. Because of this, silver nano particles can be introduced into polymer nano compos-ites for industrial and medical applications[33–37].
This work presents thefirst successful instance of eco-friendly oxi-dized polymeric soybean oil containing Ag NPs for the preparation of antibacterial materials. Because of the peroxide inclusion, the oxidized soybean oil with Ag macroperoxide initiator was used in the polymeri-zation of styrene in order to obtain polystyrene copolymer with Ag NPs (AgPSsb). Styrene polymerization with this soybean oil nanocomposite was successful in moving silver nanoparticles into the polystyrene-soybean oil graft copolymer. Polymerization kinetics, the antibacterial activity andfluorescence emission of the nanocomposites were studied.
⁎ Corresponding author.
E-mail address:bkhazer@beun.edu.tr(B. Hazer).
http://dx.doi.org/10.1016/j.msec.2016.12.010
0928-4931/© 2016 Elsevier B.V. All rights reserved.
Contents lists available atScienceDirect
Materials Science and Engineering C
The products obtained were also analyzed by size exclusion chroma-tography (SEC),1H NMR, TEM and energy dispersive X-ray spectroscopy (EDS).
2. Experimental 2.1. Materials
Soybean oil was provided by Çotanak/Altaş Yağ Su ve Tarım Ürünleri Gıda İnşaat Otomotiv Nakliyat San. ve Tic. AŞ Ordu Turkey. It contains palmitic acid (11.6 wt%), stearic acid (4.9 wt%), oleic acid (33.7 wt%), linoleic acid (42.0 wt%) and linolenic acid (3.63 wt%)[27]. AgNO3was supplied from Sigma-Aldrich.
2.2. Autoxidized polymeric soybean oil (Psbox)
Autoxidation of soybean oil was performed according to the modi-fied procedure reported in a recent work[30]. Briefly, 18 g of soybean oil was spreaded out into a Petri dish (Φ = 14.5 cm, oil thickness: 1.0 mm) was exposed to daylight in the air at room temperature. After a given time of autoxidation (ca. 1 month), a sticky, pale yellow viscous liquid polymer layer was formed.
2.3. Autoxidized polymeric soybean oil (Psbox) with Ag NPs (Agsbox) The same procedure of the autoxidation as without Ag NPs was ap-plied on the oil/fatty acids mixed with AgNO3. For example, 18 g of soy-bean oil was spreaded out into a Petri dish (Φ = 14.5 cm, oil thickness: 1.0 mm). 0.50 g of AgNO3was added into this oil and was occasionally mixed with a glass rod. The colorless oil layer exposed to the air turned into deep brown color in 3 to 4 weeks due to the formation of the silver nanoparticles[37]. In order to prepare a series of the mixture of soybean oil and the silver salt varying from 0.009 to 0.155 Molar AgNO3were spread out in glass Petri dishes (Φ = 14.5 cm) and exposed to air oxy-gen under daylight at room temperature. The oils spreaded were stirred occasionally with a glass rod. They were collected after 2 weeks and 4 weeks autoxidation in order to evaluate the catalyst effect of the Ag NPs.
2.4. Fractionation of the Psbox samples
Fractionation of the autoxidized soybean oil polymer with and with-out Ag NPs was performed by the modified procedure described in our recent study[30]. For example, the crude oxidized soybean oil polymer with Ag NPs (Agsbox) (40 g) was dissolved in 200 mL of CHCl3. Then, 800 mL of petroleum ether was added to this solution. After stirring for 2 h, it was kept in a refrigerator overnight. The upper solution phase was decanted, the precipitate (deep brown viscouse oil,first frac-tion of the Agsbox, Agsbox-I) was leached with petroleum ether and then resulting upper solution was decanted. The residue was mostly ob-tained as brown viscose liquid (or rarely black soft solid) was dried under vacuum at room temperature for 24 h (The residue is coded as Agsbox-I). The petroleum ether phases were combined, the solvent was then evaporated. The precipitate (brown viscose liquid) was dried under vacuum oven at room temperature for 24 h and coded as second fraction (Agsbox-II).
2.5. Copolymerization of Styrene with Agsbox
Polymerization of styrene was initiated by oxidized soybean oil polymer with Ag NPs according to the modified procedure described in the cited literature[30]. For a typical polymerization experiment, the mixture of 0.050 g of oxidized soybean oil polymer with Ag NPs and 4.52 g of styrene was dissolved in 5 mL of toluene in a reaction bot-tle. Argon was introduced through a needle into the tube for about 3 min to expel the air. The tightly capped bottle was then put into a
water bath at 95 °C for 6 h. Then, the contents of the tube were coagu-lated in methanol. The graft copolymer samples were dried overnight under vacuum at 30 °C. Polymerfilm (approximately 0.5 mm thickness) was casted from their chloroform solution (approximately 0.50 g of polymer sample in 15 mL Chloroform) in a Petri dish (Φ = 5.0 cm) covering with a piece of paper.
2.6. Determination of antibacterial efficiency
Escherichia coli (E. coli) IFO3972 was used in this study. The compo-sition of plate count agar growth medium was 0.5 (w/v) % peptone, 0.25 (w/v) % yeast extract, 0.1 (w/v) % glucose, 1.5 (w/v) % agar, and pH 7.0 at 25 °C.
We attempted to clarify the bacterial behavior of the polymers with a three-dimensional structure by the pour plate technique described in our previous study[38]. Briefly, casted polymer films (1.0 × 1.0 × 0.035 cm) were immersed in 10 mL of bacterial suspension and stirred for 2 min. Initial bacterial concentration was measured after 20 min at room temperature. Then samples were incubated at 37 °C for 24 h. Subsequently, the bacterial growth within the immersionfluid was analyzed after serial dilutions up to 1: 100,000. Therefore, 1 mL's of each dilution were added on agar plates (pour plate technique) and incubated for further 24 h at 37 °C. petri dishes were examined, devel-oped colonies between 15 and 250 are counted and the arithmetic aver-age of the colony numbers was taken. For the control step, bacteria suspension without polymerfilm was kept at the same conditions, and then diluted and examined.
LOG reduction¼ Log Beginning cfu=mL½ ð Þ−Log 24 h cfu=mLð Þ −Log reduction in bacteria control
ð1Þ
2.7. Instrumentation
Molecular weights were determined by size exclusion chromatogra-phy instrument, Viscotek GPCmax Auto sampler system, consisting of a pump, three ViscoGEL GPC columns (G2000H HR, G3000H HR and G4000H HR), and a Viscotek differential refractive index (RI) detector with a THFflow rate of 1.0 mL/min at 30 °C. A calibration curve was gen-erated with four polystyrene green standards: 2960, 50,400, and 696,500 Da, of low polydispersity. Data was analyzed using Viscotek Omni SEC Omnie 01 software.
Proton NMR spectra in CDCl3solutions of the samples were taken at a temperature of 25 °C with an Agilent NMR 600 MHz NMR (Agilent, Santa Clara, CA, USA) spectrometer equipped with a 3 mm broadband probe.
Fourier-transform infrared spectroscopy (FTIR) spectra were record-ed using a Perkin Elmer Pyris model FTIR spectrometer.
The toluene solution of Agsbox was dried on 200 mesh carbon coat-ed TEM grid (Electron Microscopy Sciences (CF200-Cu) (USA)) to use for analysis. A JEOL JEM-2100 (Japan) high resolution transmission elec-tron microscope (HRTEM) at 200 kV (LaB6filament) was used. Images were taken by Gatan Model 794 Slow Scan CCD Camera (USA). Low magnification TEM imaging technique was used. Gatan Digital Micro-graph software was used for noisefiltering and fast Fourier transforma-tion purposes.
UV–visible absorption spectra of the polymer solutions in toluene (0.100 g sample/5 mL of toluene) were recorded at room temperature using a Shimadzu 1700 Spectrometer with UV-quartz cuvettes (1 cm optical path) as the containers.
Thefluorescence emission spectra measurements of the polymer so-lutions in toluene (0.100 g sample/5 mL of toluene) were undertaken using Cary Eclipse model Fluorescence Spectrometer instrument under the 390-nm wavelength at room temperature.
Thermal analysis of the polymers obtained was carried out under ni-trogen using a TAQ2000 DSC and Q600 Simultaneous DSCTGA (SDT) se-ries thermal analysis systems. Differential Scanning Calorimeters (DSC) measures temperatures and heatflows associated with thermal transi-tions in the polymer samples obtained. The dried sample was heated from−60 to 190 °C under nitrogen atmosphere. Thermo Gravimetric Analysis (TGA) measures weight loss of the samples under nitrogen at-mosphere heating from 20 to 600 °C at a rate 10 °C/min.
3. Results and discussion
3.1. Synthesis of oxidized soybean oil polymer with Ag NPs
The mixture of soybean oil and solid AgNO3in an open glass contain-er was exposed to air oxygen at room tempcontain-erature in ordcontain-er to obtain oxidized soybean oil polymer with Ag NPs. The photos of soybean oil/ Ag nanocomposites in Petri dishes can be seen in SI-Fig. 1. During the autoxidation, radicals formed by the effect of day light and air oxygen reduced the silver cation to silver atom leading to silver nanoparticles
[34,37]. Reduction of AgNO3into soybean oil was carried out by daylight during the autoxidation process. The dissolution of Ag NPs needs dis-solved oxygen. In the presence of peroxides the oxygen-driven dissolu-tion of Ag NPs may be enhanced.
Scheme 1shows the reduction process of Ag+to Ag NPs into the soy-bean oil mixture during the autoxidation process.
3.2. Fractionated samples and molar masses
The fractionation was successfully used in the purification[39]and isolation of the higher molar mass of nanocomposite from the crude autoxidized soybean oil nanocomposite as reported in Psbox with or without Au NPs[30]. The autoxidized soybean oil polymer with Ag NPs was fractionated using solvent/non-solvent mixture (chloroform/ petroleum ether) into two fractions with yield 7–57 wt% for the first fraction and 43–93 wt% for the second fraction.
Molar masses of the fractions were measured by using size exclusion chromatography. Multimodal GPC chromatograms in the fractions of nanocomposites were analyzed for each individual curve. Thefirst frac-tions contained a higher molar mass oligomer, ranging between 22 kDa to 31 kDa of Psbox/Ag NPs, while medium molar mass ranged from 4.8 kDa to 6.1 kDa (SI-Fig. 2 andTable 1). For example, the higher molar mass sample, 15Agsb0.52 (inTable 1) was fractionated in two fractions: thefirst fraction contained the highest molar mass of Psbox
presumably comes from the autoxidation of linolenic/linoleic inclusion of the triglyceride while linoleic/oleic acids inclusion leads to medium molar mass of nanocomposite. There are Psbox samples with medium molar mass presumably obtained from linoleic and oleic acid inclusions in both fractions. The Psbox samples withb0.9 kDa molar mass are probably saturated non-polymerized moieties. The Psbox samples
Scheme 1. Reduction of AgNO3to Ag NPs by daylight during the autoxidation process.
Table 1
Molar masses of thefirst and second fractions of the polymeric soybean oil/Ag nanocom-posites. (n.d. means not determined). (Soybean oil: 920 g/mol, d = 0.917 g/mL; AgNO3:
170 g/mol). (Yield, wt% means percent of the ratio of the fractionated soybean oil polymer with Ag NPs to feeding substrates: soybean oil and AgNO3).
Code AgNO3
in Sboil Ox. time
I. Fraction II. Fraction
Yield Mw × 10−3/PDI Yield Mw × 10−3/PDI
(mol/L) (day) (wt%) (Da) (wt%) (Da) 15Agsb0.52 0.153 15 14 22.4/1.1 86 n.d. 4.8/1.4 2.9/1.2 0.8/1.1 0.6/1.1 15Agsb0.28 0.082 15 16 22.7/1.1 84 n.d. 4.9/1.4 3.4/1.2 7.8/1.1 0.8/1.1 15Agsb0.18 0.053 15 19 22.2/1.1 81 n.d. 4.9/1.4 2.6/1.3 7.5/1.1 0.4/1.1 15Agsb.063 0.018 15 26 26.4/1.1 74 n.d. 5.5/1.4 2.8/1.3 0.8/1.1 0.5/1.1 15Agsb.031 0.009 15 7 26.9/1.1 93 n.d. 5.6/1.4 3.1/1.3 0.9/1.1 0.5/1.1 20Agsb0.53 0.155 20 57 27.3/1.2 43 n.d. 5.1/1.5 4.7/1.5 0.6/1.2 0.7/1.1 26Agsb0.52 0.153 26 35 24.7/1.1 65 n.d. 5.1/1.4 3.8/1.4 0.9/1.1 0.7/1.1 26Agsb0.28 0.082 26 28 28.1/1.1 62 19.3/1.1 5.8/1.4 4.1/1.4 0.9/1.1 0.7/1.1 26Agsb0.18 0.053 26 19 31.0/1.2 81 21.0/1.1 6.0/1.4 2.6/1.3 0.9/1.2 0.4/1.1 26Ag.063 0.018 26 44 30.5/1.1 56 20.6/1.1 6.1/1.4 2.8/1.3 0.9/1.2 0.5/1.1 26Ag.031 0.009 26 50 26.8/1.1 50 n.d. 6.1/1.4 3.7/1.2 0.9/1.1 0.9/1.1
with medium and low molar mass are present in both fractions while the Psbox samples with the highest molar mass are present only in thefirst fraction. As shown in our recent article[30], catalyst effect of the gold nano particles was immediately observed after ten days autox-idation. To understand catalyst effect of the Ag NPs on the autoxidation, the same amount of soybean oil and soybean oil mixture with AgNO3 were eco-friendly autoxidized regarding to autoxidation of soybean oil depends on the oxidation time and feeding oil thickness[25]. We ob-served that autoxidation of soybean oil with Ag nanoparticles did not cause an increase in molar mass of oxidized soybean oil polymer when compared to the molar mass of the oxidized soybean oil alone
[25]. We can say that the Ag NPs did not show any catalyst effect in the autoxidation by means of increase of molar mass while Au NPs cause high increase in molar mass.
3.3. Polymerization of styrene initiated by Agsbox macroperoxide initiator The autoxidized soybean oil polymer, macroperoxide initiator, was used in the free radical polymerization of styrene in toluene solution at 95 °C for 6 h. Free radical polymerization initiated by a peroxide ini-tiator is usually carried out at 80 °C[14]. However, in order to obtain high polymer yield, the copolymerization was carried out at higher tem-perature. Poly (styrene-g-soybean oil) graft copolymers were obtained by the copolymerization of styrene with soybean oil macroperoxide initiator.
3.4. The concentration of macroperoxide versus both monomer conversion and molar mass of the copolymer
Three different types of polymerization were carried out in order to evaluate free radical polymerization of styrene; (i) initiated by pure Psbox without Ag NPs, (ii) initiated by Agsbox macroperoxide initiator, and (iii) thermal polymerization of styrene without any initiator.
In the first scenario, a series of the mixture of styrene and macroperoxide in a range of 0.35–15 wt% were polymerized in toluene solution. The polymerization conditions and results are presented in SI-Table 1. The polymer yield varied between 6 and 25 wt% with the molar mass in a range of 33,674–144,339. GPC traces can be seen in SI-Figs.s 3, 4 and 5.
Fig. 1shows the variation in the conversion and the molar mass as a function of the macroperoxide concentration. An increase in macroperoxide concentration causes increase in monomer conversion but decrease in molar mass of the copolymer obtained as expected in a free radical polymerization system.
3.5. The effect of the polymerization time on the conversion and the molar mass of the copolymer
In the second scenario, the effect of the polymerization time on the conversion and the molar mass of the copolymer obtained was studied. The polymerization conditions and results were presented in SI-Table 2. As polymerization time increases, the monomer conversion increases but the molar mass of the copolymer obtained remains unchanged. The variation of conversion and the molar mass as a function of the po-lymerization time is shown inFig. 2.
3.6. The Effect of molar concentration of Ag NPs on the conversion and the molar mass of the copolymer
In the third scenario, the polymerization of styrene initiated by the macroperoxide initiators with different concentration of Ag NPs was carried out. The effect of the variation of the molar concentration of the Ag NPs on the conversion was studied. The effect of Ag NPs molar concentration on the conversion and the molar mass of the copolymer is shown inFig. 3. The polymerization conditions and results are summarized in SI-Table 3. As the concentration of Ag NPs in-creases in the soybean oil macroperoxide initiator, the monomer conversion decreases and the molar mass of the copolymer also decreases slightly from 39,823 to 34,755 Da. One can say that increase of Ag NPs concentration in the soybean oil macroperoxide causes a chain transfer and slightly decreases the copolymer yield and the molar mass.
In order to make a comparison, the polymerization of styrene initiat-ed by Psbox obtaininitiat-ed by the same autoxidation conditions without Ag NPs was undertaken. The results are given in SI-Table 4. In addition to this, styrene polymerization using Psb-523-II with different time of po-lymerization time was also done. SI-Table 5 contains the popo-lymerization conditions and the results used in the calculation of the overall rate con-stant from the line drawn inFig. 4indicated the variation of monomer conversion and copolymer molar mass versus initiator concentration. Both polymerizations initiated by Agsbox and Psbox show the same re-sults in terms of polymerization kinetics. In this manner, copolymer molar mass increases but the monomer conversion decreases as initia-tor Psb523-II (without Ag NPs) concentration increases. Furthermore, we will discuss in the next section to calculate the overall rate constants calculated from the polymerization results obtained by the macroperoxide initiator obtained with Ag NPs and without Ag NPs (Psb523-II).
Fig. 1. The variation of the feeding concentration of macroperoxide (26Agsb0.52/0.153 M AgNPs) versus both monomer conversion and molar mass of the copolymer.
Fig. 2. The variation of monomer conversion and the molar mass of copolymer obtained as a function of polymerization time in the styrene polymerization initiated by the macroperoxide (26Agsb0.52/0.153 M Ag NPs).
3.7. Polymerization kinetics, overall rate constant (K)
Autoxidized soybean oil macroperoxide with or without Ag NPs was utilized as an initiator for the radical polymerizations of styrene. At low conversions of monomer (less than about 15%) it can safely be assumed that the concentrations of monomer and initiator remain constant throughout the polymerization, such that [M] = [M]0and [I] = [I]0. In this case, Eq.(1)can be rewritten as
Rp¼ −Δ M½ Δt ¼ kp½ o I½oM 1=2 kdf kt 1=2 ð2Þ The rate of polymerization, Rp, is given by
Rp¼ K2
M ½ 2
I
½ ð3Þ
where K is the overall rate constant, [M] and [I] are the monomer and soybean oil macroperoxide initiator concentrations, respectively.Fig. 5
shows the variation of the Rp2vs [M]2[I] for styrene polymerization ini-tiated by the macroperoxides with Ag NPs (Agsb-0.52, circle dots) and by the macroperoxides without Ag NPs (the Psbox-523, square dots). The overall rate constant was estimated the same as K = 1.95 × 10−4 for both macroinitiators at 95 °C from the slope of the lines obtained from Eq.3.
Interestingly, silver nanoparticles are not efficient in the free radical polymerization. This value is quite lower than that of benzoyl peroxide in styrene polymerization, K = 3.31 × 10−4at 80 °C[21].
3.8. Thermal polymerization of styrene at 95 °C alone
The polymerization of styrene was carried out byself in toluene solu-tion at 95 °C in order to evaluate the homopolystyrene formasolu-tion during the styrene copolymerization initiated by soybean oil macroperoxide initiator. This applied temperature produces thermally homo-polystyrene together with homo-polystyrene-soybean oil copolymer. There-fore, a series of the thermal polymerization of styrene with varied time of polymerization was conducted. Results and conditions are listed in SI-Table 6. Homopolymer formation was lower than 3 wt% for the first 3 h. It reaches to 9 wt% of monomer conversion after 7 h of poly-merization while the polypoly-merization with macroperoxide initiator reaches to 27 wt% of conversion. For comparison, the results are plotted inFig. 6. Because of high molar mass of PS formation thermally, the GPC chromatograms of PS-g-Soybean oil copolymers were all bimodal. This higher molar mass of polystyrene may result from the thermal
Fig. 3. Polymerization of styrene initiated by the 10.4 wt% of Agsbox with different Ag NPs: (a) 26Agsb0.031/0.92 M Ag NPs, (b) 26Agsb0.063/1.82 M Ag NPs, (c) 26Agsb0.18/5.80 M Ag NPs, (d) 26Agsb0.28/8.81 M Ag NPs, (e) 26Agsb0.52/16.4 M Ag NPs.
Fig. 4. The variation of monomer (styrene) conversion and copolymer molar mass versus initiator Psb523-II (without Ag NPs) concentration.
Fig. 5. Variation of the Rp2
vs [M]2
[I] for styrene polymerization initiated by the Agsb-0.52 (circle dots) and initiated by the Psbox-523 (square dots). The overall rate constant for the macro peroxide initiators with and without Ag NPs is the same as K = 1.95 × 10−4.
Fig. 6. Conversion versus time dependence for styrene polymerization initiated by Psb523-II (circle dots) and thermal polymerization (square dots) in toluene at 95 °C.
polymerization of styrene that acts positively on the graft copolymer in terms of plasticizer effect[40–42].
3.9. Characterization of the products
After purification of soybean oil macro peroxide with or without Ag NPs via the fractionation[30,39], structural characterization of the prod-ucts was carried out using NMR and FT-IR techniques.1H NMR spectra of the soybean oil macroperoxide and its styrene copolymer showed the characteristic signals.1H NMR spectra of Agsb0.28–1.fr, Agsb0.28-II.fr, PSsb523-1.06, and AgPSsb0.52 are seen inFig. 7. Characteristic sig-nals of oxidized soybean oil polymer in the1H NMR spectra are mostly the same as in commercial epoxidized soybean oil[42,43].
FT-IR was only used for the confirmation of the chemical structure of the PS-g-AgPsbox copolymer with characteristic signals of phenyl ring of PS blocks at 1602 cm−1and carbonyl group of Psbox blocks at 1748 cm−1. These characteristic signals can be seen in SI-Fig. 6.
3.10. Characterization of the Ag NPs in the nanocomposite samples 3.10.1. Surface plasmon resonance
A typical primary characteristic of metal/organic nanoparticles is surface plasmon resonance (spr). This simple phenomenon is widely used to determine the position and half-wide of the plasmon-related absorption peak. The UV-VIS absorption spectra of the toluene solutions of the nanocomposites were taken in order to see their spr properties. The soybean oil polymer with Ag NPs and its polystyrene conjugate showed spr, too. The spr of the solutions of Agsbox and AgPSsb in tolu-ene was observed asλmax= 417–451 nm and 419–448 nm, respective-ly while there is not any absorption of the higher region from 380 nm for starting materials, oxidized soybean oil polymer and pure-polystyrene (the spectra were not provided). UV–vis absorption absorption spectra of the soybean oil nanocomposites can be seen in supporting informa-tion in SI-Fig. 7 (a) (b).λmaxvalues of the absorbed light of the nano-composite samples were also listed inTable 2.
3.10.2. Fluorescence emission
Highfluorescence emission was observed in both oxidized soybean oil polymer with Ag NPs and PS-g-Psbox with Ag NPs. Thefluorescence emission from polymer-metal nanocomposites comprising poly (silylene-co-silyne)s and silver nanoparticles was also reported previous-ly[36]. Photos of the highfluorescence emission of the soybean oil nano-composite samples are given inFig. 8. Intensive bright green color of the nanocomposite samples under UV illumination is observed while there
is brown color of the samples under daylight. Fluorescence emission spec-tra of the nanocomposite samples and pristine materials in toluene solu-tions were measured using spectrometer with 380 nm excitation wavelength. Fluorescence emission spectra of the PS-g-soybean oil copol-ymers with Ag, the soybean oil macroperoxides with Ag, and starting ma-terials can be seen in SI-Fig. 8 in supporting information. We observed the maximum intensities (λmax) lower than 435 nm for pure-PS and lower than 460 nm for oxidized soybean oil polymer which have close
Fig. 8. Photographs offluorescent Psbox-Ag nanocomposites; (a) toluene solution of 26Agsb0.52 under daylight, (a’) toluene solution of 26Agsb0.52 under UV-light, (b) toluene solution of AgPSsb0.52 under daylight, (b’) toluene solution of AgPSsb0.52 under UV-light, (c) AgPSsb0.52 film under daylight, (c’) AgPSsb0.52 film under UV-light.
Table 2
Results of the surface plasmon resonance andfluorescence emission of the nanocomposites containing Ag NPs.
Sample Abs. ðIntensity;λ;maxÞ
ðλexc¼380 nmÞ Agsb 0.031 428 410 450 Agsb 0.063 440 400 475 Agsb 0.18 460 515 430 505 Agsb 0.28 460 515 425 485 548 Agsb 0.52 430 510 525 PSsbAg0.031 415 440 PSsbAg0.063 425 410 450 PSsbAg0.18 422 507 PSsbAg0.28 422 490 PSsbAg0.52 425 515 Pure-PS N380 410, 425, 435 Psbox523 N380 460
agreement with the literature[44,45]. Efficiency of the silver nanoparti-cles can be seen clearly in SI-Fig. 8. Fluorescence spectra of the silver nano-composites were observed intensity of emitted light in the higher region of those of the related precursors.λmaxvalues of the emitted light of the nanocomposite samples were also listed inTable 2. Preliminary results show that higher concentration of Ag NPs leads to the red-shift of maxi-mum wavelength position, while lower concentration causes light emit-ting with lowerλmax.
3.10.3. TEM micrographs with EDS analysis
The presence of Ag NPs in oxidized soybean oil polymer was also proved by TEM technique. TEM micrographs of the soybean oil polymer (Psbox) with Ag NPs and PS-g-Psbox with Ag NPs were taken. Amount of Ag NPs in the PS-g-Psbox copolymer matrix was observed to be less than those of the precursor. TEM images of the nanocomposites with the x-ray analysis spectra (EDS) confirming the presence of silver are given inFig. 9. The TEM images of Psbox showed a bunch of grapes of Ag NPs in size approximately 5 nm while Ag NPs in PS-g-Psbox nanocom-posite were slightly larger than 15 nm and have the spherical shapes. This larger size of the Ag NPs presumably results from some aggregation in the copolymer matrix.
3.11. Thermal analysis 3.11.1. i. Agsbox samples
Thermal analysis provides definite evidence on peroxygen groups of the oxidized soybean oil polymers. Peroxide decomposition of the
Agsbox-1st and -2nd fractions was observed in both DSC and TGA traces. The maximum decomposition temperatures of Agsbox-1st frac-tion were observed between 133 and 139 °C and in the 149–156 °C tem-perature range in the case of second fraction. The same decomposition temperatures of the peroxide groups were reported in the cited refer-ence[46]. DSC traces of Agsbox samples can be seen inFig. 10. Interest-ingly, lower peroxide decomposition temperatures were observed in thefirst fractions of the oxidized soybean oil polymer samples than in the case of the second fractions. This may be related to the peroxide content in the samples and may be explained analysis of thermogravi-metric analysis. For example,first fraction of the Agsb0.53 showed 5.7 wt% weight loss due to peroxide decomposition, while the second fraction showed the one-half of this value (Fig. 11-d and e.). The decom-position areas of Agsbox samples are underlined on the TGA curves by circle.
3.11.2. ii. AgPSsb samples
TGA and DSC curves of the polystyrene copolymers do not show per-oxide decomposition because peroxide groups of Agsbox macroperoxide initiators were already cleaved during the thermal-initiated polymerization of styrene.
Fig. 11also shows TGA curves of AgPSsb samples. The decomposition temperatures of polystyrene and oxidized soybean oil polymer overlaps at around 420 °C. InFig. 12, lower Tg's of AgPSsb copolymers than those of homo-PS can be seen. These results can be attributed to the plasti-cized affect of the plant oil[38,47]. DSC curves of PSsb copolymers with or without Ag NPs also showed the same behavior as shown in
Fig. 12. The decomposition temperatures of peroxide groups in the sam-ples obtained are also listed in SI-Tables 7 and 8.
3.12. Antibacterial effect of AgPSsb copolymer
The antibacterial effect of Ag NPs is very well known. The silver nanoparticles inclusion in oxidized soybean oil polymer was also moved into the PSsb copolymer after styrene monomer is polymerized by the oxidized soybean oil polymer with Ag NPs. The Ag NPs inclusion in the copolymer was confirmed by surface plasmon resonance, fluores-cence emission and TEM analysis. The polystyrene copolymer with Ag NPs shows the strong antibacterial effect against E. coli. These results are tabulated inTable 3. AgPSsb0.52-1 and AgPSsb0.52-2 show strong antibacterial effect while bacterium proliferation was observed on the glass plate with homo-PS and PSsb copolymer without AgNPs. Antibac-terial activity of Ag NPs depends on the concentration of Ag NPs in the
Fig. 10. DSC thermograms of the Agsbox fractions: (a) 26Agsb-0.18-2, (b) 26Agsb-0.28-2, (c) 26Agsb-0.031-2, (d) 26Agsb-0.18-1, (e) 26Agsb-0.28-1, (f) 26Agsb-0.031-1, (g) 26Agsb-0.52-1, (h) 26Agsb-0.52-2, (i) 26Agsb-0.063-2.
Fig. 11. TGA traces of the oxidized soy bean oil with Ag NPs: (a) Agsb0.031, (b) Agsb0.18, (c) Agsb0.28, (d) Agsb0.53-1.fr, (e) Agsb0.53-2.fr, (f) PSsb523-0.515, (g) PSsb523-1.78, (h) AgPSsb-0.657, (i) AgPSsb-0.050.
Fig. 12. DSC thermograms (2nd runs) of AgPSsb copolymer samples: (a) AgPSsb0.52-1, (b) AgPSsb0.52-2, (c) AgPSsb-1, (d) PSsb523-1, (e) PSsb523-2, (f) PSsb523-3.
nano composite. Therefore, antibacterial efficiency increases with concentration of Ag NPs[48]. Comparison of AgPSsb0.52-1 and -2 (Run nos. 3 and 4 inTable 3) indicates that AgPSsb0.52-2 showed higher antibacterial efficiency because it contains higher concentration of Ag NPs than that of AgPSsb0.52-1. Inoculated bacteria plates are shown in SI-Fig. 9. The strong antibacterial effect after 24 h growing of the plates containing AgPSsb copolymer samples can also be seen in SI-Fig. 9 (i) and (j). The LOG reduction (logarithmic value of live microbes eliminated from a surface by cleaning) was calculated using Eq.(1). The results were listed inTable 3where inserted into the text.
is a mathematical term used to show the relative number 4. Conclusion
Vegetable oils as materials obtained from renewable resources gain great importance to synthesize chemicals and biomaterials. Soybean oil is particularly prone to react with molecular oxygen. This autoxida-tion process does not require extra energy, and moreover the system is mild, renewable, cheap and fully eco-friendly. The mixture of soybean oil and AgNO3 was autoxidized in order to obtain a novel macroperoxide initiator containing Ag NPs for free radical polymeriza-tion of vinyl monomers leading to olefin copolymer nanocomposite, de-spite the autoxidation of poly unsaturated fatty acids impacts foods negatively, causing bad smell and taste, also influencing the appearance of food. In this work, this negative effect of autoxidation was turned to an advantage by using autoxidized soybean oil as a macroperoxide ini-tiator in the synthesis of graft copolymer/silver nanocomposite. Stabili-zation of metal nano particles using soybean oil has been very important in view of the environmental issue.
The soybean oil macroperoxide with Ag nanocomposite was suc-cessfully applied for introduction of used silver nanoparticles into olefin polymers. The highfluorescence emission of the nanocomposites ob-tained in this work can be used for preparation of promising biomaterial for imaging of the specific targets. In addition, the high antibacterial ef-ficiency of the nanocomposites makes them promising materials in paint industry in order to prevent bacterial contamination.
Supporting information
Further experimental images and analysis results are available in the Supporting Information.
Acknowledgments
This work was supported by the Bülent Ecevit University Research Fund (#BEU-2015-72118496-12 and BEU-2015-72118496-02). Kind thanks to Professor R. Haverkamp for his very valuable discussion. The Author would also like to thank to C. Kodolbaş and Dr. D. B. Hazer for
the antibacterial analysis and discussion; Dr. Ö. Duygulu for TEM analy-sis, Dr. H. Canbay for thermal analysis and T. Şanal for GPC measurements.
Appendix A. Supplementary data
Supplementary data to this article can be found online athttp://dx. doi.org/10.1016/j.msec.2016.12.010.
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