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polycaprolactone composites prepared by miniemulsion polymerization
Journal of Physics and Chemistry of Solids 119 (2018) 56–61
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Journal of Physics and Chemistry of Solids journal homepage: www.elsevier.com/locate/jpcs
Dielectric study of polystyrene/polycaprolactone composites prepared by miniemulsion polymerization
T
Saber Ibrahima, Mona Abdel Rehima, Gamal Turkyb,∗ a b
Packaging Materials Department, National Research Centre, Elbehoth Street 33, 12622, Dokki, Cairo, Egypt Microwave Physics and Dielectrics Department, National Research Centre, Elbehoth Street 33, 12622, Dokki, Cairo, Egypt
A R T I C LE I N FO
A B S T R A C T
Keywords: Polymer composite Mini-emulsion Dielectric properties Packaging
Composite of polystyrene (PS) and a biodegradable polymer, polycaprolactone (PCL), has been prepared by miniemulsion polymerization technique. In the procedures, different amounts of commercial PCL were added during polymerization of PS in presence of sodium lauryl sulfate (SLS) as a surfactant. Formation of PS and PS/ PCL nanoparticles was confirmed by Transmission Electron Microscope (TEM) and their structure was investigated using Fourier Transform Infra-Red (FTIR)and UV spectrometry. Encapsulation of PCL particles yielded nanoparticles of gradual enlargement in size as revealed by zeta sizer. However, significant information about the molecular dynamics within the composite and charge mobility can be realized by Broadband dielectric spectroscopy (BDS). So that, BDShas been employed to investigate the electrical and dielectric behavior of the considered composites over a wide range of frequency and temperature. It was found that the dielectric properties of the composites seem to be mainly due to the PS shell with no significant effect for presence of PCL in the core. The linear decrease of the real part of conductivity of the prepared blends with decreasing frequency just like the perfect insulator confirmed the encapsulation feature of the structure. The new materials can find applications in packaging, household beside biomedical fields.
1. Introduction
biodegradable polymer has been thoroughly investigated by Biresaw et al. [7–9] Extensive study of the compatibility of the polymers in the blends using model biopolymers was performed. The study covered various properties such as interfacial tension, interfacial adhesion and tensile properties [10]. Mohamed et al. applied Fourier transform infrared photo-acoustic spectroscopy (FTIR-PAS) in order to confirm the presence of molecular interaction between PS and PCL in their blends [11]. Increasing dispersion of PCL and PS homo-polymers within one another in their blends could be achieved through addition of polystyrene–polycaprolactone diblock copolymer. The prepared blends showed improved flow and thermal characteristics in the range between the individual polymer components [12]. Miniemulsion polymerization is special type of emulsion polymerization technique in which a co-stabilizer is used and a shear is applied in order to obtain polymer particles in the range of 50–100 nm [13]. Another task for the co-stabilizer is to reduce the diffusional degradation rate of water/ monomer emulsion along with reduction of monomer droplet size [14]. Synthesis of polystyrene of 50 nm particle size by miniemulsion technique has been reported. Reduction of interfacial tension and increase of colloidal stability of the nanoparticles of prepared PS can be attained by using higher levels of surfactants [15]. Zhang et al. described a
Polymer composites received much attention due to their versatile properties and applications. Preparation of the polymer composites can be carried out either by blending block technique or in situ formation of components. The advantage of the former method is that the used blending blocks have well-defined chemical structure and they do not undergo chemical change under processing conditions. Moreover, designed blending blocks and structure-property manipulation can be attained. On the other hand, the later technique for composite preparation is based upon the chemical transformation of at least one precursor during material preparation. Polystyrene is a general-purpose synthetic polymer due to its hardness, clearness and low cost per unit weight. It finds many applications as protective packaging, containers and bottles. It is also characterized by its low gas barrier properties and low biodegradability. On the other hand, biodegradable polymers are characterized by their water resistance and being in the same time biodegradable [1,2]. Therefore, developed products can be obtained through compositing synthetic and biodegradable polymers in the fields of materials and packaging applications [3–6]. Blending of PS with PCLas a
∗
Corresponding author. E-mail address: [email protected] (G. Turky).
https://doi.org/10.1016/j.jpcs.2018.03.030 Received 8 January 2018; Received in revised form 14 February 2018; Accepted 20 March 2018 Available online 23 March 2018 0022-3697/ © 2018 Elsevier Ltd. All rights reserved.
Journal of Physics and Chemistry of Solids 119 (2018) 56–61
S. Ibrahim et al.
coated copper grid (S160-3 Plano GmbH) and investigated using JEOL 200 TEM (Carl Zeiss NTS) operated at 120 kV/200 kV. Zero-loss energy filtering was used to increase the image contrast. Thermal gravimetric analysis was carried out using a Perkin Elmer thermogravimetric analyzer (TGA), with a heating rate of 10 °C/min in nitrogen atmosphere with flow rate100 mL/min and temperature range from 30 °C up to 600 °C. The dielectric measurements were performed between 0.1 Hz and 10 MHz using a Novocontrol high-resolution alpha analyzer. A Quatro temperature controller using pure nitrogen as heating agent and assuring temperature stability better than 0.2 K. assisted the analyzer. The investigated samples with thicknesses 1–2 mm were sandwiched between freshly polished brass electrodes with a top electrode diameter of 10 mm to form a parallel-plate capacitor cell. The complex permittivity (ε* = ε′ - iε″) was measured using a sinusoidal voltage with amplitude 0.1 V over a 10−2 −107 Hz frequency range in all experiments. Data were collected in isothermal frequency sweeps every 10 °C, from −50 to 120 °C.
method for preparation of polystyrene without co-stabilizer [16]. A fluorinated block copolymer prepared by ATRP and dodecafluoroheptyl methacrylate was used as the sole co-stabilizer in St miniemulsion instead of the conventional co-stabilizers. Better surface hydrophobicity was observed for the final latex. Encapsulation of nanoparticles in polymer matrix using miniemulsion polymerization technique was investigated extensively [14,17–19]. Polystyrene encapsulated nanosaponite composite suspension via miniemulsion polymerization has been reported [20]. Clay particle size and premodification of its surface were found to be crucial in order to produce stable latex suspension. Composite of silver nanoparticles encapsulated in polystyrene matrix been prepared [21,22]. The formed composite showed good antibacterial properties against Escherichia coli and Staphylococcus aureus. The electrical and dielectric investigations of polymer composites attracted significant attention due to both basic and application fields. This is according to the fact that the prepared composite has its own characteristics, which is usually distinguishable from that of its individual components individual. Two factors play the main role in that context: the loaded ratio and the expected interaction between the components. Broadband dielectric spectroscopy (BDS) has become a powerful tool for investigations of the frequency and temperature dependence of different electrical and dielectric properties of the polymers and their composites [23–26]. Its broad range of frequency [10−6 - 1012] is the main advantage over all other spectroscopy techniques since it covers all molecular dynamics, charge transportations as well as space charge or interfacial polarizations. This work deals with encapsulated polycaprolactone, as a biodegradable polymer, in polystyrene latex as a novel way to prepare biocomposite of synthetic and biodegradable polymers. Characterization of the obtained nanocapsules has been performed and detailed study of electrical and dielectric properties of the synthesized composite has been demonstrated. In this context, the dielectric properties of the prepared composites will give valuable information about the structure and influence of polycaprolactone on the electrical and dielectric properties of the host polymer.
2.3. Synthesis of composites
2. Experimental
In round bottom flask, a specified amount of styrene monomer/PCL with different ratios (PCL 5, 10, 15 and 20 wt.%) and 0.037 mol of nonpolar solvent (hexadecane, HD) were mixed and added to a solution containing 0.02 g sodium lauryl sulfate (SLS) in 73.28 g of water. The mixture was degassed (vac/N2, followed by stirring for 20 min under N2 at 300 min−1) and then stirred for 50 min at 500 rpm. After that, miniemulsion droplets were prepared by ultra-sonication for 7 min. A slight stream of nitrogen was applied, and the emulsion was cooled with ice water. The formed mini-emulsion was transferred to the reaction vessel. After short degassing, the temperature was raised to 75 °C. Then, an aqueous solution of initiator was added (330 mg of APS in 7.1 g of water degassed under N2 for 20 min). The reaction was performed at 600 rpm for 5 h. The reaction vessel was immersed in an ice bath to decrease the temperature until room temperature. The dispersion was precipitated in 300 mL of MeOH (1 wt% HQ), and the precipitation was done by dropwise addition. Polystyrene/polycaprolactone was filtrated and dried in a vacuum oven overnight.
2.1. Materials
3. Results and discussion
Styrene, Sigma-Aldrich, was purified before being used. Polycaprolactone (PCL) Mwt = 80000 g/mol, ammonium peroxide sulfate (APS), sodium bicarbonate, hexadecane (HD), hydroquinone (HQ), and sodium lauryl sulfate (SLS) were obtained from SigmaAldrich and were used as received.
Preparation of PS/PCL composite has been carried out using miniemulsion polymerization technique in order to increase miscibility and homogeneity of the newly formed composite. Different ratios of PCL (5–20% by weight) were added during polymerization of styrene. It is assumed that PCL particles are encapsulated within the PS during its formation (Scheme 1). This assumption has been confirmed by TEM images (Fig. 1). Fig. 1a, reveals that the prepared PS particles are in the range of 18–33 nm. On the other hand, addition of 15% PCL led to enlargement of the obtained particles by nearly 10 folds. These large particles confirm the encapsulation of PCL particles in form of a core and a PS shell is formed around them. The particle mean size and distribution for the formed PS/PCL composite have been measured by zeta sizer. The results are depicted in Fig. 2, which show that the particle size of pure PS is in the range of 55 nm. By increasing added amount of PCL, the mean size and size distribution is not significantly modified for PCL content lower than 10%. Increasing the amount of PCL to 15–20 wt% leads to a significant increase in the mean size of the formed particles. However, no difference in the particle mean size and size distribution was evidenced by increasing the PCL content from 15 to 20%. Molecular weight determination in the form of Mn, Mw and PDI of the pure PS and its composite with PCL, was carried out using GPC connected with a refractive index detector (RID). The values gathered in Table 1 showed that the highest molar mass was obtained for sample PS/PCL 20% while the lowest was for sample PS/PCL 10% which also
2.2. Methods The mini-emulsion droplets were prepared by ultrasonication for 7 min (90% amplitude) with an ultrasonic disintegrator (Qsonic 450 W). Particle size distribution of the prepared PS and PS/PCL were measured by zeta sizer (Nano ZS, zeta sizer, Malvern, UK) based on the dynamic light scattering technique. The functional groups in the polymer composites backbones were identified and recorded using Perkin Elmer Fourier transform infrared spectroscopy (FTIR)with range of measurements of 600–4000 cm−1. Electronic absorption of the samples is investigated by UV absorbance measured by Jasco spectrometer V-630. Constant weights of the samples (10 mg/3 mL) were dissolved in THF and measured in quartz cuvette. The molecular weights of the prepared polystyrene and composites were determined using GPC Agilent model 1515 pump system equipped with 1260 infinity refractive index detector. THF was used as eluent operating with a flow rate of 1.00 mL/min and polystyrene was a standard. Investigation of structures of the prepared PS/PCL nanocomposites was carried out using transmission electron microscope (TEM). The samples were prepared by dropping a solution of the composite on a carbon57
Journal of Physics and Chemistry of Solids 119 (2018) 56–61
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Scheme 1. Representation of encapsulation process of PCL by PS during miniemulsion polymerization.
has PDI value of 6.78. It is known that the refractive index detector separates the polymer molecules according their size. However, this detector provides uncertain data when the polymer molecules vary in composition and size such as in case of copolymers and blends [27]. In our case, the composition of the molecules are varied with their sizes which led to different response from the RID reflecting both composition and size. Nevertheless, sample PS/PCL 5% has high molar mass (Mn = 1.03 × 105 g/mol) with lowest PDI value. This can be explained by presence of PCL in low ratio did not interfere or hinder the stabilized emulsion, so that long PS chains are formed with lowest polydispersity. Chemical structures of pure PS and its interaction with PCLwere confirmed by FTIR spectroscopy. The obtained spectra in Fig. 3 depict the absorption bands of PS particles and the inset represent the overlaid absorption bands of pure PS, PS loaded with 5 and 20% PCL, respectively. The spectrum of PS shows absorption band at 32003500 cm−1which is due to OH from water and a band at 3026 cm−1 for the aromatic CH-vibration. Absorption bands at 2921 cm−1are assigned for aliphatic C-H bond. Aromatic C-H combination frequency overtones can be found in the range of 1740–2000 cm−1. Bands at 14751620 cm−1 represent aromatic C-C bond stretching vibration. The inset spectra reveal that: i) Since PS has no significant band at carbonyl region and the observed small peak is related to one of the overtones for aromatic groups in PS. However, the decrease in the fundamental band of carbonyl group of PCL is due to its overlap with one of the overtone bands, an interaction known as “Fermi resonance” [28]. ii) Increasing concentration of PCL in composite matrix from 5% to 20% led to a shift in the absorption band of carbonyl group related to PCL from 1738 to 1731 cm−1. This shift in the carbonyl absorption band confirm the
Fig. 2. Particle size distribution for pure PS and PS/PCL composites in different ratios.
interaction between PCL and PS [29]. This interaction is suggested to be between lone pair of electrons of carbonyl group in the PCL and π electrons of the aromatic ring in the PS chains i.e. n - π interaction [30,31]. The small peak shift in the FTIR spectrum (7 cm−1) is probably due to the weakness of the n-π interaction when compared to other interactions such as hydrogen bonding [32]. The composite samples were further investigated using UV absorption compared to the pure polystyrene. The spectra depicted in Fig. 4
Fig. 1. TEM micrographs of: (a) pure PS and (b) PS/PCL 15%. 58
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Table 1 Molar masses and polydispersity (PDI) values for pure PS and PS/PCL composites in different ratios. PCL wt%
Mn/(105 g mol−1)
Mw/(105 g mol−1)
PDI
0 5 10 15 20
0.80 1.03 0.38 0.66 1.06
3.0 2.9 2.5 2.6 3.6
3.49 2.80 6.78 3.94 3.39
Fig. 5. TGA thermograms of PCL, PS and PS/PCL composites in different ratios.
temperatures higher than 150oC up to about 400oC. In this stage, it is clear that the prepared PS of particle size at nano scale is considered thermally stable. The compositing PS with PCL increases remarkably the thermal stability. More inspection of the figure shows that at 350oC the weight loss decreases abruptly from 12% for PS to be only 5% forPS/PCL10% composites. Further increase of the PCL to be 15 and 20% decreases the weight loss further to be 3% and 2%, respectively. After 400oC complete decomposition of the polymer occurs. One can concludes that, for the composite samples, the three tested samples showed higher thermal stability than both pure PS and PCL. No significant difference could be noticed between samples PS/PCL 10% and PS/PCL 15%. On the other hand, sample PS/PCL 20% showed slight increase in thermal stability compared to the other two composite ratios. The three samples decomposed at temperature higher than 400oC with no dramatic weight loss lower than this temperature unlike the neat PS. So that, it can be confirmed that addition of PCL till 20% to PS increased its thermal stability to large extent unlike blending of PCL with PS which led to thermal destabilization of the formed biocomposite [11].
Fig. 3. FTIR spectrum of PS prepared by miniemulsion polymerization. The inset shows spectra of carbonyl bands for 5 and 20% PS/PCL.
3.2. Dielectric properties The real part of ac-conductivity, of the prepared PS, has been illustrated graphically against frequency at temperatures ranging from −40 up to 90 °C in Fig. 6. The conductivity of the prepared PS sample shows that the indicated temperature variation leads to differences typically exceeding three decades in dc conductivity. The effect of humidity seems to play the main role in that context. At lower temperatures (−40 and 0 C) a multi-dispersion steps behavior is shown. A remarkable frequency independent trend of conductivity is seen usually yields directly the dc conductivity [34–36]. Further increase of frequency shows bends in the ac conductivity due to some dynamics at the molecular scale as confirmed by two relaxation dynamic peaks in the ε″ (ν) illustration shown in Fig. 7. The origin of the at higher frequency peak is the segmental motion related to the glass transition usually called α-dynamic. The lower frequency peak supposed to be the Maxwell- Wagner- Siller polarization. This interfacial polarization originates from the accumulation of charge carriers (protons in our case) at the interface between the two crystal and amorphous phases in such semi crystalline structures. Fig. 8 depicts the dielectric loss of the PS/PCL10% blend against temperatures at four spot frequency points, namely, 0.1, 1, 1000 and 10 000 Hz at the two higher frequencies the two separate dynamic peaks are clearly seen once again. At lower frequency points, the conductivity contribution at higher temperature (the region of the glass transition) screened out the α-relaxation peak. This agrees well with
Fig. 4. UV spectra of PS compared to different ratios of PS/PCL composite.
showed a strong peak at 248 nm related to phenolic group present in the polystyrene structure. It can be observed that the peak related to sample PA/PCL20% is red shifted to 253 nm. This shift might be attributed to n-π interaction between PCL and aromatic rings in PS [33].
3.1. Thermal gravimetric analysis Thermal stability of the prepared composites compared with the neat PS and PCL, has been studied and the obtained thermograms are shown in Fig. 5. It can be noticed that the pure PS lost about 2% of its weight at temperature below 150oC, which can be attributed to water and solvents evaporation. Then a second degradation step starts at 59
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Fig. 9. The Real part of conductivity vs. frequency of PS and PS/PCL composites in different ratios at temperature 80oC.
Fig. 6. The Real part of conductivity vs. frequencyof PS prepared by miniemulsion polymerization at temperatures ranging from −40 up to 90. The inset shows the effect of heating on the conductivity at spot point frequency 10 Hz.
frequency as the well-known behavior of the perfect insulators. At 0.1 Hz the conductivity tends to be in the order of femto-up to picoSimens per centimeter according to the PCL concentration. More inspection of the figure shows two important notes: first, the sample PS 5 (5% PS/PCL) has the lowest conductivity at all frequencies. Second the effect of PCL concentration in increasing the conductivity of the composites lead to the plateau building up at lower frequencies at higher concentrations. One could conclude that PCL hindered the mobility of the protons from the water traces reducing the conductivity at lower loadings. Both real parts of permittivity and conductivity functions are illustrated graphically against frequency of the sample PS 20 at different temperatures, namely, −50, 0, 50 and 100 °C in Fig. 10. It is clear that both parameters are affected remarkably by temperature and frequency. One can concluded that the effect of decreasing frequency is the same as the increasing temperature in increasing the permittivity,A, as well as conductivity, B. The effect of frequency on the permittivity and conductivity at different temperatures namely, −50, 0, 50 and 100 C is illustrated graphically in Fig. 9A and B, respectively. Fig. 10 A shows that at higher frequencies, the permittivity values are collapsed together and there is no remarkable effect for temperatures or of frequency. Decreasing the frequency leads to spreading out of the permittivity that increases abruptly with decreasing frequency/increasing temperatures. This behavior can be attributed to the thermal activation of the mobile free and bonded charge carriers and/or the terminal polar groups that polarized in application of the electric field. The inset of Fig. 10A shows that the behavior of the dielectric loss (imaginary part of permittivity) is identical to that of the real part of conductivity and just distinguished from each other by some constant. Taking into consideration the two parts of Debye equation:
Fig. 7. The dependence of dielectric loss, Eps″, on the frequency at temperature −40 °C for the sample PS 5 (5% PS/PCL).
ε (ω) = ε′ − iε′′ = ε∞ +
εs − ε∞ σ − i dc . 1 + iωτ εoω
(1) (εs − ε∞) ωτ
σ
+ ε dc . The first part From which the imaginary part ε" = 1 + ω2τ 2 oω describes the molecular dynamics processes and seems to be has no role in the behavior of dielectric loss in our case, whereas the main role here is due to the second part which is related to the charge transportation. Fig. 10B shows that the conductivity decreases linearly with decreasing frequency at lower and moderate temperatures (even @ 50 °C) just like the most perfect insulating materials. At higher temperature, 100 °C,a less dependent trend or even independent on frequency is building up at lower frequencies. This directly related to the dc conductivity shows that the composite is still insulator even at 100 °C (dc conductivity of PS 20 (20% PS/PCL)is in the order of pico Siemens per centimeter). This agrees well with the effect of temperature on the conductivity at different spot point frequencies shown in the inset of Fig. 10B. The low effect of adding PCL on the dielectric and electrical properties of PS
Fig. 8. The dependence of dielectric loss, Eps″, on the frequency vs. temperature at spot frequency points as indicated for the sample PS 5 (5% PS/PCL).
that found in some polymeric systems [33,34]. The real part of conductivity is depicted against frequency at 80 °C for the five samples under investigations as shown in Fig. 9. Generally, the conductivity of all samples decreases mostly linear with decreasing 60
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higher than the neat polymers. BDS study, on the other hand, shows a less effect on the dielectric and electrical behavior of PS assuring the core shell structure. The conductivity of the prepared blends decreases more or less linearly with decreasing frequency which is the main feature of the perfect insulator. Addition of PCL at lower loadings hindered the mobility of the protons from the water traces that reduced the conductivity. This explains the reducing of the conductivity values of 5% PS/PCL blend than that of the pure PS. The obtained biocomposites can found application in packaging materials and biomedical products. Acknowledgement Financial support of this research from National Research Centre [NRC-Inhouse Project-(2016–2019)-11050105]. References [1] D.L. Kaplan (Ed.), Biopolymers from Renewable Resources, Springer, Berlin, 1998. [2] A.K. Mohanty, M. Misra, G. Hinrichsen, Macromol. Mater. Eng. 276/277 (3/4) (2000) 1. [3] N. Ljungberg, T. Andersson, B. Wesslen, J. Appl. Polym. Sci. 88 (14) (2003) 3239. [4] N. Ljungberg, B.J. Wesslen, Appl. Polym. Sci. 86 (5) (2002) 1227. [5] N. Ljungberg, B. Wesslen, Polymer 44 (25) (2003) 7679. [6] I. Soriano, C. Evora, J. Contr. Release 68 (1) (2000) 121. [7] G. Biresaw, C.J. Carriere, J. Polym. Sci. B Polym. Phys. 40 (2002) 2248. [8] G. Biresaw, C.J. Carriere, J. Appl. Polym. Sci. 83 (14) (2002) 3145. [9] G. Biresaw, C.J. Carriere, J. Appl. Polym. Sci. 43 (1) (2002) 367. [10] G. Biresaw, C.J. Carriere, Composites Part a 35 (2004) 313. [11] A. Mohamed, S.H. Gordon, G. Biresaw, Polym. Degrad. Stabil. 92 (2007) 1177. [12] I.D.J. McKay, Appl. Polym. Sci. 42 (2) (1991) 281. [13] J. Ugelstad, M.S. El-Aasser, J.W. Vanderhoff, J. Polym. Sci. Polym. Lett Ed. 11 (1973) 503. [14] J.L. Reimer, F. Schork, Ind. Eng. Chem. Res. 36 (1997) 1085. [15] C.D. Anderson, E.D. Sudol, M.S. El-Aasser, Macromolecules 35 (2) (2002) 574. [16] K. Landfester, Angew. Chem. Int. Ed. 48 (2009) 4488. [17] Z. Zhang, X. Ji, P. Wang, Colloid. Surface. Physicochem. Eng. Aspect. 441 (2014) 510. [18] A. Schoth, C. Wagner, L.L. Hecht, S. Winzen, R. Muñoz-Espí, H.P. Schuchmann, K.J. Landfester, Colloid Polym. Sci. 292 (2014) 2427. [19] D. Qi, Z. Cao, U. Ziener, Adv. Colloid Interface Sci. 211 (2014) 47. [20] K. Landfester, C.K. Weiss, Advances in Polym. Sci. vol. 229, Springer, Berlin, Heidelberg, 2010. [21] Z. Tong, Y. Deng, Polymer 48 (15) (2007) 4337. [22] R. Betancourt-Galindo, C. Cabrera Miranda, B.A. Puente Urbina, A. CastañedaFacio, et al., ISRN Nanotechnol. (2012) 1868515 pages. [23] H.E. Ali, M.H. Abdel Rehim, A.M. Youssef, G. Turky, M.A. Ali, Egy. J. Appl. Sci. 27 (10) (2012) 824. [24] G. Turky, A.M. Ghoneim, A. Kyritsis, K. Raftopoulos, M.A. Moussa, J. Appl. Polym. Sci. 122 (2011) 2039. [25] M.A. Moussa, M.H. Abdel Rehim, Sh.A. Khairy, M.A. Soliman, A.M. Ghoneim, G.M. Turky, Synth. Met. 209 (2015) 34. [26] Sh.S. Omara, M. Abdel Rehim, A. Ghoneim, Sh Madkour, A.F. Thünemann, G. Turky, A. Schönhals, Macromolecules 48 (2015) 6562. [27] K. Torabi, Fourier Transform Infrared Spectroscopy in Size Exclusion Chromatography, MSc thesis University of Toronto, 1999. [28] Q. Sun, Y. Deng, Z.L. Wang, Macromol. Mater. Eng. 289 (2004) 288. [29] D.L. Pavia, G.M. Lampman, G.S. Kriz, J.R. Vyvyan, Brooks/Cole, Cengage Learning, fourth ed., (2009), p. 19. [30] J.L. Koenig, Spectroscopy of Polymers, second ed., Elsevier, Amsterdam, 1999. [31] B.M. Rao, P.R. Rao, B. Sreenivasulu, Polym. Plastic Tech. Eng. 38 (1999) 311. [32] Z.G. Gardlund, C.D. Han (Eds.), Polymer Blends and Composites in Multiphase Systems, American Chemical Society, D.C. Washington, 1984(chapter 9). [33] A. Mohamed, S.H. Gordon, G. Biresaw, Polym. Degrad. Stabil. 92 (2007) 1177–1185. [34] A. Kyritsis, K. Raftopoulos, M. Abdel Rehim, Sh.S. Shabaan, A. Ghoneim, G. Turky, Polymer 50 (2009) 4039. [35] J. Sangoro, G. Turky, M. Abdel Rehim, C. Jacob, S. Naumov, A. Ghoneim, J. Kärger, F. Kremer, Macromolecules 42 (2009) 1648. [36] S.H. El-Sabbagh, N.M. Ahmed, G.M. Turky, M.M. Selim, Rubber nano-composites with new core-shell metal oxides as nano-fillers (Chapter 8), Progress in Rubber Nanocomposites. A Volume in Woodhead Publishing Series in Composites Science and Engineering, 2017, pp. 249–283 https://doi.org/10.1016/B978-0-08-1004098.00008-5.
Fig. 10. Frequency dependence of the real part of permittivity, A, and of conductivity, B, for the sample PS 20 (20% PS/PCL) at temperatures ranging from −50 up to 100 C in steps of 50 C. The inset of A, shows the effect of heating on the conductivity as well as the dielectric loss at higher frequency points. The inset of B shows the effect of heating on the conductivity at higher and lower spot frequency points.
even at 20 wt% confirmed the picture of considering the core-shell structure since the dielectric behavior of the composite is mainly characterize the PS shell covers a nano ball of PCL. 4. Conclusion Composites of PS/PCL were successfully prepared through miniemulsion polymerization technique. Investigation of particles morphology revealed that core-shell structure is formed which is further confirmed through evolution of particle size by increasing amount of PCL. The good compatibility between PS and the biodegradable polymer was evidenced by FTIR and UV which confirmed n-π interaction between the polymers' chains. The formed biocomposite showed remarkable thermal stability by increasing amount of PCL in latex even
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Contents lists available at ScienceDirect
Journal of Physics and Chemistry of Solids journal homepage: www.elsevier.com/locate/jpcs
Dielectric study of polystyrene/polycaprolactone composites prepared by miniemulsion polymerization
T
Saber Ibrahima, Mona Abdel Rehima, Gamal Turkyb,∗ a b
Packaging Materials Department, National Research Centre, Elbehoth Street 33, 12622, Dokki, Cairo, Egypt Microwave Physics and Dielectrics Department, National Research Centre, Elbehoth Street 33, 12622, Dokki, Cairo, Egypt
A R T I C LE I N FO
A B S T R A C T
Keywords: Polymer composite Mini-emulsion Dielectric properties Packaging
Composite of polystyrene (PS) and a biodegradable polymer, polycaprolactone (PCL), has been prepared by miniemulsion polymerization technique. In the procedures, different amounts of commercial PCL were added during polymerization of PS in presence of sodium lauryl sulfate (SLS) as a surfactant. Formation of PS and PS/ PCL nanoparticles was confirmed by Transmission Electron Microscope (TEM) and their structure was investigated using Fourier Transform Infra-Red (FTIR)and UV spectrometry. Encapsulation of PCL particles yielded nanoparticles of gradual enlargement in size as revealed by zeta sizer. However, significant information about the molecular dynamics within the composite and charge mobility can be realized by Broadband dielectric spectroscopy (BDS). So that, BDShas been employed to investigate the electrical and dielectric behavior of the considered composites over a wide range of frequency and temperature. It was found that the dielectric properties of the composites seem to be mainly due to the PS shell with no significant effect for presence of PCL in the core. The linear decrease of the real part of conductivity of the prepared blends with decreasing frequency just like the perfect insulator confirmed the encapsulation feature of the structure. The new materials can find applications in packaging, household beside biomedical fields.
1. Introduction
biodegradable polymer has been thoroughly investigated by Biresaw et al. [7–9] Extensive study of the compatibility of the polymers in the blends using model biopolymers was performed. The study covered various properties such as interfacial tension, interfacial adhesion and tensile properties [10]. Mohamed et al. applied Fourier transform infrared photo-acoustic spectroscopy (FTIR-PAS) in order to confirm the presence of molecular interaction between PS and PCL in their blends [11]. Increasing dispersion of PCL and PS homo-polymers within one another in their blends could be achieved through addition of polystyrene–polycaprolactone diblock copolymer. The prepared blends showed improved flow and thermal characteristics in the range between the individual polymer components [12]. Miniemulsion polymerization is special type of emulsion polymerization technique in which a co-stabilizer is used and a shear is applied in order to obtain polymer particles in the range of 50–100 nm [13]. Another task for the co-stabilizer is to reduce the diffusional degradation rate of water/ monomer emulsion along with reduction of monomer droplet size [14]. Synthesis of polystyrene of 50 nm particle size by miniemulsion technique has been reported. Reduction of interfacial tension and increase of colloidal stability of the nanoparticles of prepared PS can be attained by using higher levels of surfactants [15]. Zhang et al. described a
Polymer composites received much attention due to their versatile properties and applications. Preparation of the polymer composites can be carried out either by blending block technique or in situ formation of components. The advantage of the former method is that the used blending blocks have well-defined chemical structure and they do not undergo chemical change under processing conditions. Moreover, designed blending blocks and structure-property manipulation can be attained. On the other hand, the later technique for composite preparation is based upon the chemical transformation of at least one precursor during material preparation. Polystyrene is a general-purpose synthetic polymer due to its hardness, clearness and low cost per unit weight. It finds many applications as protective packaging, containers and bottles. It is also characterized by its low gas barrier properties and low biodegradability. On the other hand, biodegradable polymers are characterized by their water resistance and being in the same time biodegradable [1,2]. Therefore, developed products can be obtained through compositing synthetic and biodegradable polymers in the fields of materials and packaging applications [3–6]. Blending of PS with PCLas a
∗
Corresponding author. E-mail address: [email protected] (G. Turky).
https://doi.org/10.1016/j.jpcs.2018.03.030 Received 8 January 2018; Received in revised form 14 February 2018; Accepted 20 March 2018 Available online 23 March 2018 0022-3697/ © 2018 Elsevier Ltd. All rights reserved.
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coated copper grid (S160-3 Plano GmbH) and investigated using JEOL 200 TEM (Carl Zeiss NTS) operated at 120 kV/200 kV. Zero-loss energy filtering was used to increase the image contrast. Thermal gravimetric analysis was carried out using a Perkin Elmer thermogravimetric analyzer (TGA), with a heating rate of 10 °C/min in nitrogen atmosphere with flow rate100 mL/min and temperature range from 30 °C up to 600 °C. The dielectric measurements were performed between 0.1 Hz and 10 MHz using a Novocontrol high-resolution alpha analyzer. A Quatro temperature controller using pure nitrogen as heating agent and assuring temperature stability better than 0.2 K. assisted the analyzer. The investigated samples with thicknesses 1–2 mm were sandwiched between freshly polished brass electrodes with a top electrode diameter of 10 mm to form a parallel-plate capacitor cell. The complex permittivity (ε* = ε′ - iε″) was measured using a sinusoidal voltage with amplitude 0.1 V over a 10−2 −107 Hz frequency range in all experiments. Data were collected in isothermal frequency sweeps every 10 °C, from −50 to 120 °C.
method for preparation of polystyrene without co-stabilizer [16]. A fluorinated block copolymer prepared by ATRP and dodecafluoroheptyl methacrylate was used as the sole co-stabilizer in St miniemulsion instead of the conventional co-stabilizers. Better surface hydrophobicity was observed for the final latex. Encapsulation of nanoparticles in polymer matrix using miniemulsion polymerization technique was investigated extensively [14,17–19]. Polystyrene encapsulated nanosaponite composite suspension via miniemulsion polymerization has been reported [20]. Clay particle size and premodification of its surface were found to be crucial in order to produce stable latex suspension. Composite of silver nanoparticles encapsulated in polystyrene matrix been prepared [21,22]. The formed composite showed good antibacterial properties against Escherichia coli and Staphylococcus aureus. The electrical and dielectric investigations of polymer composites attracted significant attention due to both basic and application fields. This is according to the fact that the prepared composite has its own characteristics, which is usually distinguishable from that of its individual components individual. Two factors play the main role in that context: the loaded ratio and the expected interaction between the components. Broadband dielectric spectroscopy (BDS) has become a powerful tool for investigations of the frequency and temperature dependence of different electrical and dielectric properties of the polymers and their composites [23–26]. Its broad range of frequency [10−6 - 1012] is the main advantage over all other spectroscopy techniques since it covers all molecular dynamics, charge transportations as well as space charge or interfacial polarizations. This work deals with encapsulated polycaprolactone, as a biodegradable polymer, in polystyrene latex as a novel way to prepare biocomposite of synthetic and biodegradable polymers. Characterization of the obtained nanocapsules has been performed and detailed study of electrical and dielectric properties of the synthesized composite has been demonstrated. In this context, the dielectric properties of the prepared composites will give valuable information about the structure and influence of polycaprolactone on the electrical and dielectric properties of the host polymer.
2.3. Synthesis of composites
2. Experimental
In round bottom flask, a specified amount of styrene monomer/PCL with different ratios (PCL 5, 10, 15 and 20 wt.%) and 0.037 mol of nonpolar solvent (hexadecane, HD) were mixed and added to a solution containing 0.02 g sodium lauryl sulfate (SLS) in 73.28 g of water. The mixture was degassed (vac/N2, followed by stirring for 20 min under N2 at 300 min−1) and then stirred for 50 min at 500 rpm. After that, miniemulsion droplets were prepared by ultra-sonication for 7 min. A slight stream of nitrogen was applied, and the emulsion was cooled with ice water. The formed mini-emulsion was transferred to the reaction vessel. After short degassing, the temperature was raised to 75 °C. Then, an aqueous solution of initiator was added (330 mg of APS in 7.1 g of water degassed under N2 for 20 min). The reaction was performed at 600 rpm for 5 h. The reaction vessel was immersed in an ice bath to decrease the temperature until room temperature. The dispersion was precipitated in 300 mL of MeOH (1 wt% HQ), and the precipitation was done by dropwise addition. Polystyrene/polycaprolactone was filtrated and dried in a vacuum oven overnight.
2.1. Materials
3. Results and discussion
Styrene, Sigma-Aldrich, was purified before being used. Polycaprolactone (PCL) Mwt = 80000 g/mol, ammonium peroxide sulfate (APS), sodium bicarbonate, hexadecane (HD), hydroquinone (HQ), and sodium lauryl sulfate (SLS) were obtained from SigmaAldrich and were used as received.
Preparation of PS/PCL composite has been carried out using miniemulsion polymerization technique in order to increase miscibility and homogeneity of the newly formed composite. Different ratios of PCL (5–20% by weight) were added during polymerization of styrene. It is assumed that PCL particles are encapsulated within the PS during its formation (Scheme 1). This assumption has been confirmed by TEM images (Fig. 1). Fig. 1a, reveals that the prepared PS particles are in the range of 18–33 nm. On the other hand, addition of 15% PCL led to enlargement of the obtained particles by nearly 10 folds. These large particles confirm the encapsulation of PCL particles in form of a core and a PS shell is formed around them. The particle mean size and distribution for the formed PS/PCL composite have been measured by zeta sizer. The results are depicted in Fig. 2, which show that the particle size of pure PS is in the range of 55 nm. By increasing added amount of PCL, the mean size and size distribution is not significantly modified for PCL content lower than 10%. Increasing the amount of PCL to 15–20 wt% leads to a significant increase in the mean size of the formed particles. However, no difference in the particle mean size and size distribution was evidenced by increasing the PCL content from 15 to 20%. Molecular weight determination in the form of Mn, Mw and PDI of the pure PS and its composite with PCL, was carried out using GPC connected with a refractive index detector (RID). The values gathered in Table 1 showed that the highest molar mass was obtained for sample PS/PCL 20% while the lowest was for sample PS/PCL 10% which also
2.2. Methods The mini-emulsion droplets were prepared by ultrasonication for 7 min (90% amplitude) with an ultrasonic disintegrator (Qsonic 450 W). Particle size distribution of the prepared PS and PS/PCL were measured by zeta sizer (Nano ZS, zeta sizer, Malvern, UK) based on the dynamic light scattering technique. The functional groups in the polymer composites backbones were identified and recorded using Perkin Elmer Fourier transform infrared spectroscopy (FTIR)with range of measurements of 600–4000 cm−1. Electronic absorption of the samples is investigated by UV absorbance measured by Jasco spectrometer V-630. Constant weights of the samples (10 mg/3 mL) were dissolved in THF and measured in quartz cuvette. The molecular weights of the prepared polystyrene and composites were determined using GPC Agilent model 1515 pump system equipped with 1260 infinity refractive index detector. THF was used as eluent operating with a flow rate of 1.00 mL/min and polystyrene was a standard. Investigation of structures of the prepared PS/PCL nanocomposites was carried out using transmission electron microscope (TEM). The samples were prepared by dropping a solution of the composite on a carbon57
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Scheme 1. Representation of encapsulation process of PCL by PS during miniemulsion polymerization.
has PDI value of 6.78. It is known that the refractive index detector separates the polymer molecules according their size. However, this detector provides uncertain data when the polymer molecules vary in composition and size such as in case of copolymers and blends [27]. In our case, the composition of the molecules are varied with their sizes which led to different response from the RID reflecting both composition and size. Nevertheless, sample PS/PCL 5% has high molar mass (Mn = 1.03 × 105 g/mol) with lowest PDI value. This can be explained by presence of PCL in low ratio did not interfere or hinder the stabilized emulsion, so that long PS chains are formed with lowest polydispersity. Chemical structures of pure PS and its interaction with PCLwere confirmed by FTIR spectroscopy. The obtained spectra in Fig. 3 depict the absorption bands of PS particles and the inset represent the overlaid absorption bands of pure PS, PS loaded with 5 and 20% PCL, respectively. The spectrum of PS shows absorption band at 32003500 cm−1which is due to OH from water and a band at 3026 cm−1 for the aromatic CH-vibration. Absorption bands at 2921 cm−1are assigned for aliphatic C-H bond. Aromatic C-H combination frequency overtones can be found in the range of 1740–2000 cm−1. Bands at 14751620 cm−1 represent aromatic C-C bond stretching vibration. The inset spectra reveal that: i) Since PS has no significant band at carbonyl region and the observed small peak is related to one of the overtones for aromatic groups in PS. However, the decrease in the fundamental band of carbonyl group of PCL is due to its overlap with one of the overtone bands, an interaction known as “Fermi resonance” [28]. ii) Increasing concentration of PCL in composite matrix from 5% to 20% led to a shift in the absorption band of carbonyl group related to PCL from 1738 to 1731 cm−1. This shift in the carbonyl absorption band confirm the
Fig. 2. Particle size distribution for pure PS and PS/PCL composites in different ratios.
interaction between PCL and PS [29]. This interaction is suggested to be between lone pair of electrons of carbonyl group in the PCL and π electrons of the aromatic ring in the PS chains i.e. n - π interaction [30,31]. The small peak shift in the FTIR spectrum (7 cm−1) is probably due to the weakness of the n-π interaction when compared to other interactions such as hydrogen bonding [32]. The composite samples were further investigated using UV absorption compared to the pure polystyrene. The spectra depicted in Fig. 4
Fig. 1. TEM micrographs of: (a) pure PS and (b) PS/PCL 15%. 58
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Table 1 Molar masses and polydispersity (PDI) values for pure PS and PS/PCL composites in different ratios. PCL wt%
Mn/(105 g mol−1)
Mw/(105 g mol−1)
PDI
0 5 10 15 20
0.80 1.03 0.38 0.66 1.06
3.0 2.9 2.5 2.6 3.6
3.49 2.80 6.78 3.94 3.39
Fig. 5. TGA thermograms of PCL, PS and PS/PCL composites in different ratios.
temperatures higher than 150oC up to about 400oC. In this stage, it is clear that the prepared PS of particle size at nano scale is considered thermally stable. The compositing PS with PCL increases remarkably the thermal stability. More inspection of the figure shows that at 350oC the weight loss decreases abruptly from 12% for PS to be only 5% forPS/PCL10% composites. Further increase of the PCL to be 15 and 20% decreases the weight loss further to be 3% and 2%, respectively. After 400oC complete decomposition of the polymer occurs. One can concludes that, for the composite samples, the three tested samples showed higher thermal stability than both pure PS and PCL. No significant difference could be noticed between samples PS/PCL 10% and PS/PCL 15%. On the other hand, sample PS/PCL 20% showed slight increase in thermal stability compared to the other two composite ratios. The three samples decomposed at temperature higher than 400oC with no dramatic weight loss lower than this temperature unlike the neat PS. So that, it can be confirmed that addition of PCL till 20% to PS increased its thermal stability to large extent unlike blending of PCL with PS which led to thermal destabilization of the formed biocomposite [11].
Fig. 3. FTIR spectrum of PS prepared by miniemulsion polymerization. The inset shows spectra of carbonyl bands for 5 and 20% PS/PCL.
3.2. Dielectric properties The real part of ac-conductivity, of the prepared PS, has been illustrated graphically against frequency at temperatures ranging from −40 up to 90 °C in Fig. 6. The conductivity of the prepared PS sample shows that the indicated temperature variation leads to differences typically exceeding three decades in dc conductivity. The effect of humidity seems to play the main role in that context. At lower temperatures (−40 and 0 C) a multi-dispersion steps behavior is shown. A remarkable frequency independent trend of conductivity is seen usually yields directly the dc conductivity [34–36]. Further increase of frequency shows bends in the ac conductivity due to some dynamics at the molecular scale as confirmed by two relaxation dynamic peaks in the ε″ (ν) illustration shown in Fig. 7. The origin of the at higher frequency peak is the segmental motion related to the glass transition usually called α-dynamic. The lower frequency peak supposed to be the Maxwell- Wagner- Siller polarization. This interfacial polarization originates from the accumulation of charge carriers (protons in our case) at the interface between the two crystal and amorphous phases in such semi crystalline structures. Fig. 8 depicts the dielectric loss of the PS/PCL10% blend against temperatures at four spot frequency points, namely, 0.1, 1, 1000 and 10 000 Hz at the two higher frequencies the two separate dynamic peaks are clearly seen once again. At lower frequency points, the conductivity contribution at higher temperature (the region of the glass transition) screened out the α-relaxation peak. This agrees well with
Fig. 4. UV spectra of PS compared to different ratios of PS/PCL composite.
showed a strong peak at 248 nm related to phenolic group present in the polystyrene structure. It can be observed that the peak related to sample PA/PCL20% is red shifted to 253 nm. This shift might be attributed to n-π interaction between PCL and aromatic rings in PS [33].
3.1. Thermal gravimetric analysis Thermal stability of the prepared composites compared with the neat PS and PCL, has been studied and the obtained thermograms are shown in Fig. 5. It can be noticed that the pure PS lost about 2% of its weight at temperature below 150oC, which can be attributed to water and solvents evaporation. Then a second degradation step starts at 59
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Fig. 9. The Real part of conductivity vs. frequency of PS and PS/PCL composites in different ratios at temperature 80oC.
Fig. 6. The Real part of conductivity vs. frequencyof PS prepared by miniemulsion polymerization at temperatures ranging from −40 up to 90. The inset shows the effect of heating on the conductivity at spot point frequency 10 Hz.
frequency as the well-known behavior of the perfect insulators. At 0.1 Hz the conductivity tends to be in the order of femto-up to picoSimens per centimeter according to the PCL concentration. More inspection of the figure shows two important notes: first, the sample PS 5 (5% PS/PCL) has the lowest conductivity at all frequencies. Second the effect of PCL concentration in increasing the conductivity of the composites lead to the plateau building up at lower frequencies at higher concentrations. One could conclude that PCL hindered the mobility of the protons from the water traces reducing the conductivity at lower loadings. Both real parts of permittivity and conductivity functions are illustrated graphically against frequency of the sample PS 20 at different temperatures, namely, −50, 0, 50 and 100 °C in Fig. 10. It is clear that both parameters are affected remarkably by temperature and frequency. One can concluded that the effect of decreasing frequency is the same as the increasing temperature in increasing the permittivity,A, as well as conductivity, B. The effect of frequency on the permittivity and conductivity at different temperatures namely, −50, 0, 50 and 100 C is illustrated graphically in Fig. 9A and B, respectively. Fig. 10 A shows that at higher frequencies, the permittivity values are collapsed together and there is no remarkable effect for temperatures or of frequency. Decreasing the frequency leads to spreading out of the permittivity that increases abruptly with decreasing frequency/increasing temperatures. This behavior can be attributed to the thermal activation of the mobile free and bonded charge carriers and/or the terminal polar groups that polarized in application of the electric field. The inset of Fig. 10A shows that the behavior of the dielectric loss (imaginary part of permittivity) is identical to that of the real part of conductivity and just distinguished from each other by some constant. Taking into consideration the two parts of Debye equation:
Fig. 7. The dependence of dielectric loss, Eps″, on the frequency at temperature −40 °C for the sample PS 5 (5% PS/PCL).
ε (ω) = ε′ − iε′′ = ε∞ +
εs − ε∞ σ − i dc . 1 + iωτ εoω
(1) (εs − ε∞) ωτ
σ
+ ε dc . The first part From which the imaginary part ε" = 1 + ω2τ 2 oω describes the molecular dynamics processes and seems to be has no role in the behavior of dielectric loss in our case, whereas the main role here is due to the second part which is related to the charge transportation. Fig. 10B shows that the conductivity decreases linearly with decreasing frequency at lower and moderate temperatures (even @ 50 °C) just like the most perfect insulating materials. At higher temperature, 100 °C,a less dependent trend or even independent on frequency is building up at lower frequencies. This directly related to the dc conductivity shows that the composite is still insulator even at 100 °C (dc conductivity of PS 20 (20% PS/PCL)is in the order of pico Siemens per centimeter). This agrees well with the effect of temperature on the conductivity at different spot point frequencies shown in the inset of Fig. 10B. The low effect of adding PCL on the dielectric and electrical properties of PS
Fig. 8. The dependence of dielectric loss, Eps″, on the frequency vs. temperature at spot frequency points as indicated for the sample PS 5 (5% PS/PCL).
that found in some polymeric systems [33,34]. The real part of conductivity is depicted against frequency at 80 °C for the five samples under investigations as shown in Fig. 9. Generally, the conductivity of all samples decreases mostly linear with decreasing 60
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higher than the neat polymers. BDS study, on the other hand, shows a less effect on the dielectric and electrical behavior of PS assuring the core shell structure. The conductivity of the prepared blends decreases more or less linearly with decreasing frequency which is the main feature of the perfect insulator. Addition of PCL at lower loadings hindered the mobility of the protons from the water traces that reduced the conductivity. This explains the reducing of the conductivity values of 5% PS/PCL blend than that of the pure PS. The obtained biocomposites can found application in packaging materials and biomedical products. Acknowledgement Financial support of this research from National Research Centre [NRC-Inhouse Project-(2016–2019)-11050105]. References [1] D.L. Kaplan (Ed.), Biopolymers from Renewable Resources, Springer, Berlin, 1998. [2] A.K. Mohanty, M. Misra, G. Hinrichsen, Macromol. Mater. Eng. 276/277 (3/4) (2000) 1. [3] N. Ljungberg, T. Andersson, B. Wesslen, J. Appl. Polym. Sci. 88 (14) (2003) 3239. [4] N. Ljungberg, B.J. Wesslen, Appl. Polym. Sci. 86 (5) (2002) 1227. [5] N. Ljungberg, B. Wesslen, Polymer 44 (25) (2003) 7679. [6] I. Soriano, C. Evora, J. Contr. Release 68 (1) (2000) 121. [7] G. Biresaw, C.J. Carriere, J. Polym. Sci. B Polym. Phys. 40 (2002) 2248. [8] G. Biresaw, C.J. Carriere, J. Appl. Polym. Sci. 83 (14) (2002) 3145. [9] G. Biresaw, C.J. Carriere, J. Appl. Polym. Sci. 43 (1) (2002) 367. [10] G. Biresaw, C.J. Carriere, Composites Part a 35 (2004) 313. [11] A. Mohamed, S.H. Gordon, G. Biresaw, Polym. Degrad. Stabil. 92 (2007) 1177. [12] I.D.J. McKay, Appl. Polym. Sci. 42 (2) (1991) 281. [13] J. Ugelstad, M.S. El-Aasser, J.W. Vanderhoff, J. Polym. Sci. Polym. Lett Ed. 11 (1973) 503. [14] J.L. Reimer, F. Schork, Ind. Eng. Chem. Res. 36 (1997) 1085. [15] C.D. Anderson, E.D. Sudol, M.S. El-Aasser, Macromolecules 35 (2) (2002) 574. [16] K. Landfester, Angew. Chem. Int. Ed. 48 (2009) 4488. [17] Z. Zhang, X. Ji, P. Wang, Colloid. Surface. Physicochem. Eng. Aspect. 441 (2014) 510. [18] A. Schoth, C. Wagner, L.L. Hecht, S. Winzen, R. Muñoz-Espí, H.P. Schuchmann, K.J. Landfester, Colloid Polym. Sci. 292 (2014) 2427. [19] D. Qi, Z. Cao, U. Ziener, Adv. Colloid Interface Sci. 211 (2014) 47. [20] K. Landfester, C.K. Weiss, Advances in Polym. Sci. vol. 229, Springer, Berlin, Heidelberg, 2010. [21] Z. Tong, Y. Deng, Polymer 48 (15) (2007) 4337. [22] R. Betancourt-Galindo, C. Cabrera Miranda, B.A. Puente Urbina, A. CastañedaFacio, et al., ISRN Nanotechnol. (2012) 1868515 pages. [23] H.E. Ali, M.H. Abdel Rehim, A.M. Youssef, G. Turky, M.A. Ali, Egy. J. Appl. Sci. 27 (10) (2012) 824. [24] G. Turky, A.M. Ghoneim, A. Kyritsis, K. Raftopoulos, M.A. Moussa, J. Appl. Polym. Sci. 122 (2011) 2039. [25] M.A. Moussa, M.H. Abdel Rehim, Sh.A. Khairy, M.A. Soliman, A.M. Ghoneim, G.M. Turky, Synth. Met. 209 (2015) 34. [26] Sh.S. Omara, M. Abdel Rehim, A. Ghoneim, Sh Madkour, A.F. Thünemann, G. Turky, A. Schönhals, Macromolecules 48 (2015) 6562. [27] K. Torabi, Fourier Transform Infrared Spectroscopy in Size Exclusion Chromatography, MSc thesis University of Toronto, 1999. [28] Q. Sun, Y. Deng, Z.L. Wang, Macromol. Mater. Eng. 289 (2004) 288. [29] D.L. Pavia, G.M. Lampman, G.S. Kriz, J.R. Vyvyan, Brooks/Cole, Cengage Learning, fourth ed., (2009), p. 19. [30] J.L. Koenig, Spectroscopy of Polymers, second ed., Elsevier, Amsterdam, 1999. [31] B.M. Rao, P.R. Rao, B. Sreenivasulu, Polym. Plastic Tech. Eng. 38 (1999) 311. [32] Z.G. Gardlund, C.D. Han (Eds.), Polymer Blends and Composites in Multiphase Systems, American Chemical Society, D.C. Washington, 1984(chapter 9). [33] A. Mohamed, S.H. Gordon, G. Biresaw, Polym. Degrad. Stabil. 92 (2007) 1177–1185. [34] A. Kyritsis, K. Raftopoulos, M. Abdel Rehim, Sh.S. Shabaan, A. Ghoneim, G. Turky, Polymer 50 (2009) 4039. [35] J. Sangoro, G. Turky, M. Abdel Rehim, C. Jacob, S. Naumov, A. Ghoneim, J. Kärger, F. Kremer, Macromolecules 42 (2009) 1648. [36] S.H. El-Sabbagh, N.M. Ahmed, G.M. Turky, M.M. Selim, Rubber nano-composites with new core-shell metal oxides as nano-fillers (Chapter 8), Progress in Rubber Nanocomposites. A Volume in Woodhead Publishing Series in Composites Science and Engineering, 2017, pp. 249–283 https://doi.org/10.1016/B978-0-08-1004098.00008-5.
Fig. 10. Frequency dependence of the real part of permittivity, A, and of conductivity, B, for the sample PS 20 (20% PS/PCL) at temperatures ranging from −50 up to 100 C in steps of 50 C. The inset of A, shows the effect of heating on the conductivity as well as the dielectric loss at higher frequency points. The inset of B shows the effect of heating on the conductivity at higher and lower spot frequency points.
even at 20 wt% confirmed the picture of considering the core-shell structure since the dielectric behavior of the composite is mainly characterize the PS shell covers a nano ball of PCL. 4. Conclusion Composites of PS/PCL were successfully prepared through miniemulsion polymerization technique. Investigation of particles morphology revealed that core-shell structure is formed which is further confirmed through evolution of particle size by increasing amount of PCL. The good compatibility between PS and the biodegradable polymer was evidenced by FTIR and UV which confirmed n-π interaction between the polymers' chains. The formed biocomposite showed remarkable thermal stability by increasing amount of PCL in latex even
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