Development and characterization of functionalized Al₂O₃ and TiO₂-reinforced polybenzoxazine nanocomposites

Abstract

In the present work, benzoxazine was synthesized using caprolactam amine and cardanol, and its molecular structure was confirmed with FTIR and NMR spectroscopic techniques. Alumina (Al₂O₃) and titania (TiO₂) were functionalized using 3-aminopropyltrimethoxysilane (APTMS). The nanocomposites were developed by reinforcing with varying weight (1, 3, 5, and 7) percentages of functionalized Al₂O₃ (F-Al₂O₃) and functionalized TiO₂ (F-TiO₂) with benzoxazine. The developed nanocomposites (F-Al₂O₃/CPBz and F-TiO₂/CPBz) were characterized from their thermal, dielectric, and UV shielding studies. Data obtained from thermal studies show that 7 wt% of F-Al₂O₃-reinforced cardanol-based polybenzoxazine nanocomposite exhibits higher thermal stability than that of 7 wt% F-TiO₂-reinforced cardanol-based polybenzoxazine nanocomposite. Dielectric and UV shielding studies show that 7 wt% F-TiO₂ nanocomposite show higher value of dielectric constant (10.2) and UV shielding value (93%) than those of neat and other weight percentages of F-Al₂O₃ and F-TiO₂ reinforced composites.

Keywords:

• Polybenzoxazine
• UV shielding
• dielectric constant
• APTMS
• nanocomposites

1. Introduction

Polybenzoxazine, a new class of phenolic resin-based thermosetting polymer, which has high glass transition temperature, high modulus, and dimensional stability. These materials can be used for structural, electronic engineering, and aerospace applications.[1–4] Recently, the use of the benzoxazine resin as a matrix for highly filled composites has been achieved due to its low melt viscosity, which is one of the outstanding properties required for processing.[5–9] An interesting dielectric behavior of benzoxazine has drawn a great research attention towards the fabrication of advanced integrated circuits (which have improved the functionality to enhance its dielectric property of polybenzoxazine blended with various inorganic materials for their synergetic effect). Thereby, enormous research has been focused on benzoxazine-based hybrid materials. Moreover, it is known that the modification in chemical structure could directly have an impact on their dielectric properties.[10]

Polymers obtained from renewable resource materials have attracted the attention of both academic and industrial research. Cardanol is a well-known phenolic compound obtained as a renewable biosource and it is a byproduct of cashew nut shell. The chemically modified cardanol and its polymers exhibit an excellent performance and polymerization into specialty polymers.[11–14] Cardanol-based polybenzoxazine have received much research attention because they can be used as diluent, and have good mechanical and dielectric properties, low viscosity, and hydrophobic behavior than the conventional phenolic resins.[9,15–18]

Many researchers tried to improve the dielectric constant of the polybenzoxazine and polyethylene by incorporating TiO₂ into the matrices. They have reported that TiO₂ possesses an outstanding toughening, ability particularly with a rigid matrix such as found in many ceramics composite systems.[19–23] Therefore, the incorporation of TiO₂ into a polybenzoxazine matrix should render at least twofold benefits to the benzoxazine resin. Alumina is one of the most cost-effective and widely used materials in the family of ceramic engineering. and it has excellent properties which include higher hardness, wear resistance, resistance to strong acid, good dielectric properties, alkali attack at elevated temperatures, and high thermal conductivity.[24–29] Many researchers used alumina and titania as reinforcements to improve the dielectric constant of polybenzoxazine matrix.

In the present work, a new type of cardanol-based benzoxazine (CBz) was synthesized using cardanol as renewable resource material with caprolactam amine (CPA-NH₂). 3-aminopropyltrimethoxysilane (APTMS) functionalized alumina (Al₂O₃) and titanium dioxide (TiO₂) were synthesized and varying weight percentages (1, 3, 5, and 7) of F-Al₂O₃ and F-TiO₂ were reinforced into polybenzoxazine to obtain nanocomposites. Data obtained from thermal, dielectric, and UV shielding studies were discussed and reported.

2. Experimental

2.1. Materials

Alumina nanoparticles (Al₂O₃), APTMS and Titanium (IV) isopropoxide (TTIP) were purchased from Sigma Aldrich. Analytical grades of chloroform, Sodium hydroxide (NaOH), Sulphuric acid (H₂SO₄), Ethanol, and paraformaldehyde were purchased from SRL, India. 4, 4-diaminodiphenylmethane (DDM) was obtained from Ciba-Geigy Ltd., India. Cardanol was purchased from Satya Cashew Chemicals Pvt. Ltd. Chennai, India.

2.2. Synthesis of CBz

Caprolactam diamine was synthesized as per our earlier report [30] and its molecular structure was confirmed with FTIR and NMR spectroscopy. To a solution of caprolactam diamine (5 g, 0.011 mol) in chloroform, paraformaldehyde (1.4 g, 0.047 mol) was added and stirred for 30 min at 0 °C. Subsequently, 7.42 g of cardanol (0.023 mol) was added to the reaction mixture and stirred overnight at 70 °C. After the completion of reaction, the reaction mixture was extracted with ethyl acetate and washed with 2 N NaOH, water, brine, and concentrated the organic layer to obtain product with 92% yield and the formation of benzoxazine was confirmed from ¹H and ¹³C NMR [31] studies (Scheme 1).

2.3. Synthesis of TiO₂

Nine milliliters of titanium (IV) isopropoxide (TTIP) in 20 mL of ethanol was hydrolyzed through the sol–gel method using ethanol–water mixture (50:50 V/V ratio). The resulting slurry was stirred vigorously at room temperature to obtain a homogeneous product. The gelation process was completed by the dropwise addition of 1 M sulfuric acid (pH = 3.5). The gel was aged for 12 h at room temperature. The product obtained was filtered and washed several times with water and dried at 60 °C for 12 h. The dried sample was powdered and calcined at 400 °C for 4 h to remove the organic impurities in order to obtain TiO₂ nanoparticle, and was confirmed by XRD.[30,32]

2.4. Surface functionalization of Al₂O₃ and TiO₂

Surface functionalization of nano alumina and TiO₂ was carried out using APTMS as a coupling agent. Alumina (2 g) and titania (2 g) were separately dispersed in 95% ethanol and 5% deionized water through ultrasonication for 1 h and the pH was adjusted to 4.5 using acetic acid. Two milliliters of APTMS was then added drop by drop and the mixture was sonicated for 30 min, and further refluxed at 70 °C for 12 h under stirring. The resulting amine-functionalized alumina and titania was collected by filtration and dried under vacuum for 12 h and preserved for further use.[33–35]

2.5. Preparation of functionalized Al₂O₃ and TiO₂-reinforced polybenzoxazine nanocomposite

APTMS functionalized alumina and titanium dioxide reinforced polybenzoxazine composites were prepared by varying weight percentages of functionalized alumina and titania (0, 5, 10, 15, and 20 wt %) separately using chloroform as solvent to the CPBz monomer solution. The resulting product was poured into a Petri dish and the samples were cured at 100, 120, 160, 200, and 220 °C for each 1 h to get a functionalized alumina and titanium dioxide-reinforced film for further characterization and is shown in Scheme 2.

3. Characterization

Fourier transform infrared (FT-IR) spectra of the samples were recorded on a Perkin Elmer 6X FTIR spectrometer. The ¹HNMR and ¹³CNMR spectra were recorded with a BRUCKER 300 MHz NMR spectrometer. Samples were diluted using deuterated chloroform. Thermogravemetric analysis (TGA) was carried out using the DSTA 409 PC analyzer (Netzsch Gerateban GmbH). The dielectric studies were carried out with the help of an impedance analyser, solartron impedance/gain phase analyzer 1260) at RT using platinum (Pt) electrode at 30 °C at a frequency of 1 MHz .This experiment was repeated for four times at the same conditions. The glass transition temperature (Tg) of the samples was determined using differential scanning calorimeter (DSC 200 PC, Netzsch Gerateban GmbH).

X-ray diffraction patterns were recorded at room temperature by monitoring the diffraction angle 2θ from 10° to 70° as the standard, on a Rich Seifert (Model 3000) X-ray powder diffractometer. A JEOL JSM-6360 field emission scanning electron microscope (SEM) was used for morphological studies. An analytical TEM (JEM-3010, JEOL, Tokyo, Japan), operating at 80 kV with a measured point-to-point resolution of 0.23 nm, was used to characterize the phase morphology of the nanocomposites developed in the present work. TEM samples were prepared by dissolving the composite samples in ethanol mounted on carbon-coated copper TEM grids and dried for 1 h at 70 °C to form a film of <100 nm. The dielectric constant (DC) of F- Al₂O₃ and F-TiO₂ reinforced polybenzoxazine nanocomposites were determined with the help of an impedance analyzer (Solartron impedance/gain phase analyzer 1260) using Pt electrode at 40 °C in a frequency range of 1 MHz. The UV transmittance spectra were recorded in Jasco (V-650, Japan) spectrophotometer.

4. Results and discussion

4.1. FTIR spectra

The formation of CBz monomer was supported by FTIR spectrum and is presented in (Figure S1, supporting information). The peak that appeared at 1528 cm⁻¹ indicates the presence of trisubstituted benzene ring and the new peak that appeared at 936 cm⁻¹ represents the stretching vibration of C–O of benzoxazine. Figure 1(a) shows the FTIR spectrum of amine-functionalized Al₂O₃ and TiO₂. The peak appearing at 3442 cm⁻¹ represents the stretching vibration of N–H bond of aminosilane. The peak appearing at 1092 cm⁻¹ corresponds to the stretching vibration of Al–O–Si linkage and peaks that appeared at 785 and 586 cm⁻¹ represent the Al–O linkage. In the FTIR spectra of F-TiO_2, (Figure 1(b)) the peaks that appeared at 3442 and 1546 cm⁻¹ are assigned to stretching and bending vibration of the N–H bond of aminosilane, respectively. The peaks that appeared at 1359 and 1080 cm⁻¹ are assigned to the stretching vibrations of Ti–O–Si linkage.

Figure 1. FTIR Spectra of (a) F-Al₂O₃ and (b) F-TiO_2.

Figure 2 illustrates the FTIR of neat polybenzoxazine and varying weight percentages of Al₂O₃.The disappearance of peaks at 1528 and 936 cm⁻¹ is related to trisubstituted benzene ring and stretching vibration of C–O of benzoxazine, respectively, which indicates the ring-opening polymerization. The appearance of new peaks at 1504 cm⁻¹ represents the tetra-substituted benzene ring and the peak appearing at 2850 cm⁻¹ is attributed to O⋯H⋯N intra molecular hydrogen bonding of the polybenzoxazine. The peak appeared at 820 cm⁻¹ represents Al–O linkage, which is absent in the FTIR spectrum of neat polybenzoxazine support the reinforcement of F-Al₂O₃ into the polybenzoxazine matrix. The FTIR spectra of varying weight percentages of F-TiO₂-reinforced polybenzoxazine nanocomposites are shown in Figure 3. The disappearance of peak related to oxazine ring at 936 cm⁻¹ infers the ring-opening polymerization and a new peak appeared at 1480 cm⁻¹ represents the tetra-substituted benzene ring of polybenzoxazine. The additional peak that appeared at 815 cm⁻¹ represents Ti–O–Si linkage.[31,32]

Figure 2. FTIR spectrum of neat CPBz matrix and F-Al₂O₃/CPBz nanocomposites.

Figure 3. FTIR spectrum of F-TiO₂/CPBz nanocomposites.

4.2. NMR spectra

Figure S2 (supporting information) shows the ¹H and ¹³C NMR spectra of CBz. The peaks that appeared at 6.64–7.34 ppm were assigned to the aromatic protons. The peaks that appeared at 4.55 and 5.29 ppm are assigned to –O–CH₂–N– and Ar–CH₂–N–, respectively. The peak that appeared at 5.36 ppm is due to the vinyl protons of long alkyl side chain present in the cardanol skeleton. In addition, all other aliphatic protons appeared from 0.75 to 2.78 ppm. Figure S3 shows ¹³C NMR spectra of cardanol benzoxazine, carbonyl carbons appeared at 180 ppm, aromatic carbons appeared from 115 to 144 ppm, and aliphatic carbon atoms appeared from 14 to 36 ppm. The peak appearing at 130 ppm represents vinyl carbon of long aliphatic side chain.[31,32]

4.3. MALDI–Mass spectrum of CBz monomer

MALDI–Mass spectroscopy is an important technique used to determine the higher molecular weight of organic compounds. The formation as well as the molecular weight of CBz monomer is further confirmed by MALDI–Mass spectroscopy (Figure 4). The spectral analysis shows the molecular weight of the benzoxazine monomer as 1076, which is in good agreement with the theoretically calculated molecular weight value. Hence, above results of FTIR, ¹H & ¹³C NMR, and MALDI Mass confirm the successful formation of CBz monomer.[31]

Figure 4. MALDI–Mass spectrum of CBz.

4.4. TGA analysis

TGA thermograms of the neat polybenzoxazine and varying weight percentages of functionalized alumina and titanium dioxide-reinforced polybenzoxazine composites are presented in Figures 5 and 6 and Table 1. The percentage char yield value of neat polybenzoxazine is 13, whereas that of 1, 3, 5, and 7 wt% F-Al₂O₃ are 27, 44, 46, and 48, respectively, and for F-TiO₂ are 17, 19, 22, and 31, respectively. From the TGA analysis it is inferred that, as the weight percentages of the reinforcement increases, the thermal stability was also increased.[21] This is due to the presence of alumina and titania in the nanocomposite, that contributes to additional heat capacity and restricts the chain mobility of polybenzoxazine segments resulting from good adhesion between the nanoparticles and the surrounding polymer matrix, which stabilized the materials against thermal decomposition. Among the two reinforcements, the F-Al₂O₃ reinforced polybenzoxazine, show higher char yield at 700 °C. This is due to higher thermal stability of TiO₂ than that of alumina.[26,36]

Figure 5. TGA analysis of neat CPBz matrix and F-Al₂O₃/CPBz nanocomposites.

Figure 6. TGA analysis of F-TiO₂/CPBz nanocomposites.

Table 1. Thermal and dielectric properties of neat CPBz matrix and varying weight percentages of F-Al₂O₃ and F-TiO₂-reinforced polybenzoxazine nanocomposites.

Sample	Tg (°C)	Weight loss			Char yield (%) at 700 (°C)	Dielectric constant (K)
		10	20	30
		Temperature (°C)
Neat CBz	95	355	395	421	13	3.67
1 wt% F-Al2O3/CPBz	113	357	401	431	27	4.01
3 wt% F-Al2O3/CPBz	124	367	407	437	44	5.21
7 wt% Al2O3/CPBz	–	–	–	–	–	5.62
5 wt% F-Al2O3/CPBz	133	369	411	439	46	6.59
7 wt% F-Al2O3/CPBz	137	371	417	441	48	8.01
1 wt% F-TiO2/CPBz	162	330	401	430	17	6.1
3 wt% F-TiO2/CPBz	169	332	405	433	19	6.9
7 wt% TiO2/CPBz	–	–	–	–	–	7.5
5 wt% F-TiO2/CPBz	172	347	407	436	22	8.6
7 wt% F-TiO2/CPBz	176	357	420	455	31	10.2

4.5. DSC analysis

DSC data of neat polybenzoxazine matrix and different weight percentages of alumina and titania-reinforced polybenzoxazine nanocomposites are presented in Table 1. The Tg of neat polybenzoxazine and 1, 3, 5, and 7 wt% of alumina-reinforced nanocomposites are 95, 113, 124, 133, and 137 °C, respectively. When increasing the weight percentages of functionalized alumina, the Tg also increases. There are many factors which alter the Tg value of the polymer, among them one of the most important factors are molecular chain segment mobility, free volume, and cross linking density. As the weight percentages of alumina increases, the interaction between functionalized alumina nanoparticles and polybenzoxazine matrix increased, and in turn reduced the free volume. Hence, 7 wt% of F-Al₂O₃-reinforced polybenzoxazine shows higher Tg value than that of other samples. In the case of F-TiO₂ reinforced polybenzoxazine, the same phenomena were obtained. 7 wt% of F-TiO₂-reinforced polybenzoxazine shows the higher value of Tg (176 °C). Among the two reinforcements used for benzoxazine, the F-TiO₂-based polybenzoxazine nanocomposites possess the higher value of Tg than that of F-Al₂O₃-based polybenzoxazine nanocomposites.[26,36]

4.6. XRD analysis

XRD spectra of alumina, benzoxazine, and varying weight percentages of F-Al₂O₃ reinforced polybenzoxazine are shown in Figure 7. The XRD spectrum of Al₂O₃ shows the 2θ peaks at 25.31°, 34.89°, 37.43°, 42.84°, 52.12°, 56.88°, 65.81°, and 67.41° with orientation along (0 1 2), (1 0 4), (1 1 0), (1 1 3), (0 2 4), (2 0 4), (1 1 6), and (2 1 5) plane, respectively, confirming the existence of α-Al₂O₃. The neat polybenzoxazine displayed only a broad amorphous peak at 2θ = 19.61°, indicating the existence of amorphous phase. On the other hand, the diffraction pattern of F-Al₂O₃-reinforced polybenzoxazine witnessed a sharp and strong crystalline peaks corresponding to F-Al₂O₃ in the polybenzoxazine nanocomposites, and this confirmed the reinforcement of F-Al₂O₃ into polybenzoxazine.

Figure 7. XRD analysis of alumina, neat CPBz matrix and F-Al₂O₃/CPBz nanocomposites.

Figure 8 illustrates the XRD pattern of TiO₂ and F-TiO₂-reinforced polybenzoxazine nanocomposites. In the XRD of TiO₂, the 2θ peaks appeared at 25.49°, 37.98°, 48.20°, 54.01°, 55.33°,62.71°, 68.73°, 70.2°, and 75.26° with orientation along (101), (004), (2 0 0), (1 0 5), (2 1 1), (2 0 4), (1 1 6), (2 2 0), and (2 1 5), respectively, confirm the existence of anatase phase of TiO₂.[30,33] The average crystallite size of about 35 nm of TiO₂ was calculated using Scherer’s formula. In Figure 11, the diffraction pattern of F-TiO₂-reinforced polybenzoxazine nanocomposites system shows the appearance of sharp and strong peak at 2θ = 19.29°, and this suggests the complete dispersion of F-TiO₂ reinforced into the polybenzoxazine nanocomposites (Figure 11). The XRD pattern of all the F-TiO₂-reinforced polybenzoxazine nanocomposites samples show a similar pattern, which implies that F-TiO₂ is uniformly distributed in the polybenzoxazine nanocomposites.

Figure 8. XRD analysis of TiO₂ and F-TiO₂/CPBz nanocomposites.

Figure 9. SEM images of Al₂O₃ and TiO₂ (a and d), F-Al₂O₃ and F-TiO₂ (b and e) and 5 wt% F-Al₂O₃ and F-TiO₂ reinforced CPBz nanocomposites (c and f).

Figure 10. TEM images of (a) 5 wt% F-Al₂O₃ and (b) F-TiO₂ reinforced CPBz nanocomposites.

Figure 11. Dielectric constant of neat CPBz matrix and F-Al₂O₃/CPBz nanocomposites.

4.7. Morphological studies

Figure 9 shows the SEM micrograph of alumina and titania nanoparticles ((a) and (d)), F- Al₂O₃ and F-TiO₂ ((b) and (e)), 5 wt% of F-Al₂O₃ and F-TiO₂-reinforced polybenzoxazine nanocomposites ((c) and (e)). The SEM images of alumina and titania shows irregular shape, whereas, the surface of the functionalized alumina and titania shows the different morphology from neat nanoparticles, where neat nanoparticles are covered by APTMS. [26] The images of F-Al₂O₃ and F-TiO₂ reinforced polybenzoxazine nanocomposites shows the homogeneous nanoparticles at the nanoscale level in the polybenzoxazine matrix.

Figure 10((a) and (b)) shows the TEM images of 5 wt% of F-Al₂O₃ and F-TiO₂-reinforced polybenzoxazine nanocomposites. The images show uniform dispersion and dimension of nano-sized materials embedded within a polybenzoxazine matrix. This further confirmed that the hybrid films showed good interfacial interaction between the reinforcements (F-Al₂O₃ and F-TiO₂) and the polybenzoxazine matrix. The nanometer-level dispersion of F-Al₂O₃ and F-TiO₂ within the polybenzoxazine matrix was also ascertains the thermal stability of the resulting hybrid materials.[26,31,35,37]

4.8. Dielectric constant

Figures 11 and 12 and Table 1 presents the dielectric properties of neat polybenzoxazine, 7 wt% alumina and titania-reinforced polybenzoxazine nanocomposites and varying weight percentages of F-Al₂O₃ and F-TiO₂-reinforced polybenzoxazine nanocomposites. The value of dielectric constant of neat polybenzoxazine is 3.6, whereas the reinforcement of alumina and varying weight percentages F-Al₂O₃-reinforced polybenzoxazine nanocomposites are 4.1, 5.2, 5.6, 6.5, and 8.1, respectively. The value of dielectric constant of F-Al₂O₃ reinforcement nanocomposites is higher than that of neat polybenzoxazine and alumina. This is due to the polar groups present in the polybenzoxazine and can orient themselves, resulting in a higher value of dielectric constant. When the frequency was increased above 1 MHz, the polarization groups fails to settle itself and the values of dielectric constant of nanocomposites begins to decrease at increasing frequencies. The value of dielectric constant of titania and varying weight percentages F-TiO₂-reinforced polybenzoxazine nanocomposites are 7.5, 6.1, 6.9, 8.6, and 10.2, respectively. The value of dielelectric constant increases with increasing weight percentages of F-TiO₂ due to high polarizability of TiO₂, when compared to that of Al₂O₃.[22,26–28,38–42]

Figure 12. Dielectric constant of F-TiO₂/CPBz nanocomposites.

4.9. Optical properties

UV transmittance of F-Al₂O₃ and F-TiO₂-reinforced polybenzoxazine nanocomposites are shown in Figures 13 and 14, respectively. The UV-shielding efficiency of the nanocomposites increases as the weight % of F-Al₂O₃ and F-TiO₂ are increased. The UV-shielding values of neat PBz, 1, 3, 5 & 7 wt% F-Al₂O₃-reinforced polybenzoxazine nanocomposites are 76, 78, 80, 82, and 85%, respectively, and that of 1, 3, 5 & 7 wt% of F-TiO₂-reinforced polybenzoxazine nanocomposites are 82, 86, 90, and 93%, respectively. Among the varying weight percentages of F-Al₂O₃ and F-TiO₂ reinforced nanocomposites, 7 wt % of F-TiO₂/PBZ shows the superior UV-shielding properties (93%) than that of F-Al₂O₃-reinforced polybenzoxazine nanocomposites. It is proposed that UV-shielding properties of F-TiO₂-reinforced polybenzoxazine nanocomposites was higher, as compared to that of F-Al₂O₃-reinforced polybenzoxazine nanocomposites. As reported from the previous literatures, the band gap of Al₂O₃ and TiO₂ are 8.28 and 3.2 eV, respectively.[27,28] From the solar spectrum, the UV region was covered as near UV (315–400 nm) and far UV (280–380 nm), respectively. Based on the band gap illustration of the Al₂O₃ have lower shielding efficiency, whereas the TiO₂ possesses higher refractive index and higher shielding efficiency.[42,43]

Figure 13. UV transmittance of neat CPBz and F-Al₂O₃/CPBz nanocomposites.

Figure 14. UV transmittance of F-TiO₂/CPBz nanocomposites.

Scheme 1. Synthesis of CBz monomer.

Scheme 2. Preparation of F-Al₂O₃ and F-TiO₂/CPBz nanocomposites.

5. Conclusion

The varying weight percentages of F-TiO₂ and F-Al₂O₃-reinforced polybenzoxazine nanocomposites (1, 3, 5 & 7 wt%) were developed and their thermal, dielectric, and UV shielding properties were studied. 7 wt% F-Al₂O₃-reinforced nanocomposites possesses improved thermal properties due to effective interaction between the polybenzoxazine and F-Al₂O₃. The homogenous level of dispersion of the composites was confirmed by SEM, TEM, and XRD analysis. Data obtained from dielectric and UV shielding studies show that 7 wt% F-TiO₂-reinforced composites possesses higher value of dielectric constant (10.2) and UV shielding behaviour (93%) than those of 7 wt% F-Al₂O₃-reinforced nanocomposites.

Supplementary material

The supplementary material for this paper is available online at http://dx.doi.10.1080/15685551.2015.1092014.

Acknowledgments

The authors also thank R.Sasikumar, M.Ariraman, Polymer Composite Lab, Department of Chemical Engineering, Anna University, H. Madhesan, School of Advanced Science, VIT University, Vellore and Rama Subramanian, MFL, Chennai for their support.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work was supported by the University of Grants Commission (UGC) [grant number 41-233/2012(SR) dated 13/07/2012].