Synthesis and Properties of Phenylmethylsilicone/Organic Montmorillonite Nanocomposites by in-situ Intercalative Polymerization

Synthesis and Properties of Phenylmethylsilicone/Organic Montmorillonite Nanocomposites by in-situ Intercalative Polymerization Synthesis and Properties of Phenylmethylsilicone/Organic Montmorillonite Nanocomposites by in-situ Intercalative Polymerization Xinhua Yuan *, Wenhua Guo, Xiao Jiang, Yongqiang Liu, Shulin Pan, Jie Hu, and Songjun Li School of Material Science and Engineering, Jiangsu University, Zhenjiang, Jiangsu, 212013, People s Republic of China Summary Using methylphenyl dichlorosilane, methyl trichlorosilane cetyltrimethylammonium bromide (CTAB) as organic treatment agent, phenylmethylsilicone/organic montmorillonite (OMMT) nanocomposites were prepared by in-situ intercalative polymerization. The internal structure and morphology of the nanocomposites were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM) and transmission electron microscope (TEM). Mechanical properties, high temperature resistance and barrier performance for gas and water were also studied. The results show that molecules of silicone chains insert into the layer of montmorillonite (MMT), and the interlayer distance of MMT is expanded effectively after polymerization of phenylmethylsilicone prepolymer and methyl methacrylate, even forming exfoliated nanocomposites. Keywords: Montmorillonite; Methyl phenyl silicone resin; in-situ intercalative polymerization; Exfoliated; Nanocomposite 1. Introduction Polymer-layered silicate nanocomposites(plsns) have attracted great interest because of their superior properties comparing with pure polymer 1-4. Methods of exfoliation of silicate layers are well developed for application to many polymers. Since Usuki and coworkers first reported the superior Nylon 6 montmorillonite(mmt) nanocomposite 5,6, a large number of studies have been performed in this field, and many PLSNs were synthesized, such as epoxy 7, polyimide 8,9, polystyrene 10 and polypropylene 11,12. Frequently, organic modification of a clay is necessary to increase the compatibility with a polymer and to enlarge the interlayer distance. Cetyltrimethylammonium bromide(ctba) was intercalated into *Corresponding author. Tel.: +86-13775549209; fax: +86-511-88780191. E-mail: yuanxh1975@yahoo.com.cn. Smithers Information Ltd., 2014 layers of Na-MMT by cation exchange to prepare OMMT. Silicone has many excellent properties, such as high temperature resistance, weatherability, hydrophobic property, electrical insulation, but with poor solvent resistance and mechanical properties. Polymer/ clay nanocomposites can solve these problems. In the present research, using ultrasonic technology, phenylmethylsilicone/ommt nanocomposites were prepared by in-situ intercalative polymerization. The internal structure and morphology of the nanocomposites were characterized by XRD, SEM and TEM analyses. Mechanical properties, high temperature resistance and barrier performance for water were also studied. 2. Experimental 2.1 Materials Methylphenyl dichlorosilane, methyl trichlorosilane were purchased from Jinzhou Minghao Pharm & Chm Co., Ltd (Zhejiang, China). Sodium montmorillonite(na-mmt) was provided by Zhejiang Fenghong Clay Chemicals Co., Ltd (Zhejiang, China) and was organically modified by CTBA. Triethanolamine, toluene were purchased from sinopharm Chemical Reagent Co., Ltd (Beijing, China) and were used without further purification. Deionized water was homemade. 2.2 Preparation of Phenylmethylsilicone/OMMT Nanocomposites In a two-neck(250 ml) flask equipped with a stirrer and a constant pressure dropping funnel, nanocomposites were prepared by first adding methylphenyl dichloroesilane and methyl trichlorosilane to the mixture of toluene and deionized water. In Polymers & Polymer Composites, Vol. 22, No. 5, 2014 471

Xinhua Yuan, Wenhua Guo, Xiao Jiang, Yongqiang Liu, Shulin Pan, Jie Hu, and Songjun Li order to allow the reaction to proceed to completion, the mixture was stirred for 12 h. The reaction system was taken into water bath again after removing the acid water and washing the oil layer to the neutrality by deionized water and stirred for 0.5 h after OMMT was added. After stirring the mixture for some time under ultrasonic condition, the reaction system was taken into water bath again. Suitable amount of triethanolamine was added and the reaction system was stirred for an additional 10 min. The mixture was poured into a homemade open rectangular mold with dimension 110 mm 80 mm and 15 mm thickness followed by curing process in a vacuum oven at 120 C for 24 h. Finally, the polymer/ommt nanocomposites were obtained. 2.3 Measurements and Characterizations 2.3.1 Morphological Analysis Series FTIR was recorded on a Nicolet NEXUS470 instrument (Nicolet Instrument, Thermo Company, USA). The sample was made by potassium bromide-disk technique. For each sample, the series FTIR runs were repeated three times. Wideangle X-ray diffraction (WXRD) measurement was carried out using D/max 2500VB3+/PC (Rigaku, Japan) equipped with a Ni-filtered monochromatic Cu-Kα radiation (λ = 1.5418 Å) at a scanning rate of 1 /min and divergence slit 1. Measurements were made to examine the interlayer activity in the composite as prepared. The plates of silicone/ OMMT nanocomposites which were produced during the molding process have smooth surface. Therefore a rectangle shaped specimen (10 mm 5 mm 1 mm) were cut from these plates and directly analyzed by X-ray analysis. Bragg s Law (nλ=2dsinθ) was used to calculate the crystallographic spacing. A JEOL JSM-6480 (Japan) scanning electron microscope was used to observe the particle size of MMT and particlematrix adhesion in the cured composite on the fracture surface. The specimens were coated by gold. TEM analysis was used to confirm the morphological information obtained from the XRD data on the platelet dispersion and distribution. The morphology cannot be fully characterized only by XRD analysis. The absence of scattered intensity peaks in the XRD diagrams can not always surely demonstrate achievement of the disordered intercalated or the exfoliated structures. The ultra-thin TEM specimens from the powder of specimen were immersed in the alcohol and dispersed by ultrasonic. The solution was dripped on copper grids to be viewed with a JEOL JEM-2100 electron microscope at an accelerating voltage of 200 kv. 2.3.2 Thermal Analysis Differential scanning calorimetric (DSC) data were taken with a Netzsch PHOENIX DSC204 instrument. About 10 mg of the sample was used to be encapsulated in aluminum pans. The measurements were conducted in the temperature range of 303 923 K. A scan speed of 10 K/min was used in the measurements. Thermogravimetric (TG) data were acquired with a Netzsch STA 409 instrument. 2.3.3 Measurements of Barrier Properties for Water To determine barrier properties of water, rectangle shaped specimens (20 mm 8 mm 2 mm) of silicone/ommt nanocomposites were made. The specimens were heated in deionized water at 80 C for 0.5 h. Water adsorption rate (a) was used to denote barrier property of water and defined as follows: a = m 2 m 1 m 1 100% where, m 1 (g) and m 2 (g) represent the weight of specimen before and after boiled, respectively. 2.3.4 Mechanical Properties The tensile test was conducted on WDS electronic tensile testing machine (Chengde Precision Testing Machine Co., Ltd., China) at room temperature. The test specimens were cut in the shape 100 mm 10 mm 4 mm. Five samples were tested and the average value was taken. The tensile test speed was 5 mm/min. The compressive test was taken on WDW- 11 Computer-controlled electronic universal testing machine (Jinan Shidai Shijin Instrument Co., Ltd., China), and the loading rate is 2 mm/min. All five samples were shaped for 30 mm 10 mm 4 mm and the compression strength was taken by average value. 3. Result and Discussion 3.1 Silicone/OMMT Nanocomposites Morphological Characterization Figure 1 shows the FTIR spectra of PLS nanocomposites with different ultrasonic time. Strong bands characteristic from a free absorption peak (-OH) in Si-OH are observed at ν=3650,3750 cm -1. The stretch vibration absorption peak of Si-OH is between 3200-3600 cm -1.The peak at 2960 cm -1 is from C-H stretching in CH-Si. The sharp absorption bands at 740-850 cm -1 and 1270 cm -1 are from N-O and Si-CH 3. There is a strong absorption peak near 1431 cm -1, which is from the vibration absorption peak of benzene ring in Si-C 6 H 5. A wide and strong absorption band between 1000-1135 cm -1 which is the characteristic absorption peak of silicone resin is the antisymmetrical stretch vibration absorption spectra of Si-O-Si. As the FTIR spectra show, it is gained hydroxyl-terminated phenylmethylsilicone (Figure 2). Figure 3 shows the XRD spectra of the OMMT and PLSN with different ultrasonic time. The peak in XRD patterns corresponds to the (001) reflection peak of layered silicate. In Figure 3, the d-spacing of OMMT 472 Polymers & Polymer Composites, Vol. 22, No. 5, 2014

Synthesis and Properties of Phenylmethylsilicone/Organic Montmorillonite Nanocomposites by in-situ Intercalative Polymerization calculated using Bragg s Law is about 23.62 Å on a base of 2θ=3.74. For the PLSN with different ultrasonic time, there are no diffraction peak at low angle region of 1-10, which means that the d-spacing of OMMT within the nanocomposite is at least over 80 Å. This result indicates that molecules of silicone chains have intercalated into the layers of OMMT, and the interlayer distance of OMMT is expanded effectively after polymerization of methylphenyl dichlorosilane and methyl trichlorosilane, forming exfoliated nanocomposites. The most powerful and direct evidence to describe whether the nanocomposite is exfoliated or intercalated is by means of TEM. TEM spectra of a thin film of OMMT/silicone nanocomposite are shown in Figure 4. The overall picture shows that the MMT layers are not occupying the full volume and large regions of pure silicone are visible. The molecules of silicone chains have inserted into the interlayer of MMT, forming the structure of light and dark stripes. The layers are not orderly intercalative structure in the whole region, but basically exfoliated morphology. And the exfoliation degree will be increased as the ultrasonic time is prolonged. 3.2 Thermal Property TGA analyses of silicone/ommt nanocomposites with different OMMT content are shown in Figure 5. The overall thermal resistances of nanocomposites are lower than that of pure silicon. The initial decomposition temperature of PLS nanocomposite are decreased due to the intercalation agent and oligomer in the interlayer of OMMT. And the interlayers which acted as physical crosslinked points are messily dispersed in the resin substrate, and have few restriction of polymer chains. The silicone/ommt nanocomposite containing 6 wt.% OMMT has excellent temperature resistance. However, when the OMMT content is over 6 wt.%, the thermal Figure 1. FTIR spectra of pure silicone and PLSN containing 6 wt.% OMMT. (1) no OMMT, (2) mechanical stirring for 30 min, (3) mechanical stirring for 30 min+ultrasonic for 5 min, (4) mechanical stirring for 30 min+ultrasonic for 10 min, (5) mechanical stirring for 30 min+ultrasonic for 15 min, (6) mechanical stirring for 30 min+ultrasonic for 20 min Figure 2. Structure of the phenylmethylsilicone Figure 3. XRD spectrum of OMMT and PLSN containing 6 wt.% OMMT. (1) OMMT, (2) mechanical stirring for 30 min, (3) mechanical stirring for 30 min+ultrasonic for 5 min, (4) mechanical stirring for 30 min+ultrasonic for 10 min, (5) mechanical stirring for 30 min+ultrasonic for 15 min, (6) mechanical stirring for 30 min+ultrasonic for 20 min Polymers & Polymer Composites, Vol. 22, No. 5, 2014 473

Xinhua Yuan, Wenhua Guo, Xiao Jiang, Yongqiang Liu, Shulin Pan, Jie Hu, and Songjun Li Figure 4. TEM spectrograms of PLSN containing 6 wt.% OMMT. (a) mechanical stirring for 30 min, (b) mechanical stirring for 30 min+ultrasonic for 5 min, (c) mechanical stirring for 30 min+ultrasonic for 10 min, (d) mechanical stirring for 30 min+ultrasonic for 15 min, (e) mechanical stirring for 30 min+ultrasonic for 20 min (a) (b) (c) (d) (e) Figure 5. Effect of OMMT content on thermal property of PLS composites with ultrasonic 20 min because of the solvent volatilization, there are some pores in resin which have effect on the thermal property of PLSNs (Figure 6). property of composites begins to decline. This may be due to the enhanced amount of primary particles and the inhomogeneous dispersion of OMMT as increasing OMMT content, which leads to increased defects number. These make PLS nanocomposite cannot maintain its initial shape in the process of combustion and result in the decline of thermal resistance. And the PLSNs are prepared via solution intercalation, 3.3 Barrier Property for Water Comparing to pure polymer or mechanical blending composites, PLS nanocomposites has better barrier properties for gas and liquid. This may be due to the fact that the silicate layers have a large aspect ratio. When these layers of MMT well disperse in polymer matrix, the diffusion movement of gas or liquid molecules has to bypass these silicate layers. Therefore, the increase of efficient paths enhances the barrier properties for gas and liquid. The water absorption rate basically decreases with the increasing of OMMT content, which indicates that the barrier property for water of silicone/ommt nanocomposites is increased. The silicone/ommt nanocomposites in the study were prepared by in-situ 474 Polymers & Polymer Composites, Vol. 22, No. 5, 2014

Synthesis and Properties of Phenylmethylsilicone/Organic Montmorillonite Nanocomposites by in-situ Intercalative Polymerization solution intercalative polymerization. Therefore, solvent evaporation may leave some pores in nanocomposites which were presented in SEM images of Figure 6. These pores will obviously affect the barrier property of nanocomposites, so that the curve of the water absorption rate vs. OMMT content is not linear. When the silicone/ OMMT nanocomposite contains OMMT over 4 wt.%, the barrier property for water hardly changes. This maybe due to that only intercalation or exfoliated nano-film layer can play a role to barrier property for water, and micron or submicron particles have no barrier effect on barrier property. clay existing in these systems. These enhancements are directly attributable to the reinforcement provided by the dispersed silicate nanolayers. The silicone chains which intercalated Figure 6. SEM spectrograms of PLS nanocomposite into OMMT layers are limited by the dipole interaction and space restriction of OMMT layers, which results in the enhancement of tensile and compressive strength and the decrease Compared the line (a) and (b) in Figure 7, the water absorption rates of PLSN made by hydrolysis and condensation of monomers are higher than which made by phenylmethylsilicone. It is because that the exfoliation degree of (a) is considerably less than the (b) s. The interlayers are messily dispersed in the resin substrate which have few better barrier properties for gas and liquid. Figure 7. Effect of OMMT content on the barrier properties for water 3.5 Mechanical Properties Flexural test was performed according to the GB/T1040-92 by WDS Electronic tensile testing machines, the loading rate was 2 mm/min. Compression test was performed according to the GB1041-79 by WDW-11 computercontrolled electronic universal testing machine, the loading rate was 5 mm/ min. The results are showed in Table 1. The tensile and compressive tests were carried out to examine the influence of the inclusion of organoclay on the mechanical properties of nanocomposites. Effects of organo- MMT content on the tensile strength and compressive strength of nanocomposites are described in Table 1. The presence of organoclay substantially increases the tensile strength and compressive strength in all composites relative to the pure silicone despite the small amounts of true Table 1. Mechanical properties of PLS nanocomposites with different OMMT content OMMT content/wt.% 0 2 4 6 8 10 (a) PLSN made by phenylmethylsilicone (b) PLSN made by hydrolysis and condensation of monomers Tensile 1.247 1.846 5.446 6.264 3.751 3.171 Elongation/% 2.65 2.24 2.10 1.85 1.72 1.51 Compressive 2.834 3.786 11.503 10.767 9.362 5.652 Tensile 5.172 6.453 7.692 8.021 6.103 5.647 Elongation/% 3.84 3.45 3.13 2.91 2.83 2.65 Compressive 3.232 5.926 14.235 12.823 9.767 6.256 Polymers & Polymer Composites, Vol. 22, No. 5, 2014 475

Xinhua Yuan, Wenhua Guo, Xiao Jiang, Yongqiang Liu, Shulin Pan, Jie Hu, and Songjun Li of elongation at break of composites. The sheet OMMT particles slip by external force along the force-oriented direction, which can play a similar role of plasticizer to increase mechanical properties of nanocomposites. Similar to the decline of temperature resistance, the decrease of mechanical properties may be also due to the enhanced amount of primary particles and the inhomogeneous dispersion of OMMT as increasing OMMT content, which leads to increased defects number. These defects are prone to resulting in stress concentration and leading to strength decreasing. Compared the (a) and (b) in Table 1, the mechanical properties of PLSN made by hydrolysis and condensation of monomers are better than which made by phenylmethylsilicone. As the PLSNs of (b) were prepared by monomers in-situ intercalation polymerization, whereas the intermolecular interaction and the molecular chain winding density are both higher than the (a) s. 4. Conclusions Organoclay was prepared by intercalating ammonium cations of CTAB through an ion exchange process. Phenylmethylsilicone/ OMMT nanocomposites were prepared by in-situ intercalative polymerization. A morphological hierarchy was characterized by XRD, SEM and TEM spectra. Mechanical properties, high temperature resistance and barrier performance for water were also studied. The results show that silicone chains have inserted into the MMT layers, and the interlayer distance of MMT is expanded effectively after polymerization of phenylmethylsilicone prepolymer and methyl methacrylate, even forming exfoliated nanocomposites. OMMT content plays a great effect on the temperature resistance and mechanical properties of nanocomposites. Acknowledgements The work was supported by National Natural Science Foundation of China (20207003, 20704019), Major Program from the Science and Technology Council of Zhejiang Province and Jiangsu University Foundation for Excellent Young Teacher. The authors wish to express their appreciation to the Analytical Center at Jiangsu University for the analyses of SEM, XRD and TEM. References 1. Cypes S.H., Saltzman W.M., Giannelis E.P., Organosilicatepolymer drug delivery systems: controlled release and enhanced mechanical properties, J. Control Release, 90 (2003) 163-169. 2. Jiawen Xiong, Yunhang Liu, Xiaohui Yang, Thermal and mechanical properties of polyurethane/ montmorillonite nanocomposites based on a novel reactive modifier, Polymer Degradation and Stability, 86 (2004) 549-555. 3. Akat H., Tasdelen M.A., Yagci Y. et al., Synthesis and characterization of polymer/clay nanocomposites by intercalated chain transfer agent, European Polymer Journal, 44 (2008) 1949-1954 4. Miroslav Huskic, Majda Zigon, PMMA/MMT nanocomposites prepared by one-step in situ intercalative solution polymerization, European Polymer Journal, 43 (2007) 4891-4897 5. Usuki A., Kawasumi M., Kojima Y., Okada A., Kurauchi T., Kamigaito O., Swelling behavior of montmorillonite cation exchanged for u-amino acids by 3-caprolactam, J. Mater. Res., 8 (1993) 1174-1178. 6. Usuki A., Kojima Y., Kawasumi M., Okada A., Fukushima Y., Kurauchi T., et al., Synthesis of nylon 6-clay hybrid, J. Mater. Res., 8 (1993) 1179-1184. 7. Lan T., Kaviratna P.D., Pinnavaia T.J., Mechanism of clay tactoid exfoliation in epoxyeclay nanocomposites, Chem. Mater., 7 (1995) 2144-2150. 8. Abdalla M.O., Dean D., Campbell S., Viscoelastic and mechanical properties of thermoset PMR-type polyimideeclay nanocomposites, Polymer, 43 (2002) 5887-5893. 9. Magaraphan R., Lilayuthalert W., Sirivat A., Schwank J.W., Preparation, structure, properties and thermal behavior of rigidrod polyimide/montmorillonite nanocomposites, Compos. Sci. Technol., 61 (2001) 1253-1264. 10. Vaia R.A., Jandt K.D., Kramer E.J., Giannelis E.P., Kinetics of polymer melt intercalation, Macromolecules, 28 (1995) 8080-8085. 11. Okamoto M., Nam P.H., Maiti P., Kotaka T., Nkayama T., Takada M., et al., Biaxial flow-induced alignment of silicate layers in polypropylene/clay nanocomposite foam, Nano Lett., 1 (2001) 503-505. 12. Wang Wenyi, Zeng Xiaofei, Wang Guoquan, Chen Jianfeng, Preparation and Properties of Polypropylene Filled with Organo-Mont-morillonite Nanocomposites, Journal of Applied Polymer Science, 100 (2006) 2875-2880. 476 Polymers & Polymer Composites, Vol. 22, No. 5, 2014