STUDY OF PROCESSING AND MECHANICAL BEHAVIOR OF PP/CLAY NANOCOMPOSITES PREPARED BY MELT BLENDING

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2nd International Conference on Ultrafine Grained & Nanostructured Materials (UFGNSM) International Journal of Modern Physics: Conference Series Vol.

1 2nd International Conference on Ultrafine Grained & Nanostructured Materials (UFGNSM) International Journal of Modern Physics: Conference Series Vol. 5 (2012) World Scientific Publishing Company DOI: /S STUDY OF PROCESSING AND MECHANICAL BEHAVIOR OF PP/CLAY NANOCOMPOSITES PREPARED BY MELT BLENDING SAREH MOSLEH SHIRAZI Department of Materials Science and Engineering, Shiraz University, Shiraz, Iran ssmosleh@gmail.com KAMAL JANGHORBAN Department of Materials Science and Engineering, Shiraz University, Shiraz, Iran Janghor@shirazu.ac.ir In this research, the melt blending technique was used to prepare various polypropylene (PP) based nanocomposites containing 1,3,5,7 wt% montmorillonite (MMT). A commercial organoclay (denoted K-10) served as the filler for PP matrix and the polypropylene grafted maleic anhydride (PP-g-MA) was used as compatibalizer. The morphology of the nanocomposites was studied by X- ray diffraction (XRD), results of which showed that the nanocomposites are best described as intercalated-exfoliated systems. PP/MMT nanocomposites showed good thermal stability in the TGA analysis. Introducion of ~ 3% MMT in the nanocomposites increased the onset temperature of the degradation by 27.5 o C compared to that of pure PP. Test results showed that PP/clay nanocomposites had an enhanced tensile strength, hardness and decreased wear rates. Keywords: PP/clay nanocomposites, Melt blending, wear rates, intercalated-exfoliated 1. Introduction Researchers continue to show increased interest in the study of polymer-layered silicate nanocomposites mainly because these nanocomposites exhibit a wide range of improved properties after modification [1]. Many nanofillers and compatibilizing agents have been used successfully in the synthesis of these nanocomposites. New synthesizing techniques such as the melt blending technique, in situ polymerization, and melt intercalation have Corresponding Author: Tel.: ; fax: address: ssmosleh@gmail.com (S. Mosleh) 536

Study of Processing and Mechanical Behavior of PP/Clay Nanocomposites Prepared by Melt Blending 537 been used to develop different materials systems [2].

2 Study of Processing and Mechanical Behavior of PP/Clay Nanocomposites Prepared by Melt Blending 537 been used to develop different materials systems [2]. The substantial improvements in mechanical, thermal, and physical properties of polymer-layered silicate nanocomposites have widen the use of these polymers in industry. In the late 1980s, the Toyota Motor Company commercialized a timing belt cover made from nylon-6/nanoclay composites for one of its car models demonstrating that thermoplastic nanocomposites are one of the most promising materials for usage in domestic and industrial applications [3]. More recently researchers Kojima et al. [4] and Kato et al. [5] showed that for nylon-6 (N6)/MMT nanocomposites very small amounts of layered silicate loadings, approximately <5 wt.%, resulted in pronounced improvements of thermal and mechanical properties. These findings are in agreement with findings in our study. Effective dispersion of the nanoclays within the polymer matrix results in enhancing the mechanical properties. Morphological analyses of these structures reveal that they can be categorized into three general types: a conventional composite where the nanoclay acts as conventional filler, intercalated nanocomposite which consists of a regular insertion of polymer between the silicate layers, and exfoliated nanocomposite where 1-nm thick silicate layers are dispersed within the polymer matrix [3, 6]. These types of nanocomposite structures are shown in Fig. 1. Fig. 1 Types of polymer-layered silicate composites [1]. (a) Phase separated (microcomposite), (b) Intercalated (nanocomposite), and (c) Exfoliated (nanocomposite) Bharadwaj et al. suggest that the mechanical properties of a virgin polymer are enhanced when exfoliation occurs with extremely low concentrations of nanoclays (1 3 wt. %) as compared to conventional phase-separated composites of a filler material in a polymer. The large surface area available for interactions with the polymer matrix coupled with high aspect ratio is responsible for the enhancement in properties [7] (Fig. 2).

3 538 S. M. Shirazi & K. Janghorban Fig. 2 Structure of 2:1 phyllosilicates (MMT, Hectorite, Saponite) [3] Similarly, in a recent study we have found substantial improvements in the mechanical properties of a nanophased composite at low weight percentages (1-5 wt. %) [8]. The mechanical properties improved with an increase in nanoclay loading up to a threshold of 5 wt. %; thereafter, the material properties degraded. This improvement was coupled with a trend in which the material tends to harden [8, 9]. The hardening effect suggests that the material may be used as a bearing surface; however, its thermal barrier and tribological properties needs to be evaluated. The authors take cognizance of the fact that previously the incorporation of nanosize particles like titanium dioxide (TiO 2) [10], silicon oxide (SiO 2) [11], zirconium oxide (ZrO 2) [12], silicon carbide (SiC) [13], silicon nitride (Si 3N 4) [14], and aluminum oxide (Al 2O 3) [15, 16] to a polymer matrix has lead to enhancement in wear resistance. It is expected that incorporation of organoclays at nanolevel will also improve the wear properties of nanocomposites. In this study, the influence of nanoclay addition to a polypropylene (PP) matrix on the mechanical properties of clay polypropylene nanocomposites are investigated. 2. Experimental 2.1. Materials and preparation of nanocomposite specimens The materials used in this study were clay, polypropylene and compatibilizer (PP-g-MA). A commercial organoclay (denoted K-10) which is a natural montmorillonite was obtained from Fluka Company.Polypropylene (PP10800) produced by Iran petrochemical complex and PP-g-MA produced by Aldrich were used. All nanocomposites were prepared using melt blending in a blender order at 70 rpm and 175 o C for 10 min. After 10 min of blending, the mixture was pressing at 5 bar for 5 min. The composition of the nanocomposites is given in Table 1.

4 Study of Processing and Mechanical Behavior of PP/Clay Nanocomposites Prepared by Melt Blending 539 Specimen, s Code PP NC1 NC3 NC5 NC7 Table 1. Composition of PP/Clay nanocomposites PP (wt %) PP-g-MA (wt %) MMT (wt %) Nanocomposite characterization X-ray diffraction patterns were obtained using a D8-Advance diffractometer using monochromated Cu-Kα radiation. (λ= nm, 40 kv, 30 ma) at room temperature. The samples were scanned from 2 o to 10 o (2θ) in steps of 0.02 o using a scanning rate of 0.02 o /min. X-ray diffraction patterns of K-10 clay and polypropylene composites containing 1, 3, 5 and 7 wt.% K-10 nanoclay were prepared to characterize formation of nanocomposites with addition of organoclay Thermal stability (TGA) Thermogravimetric analysis, TGA, was carried out using a PL-1500 unit under air at a scan rate of 20 o C per minute from room temperature to 650 o C Tensile test Tensile tests on the nanocomposite specimens were performed using the Instron Tensile Tester fixed with a 20 KN load cell. The tensile testing was carried out on specimens in accordance with the ASTM D 832 testing standard Hardness test The Vickers hardness of the virgin and nano-infused polypropylene specimens was determined using a Leitz microhardness tester. Specimens of dimension mm 3 were indented with a 100-gf load for a period of 5 s. The diagonals of the indentation were measured and the Vickers hardness was automatically computed and read of a digital display. Five specimens from each weight percent category were subjected to the above tests.

5 540 S. M. Shirazi & K. Janghorban 2.6. Wear test Pin-on-disc wear test was carried out, using locally manufactured tribometer, in accordance with ASTM G-99 standard. The specific wear rate of the conventional composites and nanocomposites was determined at a constant contact load of 0.15 Kgf and sliding velocity of 0.07 m/s for the sliding distance of 100 m. 3. Results and discussion 3.1. X-ray characterization XRD pattern of K-10 clays and of clay polypropylene nanocomposites are shown in Fig. 3. The K-10 clay shows a distinct peak at the 2θ value of 3.3 o. No distinct peaks were found in the polypropylene nanocomposites containing different weight fractions of montmorillonite. During mixing, the polymer infuses and intercalates between the intergallery spacing of layered silicates and separates the clay layers gradually. The disappearance of peak indicates the separation of clay layers and the formation of intercalated or exfoliated nanocomposite. The final confirmation can be achieved only by analyzing transmission electron micrographs.similar behavior has been reported previously and TEM results showed that the structure of the modified nanocomposites changed from an exfoliated structure at 1 wt% nanoclay loading to an intercalated structure at 7 wt% nanoclay loading. [17] Fig. 3. X-ray diffraction pattern of (a) MMT K-10, (b)plane PP, (c)nc1, (d) NC3, (e) NC5, and (f) NC7

6 Study of Processing and Mechanical Behavior of PP/Clay Nanocomposites Prepared by Melt Blending TGA characterization of nanocomposites The thermal stability of polymer/mmt nanocomposites are usually studied by Thermogravimetric analysis (TGA). One of the parameters that is of interest from the TGA curves is the onset of the degradation, which is usually taken as the temperature at which 10% degradation occurs (T 0.1 ) and reported by instrument. The data are tabulated in Table 2 and shown graphically in Fig.4. Weight ( wt%) Sample T 0.1 ( o C) Temprature ( o C) Fig. 4. TGA curves of the clay polypropylene nanocomposites Table 2. TGA data for the PP/Clay nanocomposites PP NC NC NC PP NC1 NC3 NC5 NC7 NC As shown in Fig.4 and Table 2, PP nanocomposites show enhanced thermal stability. The onset temperature increases by 27.5 o C at 3% clay loading, while at higher clay loading, 5 and 7%, the onset temperature of the nanocomposites are 12 and 5.5 o C higher than pure PP. The enhanced thermal stability of the PP/clay nanocomposites is attributed to the lower permeability of oxygen and the diffusibility of the degradation products from the bulk of the polymer caused by the exfoliated clay in the composites Tensile test Tensile stress strain curves for the plane PP and nanocomposites are shown in Fig. 5. Comparison of the slopes of the plane and nanocomposite structures in the elastic region indicates an increase in gradient. This increase in slope suggests an increase in the material stiffness with an increase in nanoclay loading up to 5 wt. %. The addition of nanoclay significantly increased the tensile strength of plane PP by 22% in NC5. The nanoclay is intercalated by the PP polymer chains and confines the segmental movement

7 542 S. M. Shirazi & K. Janghorban of the PP macromolecules resulting in increased compressive modulus. In NC7 the tensile strength decreased which could be due to the agglomeration of nanoclay in the PP matrix. Stress (MPa) Strain Fig. 5. Tensile stress strain curves of clay polypropylene nanocomposite 3.4. Hardness of nanocomposites PP NC1 NC3 NC5 NC7 The hardness of plane PP and nanocomposites were shown in Fig. 6. The hardness of the nanocomposites gradually increases with increasing clay content. NC5 specimens displayed the largest hardness numbers averaging at 21.5 HV. The reason for the improvement in the hardness is due to the presence of intercalated and exfoliated clay platelets present in the polypropylene matrix. The intercalated/exfoliated clay platelets effectively restrict indentation and increase the hardness of the nanocomposites [18]. In 7 wt% clay content the hardness decreased which could be due to the agglomeration of nanoclay in the PP matrix. Fig. 6. Hardness curves of clay polypropylene nanocomposite

8 Study of Processing and Mechanical Behavior of PP/Clay Nanocomposites Prepared by Melt Blending Wear test The specific wear rate of plane PP and the nanocomposite samples is shown in Fig. 7. The specific wear rate of plane PP is 3.33e -4 mm 3 /Nm and decreases with the infusion of nanoclays at all the weight loadings. The specific wear rate of PP is 3.33e -4 mm 3 /Nm while the wear loss of PP with 5 wt. % nanoclays decreases to 5.22e -5 mm 3 /Nm. Nanocomposites with 5 wt. % nanoclay show a maximum of 84% improvement in wear resistance. The improvement in wear resistance is mainly attributed to the presence of clay platelets in the PP matrix. These nanosize clay platelets dispersed in the polymer matrix act as a barrier and also prevent large-scale fragmentation of the polymer matrix. The nanoclay platelets dispersed in the polypropylene matrix lead to interfacial strengthening and increased wear resistance [19, 20]. The high interfacial adhesion between the matrix and nanoclay is due to the high specific surface area of the nanoparticles. The nanoparticle having the same size as the segments of the surrounding polymer chains enables the material removal to be mild and aids the formation of uniform tenacious transfer film as reported elsewhere [21, 22]. Hardness contribution also plays a vital role in wear property improvement as reported elsewhere [23]. Specific Wear rate ( mm^3/nm) 3.50E E E E E E E E Conclusions Clay Content (wt.%) Fig.7. Wear loss of plane PP and nanocomposites In this study, PP/clay nanocomposites were prepared by melt blending the polypropylene with organoclay (denoted K-10) and PP-g-MA. The morphology of the nanocomposites was studied by X-ray diffraction (XRD). PP/Clay nanocomposites showed good thermal stability as determined by TGA analysis. TGA analysis showed that addition of ~ 3% clay in the nanocomposites increased the onset temperature of the degradation by 27.5 o C over that of the pure PP. The nanocomposite samples showed a maximum improvement of 22% in the tensile strength for the nanoclay content of 5 wt. %. Hardness of the nanocomposites increased to a maximum of 21.5 HV for 5 wt. % nanoclay. The wear

9 544 S. M. Shirazi & K. Janghorban resistance of nanocomposite samples increased to a maximum of 84% for 5 wt. % nanoclay. References 1. B.M. Alexander, J.W. Gilman, J Appl Polym Sci 87:1329 (2003). 2. J.M. Kenny, L. Torre, L. Valentini, J. Biagiotti, D. Puglia, In: Proceedings of China EU forum on nanosized technology, Beijing, PR China, December (2002), p M. Alexandre, P. Dubois, Mater Sci Eng 28:1 (2000). 4. Y. Kojima, A. Usiki, M. Kawasumi, A. Okada, Y. Fukushima, T. Karauchi T,J Mater Res 6:1185 (2003). 5. M.Y. Kato, A. Usiki, A. Okada, J Appl Polym Sci 66:1781 (2000). 6. L.A. Utracki, M.R. Kamal, Arab J Sci Eng 27:43 (2002). 7. R.K. Bharadwaj, A.R. Mehrabi, C. Hamilton, C. Trujilo, M. Murga, R. et al Fan,J Polymer 43:3699 (2004). 8. V.K. Moodley, K. Kanny, J Eng Mater Technol 40:1(2007). 9. C. Ding, D. Jia, H. Hui, B. Guo, H. Hong, Polym Test 20:1 (2004). 10. L. Chang, Z. Chang, C. Bredit, K. Friedrich, Wear 258:141 (2005). 11. Q. Wang, Q. Xue, W. Shen, Tribol Int 30:193 (1997). 12. Q. Wang, Q. Xue, W. Shen, J. Zhang, J Appl Polym Sci 69:135 (1998). 13. H. Cai, F.E. Yan, Q. Xue, W. Liu, Polym Test 22:875 (2003). 14. Q. Wang, Q. Xue, W. Liu, J. Chen, J Appl Polym Sci 79:1394 (2001). 15. W.G. Sawyer, K.D. Freudenberg, P. Bhimaraj, L.S. Schadler, Wear 254:573 (2003). 16. G. Shi, M.Q. Zhang, M. Rong, B. Wetzel, K. Friedrich, Wear 256:1072 (2004). 17. J. Chang, B. Seo, D. Hwang, Polymer (Guildf) 43:2969 (2002). 18. P. Jawahar, M. Balasubramanian, Int J Plast Technol 9: (2005). 19. G. Shi, M.Q. Zhang, M. Rong, B. Wetzel, K. Friedrich, Wear 256:1072 (2004). 20. Q.H. Wang, J. Xu, W. Shen, Q. Xue, Wear 239:316 (2001). 21. C.J. Shwartz, S. Bahadur, Wear 237:261 (2000). 22. J. Khedkar, L. Negulescu, E. Meletis, Wear 252:361 (2002). 23. X.H. Cheng, Y.J. Xue, C.X. Xie, Wear 253:869 (2002).

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