Isotactic polypropylene (iPP)/bentonite nanocomposites were prepared via melt blending using bentonite clay originated from Maghnia (Algeria). This clay was, at a first stage, used in its pure form (PBT) and then organically modified by Hexadecyl ammonium chloride (OBT). The effect of Maghnia bentonite dispersion on the iPP matrix was investigated by X-ray diffraction (XRD) and transmission electronic microscopy (TEM). DSC results evidenced that unmodified or organomodified bentonite can act as a nucleating agent increasing the rate of crystallites formation. Moreover, a thermogravimetry analysis confirmed a significant enhanced thermal stability of IPP/clay nanocomposites compared to pure IPP. The Flynn-Wall-Ozawa and Tang methods were applied to determine the activation energy of the degradation process. The apparent activation energy？？ of thermal degradation for IPP/clay nanocomposites was much higher than that of virgin iPP. Comparatively to PBT, results indicate that OBT has an important effect on pure iPP thermal stability. Tensile modulus, tensile strength, and elongation at break were also measured and compared with those of pure iPP. 1. Introduction Isotactic polypropylene (iPP) is one of the most interesting commodity thermoplastic accounting for about 20% of the total world’s polyolefin production, not only for its balance of physical and mechanical properties but also for its environmental friendliness (recyclability) and low cost. It is widely used in many applications, such as fibers, films for food packaging, bottles production, and tubes. Isotactic polypropylene (iPP)/clay composites are among the pioneer researched nanocomposites because iPP is one of the most widely used polyolefins, and its properties are greatly affected by clay dispersion in the polymer [1–10]. Many researches were reported on preparation and characterization of polypropylene (iPP)/clay nanocomposites, focusing on the dispersed morphology of clay particles [11–14]. Polymer degradation is the purpose of many researches on plastic waste management. The knowledge of degradation kinetics of polymers is important for modeling the degradation process. Several mechanisms were proposed to describe thermal and flame properties of polymer/clay nanocomposites. Generally, the barrier effect of clay layers for heat and volatiles plays a key role in these enhancements. Kinetic data reflect that improvement of thermal stability of polymer/clay nanocomposites is associated with an increase in the activation energy of their degradation; this is explained by the barrier effect
References
[1]
A. Vassiliou, D. Bikiaris, K. Chrissafis, K. M. Paraskevopoulos, S. Y. Stavrev, and A. Docoslis, “Nanocomposites of isotactic polypropylene with carbon nanoparticles exhibiting enhanced stiffness, thermal stability and gas barrier properties,” Composites Science and Technology, vol. 68, no. 3-4, pp. 933–943, 2008.
[2]
S. S. Ray and M. Okamoto, “Polymer/layered silicate nanocomposites: a review from preparation to processing,” Progress in Polymer Science, vol. 28, no. 11, pp. 1539–1641, 2003.
[3]
X.-L. Jiang, J.-B. Bao, T. Liu, L. Zhao, Z.-M. Xu, and W.-K. Yuan, “Microcellular foaming of polypropylene/clay nanocomposites with supercritical carbon dioxide,” Journal of Cellular Plastics, vol. 45, no. 6, pp. 515–538, 2009.
[4]
H. Nathani, A. Dasari, and R. D. K. Misra, “On the reduced susceptibility to stress whitening behavior of melt intercalated polybutene-clay nanocomposites during tensile straining,” Acta Materialia, vol. 52, no. 11, pp. 3217–3227, 2004.
[5]
E. Manias, A. Touny, L. Wu, K. Strawhecker, B. Lu, and T. C. Chung, “Polypropylene/montmorillonite nanocomposites. Review of the synthetic routes and materials properties,” Chemistry of Materials, vol. 13, no. 10, pp. 3516–3523, 2001.
[6]
W. Zheng, X. Lu, C. L. Toh, T. H. Zheng, and C. He, “Effects of clay on polymorphism of polypropylene in polypropylene/clay nanocomposites,” Journal of Polymer Science B: Polymer Physics, vol. 42, no. 10, pp. 1810–1816, 2004.
[7]
C. J. Perez and V. A. Alvarez, “Overall crystallization behavior of polypropylene-clay nanocomposites; effect of clay content and polymer/clay compatibility on the bulk crystallization and spherulitic growth,” Journal of Applied Polymer Science, vol. 114, no. 5, pp. 3248–3260, 2009.
[8]
M. A. Pérez, L. B. Rivas, S. M. Rodríguez, á. Maldonado, and C. Venegas, “Polypropylene/clay nanocomposites. Synthesis and characterization,” Journal of the Chilean Chemical Society, vol. 55, no. 4, 2004.
[9]
M. J. Solomon and A. Somwangthanaroj, “Intercalated polypropylene nanocomposites,” Dekker Encyclopedia of Nanoscience and Nanotechnology, 1483.
[10]
J.-D. He, M. K. Cheung, M.-S. Yang, and Z. Qi, “Thermal stability and crystallization kinetics of isotactic polypropylene/organomontmorillonite nanocomposites,” Journal of Applied Polymer Science, vol. 89, no. 12, pp. 3404–3415, 2003.
[11]
T. Kashiwagi, E. Grulke, J. Hilding, R. Harris, W. Awad, and J. Douglas, “Thermal degradation and flammability properties of poly(propylene)/carbon nanotube composites,” Macromolecular Rapid Communications, vol. 23, no. 13, pp. 761–765, 2002.
[12]
C. Silvestre, S. Cimmino, M. Raimo, C. Carfagna, V. Capuano, and R. Kotsilkova, “Effect of clay/diamond and clay/carbon nanosystems on structure-properties relationships of iPP,” Journal of Polymer Science Part B: Polymer Physics, vol. 42, pp. 3428–3438, 2004.
[13]
S. Bouhelal, M. E. Cagiao, S. Khellaf et al., “Nanostructure and microechanical properties of reversibly crosslinked isotactic polypropylene/clay composites,” Journal of Applied Polymer Science, vol. 115, no. 5, pp. 2654–2662, 2010.
[14]
L. Raka, A. Sorrentino, and G. Bogoeva-Gaceva, “Isothermal crystallization kinetics of polypropylene latex-based nanocomposites with organo-modified clay,” Journal of Polymer Science B: Polymer Physics, vol. 48, no. 17, pp. 1927–1938, 2010.
[15]
K. Chrissafis, K. M. Paraskevopoulos, S. Y. Stavrev, A. Docoslis, A. Vassiliou, and D. N. Bikiaris, “Characterization and thermal degradation mechanism of isotactic polypropylene/carbon black nanocomposites,” Thermochimica Acta, vol. 465, no. 1-2, pp. 6–17, 2007.
[16]
L. Wang and J. Sheng, “A kinetic study on the thermal degradation of polypropylene/attapulgite nanocomposites,” Journal of Macromolecular Science B: Physics, vol. 45, no. 1, pp. 1–11, 2006.
[17]
J. Zhu, F. M. Uhl, A. B. Morgan, and C. A. Wilkie, “Studies on the mechanism by which the formation of nanocomposites enhances thermal stability,” Chemistry of Materials, vol. 13, no. 12, pp. 4649–4654, 2001.
[18]
A. Habi, S. Djadoun, and Y. Grohens, “Morphology and thermal behavior of organo-bentonite clay/poly(styrene-co-methacrylic acid)/poly(isobutyl methacrylate-co-4-vinylpyridine) nanocomposites,” Journal of Applied Polymer Science, vol. 114, no. 1, pp. 322–330, 2009.
[19]
B. Monasse and J. M. Haudin, “Growth transition and morphology change in polypropylene,” Colloid & Polymer Science, vol. 263, no. 10, pp. 822–831, 1985.
[20]
T. A. Ozawa, “New method of analyzing thermogravimetric data,” Bulletin of the Chemical Society of Japan, vol. 38, no. 11, pp. 1881–1886, 1965.
[21]
J. H. Flynn and L. A. Wall, “A quick direct method for the determination of activation energy from thermogravimetric data,” Polymer Letters, vol. 4, pp. 323–328, 1966.
[22]
W. Tang, Y. Liu, H. Zhang, and C. Wang, “New approximate formula for Arrhenius temperature integral,” Thermochimica Acta, vol. 408, no. 1-2, pp. 39–43, 2003.
[23]
X. Zhang, M. Yang, Y. Zhao et al., “Polypropylene/montmorillonite composites and their application in hybrid fiber preparation by melt-spinning,” Journal of Applied Polymer Science, vol. 92, no. 1, pp. 552–558, 2004.
[24]
J. Varga, “β-modification of isotactic polypropylene: preparation, structure, processing, properties, and application,” Journal of Macromolecular Science, vol. 41, no. 4–6, pp. 1121–1171, 2002.
[25]
J. Varga and J. Karger-Kocsis, “Rules of supermolecular structure formation in sheared isotactic polypropylene melts,” Journal of Polymer Science B: Polymer Physics, vol. 34, no. 4, pp. 657–670, 1996.
[26]
B. Rozanski, E. Monasse, A. Szkudlarek et al., “Shear-induced crystallization of isotactic polypropylene based nanocomposites with montmorillonite,” European Polymer Journal, vol. 45, no. 1, pp. 88–101, 2009.
[27]
J. Varga, “Supermolecular structure of isotactic polypropylene,” Journal of Materials Science, vol. 27, no. 10, pp. 2557–2579, 1992.
[28]
D. N. Bikiaris, G. Z. Papageorgiou, E. Pavlidou, N. Vouroutzis, P. Palatzoglou, and G. P. Karayannidis, “Preparation by melt mixing and characterization of isotactic polypropylene/SiO2 nanocomposites containing untreated and surface-treated nanoparticles,” Journal of Applied Polymer Science, vol. 100, no. 4, pp. 2684–2696, 2006.
[29]
C. Hao, Y. Zhao, A. He et al., “Investigation on the melt spinning fibers of PP/organoclay nanocomposites prepared by in-situ polymerization,” Journal of Applied Polymer Science, vol. 116, no. 3, pp. 1384–1391, 2010.
[30]
S. A. Ahmad Ramazani, F. Tavakolzadeh, and H. Baniasadi, “Synthesis of polypropylene/clay nanocomposites using bisupported ziegler-natta catalyst,” Journal of Applied Polymer Science, vol. 115, no. 1, pp. 308–314, 2010.
[31]
S. L. Madorsky, Thermal Degradation of Organic Polymers, chapter 4, Wiley-Interscience, New York, NY, USA, 1964.
[32]
X. Xu, Y. Ding, F. Wang et al., “Effects of silane grafting on the morphology and thermal stability of poly(ethylene terephthalate)/Clay nanocomposites,” Polymer Composites, vol. 31, no. 5, pp. 825–834, 2010.
[33]
X. Yuan, C. Li, G. Guan, Y. Xiao, and D. Zhang, “Thermal degradation investigation of poly(ethylene terephthalate)/fibrous silicate nanocomposites,” Polymer Degradation and Stability, vol. 93, no. 2, pp. 466–475, 2008.
[34]
A. A. Vassiliou, K. Chrissafis, and D. N. Bikiaris, “In situ prepared PET nanocomposites: effect of organically modified montmorillonite and fumed silica nanoparticles on PET physical properties and thermal degradation kinetics,” Thermochimica Acta, vol. 500, no. 1-2, pp. 21–29, 2010.
[35]
K. Wang, S. Liang, J. Deng et al., “The role of clay network on macromolecular chain mobility and relaxation in isotactic polypropylene/organoclay nanocomposites,” Polymer, vol. 47, no. 20, pp. 7131–7144, 2006.
[36]
J. A. Tarapow, C. R. Bernai, and V. A. Alvarez, “Mechanical properties of polypropylene/clay nanocomposites: effect of clay content, polymer/clay compatibility, and processing conditions,” Journal of Applied Polymer Science, vol. 111, no. 2, pp. 768–778, 2009.
[37]
S. K. Sharma and S. K. Nayak, “Surface modified clay/polypropylene (PP) nanocomposites: effect on physico-mechanical, thermal and morphological properties,” Polymer Degradation and Stability, vol. 94, no. 1, pp. 132–138, 2009.
[38]
M. V. Burmistr, K. M. Sukhyy, V. V. Shilov et al., “Synthesis, structure, thermal and mechanical properties of nanocomposites based on linear polymers and layered silicates modified by polymeric quaternary ammonium salts (ionenes),” Polymer, vol. 46, no. 26, pp. 12226–12232, 2005.
