Fracture behaviors of fibrillar silicate clay (MMT) filled thermoplastic polyolefin (TPO) containing polypropylene (PP) blended with ethylene-propylene-diene monomer (EPDM) were systematically investigated using impact test method and -integral by locus method. Drastic increase in impact strength is observed for all developed compositions and generally shows higher value for the selected phases containing dispersed nanoclay in PP matrix. A fracture mechanics approach has been adopted by mode I test, and the effects of specimen geometry have been investigated. Increase in interlaminar fracture energy value, , and -integral value, , is marked as the crack propagated through the composite; that is, a rising “ -curve” is observed. Toughness measurements revealed that the fracture toughness increased with increasing clay content reaching maximum at 3？wt% of clay than pure PP. Moreover, enhancement of fracture toughness was more remarkable than that of stiffness. The fracture surfaces taken from different specimens were observed for exploring the fracture mechanisms using transmission electron microscopy (TEM) revealed a strong particle-matrix adhesion. 1. Introduction Polypropylene (PP) offers a very attractive combination of physical and mechanical properties at a relatively low cost, which makes it a versatile material with continuously increasing applications. However, not all the characteristics of this material are suitable for common service conditions. For instance, PP exhibits poor low-temperature impact resistance because of its low temperature and high crystallinity. In order to overcome these limitations, elastomers such as ethylene-propylene random copolymer (EPR) [1], ethylene-propylene-diene terpolymer (EPDM) [2], and poly(ethylene-co-1-octene) [3] among others [4, 5] have been added to PP, as impact modifiers. Further, due to incompatibility of PP with these elastomers, functionalized polymers have been used as blend compatibilizers to improve interfacial adhesion. Layered silicate clays are also used as fillers in polymers which have gained considerable attention due to the ability to achieve exceptional property enhancements at very low level loading. Layered silicate clays such as montmorillonite (MMT) have attracted much attention because of their unique properties, such as large aspect ratio, high surface area, and low cost. Addition of low level loading of these silicate clays to polymers markedly improves their tensile strength, stiffness, and heat resistance and facilitates processing thus reducing component weight. However, in order
References
[1]
N. Inaba, K. Sato, S. Suzuki, and T. Hashimoto, “Morphology control of binary polymer mixtures by spinodal decomposition and crystallization. 1: principle of method and preliminary results on PP/EPR,” Macromolecules, vol. 19, no. 6, pp. 1690–1695, 1986.
[2]
W. Jiang, S. C. Tjong, and R. K. Y. Li, “Brittle-tough transition in PP/EPDM blends: effects of interparticle distance and tensile deformation speed,” Polymer, vol. 41, no. 9, pp. 3479–3482, 2000.
[3]
R. R. Babu, N. K. Singha, and K. Naskar, “Interrelationships of morphology, thermal and mechanical properties in uncrosslinked and dynamically crosslinked PP/EOC and PP/EPDM blends,” Express Polymer Letters, vol. 4, no. 4, pp. 197–209, 2010.
[4]
T. McNally, P. McShane, G. M. Nally, W. R. Murphy, M. Cook, and A. Miller, “Rheology, phase morphology, mechanical, impact and thermal properties of polypropylene/metallocene catalysed ethylene 1-octene copolymer blends,” Polymer, vol. 43, no. 13, pp. 3785–3793, 2002.
[5]
L. Zhang, C. Li, and R. Huang, “Toughness mechanism in polypropylene composites: polypropylene toughened with elastomer and calcium carbonate,” Journal of Polymer Science B, vol. 42, no. 9, pp. 1656–1662, 2004.
[6]
G. P. Marshall, J. G. Williams, and C. E. Turner, “Fracture toughness and absorbed energy measurements in impact tests on brittle materials,” Journal of Materials Science, vol. 8, no. 7, pp. 949–956, 1973.
[7]
E. Plati and J. G. Williams, “The determination of the fracture parameters for polymers in impact,” Polymer Engineering and Science, vol. 15, no. 6, pp. 470–477, 1975.
[8]
C. G. Sanporean, Z. Vuluga, J. D. Christiansen, C. Radovici, E. A. Jensen, and H. Paven, “Investigation of mechanical properties of PP/Clay nanocomposites based on network cross-linked compatibilizers,” Industrial and Engineering Chemistry Research, vol. 52, no. 10, pp. 3773–3778, 2013.
[9]
J. R. Rice and D. M. Tracey, “On the ductile enlargement of voids in triaxial stress fields,” Journal of the Mechanics and Physics of Solids, vol. 17, no. 3, pp. 201–217, 1969.
[10]
B. H. Kim and C. R. Joe, “A method to evaluate critical J-integral value: locus method,” Polymer Testing, vol. 7, no. 5, pp. 355–363, 1987.
[11]
B. H. Kim, C. R. Joe, and D. M. Otterson, “On the determination of fracture toughness in polymers,” Polymer Testing, vol. 8, no. 2, pp. 119–130, 1988.
[12]
Y. S. Lee, W.-K. Lee, S.-G. Cho, I. Kim, and C.-S. Ha, “Quantitative analysis of unknown compositions in ternary polymer blends: a model study on NR/SBR/BR system,” Journal of Analytical and Applied Pyrolysis, vol. 78, no. 1, pp. 85–94, 2007.
[13]
P. Sivaraman, L. Chandrasekhar, V. S. Mishra, B. C. Chakraborty, and T. O. Varghese, “Fracture toughness of thermoplastic co-poly (ether ester) elastomer-Acrylonitrile butadiene styrene terpolymer blends,” Polymer Testing, vol. 25, no. 4, pp. 562–567, 2006.
[14]
A. Hassan, M. U. Wahit, and C. Y. Chee, “Mechanical and morphological properties of PP/NR/LLDPE ternary blend: effect of HVA-2,” Polymer Testing, vol. 22, no. 3, pp. 281–290, 2003.
[15]
H. Anuar, S. B. Abd Razak, N. M. Kahar, and N. A. Jamal, “Effects of high energy radiation on mechanical properties of PP/EPDM nanocomposite,” Advanced Materials Research, vol. 264, pp. 738–742, 2011.
[16]
L. Valentini, J. Biagiotti, J. M. Kenny, and M. A. López Manchado, “Physical and mechanical behavior of single-walled carbon nanotube/polypropylene/ethylene-propylene-diene rubber nanocomposites,” Journal of Applied Polymer Science, vol. 89, no. 10, pp. 2657–2663, 2003.
[17]
H.-S. Lee, P. D. Fasulo, W. R. Rodgers, and D. R. Paul, “TPO based nanocomposites. Part 1: morphology and mechanical properties,” Polymer, vol. 46, no. 25, pp. 11673–11689, 2005.
[18]
G. M. Shashidhara and S. K. Devi, “Studies on PP/SBS blends with and without nanoclay,” Indian Journal of Engineering and Materials Sciences, vol. 18, no. 1, pp. 69–78, 2011.
[19]
G. Jannerfeldt, L. Boogh, and J.-A. E. M？nson, “Tailored interfacial properties for immiscible polymers by hyperbranched polymers,” Polymer, vol. 41, no. 21, pp. 7627–7634, 2000.
[20]
R. W. Sandoval, D. E. Williams, J. Kim, C. B. Roth, and J. M. Torkelson, “Critical micelle concentrations of block and gradient copolymers in homopolymer: effects of sequence distribution, composition, and molecular weight,” Journal of Polymer Science B, vol. 46, no. 24, pp. 2672–2682, 2008.
[21]
R. Asaletha, P. Bindu, I. Aravind et al., “Stress-relaxation behavior of natural rubber/polystyrene and natural rubber/polystyrene/natural Rubber-graft-polystyrene blends,” Journal of Applied Polymer Science, vol. 108, no. 2, pp. 904–913, 2008.
[22]
W. S. Chow, Z. A. M. Ishak, J. Karger-Kocsis, A. A. Apostolov, and U. S. Ishiaku, “Compatibilizing effect of maleated polypropylene on the mechanical properties and morphology of injection molded polyamide 6/polypropylene/organoclay nanocomposites,” Polymer, vol. 44, no. 24, pp. 7427–7440, 2003.
[23]
D. M. Bigg, “Mechanical properties of particulate filled polymers,” Polymer Composites, vol. 8, no. 2, pp. 115–122, 1987.
[24]
T. B. Lewis and L. E. Nielsen, “Dynamic mechanical properties of particulate-filled composites,” Journal of Applied Polymer Science, vol. 14, no. 6, pp. 1449–1471, 1970.
[25]
G. Erhard, Designing with Plastics, Hanser, Munich, Germany, 2006.
[26]
E. Vassileva and K. Friedrich, “Epoxy/alumina nanoparticle composites. I: dynamic mechanical behavior,” Journal of Applied Polymer Science, vol. 89, no. 14, pp. 3774–3785, 2003.
[27]
K. T. Gam, M. Miyamoto, R. Nishimura, and H.-J. Sue, “Fracture behavior of core-shell rubber-modified clay-epoxy nanocomposites,” Polymer Engineering and Science, vol. 43, no. 10, pp. 1635–1645, 2003.
[28]
K. L. Johnson and J. A. Greenwood, “An adhesion map for the contact of elastic spheres,” Journal of Colloid and Interface Science, vol. 192, no. 2, pp. 326–333, 1997.
[29]
C.-S. Ha, Y. Kim, and W.-J. Cho, “Fracture toughness investigation of the dynamically vulcanized EPDM/PP/ionomer ternary blends using the J-integral via the locus method,” Journal of Materials Science, vol. 31, no. 11, pp. 2917–2924, 1996.
[30]
H. G. Tattersall and G. Tappin, “The work of fracture and its measurement in metals, ceramics and other materials,” Journal of Materials Science, vol. 1, no. 3, pp. 296–301, 1966.
[31]
D. S. Parker, H.-J. Sue, J. Huang, and A. F. Yee, “Toughening mechanisms in core-shell rubber modified polycarbonate,” Polymer, vol. 31, no. 12, pp. 2267–2277, 1990.
[32]
F. M. Mirabella Jr., S. P. Westphal, P. L. Fernando, E. A. Ford, and J. G. Williams, “Morphological explanation of the extraordinary fracture toughness of linear low density polyethylenes,” Journal of Polymer Science B, vol. 26, no. 9, pp. 1995–2005, 1988.
