Mechanical Properties and Fracture Behavior of Polypropylene Reinforced with Polyaniline-Grafted Short Glass Fibers O. Flores, 1 A. Romo-Uribe, 1 M. E. Romero-Guzma ´n, 1 A. E. Gonza ´lez, 1 R. Cruz-Silva, 2 B. Campillo 1,3 1 Instituto de Ciencias Fı ´sicas, Universidad Nacional Auto ´noma de Me ´xico, Avenida Universidad s/n Colonia Chamilpa, Cuernavaca Morelos 62210, Me ´xico 2 Centro de Investigacio ´n en Ingenierı ´a y Ciencias Aplicadas, Universidad Auto ´noma del Estado de Morelos, Cuernavaca Morelos 62210, Me ´xico 3 Facultad de Quı ´mica, Universidad Nacional Auto ´noma de Me ´xico, Ciudad Universitaria DF 04510, Me ´xico Received 8 April 2008; accepted 8 October 2008 DOI 10.1002/app.29453 Published online 23 January 2009 in Wiley InterScience (www.interscience.wiley.com). ABSTRACT: This research was focused on the mechani- cal properties of electrically conducting composites based on polyaniline (PAn)-coated short glass fibers (SGFs) immersed in an isotactic polypropylene (iPP) matrix. In these composites, PAn was actually grafted onto the SGF surface, and so it was denoted PAn-g-SGF. The tensile, flexural, and interlaminar fracture toughness was investi- gated. To study the influence of PAn-g-SGF, three different concentrations (10, 20, and 30 wt %) were melt-mixed in the iPP resin with a batch mixer. X-ray patterns of the as- molded plaques of iPP and its composites showed an iso- tropic orientation. Uniaxial tensile deformation revealed that the Young’s modulus and tensile stress increased as the concentration of PAn-g-SGF increased; on the other hand, the strain at failure was significantly reduced (by 2 orders of magnitude) with respect to the neat iPP. Scan- ning electron microscopy studies on the failure specimens indicated that the significant reduction of the strain at fail- ure was due to the low interfacial bonding between the fibers and the surrounding matrix. Moreover, X-ray scat- tering analyses of the fractured regions showed that the uniaxial deformation enabled significant molecular orienta- tion in the iPP, whereas the fractured composites remained isotropic. Detailed scanning electron microscopy analyses showed that the fracture mechanism arose from the fracture of the PAn-g-SGFs; the percolated PAn-g-SGFs formed a path for the stress transfer. Because the failure was dominated by both filler decohesion and polymeric chain rupture, the strength was not influenced signifi- cantly by the amount of PAn-g-SGFs. V V C 2009 Wiley Periodi- cals, Inc. J Appl Polym Sci 112: 934–941, 2009 Key words: composites; conducting polymers; fracture; mechanical properties INTRODUCTION Many new possibilities have been revealed by the production of intrinsically conductive polymers, such as protection from direct electrostatic discharge (ESD) and, in general, electromagnetic interference field (EMI) shielding. The benefits include weight reduction, physical flexibility, and tunable shielding responses. To use them as dissipative materials for ESD shielding, their electrical conductivity has to be between 10 11 and 10 4 S/cm (ANSI/EIA-541). Poly- aniline (PAn) has been increasingly studied in recent years, being one of the most promising electrically conducting polymers because of its high polymeriza- tion yield, good environmental stability combined with moderate electrical conductivity, and relatively low cost. 1–7 However, blends of PAn with thermo- plastics usually show decreases in the mechanical properties, and this makes them unsuitable for man- ufacturing strong devices with the aforementioned ESD and EMI protection properties. The introduction of reinforcing fibers has long been a remedy in the polymer industry to improve the mechanical properties of different composites. Among them, glass fibers have been shown to be a good reinforcement for the production of materials Journal of Applied Polymer Science, Vol. 112, 934–941 (2009) V V C 2009 Wiley Periodicals, Inc. Correspondence to: A. Romo-Uribe (aromo-uribe@fis. unam.mx). Contract grant sponsor: Direccio ´ n General de Asuntos del Personal Acade ´mico/Programa de Apoyo a Proyectos de Investigacio ´n e Inovacio ´n Tecnolo ´ gica (to A.E.G.); contract grant number: IN106008. Contract grant sponsor: Consejo Nacional de Ciencia y Tecnologı ´a (to A.R.-U.); contract grant number: CIAM 2006 58646. Contract grant sponsor: Direccio ´ n General de Asuntos del Personal Acade ´mico/Universidad Nacional Auto ´ noma de Me ´xico (to M.E.R.-G.).