Mechanical Properties of Functionally Graded Carbon Black–Styrene Butadiene Rubber Composites: Effect of Modifying Gradation and Average Filler Loading Sandeep Ahankari, 1 Kamal K. Kar 1,2 1 Materials Science Programme, Advanced Nanoengineering Materials Laboratory, Indian Institute of Technology Kanpur, Kanpur 208016, India 2 Department of Mechanical Engineering, Advanced Nanoengineering Materials Laboratory, Indian Institute of Technology Kanpur, Kanpur 208016, India Received 11 July 2011; accepted 30 November 2011 DOI 10.1002/app.36704 Published online in Wiley Online Library (wileyonlinelibrary.com). ABSTRACT: The mechanical properties of functionally graded polymeric composites (FGPCs) with varying carbon black loading and the effect of stacking sequence in styrene butadiene rubber (SBR) matrix were studied. For a given average amount of nanofiller, the modulus of FGPCs for any given stacking sequence of layers is higher when com- pared with its uniformly dispersed polymeric composites (UDPCs) counterpart. Tensile strength, elongation at break, and tear strength either increase or decrease depending on the stacking sequence and average loading of the filler in FGPCs. In addition, the smoother gradation (i.e., lesser dif- ference in the amounts of CB content in adjacent layers) and a wide gap of difference in CB content in a stack has a profound effect on the modulus and tensile strength of FGPCs. Dynamic mechanical analysis shows lesser damp- ing in FGPCs than UDPCs. V C 2012 Wiley Periodicals, Inc. J Appl Polym Sci 000: 000–000, 2012 Key words: functionally graded material; composites; mechanical properties; dynamic mechanical analysis INTRODUCTION Functionally graded materials (FGMs) are a category of relatively recent and promising materials that have emerged from the need to optimize the per- formance of a component in the target applications. In a homogeneous material the properties are con- stant, whereas in an FGM, the material composition, microstructure and hence properties vary continu- ously with position, usually in one coordinate direc- tion. 1–3 The applications of metal/ceramic FGMs are exploited in air-craft and energy sectors. 4–6 But in polymer-based FGMs, the lack of awareness of dif- ferent processing techniques hinders the exploration of its applicability in diversified areas. Still people have tried to make the gradation of properties in polymers like hardness, wear resistance, impact re- sistance, toughness, etc. and noticed majority of its applications in biomedical and optical fields. 1–3 Klingshirn et al. have studied the effect of gradation of SiC particles and glass fibers on the polymeric composites employing centrifuging technique before polymerization. 7 Akiyama et al. have analyzed the effect of gradation of crystalline phase on the semi- crystalline polymers. 8 Ikeda has prepared the func- tionally graded composites by layering method using styrene butadiene rubber (SBR) matrix with gradation of network chain density along thickness direction and compared them with homogeneous compounding sheets. 9,10 Free vibration analysis has been done on fly ash reinforced functionally graded rubber composite sandwiches to investigate damp- ing ratio and natural frequency. 11 There are various applications where controversial properties are required which suggests a need of a multifunctional material, e.g., slippers, rubber pads, etc. It was earlier elucidated that for a given volume fraction of nanofiller in polyisoprene (natural rub- ber) matrix, functionally graded polymeric compo- sites (FGPCs) show much enhanced modulus than uniformly dispersed polymeric composites (UDPCs). 12,13 The major receding factor for the de- velopment of these FGPCs is the reduction in failure properties like tensile strength, elongation at break, tear strength, etc. when compared with its UDPC counterparts. Here, keeping in mind the importance of mechanical properties of polymer composites in polymer industry, an attempt is made to prepare FGPCs using synthetic polymer i.e., styrene butadi- ene rubber (SBR) as matrix and carbon black (CB) as grading material by construction-based layering method. 11 The article aims at the investigation of an impact of different stacking sequences on its Correspondence to: K. K. Kar (kamalkk@iitk.ac.in). Journal of Applied Polymer Science, Vol. 000, 000–000 (2012) V C 2012 Wiley Periodicals, Inc.