Mechanical and Morphological Properties of Carbon Fiber Reinforced–Modified Epoxy Composites B. R. Guduri, A. S. Luyt Department of Chemistry, University of the Free State (Qwaqwa Campus), Phuthaditjhaba 9866, South Africa Received 24 March 2005; accepted 22 February 2006 DOI 10.1002/app.24592 Published online in Wiley InterScience (www.interscience.wiley.com). ABSTRACT: Epoxy, prepared through aminomethyl 3,5,5-trimethylcyclohexylamine hardening of diglyci- dylether of bisphenol-A (DGEBA) prepolymer, toughened with polycarbonate (PC) in different proportions, and rein- forced with carbon fiber, was investigated by differential scanning calorimetry, tensile and interlaminar shear strength testing, and scanning electron microscopy (SEM). A single glass transition temperature was found in all compo- sitions of the epoxy/PC blend system. The tensile properties of the blend were found to be better than that of the pure epoxy matrix. They increased with PC content up to 10%, beyond which they decreased. The influence of carbon fiber orientation on the mechanical properties of the composites was studied, where the fiber content was kept constant at 68 wt %. Composites with 45° fiber orientation were found to have very weak mechanical properties, and the mechanical properties of the blend matrix composites were found to be better than those of the pure epoxy matrix composites. The fracture and surface morphologies of the composite samples were characterized by SEM. Good bonding was observed between the fiber and matrix for the blend matrix compos- ites. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 3529 –3536, 2006 Key words: epoxy resin; polycarbonate; carbon fiber; com- posite; tensile properties; differential scanning calorimetry; interlaminar shear strength; morphology INTRODUCTION Polymeric composites are a combination of two or more materials in different phases that should give rise to better performance than what each material has individually. 1,2 Carbon fiber/polymeric matrix com- posites is a class of advanced materials that have been developed for a variety of applications in areas of high technology, such as aerospace, automobile, air craft, defense industry, and sporting goods. To take advan- tage of the excellent mechanical properties of carbon fibers in a composite, an optimized interfacial adhe- sion between the fiber and matrix is necessary. In view of the fact that stress is transferred from one fiber to another through the matrix, the interface be- tween the matrix and fiber plays a major role in the overall mechanical performance of composite materi- als. The composite materials and prepreg used for primary structures should have high specific tensile strength and modulus. Toughened polymer compos- ites have attracted much interest, because of their low production costs and good processability. As is well known, epoxy resin is one of the most widely used matrices for carbon fiber-reinforced composite mate- rials, by virtue of its good impregnation and adhesion to carbon fiber. 3–7 One of the most promising ap- proaches for achieving these often opposing material properties is through thermoplastic/thermoset blends. Toughening of crosslinked epoxy resin by blending with various thermoplastics has been inves- tigated extensively. Polycarbonate (PC) has attracted special attention due to its high toughness. It has been well recognized that reactions between PC and epoxy can occur in the following situations: 1 during the preparation of the PC-epoxy mixture and 2 during the curing of the PC-epoxy blend. Transesterification be- tween PC and epoxy has been reported when the PC-epoxy was cured by tertiary amine, 8,9 anhy- dride, 10 –13 quaternary ammonium salt, 10,14 and aro- matic amine. 10,15–19 The PC could transamidate with amine when the PC-epoxy was cured with aliphatic amine. 10,20 Chen et al. 21 studied the miscibility and fracture behavior of an epoxy resin-PC blend. They reported that the blend was miscible and had better mechanical properties. With the recent development of high-temperature, high-performance thermoplas- tics, examples being polyetherimide, poly(1,6-dimeth- yl-1–1,4-phenylene ether or oxide), and poly(ether ether ketone), the blending of thermosets with these high glass transition thermoplastics is a potentially novel way to improve their processability. 22–29 Correspondence to: B. R. Guduri (bguduri@csir.co.za). Contract grant sponsor: The National Research Founda- tion, South Africa; contract grant number: GUN 2050677. Contract grant sponsor: The University of the Free State. Journal of Applied Polymer Science, Vol. 101, 3529 –3536 (2006) © 2006 Wiley Periodicals, Inc.