Influence of Multiwalled Carbon Nanotubes on the Processing Behavior of Epoxy Powder Compositions and on the Mechanical Properties of their Fiber Reinforced Composites Gleb Vaganov, 1,2 Vladimir Yudin, 1,2 Jyrki Vuorinen, 3 Evgeniy Molchanov 1 1 Institute of Macromolecular Compounds RAS, 199004, St. Petersburg, V.O. Bolshoy pr. 31, Russian Federation 2 Kazan Federal University, 420008, Kazan, 18 Kremlyovskaya St., Republic of Tatarstan, Russian Federation 3 Tampere University of Technology, 33720 Tampere, Korkeakoulunkatu 6, Finland This study reports the preparation of advanced carbon fiber composites with a nanocomposite matrix pre- pared by dispersing multiwall carbon nanotubes (CNTs) in a powder type epoxy oligomer with two different processing techniques (1) master batch dilution tech- nique and (2) direct mixing (with the help of twin-screw extruder in both cases). The master batch technique shows a better efficiency for the dispersion of the CNTs aggregates. The rheological results demonstrate that the incorporation of the CNTs into the epoxy oligomer leads, as expected, to a marked increase in the viscosity and of the presence of a yield stress point that also depends on the processing technique adopted. Carbon fiber (CFRP) and glass fiber (GFRP) composite materials were produced by electrostatic spraying of the epoxy matrix formulations on the car- bon and glass fabric, respectively, followed by calen- dering and mold pressing. The mechanical properties of the obtained epoxy/CNT-matrix composite materials, such as interlaminar fracture toughness, flexural strength, shear storage and loss moduli are discussed in terms of the processing techniques and fabric mate- rial. The incorporation of 1 wt% CNTs in the epoxy matrix results in a relevant increase of the fracture toughness, flexural strength and modulus of both CFRP and GFRP. POLYM. COMPOS., 00:000–000, 2015. VC 2015 Society of Plastics Engineers INTRODUCTION Nowadays, materials used in aerospace, automotive and shipbuilding industries should meet increasingly more demanding requirements. They are demand to simultane- ously combine high strength and rigidity, good resistance to dynamic loads and low weight, high long-term strength and increased reliability. The incorporation of CNTs in conventional continuous carbon fiber or glass fiber rein- forced polymer composites has attracted the attention of the research and industrial communities due to their unique mechanical and electrical properties [1–3]. CNTs polymer nanocomposites possess enhanced stiffness and strength, good electrical conductivity at relatively low fil- ler concentrations [1, 4, 5]. Besides the enchancement of the electrical conductivity at extremely low nanotube con- tents [4], the improvement of mechanical properties of polymer nanocomposites has been of special interest [6, 7]. The exceptionally high aspect ratio in combination with a low density, high strength, and stiffness makes CNTs a potential candidate as reinforcement for poly- mers. Several approaches have been reported to integrate CNTs into traditional fiber/polymer composites: infusion/ impregnation of a CNT-resin mixture into the primary fiber assembly [8, 9], direct growth of CNTs on reinforce- ment fabric substrates through chemical vapor deposition (CVD) [10], direct placement of CNTs between layers of the preform [1], electrophoretic deposition (EPD) onto the surface of fabric layers [11], reactions between function- alized CNTs and fibers [1], electrostatic assembly of oxi- dized CNTs onto functionalized fibers [12]. In all cases, the delamination resistance and out-of-plane properties were shown to improve through interactions between the propagating cracks and the CNTs through different mech- anisms such as CNT debonding, crack deflection, crack pinning and CNT pull out. One of the limitations for using CNTs as reinforcement in polymers is obtaining a uniform dispersion in the Correspondence to: Gleb Vaganov; e-mail: glebvaganov@mail.ru DOI 10.1002/pc.23419 Published online in Wiley Online Library (wileyonlinelibrary.com). VC 2015 Society of Plastics Engineers POLYMER COMPOSITES—2015