Anisotropic Thermal Conductivity of Polypropylene Composites Filled With Carbon Fibers and Multiwall Carbon Nanotubes Ilya Mazov, 1 Igor Burmistrov, 1,2 Igor Il’inykh, 1 Andrey Stepashkin, 1 Denis Kuznetsov, 1 Jean-Paul Issi 3 1 Department of Functional Nanosystems and High-Temperature Materials, National University of Science and Technology “MISIS” Leninskiy pr. 4, Moscow, Russia 119049 2 Department of Chemical Technology, Saratov Technical State University, Saratov, Russia 410054 3 Institute of Condensed Matter and Nanosciences, Universit  e catholique de Louvain, Place de l’Universit  e 1, 1348 Louvain-La-Neuve, Belgium Polypropylene-based composites filled with carbon fibers and multiwall carbon nanotubes were produced by coagulation precipitation technique. Composite articles were produced by conventional injection mold- ing technique. It was shown that the addition of carbon nanotubes (10% of total amount of carbon fibers) results in significantly increased anisotropic thermal conductiv- ity of the composite due to formation of thermal conduc- tive bridges between carbon fibers, which are oriented during molding. The addition of CNTs has a significant effect with more than a 50–70% increase of both the axial and transverse thermal conductivity of the compos- ite. Produced composites were used for injection mold- ing of polymeric radiators for LED lamps, showing sufficient heat dissipation efficiency allowing using them for industrial application in the field. POLYM. COMPOS., 00:000–000, 2014. V C 2014 Society of Plastics Engineers INTRODUCTION In recent years carbon nanotubes are increasingly used for the synthesis of polymer-based composite materials with enhanced properties. Among them carbon nanotubes (CNTs) and carbon fibers (CFs) are widely used due to their superior mechanical properties and their high electri- cal and thermal conductivities [1–3]. CF- and CNT-filled plastics are of great interest because of simultaneous improvement of mechanical, thermal and electrical properties. Thermally conductive polymers can be used in wide variety of applications— electronics, aerospace, energy storage, etc. One of the promising applications for such materials is their usage as a component of heat dissipating interfaces, such as radia- tors for electronic circuits, displays or LED lamps. The last application field is growing in recent years due to the progress in industrial fabrication of LED light sources. One of the most important factors for determin- ing LED lamp efficiency and life cycle is the ratio between current consumption and heat dissipation flow. Typical LED life cycle can reach 100,000 h in favorable temperature operation modes. Moreover, the power of emitted light decreases with an increase of the tempera- ture of the LED p-n junction. Typically metallic radiators made of aluminum or sim- ilar metals and/or alloys are used for cooling LED lamps. However, it is promising to use thermally conductive plastics as radiator materials due to their enhanced work- ability. Indeed, such materials can be processed by typical injection casting machines at moderate temperatures and pressures with lower requirements for mechanical proc- essing as compared to the same metallic devices. The typical room temperature thermal conductivity of pristine isotropic crystalline polymers does not exceed 1 W/mK (0.15–0.67 for polyethylene with a crystallinity ratio of 0.4–0.9, respectively) and ranges from 0.1 to 0.22 W/mK for polypropylene. Effective cooling of LED crystals can be achieved with radiator materials with ther- mal conductivities not less than 1–1.5 W/mK [4]. Ther- mal conductivity of plastics can be significantly improved by the addition of CFs and CNTs [5, 6]. The thermal conductivity (TC) value of the CFs was estimated elsewhere [7–9]. Because of the almost parallel alignment of the graphene layers and to the presence of Correspondence to: I. Mazov; e-mail: ilya.mazov@gmail.com Contract grant sponsors: FASI project of Ministry of Education and Sci- ence and RFBR project of Academy of Science of the Russian Federa- tion, Development Program of National University of Science and Technology (NUST MISIS, Program of Development). DOI 10.1002/pc.23104 Published online in Wiley Online Library (wileyonlinelibrary.com). V C 2014 Society of Plastics Engineers POLYMER COMPOSITES—2014