Cost-effective open microwave heating of polymer resin using interdigital electrode array film and dispersed carbon nanotubes Shinya Hatori a , Ryosuke Matsuzaki a,⇑ , Akira Todoroki b a Department of Mechanical Engineering, Tokyo University of Science, 2641 Yamazaki, Noda, Chiba 278-8510, Japan b Department of Mechanical Sciences and Engineering, Tokyo Institute of Technology, 2-12-1-I1-58, Ookayama, Meguro, Tokyo 152-8552, Japan article info Article history: Received 15 April 2013 Received in revised form 3 September 2013 Accepted 30 November 2013 Available online 16 December 2013 Keywords: A. Carbon nanotubes A. Polymers B. Electrical properties E. Microwave processing abstract Conventional microwave heating requires an expensive facility and its enclosed-type oven limits the size of curable products. This article proposes an open-type microwave heating of a polymer resin using microwaves produced by an interdigital electrode array film positioned between the composites and the mold. The proposed method has the advantages of reduced facility cost and applicability to large composite structures. The dispersion of carbon nanotubes (CNTs) in the resin also enables the use of a relatively low applied voltage for the heating. This is because the CNT-filled resin has a high dielectric loss tangent. The generated heat was observed to increase with the CNT content and a heating efficiency of 70% was achieved. It was particularly observed that a significant temperature increase occurred at 0.08 wt% CNT content owing to the electric percolation phenomenon. Moreover, selective microwave heating using an electrode array also enabled the achievement of a more inhomogeneous increase in temperature. Ó 2013 Elsevier Ltd. All rights reserved. 1. Introduction Fiber-reinforced plastics (FRPs) are mainly used in aerospace engineering because of their high specific strength and stiffness. They are generally composed of thermosetting resins such as epoxy and unsaturated polyester, and the manufacturing process requires thermal curing. In conventional thermal curing using an oven or autoclave, thermal energy is transferred to the material through the atmosphere. A long cycle is therefore required for complete cur- ing of the resin. Moreover, the massive thermal energy wastage of the process results in a negative heating efficiency. The speed and energy conservation of microwave heating has led to increased interest in it as an alternate curing method [1,2]. In microwave heating, a polymer resin in an electric field trans- duces electromagnetic energy into thermal energy through dielec- tric loss. The phenomenon of internal heating directly raises the overall temperature of the resin [3–7]. Papargyris et al. [5] com- bined microwave heating with the resin transfer molding tech- nique to achieve 50% reduction in the cure cycle time. Zhou et al. [6] and Tanrattanakul and Jaroendee [7] compared the mechanical properties of epoxy composites cured by thermal heating and microwave heating, and found that the latter were as good as the former, and the curing time was also reduced. Recent studies have investigated the dispersion of conductive fillers such as carbon nanotubes (CNTs) and carbon black (CB) in liquid resins, with the aim of improving the generated heat and cure cycle of microwave heating [8–10]. CNTs have been of particular interest owing to their high aspect ratio and low specific weight, and it has been shown that their unique structures facilitate enhanced mechanical and electrical properties [11–17]. Higginbo- tham et al. [8] showed that the microwave heating of CNT mixtures could be used to improve polymer processing through the shorten- ing of the processing time and the consequent reduced production cost. Liu et al. [9] investigated the response of high-density polyeth- ylene (HDPE)/CB composites to microwave heating and observed that the addition of CB particles improved the microwave heat- ability of HDPE, and that the heat-ability of the composites varied with the CB content. However, because conventional ovens and microwave heating equipment need to enclose the composite structures, they must be larger than the structures. High costs are therefore involved in the development of equipment for heating large structures, even though the actual microwave heating saves energy. Moreover, the inhomogeneous dielectric loss tangent of the carbon filler mixture may result in an inhomogeneous tempera- ture increase during microwave heating [18]. Furthermore, the generated heat is difficult to anticipate and must be experimentally evaluated, which reduces production efficiency. These disadvan- tages pose serious challenges to the commercial development of FRP by microwave heating. There is therefore a compelling need for a new method of efficiently heating resins that does not require an expensive device. 0266-3538/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.compscitech.2013.11.029 ⇑ Corresponding author. Tel./fax: +81 4 7124 1501. E-mail address: rmatsuza@rs.tus.ac.jp (R. Matsuzaki). Composites Science and Technology 92 (2014) 9–15 Contents lists available at ScienceDirect Composites Science and Technology journal homepage: www.elsevier.com/locate/compscitech