UDK 678.7:621.793 Original scientific article/Izvirni znanstveni članek ISSN 1580-2949 MTAEC9, 47(1)25(2013) GRAPHITE-FLAKE CARBON-BLACK-REINFORCED POLYSTYRENE-MATRIX COMPOSITE FILMS DEPOSITED ON GLASS-FIBER WOVEN FABRICS AS PLANE HEATERS KOMPOZIT POLISTIRENA, OJAČAN Z GRAFITNIMI LUSKAMI IN SAJAMI, NANESEN NA TKANINO IZ STEKLENIH VLAKEN ZA PLOŠČATE GRELNIKE Mustafa Erol12,3, Erdal ^elik12 JDokuz Eylul University, Department of Metallurgical and Materials Engineering, Buca, 35160 Izmir, Turkey 2Dokuz Eylul University, Center for Production and Applications of Electronic Materials (EMUM), Buca, 35160 Izmir, Turkey 3Dokuz Eylul University, Graduate School of Natural and Applied Sciences, Buca, 35160 Izmir, Turkey m.erol@deu.edu.tr Prejem rokopisa — received: 2012-05-07; sprejem za objavo - accepted for publication: 2012-07-04 Graphite-flake carbon-black/polystyrene composite films as plane heaters are promising materials since they are smarter than the traditional heating elements. In the present study, we are concerned mainly with the production, characterization and industrial application of graphite-flake carbon-black-reinforced polystyrene-matrix composite films deposited on glass-fiber woven fabrics as plane heaters. Within this scope, graphite flakes and carbon-black powders were dispersed in polystyrene gel and deposited on glass-fiber woven fabrics with different weight ratios. Subsequently, the films were dried at 60 °C for 30 min in the air. Structural and surface properties of the produced films were characterized with XRD and SEM, respectively. Electrical and heating properties were determined with a hand-made experimental setup containing a multimeter and a thermocouple. It was found that uniform and partially ordered films depending on the weight ratio and percolation threshold were obtained as plane heaters. Planar heating of up to 60 °C was observed with a 24-V DC power supply. Keywords: plane heater, composite, graphite flake, carbon black, conductive polymer Kompozitne plasti polistirena z grafitnimi luskami - sajami so obetajoči materiali za ploščate grelnike, ker so „pametnejši" od tradicionalnih grelnih elementov. V tej študiji obravnavamo proizvodnjo, karakterizacijo in industrijsko aplikacijo kompozitne tanke plasti polistirena, ojačanega z grafitnimi luskami - sajami, nanesenega na tkanino iz steklenih vlaken, za ploščate grelnike. S tem namenom so bile v tej študiji grafitne luske in saje razpršene v polistirenskem gelu, nanesene v različnem masnem razmerju na tkanino iz steklenih vlaken. Nato so bile tanke plasti sušene pri 60 °C 30 min na zraku. Strukturne in površinske lastnosti nastalih tankih plasti so bile ocenjene z XRD in SEM. Električne in grelne lastnosti so bile določene z ročno izdelano sestavo, ki vsebuje multimeter in termoelement. Ugotovljeno je bilo, da je pri ploščatih grelnikih enakomerna in delno urejena plast odvisna od razmerja mas in deleža pronicanja. Pri uporabi enosmerne napetosti 24 V je bilo opaženo segrevanje ploščatih grelcev do 60 °C. Ključne besede: ploščati grelnik, kompozit, grafitne luske, saje, prevoden polimer 1 INTRODUCTION Polymers with their specific nature are known as good insulators for electronic applications. Developments of the polymers, together with the new researches, have focused on desired conductivities and a wide range of application for decades. The conductivity of polymers can be obtained in two ways: (a) by producing a polymer that is intrinsically conductive or can be made so by doping and (b) by loading an electrically insulating matrix with conductive fillers1. The fillers, which involve conductivity, are generally based on metallic materials such as Ni, Cu, Ag, Al and Fe2-4 as well as carbon derivates such as carbon black, carbon fiber, graphite and carbon nanotube5-8. Natural graphite is mostly used in refractories, steel-making (as a heating element/electrode), expanded graphite, brake linings, foundry facings and lubricants. The heating property of graphite is a significant issue for electric-arc furnaces in the steel industry. As heating has been an important process for humankind for ages, the above issue has also been present since the discovery of fire up until today's modern heating technologies. With respect to heating, fires, stoves, heat exchangers, air conditioners, furnaces, irons, floor heaters, etc. are the products that fulfill this requirement. These heating systems generally use fossil fuels (wood, petroleum, natural gas, etc), as well as solar energy and electricity. Due to the physical nature of heated air, it flows from bottom to top in a heated place. Taking this into account, efficient systems for heating, like floor heaters, can be selected. There are many detailed researches on floor heating in several reports9-12. In addition, due to their conductive properties, graphite and carbon-black powders were incorporated into its structure to provide for the resistivity of the final composite structure. Nevertheless, to the best of our knowledge, no experimental work has been reported in the literature on the self-heating properties of polymer-graphite and carbon-black composites and their application as plane heaters using composite films. The fabrication of uniform graphite-flake carbon-black/polystyrene composite films is impossible by using conventional methods such as melting and heating because of several difficulties. To circumvent this problem, as explained in ref.1, a similar gelation technology was employed to dissolve polystyrene pellets in a quickly evaporating solvent. Graphite-flake and carbonblack powders were dispersed in a polystyrene-chloroform gel matrix with different concentrations. The obtained gel containing these powders was deposited on glass-fiber woven fabrics to obtain the intended plane heaters. Then the structure, the surface morphology, as well as electrical and heating properties of the deposited composite films were investigated. 2 EXPERIMENTAL DETAILS Graphite flakes (Tupras), carbon black (Selen Chemistry), polystyrene pellets (Tupras Petkim) and chloroform (Aldrich) were commercially provided to produce a new-generation heating element. Polystyrene pellets were dissolved in chloroform using an ultrasonic bath for 60 min and subsequently a viscous gel was obtained prior to depositing the composite films. Graphite-flake and carbon-black powders were basically added to obtain the gel as schematically illustrated in Figure 1. After these processes, graphite-flake carbon-black-reinforced polystyrene-matrix mixtures were prepared for the plane-heating composite element. The strategy for determining the composite samples was based on a composite including the total powder weight against the polystyrene weight with a ratio of 0.6 that is referred to as X. Here the coefficient of X as 1, 2 and 4 means that the ratios are 0.6, 1.2 and 2.4, respectively. Beside this, the weight ratio of carbon black/graphite flake was determined as C/G = 0.62 for the composites including 1X, 2X and 4X. In order to determine individual effects of the powders on the properties, the composites containing just carbon black and just graphite were prepared as 1XC and 1XG, respectively. The details and definitions of the above mixture specifications were noted in Table 1. Table 1: Mixture specifications and content data Tabela 1: Pregled mesanic in podatki o vsebnosti Precursor 4X* 2X* 1X* 1XG* 1XC* Polystyrene (g) 1 1 1 1 1 Chloroform (ml) 8 8 8 8 8 Carbon black (g) 0.92 0.46 0.23 0.6 0 Graphite (g) 1.48 0.74 0.37 0 0.6 *X indicates a composite having the mass ratio C/G Coefficients of X indicate (C + G)/P 0.62 As the substrate choice is an important parameter for any film-deposition technique, glass-fiber, woven fabric substrates with a planar density of 100 g/m2 were chosen because of their flexibility and high-temperature service abilities. The produced mixtures were spray painted on these substrates using an air-compressor-based mechanism. After that deposited films were dried to remove the solvent at 60 °C for 30 min on a hot plate for three times. X-ray diffraction (XRD, Rigaku D/MAX-2200/PC) patterns of the coatings were determined to identify the phase structure using a diffractometer with CuK« irradiation. The surface properties of the films were examined with the help of scanning electron microscopy (SEM, JEOL JSM 6060). Figure 1: Schematic illustration of the process Slika 1: Shematski prikaz procesa Figure 2: Experimental setup for determining electrical and heating properties of composite films Slika 2: Eksperimentalni sestav za določanje električnih in grelnih lastnosti kompozitnih tankih plasti Electrical and heating properties of the composite coatings were determined using the basic experimental setup as illustrated in Figure 2. This basic setup consisted of a digital thermometer, a 24-V direct-current (DC) power supply and a multimeter (used as an ampermeter in this circuit). Square specimens with the dimensions of 30 mm x 30 mm were cut and electrodes were painted on two edges with a silver paste as depicted with the orange color in Figure 2. The specimens were fixed to the circuit using copper jaws. The circuit current and the time versus the temperature data were noted from this set up. The resistances of the film were basically calculated using Ohm's law. 3 RESULTS AND DISCUSSION The XRD patterns of the produced composite films on the glass-fiber woven fabrics are demonstrated in Figure 3 in order to prove that their structure consists of both graphite flakes and carbon-black powder. As seen from the XRD patterns, the main peaks of graphite and carbon were determined at the diffraction angle of 26.6°. With respect to increasing the total powder amount, higher proportional-intensity data was recorded retaining the mixture contents listed in Table 1. In addition, crystalline-like polystyrene structure was clearly found 10 20 30 40 50 60 1000 800 600 400 200 0 1500 1000 500 — 6000