Photonic crystals in biology - NanoTR-VI

PPPPP,PP,P(PR RmPoster Session, Thursday, June 17Theme F686 - N1123Differential Scanning Calorimetry Investigation of Conductive Nanocomposites Based on EVACopolymer and Expanded Graphite112113444UI. H. TavmanUP P*, K. SeverP P, Y. SekiP P, A. EzanPPA. TurgutPPI. Özdemir P P, I. KrupaP P, M. OmastovaP P, I. NovakP1PMechanical Engineering Dept., Dokuz Eylul Univ., 35100 Bornova Izmir, Turkey2PTDepartment of Chemistry, Dokuz Eylül University, Buca, 35160 zmir, TurkeyPFaculty of Engineering, Bartin University, Bartin, TurkeyPPolymer Institute, SAS, Dúbravská cesta 9, 842 36 Bratislava, Slovakia43Abstract- Polymers which are normally insulating materials, may be made electrically and thermally conductive by the addition ofconductive fillers. In this study the nanocomposites consist of the ethylene- vinyl acetate copolymer (EVA) as base material, the conductivefillers used are expanded graphite (EG) and untreated graphite (UG). Nanocomposites containing up to 50 weight % of filler material wereprepared by mixing them in a Brabender Plasticorder. A differential scanning calorimetry study reveals us a decrease in glass transitiontemperature of the composite with increase in particle content.During the last decade there has been an increasinginterest in the field of polymer nanocomposites since themodification of polymer matrix with small amounts ofnanoparticles proved to be effective in enhancing themechanical, electrical, thermal, fire retardant, barrier andoptical properties of a variety of polymers. Polymergraphitenanocomposites are interesting due to theirpotential conductive properties. Graphite is found in naturein the form of graphite flakes or powder of various particlesizes. Graphite flakes, such as clays, are composed oflayers, normally smaller than 100 nm in thickness[1]. Ifthe appropriate process conditions are applied, graphitenanocomposites offer the potential to produce materialswith excellent mechanical, electrical, and thermalproperties at reasonable cost, which opens up many newapplications[2]In this study Ethylene- vinyl acetate copolymer (EVA)containing 14 wt% of vinyl acetate (VA) was used asmatrix material. Its melt flow index is 9.8 g/10min(190°C/2.16 kg). The filler materials were expandedgraphite (EG) and untreated graphite (UG). Ethylenevinylacetate copolymer (EVA) – graphite mixtures wereprepared in a Brabender Plasticorder PLE 331 internalmixer at 150 °C for a total mixing time of 10 min, themixing chamber capacity being 30ml. The rotors turned at35 rpm in a counter-rotating fashion with a speed ratio of1.1. After 10 minutes, the mixing chamber of theBrabender apparatus was opened and the resulting mixturetaken out. The resultant mixture was then put in acomression moulding die and compressed in acompression molding press at 120°C, under 40 kP pressurefor one minute to obtain samples in the form of sheets of1mm in thickness. During the mixing process theexpanded graphite exfoliates. The exfoliation processstarts on the edges of EG grains and the exfoliated graphiteflakes have nano-sized dimensions with bigger surfaceareas compared to micro-sized dimensions of the UGpellets.The glass transition (TRgR), melting(TRmR), crystallization(TRcR) temperatures, as well as melting(hRmR) andcrystallization (hRcR) enthalpies for pure EVA and alsonanocomposites 6 and 15 weight % of EG; 6 and 15weight % of UG were measured by DSC at aheating/cooling rate of 10 °C /min. The results obtainedusing Perkin-Elmer DSC were given in Table 1. There wasa decrease in glass transition temperature of thenanocomposites with respect to pure EVA, the decrease isslightly stronger for EG filled samples then UG filledsamples. The melting(TRmR) and crystallization (TRcR)temperatures were practically unchanged for thenanocomposites.The EVA- EG nanocomposite showed a lowerpercolation threshold of electrical conductivity which isabout 5% of volumetric filler content, compared to about15% of volumetric filler content for EVA-UG composites.Electrical conductivity of EVA- EG nanocomposites wasalso higher than electrical conductivity of EVA-UGcomposites filled with micro-sized filler at the sameconcentrations.Table 1. DSC analysis results of EVA/UG and EVA/EG nanocompositesT g T hRm TRc hRcSample Code oooPC) (P PC) (j/g) (P PC) (j/g)Pure Eva -28.2 87.71 89.53 72.71 -6.49EVA-EG94/6 -32.32 87.39 74.67 73.25 -8.01EVA-UG96/4 -30.58 88.23 76.14 73.25 -7.53EVA-EG85/15 -33.35 87.74 60.55 73.92 -2.75EVA-UG85/15 -31.39 87.55 67.11 73.41 -5.01TRgR: Glass transition temperatureTRmR: Melting temperatureTRcR: Crystallization temperaturehRmR: Melting enthalpyhRcR: Crystallization enthalpyThis research was supported by the Scientific Support ofthe bilateral Project No. 107M227 of TUBITAK and SASand partly by the project VEGA No. 2/0063/09.*Corresponding author: HTismail.tavman@deu.edu.trT[1] Guterres, J-M, Basso, N.R.S, Galland, GB, 2010,Polyethylene/Graphite Nanocomposites Obtained by In SituPolymerization, Fabiana De C. Fim, Journal of Polymer Science:Part A: Polymer Chemistry, 48: 692–698.[2] H. Fukushima,H. , Drzal, L-T., Rook, B. P. , Rich, M. J.,2006, Thermal Conductivity of Exfoliated GraphiteNanocomposites, Journal of Thermal Analysis and Calorimetry,85(1): 235–238.6th Nanoscience and Nanotechnology Conference, zmir, 2010 726