STUDY on carbon micro/nanoparticals influence on electrical properties of carbon fiber reinforced epoxy matrix composites Blanka Tomková, Jana Novotná, Miroslava Pechočiaková Department of Material Engineering, Technical University, Liberec, Czech Republic Experimental Material: For experimental analysis were prepared epoxy specimens made from Bisphenol A-based low viscosity epoxy resin and cyklo-alifatic polyamine curing agent. As fillers were used following carbon materials in same concentration (2,5wt%): graphene particles (GNP), milled carbon particles from acrylic waste (mCPAN), commercially available Carbiso short carbon fibers (CMF), milled Carbiso fibers (mCMF), and milled recycled carbon fibers (mRCF), see Figure 1 and 2. Milling: mCMF, mRCF and mCPAN were made by the dry pulverization using high energy planetary ball milling of Fritsch Pulverisette 7. Samples CMF and GNP were not milled. Size of fillers: Parameters of CMF are specified by producer, who states average diameter about 7 µm and average length about 100 µm. Size of other samples was determined from structural micrographs using image analysing software NIS Elements9. Micrographs were scanned on SEM microscopes VEGA 3 TESCAN and VEGA TS 5130, see Table 1. Methods of measurement: AC conductivity was measured using AGILENT 4294. The measurements were carried out in the frequency range 100 Hz – 3MHz according to ASTM D150-98. Impact strength and energy were tested to analyse the influence of carbon nanofillers on epoxy matrix impact resistence. The test was run according to ISO 179-1:201011. Differential Scanning Calorimeter DSC6 was used to analyse glass transition of analysed set of filled epoxy specimen. The specimens were heated in an inert nitrogen atmosphere from 25°C up to presumed softening temperature of used epoxy resin (120°C) at a heating rate of 10°C/min. Using dynamic mechanical analysis DMA DX04T in 3PB mode the changes of elastic/plastic properties were scanned. The tests have been realized only up to 60°C (working temperature of used resin) at the heat rate of 3°C/min under the 1 Hz load frequency. (A) (B) (C) (D) (E) Figure 1. Schema of preparation a samples Figure 2. Sample A - CMF, Sample B - mCMF, Sample C - mRCF, Sample D – mCPAN, Sample E - GNP Discussion Experimental measurements have shown that use carbon nanoparticles as matrix fillers in 2,5% volume ratio had mostly none or rather weakening effect on properties of used epoxy matrix. Remarcable effect showed only CMF filling, which is standard short fiber carbon reinforcement. Other particles filling exhibit little influence on electrical properties, see Figure 5., in case of thermomechanical properties it even shows the drop (weakening effect). With respect to previously published works [13-16], and used material models, it is somewhat unexpected behavior, so we need to study this phenomenon more deeply. As for mechanical properties, the effect of fillers was more or less none, except for CMF, which showed their reinforcing effect, and GNP, which apparently shifted the Impact strength of matrix, see Figure 3. A comprehensive overview of the results is presented in Table 2. For now we don’t know, whether it is due to properties of used carbon particles, non optimal concentration of filling, or because this type of fillers is simply inappropriate for used matrix system, and it may work with other types of epoxy resins. Table 1. Measured data of average areas Properties GNP mCPAN CMF mCMF mRCF Equivalent particle diameter [µm] 0,36 0,62 7,0 3,2 1,51 Table 2. Selected properties of neat and CF filled epoxy Properties Neat Epoxy GNP mCPAN CMF mCMF mRCF AC conductivity [S.m-1] at 10 kHz 13,4.10-8 9,12.10-8 7,55.10-8 18,2.10-8 8,34.10-8 8,51.10-8 AC conductivity [S.m-1] at 100 kHz 16,2.10-7 11,2.10-7 9,10.10-7 22,1.10-7 9,51.10-7 10,0.10-7 AC conductivity [S.m-1] at 1000 kHz 1,62.10-5 1,24.10-5 0,99.10-5 2,35.10-5 1,06.10-5 1,07.10-5 Impact strength [kJ.m-2] 38,27 57,02 34,6 66,41 39,43 34,50 Flexural modulus [GPa] 3,28 3,45 3,31 3,78 3,52 3,33 Tensile modulus [GPa] calculated from 3PB 3,55 3,21 3,22 4,01 3,04 3,23 Tg [°C] 58,75 54,56 57,12 57,46 49,54 53,63 Figure 4. DSC Figure 6. DMA Figure 3. Mechanical properties Figure 5. AC conductivity Summary Achieved results show a good potential of CMF but rather poor influence of milled nanoparticles. So we would like to analyse this behavior more deeply, and study, why the use of smaller particles does not improve abovementioned properties, and what would be their influence in different concentrations. We will also test its influence on different type of resin systems, and incorporate achieved results in further research on design and development of fiber reinforced polymer composites. Finally we would like to transfer our findings into practical industrial applications. Literature 13. Fiedler, B., and others: Fundamental aspects of nano-reinforced composites; Composite Science and Technology 66, 3115 - 3125 (2006). 14. Kim, HS., Hahn, HT.: Graphite fiber composites interlayered with single-walled carbon nanotubes; J Comp Mater 45, 1109 –1120 (2011). 15. Guadagno, L., and others: Correlation between electrical conductivity and manufacturing processes of nanofilled carbon fiber reinforced composites; Composites Part B 80 7-14 (2015). 16. Qina, W., and others: Mechanical and electrical properties of CFcomp. with incorporation of graphene nanoplatelets at the fiber–matrix interphase Composites; Carbon 78, 99-105 (2015). Acknowledgements Authors are grateful for the financial support from the Student research project 2017 No.21195 supported by Czech Ministry of Education, and by Faculty of Textile, Technical University of Liberec. Authors are grateful for the useful help to prof. Mgr. J.Erhart PhD. and Ing. Jana Grabmüllerová. Technical University of Liberec, Studentská 1402/02, 461 17 Liberec 1, Czech Republic tel.: +420 485 353 280 fax: +420 485 353 542 e-mail: jana.novotna3@tul.cz