Carbon epoxy electrical properties

Two case studies are presented in which polymer nanotube composites are proposed as replacements for conventional materials. We evaluate the technical and economic feasibility of using them as smart materials for strain gauges thus, exploiting their electrical properties, and as structural materials for aircraft panels bringing into play their mechanical properties. Our analysis shows that as new strain gauge materials, polymer nanotube composites offer many advantages. As a possible replacement for aluminum in an aircraft panel, it is found that a hybrid composite of (Epoxy 33% carbon fabric + 30% carbon fibers + 3% CVD-MWNT) is an attractive candidate. 

Epoxies are excellent electrical insulators. Electrical properties are reduced on increasing the polarity of the molecules. Addition of metallic fillers, metallic wools and carbon black convert the non-conductive epoxy formulation into an electrically conductive system. Non-conductive fillers increase the arc resistance and to some extent increase the dielectric constant. 

Table 5.6 Electrical properties of carbon black filled epoxy resins cured with different curing agents at 23°C.

The properties are anisotropic to varying degrees (i.c.. mechanical, thermal, and electrical properties vary with direction in the material). The highest anisotropy is illustrated by the properties of a fully aligned 60% (by volume) carbon fiber epoxy laminate, where the properties parallel with the fiber direction can be thirty times greater than in the perpendicular direction, whereas in a molded short-fiber system the ratio of properties in perpendicular directions may only be a factor of two. The fibers themselves may have even higher anisotropy (e.g.. carbon and aramid fibers). 

The majority of base materials for circuit boards are combinations of a copper foil with a laminate, where the laminate itself consists of a carrier material and a resin. Thus properties of the base material such as mechanical strength, dimensional stability, and processi-bility are determined primarily by the carrier material. On the other hand, the resin materials are responsible for the thermomechanical and electrical properties as well as for its resistance against chemicals and moisture. Frequently used carrier materials are based on glass and carbon fibers, papers, and polyamide, whereas the majority of the laminating resins are thermosets such as epoxies, phenolics, cyanates, bismaleimide triazine (BT) resins, maleimides, and various combinations of these [13]. 

Examples of performance in TP matrix with carbon or graphite fibers include the use of epoxy and nylon (PA). Nylon 6 (DuPont) with a 30 wt% fiber content will increase flexural strength by about three times, and flexural stiffness may be raised by a factor of seven. Electrical properties, fiiction behavior and wear resistance may also be improved. The electrical applications largely fall into two categories to impart conductivity and prevent build-up of electrostatic discharge (which may... 

Sandler J, Shaffer MSP, Prasse T, Bauhofer W, Schulte K and Windle A H (1999) Development of a dispersion process for carbon nanotubes in an epoxy matrix and the resulting electrical properties, Polymer 40 5967-5971. 

Electrical properties have been reported on numerous carbon fiber-reinforced polymers, including carbon nanoflber-modified thermotropic liquid crystalline polymers [53], low-density polyethylene [54], ethylene vinyl acetate [55], wire coating varnishes [56], polydimethyl siloxane polypyrrole composites [50], polyacrylonitrile [59], polycarbonate [58], polyacrylonitrile-polycarbonate composites [58], modified chrome polymers [59], lithium trifluoromethane sulfonamide-doped polystyrene-block copolymer [60], boron-containing polyvinyl alcohols [71], lanthanum tetrafluoride complexed ethylene oxide [151, 72, 73], polycarbonate-acrylonitrile diene [44], polyethylene deoxythiophe-nel, blends of polystyrene sulfonate, polyvinyl chloride and polyethylene oxide [43], poly-pyrrole [61], polypyrrole-polypropylene-montmorillonite composites [62], polydimethyl siloxane-polypyrrole composites [63], polyaniline [46], epoxy resin-polyaniline dodecyl benzene sulfonic acid blends [64], and polyaniline-polyamide 6 composites [49]. 

Until 2003, Chen s [28], Qu s [29-31], and Hu s [32] groups independently reported nanocomposites with polymeric matrices for the first time the. In Hsueh and Chen s work, exfoUated polyimide/LDH was prepared by in situ polymerization of a mixture of aminobenzoate-modified Mg-Al LDH and polyamic acid (polyimide precursor) in N,N-dimethylactamide [28]. In other work, Chen and Qu successfully synthesized exfoliated polyethylene-g-maleic anhydride (PE-g-MA)/LDH nanocomposites by refluxing in a nonpolar xylene solution of PE-g-MA [29,30]. Then, Li et al. prepared polyfmethyl methacrylate) (PMMA)/MgAl LDH by exfoliation/adsorption with acetone as cosolvent [32]. Since then, polymer/LDH nanocomposites have attracted extensive interest. The wide variety of polymers used for nanocomposite preparation include polyethylene (PE) [29, 30, 33 9], polystyrene (PS) [48, 50-58], poly(propylene carbonate) [59], poly(3-hydroxybutyrate) [60-62], poly(vinyl chloride) [63], syndiotactic polystyrene [64], polyurethane [65], poly[(3-hydroxybutyrate)-co-(3-hydroxyvalerate)] [66], polypropylene (PP) [48, 67-70], nylon 6 [9,71,72], ethylene vinyl acetate copolymer (EVA) [73-77], poly(L-lactide) [78], poly(ethylene terephthalate) [79, 80], poly(caprolactone) [81], poly(p-dioxanone) [82], poly(vinyl alcohol) [83], PMMA [32,47, 48, 57, 84-93], poly(2-hydroxyethyl methacrylate) [94], poly(styrene-co-methyl methacrylate) [95], polyimide [28], and epoxy [96-98]. These nanocomposites often exhibit enhanced mechanical, thermal, optical, and electrical properties and flame retardancy. Among them, the thermal properties and flame retardancy are the most interesting and will be discussed in the following sections. 

Fan Z, Zheng C, Wei T, Zhang Y, Luo G (2009) Effect of carbon black on electrical property of graphite nanoplatelets/epoxy resin composites. Polym Eng Sci 49 2041 Filippone G, Causa A, Filippone G, Causa A, de Luna MS, Sanguigno L, Aciemo D (2014) Assembly of plate-like nanoparticles in immiscible polymer blends—effect of the presence of a preferred liquid-liquid interface. Soft Matter 10 3183 Fisher ME, Essam J (1961) Some cluster size and percolation problems. J Math Phys 2 609 Foygel M, Morris R, Anez D, French S, Soholev VL (2005) Theoretical and computational studies of carbon nanotube composites and suspensions electrical and thermal conductivity. Phys Rev B 71 104201... 

Lee, H. et al. 2008. Improvements of electrical properties containing carbon nanotube in epoxy/graphite bipolar plate for polymer electrolyte membrane fuel ceBs. Journal of Nanoscience and Nanotechnology 8 5464-5466. 

S. Bal, "Influence of dispersion states of carbon nanotubes on mechanical and electrical properties of epoxy nanocomposites," Journal of Scientific and Industrial Research, vol. 66, pp. 752-756, 2007. 

Carbon nanotubes dispersed as conductive fillers in an epoxy matrix result in electrical properties which can be compared to those obtained using an optimized... 

Saito R, Dresselhaus G et al (1998) Physical properties of carbon nanotubes. Imperial College, London Salinas-Ruiz MdM (2009) Development of a rubber toughened epoxy adhesive loaded with carbon nanotubes, for aluminium - polymer bonds. PhD thesis. School of Applied Science, Cranfield University Sandler J, Shaffer MSP et al (1999) Development of a dispersion process for carbon nanotubes in an epoxy matrix and the resulting electrical properties. Polymer 40 5967... 

Alloui, A., Bai, S., Cheng, H., Bai, J. - Mechanical and electrical properties of a MWNT/epoxy composite . Composites Sci. Technol. 62 (2002) 1993-1998 Ruoff, R., Lorents, D. - Mechanical and thermal properties of carbon nanotubes . 

---