Improvement in electrical, thermal and mechanical properties of ...

Zhou et al. – eXPRESS Polymer Letters Vol.2, No.1 (2008) 40–48Figure 5. DMA results of neat and nanophased epoxyFigure 6. Normalized weight vs. temperature curves ofneat and nanophased epoxytangular bars measuring 2 mm × 30 mm × 12 mmby a diamond saw.The loss factor curve, tanδ, of the neat epoxy andits nanocomposites measured by DMA are shownin Figure 5. The peak height of loss factor decreasedwith higher CNT content, but the temperaturedetermined from the peak position of tanδ, T g ,increased 17°C. In addition, the width tanδ increasedwith higher CNT content. Similar results have beenobserved in other nanocomposites [21]. Figure 5also shows the DMA plots of storage modulus vs.temperature as a function of loading carbon nanotubes.The storage modulus steadily increasedwith higher CNT weight percents. The addition of0.4 wt% of carbon nanotube yielded a 93% increaseof the storage modulus at 30°C. The high aspectratio and elastic modulus of CNTs, as compared tonanoclay and nanoparticles [7, 8], increase the storagemodulus with smaller amounts of CNTs.Thermogravimetric Analysis (TGA) was conductedwith a TA Instruments TGA2950 in nitrogen gas ata heat rate of 10°C/min, from ambient to 600°C.The TGA samples were cut into small pieces usingan ISOMET Cutter and were machined using amechanical grinder to maintain sample weightsbetween 5–20 mg. Universal Analysis 2000-TAInstruments Inc., a data acquisition system, generatedthe real-time characteristic curves. All TGAtests are run in nitrogen gas. Figure 6 shows theTGA results of neat and nanophased epoxy. Thenormalized weights vs. temperature curves of fivematerials overlap. All samples started to decomposearound 340°C and completely decomposedaround 460°C. The derivative peaks of weight vs.temperature curves show the decomposition temperature.But CNT has little effect on decompositiontemperature of epoxy.3.3. Mechanical responseFlexural tests were performed according to ASTMD790-86 under a three-point bend configuration.The tests were conducted in a 10 kN servo-hydraulictesting machine equipped with a Test Ware dataacquisition system. The machine was run under displacementcontrol mode at a crosshead speed of2.0 mm/min. All the tests were performed at roomtemperature. Test samples were cut from the panelsusing a Felker saw fitted with a diamond coatedsteel blade. Five replicate specimens from four differentmaterials were prepared for static flexuretests.Typical stress-strain behavior from the flexuraltests is shown in Figure 7. All specimens failedimmediately after the tensile stress reached themaximum value. The stress-strain curves showedconsiderable non-linearity before reaching themaximum stress, but no obvious yield point wasfound in the curves. Five specimens were tested foreach condition; the average properties obtainedfrom these tests are listed in Table 1.Table 1. Mechanical properties of neat and nanophasedepoxyModulus[GPa]Strength[MPa]Failure strain[%]Neat epoxy 2.46 093.5 4.020.1% CNT 2.54 109.0 6.060.2% CNT 2.60 115.0 6.800.3% CNT 2.65 121.0 7.580.4% CNT 2.75 113.0 5.1244