Influence of temperature on tensile behavior of multiwalled carbon nanotube modified epoxy nanocomposites
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investigation was carried out to characterize the tensile behavior of multiwalled carbon nanotube (MWCNT) modified epoxy nanocomposites in the glassy, viscoelastic, and rubbery regimes. 1 and 2 wt% MWCNT predispersed epoxy was used in this study. The cured samples were characterized using dynamic mechanical analysis for selection of different temperatures. The stress–strain behavior and toughness were determined in the temperature band of 25–140 °C. Addition of 1% CNT resulted in 16% improvement in the storage modulus at glassy state but 6% reduction in storage modulus was seen for 2% CNT-epoxy system. Tensile results showed that the strength and modulus have improved for 1% CNT-epoxy system. This study also revealed that for all the three systems, failure strain was maximum near the glass transition temperature (Tg) and significantly reduced above Tg. Also the CNT-modified epoxies showed improved toughness.
I. INTRODUCTION
The mechanical properties of polymers are dependent predominantly on the testing temperatures due to their viscoelastic nature. Epoxy-based polymers exhibit a relatively high modulus at low temperatures, and a reduction in modulus by several orders of magnitude at temperatures above their glass transition temperature (Tg). This drop in modulus is accompanied by a larger strain-to-failure with increasing temperatures. Based on this trend, the material changes from brittle to ductile, maximal toughness typically occurs at a testing temperature in the vicinity of Tg, where the chains are becoming more mobile allowing the network to sustain larger strains without losing much strength.1,2 At temperatures above Tg, materials exhibit rubber-like behavior. Since the amplitude of vibrational motion becomes greater at these temperatures, it leads to the distortion of the crosslinked network and hence results in a drastic reduction in failure strain.3 Epoxies are widely used as the matrices of choice for structural applications and are normally used in a variety of environmental conditions which cover a wide range of temperatures from room temperature (RT) to elevated temperatures. Also, it is essential to elaborate the effectiveness of nanoparticles in epoxies throughout a wide range of temperatures for specified applications. However, before such applications can be attempted, the critical mechanical performance of epoxy nanocomposites a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2014.197 J. Mater. Res., Vol. 29, No. 15, Aug 14, 2014
at both low and high temperatures must be thoroughly understood. It is evident that carbon nanotubes (CNTs) can be used to reinforce the polymer for improved mechanical properties. Two main issues that are critical to effectively improve the material properties of polymers by adding CNTs as filler are the interfacial bonding and proper dispersion of the individual CNTs in the polymeric matrix. Investigations focusing on the interfacial bonding between the nanotube and polymer matrix have been performed by many authors.4,5 Severa
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