Study of Mechanical Responses and Thermal Expansion of CNF-modified Polyester Nanocomposites Processed by Different Mixi
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Study of Mechanical Responses and Thermal Expansion of CNF-modified Polyester Nanocomposites Processed by Different Mixing Systems Muhammad E. Hossain, Mohammad K. Hossain1, Mahesh Hosur and Shaik Jeelani Center for Advanced Materials (T-CAM), Tuskegee University 101 Chappie James Center, Tuskegee, AL 36088, U.S.A. ABSTRACT In this study, different dispersion techniques such as sonication at high frequency, mechanical mixing, and magnetic stirring methods were employed to infuse 0.1 to 0.4 wt.% carbon nanofiber (CNF) into polyester matrix to study the influence of CNF on mechanical and thermal properties of the polyester nanocomposites. Dispersion of CNF studied using scanning electron microscopy (SEM) micrographs revealed excellent dispersion of CNF using sonication when 0.2 wt.% CNF was mixed in polyester resulting in enhanced mechanical response. On the other hand, agglomerations were observed in samples prepared with other mixing methods. Polyester with 0.2 wt.% CNF samples prepared by sonication resulted in 88% and 16% increase in flexural strength and modulus, respectively, over neat samples. Quasi-static compression tests showed similar increasing trend with addition of 0.2 wt.% CNF. Dynamic mechanical analysis (DMA) showed 35% and 5 °C improvement in the storage modulus and glass transition temperature (Tg), respectively, in the 0.2 wt.% loaded samples. Thermal mechanical analysis (TMA) performed on neat and samples with 0.2 wt.% CNF showed lower coefficient of thermal expansion (CTE) in nanophased sample compared to neat. Fracture morphology evaluated using SEM revealed relatively rougher surface in CNF-loaded polyester compared to neat as a result of better interaction between fiber and matrix due to the presence of CNF. INTRODUCTION Polyester resin is widely used for advanced composites where low cost, good strength and stiffness, processability, dimensional stability, and chemical resistance are required. However, mechanical properties of this polymer matrix, such as the strength, modulus, and toughness of polyester resins may not be enough for some end-use applications. In order to utilize polyester resin for such applications, addition of nanosize fillers to the resin which results in enhanced properties is a useful approach [1]. The performance of nanocomposites is highly dependent on uniform distribution of nanoparticles into the host polymer. Maximum performance of nanocomposites can be achieved with homogeneous dispersion of nanoparticles into a polymer matrix while non-homogeneous dispersion causes even degradation of the host polymer’s properties. In this rationale, an efficient technique is required to be employed to disperse carbon nanofiber (CNF) into the polyester matrix in order to obtain the enhancement in the properties of polyester composites. Prolongo et al. [2] recommended carrying out several stages of CNF dispersion along chemical modification and functionalization of CNF and combining different dispersing techniques including sonication with high frequency, magnetic stirring, and hig
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