Effect of Seawater on Thermal Behavior of Conventional and Nanophased Carbon/Epoxy Composites
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Effect of Seawater on Thermal Behavior of Conventional and Nanophased Carbon/Epoxy Composites Mohammad K Hossain, Kazi A Imran, Mahesh Hosur, and Shaik Jeelani Center for Advanced Materials (T-CAM), Tuskegee University 101 Chappie James Center, Tuskegee, AL 36088, U.S.A. ABSTRACT The effect of seawater on thermal behavior of conventional and nanophased carbon/epoxy composites was investigated in this study. Composites were fabricated with 1 wt.%, 2 wt.%, and 3 wt.% nanoclay by vacuum assisted resin transfer molding (VARTM) process and compared with neat samples with and without exposure to seawater. Thermal characterization was performed by the dynamic mechanical analysis (DMA) and thermogravimetric analysis (TGA). Samples exposed to the seawater for 30- and 60-day periods revealed that samples with nanoclay retained better thermal properties compared to the neat samples. Storage modulus was reduced by 6.28%, 6.76%, 6.15%, and 7.05% for neat, 1 wt.%, 2 wt.%, and 3 wt.% nanoclay infused samples, respectively, after the samples were exposed to seawater for 60 days . From TGA results, it was observed that the thermal stability is not related to nanoclay content and conditoning. Optical microscope (OM) and scanning electron microscope (SEM) studies revealed no significant change in surface morphology in the 30-day conditioning samples. INTRODUCTION Composite structures are typically subjected to different environmental conditions that might affect their thermal properties. Fiber reinforced polymeric (FRP) composites may be used to recover oil and gas from more depth economically due to their high strength and stiffness to weight ratio, low density, corrosion resistance, and good fatigue and mechanical properties compared to metallic materials [1, 2]. However, moisture absorption decreases properties of polymeric composites weakening the bond between fiber and matrix and softening matrix materials. Moisture absorption by carbon/epoxy composites decreases mechanical properties and reduces service temperature [3, 4]. However, moisture absorption does not change carbon fiber properties significantly [5]. Moisture absorption is dominated by relaxation at low temperature but chemical degradation, cracking, and debonding may occur at high temperature. Chemical degradation hydrolyzes the resin and depolymerizes the chain [6]. Moisture reduces the glass transition temperature and stiffness [7]. Epoxy with approximately 2 wt.% nanoclay loading showed optimum results and no agglomerated particle was found [8]. Thermal properties including heat resistant, flame retardancy, and thermal stability of carbon fiber reinforced composites can be improved by adding a small amount of nanoclay as fillers [9]. Nanoclay has excellent barrier properties that can be used to reduce the permeability of moisture [10]. Epoxy exhibited ductile behavior at room temperature but it became brittle at a low temperature [11]. Polyester based composites degrade by hydrolysis reaction and debonding, and reduce their properties when exposed to seawater [12].
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