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Naturally woven coconut sheath, a new natural fiber available in the form of woven mat is used as fiber reinforcement in polyester matrix. The hybridization effect of montmorillonite (MMT) on naturally woven coconut sheath/polyester composite has been investigated experimentally for free vibration characteristics using impulse excitation technique (IET). In the present study, naturally woven coconut sheath/clay-reinforced hybrid polyester composites were fabricated using a compression molding machine. The effect of organoclay addition (1, 2, 3 and 5 wt%), alkali (ATC) and silane treatment (STC) of the coconut sheath surface on free vibration characteristics were analyzed. Scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD) techniques were used to characterize the morphology of coconut sheath and structure of clay dispersed polyester. The dynamic mechanical analysis (DMA) and Fourier transform infrared (FTIR) analysis were carried out to analyze the effect of surface topology on chemically treated coconut sheath. The mechanism of chemical modifications on natural frequencies and the resultant improvement in the temperature dependence mechanical properties have also been reported. Enhanced vibration properties are observed up to 3 wt% of clay dispersion in hybrid composites, then it gets reduced for higher clay (>3 wt%) content. Modal damping of the hybrid composite is influenced by the addition of nanoclay and the surface treatments of the coconut sheath. Experimentally obtained natural frequencies are in good agreement with analytical and numerical results.

In this investigation, naturally woven coconut sheath is used as a new type of reinforcement. The hybrid composites are developed with the combination of naturally woven coconut sheath/E-glass/nanoclay using unsaturated polyester matrix and the effect of nanoclay on the mechanical and free vibration behavior is studied. It is found that the addition of nanoclay improved the mechanical and damping properties of the composite owing to the improved stiffness of the matrix by better dispersion of clay. In addition, the effect of alkali and silane treatments on fibers and different stacking sequence were investigated. It was observed that the alkali treatment of fibers improved the mechanical properties of the composites when cellulose fiber was present. This investigation presented a peculiar result in the case of silane treatment with the nanoclay, which is in contradiction with the earlier works. The stacking sequence of coconut sheath/coconut sheath/glass with alkali treatment of fibers provides the optimum increase in mechanical strength and free vibration characteristics. X-ray diffraction and transmission electron microscope were performed to understand the dispersion of nanoclay and its strengthening mechanism. In addition, scanning electron microscopy was used for fractography analysis. This investigation suggests an alternative material for the field of composites.

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