Preparation and characterization of oil palm empty fruit fibre polycaprolactone nickel zinc-ferrite and nickel oxide composites for microwave shielding

Electromagnetic shielding is an issue that needs to be resolved in the design and development of many electronic systems and components. A number of light-weight polymers have been proposed with shielding effectiveness (SE) as high as 80dB. However not all electromagnetic interference or compatibility applications demand materials with very high shielding effectiveness value. For example, the Wireless Avionics Intra-Communications protocol imposed only a minimum shielding effectiveness of only 5dB for the aircraft structural design. This thesis presents the development of natural oil palm fruit fibre reinforced polycaprolactone (PCL) composites filled with nickel zinc ferrite (NZF) for microwave shielding and absorbing applications. The oil palm empty fruit bunch fibre (OPEFB) exhibit good mechanical properties when compared with other natural fibres. The OPEFB fibres and PCL are biodegradable, cheap and less hazardous compared to many other industrial materials. OPEFB+PCL composites with NZF fillers provide cost effective solutions for applications requiring a minimum of 5dB shielding effectiveness. In this work, the properties OPEFB+PCL composites with nickel oxide (NiO) fillers were examined in the microwave frequencies. Different composition of NZF and NiO fillers will give different absorbing properties in the OPEFB+PCL matrix. Too low percentage of fillers in the OPEFB+PCL will not provide sufficient SE whilst too high percentage would be excessively expensive. The fillers were prepared by the conventional solid state method. Different compositions of filler were doped and blended to produce NZF+OPEFB+PCL and NiO+OPEFB+PCL composites. The crystalline structure of the composites was analyzed using X-ray diffraction (XRD) machine. The elemental compositions were examined using Scanning Electron Microscopy (SEM) and Fourier transform infrared (FTIR) techniques. Thermal analyses were carried out using TGA and DTG,scanning electron microscope (SEM) and energy dispersive X-ray analysis (EDX). The theoretical calculation of the transmission and reflection coefficients of the sample placed in the waveguide was computed using Nicholson-Ross-Weir method and Finite Element Method. Then later was accomplished using COMSOL software. The transmission and reflection coefficients as well dielectric properties were measured using an Agilent N5230A Network Analyzer from 8GHz to 12 GHz at room temperature. The permittivity of the composites was found to be dependable on the mixing ratio values between OPEFB, PCL, NiO and NZF. The dielectric constants of the composites were found between 1.87 and 5.82 with corresponding loss factor from 0.09 to 1.21 in the X-band frequency. OPEFB+PCL composites showed magnetic properties when doped with just a small percentage of NZF doping. Increasing the NZF content in the composites from 2.5 % to 15% will increase the real part of permeability from 1.043 to 1.095 whilst the imaginary part increased from 0.042 to 0.054. Both the dielectric constant and loss factor of OPEFB+PCL+NiO and OPEFB+PCL+NZF composites were found to be linearly dependent on the percentage of the fillers. Both the dielectric constant and loss factor of the composites can be predicted from the regression equations by inserting values of the fractional composition of the fillers. Both the dielectric constant and loss factor of the OPEFB+PCL composite increased with increasing percentages of NZF fillers. These in turn will lead to higher values of the magnitude reflection coefficient |S11| and lower transmission coefficient |S21| in accordance with the impedance matching theory. The total shielding effectiveness for OPEFB+PCL, NiO+OPEFB+PCL and NZF+OPEFB+PCL composites were found between 1.11 to 1.46 dB, 2.91 to 3.69 dB and 5.06 to 6.19dB, respectively. The minimum 5dB shielding effectiveness required for commercial aircraft structural shielding can be satisfied by using OPEFB+PCL composites with only 2.5% NZF fillers.

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