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In this work, three laminated Epoxy composites reinforced with five woven layers of E-glass fabrics, jute fabrics and kenaf fabrics were characterized by broadband dielectric spectroscopy. The dielectric analysis was performed in temperature range from 20 to 180 C and frequency range from 0.1 Hz to 1 MHz. The Epoxy matrix shows the presence of four relaxation processes, which are attributed to the β relaxation process, α relaxation process, the quasi-continuous conduction and the dc conduction. In the laminated composite reinforced with the E-glass fabric, only one additional relaxation process was detected, which was attributed to the interfacial polarization effect known as Maxwell-Wagner-Sillar polarization. However, for the laminated composites reinforced with jute and kenaf fabrics, two additional relaxation processes were observed. While the first one was associated with the water dipoles polarization imputed to the presence of polar water molecules in jute and kenaf fabrics, the second was linked to the interfacial polarization effect. The latter phenomenon was investigated by an analytical study using the Havriliak-Negami model. The best adhesion between reinforcement and Epoxy matrix was obtained with E-glass fabrics. This study was supported by the thermal properties using a differential scanning calorimetry. POLYM. COM-POS., 40:2142-2153, 2019

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An exhaustive study of dielectric and impedance analysis on two Alfa‐fiber‐reinforced unsaturated polyester hybrid composites was performed. Alfa fiber reinforcements were hybridized by wool and PE/PET fibers in the relative volume fraction ratio 17:2:1. However, these reinforcements differ by the number of mechanical separation of Alfa fibers in the Shirley analyzer. For Composite (1), Alfa fibers were separated mechanically once in the Shirley analyzer whereas for the Composite (2), they were separated mechanically twice in the Shirley analyzer. Dielectric parameters analysis (ɛ′, ɛ″) revealed the presence of the α‐relaxation process at intermediate temperature range for the matrix and the water dipoles polarization at low temperatures for the Composite (1). No dynamic dielectric relaxation was observed for the Composite (2) at low temperatures. However, dielectric properties were controlled by the dc conductivity effect at higher temperatures. The Kramers‐Kronig relation was used to eliminate its effect. Hence, α mode relaxation was observed for the matrix and the interfacial polarization effect was observed for its composites. The attenuated effect of this latter for the Composite (2) was attributed to its homogeneous structure. Electrical conductivity analysis using the Jonscher law allowed determining the transport mechanism for all studied materials and confirmed such result. Complex impedance analysis supported the homogeneous structure for the Composite (2). POLYM. COMPOS., 40:1774–1785, 2019. © 2018 Society of Plastics Engineers

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In this work, we undertook a comparative study of the dynamic dielectric analysis of two composites: natural-fiber-reinforced unsaturated polyester (NFRUP) and E-glass-mat-reinforced unsaturated polyester (EGMRUP). In both composites, two common relaxation processes were identified, the first of which was the a-mode relaxation associated with the glass transition of the matrix. The second one was associated with conductivity that occurred because of the carriers' charge diffusion and was observed at temperatures above the glass transition and at low frequencies. However, the interfacial or Maxwell-Wagner-Sillars polarization was noticed only in the NFRUP composite. This dielectric study also revealed that compared to E-glass fibers, natural fibers enhanced the thermal insulation in the composite. Also, the study of the fiber adhesion in the matrix with scanning electron microscopy, differential scanning calorimetry, and tensile testing revealed a great compatibility of the fibers with the matrix in both composites.