Influence of pretreatment on mechanical and dielectric properties of short sunn hemp fiber-reinforced polymer composite in correlation with fine structure of the fiber

Present investigation is aimed on chemically modified of Sunn Hemp (Crotalaria juncea) fiber for composite fabrication. An increment in cellulose crystallinity with crystallite size is observed from X-ray diffraction study. The signature of impurities removal and an uneven surface are confirmed from Fourier Transmission Infrared Spectroscopy and Field Emission Scanning Electron Microscopy. Afterwards, both raw sunn hemp-reinforced fiber composite and dewaxed sunn hemp fiber-reinforced composite were fabricated using hand lay out method and the mechanical as well as dielectric properties of composite are studied. A better mechanical strength is found in DSHC which may attribute to rough surface and increased cellulose crystallinity through dewaxing process that promoted a fine interfacial bonding between fiber and matrix. Dielectric constants and losses are found to be less in dewaxed sunn hemp fiber-reinforced composite in comparison to raw sunn hemp-reinforced fiber composite due to decrease of water polar groups, which lead to lessening the effect of space charge polarization by treatment. Complex impedance and modulus study revealed the presence of single relaxation process in both systems. Lower ac conductivity value is observed in dewaxed sunn hemp fiber-reinforced composite due to decreasing of conducting polar OH groups. As a whole, the effort is established to correlate the mechanical and dielectric properties with fine structural parameters of the fiber.

Mechanical Properties of Resin Reinforced Fiber-Ceramic-Fiber Composites Prepared by Vacuum Assisted Resin Transfer Molding

Ceramic-fiber composites have important applications in protection field. In this work, the stable and reliable resin reinforced fiber-ceramic-fiber (RRFCF) composites with sandwich structure were prepared by using the vacuum assisted resin transfer molding (VARTM) process. The mechanical properties of the prepared RRFCF composites with different configurations were studied. Results showed that the thickness values of the glassfiber-reinforced plastic layers (panel thickness: ta and backplane thickness: tc) had significant influences on the unique mechanical properties of the RRFCF composites. The stress distribution of RRFCF composites with different configurations under loading was analyzed by simulation. The fatigue behaviors of Z-type (ta < tc) and F-type (ta > tc) RRFCF composites were investigated and found to be in good agreement with the simulated results. Moreover, the flexural strength and modulus of Z-type composites were obtained and found to be higher than those of F-type composites. These results have important guiding significance for the engineering application of RRFCF composites.