Study Of Two-stage-enhancement Mechanism Of Aramid Fiber Composites Interface

Aramid fiber interface performance has always been a difficult problem in the field of composite materials.At present,the main way of interface enhancement of Aramid fiber reinforced polymer(AFRP)composite is the surface modification of fibers.In general,physical modification methods have serious damage to fibers,and the chemical modification method has limited effect on the interface properties.For this reason,a two-stage enhancement method for improving the interfacial properties of aramid fiber composites is proposed in this paper.An aramid fiber surface modification method was established to achieve the first-stage-enhancement of AFRP interface by impregnation of aramid fiber with waterborne polyurethane,and the second-stage-enhancement was achieved with the incorporation of efficient adhesive epoxy(EAEP)matrix.Finally,the mechanism of the flexible interfacial layer of AFRP was established.1.A first-stage-enhancement of AFRP interface was prepared by designing a waterborne polyurethane sizing agent and impregnating aramid fibers.Molecular structure of the sizing agent was confirmed by FTIR and NMR spectra.The surface roughness,chemical activity and polarity of the aramid fibers are achieved by surface treatment.The interlaminar shear strength(ILSS)and transverse fiber bundle tensile(TFBT)of modified AFRP was 59.1%and 21.6%higher than unmodified composites,respectively,which was attributed to the enhanced interfacial strength between aramid fiber and matrix.2.EAEP was synthesized from 4,4'-diphenylmethane diisocyanate(MDI)and epoxy.Epoxy toughened by EAEP was designed and two-stage-enhancement composites were further fabricated.The mechanical properties of EAEP toughened epoxy and the interface performance of composites were studied.The fracture toughness(KIC)and impact Strength of EAEP toughened epoxy were 126%and 60%higher than general epoxy,respectively.The transverse fiber bundle tensile(TFBT)and interface shear strength(ILSS)value reached to 34.6MPa and 52.5MPa,which was 26.3%and 14.5%higher than unmodified AFRP.3.Monofilament composites were prepared from modified aramid fiber and EAEP toughened epoxy.The interface structure and performance of monofilament composites were studied.F-AFM shows thickness of interface layer reached 1?m with the incorporation of flexible interface layer.The interface shear strength(IFSS)value was 23.7%higher than unmodified aramid fiber composite,and Raman spectroscopy test result showed that the interface stress was relaxed,which improved the interface performance,in modified aramid fiber composites,because of the flexible interface layer.