Study On The Properties Of 3-D Braided Carbon/Kevlar Fibers Reinforced Epoxy Resin Hybrid Composites

Biocompatible epoxy-based hybrid composites reinforced with three-dimensional braided carbon/Kevlar fibers(C/K/EP)were prepared by RTM processfor bone fracture fixation. Mechanical properties, friction and wear characteristics,moisture absorption behaviors and influence of fiber surface treatment on 3-Dbraided C/K/EP hybrid composites were investigated, which provided an importantbase for farther use.Based on research on the binary system composites of carbon fiber and Kevlarfiber, it was found that fiber surface treatment could greatly improve the interfacialproperties of composites. Carbon fiber was treated by anodic oxidation inammonium dibasic phosphate ((NH₄)₂HPO₄) solution. Kelvar fiber was treated bychemical etching in phosphoric acid (H₃PO₄). SEM observation and XPS analysis ofsurface-treated fibers revealed that surface treatment changed the physical andchemical conditions of fiber surfaces. Composite treatment ((NH₄)₂HP_O4+H₃PO₄)was selected to modify hybrid carbon/Kevlar fibers, which improved both interfacialadhesion and mechanical properties of the unidirectional and 3-D hybrid composites.Mechanical testing results indicated that 3-D braided Kevlar fiber-epoxycomposites (K_3D/EP) exhibited low flexural strength and modulus. The hybridcomposites with larger carbon fiber volume fraction had better flexural properties.The hybrid composites with a C/K ratio of 3/2 was found to have the highest flexuralstrength. An obvious positive hybrid effect on the flexural strength was observed.The transverse shear strength of the hybrid composites decreased with carbon fibervolume fraction, while the longitudinal shear strength showed an opposite trend.Both the transverse and longitudinal shear strength of the hybrid composites werehigher than the values predicated by the Rule of Mixture when carbon fiber volumefraction was between 15-34%. Epoxy-based composites reinforced with 3-D braidedcarbon fiber (C_3D/EP) had poor impact properties, which was enhanced with theincorporation of Kevlar fiber. With increasing in carbon fiber volume fraction,flexural strength retention increased initially, followed by a reduction. In short, thehybrid composites with hybrid ratio C/K=3/2 had the best mechanical properties.The friction and wear properties of 3-D braided C/K/EP hybrid composites andtheir affecting factors were investigated in detail. It was concluded that under dryconditions, wear rate of the composites increased with the load. The compositesshowed the lowest friction coefficient at a load of 150N. Friction coefficient andwear rate of 3-D braided C/K/EP hybrid composites were much smaller under waterlubrication. SEM results showed that the wear mechanism of 3-D braided C/K/EPhybrid composites was furrow wear. Hybrid ratio had an effect on the friction andwear properties of the composites. 3-D braided C/K/EP hybrid composites had thehighest wear resistance at a hybrid C/K ratio of 3/2. It was interesting to note that thewear resistance of the hybrid composites was much better than the widely usedtitanium alloy under the same conditons.Studies on the moisture absorption behaviors of 3-D braided C/K/EP hybridcomposites suggested that the moisture absorption of C3D/EP, C/K/EP and K3D/EPcomposites at 37℃ could be described by Fick's law. The hybrid composites withhigh Kevlar fiber loadings demonstrated higher moisture absorption rate andequilibrium absorption content as Kelvar fiber absorbed moisture. The mechanicalproperties of the unidirectional and 3-D braided composites dropped caused by theinterface degradation as a result of moisture ingress. The absorption rate of 3-Dbraided C/K/EP hybrid composites at 100℃ was markedly higher than that at 37℃.No difference in the equilibrium absorption content was observed when the mediumtemperature changed from 37℃ to 100℃. After 24h moisture absorption, theflexural and shear properties of the hybrid composites declined appreciably.In conclusion, 3-D braided C/K/EP hybrid composites can meet the needs ofinternal fixation devices in terms of their mechanical properties, wear resistance, andmoisture absorption behaviors. They are novel materials for bone fixation with greatmarket potentials.