Thermal and mechanical properties of flax char/carbon fiber reinforced polyamide 66 hybrid composites

In this study, flax fiber char (CH), a kind of biomass carbon material obtained by thermochemical conversion of flax fibers in a nitrogen environment in a fixed bed reactor, was used as a reinforcing constituent together with carbon fiber (CF) to produce polyamide 66 (PA66) hybrid composites. The potential use of biochar as a promising substitutional filler candidate for CF in composite applications was deemed in principle. Biochar and carbon fiber surfaces were treated with nitric acid followed by modification with a 3-aminopropyltriethoxysilane coupling agent to improve their interfacial compatibility with PA66. The overall characterization of the composite materials was conducted by performing the thermal gravimetric analysis and differential scanning calorimetry measurements and tensile and water absorption tests. Scanning electron microscopy was further employed to examine the fracture surface of the specimens. The findings obtained revealed that silane -modified CF and CH altered composite material crystallization behavior, thus enhancing the ultimate composite tensile strength and Young's modulus. Moreover, the tailored interfacial interactions associated with enhanced thermal stability were determined to reduce water absorption capacity for composites with CH. In brief, CH may be substituted with CF, cost-effectively, at a 50:50 w/w ratio of total reinforcement (10 wt%) in PA66 without compromising ultimate composite performance.

Automated summary

The study demonstrates that biochar can be used as a substituting reinforcing constituent for carbon fiber in polyamide 66 hybrid composites, and surface modification can enhance interfacial compatibility. The incorporation of modified carbon fiber and flax fiber char in composite materials can improve the ultimate tensile strength and Young's modulus of the composites.