Carbon fiber (CF)-reinforced thermoset resin matrix composites are widely used in aerospace, national defense, and military due to their outstanding mechanical and thermal properties. The recycling of CFs has social and economic benefits. After curing, the thermoset resin has a three-dimensional cross-linked network structure, making it challenging to balance its mechanical and thermal properties with the degradation and recycling efficiency. The severe recycling conditions can damage CFs. In this study, a new resin system is designed and prepared based on vinylogous urethane vitrimers (VUvs) containing dynamic bonds and bisphenol A-aniline-based benzoxazine (BA-a) with improved mechanical (impact strength up to 16.9 kJ/m 2 ) and thermal properties (higher than 300 °C for T d5 ) that can be degraded under mild conditions (70 °C, 4 h). Moreover, the monofilament tensile strength of the recovered CF of BA-a/VUv CF-reinforced composites was identical to that of the original CF. Thus, this robust and degradable material system is ideal for the high performance of CF composites and for recycling valuable CFs.
Polybenzoxazines are emerging as a class of high-performance thermoset polymers that can find their applications in various fields. However, its practical application is limited by its low toughness. The cyclic β-cyclodextrin and a newly synthesized derivative (β-cyclodextrin-MAH) were separately blended with benzoxazine to improve the toughness of polybenzoxazine. The results revealed that the maximum impact strength of the blend was 12.24 kJ·m−2 and 14.29 kJ·m−2 when 1 wt.% of β-Cyclodextrin and β-Cyclodextrin-MAH, respectively, were used. The strengths were 53% and 86% higher than that of pure polybenzoxazine. The curing reaction, possible chemical structures, and fractured surface were examined using differential scanning calorimetry, Fourier transform infrared spectroscopy, and scanning electron microscopy techniques to understand the mechanism of generation of toughness. The results revealed that the sea-island structure and the presence of hydrogen bonds between polybenzoxazine and β-cyclodextrin and β-cyclodextrin-MAH resulted in the generation of toughness. Furthermore, the curves generated during thermogravimetric analysis did not significantly change, revealing the good thermal properties of the system. The phase-separated structure and the hydrogen bonds present in the system can be exploited to prepare synergistically tough polybenzoxazine exhibiting excellent thermal properties. This can be a potential way of modifying the thermoset resins.
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