Mechanical property improvement of recyclable carbon fiber reinforced rigid-flexible polybenzoxazine/silica based polyhexahydrotriazine IPN

Thermosetting resin matrix composites are difficult to degrade due to their irreversible cross-linking structures, which makes carbon fiber composites difficult to recycle and imposes a huge burden on environment. Here we propose a series of recycle rigid-flexible polybenzoxaizne/silicon-based polyhexahydrotriazine interpenetrating network (IPN) resins through sequential controllable curing reaction, among them, polybenzoxazine and polyhexahydrotriazine are hard segments and soft segments, respectively, and these two crosslinked networks are interspersed with each other. The results showed char yields of these resins at 800 °C under N2 are up to 47.6 %. These IPN resins are used as matrix to prepare carbon fiber-reinforced composites, mechanical test results show that these composites exhibit impressive increases in tensile strength, flexural strength and shearing strength, with minimums of 2393.98 MPa, 1204.90 MPa and 111.07 MPa respectively, which are higher than those of carbon fiber reinforced composites reported. Meanwhile, due to the intermolecular hydrogen bonding, the IPN composites showed maximum water drop angle reached 129.1°, which was nearly 15° higher than that of polybenzoxazine composites. Additionally, these IPN matrix and fibers can be easily recycled from the composites by degradation without damage.