Improving the flame retardancy and mechanical properties of epoxy composites significantly with a low-loading CNT-based hierarchical hybrid decorated with reactive hyperbranched polyphosphoramide

A reactive hyperbranched polyphosphoramide (HBPPA) was in situ polymerized on CNT surface to generate a novel CNT hybrid (HBPPA@CNT) with abundant terminal amine groups which can induce epoxy (EP) curing network around CNT hybrid and gain an excellent cure system. Benefited from the good dispersion state and the improved interfacial bonding, EP/HBPPA@CNT composite exhibited good flame-retarding performance (LOI of 28.5 %, UL94 V-1 rating, and flame retardancy index of 1.26) and outstanding mechanical performance simultaneously at a low loading of 2 wt%. Its tensile strength and impact strength increased by 67.9 % and 71.8 % respectively. Moreover, the peak heat release rate (PHRR), total heat release (THR) decreased by 17.0% and 15.6% respectively. After being decorated by HBPPA, the CNT hybrid was not only well dispersed in the EP matrix to achieve the superior reinforcing properties, but also linked together by the reactive P-rich compounds deriving from HBPPA to form a continuous char layer shielding the heat and mass transfer effectively. The synergistic effect between HBPPA and CNT resulted in good mechanical performance and fire safety of EP composites, which may provide a novel and facile approach to functionalize carbon materials for expanding its application value in polymer-matrix composites.