Novel Co 3 O 4 /covalent organic frameworks nanohybrids for conferring enhanced flame retardancy, smoke and CO suppression and thermal stability to polypropylene

Co3O4/COFs nanohybrids are prepared through ball milling of covalent organic frameworks (COFs) nanosheets synthesized from condensation reaction between melamine and o-Phthalaldehyde and then modified with Co3O4 particles first. Polypropylene (PP) composite with different weight loading of Co3O4/COFs nanohybrids has also been prepared. Successful preparation of Co3O4/COFs nanohybrids has been proved by the typical reflections of Co3O4 including (111), (220) and (222) in XRD pattern, O–Co–O (663 cm−1) and Co–O (569 cm−1) stretching vibrations in FTIR spectrum and Co3O4 particles with a diameter from 20 to 50 nm on COFs nanosheets in TEM image. Flame retardant, smoke and carbon monoxide (CO) suppression and thermal properties of PP have been enhanced obviously. The temperature at initial degradation and the maximum weight loss rate of PP loaded with 3.2 wt% Co3O4/COFs nanohybrids increase 21 °C and 49 °C under air compared with that of untreated PP, respectively. The total smoke release (TSR) of PP loaded with 0.2 wt% Co3O4/COFs nanohybrids decreases by 22% compared with that of PP 0. The pyrolysis products of PP composite including hydrocarbons, carbon dioxide and CO also decrease. The feasible mechanism for inhibiting fire hazard of PP composite has also been proved. This work broadens application of COFs derivative into polymer matrix.