The preparation of layered double hydroxide wrapped with triazine-based organic framework to enhance the flame retardancy for polypropylene

Layered double hydroxide (LDH) can be used as a flame retardant (FR) for polypropylene (PP) because of its excellent flame retardancy and smoke-suppression effects. However, the agglomeration of LDH seriously affects its dispersity in the PP matrix, thus limiting its application as a FR polymer. This study aimed to enhance the dispersion of LDH in the PP matrix for improving its flame retardancy performance. Herein, a reactive triazine-based organic framework (TOF) was designed and formed by the in situ polymerisation of cyanuric chloride and melamine, and then the LDH surface was covered with TOF to obtain a novel core–shell FR (LDH@TOF), with TOF as the ‘shell’ and LDH as the ‘core’. Subsequently, LDH@TOF was melted into the PP matrix as nanofillers to prepare PP and LDH@TOF composites (PP/LDH@TOF). As expected, the PP/LDH@TOF composites exhibited superior flame-retarding performance (limiting oxygen index of 29.2% and UL-94 V-0 rating) and favourable smoke-suppression performance at 20 wt% of LDH@TOF loading. Moreover, the peak heat release rate, total heat release and total smoke production of PP/LDH@TOF composites decreased by 29.9%, 12.1% and 12.4%, respectively, compared with those of PP and LDH composites. The outstanding flame retardancy properties of the PP/LDH@TOF composites were attributed to the better dispersibility of LDH@TOF in the PP matrix, the synergy of the physical barrier effect of nanosheets and the dense carbonisation acceleration of LDH@TOF. The findings of this study provide a highly efficient approach for functionalising LDH for expanding its application value of PP composites.