Preparation of novel hollow metal organic framework for enhancing flame retardancy of paraffin/EP thermal energy storage materials

Paraffin is a potential thermal energy storage material, but leakage and flam-mability are the two major problems affecting its storage and safe use. Here, a novel flame retarded paraffin/epoxy resin composite was developed by using paraffin, epoxy resin and hollow metal organic framework (W-UiO66-PPA) as thermal energy storage material, supporting material and flame retardant, respectively. The thermal energy storage and flame retardancy performances were examined with differential scanning calorimetry, vertical burning, limit-ing oxygen index and cone calorimeter tests. The results show that the paraf-fin/epoxy resin retains intact without leakage when the content of paraffin reaches 40 wt%, and this material exhibits high melting latent heat and remarkable thermal recycling property. In addition, the flame retarded paraffin/epoxy resin shows excellent flame retardancy, which is attributed to the following three aspects: (1) the hollow structure with open vertices of W-UiO66 is capable of absorbing and collecting the combustible gasses produced by the combustion of epoxy resin; (2) the Zr and W elements of W-UiO66 can facilitate catalytic charring and form a dense char layer; (3) phosphorous-containing free radicals are able to capture OH. and O. free radicals during the combustion of paraffin and epoxy resin, thus interrupting the combustion chain reaction. On the whole, the flame retarded paraffin/EP possesses excellent thermal energy storage, thermal recycling, and flame retar-dancy properties. Our work provides a fantastic inspiration for the rational design of other flame retarded form-stable phase change materials.