The synergistic effect of layered double hydroxides with other flame retardant additives for polymer nanocomposites: a critical review

Layered double hydroxides (LDHs) are a new type of inorganic flame retardant additive for polymer nanocomposites. Although their unique structural properties and tunable chemical compositions make them highly promising, it has been noticed that on their own, LDHs can hardly fulfill all the requirements for commercial applications. In recent years, the application of LDHs together with other synergistic additives has been proposed as a new route for obtaining highly efficient flame retardant polymer nanocomposites. It is believed that the synergistic additives can overcome the shortcomings of LDHs. As great progress has been made in this field so far, we believe that a timely review is warranted. Thus, in this contribution, the synergistic effect of LDHs with other flame retardant additives including (1) phosphorus-containing compounds, (2) graphene and carbon compounds, (3) intumescent flame retardants, (4) magnesium hydroxide, (5) borate-containing compounds, and (6) some other flame retardant compounds will be critically reviewed. For each type of additive, the synergistic mechanism with LDHs, and their performance on both flame retardancy and thermal stability will be discussed. We believe that this work will inspire and guide researchers from a wide range of backgrounds and help to pave the way for major breakthroughs in both fundamental studies and industrial applications in this field.