Fire-retardant unsaturated polyester thermosets: The state-of-the-art, challenges and opportunities

The increasing demands placed upon structural thermosets, such as epoxy and unsaturated polyester (UP), and ever-increasing regulations for fire safety, have driven the development of high-performance ecofriendly fireretardant thermoset polymers. This review provides a historical overview of fire-retardant UP that aims to review the state-of-the-art design and efficiency of fire-retardant strategies developed in the last decade, and pave the way for developing next-generation fire-retardant UP materials in the future. In general, there are three approaches for creating fire-retardant UP with reactive and additive fire-retardants (FRs). One promising strategy is to develop intrinsically fire-retardant UP resins by using FRs monomers. Another favorable approach is the copolymerization of UP resin with reactive FRs comonomers. The last but encouraging method is the hybridization of phosphorus additive FRs with metal hydroxides. Recently, the design of polymeric, nanostructured and core-shell structured FRs has emerged as a subject of enormous scientific interest. Although advantages of current fire-retardant systems, there have remained some key challenges with them, such as their adverse impacts on the processability, curing behavior, and mechanical properties of UP. This work reviews the state-of-theart, design, performance, and applications of fire-retardant UP thermosets. Also, additive FRs are classified according to the fire-retardant index (FRI) and the required level of FRs to achieve a UL-94 V-0 rating. Finally, we discuss current challenges and possible directions for future research on the promising fire-retardancy strategies for UP thermosets.

Automated summary

The increasing demands for structural thermosets and regulations for fire safety have driven the development of high-performance eco-friendly fire-retardant thermoset polymers. There are three main approaches for creating fire-retardant UP, including intrinsically fire-retardant resins, copolymerization with reactive FRs, and hybridization with phosphorus additive FRs. Despite the advantages, challenges remain in terms of processability, curing behavior, and mechanical properties.