Recycling of flame retardant polymers: Current technologies and future perspectives

Polymers are indispensable to humans in different applications due to their ease of manufacturing and overall performance. However, after a material lifetime, there is a large amount of polymer-based waste, which greatly contributes to the loss of valuable resources and environmental pollution. Thermoplastics may be readily recycled, but because of their flammability, large amounts of flame retardant (FR) additives are required for many applications. This results in a significant volume of FR polymeric wastes too, particularly halogenated plastics, which are subject to severe recycling regulations. In general, thermoplastics containing FRs are raising concerns, as their effective recycling is strongly influenced by the chemical composition, additive content, and physicochemical characteristics of the waste stream. The recycling of FR thermosets is even more challenging due to their crosslinked and cured nature, which makes them resistant to melting and reprocessing. In many cases, traditional mechanical recycling methods, such as grinding and melting, are not applicable to thermosetting polymers. Current recycling methods do not always consider the recovery of the thermosetting/thermoplastic matrix and the presence of toxic FRs in the polymer network. Sorting and solvent washing treatment are important steps, which are usually performed before recycling the FR polymeric waste to reduce contamination in the following steps.