Non-combustible polymer composites with extremely high filler loading via polytetrafluoroethylene fibrillation

The incorporation of halogen-free flame retardants (FRs) into polymer matrices is a cost-effective and eco-friendly method for suppressing flames and smoke and enhancing fire safety. In energy applications, a high FR loading (e.g., >80 wt%) is often necessary owing to the excessive heat and toxic gases generated by the devices and components. However, achieving this in conventional polymer composites is significantly impeded by poor processability stemming from increased melt viscosity. This study proposes a new approach to fabricate highly loaded flame-retardant composites with an extremely high FR content of 95 wt% via fibrillation of thermally stable polytetrafluoroethylene (PTFE), which holds two different types of FRs, magnesium hydroxide (MH) and expandable graphite (EG). The hybrid composites exhibited excellent flame retardancy owing to the synergistic effects of the distinct mechanisms of the two fillers, securing a top V-0 rating in the UL-94 vertical burning test and a limiting oxygen index (LOI) exceeding 95 %. Importantly, their total heat release (THR) from the cone calorimeter test was less than 1 MJ/m2, an anomalously low value that meets the criteria for non-combustible materials (THR <8 MJ/m2). Alongside their non-combustible attributes, the composites also have high thermal conductivity, reaching up to 1.60 W/m·K, due to the presence of thermally conductive EGs. We believe that these composites and their fabrication methodology can offer new insights into the design of flame-retardant composites, which are likely to be applicable in practical applications involving severe fire hazards, such as batteries, electronics, and electric vehicles.