Flame-retardant composites and analysis of their residual strengths after tailored flame tests

In recent decades, fibre-reinforced polymers (FRPs) have become a key factor to realise lightweight design, e.g., to safe fuel in mobility applications. As FRPs are usually combustible, flame retardants (FRs) are necessary to fulfil critical requirements. On the one hand, FRs can negatively affect thermo-mechanical properties of composites and should therefore used as little as possible. On the other hand, frequently used infusion processes to manufacture FRPs are no longer possible due to filtration effects, if the FRs are present as particles. However, novel in this study is the use of a combined prepreg and infusion process to solve both challenges by implementing FRs only in the most exposed plies. Simultaneously, this method enables the manufacturing of large parts with implemented FR particles, without compromising the lightweight potential or causing adhesion challenges through the use of FR gel-coats. As part of this study, tailored flame tests with adequate reproducibility were developed for qualitative comparisons between different configurations and the residual compressive strength was determined afterwards, because the structural integrity in fire scenarios is of special importance in mobility applications. It was found, that despite a very low global amount of ≈ 1.5 - 3 % red phosphorus leads to significant improvements in the residual strength compared to unmodified configurations. • Combined prepreg and infusion process to prevent filtration effects. • Tailored flame tests for qualitative comparisons between configurations. • Clearly improved flame resistance using only small total amounts of red phosphorus. • Residual strength after fire load increased modifying only 1/8 of load-bearing plies. • Additional lightweight potential compared to gelcoats.