Due to strict safety regulations, the automotive industry requires an effective reduction
of flammability in polymer components. Flame retardants are usually added to the polymer
matrix, affecting the viscosity of the matrix. Another possible solution is the application
of coatings containing flame retardants, which can additionally ensure good surface
quality and protection against external influences. In our research, the flammability
of reference and flame retarded gelcoat base materials was investigated using oxygen
index (LOI), UL-94, and mass loss type cone calorimetry (MLC) tests. Based on the
flammability tests, the best results were obtained with the gelcoat formulation containing
15%P ammonium polyphosphate (APP) and the mixed formulation containing 5%P APP and
5%P resorcinol bis(diphenyl phosphate) (RDP), with a 55% and 64% reduction in the
total heat release compared to the reference gelcoat, respectively. The two best-performing
coatings were applied to polypropylene (PP) samples. 15%P APP reduced the peak heat
release rate of PP by 89% compared to the reference. The gelcoat formulation containing
15%P APP was applied to polyurethane (PUR) automotive components, where the coating
reduced the maximum heat release rate by 53% and shifted the time to peak heat release
rate by 447 s.
