Investigation of combustion and mechanical properties of huntite-hydromagnesite and intumescent flame retardants in polypropylene composites

Achieving high mechanical performance in a polymer composite is one of the primary concerns when using mineral-based flame retardants. Mineral-based flame retardants should be added to the matrix at 50%–70% to achieve a high level of flame retardancy. High mineral content increases the modulus of elasticity and reduces the ductility of the material. This can be disastrous in applications where flexibility is critical. To overcome this problem, minerals can be used in combination with other effective flame retardants. In this study, the combination of halogen-free mineral-based huntite/hydromagnesite (H/H) and phosphorus-nitrogen-based intumescent flame retardants was investigated to improve the flame retardancy and maintain the flexibility of polypropylene (PP). For this purpose, PP carrier composites were prepared by extrusion by decreasing the mineral concentration in the active formulations and increasing the ratio of phosphorus-based flame retardants. These composites were subjected to mechanical, morphological (SEM), color, and flammability (UL94) tests. As a result, composites with UL94 V0 flammability and 18% to 104% higher tensile strength than equivalent H/H-based flame retardants were obtained.