The two obvious drawbacks of aluminum trihydrate (ATH) as a flame retardant to polymers are its low efficiency and poor resistance to both acid and alkali. To overcome these faults, ATH‐filled fire‐retarded polypropylene (PP) was modified by microencapsulated red phosphorus (MRP) and the flammability, acid and alkali resistance of the obtained PP/ATH/MRP composite were investigated. Results reveal that addition of 63 wt% ATH cannot impart V‐0 rating to PP in UL‐94 test, but incorporating 50 wt% ATH/MRP composite flame retardant can endow PP with V‐0 rating. ATH synergizes notably with MRP in enhancing fire retardancy of PP and the presence of suitable MRP can boost acid and alkali resistance of PP/ATH composite remarkably. The production of high‐quality char layer upon combustion is the key reason for improvement of fire retardance. MRP‐induced charring of PP is responsible for the heightened acid and alkali resistance of PP/ATH composite. This work offers a simple and cheap route to overcome the drawbacks of ATH and will expand the application field of flame‐retarded polymers with ATH.Highlights
MRP synergizes notably with ATH in flame‐retarding PP.
Formation of high‐quality char layer answers for improved fire retardance.
Presence of MRP enhances chemical resistance of PP/ATH composite considerably.
MRP‐induced charring of PP is the root cause for enhanced chemical resistance.