Jichun Liu

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.

Ethylene vinyl acetate copolymer (EVA) was modified by expandable graphite (EG) and polyphosphoric acid (PPA) in melt state and the obtained EVA/EG/PPA composite was studied regarding its fire behavior, thermal endurance, water resistivity, processability, and mechanical property. The outcomes evince that the combination of EG and PPA in proper mass ratio can improve fire retardancy, thermal stability, processability, and reduce smoke and toxic gas releases of EVA upon combustion significantly. The EG/PPA combination exhibits very high flame retardant efficiency to EVA in that only 10 wt% loading is enough to make EVA obtain V‐0 rating in UL‐94 test. Moreover, the flame‐retarded EVA/EG/PPA composite displays excellent water resistance and acceptable mechanical property. The EVA/EG/PPA (90/7.5/2.5) composite can produce coherent intumescent char on composite surface, which has good heat endurance and hinders heat transmission from fire to interior of composite. The flame retardation occurs in condensed phase and the intumescent char plays a pivotal role. The presence of PPA endows EVA composite with good melt flowability, which has presented a striking contrast to other flame retardants.Highlights: The combination of EG and PPA has very high flame retardant efficiency to EVA. The EVA/EG/PPA composite has better fire safety and processability than EVA. The EVA/EG/PPA composite still maintains acceptable mechanical property. The expanded char from EVA/EG/PPA composite hinders heat transfer effectively.

Polypropylene (PP) was modified by expandable graphite (EG) and magnesium hydroxide (MH) to enhance its flame retardancy. The impact of EG particle size on fire behavior of PP/MH/EG ternary composite was studied in detail. The results reveal that EG synergizes markedly with MH in flame‐retarding PP. The PP/MH/EG composite with larger EG particle size displays better flame retardancy, smoke inhibition, acid resistivity, processability, and less toxic gas release upon combustion. The striking contrast derives from differences of charring behavior in condensed phase. The composite with larger EG particle size can produce intumescent char with larger expansion volume and better compactness and continuity, which hinders heat transfer inside polymer composite. Owing to much smaller expansion volume, the composite containing smaller EG particle size cannot generate effective fireproof barrier. As a consequence, this composite exhibits worse fire retardance and smoke inhibition in contrast with the composite with larger EG particle size.