A novel organic-inorganic hybrid K-HBPE@APP performing excellent flame retardancy and smoke suppression for polypropylene

To overcome the flammability and severe dripping of polypropylene (PP), a novel organic-inorganic hybrid KHBPE@APP (microencapsulated APP by a hyperbranched polyester (HBPE) via silane coupling agent (KH-550)) was obtained and used as a high-efficient flame retardant and smoke suppressant. Herein, HBPE acted as the charring agent for APP. 20 wt% of K-HBPE@APP imparted PP excellent flame retardancy, V-0 rating (UL-94 test) and 82.6% decrease in the peak of heat release rate (PHRR). However, PP with 25 wt% of mechanically mixed APP and HBPE achieved V-1 rating (UL-94 test) and 77.3% decrease in PHRR. That is because the direct contact and sufficient interaction between APP and HBPE gives full play to their synergy. Besides, K-HBPE@APP accelerated the formation of cross-linked P-O-C/Si-O-Si/-Si-O-C/Si-O-P/P-O-Phi structures, leading to a strong and compact char layer with a result of dramatic reduction in heat release rate and smoke production. Furthermore, K-HBPE@APP was highly water-resistant and has good compatibility with PP matrix. In particular, the flame-retarded PP had similar tensile strength to pure PP and enhanced impact strength.