Surface microencapsulation modification of aluminum hypophosphite and improved flame retardancy and mechanical properties of flame-retardant acrylonitrile-butadiene-styrene composites

Surface microencapsulated aluminum hypophosphite ( SiAHP) was successfully prepared via the condensation polymerization of N-(beta-aminoethyl)-gamma-aminopropylmethyldimethoxysilane. The notched impact strength of the ABS/SiAHP composites was significantly enhanced compared to the corresponding ABS/AHP composites because the microencapsulated SiAHP improved the compatibility of SiAHP and the ABS matrix, and the vertical burning rate of the ABS composite with only 22.0 wt% SiAHP achieved V-0. The cone calorimeter tests demonstrated that the peak heat release rate (PHRR) and peak smoke production rate (PSPR) values of the ABS/22 wt% SiAHP composite were decreased by 81.1% and 49.5%, respectively, compared to those of the ABS/22 wt% AHP composite. Moreover, the total heat release (THR) and the total smoke production (TSR) values of the ABS/SiAHP composites were all lower than those of the ABS/AHP composites. These results clearly indicated that the silicone microencapsulation modification of SiAHP not only enhanced the flame retardancy efficiency of the FR ABS/SiAHP composite but also effectively restrained the smoke production rate of the ABS. A comparison of digital photographs and SEM images of the residues of the ABS/AHP and ABS/SiAHP composites after the cone calorimeter tests revealed that the residue of the ABS/SiAHP composites exhibited a denser and more compact surface char layer structure than that of the ABS/AHP composite. Energy-dispersive X-ray spectroscopy (EDS) measurement indicated that SiAHP more effectively promoted the carbon formation in the FR ABS composite at the surface compared to AHP. The threedimensional compact char layer network containing C and Si effectively improved the flame retardancy of the ABS/SiAHP composite. Therefore, the flame retardancy of the ABS/SiAHP composite was attributed more to condensed-phase mechanisms than the flame retardancy of the ABS/AHP composite.