Surface modification of ammonium polyphosphate and its effect on properties of natural rubber composites

Abstract

"First, a layer of inorganic self-assembled microencapsulated ammonium polyphosphate （APP) （SiO2@APP) was formed on the surface of APP using alkaline silica sol, and then grafting modified APP （KH 580-SiO2@APP) flame retardant was prepared via grafting modification of the silane coupling agent 3-mercaptopropyltriethoxysilane （KH 580) onto the surface of SiO2@APP by sol-gel method. Meanwhile, natural rubber （NR) composites were prepared by the application of KH 580-SiO2@APP to NR, and the effects of APP surface modification on the hydrophobicity, thermal stability, flame retardancy, and physical and mechanical properties of NR composite materials were studied. The results indicated that the surface modification of APP was successful. Compared with APP, the water contact angle of the resulting SiO2@APP increased by 205.7% and the thermal stability increased by about 25.7% after the modification with alkaline silica sol, and in the meantime, compared with APP/NR composite material, the tensile strength of SiO2@APP/NR composite increased by 43.7%, but the limited oxygen index （LOI) decreased. After the modification of SiO2@APP with the silane coupling agent KH 580, the water contact angle of the resul-ting KH 580-SiO2@APP increased by 9.1% and the increase in thermal stability was nearly 11.6%. In additon, the tensile strength of KH 580-SiO2@APP/NR composite was improved to 16.2 MPa, and the elongation at break increased by 539%, while the LOI decreased slightly to 24.3%. "

Keywords

• natural rubber， ammonium polyphosphate， surface modification， sol-gel method， silane coupling agent， physical and mechanical property，flame retardancy，