Surface modification of ammonium polyphosphate with titanate coupling agent and its application on flame retardant polypropylene

Ammonium polyphosphate(APP) was modified with titanate coupling agent (TC-114) by gas-phase mentod and liquid-phase method, individually. Results of water solubility, scanning electron microscope (SEM) and thermogravimetric analysis (TGA) show that the modification improves the water resistance, dispersibility and thermostability of APP. Then modified APP was incorporated with dipentaerythritol (DPER) in flame retarded polypropylene (FR-PP). The flame retardancy of FR-PP was characterized by mechanical performances, combustion behavior, thermal behavior and microscopic morphology of condensed phase. Modified APP shows better compatibility with PP matrix than neat APP, while mechanical and rheological behaviors of FR-PP are also improved because of the loading of modified APP. Furthermore, results of TGA, limiting oxygen index (LOI), UL-94 and cone calorimeter tests show that the thermal stability and flame retardancy of FR-PP are enhanced by APP modified with TC-114. Especially modified APP by liquid-phase method, FR-PP can pass V-1 rating in UL-94 tests at the thickness of 1.6 mm, its LOI value increases from 26.9% to 30.4%, and the peak value of heat release rate is decreased by 26%. SEM photographs of char residues from cone calorimeter test demonstrate that the modified APP is beneficial to formation of a complete and compact char during combustion.