Surface modification of ammonium polyphosphate with vinyltrimethoxysilane: Preparation, characterization, and its flame retardancy in polypropylene

Ammonium polyphosphate (APP) was modified by vinyltrimethoxysilane (VTMS) and characterized by water solubility test, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and thermogravimetric analysis (TGA). Surface modification of APP improved not only the water resistance, dispersity and compatibility with polypropylene (PP) matrix, but also the flame retardancy. The possible mechanisms of modified APP (MAPP) were studied by XPS and TG-Fourier transform infrared (TG-FTIR) analysis. XPS data show that modification was achieved by partial substitution of P-O-N by P-O-Si, while TG-FTIR indicate that the second degradation stage of MAPP was delayed to a higher temperature range because of the formation of a more thermally stable P-O-Si instead of P-O. PP/dipentaerythritol (DPER)//MAPP were prepared by melt blending and extrusion in a twin-screw extruder. The combustion behaviors of the flame retarded PP (FR-PP) were studied through the limiting oxygen index, UL 94 vertical burning test and cone calorimeter test, while SEM, SEM-energy dispersive XPS (SEM-EDX) and strength analysis were used to analyze the condensed phase residues from cone calorimeter test. Results indicate that the surface modification of APP with VTMS enhanced the formation of impacted and compact char by means of the synergistic effect of Si, P and N, and improved the flame retardant performance of FR-PP through good protection for the underlying polymer matrix. (C) 2015 Elsevier Ltd. All rights reserved.

采用乙烯基三甲氧基硅烷（VTMS）对聚磷酸铵（APP）进行改性，并通过水溶性测试、X射线光电子能谱（XPS）、扫描电子显微镜（SEM）和热重分析（TGA）对其进行表征。APP的表面改性不仅提高了其耐水性、分散性以及与聚丙烯（PP）基体的相容性，还提高了阻燃性。通过XPS和热重 - 傅里叶变换红外光谱（TG - FTIR）分析研究了改性APP（MAPP）可能的作用机制。XPS数据表明，改性是通过P - O - Si部分取代P - O - N实现的，而TG - FTIR显示由于形成了热稳定性更高的P - O - Si而非P - O，MAPP的第二降解阶段延迟到了更高的温度范围。在双螺杆挤出机中通过熔融共混和挤出制备了PP/二季戊四醇（DPER）//MAPP。通过极限氧指数、UL 94垂直燃烧试验和锥形量热仪试验研究了阻燃PP（FR - PP）的燃烧行为，同时利用SEM、SEM - 能谱仪（SEM - EDX）和强度分析对锥形量热仪试验中的凝聚相残留物进行分析。结果表明，采用VTMS对APP进行表面改性通过Si、P和N的协同作用促进了致密炭层的形成，并通过对下层聚合物基体的良好保护提高了FR - PP的阻燃性能。（C）2015爱思唯尔有限公司。保留所有权利。