Studies On The Preparation Of Water-Insoluble Ammonium Polyphosphate Via Dispersion Polymerization And Its Flame Retardancy In Polypropylene

Ammonium polyphosphate (APP) is an important kind of halogen-freephosphorus flame retardants. APP has six crystalline forms of Ⅰ to Ⅵ. Thecommonly used forms are APP-I and APP-Ⅱ. Compared with APP-I, APP-Ⅱ has ahigher polymerization degree and it is less prone to absorb moisture and hydrolyze. Inaddition, APP-Ⅱ has better thermal stability and flame retardance as well assmoke-suppression, and it is easy to be processed. But the preparation of APP-Ⅱ isvery difficult. All the current production methods have some problems, such ascomplex process, needing special complicated reactor equipment and higherinvestment. Therefore, it has important theoretical and practical significances todevelop a new preparation process of APP-Ⅱ.In order to solve the problems of existing methods, dispersion polymerizationprocess of APP-Ⅱ was studied using urea and diammonium hydrogen phosphate (DAP)as raw materials, polyethylene glycols (PEG) as a dispersant and diesel oil (260-280oCdistillate) as a solvent. Owing to the existence of the solvent, this production operationis easy and the needing apparatus is simple, so its production cost is lower. Theexperimental results showed that optimum preparation conditions of the type Ⅱ APPwas that the mole ratio of urea to DAP was1.1:1, the reaction temperature was220oCand the reaction time was16h while wet ammonia gas piped into the reaction system.The synthesized APP product has average polymerization degree of204, nitrogencontent of14.04%, pentoxide content of71.06%, and water solubility of0.50g/100mL.The products were mainly APP-Ⅱ, which was characterized by FTIR and XRD.The flame retardancy of the prepared type Ⅱ APP and type Ⅰ APP inpolypropylene have been studied. The experimental results showed that the nitrogenand phosphorus composite flame retardant of mass ratio of APP-Ⅱ to1,3,5-tri(2-hydroxyethyl) cyanuric acid (THEIC) was2.5:1presented good flameretardancy in PP. When the amount of flame retardants in polypropylene reached30wt%, the sample had LOI of30.7%and achieved FV-0. When APP-Ⅱ was replacedby APP-I, the LOI value was only27.8%and the FV rating were decreased. The cone calorimeter tests showed that the heat release rate, mass loss rate and total heat releaseof APP-Ⅱ retarded PP decreased significantly, heat release and mass loss was moregentle. Compared with APP-Ⅰretarded PP, the peak heat release of APP-Ⅱretarded PPwas lower.