Study On Synthesis And Modification Of High Efficiency Flame Retardant Ammonium Polyphosphate

Ammonium polyphosphate（APP）is a highly effective halogen-free flameretardant. Many properties of APP depend on the degree of polymerization, suchas solubility in water, thermal stability and compatibility with materials. Atpresent time, APP was mainly prepared using phosphoric acid and urea as rawmaterials in our country. Due to the backwardness of production processes andconditions, average polymerization degree of APP obtained was low (<100),which had greatly limited its application.Therefore, the synthetic technology of APP was deeply investigated in thispaper using phosphoric acid and urea as raw materials. The preparation processwas optimized by the combination of the single factor and orthogonalexperiments. The optimal technological conditions were as follows: the moleratio of phosphoric acid to urea1:1.9, heating rate of pre-polymerization stage2～3℃/min, pre-polymerization temperature130℃, curing temperature230℃and curing time90min. The APP synthesized under the optimal conditions wascharacterized by IR spectra, XRD and NMR. The results indicated that APP-Iwas obtained under the optimal conditions, with an average degree ofpolymerization of126. Besides, the technological parameter was equallyapplicable to the synthesis of APP by industrial phosphoric acid and urea,without great change on the degree of polymerization.However, general APP has some shortcomings: low thermal decompositiontemperature, easily attacked by moisture and migrates to the surface of polymersin the practical applications. Microencapsulated APP was prepared withmelamine-formaldehyde (MF) resin as the shell layer by in situ polymerizationto deal with the problems above-mentioned. The synthetic technology ofmicrocapsules was studied in detail and the optimum conditions were as follows: the mole ratio of melamine to formaldehyde1:3, pre-polymerization temperature70℃~85℃, prepolymerization time30~60min, pH value of pre-polymerizationstage9.0, mass ratio of the shell material to the core material1:4, curingtemperature70～80℃, curing time2h and pH value of curing stage around5.0.The component of the wall was analyzed by IR and XPS spectra, and propertiesof microcapsules were characterized using SEM, TG, particle size analysis andso on.The results showed that APP was completely covered with MF resin. Themicrocapsules obtained possessed excellent properties such as dense surface,narrow particle size distribution, almost insoluble in water，the significantlyenhanced thermal decomposition temperature of260℃, which is moreconducive to apply in polymer.The flame-retardant paper was made by adding microencapsulated APP tothe pulp. Limiting oxygen index (LOI) tests and vertical burning tests showedthat MFAPP has an obvious effect of flame retardancy. The LOI value of thepaper/MFAPP at35%loading can reach above25.0，up to non-flammable level．...