Study On The Synergistic Modification Of Ammonium Polyphosphate And Its Application In Flame Retardant Polypropylene

Ammonium polyphosphate（APP） is one of the most important componets in intumescent flame retardant（IFR）. APP can be used asan acid source and a blowing source at the same time in IFR system. APP has been a hot area of research in flame retardant field for several years due to its high phosphorus and nitrogen content, good thermal stability, nearly neutral, good flame retardant effect. However, the weaker water resistance and poor compatibility of APP with PP matrix restrict its application considerably. Numerous methods have been used to the surface modification of APP. To deal with the above problems more efficient, the surface modification mechanism of APP with coupling agent was studied in particular. Based on above results, a new treatment method with surface modification, synergistic and superfining effect was proposed by selecting the appropriate modifiers and experimental methods. The research work of this dissertation is composed of the following parts:1. First, APP was modified by four coupling agent: γ-Mercaptopropyl trimethoxysilane（KH-590）, vinyltriethoxysilane（A-151）, vinyltrimethoxysilane（A-171） and titanate coupling agent（TC-114）. The effcts of modification with these four coupling agengts on water solubility and thermal thermostability were studied. The surface modification of APP with these four coupling agents has shown some improvements in water solubility and dispersibility. And, the best modification effect can be achieved when vinyltrimethoxysilane（A-171） is used as modifying agent. The water solubility of MAPP at 25℃ decreased from 1.1350 g/100 m L H2 O to 0.5455 g/100 m L H2 O when the A-171 dosage was 3%. MAPP shows better compatibility and dispersibility in PP matrix than APP. The XPS Data show that modification was achieved by partial substitutionof P-O-N by P-O-Si. SEM images and water solubility tests show that the surface modification of APP with A-171 decreased its water solubility, and increased its dispersion and thermal stability. The Tma x and the maximum mass loss rate changed from（573℃;-12.21%/min） to（737℃;-3.44%/min）, and 24.87% residue is obtained, which was higher than the untreated APP because of themore thermal stable P-O-Si. When MAPP was incorporated into thePP/DPER composites instead of APP, an obvious improvement in flame retardancy was observed, not only with an increase in LOI value, but also because of the UL 94 V-0 ratings that were reached for PP composites at a loading of 25%. Furthermore, the decrease of PHRR values is 24%. Studies on the char residue show that a more complete and compact char were formed, which protects the underlying polymer from further combustion during burning. These results indicate that the surface modification of APP with A-171 enhanced the char formation behavior of FR-PP composites and suppressed the combustion behavior. 2. Surface modified ammonium polyphosphate were prepared by means of coating with magnesium hydroxide（MDH） in liquid environment. The MDH was prepared by the chemical reaction between magnesium sulfate and ammonia water or the hydrolysis of magnesium ethylate. Results show that the water solubility of modified APP is decreased. However, the modification effect will be worse with the increased amount of magnesium sulfate or magnesium ethylate. Results of thermal analysis show that the maximum weight loss rate of midified APP decreased from 17.61%/min（APP） to 5.88%/min and 4.78%/min, respectively. And, the residue at 800℃ increased from 17.51%（APP） to 24.91% and 29.24%. It is important to note that the modified APP exhibits the third thermal decomposition stage during 700⁸00℃. When modified APP was incorporated into the PP/DPER composites instead of APP, an obvious improvement in flame retardancy was observed. The LOI value increased from 26.6% to 29.8% and 30.6%,the UL 94 V-0 ratings were reached for the samples at the thickness of 3.2mm. Furthermore, the decrease of PHRR values is 30%. Studies on the char residue show that a more complete and compact char were formed, which protects the underlying polymer from further combustion during burning. These results indicate that the surface modification of APP with MDH enhanced the charformation behavior of flame retardant PP composites and suppressed the combustion behavior.3. A new surface-modification method was adopted to decrease water solubility and enhance flame retradancy of ammonium polyphosphate（APP） by means of coating with aluminium hydroxide（ATH） in liquid environment. The optimal conditions are as follows: the dosage of Al Cl3 is 2 g, reaction temperature is 60℃, the reaction time is 2 h.Results at the optimal conditions are as follows: the yield is 95.43%, the specific surface area ofmidified APP is 15.37 m2/g and the water solubility at 25℃ is 0.2920 g/100 m L. Results of scanning electron microscope（SEM） and X-ray photoelectron spectroscopy（XPS） demonstrated that ATH and Al PO₄ were deposited on the surface of APP particles, and lower water resistance and rougher surface were verified. The maximum mass loss rate of modified APP changed from（580 °C;-17.61%/min） to（563 °C;-12.21%/min）, and 21.91% residue is obtained at 800 °C, which was higher than APP（13.4%）. Furthermore, the modified APP was applied with dipentaerythritol（DPER） to prepare flame retarded PP. Results show that loading of the coated APP has improved flame retardancy of FR-PP composites remarkably. Compared with unmodified APP, PP/DPER/ modified APP can pass V-0 in UL 94 test, LOI value increases from 26.6% to 31.8%, and the peak heat release rate（PHRR） decreases from 475 k W/m2 to 283 k W/m2. Finally, study on char residues of FR-PP composites indicates that APP coated with ATH makes char layer more complete and more compact, which contributes to the improvement of flame retardancy.4. Surface modified ammonium polyphosphate were prepared by the hydrolysis of aluminium isopropoxide（AIP） in liquid environment. The water solubility showed that there has been a significant decrease for modified APP. The SEM images reflect that the surface morphology of modified APP changed a lot and good dispersion and compatibility with PP matrix was expected. Result of XPS show that the surface coating on modified APP are the mixture of ATH and Al PO₄. Thermogravimetric analysis demonstrated that the thermal stability of modified APP was improved and the maximum mass loss rate at high temperature was decreased. The residue at 800℃ was also increased. Meanwhile, the addition of modified APP could improve the flame retardancy of PP with that of APP When the modified APP/DPER was added to 25 wt.%, the LOI value increased from 26.6% to 30.9% and the UL 94 rating raised to V-0（3.2mm）. Cone calorimeter tests indicate that the PHRR and THR decreased significantly. Studies on the char residues show that the presence of modified APP enhanced the char-forming behavior of PP during combustion. More dense and isolated char is formed during the combustion, which protect the underlying polymer from further combustion during burning. All these results indicate that we can improve performance of APP with inorganic modification method as well as these organic modification methods.5. To detect the improvement on the char-formation behavior of flame retardant PP which caused by modified APP, the effect of Al PO₄/ATH on the char formation behavior of flame retarded PP which based on ammonium polyphosphate APP/DPER system is investigated. The flame retardanc y and combustion behavior of flame retardant PP are studied through the limiting oxygen index（LOI）, UL-94 vertical burning test and cone calorimeter test. Results indicate that the partial replacement of APP by Al PO₄/ATH in the flame retardant PP composites shows obvious synergistic effect during combustion. The interactions between Al PO₄/ATH and APP are examined by means of thermogravimetry（TG） analysis. FTIR measurements have been carried out on condensed residues of APP/Al PO₄ and APP/ATH mixtures heat treatment. Based on the above results, the flame retardant mechanism is proposed and discussed.