Preparation Of Hydorphobic Ammonium Polyphosphate Via DOPO Modiifcation And Its Application To PP

Polypropylene (PP), one of the most common thermoplastic polymermaterial, is widely used in many fields. But PP is combustible to release largeheat and drip seriously during burning, causing. Thus its inflammability greatlyrestricts its application in many fields. In view of this, it is significant to enhancethe flame retardant performance of PP.Among current flame-retardant system, the intumescent flame retardants(IFR) are considered as effective halogen-free flame retardants. The typicalintumescent flame-retardant system is based on acid source, carbonization agentand blowing agent, in which ammonium polyphosphate (APP) is the keyconstitute to flame retardancy, characterizing low price, low toxicity and highthermal stability. There are, however, some disadvantages for APP. One is thatAPP is easy to solve in water and aggregate after absorbing moisture in the air;the other is that its hydrophilicity causes the poor compatibility in polymer matrix and thereby bring harmful effects on the mechanical and processingproperties of the composite. Therefore, we proposed a new method to obtain thenovel hydrophobic and water-insoluble APP via the introduction of organicgroup.9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) waschosen to react with melamine (MEL) at150℃to obtain melamine salt(DOPO-MEL) with a novel structure. And then diammonium phosphate (DAP)was added to react with DOPO-MEL. DOPO was introduced into APPmolecular structure by in-situ polymerization, forming a novel hydrophobic APP(DOAPP).The chemical structure of synthetic DOAPP was analyzed and discussed byX-ray diffraction (XRD), fourier transform infrared spectroscopy (FTIR),nuclear magnetic resonance analysis (31P-NMR) and X-ray photoelectronspectroscopy (XPS). The contact angle and the water solubility of DOAPP weretested, and its hydrophobic mechanism was discussed. The sedimentation ofDOAPP and commercial APP in liquid parafin were compared. The thermaldegradation mechanism of DOAPP was analyzed and discussed bythermogravimetry-mass spectrum (TG-MS) and its flame retardancy wasforecasted; At last, PP composites were prepared by melt blending with theloading of DOAPP, synthesized APP (S-APP) and commercial APP (C-APP)and their flame retardancy and mechanic properties were compared.The results showed that the cystal structure of DOAPP is a combination ofAPP-II crystalline structure and the partial DOPO’s crystal structure, moreover, some other new new lattice planes formed in DOAPP due to the introduction ofDOPO, suggesting ammonium polyphosphate formed with a new crystalstructure. Due to an annular cross linked structure of phosphorus containingphenanthrene, DOAPP had higer thermal stability than S-APP and C-APP, witha residue rate of29.7%at800℃, indicating that DOAPP could promote charformation of polymer. Because of the introduction of DOPO, DOAPP isthermally decomposed in free radical chain reactions, and released largeamounts of noncombustible gases to resist the combustion of polymer. Thecontact angle of DOAPP reached105°and is insoluble in water. In addition,DOAPP has good dispersibility and compatibility in liquid paraffin.The combustion performance and mechanical property tests showed thatthe limiting oxygen index reached35.0%for PP composite with the addition of30%of DOAPP, and UL-94test passed V-0level without dripping. Moreimportantly, the tensile strength of PP/DOAPP was31.9MPa, and the notchedimpact strength was7.2J/m2, showing no harm to the mechanic property of PPcomposite. The contrast test showed that the flame retardancy of DOAPP andthe compatibility of DOAPP with PP were superior to C-APP and S-APP.