Fabrication Of Gradient And Halogen-free Flame Retard Ant System And The Performance In Polymer Materials

Because of its cheap price and high effeciency, halogen containing compoundsplayed as a significant role in flame retardants in last century. However, it was foundthat some disadvanstages exists in halogen containing flame retardants, such astoxicity, toxic gases release and pollution. Some of them have been abandoned inEurope and America. The safe and eco-friendly flame retardants have been needed.Recently, halogen-containing flame retardants have gradually been replaced byintumescent flame retardants. And the issues have been focused on the novel flameretardant system, which possesses the advantages in high efficiency, low smokerelease and anti-dripping. Traditionally, the effective intumescent flame retardantsystem is a combination of acid source, char-forming agent and gas source. Theapplication for these flame retardants has been severely restricted because of watersolubility, aggregation and compatibility. Thus, the modification of traditional flameretardants and the investigation on the new flame retardant are of great significance.In this article, the research focuses on the modification of halogen-free flameretardants and constructs a gradient and halogen-free system with multifunctionalflame retardant effects. The investigation on the thermal and flame retardant behaviorof polymer composites can conclude their gradient flame retardant process. And theeffect of different microcapsules on the improvement of flame retardancy wassystematically discussed. During this procedure, the gradient mechanism ofmicrocapsules was obtained. Except that, the novel flame retardant is also preparedand the flame retardancy in polymer materials is investigated. The synergistic effectsand mechanism between flame retardants was analyzed. On on hand, it can confirmthe practicability for the microencapsulation of flame retardants; on the other hand,the work presents the experimental and theoretical basis for the application of theseflame retardants.The one-step microencapsulation was adapted in modifying the surface ammonium polyphosphate (APP). By this process, the defects for APP were improvedafter melamine (MEL) was introduced into the microcapsules. And the introduction ofmicrocapsules is feasible to enhance the flame retardancy. The structure ofmicroencapsulated APP was confirmed by a series of characterization. Besides, thesynergistic flame retardant behavior of APP and expandable graphite (EG) in rigidpolyurethane foam was systematically investigated. The results demonstrate that themaximum heat release rate of composites can decrease from583kW/m2to279kW/m2by microencapsulation. And it possesses26.2%limited oxygen index (LOI) value andUL-94V-0rating. Based on the analysis of char residue, the flame retardantmechanism of microencapsulated APP and EG in rigid polyurethane foam wasproposed.The co-microencapsulation method is adapted to modify APP and aluminumhydroxide (ATH). Most of all, MEL in the microcapsules can enhance the flameretardancy of polypropylene (PP) composites. It indicates that the synergistic effectbetween APP and ATH exists in flame retarding polymer materials. Thus, the simpleand eco-friendly halogen-free intumescent system was built. The introduction ofmicrocapsules can weaken the polarity difference between flame retardants andpolymer matrix that is feasible for the dispersion and compatibility of fillers in matrix.The thermal and flame-retarding behavior was systematically investigated. Itdemonstrates that microcapsules can further decrease the maximum heat release rateof PP composites. It can reach25.5%LOI value and UL-94V-0ratings. Except that,the water resistance of APP/ATH in PP matrix can be improved by microcapsules. Byresearching the char residue, a potential flame retardant mechanism ofco-microencapsulated APP and ATH in PP was obtained.The two-step microencapsulation was adapted in modifying APP. The aim is toimprove the defects of APP and introduce MEL and pentaerythritol (PER) into thesurface of APP at the same time. Fourier transform infrared spectroscopy (FTIR)certified the chemical structure of microencapsulated APP and transmission electronmicroscopy (TEM) demonstrates the core/shell structure of microencapsulated APP.The introduction of microcapsules can decrease the maximum heat release rate from 526.5kW/m2to301.8kW/m2. And it can obtain25.5%LOI value and UL-94V-1ratings for PP/MAPP system. By analyzing the char residue of PP composites aftercombustion, the crosslinking reaction between microcapsules and APP can beconfirmed. And the flame retardant mechanism of microencapsulated APP in PPmatrix is revealed.SiO2particles were introduced into the surface of melamine phosphate (MP) viasol-gel method. The chemical structure of microencapsulated MP can be certified byFTIR and x-ray photoelectron spectroscopy (XPS). Scanning electron microscope(SEM) reveals SiO2particles attached onto the surface of MP. Moreover,thermogravimetric analysis (TGA) demonstrates that the thermal interaction betweenmodified MP and dipentaerythritol (DPER) occurs. And the flame retardancy testsindicate that SiO2particles can further improve the flame retardancy ofABS/MP/DPER. It can reach31.2%LOI value and UL-94V-0rating. After theanalysis of char residue, the synergistic effect between MP and DPER is confirmed inflame retarding ABS. And the incorporation of SiO2particles can effectively improvethe quality of char layer and flame retardancy of ABS composites. Except that, theflame retardant mechanism of fillers in ABS is achieved.A novel phosphorus and nitrogen-containing flame retardant (MPA) wasprepared by phytic acid (PA) and MEL. It is originated from the biomass materialsand possesses high content of phosphorus. TGA tests demonstrate that the thermalinteraction between MPA and DPER happens and the char residue reaches40%at600°C. The tests illustrate that the LOI value and vertical combustion rating ofPP/MPA/DPER is28.5%and UL-94V-0, respectively. FTIR spectra demonstrate thatthe char residue of PP/MPA/DPER after combustion possesses the crosslinkingstructure of P-O-C groups. After analysis, it also presents a synergistic andintumescent flame retardant mechanism.