Synthesis Of Intumescent Flame Retardants And Thereof Flame Retardant Polypropylene

Polypropylene（PP）is used widely in industry,transportation and civil products because of its good processing properties and excellent mechanical properties.However,polypropylene with an inherent hydrocarbon structure is highly flammable and is accompanied with large amounts of dripping and toxic fumes during combustion,it cause a threat to the environment and personal property,and also seriously limits its application in certain specific areas.Thus,it is essential to improve the fire safety of PP.Intumescent flame retardant（IFR）has the characteristics of halogen-free,anti-dripping and smoke suppression,which is in accord with the concept of green chemical development and is very suitable for polyolefins that burn easily with molten dripping.In this thesis,Mn²⁺-doped piperazine phosphate salt char-forming agent and bio-based intumescent flame retardant were synthesized through molecular design,and two kinds of flame retardant PP composites（PP/IFRs）were prepared successfully.The flame retardancy,thermal stability,mechanical properties and flame retardant mechanism of the FRPPs.The main research contents and results are as follows:（1）Mn²⁺-doped piperazine phosphate salt carbon former（HP-Mn）was synthesized through ionic reaction using hydroxy ethylidene-1,1-diphosphonic acid（HEDP）,piperazine（PA）and manganese acetate tetrahydrate（Mn Ac?4H₂O）as raw materials.Using polyethyleneimine（PEI）,tartaric acid（TA）and nickel chloride hexahydrate（Ni Cl₂?6H₂O）as raw materials,the bio-based intumescent flame retardant（MAPP）was synthesized by surface modification of ammonium polyphosphate（APP）through layer-by-layer self-assembly.The chemical structures and properties of the target products were characterized by Fourier infrared spectroscopy（FTIR）,X-ray diffraction spectroscopy（XRD）,X-ray energy spectrometry（XPS）,scanning electron microscopy（SEM）and thermogravimetric analysis（TGA）,respectively.（2）A kind of IFR system was constructed on the base of APP and HP-Mn,and the PP/IFR composites were prepared using melt-blending method on an internal mixer,and the flame retardancy,thermal stability,mechanical properties and possible flame retardant mechanism of PP/IFR composites were investigated.The results showed that the introduction of APP/HP-Mn flame retardant system significantly improved the flame retardancy of PP composites.At loading level of 25 wt.%（APP/HP-Mn）_1/1,the results of the combustion test displayed that the composite achieved LOI value of 30.7%and UL-94 V-0 rating.At the same time,the peak heat release rate（PHRR）and total smoke release（TSP）of PP/25wt.%（APP/HP-Mn）_1/1 composite were reduced by 74%and 30%as compared with the pure PP,respectively.TGA results revealed that the introduction of APP/HP-Mn decreased the onset decomposition temperature of the composites whilst increased the residual yield.It indicates that the APP/HP-Mn system could promote the early degradation of the matrix to form an protective carbon layer which could isolate the transition of the heat and oxygen,and thus preventing the further decomposition of the internal matrix.The results of TG-FTIR and residual carbon analysis demonstrated that APP and HP-Mn have a synergistic flame retardant effect.On the one hand,the released non-combustible gases,phosphorus oxygen radicals and Mn²⁺can effectively dilut the combustible gases and capture radicals,on the other hand,the polyphosphate cross-linked to form an expanded carbon layer which can become more continuous and dense owing to the catalytic cross-linking effect of Mn²⁺,thus effectively improving the flame retardant efficiency.The results of the mechanical measurements show that in the case of the same loading level（25 wt.%）,the tensile strength and impact strength are increased from 27.4 MPa and 3.0 k J m^-2for PP/25wt.%APP to 29.8 MPa and 3.8 k J m^-2 for PP/25wt.%（APP/HP-Mn）_1/1,respectively.（3）A kind of IFR system was constructed on the base of APP and MAPP,and the PP/IFR composites were prepared using melt-blending method on an internal mixer.The flame retardancy,thermal stability and mechanical properties of PP/IFR composites were investigated,and the possible flame retardant mechanism was also disclosed.The results revealed that the PP/25wt.%MAPP composites obtained a high LOI value of 31.5%,which is a flame-retardant material.Meanwhile,its peak release rate（PHRR）and total smoke release（TSP）were reduced by 75.6%and34.4%as compared with the pure PP,and gave the highest flame retardance index value（3.62）and the lowest FGI value（0.45 k W/m²s）.It indicates that the MAPP displayed better fire safety than the unmodified APP.The TGA results demonstrated that the onset decomposition temperature of the composite material and the maximum decomposition temperature were reduced but the residue yiels was increased with the incorporation of MAPP,indicating that the MAPP could promote the early decomposition of the matrix to form an expanded carbon layer which acted as a physical barrier to protect the internal matrix.The combined results of TG-FTIR spectra and carbon residue analysis showed that the MAPP displayed synergistic flame retardant mechanism of gas phase and condensed phase.The flame retardant effectiveness was achieved by the release of non-combustible gas and the formation of carbon layer with high quality.The results of mechanical measurements revealed that the negative impact of flame retardant on mechanical properties of composite was decreased due to the improved adhesion between the MAPP and PP matrix.