Synthesis Of Compounds Containing Multiple Flame Retardant Elements And Study On Mechanism Of Flame Retardant Polycarbonate

Polycarbonate（PC）has many advantages including good transparency,impact strength,thermal stability and dimensional stability,and thus has been used in construction,glass assembly,automotive,electric and other fields.Although the pure PC displays UL-94 V-2 rating,it still cannot meet the harsh requirements for flame retardancy（UL-94V-0 level）in some special fields.In this thesis,three kinds of compounds with multiple flame retardant elements were synthesized through molecular design,and were used to improve the flame retardancy of PC and broaden their application fields.The effects of the synthesized compounds on the flame retardancy,combustion behavior,thermal stability and mechanical properties of the composites were systematically studied,and their flame retardant mechanism was revealed.The main research contents are as follows:（1）A DOPO-based flame retardant（DPAPZ）rich in P/N（10.02 wt%of P and 13.58 wt%of）was synthesized from aminopyrazine（APZ）and9,10-Dihydro-9-oxa-10-phosphaphenanthrene-10-oxide（DOPO）.FTIR,¹H and ³¹P NMR spectra confirmed that the target product was successfully synthesized,and TGA results showed that DPAPZ has higher thermal stability than both APZ and DOPO.With the incorporation of 6wt%DPAPZ,the PC/DPAPZ-6 composite reached UL-94 V-0 rating without dripping.Cone calorimeter test（CCT）results showed that the peak heat release rate（PHRR）and total heat release（THR）of PC/DPAPZ-6 blends were 44.8%and 47.0%lower than those of pure PC,respectively,and a more expanded carbon layer was formed after combustion.The TGA results of the composites indicated that phosphoric acid,which produced from the decomposition of DOPO group at low temperatures,catalyzed the PC matrix to form a carbon layer at early decomposition stage.The actual content of the carbon residue from the composites was higher than the theoretical value.The combined thermogravimetric-infrared（TG-IR）results showed that the NH₃ and phosphorus-containing radicals（PO·,PO₂··and P₂O₄·,etc.）diluted the flammable gas concentration and quenched those reactive free radicals which promoted the growth of the reaction chain in the combustion process,respectively.Furthermore,the peak intensities of typical combustible gas phase products and toxic fumes of the composites were significantly reduced after the addition of DPAPZ.The results of mechanical properties showed that the tensile strength of the composites displayed almost no change but the elongation at break decreased slightly with the addition of DPAPZ.（2）Using aminophenyl silicone oil（ASO）and diphenylphosphinic acid chloride（DPPC）as raw materials,a P/N/Si-containing diphenylphosphine amide silicone oil flame retardant（PASO）was synthesized.The chemical structure and thermal stability of PASO were characterized by FTIR,¹H NMR,³¹P NMR and TGA,respectively.The synthesized PASO exhibited good flame retardancy on the PC,and the PC/PASO-1 composite reached UL 94 V-0 rating and a limiting oxygen index（LOI）value of 31%in the presence of 1 wt%PASO and 5 wt%talc as anti-dripping agent.The CCT results showed that the flame-retarded PC composites exhibited higher fire safety.Compared with the pure PC,the PHRR and THR value of PC/PASO-1 composites were reduced by61.5%and 8.8%,respectively,and the fire growth index（FIGRA）was reduced from 1.66 k W/m² s of pure PC to 1.23 k W/m² s.The results of Raman spectroscopy and scanning electron microscopy（SEM）showed that a denser carbon layer with higher degree of graphitization were formed after combustion.The TGA results showed that both talc and PASO could promote the decomposition of PC on advance,and the isomerization reaction would release H₂O and CO₂,which would generate xanthene which is helpful for the carbon formation.The TG-IR results revealed that PASO decomposed to produce a small amount of phosphorus-containing gaseous products（eg PO·）,which can act as a free radical scavenger to quench·H and·OH,thereby interrupting the chain free radical combustion reaction of the polymer.The mechanical properties test results showed that the PC/PASO-1 composites gave the tensile strength of 65.5 MPa,the elongation at break of 96.4%,and the impact strength of 52.3 kJ/m²,which are comparable to that of pure PC.（3）A P/N/Si-containing phenylphosphoramide silicone oil flame retardant（ASPD）was synthesized using ASO and phenylphosphoryl dichloride（PPDC）as raw materials.The chemical structure and thermal stability of ASPD were confirmed vai FTIR,¹H NMR,³¹P NMR and TGA,respectively.The PC/ASPD-2 composite containing 2 wt%ASPD and 3 wt%talc achieved a satisfactory UL 94 V-0 rating with a LOI value of 31.4%.The CCT results showed that the values of PHRR,THR,average CO release（Av-COY）and average CO₂ release（Av-CO₂Y）of flame-retarded PC were significantly reduced,indicating that the addition of ASPD can effectively reduce the release of heat and toxic and harmful smoke during combustion.The fire performance index（FPI）increased from 0.31 of the pure PC to 0.36 of PC/ASPD-2,and higher FPI value meaned lower fire risk.The analysis of residual carbon elements showed that in the condensed phase,a phosphorus-containing cross-linked carbonized layer was formed after the addition of ASPD,and the silicon-containing fragments migrated to the surface to form an inert protective layer.The TGA results showed that ASPD exhibited a similar catalytic decomposition effect of PASO,and reduced the maximum weight loss rate of PC composites whilst increased the carbon residue at800℃.The TG-IR results showed that the phosphorus and nitrogen-containing components continued to exert quenching and dilution effects.The results of mechanical properties showed that the stress concentration effect was significantly reduced when the content of talc was reduced from 5 wt%to 3 wt%.PC/ASPD-2 had a higher impact strength（57.5 kJ/m²）than that of PC/PASO-1（52.3 kJ/m²）,and its elongation at break（97.9%）is even slightly higher than that of the pure PC（96.3%）.