| Intumescent flame retardant (IFR) have been extensively used in halogen-free flameretardant polymeric materials because of its halogen-free, smoke suppression and so on.However the diadvantage of IFR are existed in high additive amount, low flame retardantefficiency and high water solubility, etc. In order to solve these problems, boron-containingpolysiloxane (pBSi) and phosphorus, nitrogen containing polyborosiloxane (pPNBSi) weredesigned and synthesized. IFR and pBSi (or pPNBSi) were used for the preparation of flameetardant polypropylene (PP). Synergistic effects of pBSi (or pPNBSi) on intumescentflame-retardant polypropylene were studied. Furthermore, the synergistic flame retardantmechanism between pBSi (or pPNBSi) and IFR were investigated by thermogravimetricanalysis (TG), thermogravimetric-fourier transform infrared spectroscopy (TG-IR) andFourier transform infrared spectroscopy (FT-IR). The main research contents and results arelisted as following:First, boron-containing polysiloxane (pBSi) was synthesized by using octamethylcyclotetrasiloxane (D4), boric acid, tetraethoxysilane (TEOS), etc. And flame-retardant PPwas prepared by using IFR as flame retardant and pBSi as synergistic agent. The effects ofpBSi on intumescent flame-retardant PP were studied. The results showed that, pBSi hasexcellent thermal stability and outstanding char yield in air. And there was an obvioussynergistic effect between pBSi and IFR. When the content of pBSi was3.0wt%(the totalcontent of flame retardant was25.0wt%), the LOI of flame-retardant PP was increased from29.0%to34.8%, and the vertical combustion performance was improved from UL-94V-1toUL-94V-0. Cone calorimeter results showed that, the peak of heat release rate (pHRR) wasreduced from354.0kW/m2to204.9kW/m2, which was reduced by41.9%.At the same time,the peak of smoke release rate (pSPR) was reduced by15.3%. Compared with SiO2,4Azeolite and ZB, pBSi and IFR possessed better synergistic effect. Meanwhile, the water andacid resistance of PP/IFR/pBSi were improved obviously. After being treated in hot water(70℃) or sulfuric acid solution for168hours, PP/IFR/pBSi still had good flame retardantperformance. The LOI was as high as31.2%and33.0%, and the vertical combustionperformance remained UL-94V-0. Second, phosphorus and nitrogen containing polyborosiloxane (pPNBSi) wassynthesized by using tetramethyl tetravinyl cyclotetrasiloxane (VD4),9,10-Dihydro-9-oxa-10-Phosph-aphenan-threne-10-oxide(DOPO), N-β-aminoethyl-γ-aminopropyl methyldimethoxysilane (NMDMS). And flame-retardant PP was prepared by using IFR as flameretardant and pPNBSi as synergistic agent. The effects of pBSi on intumescentflame-retardant polypropylene were studied. The results showed that, compared with pBSi,there was a better synergistic effect between pPNBSi and IFR in flame retardant PP. Whenthe content of pPNBSi was only2.0wt%(the total content of flame retardant was20.0wt%),the LOI of flame reatardnat PP was increased from27.0%to31.5%. The vertical combustionperformance was improved to UL-94V-0. Micro-calorimeter results showed that, the peak ofheat release rate (pHRR) and the total heat release (THR) were937.0W/g and31.2kJ/g, whichwere reduced by11.6%and15.9%. Furthermore, compared with SiO2, DOPO and ZB, therewas better synergistic effect between pBSi and IFR. Meanwhile, the water and acid resistanceof PP/IFR/pBSi were also improved obviously. After being treated in hot water (70℃) orsulfuric acid solution for168hours, PP/IFR/pPNBSi still has good flame retardancy.Third, the synergistic flame retardant mechanism between pBSi (or pPNBSi) and IFRwere investigated by TG, FT-IR and TG-IR. And the possible flame retardant mechanismbetween pBSi (or pPNBSi) and IFR was that, in the solid phase, IFR formed inflation carbonlayer, at the same time pBSi produced ceramic-like layer covering on the surface of char layer,thus improving the qulity of the char layer. Moreover, the P-C bond which belonged tophosphorus heteropoly phenanthryl groups of pPNBSi, may fracture and produce phosphorusoxygen free radical which could extinct the oxygen free radicals and alkane free radicalsduring the combustion process. Meanwhile, phenyl phosphoric acid produced by phosphorusheteropoly phenanthryl groups and formed phosphorus compound which was glass state. Andthen the phosphorus compound produced ceramic-like layer covering on the surface ofinflation carbon layer which expressed a better synergistic effect. |
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