Preparation Of Flame Retardant Functionalized Montmorillonite Nanoparticles And Application In Polyvinyl Alcohol

With the increasing requirements of environmental protection, montmorillonite(MMT)was widely favored by researchers, because of its halogen-free, low smoke, low price and excellent overall performance, as well as layered flame retardant nano synergistic agent.However, its application has been restricted because of its poor dispersion in the polymer matrix, and relatively low flame retardant efficiency. Therefore, it is demanded significantly to develop novel flame retardant modified montmorillonite nanoparticles and apply to the polymers.In this paper, a novel ternary integrated P-N-Si halogen-free flame retardant named phenoxy-bis-(triethoxysilylpropyl) phosphamide(BTSP) was successfully synthesized by the reaction of phenylphosphonic dichloride and(?-aminopropyl) triethoxysilane. The chemical structure of BTSP was characterized by 1H NMR, 31 P NMR and FT-IR. The optimal reaction conditions for BTSP was investigated by the reaction solvent, reaction temperature, reaction time, molar ratio and acid-blinding agent. The thermal decomposition behavior of BTSP was studied by thermogravometric analysis(TGA) and the results showed that the initial decomposition temperature of BTSP was 150? and the char residue was about 14.6% at600?.Two flame retardant functionalized montmorillonite nanoparticles(MMT-BTSP,MMT-PNP) were prepared by modifying sodium montmorillonite(Na-MMT) with flame retardant BTSP and N-(diphenylphosphino)-1,1-diphenyl-N-(3-(triethoxysilyl) propyl)phosphinamine(PNP, self-made in our lab). The structure for modified MMT was characterized by FT-IR, XRD and TEM. The results showed that BTSP and PNP intercalated to the layers of montmorillonite successfully. The optimal preparation conditions forMMT-BTSP and MMT-PNP were investigated by the molar ratio, reaction time, reaction temperature, and pH value. TGA results showed that MMT-BTSP and MMT-PNP had excellent thermal stability, and the char residue at 800? were 84.9% and 83.6%, respectively,which were slightly lower than the Na-MMT(89.3%). However, the initial decomposition temperature was greatly improved.The MMT-BTSP and MMT-PNP have been applied to polyvinyl alcohol(PVA), and the PVA/flame retardant functionalized montmorillonite nanocomposites(PVA/MMT-BTSP and PVA/MMT-PNP) were prepared successfully. XRD results indicated that PVA molecular chains were intercalated to modified MMT successfully, and formed intercalated nanocomposites. TGA results showed that modified MMT could increase the char residue at800?of PVA composites, and improved thermal stability obviously. Micro-scale combustion calorimetry test(MCC) and Limiting oxygen index test(LOI) have been used to study the flame retardancy of PVA/MMT nanocomposites, showing that the peak heat release rate(PHRR) and heat release capacity(HRC) of PVA/flame retardant functionalized montmorillonite nanocomposites were lower than pure PVA and PVA/MMT-Na, and limiting oxygen index(LOI) was higher. That revealed modified MMT could improve the flame retardancy of PVA composites. However, the amount of modified MMT was so small that the improvement of flame retardant performance is not significant. Light transmitting test showed that pure PVA materials had excellent light transmission, and modified MMT reduced the light transmittance of the nanocomposites. But the PVA/MMT nanocomposites still had good light transmission. Mechanical performance tests displayed that compared to pure PVA, the tensile strength of PVA/MMT nanocomposites increase, as well as the elongation at break dropped, significantly.PVA/DEPA/MMT-BTSP and PVA/DEPA/MMT-PNP nanocomposites were prepared through compounding montmorillonite with bis-hydroxy P-N flame retardant diethyl-N,N'-bis(2-hydroxyethyl) phosphoramide(DEPA, self-made in our lab) in PVA matrix. The thermal decomposition behavior of PVA/DEPA/MMT nanocomposites has been investigated by TGA test and the results showed that the thermal stability and char-forming ability of thenanocomposites were improved by synergistic effect between MMT and flame retardant DEPA, were better than the PVA/DEPA or PVA/MMT composites. MCC and LOI test demonstrated that the synergistic effect of DEPA and MMT reduced significantly the flammability of the polymer, increasing the LOI of PVA/DEPA/MMT nanocomposites to more than 26.0%. And flame retardant property of PVA/DEPA/MMT nanocomposites improved significantly. Mechanical performance tests showed that the addition of DEPA led to the tensile strength reduced and the elongation at break increased for PVA/DEPA composites. However, compared to PVA/DEPA composites, PVA/DEPA/MMT nanocomposites had higher tensile strength and lower elongation at break. It revealed that MMT had a reinforcing effect on PVA materials obviously.