Organic Modification Of Montmorillonite And Its Application Into Silicone Rubber Composites

Montmorillonite （MMT） is a typical layered silicate mineral including the sheetstructure, the characteristics of expansion, water absorption, high dispersion, cationexchange, etc. It has a feature of plentiful resource, low prices and wide applications. Siliconerubber is an elastic polymer, with the molecular chains having inorganic and organic nature,great flexibility, but weak force, due to its spiral structure of silicon-oxygen chains. Fumedsilica is usually used as a reinforcing agent （incorparation volume:30%⁵0%） in siliconerubber systems to enhance its physical and mechanical properties. But the disadvantage ofthis reinforcing agent is its high price. Therefore, modification of MMT is being studied bysome effective organic ways. Thus, MMT is filled into the silicone rubber, aiming toimprove its properties.This article focuses on the synthesis of hyperbranched ammonium salt, themodifications of MMT, and the preparation of silicone rubber composites. First, N,N-2-dihydroxyethyl-3-amino methyl propionate was selected as the monomer （AB₂） topreparate hyperbranched quaternary ammonium salt, using a method of Quasi-one-stepmethod. Second, Na-MMT was modified by different organic modification agents, such asquaternary ammonium salt, hyperbranched quaternary ammonium salt, and silicone oil.Third, the modified MMT was applied into the silicone rubber with different ratios. Thestructure and properties of the composites were measured and characterized.UV, FTIR, GPC,¹H-NMR, TGA and DTG methods were used to characterize thestructure and properties of hyperbranched quaternary ammonium salt. UV tests showedthat the content of functional groups（C=O、C-O、C-N） and the molecular weight bothwere increased, and a large number of terminal hydroxyl （-OH） existed in thehyperbranched polymer. This hyperbranched polymer had a good thermal stability. Results showed that T_-5%was elevated from113℃to191℃, T_-10%was increased from156℃to216℃, and the maximum mass loss rate was decreased from1.0719%（℃）^-1to0.6607%（℃）^-1.The orthogonal test was used in the evaluation of organic modification of Na-MMT.The best factors for the preparation of hyperbranded MMT was as following: acetone wasselected as solvent; weight percentage was50%; reaction temperature was120℃; stirringrate was1500r/min. Structure analysis results showed that the interlayer space of theHQAS was expanded from1.42nm to1.98nm. The hyperbranched quaternary ammoniumsalt modified Na-MMT had a good thermal stability, with an improvement of remainingweight from81.7%to79.4%, at700℃.The modified MMT was applied to the silicone rubber matrix, and the structure andproperties were tested. Results showed that the tensile strength of3%hyperbranded-OMMT filled RTV was5.4MPa, increased about28.5%, and the elongation at break wasenhanced to425%, nearly1time. A large number of terminal hydroxyl exsited in thesuface of the hyperbranched MMT, and thus it was easy to insert silicone rubber betweenthe silicate layers. It was demonstrated that swelling density was increased to the highest,and T-5%and T-10%were increased about33℃and29℃. Analysis of its melting propertiesshowed that,3%hyperbranched MMT added into RTV, the melting temperature of thecomposite was increased from-40.9℃to-38.1℃at low temperature （-100℃～0℃）（DSC）.In conclusion, the hyperbranched organic montmorillonite was successfully preparedby using hyperbranched quaternary ammonium salt. It has excellent dispersion, surfaceactivity, thermal stability and so on. Moreover, the silicone rubber/montmorillonitecomposites can be obtained with better mechanical and thermal properties after theaddition of these novel reinforcing agents.