Study On Organically Surface Modification Of Sepiolite And Its Effect On Polystyrene/Sepiolite Composites' Thermal Properties

In this thesis, the preparation and characterization of organo-sepiolites andploystyrene/sepiolite composites were studied.Sepiolite is an abundant and inexpensive mineral that has high mechanical strength aswell as high chemical resistance. The general structure of sepiolite is formed by analternation of blocks and tunnels that grow up in the fiber direction (c-axis). Each block isconstructed by two tetrahedral silica sheets enclosing a central magnesia sheet. In the innerblocks, all corners of silica tetrahedra are connected to adjacent blocks, but in outer blocks,some of the corners are Si atoms bound to hydroxyl groups (Si-OH). These silanol groupsat the external surface of the silicate are usually accessible to organic species, acting asneutral adsorption sites. In addition to this, some isomorphic substitutions in the tetrahedralsheet of the mineral lattice, such as Al³⁺ instead of Si⁴⁺, form negatively charged adsorptionsites. Such sites are occupied by exchangeable cations that compensate for the electricalcharge. These characteristics of sepiolite make it a powerful sorbent for neutral organicmolecules and organic cations.In this experiment, sepiolite was modified by cationic surfactant cetyltrimethylammonium bromide(CTAB) and silane coupling agentγ-methacryloxy propyl trimethoxysilane(KH570), respectively. The organo-sepiolite was then characterized byFourier-transformed infrared(FT-IR), X-ray diffraction(XRD) and sessile droplet contactangle of water. The results indicated that the interlayer spacing of the organo-sepiolitechanged after modification. The interlayer spacing of sepiolite modified by CTAB(d₁₁₀=1.241 nm) increased slightly as compared to the pristine sepiolite (d₁₁₀=1.224 nm).Contrariwise, the interlayer spacing of sepiolite modified by KH570 (d₁₁₀=1.194 nm)decreased a little. The results of sessile droplet contact angle of water on surfaces oforgano-sepiolite showed that the contact angle of water changed with the reaction time andthe KH570 content. When the content of KH570 was 1 mL/lg sepiolite, the reaction timewas 6 hrs, the contact angle of water was up to 55°.Furthermore, polystyrene/sepiolite composites, based on organo-sepiolite and styrenemonomer were synthesized by suspension polymerization or emulsionpolymerization. FT-IR, XRD and thermal analysis have been employed in thecharacterization of the resulting composites. The result of FT-IR showed that polystyrene in the composite was atactic polystyrene. Experiment result proved that the major influencingfactors on thermal stability of composite were the diffusion of the polymer chains into thesepiolite agglomerates. Differential scanning calorimetry (DSC), Differential thermalanalysis (DTA) and Thermogravimetric analysis (TGA) results indicated that the glasstransition temperature and initial decomposition temperature of the composite increasedafter adding the organo-sepiolite modified by CTAB or KH570. The composite glasstransition temperature increased 2.9℃, and initial decomposing temperature increased 59℃by adding 0.25wt% organo-sepiolite modified by KH570.