Organic-modifier-free pathways for the preparation of polymer -metal oxide nanocomposites.

摘要

Novel preparation strategies for the formation of polymer - metal oxide nanocomposites have been developed to eliminate the need for surface organic-modifiers and thereby to avoid the disadvantages of the modifiers, such as their plasticizer effects and low thermal stabilities. The success of these strategies relies on the smart design of the synthetic or naturally occurring metal oxides and the composite preparation methodology.;Synthetic clay materials exhibit high purity, uniform surface properties and composition, and are promising substitutes for natural clay minerals with more variable properties. We synthesized three types of saponite-like silicates with different octahedral sheet compositions and different layer stacking orders depending on synthesis methodology. When bis(triethoxylsilyl) methane was used as the Si source, an inorganic-organic hybrid clay material, which had -CH2- tetrahedra bridging groups in the basal plane, was achieved.;Among the synthetic saponites, an irregularly stacked derivative (denoted SAP) was examined as an epoxy polymer reinforcing agent. SAP exhibited a large surface area (920 m2/g), small lateral dimension (20--30 nm), irregularly stacked layered morphology with porous surfaces, which allowed polymer intercalation without any surface modifications. A Uniform dispersion of SAP nano-aggregates was achieved for the epoxy - SAP nanocomposites, providing improved strength, modulus and toughness of the polymer. For example, for a glassy epoxy system, a 10% by weight loading of SAP provided a 10% increase in strength, 30% increase in modulus and 45% increase in toughness, compared with the pristine polymer. In addition, the nanocomposites had the same glass transition temperature as the pristine epoxy, because the plasticizer effects of the organic modifiers were avoided.;Palygorskite, a silicate clay with a pleated 2:1 layered structure, has a lath-like particle morphology, and low surface charges that make it an attractive candidate for the formation of polymer nanocomposites. The pristine clay mineral provided reinforcement to epoxy matrix without organic modification. The silylated derivatives of palygorskite provided better dispersions in rubbery epoxy matricx than the pristine mineral, affording further improvements in mechanical properties, especially at low loadings levels of 2 and 5% (w/w).;Mesostructured silicas with pore sizes larger than 20 nm allowed polyethylene intercalation in the porous regions without silica surface modifications. Even with an inhomogeneous dispersion of mesoporous silica, the polymer mesocomposites exhibited improvement in tensile strength and modulus that were analogous with those achieved in polyethylene - clay systems where extensive modifications were required.