Influence of the epoxy/amine stoichiometry on the thermomechanical properties of nanocomposites based on high Tg epoxy and organophilic clays.

In layered silicate-epoxy nanocomposites organic modification of the silicates makes them compatible with the epoxy which intercalates into the clay galleries. The effect of clay dispersion on epoxies of high Tg is not clear. Decreases of the epoxy Tg have been frequently reported. The presence of clay may cause stoichiometry imbalances that conduces to the formation of imperfect networks

Partially exchanged organophilic bentonites

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Partially exchanged organophilic bentonites

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Chemical modification of smectite clays

Today, speciality use organoclays are being developed for an increasingly large number of specific applications. Many of these, including use in cosmetics, polishes, greases and paints, require that the material be free from abrasive impurities so that the product retains a smooth `feel'. The traditional `wet' method preparation of organoclays inherently removes abrasives naturally present in the parent mineral clay, but it is time-consuming and expensive. The primary objective of this thesis was to explore the alternative `dry' method (which is both quicker and cheaper but which provides no refining of the parent clay) as a process, and to examine the nature of the organoclays produced, for the production of a wide range of commercially usable organophilic clays in a facile way. Natural Wyoming bentonite contains two quite different types of silicate surface (that of the clay mineral montmorillonite and that of a quartz impurity) that may interact with the cationic surfactant added in the `dry' process production of organoclays. However, it is oil shale, and not the quartz, that is chiefly responsible for the abrasive nature of the material, although air refinement in combination with the controlled milling of the bentonite as a pretreatment may offer a route to its removal. Ion exchange of Wyoming bentonite with a long chain quaternary ammonium salt using the `dry' process affords a partially exchanged, 69-78%, organoclay, with a monolayer formation of ammonium ions in the interlayer. Excess ion pairs are sorbed on the silicate surfaces of both the clay mineral and the quartz impurity phases. Such surface sorption is enhanced by the presence of very finely divided, super paramagnetic, Fe2O3 or Fe(O)(OH) contaminating the surfaces of the major mineral components. The sorbed material is labile to washing, and induces a measurable shielding of the 29Si nuclei in both clay and quartz phases in the MAS NMR experiment, due to an anisotropic magnetic susceptibility effect. XRD data for humidified samples reveal the interlamellar regions to be strongly hydrophobic, with the by-product sodium chloride being expelled to the external surfaces. Many organic cations will exchange onto a clay. The tetracationic cyclophane, and multipurpose receptor, cyclobis(paraquat-p-phenylene) undergoes ion exchange onto Wyoming bentonite to form a pillared clay with a very regular gallery height. The major plane of the cyclophane is normal to the silicate surfaces, thus allowing the cavity to remain available for complexation. A series of group VI substituted o-dimethoxybenzenes were introduced, and shown to participate in host/guest interactions with the cyclophane. Evidence is given which suggests that the binding of the host structure to a clay substrate offers advantages, not only of transportability and usability but of stability, to the charge-transfer complex which may prove useful in a variety of commercial applications. The fundamental relationship between particle size, cation exchange capacity and chemical composition of clays was also examined. For Wyoming bentonite the extent of isomorphous substitution increases with decreasing particle size, causing the CEC to similarly increase, although the isomorphous substitution site: edge site ratio remains invarient throughout the particle size range studied.

Síntese e caracterização de nanocompósitos à base de poliuretano dispersos em água com argilas hidrofílica e organofílica

A área de pesquisa de materiais nanoestruturados tem recebido destacada atenção nos últimos anos por parte da comunidade científica, ressaltando-se os nanocompósitos à base de polímero e argila. Nesta Dissertação foram sintetizados nanocompósitos à base de poliuretano (NWPUs) com argilas do tipo montmorilonita (MMT), hidrofóbicas (organofílicas) e hidrofílica. Os monômeros empregados na síntese foram poli(glicol propilênico) (PPG); polibutadieno líquido hidroxilado (HTPB); ácido dimetilolpropiônico (DMPA), diisocianato de isoforona (IPDI) e hidrazina (HYD), como extensor de cadeia. Nas formulações, foram variadas as proporções de HTPB e o teor das argilas. As argilas organofílica Cloisite 30B e hidrofílica Cloisite Na+ foram incorporadas em 1, 3 e 5 %, enquanto que a organofílica Cloisite 15A foi incorporada no teor de 1%. As dispersões foram caracterizadas quanto ao teor de sólidos totais, tamanho médio de partículas e viscosidade. Os filmes vazados a partir das dispersões foram caracterizados por espectroscopia na região do infravermelho (FTIR), difração de raios-x (XDR), microscopia eletrônica de varredura (SEM) e microscopia de força atômica (AFM). A resistência térmica e a transição vítrea dos materiais foram determinadas por termogravimetria (TG) e calorimetria diferencial de varredura (DSC), respectivamente. O teor de absorção de água e o comportamento mecânico dos filmes foram avaliados. Foi verificada, por XRD, a ausência do pico de cristalinidade, característico das argilas puras e não-deslaminadas. As micrografias obtidas por SEM confirmam uma dispersão homogênea das argilas na matriz poliuretânica. Os filmes à base de nanocompósitos (NWPUs) apresentaram propriedades mecânicas superiores às apresentadas por aqueles obtidos a partir das dispersões sem a presença de argila (WPUs). A adesão dos revestimentos formados, pela aplicação das dispersões em diversos substratos, também foi verificada visualmente. Os resultados das análises mostraram que houve a formação de nanocompósitos à base de água, formados tanto a partir da argila hidrofílica quanto das organofílicas

Part I: Binders & technologies - Basic principles

The first three reports in this series (Parts I, II and III) deals with binders and technologies used in stabilisation/ solidification (S/S) practice and research in the UK. This first part covers 'basic principles'while the second covers 'research' and the third 'applications'. The purpose of this work, which forms part of the Network STARNET on stabilisation/solidification treatment and remediation, is to identify the knowledge gaps and future research needs in this field. This paper describes the details and basic principles of available binders and technologies in the UK. The introduction in the report includes background on S/S, legislation aspects, overview of STARNET and its activities and details of commonly used binder selection criteria. The report is then divided into two main sections. The first covers binders and includes cement, blastfurnace slag, pulverised fuel ash, lime, natural and organophilic clays, bitumen, waste binders and concludes with proprietary binders. The second part details implementation processes for S/S treatment systems starting with ex-situ treatment systems, such as plant processing, direct mixing and in-drum processing and finishes with in-situ treatment processes, such as mechanical mixing and pressure mixing. © 2005 Taylor & Francis Group.

Mesoestruturas porosas a partir de materiais naturais

The MCM-41 mesoporous synthesis was done using rice hulls ash and chrysotile as natural alternative silica sources. For the using of these sources, chemical and thermic treatments were done in both materials. After chemical and thermic treatments, these materials were employed on the MCM-41 mesoctructures synthesis. The natural materials treated and employed in the synthesis were characterized by several techniques such as X-ray diffraction, N2 adsorption and desorption, scanning electronic microscopy and thermogravimetric analysis. MCM-41 standart samples synthetized with aerosil 200 commercial sílica were used to evaluation. The formed material from rice hulls ash showed values from BET specific area about 468 m².g-1, N2 adsorption and desorption isotherms and loss mass similar to reference materials. The silica from chrysotile calcined and leached was employed to mesoporous materials synthesis. The BET specific area showed values about 700 m².g-1, N2 adsorption and desorption isotherms type IV and loss mass similar to mesoporous materials. The formed material from calcined and leached chrysotile, without calcination, applied to phenol remotion carried high performance liquid chromatography and evaluated with organophilic clays with different treatments. By the characterization techniques were proved that mesoporous materials with lesser order that reference samples. The material formed from rice hulls ash without the calcination step achieved better adsorption results than organophilic clays

Mesoestruturas porosas a partir de materiais naturais

The MCM-41 mesoporous synthesis was done using rice hulls ash and chrysotile as natural alternative silica sources. For the using of these sources, chemical and thermic treatments were done in both materials. After chemical and thermic treatments, these materials were employed on the MCM-41 mesoctructures synthesis. The natural materials treated and employed in the synthesis were characterized by several techniques such as X-ray diffraction, N2 adsorption and desorption, scanning electronic microscopy and thermogravimetric analysis. MCM-41 standart samples synthetized with aerosil 200 commercial sílica were used to evaluation. The formed material from rice hulls ash showed values from BET specific area about 468 m².g-1, N2 adsorption and desorption isotherms and loss mass similar to reference materials. The silica from chrysotile calcined and leached was employed to mesoporous materials synthesis. The BET specific area showed values about 700 m².g-1, N2 adsorption and desorption isotherms type IV and loss mass similar to mesoporous materials. The formed material from calcined and leached chrysotile, without calcination, applied to phenol remotion carried high performance liquid chromatography and evaluated with organophilic clays with different treatments. By the characterization techniques were proved that mesoporous materials with lesser order that reference samples. The material formed from rice hulls ash without the calcination step achieved better adsorption results than organophilic clays

Enhanced electrochemical properties of nanocomposite polymer electrolyte based on copolymer with exfoliated clays

In this present work, a polymer electrolyte based on polymer/clay nanocomposite has been developed. Montmorillonite (MMT) clay was used as the filler. due to its special size in length and thickness, and its sandwich type structure. The obtained gel polymer electrolytes have high ionic conductivity up to 2.5 mS cm(-1) with high cationic transference number (about 0.64) at room temperature. The influences of the filler on the membrane morphology. the solvent uptake, the ionic conductivity, and the cation transport number were investigated, and thus the significant contribution from the exfoliated organophilic MMT was identified.