The Li+, Na+ and K+ ion exchange reaction process on the surface of mixed oxide SiO2/TiO2/Sb2O5 surface prepared by the sol-gel processing method

The porous mixed oxide SiO2/TiO2/Sb2O5 obtained by the sol-gel processing method presented a good ion exchange property and a high exchange capacity towards the Li+, Na+ and K+ ions. In the H+/M+ ion exchange process, the H+ / Na+ could be described as presenting an ideal character. The ion exchange equilibria of Li+ and K+ were quantitatively described with the help of the model of fixed tetradentate centers. The results of simulation evidence that for the H+ / Li+ exchange the usual situation takes place: the affinity of the material to the Li+ ions is decreased with increasing the degree of ion exchange. On the contrary, for K+ the effects of positive cooperativity, that facilitate the H+ / K+ exchange, were revealed.

Síntese de hidroxiapatita pelo método sol-gel utilizando precursores alternativos: nitrato de cálcio e ácido fosfórico

A hidroxiapatita [Ca10(PO4)6(OH)2, HA] foi sintetizada utilizando-se a rota sol-gel partindo-se de ácido fosfórico e nitrato de cálcio como precursores de cálcio e fósforo, respectivamente e como solvente utilizou-se o metanol na preparação do sol que posteriormente será utilizado na obtenção de recobrimentos de hidroxiapatita sobre substratos de ligas de titânio. O sol permaneceu estável e não ocorreu gelatinização em temperatura ambiente durante sete dias. O sol transformou-se em um gel branco somente após a remoção do solvente a 100ºC. O produto assim obtido foi calcinado em 300°C, 500°C e 700°C e caracterizou-se por DRX, FT-IR, MEV/EDS e TGA/DSC. As fases de HA sintetizada tornaram-se estáveis sem sub-produtos a 700°C. A difração de raios X mostrou que a estrutura apatita é aparente em 300°C. O tamanho do cristal e o teor de HA aumentaram com o aumento da temperatura de calcinação. A análise por MEV mostrou a presença de poros que são importantes para aplicações biomédicas, favorecendo a adesão entre o tecido ósseo neoformado e a apatita sintética, ou seja, osseointegração.

Síntese e caracterização textural do catalisador CeO2/TiO2 obtido via sol-gel: fotocatálise do composto modelo hidrogenoftalato de potássio

Este trabalho descreve um método de modificação do TiO2 obtido pelo processo sol-gel, através da adição de óxido de cério no momento da síntese. O material foi caracterizado por adsorção de N2 a 77K. A adição de CeO2 aumenta a área específica do catalisador em 135% e reduz o diâmetro de poros. A atividade catalítica desses materiais foi verificada frente à reação de foto-decomposição do hidrogenoftalato de potássio e comparada ao TiO2 comercial P25 da Degussa.

Use of modified silica gel for concentrating Pb (II) and Cd (II) occurring in form of complex anions

The performance of silica gel, modified by the impregnation with a high molecular weight quaternary amine (triethyl octadecyl ammonium iodide), used for the concentration of heavy metals occurring in water is studied. The material under study captures Cd, Pb, which are capable of forming stable complexes with I- ions.The results obtained about the metal capture, under dynamic conditions, are described and metal ions are removed by desorption with EDTA and quantified by AAS.

Adsorption of hidrogen peroxide on the surface of silica - titania mixed oxide obtained by the sol-gel processing method

This work describes the sol-gel mixed oxide SiO2/TiO2 property, ST, as prepared, and submitted to heat treatment a 773 K, STC. SEM and EDS images show, within magnification used, a uniform distribution of the TiO2 particles in SiO2/TiO2 matrix. Both, ST and STC adsorb hydrogen peroxide on the surface and through EPR and UV-Vis diffuse reflectance spectra, it was possible to conclude that the species on the surface is the peroxide molecule attached to the Lewis acid site of titanium particle surface, alphaTi(H2O2)+. As the material is very porous, presumably the hydrogen peroxide molecule is confined in the matrix pores on the surface, a reason why the adsorbed species presents an exceptional long lived stability.

Rigid Rod Polymer Fillers in Acrylic Denture and Dental Adhesive Resin Systems

Polymeric materials have been used in dental applications for decades. Adhesion of polymeric materials to each other and to the tooth substrate is essential to their successful use. The aim of this series of studies was two-folded. First, to improve adhesion of poly(paraphenylene) based rigid rod polymer (RRP) to other dental polymers, and secondly, to evaluate the usability of a new dentin primer system based on RRP fillers. Poly(paraphenylene) based RRP would be a tempting material for dental applications because of its good mechanical properties. To be used in dental applications, reliable adhesion between RRP and other dental polymers is required. In this series of studies, the adhesion of RRP to denture base polymer and the mechanical properties of RRP-denture base polymer-material combination were evaluated. Also adhesion of BisGMA-TEGDMA-resin to RRP was determined. Different surface treatments were tested to improve the adhesion of BisGMA-TEGDMA-resin to RRP. Results were based on three-point bending testing, Vickers surface hardness test and scanning electron microscope analysis (SEM), which showed that no reliable adhesion between RRP and denture base polymer was formed. Addition of RRP filler to denture base polymer increased surface hardness and flexural modulus but flexural strength decreased. Results from the shear bond strength test and SEM revealed that adhesion between resin and RRP was possible to improve by surface treatment with dichloromethane (DCM) based primer and a new kind of adhesive surface can be designed. The current dentin bonding agents have good immediate bond strength, but in long term the bond strength may decrease due to the detrimental effect of water and perhaps by matrix metalloproteinases. This leads to problems in longevity of restorations. Current bonding agents use organic monomers. In this series of studies, RRP filled dentin primer was tested in order to decrease the water sorption of the monomer system of the primers. The properties of new dentin primer system were evaluated in vitro by comparing it to commercial etch and rinse adhesive system. The results from the contact angle measurements and SEM showed that experimental primer with RRP reinforcement provided similar resin infiltration to dentin collagen and formed the resin-dentin interface as the control primer. Microtensile bond strength test and SEM revealed that in short term water storing, RRP increased bond strength and primer with BMEP-monomer (bis[2-(methacryloyloxy)-ethyl]phosphate) and high solvent concentration provided comparable bonding properties to the commercial control primers. In long term water storing, the high solvent-monomer concentration of the experimental primers decreased bond strength. However, in low solvent-monomer concentration groups, the long-term water storing did not decrease the bond strength despite the existence of hydrophilic monomers which were used in the system. These studies demonstrated that new dentin primer system reached the mechanical properties of current traditional etch and rinse adhesive system in short time water storing. Improved properties can be achieved by further modifications of the monomer system. Studies of the adhesion of RRP to other polymers suggest that adhesion between RRP and other dental polymers is possible to obtain by certain surface treatments.

Formation of polyelectrolyte multilayers and polyelectrolyte complexes in dual polymer treatment of papermaking pulp

The goal of this study was to find a new approach to modify chemically the properties of paper by improving fiber quality. This Master’s thesis includes the multiple polymer treatment in general and themeasurement methods with which the formation of multilayers and complexes can be noticed. The treatment by an oppositely charged dual polymer system is a good approach to increase paper strength. In this work, starch, a cationic polymer, and carboxymethyl cellulose (CMC), an anionic polymer, were used step-by-step to improve paper strength. The adsorption of cationic starch and CMC on cellulose fibers were analyzed via polyelectrolyte titration. The results showed that paper strength was enhanced slightly with a layer-by-layer assembly of the polymers. However, if the washing stage, which was required for layer-by-layer assembly, was eliminated, the starch/CMC complex was deposited on fibers more efficiently, and the paper strength was improved more significantly.

Effects of Silica Based Biomaterials on Bone Marrow Derived Cells - Material Aspects of Bone Regeneration

Silica based biomaterials, such as melt-derived bioactive glasses and sol-gel glasses, have been used for a long time in bone healing applications because of their ability to form hydroxyapatite and to stimulate stem cell proliferation and differentiation. In this study, bone marrow derived cells were cultured with bioactive glass and sol-gel silica, and seeded into porous polymer composite scaffolds that were then implanted femorally and subcutaneously in rats to monitor their migration inside host tissue. Bone marrow derived cells were also injected intraperitoneally. Transplanted cells migrated to various tissues inside the host, including the lung, liver spleen, thymus and bone marrow. The method of transplantation affected the time frame of cell migration, with intraperitoneal injection being the fastest and femoral implantation the slowest, but not the target tissues of migration. Transplanted donor cells had a limited lifetime in the host and were later eliminated from all tested tissues. Bioactive glass, however, affected the implanted cells negatively. When it was present in the scaffold no donor cells were found in any of the tested host tissues. Bioactive glass S53P4 was found to support both osteoblastic and osteoclastic phenotype of bone marrow derived cells, but it was resistant to the resorbing effect of osteoclastic bone marrow derived cells, showing that bioactive glass is rather dissolved through physicochemical reactions than resorbed by cells. Fast-dissolving silica sol gel in microparticulate form was found to increase collagen formation by bone marrow derived cells, while slow dissolving silica microparticles enhanced their proliferation, suggesting that the dissolution rate of silica controls the response of bone marrow derived cells.

EDTA- and DTPA-functionalized silica gel and chitosan adsorbents for the removal of heavy metals from aqueous solutions

Adsorbents functionalized with chelating agents are effective in removal of heavy metals from aqueous solutions. Important properties of such adsorbents are high binding affinity as well as regenerability. In this study, aminopolycarboxylic acid, EDTA and DTPA, were immobilized on the surface of silica gel, chitosan, and their hybrid materials to achieve chelating adsorbents for heavy metals such as Co(II), Ni(II), Cd(II), and Pb(II). New knowledge about the adsorption properties of EDTA- and DTPA-functionalizedadsorbents was obtained. Experimental work showed the effectiveness, regenerability, and stability of the studied adsorbents. Both advantages and disadvantages of the adsorbents were evaluated. For example, the EDTA-functionalized chitosan-silica hybrid materials combined the benefits of the silica gel and chitosan while at the same time diminishing their observed drawbacks. Modeling of adsorption kinetics and isotherms is an important step in design process. Therefore, several kinetic and isotherm models were introduced and applied in this work. Important aspects such as effect of error function, data range, initial guess values, and linearization were discussed and investigated. The selection of the most suitable model was conducted by comparing the experimental and simulated data as well as evaluating the correspondence between the theory behind the model and properties of the adsorbent. In addition, modeling of two-component data was conducted using various extended isotherms. Modeling results for both one- and twocomponent systems supported each other. Finally, application testing of EDTA- and DTPA-functionalized adsorbents was conducted. The most important result was the applicability of DTPA-functionalized silica gel and chitosan in the capturing of Co(II) from its aqueous EDTA-chelate. Moreover, these adsorbents were efficient in various solution matrices. In addition, separation of Ni(II) from Co(II) and Ni(II) and Pb(II) from Co(II) and Cd(II) was observed in two- and multimetal systems. Lastly, prior to their analysis, EDTA- and DTPA-functionalized silica gels were successfully used to preconcentrate metal ions from both pure and salty waters

Avaliação da eficiência de um gel hidroretentor como retardante de fogo

Diversas medidas de proteção contra incêndios têm sido adotadas para minimizar os efeitos negativos do fogo. Produtos vêm sendo testados e aplicados na conservação da umidade de materiais combustíveis para evitar ou retardar a propagação do fogo. Este estudo buscou avaliar a capacidade de um polímero hidrorretentor de manter a umidade do material combustível morto, em diferentes dosagens de aplicação, com vistas à sua utilização como retardante de fogo. Foram feitas 40 parcelas de 1 m x 1 m com 1,2 kg de capim-gordura (Melinis minutiflora P. Beauv.) cada, distribuídas uniformemente. Foi utilizada uma calda de concentração de 0,1 g/l do produto nas dosagens de 0; 1,0; 1,5; 2,0; 2,5; 3,0; 3,5; e 4,0 l/m². O estudo foi realizado em parcelas subdivididas com cinco repetições cada e 16 subparcelas. A capacidade de retenção de água foi medida a partir da diferença do peso de matéria úmida e peso de matéria seca do material após ser seco em estufa. Os valores de médias foram estatisticamente diferentes no teste de Tukey a 5% de probabilidade, mas não apresentaram nenhuma correspondência com a sequência de valores dos tratamentos. O Tratamento 6 foi o que obteve a maior média de umidade (35,50%), enquanto o Controle apresentou o menor valor (27,80%). O uso do gel hidrorretentor não conferiu aumento significativo de umidade ao material combustível ao passar dos dias, nas dosagens testadas e nas condições ambientais do estudo, determinando que esse produto não tem uso recomendado na prevenção de incêndios.

Polymer surface modification by atomic layer deposition

Current industrial atomic layer deposition (ALD) processes are almost wholly confined to glass or silicon substrates. For many industrial applications, deposition on polymer substrates will be necessary. Current deposition processes are also typically carried out at temperatures which are too high for polymers. If deposition temperatures in ALD can be reduced to the level applicable for polymers, it will open new interesting areas and applications for polymeric materials. The properties of polymers can be improved for example by coatings with functional and protective properties. Although the ALD has shown its capability to operate at low temperatures suitable for polymer substrates, there are other issues related to process efficiency and characteristics of different polymers where new knowledge will assist in developing industrially conceivable ALD processes. Lower deposition temperature in ALD generally means longer process times to facilitate the self limiting film growth mode characteristic to ALD. To improve process efficiency more reactive precursors are introduced into the process. For example in ALD oxide processes these can be more reactive oxidizers, such as ozone and oxygen radicals, to substitute the more conventionally used water. Although replacing water in the low temperature ALD with ozone or plasma generated oxygen radicals will enable the process times to be shortened, they may have unwanted effects both on the film growth and structure, and in some cases can form detrimental process conditions for the polymer substrate. Plasma assistance is a very promising approach to improve the process efficiency. The actual design and placement of the plasma source will have an effect on film growth characteristics and film structure that may retard the process efficiency development. Due to the fact that the lifetime of the radicals is limited, it requires the placement of the plasma source near to the film growth region. Conversely this subjects the substrate to exposure byother plasma species and electromagnetic radiation which sets requirements for plasma conditions optimization. In this thesis ALD has been used to modify, activate and functionalize the polymer surfaces for further improvement of polymer performance subject to application. The issues in ALD on polymers, both in thermal and plasma-assisted ALD will be further discussed.

Water absorbent polymer in sugarcane crop

The water absorbent polymer effect on vegetative growth and production of Theoretical Recovery Sugar (TRS) of sugarcane cv. RB 86 7515 was evaluated on two field tests installed in randomized blocks, with four treatments and five repetitions. The polymer doses were 0; 4; 8 and 12 g m-1 of furrow (test 1) and 0; 1.4; 2.8 and 4.2 g m-1 of furrow (test 2). Test 1 (dec/2007 to may/2009) was implanted in a Distroferric Red Argisol soil in Presidente Prudente - State of São Paulo (SP), Brazil; and the test 2 (Aug/2008 to Aug/2009) was implanted in a Red Yellow Argisol soil in Lucélia - State of São Paulo (SP), Brazil. In test 2, there were no significant differences for any evaluated parameters. In both tests the polymer doses equal to or less than 4 g m-1 of furrow showed no significant effect on the evaluated parameters. In test 1, the polymer doses of 8 and 12 g m-1 of the conditioning polymer increased the number of tillers in stage II of development and led to the largest amount of straw. The gross income per hectare has positive relation with the polymer doses. The polymer had no significant effect on the sugarcane stems productivity and technological parameters.

Feasibility study of metal to polymer hybrid joining

The increasing demand for lightweight components has led to a huge exploitation of non-metallic materials such as polymers, fibers and elastomers in industrial and manufacturing processes. Recent trends towards cost effectiveness, weight reduction and production flexibility in industrial production and manufacturing processes has led to a growing interest in hybrid components where two or more dissimilar materials coexist to achieving specifically optimized characteristics. The importance of this research is to serve as a bridge to understanding the theories behind various joining techniques and the adaptation of the process for metal to polymer hybrid joints. Moreso, it helps companies to select the most productive and yet economical joining process for realization of lightweight metal to polymer hybrid components. This thesis is a literature review analyzing various materials that has been published on various joining methods for metal to polymer hybrid joints on the feasibility and eventual realization of the joint between these dissimilar materials. This study is aimed at theoretically evaluating the feasibility of joining processes between metal and plastic components by exploiting exhaustively joining and welding sources.

Effect of Hevea brasiliensis latex sap gel on healing of acute skin wounds induced on the back of rats

Objective : to evaluate the effect of topical delivery of latex cream-gel in acute cutaneous wounds induced on the back of rats. Methods : we subjected sixteen rats to dermo-epidermal excision of a round dorsal skin flap, with 2.5cm diameter. We divided the animals into two groups: Latex Group: application of cream-gel-based latex throughout the wound bed on postoperative days zero, three, six and nine; Control group: no treatment on the wound. Photographs of the lesions were taken on the procedure day and on the 6th and 14th postoperative days, for analyzing the area and the larger diameter of the wound. We carried out euthanasia of all animals on the 14th postoperative day, when we resected he dorsal skin and the underlying muscle layer supporting the wound for histopathological study. Results : there was no statistically significant difference in the percentage of wound closure, in the histopathological findings or in the reduction of the area and of the largest diameter of the wounds among the groups studied on the 14th postoperative day. Conclusion : according to the experimental conditions in which the study was conducted, latex cream-gel did not interfere in the healing of acute cutaneous wounds in rats.