Cimentos injetáveis à base de fosfatos de cálcio para vertebroplastia

O principal objectivo desta investigação foi o desenvolvimento cimentos de fosfatos de cálcio com injetabilidade melhorada e propriedades mecânicas adequadas para aplicação em vertebroplastia. Os pós de fosfato de tricálcico (TCP) não dopados e dopados (Mg, Sr e Mn) usados neste estudo foram obtidos pelo processo de precipitação em meio aquoso, seguidos de tratamento térmico de forma a obter as fases pretendidas, α− e β−TCP. A substituição parcial de iões Ca por iões dopantes mostrou ter implicações em termos de estabilidade térmica da fase β−TCP. Os resultados demonstraram que as transformações de fase alotrópicas β↔α−TCP são fortemente influenciadas por variáveis experimentais como a taxa de arrefecimento, a presença de impurezas de pirofosfato de cálcio e a extensão do grau de dopagem com Mg. Os cimentos foram preparados através da mistura de pós, β−TCP (não dopados e dopados) e fosfato monocálcico monidratado (MCPM), com meios líquidos diferentes usando ácido cítrico e açucares (sucrose e frutose) como agentes retardadores de presa, e o polietilenoglicol, a hidroxipropilmetilcelulose e a polivinilpirrolidona como agentes gelificantes. Estes aditivos, principalmente o ácido cítrico, e o MCPM aumentam significativamente a força iónica do meio, influenciando a injetabilidade das pastas. Os resultados também mostraram que a distribuição de tamanho de partícula dos pós é um factor determinante na injetabilidade das pastas cimentícias. A combinação da co-dopagem de Mn e Sr com a adição de sucrose no líquido de presa e com uma distribuição de tamanho de partícula dos pós adequada resultou em cimentos de brushite com propriedades bastante melhoradas em termos de manuseamento, microestrutura, comportamento mecânico e biológico: (i) o tempo inicial de presa passou de ~3 min to ~9 min; (ii) as pastas cimentícias foram totalmente injectadas para uma razão liquido/pó de 0.28 mL g−1 com ausência do efeito de “filter-pressing” (separação de fases líquida e sólida); (iii) após imersão numa solução durante 48 h, as amostras de cimento molhadas apresentam uma porosidade total de ~32% e uma resistência a compressão de ~17 MPa, valor muito superior ao obtido para os cimentos sem açúcar não dopados (5 MPa) ou dopados só com Sr (10 MPa); e (iv) o desempenho biológico, incluindo a adesão e crescimento de células osteoblásticas na superfície do cimento, foi muito melhorado. Este conjunto de propriedades torna os cimentos excelentes para regeneração óssea e engenharia de tecidos, e muito promissores para aplicação em vertebroplastia.

Design of advanced reverse osmosis and nanofiltration membranes for water purification

Most commercially available reverse osmosis (RO) and nanofiltration (NF) membranes are based on the thin film composite (TFC) aromatic polyamide membranes. However, they have several disadvantages including low resistance to fouling, low chemical and thermal stabilities and limited chlorine tolerance. To address these problems, advanced RO/NF membranes are being developed from polyimides for water and wastewater treatments. The following three projects have resulted from my research. (1) Positively charged and solvent resistant NF membranes. The use of solvent resistant membranes to facilitate small molecule separations has been a long standing industry goal of the chemical and pharmaceutical industries. We developed a solvent resistant membrane by chemically cross-linking of polyimide membrane using polyethylenimine. This membrane showed excellent stability in almost all organic solvents. In addition, this membrane was positively charged due to the amine groups remaining on the surface. As a result, high efficiency (> 95%) and selectivity for multivalent heavy metal removal was achieved. (2) Fouling resistant NF membranes. Antifouling membranes are highly desired for “all” applications because fouling will lead to higher energy demand, increase of cleaning and corresponding down time and reduced life-time of the membrane elements. For fouling prevention, we designed a new membrane system using a coating technique to modify membrane surface properties to avoid adsorption of foulants like humic acid. A layer of water-soluble polymer such as polyvinyl alcohol (PVA), polyacrylic acid (PAA), polyvinyl sulfate (PVS) or sulfonated poly(ether ether ketone) (SPEEK), was adsorbed onto the surface of a positively charged membrane. The resultant membranes have a smooth and almost neutrally charged surface which showed better fouling resistance than both the positively charged NF membranes and commercially available negatively charged NTR-7450 membrane. In addition, these membranes showed high efficiency for removal of multivalent ions (> 95% for both cations and anions). Therefore, these antifouling surfaces can be potentially used for water softening, water desalination and wastewater treatment in a membrane bioreactor (MBR) process. (3) Thermally stable RO membranes. Commercial RO membranes cannot be used at temperature higher than 45°C due to the use of polysulfone substrate, which often limits their applications in industries. We successfully developed polyimides as the membrane substrate for thermally stable RO membranes due to their high thermal resistance. The polyimide-based composite polyamide membranes showed desalination performance comparable to the commercial TFC membrane. However, the key advantage of the polyimide-based membrane is its high thermal stability. As the feed temperature increased from 25oC to 95oC, the water flux increased 5 - 6 times while the salt rejection almost kept constant. This membrane appears to provide a unique solution for hot water desalination and also a feasible way to improve the water productivity by increasing the operating temperature without any drop in salt rejection.

Applications for nanomaterials in critical technologies

This thesis is devoted to the development, synthesis, properties, and applications of nano materials for critical technologies, including three areas: (1) Microbial contamination of drinking water is a serious problem of global significance. About 51% of the waterborne disease outbreaks in the United States can be attributed to contaminated ground water. Development of metal oxide nanoparticles, as viricidal materials is of technological and fundamental scientific importance. Nanoparticles with high surface areas and ultra small particle sizes have dramatically enhanced efficiency and capacity of virus inactivation, which cannot be achieved by their bulk counterparts. A series of metal oxide nanoparticles, such as iron oxide nanoparticles, zinc oxide nanoparticles and iron oxide-silver nanoparticles, coated on fiber substrates was developed in this research for evaluation of their viricidal activity. We also carried out XRD, TEM, SEM, XPS, surface area measurements, and zeta potential of these nanoparticles. MS2 virus inactivation experiments showed that these metal oxide nanoparticle coated fibers were extremely powerful viricidal materials. Results from this research suggest that zinc oxide nanoparticles with diameter of 3.5 nm, showing an isoelectric point (IEP) at 9.0, were well dispersed on fiberglass. These fibers offer an increase in capacity by orders of magnitude over all other materials. Compared to iron oxide nanoparticles, zinc oxide nanoparticles didn’t show an improvement in inactivation kinetics but inactivation capacities did increase by two orders of magnitude to 99.99%. Furthermore, zinc oxide nanoparticles have higher affinity to viruses than the iron oxide nanoparticles in presence of competing ions. The advantages of zinc oxide depend on high surface charge density, small nanoparticle sizes and capabilities of generating reactive oxygen species. The research at its present stage of development appears to offer the best avenue to remove viruses from water. Without additional chemicals and energy input, this system can be implemented by both points of use (POU) and large-scale use water treatment technology, which will have a significant impact on the water purification industry. (2) A new family of aliphatic polyester lubricants has been developed for use in micro-electromechanical systems (MEMS), specifically for hard disk drives that operate at high spindle speeds (>15000rpm). Our program was initiated to address current problems with spin-off of the perfluoroether (PFPE) lubricants. The new polyester lubricant appears to alleviate spin-off problems and at the same time improves the chemical and thermal stability. This new system provides a low cost alternative to PFPE along with improved adhesion to the substrates. In addition, it displays a much lower viscosity, which may be of importance to stiction related problems. The synthetic route is readily scalable in case additional interest emerges in other areas including small motors. (3) The demand for increased signal transmission speed and device density for the next generation of multilevel integrated circuits has placed stringent demands on materials performance. Currently, integration of the ultra low-k materials in dual Damascene processing requires chemical mechanical polishing (CMP) to planarize the copper. Unfortunately, none of the commercially proposed dielectric candidates display the desired mechanical and thermal properties for successful CMP. A new polydiacetylene thermosetting polymer (DEB-TEB), which displays a low dielectric constant (low-k) of 2.7, was recently developed. This novel material appears to offer the only avenue for designing an ultra low k dielectric (1.85k), which can still display the desired modulus (7.7Gpa) and hardness (2.0Gpa) sufficient to withstand the process of CMP. We focused on further characterization of the thermal properties of spin-on poly (DEB-TEB) ultra-thin film. These include the coefficient of thermal expansion (CTE), biaxial thermal stress, and thermal conductivity. Thus the CTE is 2.0*10-5K-1 in the perpendicular direction and 8.0*10-6 K-1 in the planar direction. The low CTE provides a better match to the Si substrate which minimizes interfacial stress and greatly enhances the reliability of the microprocessors. Initial experiments with oxygen plasma etching suggest a high probability of success for achieving vertical profiles.

Hybrid materials for biomedical applications

The increased longevity of humans and the demand for a better quality of life have led to a continuous search for new implant materials. Scientific development coupled with a growing multidisciplinarity between materials science and life sciences has given rise to new approaches such as regenerative medicine and tissue engineering. The search for a material with mechanical properties close to those of human bone produced a new family of hybrid materials that take advantage of the synergy between inorganic silica (SiO4) domains, based on sol-gel bioactive glass compositions, and organic polydimethylsiloxane, PDMS ((CH3)2.SiO2)n, domains. Several studies have shown that hybrid materials based on the system PDMS-SiO2 constitute a promising group of biomaterials with several potential applications from bone tissue regeneration to brain tissue recovery, passing by bioactive coatings and drug delivery systems. The objective of the present work was to prepare hybrid materials for biomedical applications based on the PDMS-SiO2 system and to achieve a better understanding of the relationship among the sol-gel processing conditions, the chemical structures, the microstructure and the macroscopic properties. For that, different characterization techniques were used: Fourier transform infrared spectrometry, liquid and solid state nuclear magnetic resonance techniques, X-ray diffraction, small-angle X-ray scattering, smallangle neutron scattering, surface area analysis by Brunauer–Emmett–Teller method, scanning electron microscopy and transmission electron microscopy. Surface roughness and wettability were analyzed by 3D optical profilometry and by contact angle measurements respectively. Bioactivity was evaluated in vitro by immersion of the materials in Kokubos’s simulated body fluid and posterior surface analysis by different techniques as well as supernatant liquid analysis by inductively coupled plasma spectroscopy. Biocompatibility was assessed using MG63 osteoblastic cells. PDMS-SiO2-CaO materials were first prepared using nitrate as a calcium source. To avoid the presence of nitrate residues in the final product due to its potential toxicity, a heat-treatment step (above 400 °C) is required. In order to enhance the thermal stability of the materials subjected to high temperatures titanium was added to the hybrid system, and a material containing calcium, with no traces of nitrate and the preservation of a significant amount of methyl groups was successfully obtained. The difficulty in eliminating all nitrates from bulk PDMS-SiO2-CaO samples obtained by sol-gel synthesis and subsequent heat-treatment created a new goal which was the search for alternative sources of calcium. New calcium sources were evaluated in order to substitute the nitrate and calcium acetate was chosen due to its good solubility in water. Preparation solgel protocols were tested and homogeneous monolithic samples were obtained. Besides their ability to improve the bioactivity, titanium and zirconium influence the structural and microstructural features of the SiO2-TiO2 and SiO2-ZrO2 binary systems, and also of the PDMS-TiO2 and PDMS-ZrO2 systems. Detailed studies with different sol-gel conditions allowed the understanding of the roles of titanium and zirconium as additives in the PDMS-SiO2 system. It was concluded that titanium and zirconium influence the kinetics of the sol-gel process due to their different alkoxide reactivity leading to hybrid xerogels with dissimilar characteristics and morphologies. Titanium isopropoxide, less reactive than zirconium propoxide, was chosen as source of titanium, used as an additive to the system PDMS-SiO2-CaO. Two different sol-gel preparation routes were followed, using the same base composition and calcium acetate as calcium source. Different microstructures with high hydrophobicit were obtained and both proved to be biocompatible after tested with MG63 osteoblastic cells. Finally, the role of strontium (typically known in bioglasses to promote bone formation and reduce bone resorption) was studied in the PDMS-SiO2-CaOTiO2 hybrid system. A biocompatible material, tested with MG63 osteoblastic cells, was obtained with the ability to release strontium within the values reported as suitable for bone tissue regeneration.

Acreditação do Laboratório de Metrologia da Frilabo para Ensaios e Calibrações em Temperaturas

O trabalho desenvolvido centrou-se na preparação da acreditação NP EN ISO/IEC 17025 do Laboratório de Metrologia da empresa Frilabo para prestação de serviços na área das temperaturas, no ensaio a câmaras térmicas e na calibração de termómetros industriais. Considerando o âmbito do trabalho desenvolvido, são abordados nesta tese conceitos teóricos sobre temperatura e incertezas bem como considerações técnicas de medição da temperatura e cálculo de incertezas. São também referidas considerações sobre os diferentes tipos de câmaras térmicas e termómetros. O texto apresenta os documentos elaborados pelo autor sobre os procedimentos de ensaio a câmaras térmicas e respetivo procedimento de cálculo da incerteza. Também estão presentes neste texto documentos elaborados pelo autor sobre os procedimentos de calibração de termómetros industriais e respetivo procedimento de cálculo da incerteza. Relativamente aos ensaios a câmara térmicas e calibração de termómetros o autor elaborou os fluxogramas sobre a metodologia da medição da temperatura nos ensaios, a metodologia de medição da temperatura nas calibrações, e respetivos cálculos de incertezas. Nos diferentes anexos estão apresentados vários documentos tais como o modelo de folha de cálculo para tratamento de dados relativos ao ensaio, modelo de folha de cálculo para tratamento de dados relativo às calibrações, modelo de relatório de ensaio, modelo de certificado de calibração, folhas de cálculo para gestão de clientes/equipamentos e numeração automática de relatórios de ensaio e certificados de calibração que cumprem os requisitos de gestão do laboratório. Ainda em anexo constam todas as figuras relativas à monitorização da temperatura nas câmara térmicas como também as figuras da disposição dos termómetros no interior das câmaras térmicas. Todas as figuras que aparecem ao longo do documento que não estão referenciadas são da adaptação ou elaboração própria do autor. A decisão de alargar o âmbito da acreditação do Laboratório de Metrologia da Frilabo para calibração de termómetros, prendeu-se com o facto de que sendo acreditado como laboratório de ensaios na área das temperaturas, a realização da rastreabilidade dos padrões de medida internamente, permitiria uma gestão de recursos otimizada e rentabilizada. A metodologia da preparação de todo o processo de acreditação do Laboratório de Metrologia da Frilabo, foi desenvolvida pelo autor e está expressa ao longo do texto da tese incluindo dados relevantes para a concretização da referida acreditação nos dois âmbitos. A avaliação de todo o trabalho desenvolvido será efetuada pelo o organismo designado IPAC (Instituto Português de Acreditação) que confere a acreditação em Portugal. Este organismo irá auditar a empresa com base nos procedimentos desenvolvidos e nos resultados obtidos, sendo destes o mais importante o Balanço da Melhor Incerteza (BMI) da medição também conhecido por Melhor Capacidade de Medição (MCM), quer para o ensaio às câmaras térmicas, quer para a calibração dos termómetros, permitindo desta forma complementar os serviços prestados aos clientes fidelizados à Frilabo. As câmaras térmicas e os termómetros industriais são equipamentos amplamente utilizados em diversos segmentos industriais, engenharia, medicina, ensino e também nas instituições de investigação, sendo um dos objetivos respetivamente, a simulação de condições específicas controladas e a medição de temperatura. Para entidades acreditadas, como os laboratórios, torna-se primordial que as medições realizadas com e nestes tipos de equipamentos ostentem confiabilidade metrológica1, uma vez que, resultados das medições inadequados podem levar a conclusões equivocadas sobre os testes realizados. Os resultados obtidos nos ensaios a câmaras térmicas e nas calibrações de termómetros, são considerados bons e aceitáveis, uma vez que as melhores incertezas obtidas, podem ser comparadas, através de consulta pública do Anexo Técnico do IPAC, com as incertezas de outros laboratórios acreditados em Portugal. Numa abordagem mais experimental, pode dizer-se que no ensaio a câmaras térmicas a obtenção de incertezas mais baixas ou mais altas depende maioritariamente do comportamento, características e estado de conservação das câmaras, tornando relevante o processo de estabilização da temperatura no interior das mesmas. A maioria das fontes de incerteza na calibração dos termómetros são obtidas pelas características e especificações do fabricante dos equipamentos, que se traduzem por uma contribuição com o mesmo peso para o cálculo da incerteza expandida (a exatidão de fabricante, as incertezas herdadas de certificados de calibração, da estabilidade e da uniformidade do meio térmico onde se efetuam as calibrações). Na calibração dos termómetros as incertezas mais baixas obtêm-se para termómetros de resoluções mais baixas. Verificou-se que os termómetros com resolução de 1ºC não detetavam as variações do banho térmico. Nos termómetros com resoluções inferiores, o peso da contribuição da dispersão de leituras no cálculo da incerteza, pode variar consoante as características do termómetro. Por exemplo os termómetros com resolução de 0,1ºC, apresentaram o maior peso na contribuição da componente da dispersão de leituras. Pode concluir-se que a acreditação de um laboratório é um processo que não é de todo fácil. Podem salientar-se aspetos que podem comprometer a acreditação, como por exemplo a má seleção do ou dos técnicos e equipamentos (má formação do técnico, equipamento que não seja por exemplo adequado à gama, mal calibrado, etc…) que vão efetuar as medições. Se não for bem feita, vai comprometer todo o processo nos passos seguintes. Deve haver também o envolvimento do todos os intervenientes do laboratório, o gestor da qualidade, o responsável técnico e os técnicos, só assim é que é possível chegar à qualidade pretendida e à melhoria contínua da acreditação do laboratório. Outro aspeto importante na preparação de uma acreditação de um laboratório é a pesquisa de documentação necessária e adequada para poder tomar decisões corretas na elaboração dos procedimentos conducentes à referida. O laboratório tem de mostrar/comprovar através de registos a sua competência. Finalmente pode dizer-se que competência é a palavra chave de uma acreditação, pois ela manifesta-se nas pessoas, equipamentos, métodos, instalações e outros aspetos da instituição a que pertence o laboratório sob acreditação.

Secagem da microalga Spirulina em camada delgada utilizando secador com bomba de calor

A Spirulina apresenta propriedades antioxidantes o que favorece seu uso como alimento funcional, fato que tem motivado a sua comercialização para a formulação de alimentos diversos e com finalidades terapêuticas. A secagem ganha importância durante produção de Spirulina, uma vez que a umidade necessária, para garantir que não ocorra degradação da biomassa desidratada durante o armazenamento, é alcançada através do conhecimento dos parâmetros que caracterizam a operação. Neste estudo foi utilizada a secagem com bomba de calor, um método alternativo, pois viabiliza a operação com temperaturas inferiores as tradicionalmente utilizadas, além de seu funcionamento ser independente das condições meteorológicas do ambiente. O trabalho experimental da secagem de Spirulina sp. foi iniciado com um estudo comparativo entre a secagem com bomba de calor (SBC) e a secagem tradicional (ST). O efeito dos diferentes métodos utilizados sob a amostra foi comparado em relação à cinética da operação e as características da microalga desidratada (cor, ficocianina, compostos fenólicos totais e atividade antioxidante total). As temperaturas do ar foram de 50 e 60ºC e a umidade absoluta da SBC foi dez vezes inferior a utilizada durante a ST. Os parâmetros que caracterizam a secagem foram influenciados pela temperatura do ar, bem como, pela baixa umidade absoluta na SBC. Os valores do tempo total da SBC foram 40% inferiores aos encontrados para a secagem ST, em ambas as temperaturas do ar. A maior preservação das características da Spirulina foi obtida na SBC e temperatura do ar de 50°C, e nesta condição os valores foram 14% (ficocianina), 60% (compostos fenólicos) e 10% (atividade antioxidante) superiores aos encontrados na mesma condição para a ST. Isto evidencia que o método de secagem é determinante na qualidade do produto desidratado. Posteriormente, foi realizado o estudo da cinética da SBC, bem como a otimização da operação de secagem e a reidratação das amostras desidratadas nas diferentes condições de secagem. O estudo foi realizado através de um planejamento fatorial 32, tendo como fatores de estudo a temperatura do ar (30, 40 e 50ºC) e a espessura da bandeja (1, 3 e 5 mm). As respostas utilizadas foram ficocianina, compostos fenólicos, atividade antioxidante total e cor da microalga desidratadas. Também foram realizadas a microscopia eletrônica de varredura (MEV) e as curvas termogravimétricas (DSC) das amostras desidratadas. A secagem apresentou um curto período de taxa constante, delimitado pela umidade crítica, sendo que, seus valores foram influenciados apenas pela temperatura do ar de secagem. O modelo Logarítmico forneceu elevados valores de R2ajust e os menores valores de soma dos erros quadráticos (SSE) e de critério informativo de Akaike (AIC). Os valores das energias de ativação para as espessuras de 1, 3 e 5 mm, foram na faixa de 20-23 kJ mol-1. A condição de operação mais adequada, para a secagem de Spirulina sp. com bomba de calor, foi obtida na temperatura do ar de 50°C e espessura da bandeja de 5 mm, com valores de ficocianina, compostos fenólicos, atividade antioxidante total e diferença de cor de 19,60 mg g-1, 1508 µgEAG g-1, 52,6% e 5,71, respectivamente. Os termogramas (DSC) evidenciaram que em 50 ºC e espessura de 5 mm, o produto apresentou maior estabilidade térmica. As amostras de Spirulina sp. desidratadas apresentaram estrutura morfológica (MEV), aparentemente, rígida e heterogênea, e os seus percentuais de reidratação corresponderam a 85-91% da umidade da microalga in natura.

Aplicação de peroxidase para degradação de deoxinivalenol

Deoxinivalenol (DON), uma das principais micotoxinas encontradas em matrizes alimentares, é um composto químico que possui em sua estrutura um anel epóxido que lhe confere alto grau de toxicidade. A aplicação de enzimas em processos de degradação de DON vem se destacando, pela estabilidade durante o processo reacional e baixo custo de produção. O objetivo desse trabalho foi estudar o potencial de peroxidase proveniente de farelo de arroz (FA) e farelo de soja (FS) para degradar DON. As condições de obtenção da PO a partir de FA foram definidas por planejamento experimental DCCR 23 , sendo extraída de 5 g de farelo com 50 mL de tampão fosfato 0,04 mol L-1 pH 5, agitados orbitalmente durante 60 min a 100 rpm, e para a PO obtida de FS as condições diferenciaram somente quanto a solução extratora, tampão fosfato 0,01 mol L-1 pH 4,7. A técnica que apresentou melhores índices de purificação para a enzima foi a partição trifásica apresentando fator de purificação e recuperação de 5,6 e 50 % para a obtida de FA e 13,61 e 50 % para FS. A PO de FA apresentou maior atividade em tampão fosfato 5 mmol L-1 pH 5,5 para as formas bruta e pura, diferindo na temperatura de reação de 25 °C e 10 °C, KM de 0,15 e 0,06 mmol L-1 e Vmáx de 769 e 667 U mg-1 , respectivamente. A PO de FS as condições foram: tampão fosfato 5 mmol L-1 pH 5, reação a 35 e 30 °C durante 10 e 5 min, KM de 0,17 e 0,05 mmol L-1 e Vmáx de 196 e 182 U mg-1 , respectivamente. A PO de FA demonstrou maior estabilidade em pH 5 enquanto que a de FS em pH 6, ambas enzimas apresentaram maior estabilidade térmica a 0 °C, as massas moleculares encontradas por eletroforese foram 41 e 34 kDa, respectivamente. Ao final das etapas de obtenção, purificação e caracterização obteve-se uma atividade específica de 116 e 794 U.mg-1 , e 4363 e 17453 U g-1 , respectivamente para PO de FA e FS. A determinação de DON e De-DON foi realizada por HPLC-DAD e LC-ESI-MS/MS para avaliação dos ensaios de degradação. A enzima comercial HRP, mostrou maior potencial de redução sobre DON (55% após 1 h de reação), no entanto em 3 h de reação, a concentração inicial da micotoxina DON foi verificada, o que evidencia que a redução pode ocorrer por adsorção ou por formação de um composto de degradação que apresente a mesma massa molecular. O emprego da enzima PO obtida de FA e FS na degradação necessita de uma avaliação cinética micotoxicologica para definição das condições de redução significativa dos níveis de DON.

Evaluation of the Genotoxicity of Chitosan Nanoparticles for Use in Food Packaging Films

The use of nanoparticles in food packaging has been proposed on the basis that it could improve protection of foods by, for example, reducing permeation of gases, minimizing odor loss, and increasing mechanical strength and thermal stability. Consequently, the impacts of such nanoparticles on organisms and on the environment need to be investigated to ensure their safe use. In an earlier study, Moura and others (2008a) described the effect of addition of chitosan (CS) and poly(methacrylic acid) (PMAA) nanoparticles on the mechanical properties, water vapor, and oxygen permeability of hydroxypropyl methylcellulose films used in food packaging. Here, the genotoxicity of different polymeric CS/PMAA nanoparticles (size 60, 82, and 111 nm) was evaluated at different concentration levels, using the Allium cepa chromosome damage test as well as cytogenetic tests employing human lymphocyte cultures. Test substrates were exposed to solutions containing nanoparticles at polymer mass concentrations of 1.8, 18, and 180 mg/L. Results showed no evidence of DNA damage caused by the nanoparticles (no significant numerical or structural changes were observed), however the 82 and 111 nm nanoparticles reduced mitotic index values at the highest concentration tested (180 mg/L), indicating that the nanoparticles were toxic to the cells used at this concentration. In the case of the 60 nm CS/PMAA nanoparticles, no significant changes in the mitotic index were observed at the concentration levels tested, indicating that these particles were not toxic. The techniques used show promising potential for application in tests of nanoparticle safety envisaging the future use of these materials in food packaging.

Obtenção e caracterização de nanopartículas de argilominerais

Natural nanoclays are of great interest particularly for the production of polymer-based nanocomposites. In this work, kaolinite clays from two natural deposits in the State of the Rio Grande do Norte and Paraiba were purified with thermal treatment and chemical treatments, and characterized. Front to the gotten data, had been proposals methodologies for elimination or reduction of coarse particle texts, oxide of iron and organic substance. These methodologies had consisted of the combination of operations with thermal treatments, carried through in electric oven, and acid chemical attacks with and hydrogen peroxide. The Analyzers Thermogravimetric was used to examine the thermal stability of the nanoclays. The analysis indicated weight losses at temperatures under 110 ºC and over the temperature range of 350 to 550 ºC. Based on the thermal analysis data, the samples were submitted to a thermal treatment at 500 °C, for 8 h, to remove organic components. The X-ray diffraction patterns indicated that thermal treatment under 500 °C affect the basic structure of kaolinite. The BET surface area measurements ranged from 32 to 38 m2/g for clay samples with thermal treatment and from 36 to 53 m2/g for chemically treated samples. Thus, although the thermal treatment increased the surface area, through the removal of organic components, the effect was not significant and chemical treatment is more efficient, not affect the basic structure of kaolinite, to improve particle dispersion. SEM analysis confirms that the clay is agglomerated forming micron-size particles

Aproveitamento da fibra do epicarpo do coco babaçu em compósito com matriz epóxi: estudo do efeito do tratamento da fibra

Nowadays the environmental issues are increasingly highlighted since the future of humanity is dependent on the actions taken by man. Major efforts are being expended in pursuit of knowledge and alternatives to promote sustainable development without compromising the environment. In recent years there has been a marked growth in the development of reinforced composite fiber plants, as an alternative for economic and ecological effects, especially in the substitution of synthetic materials such as reinforcement material in composites. In this current study the chemical- physical or (thermophysics )characteristics of the babassu coconut fiber, derived from the epicarp of the fruit (Orbignyda Phalerata), which the main constituents of the fiber: Klason lignin, insoluble, cellulose, holocellulose, hemicellulose and the content of ash and moisture will be determined. A study was conducted about the superficial modification of the fibers of the epicarp babassu coconut under the influence of chemical treatment by alkalinization, in an aqueous solution of NaOH to 2.5% (m/v) and to 5.0% to improve the compatibility matrix / reinforcement composite with epoxy matrix. The results of the changes occurred in staple fibers through the use of the techniques of thermogravimetric analyses (TG) and differential scanning calorimetry (DSC). The results found on thermal analysis on samples of fiber without chemical treatment (alkalinities), and on fiber samples treated by alkalinization show that the proposed chemical treatment increases the thermal stability of the fibers and provides a growth of the surface of area fibers, parameters that enhance adhesion fiber / composite. The findings were evaluated and compared with published results from other vegetable fibers, showing that the use of babassu coconut fibers has technical and economic potential for its use as reinforcement in composites

Proton conductivity and luminiscence properties of lanthanide aminotriphosphonates

Metal phosphonates are multifunctional solids with tunable properties, such as internal H-bond networks, and high chemical and thermal stability [1]. In the present work, we describe the synthesis, structural characterization, luminescent properties and proton conduction performance of a new family of isostructural cationic compounds with general formula [Ln(H4NMP)(H2O)2]Cl·2H2O [Ln = La3+, Pr3+, Sm3+, Gd3+, Tb3+, Dy3+, Ho3+, H6NMP = nitrilotris(methylphosphonic acid)]. These solids are formed by positively charge layers, which consist of isolated LnO8 polyhedra and bridge chelating NMP2- ligands, held apart by chloride ions and water molecules. This arrangement result in extended interlayer hydrogen networks with possible proton transfer pathways. The proton conductivity of Gd3+ sample, selected as prototype of the series, was measured. In the range between range 25º and 80 ºC, the conductivity increase with the temperature up to a maximum value of 3.10-4 S·cm-1, at relative humidity of 95 %. The activation energy obtained from the Arrhenius plot (Figure 1) is in the range corresponding to a Grotthuss transfer mechanism.

Desevolvimento de nanocompósitos de poli(metacrilato de metila)/argila processados por mistura no estado fundido

Poly(methyl methacrylate)/clay nanocomposites were prepared by melt mixing using a montmorillonite-rich clay (MMT). The clay in natura was treated with acrylic acid to facilitate the dispersion in the polymer matrix. A masterbatch of PMMA/clay was prepared and combined with the pure PMMA and then subjected to extrusion process using singlescrew and twin-screw extruders followed by injection. Nanocomposites were processed with clay contents of 1, 3, 5 and 8 wt.%. The effect of shear processing on the morphology of the nanocomposites was evaluated by XRD, SEM and TEM. Thermal and mechanical properties of the nanocomposites were investigated through TGA, DSC, HDT, VICAT, tensile and impact tests, to evaluate the effect of the addition of clay to the PMMA matrix. Flammability tests were also conducted to investigate the effect of the addition of clay on the flame retardation properties. SEM images of the nanocomposites indicated the presence of clay agglomerates, which resulted in the reduction of properties such as thermal stability, mechanical strength and impact resistance, and increased the rate of burning for materials processed by both extrusion routes

Otimização e análise mecânica de pastas geopoliméricas para uso em poços sujeitos à injeção cíclica de vapor

Oil wells subjected to cyclic steam injection present important challenges for the development of well cementing systems, mainly due to tensile stresses caused by thermal gradients during its useful life. Cement sheath failures in wells using conventional high compressive strength systems lead to the use of cement systems that are more flexible and/or ductile, with emphasis on Portland cement systems with latex addition. Recent research efforts have presented geopolymeric systems as alternatives. These cementing systems are based on alkaline activation of amorphous aluminosilicates such as metakaolin or fly ash and display advantageous properties such as high compressive strength, fast setting and thermal stability. Basic geopolymeric formulations can be found in the literature, which meet basic oil industry specifications such as rheology, compressive strength and thickening time. In this work, new geopolymeric formulations were developed, based on metakaolin, potassium silicate, potassium hydroxide, silica fume and mineral fiber, using the state of the art in chemical composition, mixture modeling and additivation to optimize the most relevant properties for oil well cementing. Starting from molar ratios considered ideal in the literature (SiO2/Al2O3 = 3.8 e K2O/Al2O3 = 1.0), a study of dry mixtures was performed,based on the compressive packing model, resulting in an optimal volume of 6% for the added solid material. This material (silica fume and mineral fiber) works both as an additional silica source (in the case of silica fume) and as mechanical reinforcement, especially in the case of mineral fiber, which incremented the tensile strength. The first triaxial mechanical study of this class of materials was performed. For comparison, a mechanical study of conventional latex-based cementing systems was also carried out. Regardless of differences in the failure mode (brittle for geopolymers, ductile for latex-based systems), the superior uniaxial compressive strength (37 MPa for the geopolymeric slurry P5 versus 18 MPa for the conventional slurry P2), similar triaxial behavior (friction angle 21° for P5 and P2) and lower stifness (in the elastic region 5.1 GPa for P5 versus 6.8 GPa for P2) of the geopolymeric systems allowed them to withstand a similar amount of mechanical energy (155 kJ/m3 for P5 versus 208 kJ/m3 for P2), noting that geopolymers work in the elastic regime, without the microcracking present in the case of latex-based systems. Therefore, the geopolymers studied on this work must be designed for application in the elastic region to avoid brittle failure. Finally, the tensile strength of geopolymers is originally poor (1.3 MPa for the geopolymeric slurry P3) due to its brittle structure. However, after additivation with mineral fiber, the tensile strength became equivalent to that of latex-based systems (2.3 MPa for P5 and 2.1 MPa for P2). The technical viability of conventional and proposed formulations was evaluated for the whole well life, including stresses due to cyclic steam injection. This analysis was performed using finite element-based simulation software. It was verified that conventional slurries are viable up to 204ºF (400ºC) and geopolymeric slurries are viable above 500ºF (260ºC)

Efeito da adição dos azocorantes DR73 e DB79 nas propriedades do poli(metacrilato de metila)

Currently new polymeric materials have been developed to replace other of traditionally materials classes. The use of dyes allows to expand and to diversify the applications in the polymeric materials development. In this work the behavior and ability of azo dyes Disperse Blue 79 (DB79) and Disperse Red 73 (DR73) on poly(methyl methacrylate) (PMMA) were studied. Two types of mixtures were used in the production of masterbatches: 1) rheometer 2) solution. Processing by extrusion-blow molding of PMMA was carried out in order to evaluate the applications of polymeric films. Thermal analysis were performed by thermogravimetry to evaluate polymer and azo dyes thermal stability. Colorimetric analysis were obtained through monitoring the spectral variations associated with sys/trans/anti azo dyes isomerization process Colorimetric data were treated and evaluated in accordance to the color system RGB and CIEL*ab, by monitoring the color change as function of time. Mechanical properties, characterized by tensile tests, were evaluated and correlated with the presence and content of azo dyes in the samples. Analyses by scanning electronic microscopy (SEM) were performed on the surfaces of samples to check the azo dye dispersion after the mixing process. It was concluded that the production of PMMA/azo dyes is possible and feasible, and the mixtures produced had synergy of properties for use in various applications

Obtenção e caracterização de dióxido de estanho nanoestruturado pelo método de síntese contínua por combustão em solução

Continuous Synthesis by Solution Combustion was employed in this work aiming to obtain tin dioxide nanostructured. Basically, a precursor solution is prepared and then be atomized and sprayed into the flame, where its combustion occurs, leading to the formation of particles. This is a recent technique that shows an enormous potential in oxides deposition, mainly by the low cost of equipment and precursors employed. The tin dioxide (SnO2) nanostructured has been widely used in various applications, especially as gas sensors and varistors. In the case of sensors based on semiconducting ceramics, where surface reactions are responsible for the detection of gases, the importance of surface area and particle size is even greater. The preference for a nanostructured material is based on its significant increase in surface area compared to conventional microcrystalline powders and small particle size, which may benefit certain properties such as high electrical conductivity, high thermal stability, mechanical and chemical. In this work, were employed as precursor solution tin chloride dehydrate diluted in anhydrous ethyl alcohol. Were utilized molar ratio chloride/solvent of 0,75 with the purpose of investigate its influence in the microstructure of produced powder. The solution precursor flux was 3 mL/min. Analysis with X-ray diffraction appointed that a solution precursor with molar ratio chloride/solvent of 0,75 leads to crystalline powder with single phase and all peaks are attributed to phase SnO2. Parameters as distance from the flame with atomizer distance from the capture system with the pilot, molar ratio and solution flux doesn t affect the presence of tin dioxide in the produced powder. In the characterization of the obtained powder techniques were used as thermogravimetric (TGA) and thermodiferential analysis (DTA), particle size by laser diffraction (GDL), crystallographic analysis by X-ray diffraction (XRD), morphology by scanning electron microscopy (SEM), transmission electron microscopy (TEM), specific surface area (BET) and electrical conductivity analysis. The techniques used revealed that the SnO2 exhibits behavior of a semiconductor material, and a potentially promising material for application as varistor and sensor systems for gas