A low cost and environmental friendly extrusion process of the Polyacrylonitrile (PAN) polymer was viabilized by using the 1,2,3-propanetriol (glycerol) as a plasticizer. The characterization of the fibers obtained by this process was the object of study in the present work. The PAN fibers were heat treated in the range of 200 °C to 300 °C, which is the temperature range related to the stabilization/oxidation step. This is a limiting phase during the carbon fiber processing. The characterization of the fibers was made using infrared spectroscopy, thermal analysis and microscopy. TGA revealed that the degradation of the extruded PAN co-VA fibers between 250 °C and 350 °C, corresponded to a 9% weight loss to samples analyzed under oxidizing atmosphere and 18% when the samples were analyzed under inert atmosphere. DSC showed that the exothermic reactions on the extruded PAN co-VA fibers under oxidizing synthetic air was broader and the cyclization started at a lower temperature compared under inert atmosphere. Furthermore, FT-IR analysis correlated with thermal anlysis showed that the stabilization/oxidation process of the extruded PAN fiber were coherent with other works that used PAN fibers obtained by other spinning processes.

Polyacrylonitrile fiber encompasses a broad range of products based on acrylonitrile (AN) which is readily copolymerized with a wide range of ethylenic unsaturated monomers giving rise to polymers with different characteristics and applications. Such products can be designed for cost-effective, flame and heat resistant solutions for the textile industry, aircraft and automotive markets. In the present work acrylonitrile was copolymerized with vinylidene chloride (VDC) by conventional suspension polymerization process via redox system, with an initial content of 10%/mass of the VDC monomer. The copolymer average molecular weight was obtained by Gel Permeation Chromatography (GPC) and by intrinsic viscosity analysis. To control the polymerization process continuously, qualitative and quantitative analysis of the chloride content in the PAN AN/VDC copolymer structure was accomplished by using X-ray fluorescence and potentiometric titration techniques. A good correlation was found between these two techniques, leading to a straightforward verification of VDC in the polymer structure. The thermal behavior of PAN AN/VDC copolymer was performed by Differential Scanning Calorimetry (DSC) and Thermogravimetric Analysis (TGA). The results showed that VDC monomers exhibited a nearly stoichiometric reaction with acrylonitrile, copolymerizing about 90% of its initial mass. VDC changed significantly the polyacrylonitrile thermal behavior, decreasing the polymer degradation temperature by about 40-50°C.

O presente trabalho resume os processos de fiação convencionais usados na obtenção de fibras de poliacrilonitrila (PAN). Um breve histórico do desenvolvimento da fibra de PAN é apresentado. A empregabilidade das fibras de PAN está atribuída principalmente ao setor têxtil e aeronáutico (como principal precursora para fibras de carbono). Atualmente, o processo de fiação úmida tornou-se o único meio para produção industrial de fibras de PAN, que emprega o DMF (dimetilformamida) como principal solvente para esta técnica de fiação. Descreve-se um novo método de fiação da PAN que dispensa o emprego de solventes altamente tóxicos. Essa tecnologia inovadora permite fiação por fusão da PAN que pode empregar a glicerina (proveniente da produção do biodiesel) como seu principal plastificante.

This paper summarizes the conventional spinning processes used to obtain polyacrylonitrile (PAN). A brief history of the development of PAN fiber is presented. The employability of PAN fibers is attributed mainly to the textile sector and aviation (as main precursor for carbon fibers). Currently, the wet spinning process became the only means of industrial production of PAN fibers, which employs DMF (dimethylformamide) as the main solvent for this technique of spinning. We describe a new method of spinning of PAN with no need of using highly toxic solvents. This innovative technology enables spinning by melting PAN using glycerin (from biodiesel production) as the primary plasticizer.

Neste trabalho são apresentados resultados de análise térmica para poliacrilonitrila (PAN) plastificada com glicerina. Foram observados os efeitos da glicerina de alta pureza (glicerol) e demais aditivos à base de glicóis na fusão e degradação térmica da PAN pela técnica de DSC sob alta taxa de aquecimento (90 °C/min) e atmosfera inerte. Foi constatado que o glicerol reduziu a temperatura de fusão da PAN de 290 °C para 217 °C. Em uma etapa preliminar foi empregado o método de Kissinger para verificar o efeito da composição química da PAN sob sua degradação térmica. A energia de ativação aparente para o copolímero de PAN foi calculada em 149 kJ.mol-1. Sugeriu-se que a presença do comonômero acetato de vinila (AV) na composição química da PAN proporcionou menor entalpia de degradação (353 J.g-1) em comparação com outros comonômeros constituintes de uma PAN precursora de fibras de carbono (988 J.g-1).

This paper presents results from thermal analysis of polyacrylonitrile (PAN) plasticized with glycerin, where effects from the high purity glycerin (glycerol) and other additives to glycol were studied. Using differential scanning calorimetry (DSC) at high heating rate (90 °C/min) and inert atmosphere, we observed a decrease in the melting temperature of PAN (from 290 °C to 217 °C) owing to the presence of glycerol. The Kissinger's method was used to investigate the kinetics of thermal degradation for acrylonitrile (AN) with vinyl acetate (AV). The apparent activation energy for the copolymer AN/AV was calculated as 149 kJ.mol-1. The AV comonomer resulted in a lower degradation enthalpy for the copolymer AN/AV (353 J.g-1) compared with the comonomers comprising a precursor PAN for carbon fibers (988 J.g-1).

Nano-carbon materials, such as carbon nanotubes and carbon nanofibers, are being thought to be used as multifunctional reinforcement in composites. The growing of carbon nanofiber at the carbon fiber/epoxy interface results in composites having better electrical properties than conventional carbon fiber/epoxy composites. In this work, carbon nanofibers were grown in situ over the surface of a carbon fiber fabric by chemical vapor deposition. Specimens of carbon fiber/nanofiber/epoxy (CF/CNF/epoxy) composites were molded and electrical conductivity was measured. Also, the CF/CNF/epoxy composites were tested under flexure and interlaminar shear. The results showed an overall reduction in mechanical properties as a function of added nanofiber, although electrical conductivity increased up to 74% with the addition of nanofibers. Thus CF/CNF/epoxy composites can be used as electrical dissipation discharge materials.

To address a critical aspect of the fast growing use of composites in aircraft and aerospace industry, the influence of the porosity on the shear strength of composites property was investigated as a mean for determining the critical values of porosity. Acid digestion techniques were applied to determine the void volume ratio of two families of carbon epoxy laminates (8 and 16 plies). Ultrasonic inspections revealed the corresponding attenuation coefficients. The void morphology was investigated by optical microscopy. Results from Interlaminar shear and Iosipescu shear tests were correlated with the attenuation coefficient to determine critical values of porosity using a modified Mar-Lin fracture criteria. It has been shown that the shear strength decrease with the increase of void volume ratio and the effects are more significant in thicker laminates. This work showed that by using the Mar-Lin criteria the singularity order, which is an indicative of the sensibility to voids in composites, is dependent of type of loading and void distribution.

Resumo: O principal objetivo do presente trabalho foi a determinação do módulo de cisalhamento G12 e a máxima resistência ao cisalhamento (ô12) utilizando o ensaio de cisalhamento losipescu. Os testes foram conduzidos com dois tipos de compósitos, fibra de carbono/epóxi e fibra de vidro/epóxi utilizados na indústria aeroespacial e também uma matriz de resina moldada. Os resultados indicam a efetiva contribuição das fibras de reforço para a resistência ao cisalhamento (ô12) e para o módulo de cisalhamento (G12) comparado com a matriz polimérica sem reforço.

Abstract: The main aim of the present work was the determination of the shear modulus (GI2) and the maximum shear strength (ôI2) using the losipescu Shear Test. Tests were carried out on two types of composites, carbon fiber/epoxy and glass fiber/epoxy, used in the aerospace industry, and also a molded epoxy resin matrix. The results indicate the effective contribution of fiber reinforcements to the shear strength (ô12) and shear modulus (G12) compared to the no reinforcement polymer matrix.

The purpose of this study was to assess the radiopacity and microhardness of different types of resin-based composites (RBC - hybrid; microhybrid; flowable; cement and polyacid modified) before and after being submitted to artificial accelerated aging. Fifty specimens (7 mm in diameter and 2 mm thick) were fabricated, 10 for each material. The specimens were light-cured and submitted to radiopacity and microhardness tests. After obtaining initial radiopacity and microhardness values, the specimens were taken to the artificial accelerated aging, and new measurement of radiopacity and microhardness of the samples was performed. Data were submitted to statistical analysis (Student's t-test - p < 0.05). None of the materials studied showed changes in radiopacity after artificial accelerated aging. There was a significant decrease in microhardness for the microhybrid and polyacid-modified RBC´s. This study suggests that radiopacity remains unaltered after materials are submitted to artificial accelerated aging. Microhardness, however, may vary due to plasticization of the aged RBC matrix.

The aim of this article is to present a singular and practical method to compare roentgenograms, concerning optical density and contrast. This method is specifically indicated for research related to stepwedge penetrometer and photodensitometer

El objetivo de este artículo es presentar un método singular y práctico para comparar roentgenogramas, referentes a la densidad óptica y al contraste. Este método se indica específicamente para la investigación con el penetrómetro stepwedge y el fotodensitómetro

INTRODUÇÃO: Ocorreram mudanças no padrão de desenvolvimento da lesão de cárie. As lesões tem progredido e atingido a dentina, sem demonstrar alterações nos aspectos clínicos. OBJETIVOS: Determinar a prevalência de cárie em escolares de 12 anos no município de Franca - SP, Brasil, no ano de 2003 e avaliar o valor adicional da radiografia interproximal para detecção de lesões de cárie em dentina de molares permanentes na prevalência de cárie. MATERIAIS E MÉTODOS: Desenvolveu-se um estudo transversal com uma amostra probabilística; em que foram realizados exames epidemiológicos por um examinador calibrado, em 256 escolares das redes de ensino público e particular, utilizando a metodologia recomendada pela OMS; e em 66% da amostra, foram obtidas radiografias interproximais da região de molares permanentes. As imagens foram analisadas por um examinador calibrado; considerando dente com lesão de cárie oculta, aquele que apresentava radiolucidez em dentina no exame radiográfico e no entanto, estava hígido no levantamento epidemiológico. RESULTADOS: A prevalência de cárie dentária no exame epidemiológico sem (OMS) e com (OMS/R) a inclusão da lesão de cárie oculta foi de 54% e 64%, e os índices CPOD, 1,73 e 1,92 respectivamente. CONCLUSÃO: O emprego do método de diagnostico radiográfico interproximal aumentou significativamente (p<0,001) a prevalência da cárie na população estudada.

INTRODUCTION: The pattern of development of carious lesions has changed. The carious lesion has been progressive and reaches the dentin without showing alterations in the clinical aspects. OBJECTIVES: To determine the prevalence of caries in 12-year-old students in the city of Franca - São Paulo, Brazil, during the year of 2003, and to evaluate the additional value of bitewing radiograph to detect hidden carious lesions in permanent molar dentin. MATERIALS AND METHODS: A probabilistic sample composed of two hundred and fifty six (256) students, from public and private schools, was submitted to a cross-sectional study through examination by a calibrated examiner, in order to detect the caries prevalence, using the methodology recommended by the World Health Organization (WHO). For 66% of the sample, bitewing radiographs of the permanent molar region were obtained. The images were analyzed by a calibrated examiner, who established the presence of hidden caries in teeth with radiolucency in dentin, yet considered healthy in the epidemiological survey. RESULTS: The prevalence of dental caries in epidemiological exam without (WHO) and with (WHO/R) the inclusion of hidden caries lesion was 54% and 64%, and the DMFT index was 1.73 and 1.92 respectively. CONCLUSION: Utilization of the method of bitewing radiographic diagnosis significantly increased (p<0.001) the prevalence of caries in the studied population.

This study observed alteration in the radiopacity and microhardness of expired resin-based materials compared to non-expired materials and the operating characteristics of the X-ray source used. Five 2 mm-thick cured specimens were prepared for each material: composite resins (P60®, Z100®), and a compomer (Dyract AP®). Radiopacity of the specimens was evaluated comparing the density of the resin-based material to an equivalent (mm) density of a 99.5% pure aluminum step wedge using a transmission densitometer. Surface microhardness measurements were carried out using a calibrated Vickers indenter on three different points of the same surface. ANOVA and Tukey tests (pre-set alpha = 0.05) revealed that expired materials showed no significant change in radiopacity. One material (Filtek P60) demonstrated lower radiopacity with lower KVp. Change in microhardness wa s statistically significant for Z100: for this material, the microhardness after expiration was significantly lower than before the expiration date.

O crescimento de população de células dos ductos intercalares, ductos estriados e túbulos granulares convolutos de glândulas submandibulares do camundongo durante o período de 14 a 84 dias de vida pós-natal, foi avaliada por métodos morfométricos. Os dados de número absoluto de células em cada tipo de ducto foram submetidos a ajuste de curva por análise de regressão linear e as equações obtidas foram: y = 13,22 + 0,87x para as células dos ductos intercalares no período de crescimento de 14 a 84 dias; y = 18,82 + 3,69x e y = 176,03 - 1,93x para as células dos ductos estriados nos períodos de crescimento e decaimento, respectivamente, de 14 a 35 e 35 a 84 dias; e y = 90,59 + 4,60x para as células dos túbulos granulares convolutos no período de crescimento de 28 a 84 dias. À partir dessas equações, o acúmulo diário (velocidade de crescimento) ou a perda diária (velocidade de decaimento) de células em cada período, foram calculados. Assim, a velocidade de crescimento das células dos ductos intercalares foi 0,87 x 10(5) células/dia; as velocidades de crescimento e decaimento de células dos ductos estriados foram, respectivamente, 3,69 x 10(5) células/dia e -1,93 x 10(5) células/dia; e a velocidade de crescimento das células dos túbulos convolutos foi 4,60 x 10(5) células/dia. Análise do acúmulo ou da perda de células e o balanço entre o crescimento das várias populações celulares ductais, mostraram numericamente que as células dos ductos estriados transformaram-se em células dos túbulos granulares convolutos e que o crescimento total na população dessas últimas células também depende da formação de novas células por atividade proliferativa, provavelmente nos ductos intercalares.

The growth of cell populations of intercalated ducts (ID), striated ducts (SD) and convoluted granular tubules (CGT) of the submandibular gland of the mouse was analyzed, during the period of 14 to 84 days of postnatal life, by means of morphometric methods. The absolute number of cells in each type of duct was submitted to curve fitting by means of linear regression analysis, and the obtained equations were: y = 13.22 + 0.87x for ID cells in the growth period of 14 to 84 days; y = -18.82 + 3.69x and y = 176.03 - 1.93x for SD cells in the periods of growth and decay of cells, from 14 to 35 and 35 to 84 days, respectively; and y = 90.59 + 4.60x for CGT cells in the growth period of 28 to 84 days. Based on these equations, the daily accumulation (growth rate) or loss (decaying rate) of cells in the period covered by each equation was calculated. Thus, the rate of growth of ID cells was 0.87 x 10(5) cells/day; the growth and decline rates of SD cells were 3.69 x 10(5) cells/day and -1.93 x 10(5) cells/day, respectively; and the growth rate of CGT cells was 4.60 x 10(5) cells/day. The analysis of the accumulation or loss of cells and the balance of cell populations in the various types of ducts revealed that SD cells were transformed into CGT cells and that the growth of these cells’ population also depends on the formation of new cells through proliferative activity, probably in the intercalated ducts.

O estudo busca caracterizar as práticas docentes - a nível de planejamento, execução e avaliação de atividades e de ensino-aprendizagem - utilizadas por professores de alguns cursos da área de saúde, no Brasil: Odontologia, Medicina, Enfermagem, Farmácia, Psicologia, Nutrição, Serviço Social e Medicina Veterinária. A amostra foi constituída por 29 professores, inscritos em uma disciplina de Didática a nível de Pós-Graduação, que responderam a um questionário composto por questões semi-abertas. As respostas obtidas apontam para uma prática de educação "bancária", segundo a denominação de Paulo Freire, caracterizada por ênfase na transmissão de informações, cargas horárias muito grandes, pouca integração das disciplinas e aulas expositivas.

The study aims to describe teaching practices - in planning, execution and evaluation of the teaching-learning process - used by faculty of some courses in the health field in Brazil: Odontology, Medicine, Nursing, Pharmacy, Psychology, Nutrition, Social Work and Veterinary Medicine. The sample was made up by 29 faculties enrolled in a didactic subject course at graduate programs. They answered a questionnaire with semi-open questions. The answers obtained point to a "banking" education practice, according to Paulo Freire. This kind of education is characterized by: 1) emphasis on the transmission of information; 2) many hours of education; 3) little integration between courses and 4) lecture classes.

El estudio busca caracterizar las prácticas docentes a nivel de la planeación, ejucución y evaluación de actividades de enseñanza-aprendizaje, utilizadas por los profesores de algunos cursos del área de la salud en Brasil: Odontología, Medicina, Enfermería, Farmacia, Psicología, Serviço Social, Nutrición y Medicina Veterinaria. La muestra fue constituida por 29 profesores, inscritos en una disciplina de didáctica a nivel de postgraduación, que respondieron a un cuestionario compuesto por preguntas semi abiertas. Las respuestas obtenidas apuntan a una práctica de educación "bancaria", según la denominación de Paulo Freire, caracterizado por el énfasis en la transmisión de informaciones, cargas horarias muy grandes, poca integración de las disciplinas y clases magistrales.

The study aims to describe teaching practices - in planning, execution and evaluation of the teaching-learning process - used by faculty of some courses in the health field in Brazil: Odontology, Medicine, Nursing, Pharmacy, Psychology, Nutrition, Social Work and Veterinary Medicine. The sample was made up by 29 faculties enrolled in a didactic subject course at graduate programs. They answered a questionnaire with semi-open questions. The answers obtained point to a "banking" education practice, according to Paulo Freire. This kind of education is characterized by: 1) emphasis on the transmission of information; 2) many hours of education; 3) little integration between courses and 4) lecture classes.

El estudio busca caracterizar las prácticas docentes a nivel de la planeación, ejucución y evaluación de actividades de enseñanza-aprendizaje, utilizadas por los profesores de algunos cursos del área de la salud en Brasil: Odontología, Medicina, Enfermería, Farmacia, Psicología, Serviço Social, Nutrición y Medicina Veterinaria. La muestra fue constituida por 29 profesores, inscritos en una disciplina de didáctica a nivel de postgraduación, que respondieron a un cuestionario compuesto por preguntas semi abiertas. Las respuestas obtenidas apuntan a una práctica de educación "bancaria", según la denominación de Paulo Freire, caracterizado por el énfasis en la transmisión de informaciones, cargas horarias muy grandes, poca integración de las disciplinas y clases magistrales.

O estudo busca caracterizar as práticas docentes - a nível de planejamento, execução e avaliação de atividades e de ensino-aprendizagem - utilizadas por professores de alguns cursos da área de saúde, no Brasil: Odontologia, Medicina, Enfermagem, Farmácia, Psicologia, Nutrição, Serviço Social e Medicina Veterinária. A amostra foi constituída por 29 professores, inscritos em uma disciplina de Didática a nível de Pós-Graduação, que responderam a um questionário composto por questões semi-abertas. As respostas obtidas apontam para uma prática de educação "bancária", segundo a denominação de Paulo Freire, caracterizada por ênfase na transmissão de informações, cargas horárias muito grandes, pouca integração das disciplinas e aulas expositivas.