Electrochemical feasibility study of methyl parathion determination on graphite-modified basal plane pyrolytic graphite electrode

A low-cost electrochemical method was developed for the determination of trace-level of methyl parathion (MP) based on the properties of graphite-modified basal plane pyrolytic graphite electrode (graphite-bppg). A combination of graphite-bppg with square-wave voltammetric (SWV) analysis resulted in an original, sensitive and selective electrochemical method for determination of MP pesticide in drinking water. The electrode was constructed and the electrochemical behavior of MP was studied. Immobilization is achieved via film modification from dispersing graphite powder in deionized water and through pipeting a small volume onto the electrode surface allowing the solvent to volatilize. The strong affinity of the graphite modifier for the phosphorous group of the MP allowed the deposition of a significant amount of MP in less than 60 seconds. The cyclic voltammetric results indicate that the graphite-bppg electrode can enhance sensitivity in current intensity towards the quasi-reversible redox peaks of the products of the cathodic reduction of the nitro group at negative potential (peak I = 0.077 V and peak II = –0.062 V) and that the cathodic irreversible peak (peak III = –0.586 V) in comparison with bare bppg electrode and is also adsorption controlled process. Under optimized conditions, the concentration range and detection limit for MP pesticide are respectively 79.0 to 263.3 mmol L-1 and 3.00 mmol L-1. The proposed method was successfully applied to MP determination in drinking water and the performance of this electrochemical sensor has been evaluated in terms of analytical figures of merit.

Avaliação do comportamento ao desgaste de compósitos poliméricos

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Estudo sobre as possibilidades de recuperação de resíduos provenientes da fabricação de pás eólicas

Pós-graduação em Ciência e Tecnologia de Materiais - FC

Estudo das intempéries nas propriedades mecânicas e viscoelásticas de compósitos PPS/Fibras de carbono e EPOXI/Fibras de carbono de uso aeronaútico

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

In vitro analysis of shear bond strength and adhesive remnant index comparing light curing and self-curing composites

OBJETIVO: Avaliar in vitro a resistência ao cisalhamento de compósitos autopolimerizáveis (Concise e Alpha Plast) e fotopolimerizáveis (Transbond XT e Natural Ortho) utilizados na colagem de braquetes metálicos da marca Morelli, analisando o índice de adesivo remanescente (ARI) e da integridade da superfície do esmalte por meio de microscopia eletrônica de varredura (MEV). MÉTODOS: foram utilizados 40 pré-molares humanos extraídos. As raízes dos dentes foram incluídas em gesso-pedra especial, no interior de tubos de PVC usados para a confecção dos corpos de prova. Esses corpos de prova foram divididos em quatro grupos: grupo G1, braquetes associados ao compósito Concise; grupo G2, braquetes associados ao compósito Alpha Plast; grupo G3, braquetes associados ao compósito Transbond XT; e grupo G4, braquetes associados ao compósito Natural Ortho. Os grupos foram submetidos ao teste de cisalhamento em máquina universal de ensaios, a uma velocidade de 0,5mm por minuto. RESULTADOS: houve diferença estatística entre os grupos G3 e G4, sendo os valores de G4 superiores; no entanto, não foram encontradas diferenças estatisticamente significativas entre os grupos G1, G2 e G3 e G1, G2 e G4. Na análise do ARI não foram encontradas diferenças estatísticas entre os grupos, predominando escores baixos. De acordo com a análise da MEV, constatou-se o rompimento dos compósitos e a integridade do esmalte entre os grupos. CONCLUSÃO: a resistência ao cisalhamento foi satisfatória e semelhante entre os compósitos utilizados, sendo que a resina Natural Ortho apresentou-se superior à Transbond XT.

Resina epóxi reforçada com tecido de carbono não dobrável por processo RTM

Com o objetivo de ganhar competitividade no mercado internacional e contribuir para o desenvolvimento tecnológico no país, o presente trabalho apresenta a técnica de processamento de moldagem por transferência de resina (RTM), utilizada na fabricação de materiais compósitos estruturais e ainda pouco estudada no Brasil. Os compósitos processados por essa técnica apresentam maior fração volumétrica de fibras, melhor acabamento superficial e pouca ou nenhuma necessidade de acabamento do componente produzido. Este trabalho compreende a caracterização de compósitos produzidos com resina epóxi monocomponente RTM6 e o tecido não dobrável de fibra de carbono. Os compósitos produzidos pela Hexcel Composites foram analisados pela técnica de ultrassom C-Scan e os resultados mostraram que os laminados processados estão homogêneos quanto à impregnação. Ensaios mecânicos mostram que os laminados com tecido apresentam características comparáveis à dos compósitos produzidos em autoclave com maiores porcentagens de reforço. Em fadiga, os laminados apresentaram um alto e curto intervalo, com tensões próximas à de tração. Quanto ao comportamento térmico observou-se melhora nas propriedades com a adição do reforço de fibras de carbono, que promoveram o aumento da temperatura de transição vítrea (Tg). Quanto ao comportamento viscoelástico, foi observado a influencia da temperatura e freqüência no material. Considerando as propriedades mecânicas e térmicas, ambos os compósitos foram classificados como adequados à aplicação proposta.

Methods for obtaining reabsorbable composites, composites, membrane, scaffold and its uses

The present invention relates to novel methods of obtaining reabsorbable composites, based on bacterial cellulose and collagen, for application in tissue repairing Additionally, the present invention relates to the composites obtained by the methods described herein and their uses.

Free radical entrapment and crystallinity of resin composites after accelerated aging as a function of the expiration date

This study evaluated the spin concentration and the crystallinity in different classifications of dental composites as a function of the material condition (new, aged and expired). Specimens were obtained according to the factors: composites: Filtek P60, Filtek Z250, Filtek Z350XT, and Filtek Silorane; and material conditions: new, aged, and expired. The syringe composites underwent an accelerated aging protocol (Arrhenius model). The magnetic properties of the composites were characterized using Electron Paramagnetic Resonance (EPR) and the concentration of spins (number of spins/mass) was calculated. The crystallinity of the composites tested was characterized with X-ray diffraction (XRD). Filtek P60 and Filtek Z250 presented similarities in terms of spin concentration and crystallinity, irrespective of the material condition. The aging protocol influenced the composite Filmic Z350XT that exhibited a significant increase in the spin concentration. Besides, lower intensity peaks of the organic matrix and amorphous silica were also observed for both aged and expired Filtek Z350XT. Although a significant lower spin concentration was observed for the silorane composite in comparison to that of the methacrylates, a decrease in the relative intensity of peaks of the amorphous region related to the organic components in the diffractograms was observed. The material conditions tested influence the crystallinity and the magnetic properties of the composites evaluated. (C) 2014 Elsevier Ltd. All rights reserved.

Fabrication of Zinc Oxide Nanowires/Polymer Composites by Two-Photon Polymerization

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Effect of resin composites with sodium trimetaphosphate with or without fluoride on hardness, ion release and enamel demineralization

Purpose: To evaluate the effect of the addition of sodium trimetaphosphate (TMP) with or without fluoride on enamel demineralization, and the hardness and release of fluoride and TMP of resin composites. Methods: Bovine enamel slabs (4x3x3 mm) were prepared and selected based on initial surface hardness (n= 96). Eight experimental resin composites were formulated, according to the combination of TMP and sodium fluoride (NaF): TMP/NaF-free (control), 1.6% sodium fluoride (NaF), and 1.5%, 14.1% and 36.8% TMP with and without 1.6% NaF. Resin composite specimens (n= 24) were attached to the enamel slabs with wax and the sets were subjected to pH cycling. Next, surface and cross-sectional hardness and fluoride content of enamel as well as fluoride and TNT release and hardness of the materials were evaluated. Data were statistically analyzed using ANOVA (P< 0.05). Results: The presence of fluoride in enamel was similar in fluoridated resin composites (P> 0.05), but higher than in the other materials (P< 0.05). The combination of 14.1% TMP and fluoride resulted in less demineralization, especially on lesion surface (P< 0.05). The presence of TMP increased fluoride release from the materials and reduced their hardness.

Time reduction of light curing: Influence on conversion degree and microhardness of orthodontic composites

Introduction: The aim of this study was to assess the influence of curing time and power on the degree of conversion and surface microhardness of 3 orthodontic composites. Methods: One hundred eighty discs, 6 mm in diameter, were divided into 3 groups of 60 samples according to the composite used-Transbond XT (3M Unitek, Monrovia, Calif), Opal Bond MV (Ultradent, South Jordan, Utah), and Transbond Plus Color Change (3M Unitek)-and each group was further divided into 3 subgroups (n = 20). Five samples were used to measure conversion, and 15 were used to measure microhardness. A light-emitting diode curing unit with multiwavelength emission of broad light was used for curing at 3 power levels (530, 760, and 1520 mW) and 3 times (8.5, 6, and 3 seconds), always totaling 4.56 joules. Five specimens from each subgroup were ground and mixed with potassium bromide to produce 8-mm tablets to be compared with 5 others made similarly with the respective noncured composite. These were placed into a spectrometer, and software was used for analysis. A microhardness tester was used to take Knoop hardness (KHN) measurements in 15 discs of each subgroup. The data were analyzed with 2 analysis of variance tests at 2 levels. Results: Differences were found in the conversion degree of the composites cured at different times and powers (P < 0.01). The composites showed similar degrees of conversion when light cured at 8.5 seconds (80.7%) and 6 seconds (79.0%), but not at 3 seconds (75.0%). The conversion degrees of the composites were different, with group 3 (87.2%) higher than group 2 (83.5%), which was higher than group 1 (64.0%). Differences in microhardness were also found (P < 0.01), with lower microhardness at 8.5 seconds (35.2 KHN), but no difference was observed between 6 seconds (41.6 KHN) and 3 seconds (42.8 KHN). Group 3 had the highest surface microhardness (35.9 KHN) compared with group 2 (33.7 KHN) and group 1 (30.0 KHN). Conclusions: Curing time can be reduced up to 6 seconds by increasing the power, with a slight decrease in the degree of conversion at 3 seconds; the decrease has a positive effect on the surface microhardness.

The impact of the addition of iodoform on the physicochemical properties of an epoxy-based endodontic sealer

Due to the low radiopacity of Sealer 26, iodoform is frequently empirically added to this sealer. Thus, the interference of this procedure with the physicochemical properties of Sealer 26 must be evaluated. Objective: This study evaluated the influence of the addition of iodoform on setting time, flow, solubility, pH, and calcium release of an epoxy-based sealer. Material and Methods: The control group was pure Sealer 26, and the experimental groups were Sealer 26 added with 1.1 g, 0.55 g or 0.275 g of iodoform. Setting time evaluation was performed in accordance with the ASTM C266-03 speciflcation. The analysis of flow and solubility was in accordance with the ISO 6876-2001 speciflcation. For the evaluation of pH and calcium ion release, polyethylene tubes were filled with the materials and immersed in flasks with 10 ml of deionized water. After 24 h, 7, 14, 21, 28, and 45 days pH was measured. In 45 days, the calcium released was evaluated with an atomic absorption spectrophotometer. Results: The addition of iodoform increased setting time in comparison with pure sealer (P < 0.05). As for flow, solubility, and calcium release, the mixtures presented results similar to pure sealer (p > 0.05). In the 24 h period, the mixture with 1.1 g and 0.55 g of iodoform showed lower pH than pure sealer and than sealer added with 0.275 g of iodoform (P < 0.05). Conclusions: The iodoform added to Sealer 26 interferes with its setting time and solubility properties. Further studies are needed to address the clinical signiflcance of this interference.

A split-mouth randomized clinical trial of conventional and heavy flowable composites in class II restorations

Objective: The aim of this study was to evaluate the 2-year clinical performance of class II restorations made with a composite resin with two different viscosities.Methods: 47 patients received two class II restorations (n = 94), one made with GrandioSO (conventional viscosity CV), and the other with GrandioSO Heavy Flow (flowable viscosity FV), subjecting both materials to the same clinical conditions. The self-etching adhesive Futurabond M was used for all restorations. The composites were inserted using the incremental technique. The restorations were evaluated using the modified USPHS criteria according to the periods: baseline, 6 months, 1 year and 2 years after restorative procedures.Results: After 24 months, 40 patients attended the recall and 78 restorations were evaluated. In all periods, no secondary caries was observed. After 6 months, there were slightly overall changes of scores for most parameters. After 24 months, the higher number of changes from score Alfa to Bravo was observed for marginal discolouration (32.5% CV and 39.5% FV) and colour match (15% CV and 31.6% FV), followed by proximal contact (25% CV and 23.7% FV) and marginal adaptation (20% CV and 21.1% FV). For wear, surface texture and postoperative sensitivity the changes were very small. Just two restorations were lost during the 24-month follow up. Less than 5% of all restorations showed postoperative sensitivity. Chi-square test showed no significant differences between the two materials for all parameters analysed.Conclusion: After 2 years of clinical service, no significant differences were observed between GrandioSO conventional and GrandioSO Heavy Flow for the parameters analysed. Both materials provided acceptable clinical behaviour in class II restorations. Clinical Significance: This study presents the possibility of using a flowable composite with high filler content, for performing class II restorations. (C) 2014 Elsevier Ltd. All rights reserved.

Enhanced photoabsorption properties of composites of Ti/TiO2 nanotubes decorated by Sb2S3 and improvement of degradation of hair dye

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Benzoxazine Resin/Carbon Nanotube Nanostructured Composite's Degradation Kinetic

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)