Instrumented indentation applied to the mechanical characterization of polyurethane derived from castor oil

Neste trabalho são investigadas as propriedades mecânicas de poliuretana derivada do óleo de mamona, utilizando a técnica de indentação instrumentada com penetradores de geometrias piramidal e esférica. Foi analisada a influência da forma do penetrador utilizado nos ensaios de indentação instrumentada para se obter valores das propriedades mecânicas de polímero derivado de óleo de mamona. Os penetradores utilizados são de pontas piramidais dos tipos Berkovich e canto de cubo e esférico de raio igual a 150 μm em um Nanoindenter XP TM com cargas aplicadas entre 1 e 200 mN. As penetrações variam de acordo com o formato do penetrador, sendo maiores para pontas agudas. A dureza e o módulo de elasticidade foram determinados, utilizando o método de Oliver e Pharr. Verificou-se que os valores medidos para a dureza são maiores para penetradores mais agudos. Os valores obtidos com a ponta piramidal Berkovich foram de 0,14 GPa para pequenas penetrações e 0,12 GPa para maiores penetrações. Já os valores obtidos com ponta canto de cubo foram 25 a 30% maiores. Isso está relacionado com os volumes das regiões que apresentam deformações plásticas elevadas, no caso de penetradores agudos comparados com os volumes das regiões que sofrem deformações viscoelásticas. A viscosidade aparente determinada, utilizando penetrador esférico em testes de força aplicada constante, é igual a (22 ± 2) × 10(12) Pa.s.The mechanical properties of polyurethane derived from castor oil, obtained by instrumented indentation technique with pyramidal and spherical indenters are reported. The influence of the indenter shape on the values of mechanical properties of the polymer was investigated. The indentations were made with pyramidal Berkovich, cube corner and a spherical indenter with radius of 150 μm in a Nanoindenter XP TM. The applied loads varied between 1 and 200 mN. The penetration depth increases for acute indenters, being higher for the cube corner tip. The hardness and elastic modulus were determined using the method of Oliver and Pharr. It was found that the measured values for hardness are higher for more acute indenters. The hardness with the pyramidal Berkovich tip was 0.14 GPa for small penetrations and 0.12 GPa for higher penetration depths. The values obtained with a cube corner tip were 25 to 30% higher. This is related to the volumes of regions with high plastic deformation in the case of acute indenters compared to the volumes of regions that present viscoelastic deformation. The apparent viscosity determined using the spherical indenter, in tests with applied constant forces, is equal to (22 ± 2) × 10(12) Pa.s.CNPqFAPES

Biodegradation of polyurethane derived from castor oil

The aim of this research was to study the biodegradation of a polymer derived from castor oil, which is a renewable, natural material that is a practical alternative for the replacement of traditional polyurethane foams. Due to its molecular structure, which contains polyester segments derived from vegetable oil, the polymeric surface is susceptible to microorganism attack. This study tested the biological degrading agent that was in contact with the microorganisms resulting from microbiological grease degrading agents, when foam was inoculated. Solid-media agar-plate tests were conducted for their potential to evaluate the biodegradation of polymeric particles by specific strains of microorganisms during 216 hours. The growth rate was defined. This technique provides a way of distinguishing the degradation abilities of microorganisms from the degradability of materials

Utilização da poliuretana derivada do óleo da mamona em dispositivos protéticos: estudo preliminar

With a view to using it as lining material for below knee prosthesis, this research developed and tested the mechanical resistance of a new polyurethane derived from castor oil, using of tensile strength measurement, and compared to with two other materials. The silicone elastomer and synthetic rubber foam, both of current use for the same purpose. The castor oil polyurethane and the silicone elastomer were tested either in a care, summing up five types of materials investigated. The parameters taken into consideration for analysis were the maximal load supported, the maximal at rupture, the elongation at rupture and modulus of elasticity for each material. The results showed the silicone elastomer with and without the mesh core was the most resistant material and that the resistance of the plain castor oil polyurethane is close to that of rubber foam. When combined with the mesh core, the resistance of the polyurethane became similar to that of the plain silicone elastomer. However, the polyurethane was the materials more flexible than silicone elastomer and than rubber foam. It was concluded that, despite weaker, the resistance of castor oil polyurethane can be increased by the combination with the mesh core, still preserving its greater flexibility and shock absorbing and load distribution capacity, as compared to the silicone elastomer. In this form it is, therefore an adequate material to make soft sockets for below knee prostheses.Com vistas a sua utilização na confecção de luvas ou soquetes macios para os revestimentos dos encaixes de próteses infra-patelares, o presente trabalho desenvolveu e testou a resistência mecânica de uma nova poliuretana derivada do óleo da mamona por meio de ensaios de tração, comparativamente com dois outros tipos de materiais, o elastômero de silicone e uma espuma de borracha sintética, de uso corrente para a mesma finalidade. A poliuretana e o elastômero de silicone foram também testados em uma forma associada com uma alma de malha tubular elástica, totalizando cinco tipos de materiais investigados. Foram considerados parâmetros para análise a carga máxima suportada, a tensão máxima, a tensão máxima de ruptura, o alongamento até a ruptura e o módulo de elasticidade de cada material. Os resultados mostraram que o silicone, com e sem a presença da alma de malha tubular, foi o material mais resistente e que a poliuretana derivada do óleo da mamona apresentou resistência próxima à da espuma de borracha, quando pura, e próxima à do silicone puro, quando associada à malha tubular. Entretanto, a poliuretana mostrou-se um material mais flexível que o silicone. Concluiu-se que, apesar de menos resistente no estado puro, a poliuretana, derivada do óleo da mamona, pode ter sua resistência aprimorada com a associação da malha tubular, mantendo-se ainda mais flexível, com melhor capacidade de absorção e distribuição de carga que o silicone, sendo, portanto, um material adequado para a confecção de luvas protéticas sob o ponto de vista da resistência

Emprego experimental da poliuretana derivada de óleo de mamona (Ricinus communis L: ) em implantes lamelares, interlamelares e penetrantes na córnea de coelhos

Há muito que se estudam métodos e materiais reparadores de córnea, em busca de uma melhor reposição tecidual e, principalmente, manutenção ou recuperação da visão. A pesquisa de novos biomateriais tem permitido produzir próteses capazes de desempenhar a função requerida, sem reação importante. Conhecendo-se os bons resultados obtidos com a utilização da poliuretana vegetal derivada de óleo de mamona (Ricinus communis L. ) em vários procedimentos, estudou-se sua implantação, em forma de membrana, na córnea, objetivando oferecer novo material para a reparação de lesões corneanas e a confecção de ceratopróteses biologicamente inertes. Utilizaram-se 28 coelhos, divididos em dois grupos (G1 e G2) e estes em subgrupos para avaliações de implantes lamelares e interlamelares aos 2, 7, 15, 30, 60 e 120 dias, e implantes penetrantes, aos 2, 7, 15, 30 e 60 dias de pós-operatório. Estudaram-se parâmetros como neovascularização, inflamação, transparência de córneas e implantes, bem como a aderência e viabilidade destes, através de exames oculares, e histopatológicos à microscopia óptica. Observou-se reação inflamatória branda em todos os períodos. Os implantes lamelares e penetrantes permitiram reparação da córnea e manutenção da integridade dos globos oculares, embora sofressem deiscência entre 5 e 28 dias de pós-operatório. Concluiu-se pela boa biocompatibilidade do material e pela possibilidade de empregar-se o polímero na reparação corneana e, possivelmente, em ceratopróteses.The purpose of this study was to investigate the feasibility of using membranes made of a castor bean oil polymer as a new material for corneal repair or keratoprosthesis. The polymer shows good biocompatibility when used as prosthesis material on various sites (e.g. testis, bone, teeth). Twenty-eight rabbits weighing from 2.5 to 3.5 Kg were submitted to lamellar, interlamellar and penetrating keratoplasties. Clinical and histopathological evaluations were performed from the 2nd to the 120th post-operative day. Lamellar and penetrating implants presented good corneal cicatrization, although all membranes were extruded around the 15th day. All globes submitted to penetrating keratoplasties kept the integrity of the anterior chamber, with some of them showing some degree of synechiae. Interlamellar implants did not present important clinical reactions. The histopathological study demonstrated few inflammatory signs in all implants, with some epithelial linning appearing over the penetrating grafts. It was concluded that the castor bean oil polymer presented good biocompatibility and may be used in emergencial situations for temporary closure, as a globe salvage procedure. It is suggested that the castor bean oil polymer should be further studied in keratoprosthesis, due to its advantages (good biocompatibility, lower price and vast shape, porosity, thickness and refractive index possibilities)

Evaluation of the performance of a castor-oil based formulation in limiting pesticide residues in strawberry crops

A study was made to evaluate the effect of a castor oil-based detergent on strawberry crops treated with different classes of pesticides, namely deltamethrin, folpet, tebuconazole, abamectin and mancozeb, in a controlled environment. Experimental crops of greenhouse strawberries were cultivated in five different ways with control groups using pesticides and castor oil-based detergent. The results showed that the group 2, which was treated with castor oil-based detergent, presented the lowest amount of pesticide residues and the highest quality of fruit produced

The spectrophotometric determination of the pka of pyrrolidinedithiocarbamic and piperidinedithiocarbamic acids, based on diode array measurements

A spectrophotometric method, based on the use of a diode array spectrophotometer, is proposed in order to determine the pKa of pyrrolidinedithiocarbamic (HPyr-I) and piperidinodithiocarbamic (HPip-II) acids. The high speed of data acquisition of the equipment made it possible to minimize the problem of acid decomposition. The values obtained were 3.10(I) and 3.51(II) in I = 0.50 mol L-1 (NaClO4) at 25.0 °C, and are consistent with the acid decomposition mechanism. A discussion is presented based on the shape of the compound spectra in acidic and basic media and their relation to the order of the pKa values for I and II