Nelson Cárdenas Olivier

Mechanical behavior of pumpkin fruits subjected to compression during maturation

During handling operations, many problems that reduce the quality of vegetables may occur. Mechanical injuries are the leading cause of postharvest losses for the pumpkin, and can take place at any point of the production chain. This study aimed at evaluating the pumpkin fruits behavior, during their ripening stages, on the values ??of maximum compression force for fixed deformations, and determining the proportional deformability modulus of the fruits under compression at the repose position . Fruits were harvested at 15, 30 , 40 , 50 and 60 days after flowering and uniaxially compressed between two parallel plates . The results allowed to conclude that both the required compression force and the proportional deformability modulus increased during the maturation course, reaching a maximum force of 1,778 N and a maximum deformation modulus of 164 MPa, after 30 days. After this period, both the maximum force and the modulus values ??decreased, reaching 1,514.8 N of maximum force and a modulus of 132.09 MPa, after 60 days of ripening . Over the course of a longer maturation time, the fruit firmness increased, therefore requiring an increase in the maximum load to achieve greater deformation. The ideal period for harvest and transport of ‘Jacarezinho’ pumpkin fruits was set from 30 to 40 days after anthesis.

The production of hydroxyapatite prototypes from solid bodies of gypsum/polyvinyl alcohol composites

Prototypes of porous hydroxyapatite (HAp) were produced from Gypsum/PVA composite, using a mass proportion of 15% polymer. The material was obtained by means of chemical conversion in (NH4)2HPO4 0.5 mol.L-1 solution and NH4OH 6.0 mol.L-1 alkaline medium for pH control, maintained between 6.0 and 9.0. The reaction occurred at a temperature of 100oC at different test times. The obtained HAp was characterized by several techniques, such as FTIR, which identified the SO42- groups characteristic for the Gypsum block, and the PO43- groups that are attributed to the biomaterial HAp, besides XRD and SEM, which made it possible to confirm a successful conversion of the material. Tests for mechanical resistance to compression (σc) were carried out for both materials as well.

Mechanical characterization of mango fruit using compression tests

Brazil is one of the largest producers of mangoes, and the São Francisco Valley accounts for about 87% of Brazilian exports of this product to the European market. This study aimed to characterize the mechanical behavior of the fruits according to the maturation stages, in order to prevent physical damage caused by improper handling of the fruit during harvest, storage, processing and transportation. The compression tests were performed on the mango cultivars (Mangifera indica L.) Keitt and Tommy Atkins at different maturation stages in order to characterize the internal elastic modulus and determine the maximum stress until rupture of the sleeve. The fruits showed a decrease in mechanical properties corre‐ lated with the increase of maturation stage, for both cutivars. The Tommy Atkins variety showed better mechanical properties probably related to a higher concentration of fibers in the pulp which yields better mechanical stabilization.

Production of Hydroxyapatite/Polyhydroxibutirate Based Composites for Biomaterials Applications

Hydroxyapatite (HA) is a ceramic material broadly studied due to its great similarity with the human bone. However, this material presents high stiffness and young modulus in comparison with the bone tissue. The polyhydroxybutyrate (PHB) is a themoplatic and biodegradable polymer that presents bone like young modulus and gradative degradation that results in a permanence of the mechanical properties after implantation. The aim of this study is to evaluate the effect of the infiltration of melted PHB on the mechanical properties of porose HA bodies. The composite samples were characterized by SEM, EDS and compressive strength. The samples produced with 10% paraffin and sintered at 1200 °C showed the best mechanical properties and reached an increase of the compressive strength from 29,00 ± 4,70 MPa before infiltration to 83,00 MPa ± 4,41 after infiltration with PHB for a final porosity of 5%.

Determination of mango ripening degree by electrical impedance spectroscopy

Abstract The kinetics of ripening of fruits, followed by subsequent degradation process represent important biochemical mechanisms with high aggregate value for agribusiness sector. In contrast to the destructive assays for identification of ripening degree of fruits, the development of non-invasive techniques introduces potential advantages concerning to the development of new methods for fruit production control. In this direction, the electrical impedance spectroscopy was used for the identification of the maturation degree of fruits based on variation of bulk resistance dependence with maturation of fruits, due to the variation in the liquid content in fruit fibers. The results revealed the strong correlation between mechanical assays and electrical parameters, characterizing an important advantage in terms of a non-invasive and non-destructive method for ripening identification degree.

Production of Single-Phase Hydroxyapatite Porous Bodies from Gypsum/Polystyrene

Porous bodies were produced using hydroxyapatite as a starting material, gypsum, high purity material, low cost and that can be molded into the desired shape. Also, beads of polystyrene polymer. The first step of this work was to produce porous gypsum blocks obtained by mixing gypsum, water and polystyrene. After drying, they were submerged in acetone solvent for solubilizing the polymer and pore formation. The porous hydroxyapatite was synthesized in a second stage, where the porous gypsum blocks were immersed in a solution of (NH4)2HPO4 0.5 mol L-1 to 100 ° C and pH 7.0-9.0 for 24 hours. From this method, it was possible to produce bodies single phase hydroxyapatite with a maximum porosity of 70 ± 3% and a compressive strength of 1.48 ± 0.17 MPa.

Modeling of Two-Dimensional Orthotropic Heat Conduction in Porous Gypsum

The gypsum is a versatile material that shows low thermal conductivity, which makes this material very suitable for application as thermal insulation. The increase of the porosity of gypsum bodies promotes a decrease on the thermal conductivity. This effect optimize the range of applications of gypsum on the thermal insulate field. The present study aimed the numerical modeling of two-dimensional heat conduction by finite differences in a steady state to evaluate the ortotrophy of the thermal conductivity of porous gypsum using the elements of the protected hot plate method. Computer simulations were performed using thermal conductivity of the gypsum equal to 0.35 W/m.K. This value was varied on the x and y directions by 5%, 10% and 15%. The heat flow applied to the numerical simulations were equal 75 W/m2, 100 W/m2 to 125 W/m2.It was possible to produce temperature profiles where is visible the displacement of isotherms as a function of the change in thermal conductivity in the x direction.

COMPORTAMENTO MECÂNICO DA ABÓBORA UTILIZANDO ENSAIOS DE COMPRESSÃO

Os materiais biologicos possuem propriedades elasticas e viscoelasticas, cujo conhecimento torna-se importante para o desenvolvimento de equipamentos e tecnicas adequadas de colheita, transporte e processamento de produtos horticolas. O presente trabalho apresenta os resultados das tensoes transversais maximas que causam a ruptura de abobora (Cucurbita moschata) das variedades leite e jacarezinho, atraves de ensaios mecânicos de compressao axial, evidenciando, dessa forma, quais as cargas maximas que sao capazes de provocar o rompimento das estruturas destes frutos. Foram analisadas as particularidades referentes a geometria das duas variedades de aboboras, realizando-se cortes em suas secoes transversais, para que fossem determinadas as tensoes de flexao e de compressao atuantes nas estruturas rigidas das hortalicas estudadas. Corpos de prova cilindricos, extraidos das polpas das aboboras, foram submetidos a ensaios de compressao axial, com o objetivo de se determinarem os coeficientes de Poisson distintos para ambas as variedades, cujos valores medidos sao 0,50 e 0,46, para as variedades leite e jacarezinho, respectivamente. O Modelo proposto para a analise da fratura nos frutos de abobora mostrou-se compativel com os dados experimentais resultando em um modo de falha por fratura longitudinal ao eixo de aplicacao das cargas. A carga transversal resultante e no minimo 4 vezes maior que a carga maxima de compressao aplicada para ambas as variedades.