Rubén Jesus Sánchez Rodríguez

Thermogravimetric Stability of Polymer Composites Reinforced with Less Common Lignocellulosic Fibers - an Overview

Environmental, economic, and technical reasons justify research efforts aiming to provide natural materials with possibility of replacing synthetic fiber composites. Commonly known lignocellulosic fibers, such as jute, sisal, flax, hemp, coir, cotton, wood, and bamboo have not only been investigated as reinforcement of polymeric matrices but already applied in automobile components. Less common fibers, such as curaua, henequen, fique, buriti, olive husk, and kapok are recently being studied as potential reinforcement owing to their reasonable mechanical properties. The relatively low thermal stability of these fibers could be a limitation to their composites. The works that have been dedicated to analyze the thermogravimetric stability of polymer composites reinforced with less common lignocellulosic fibers were overviewed.

The dynamic-mechanical behavior of epoxy matrix composites reinforced with ramie fibers

The exceptional tensile strength of ramie fiber has motivated investigations on its application as reinforcement in polymeric composites. In this study the temperature variation of the dynamic-mechanical parameters of epoxy matrix composites incorporated with up to 30% in volume of ramie fiber were investigated by DMA tests. The parameters were the storage modulus, loss modulus and tangent delta. The investigation was conducted in the temperature from 20 to 200°C in an equipment operating in its flexural mode at 1 Hz under nitrogen. The results showed that the incorporation of ramie fiber tends to increase the viscoelastic stiffness of the epoxy matrix. It was also observed sensible changes in the structure damping capacity when the fraction of fiber is increased in the composite. These results indicate that the segmental mobility of the epoxy chains is affected by interaction with ramie fibers in the composite.

Thermogravimetric Stability Behavior of Less Common Lignocellulosic Fibers - a Review

A review on the thermogravimetric behavior of some less-common natural lignocellulosic fibers is presented. The review was limited to works analyzing results on the weight loss variation with temperature by means of the thermogravimetric (TG) curve and its derivative (DTG) for uncommon fibers such as curaua, rice, wheat straw, henequen, piassava, fique, date palm, buriti, artichoke, grass, okra, sponge gourd, caroa and olive husk. Relevant parameters obtained from corresponding TG/DTG curves were discussed to highlight distinctions and similarities in the thermal stability of these fibers. The concept of fiber thermal degradation is critically examined in view of the decomposition stages associated with the main constituents: water, hemicellulose, lignin and cellulose. The effect of fiber thermal degradation on possible application as polymer composite reinforced is remarked.

Reciclagem de resíduo proveniente da produção de papel em cerâmica vermelha

This work has for objective to evaluate the effect of the incorporation of waste from the paper production, in up to 10 wt % on the properties and microstructure of a clayey body used in the fabrication of bricks. The raw materials, the paper waste and the clayey body were, respectively, obtained from the area of Santo Antonio de Padua and Campos dos Goytacazes, north of the State of Rio de Janeiro. Specimens were prepared by uniaxial pressing at 20 MPa before firing at 750 °C. The evaluated physical and mechanical properties were: linear shrinkage, water absorption and flexural strength. The microstructure of the ceramics was evaluated by SEM. The results showed that the waste addition changes the physical and mechanical properties of the ceramic, generating a deleterious effect on the water absorption and flexural rupture strength for incorporations above 5 wt %. By contrast, incorporations of 3 wt % of the waste were found to be a viable alternative for the final disposal of waste from the paper production.

Fabrication of Artificial Stone from Marble Residue by Resin Transfer Molding

Artificial stones have recently been worldwide commercialized but are still not produced in Brazil. This has motivated efforts for the local fabrication of a similar stone. Thus, an artificial ornamental stone (AOS) was fabricated by means of a resin transfer molding (RTM) process. Marble residues were placed inside a hermetic mold under vacuum. A still fluid polyester resin, already mixed with a catalyst and a thinner, was injected into the mold. After curing, the density and water absorption of the AOS were evaluated. The material was also subjected to both compression and bend mechanical tests. The AOS microstructure was analyzed by scanning electron microscopy, which was then related to the obtained physical and mechanical properties.

Influence of Compaction Pressure and Particle Content on Thermal and Mechanical Behavior of Artificial Marbles with Marble Waste and Unsaturated Polyester

Compact artificial stones are widely used in buildings around the world, and the expected demand to the next years is increasing. In this study, stone fragments from marble processing are recycled as raw materials for produce compact artificial stones using compaction in a vacuum environment (100 mm Hg). Crushed marble waste (80 and 85%wt) are mixed with unsaturated polyester resin as binder. Materials were processed under compaction pressures of 1 and 10 MPa, for 20 minutes at 90 °C. Artificial marble with flexural ultimate strength of 25 MPa, water absorption below 0.2% and homogeneous particles distribution were obtained to materials produced with 80%wt of marble particles. To artificial marbles with 85%wt of particles, lower flexural ultimate strength and higher water absorption were observed (18 MPa and 0.4% respectively). In addition, the greater compaction pressure used improves slightly values obtained in 3 points bending test. Furthermore, tangent delta peaks at 115 °C were observed to evaluated artificial marbles.

Formulation and Characterization of Polypropylene Composites Alkali Treated Bagasse Fiber

Polymer composites reinforced with natural fiber that were obtained as industrial wastes, are of particular interest due to both the environmental benefits and economical advantages. In the present work sugarcane bagasse fibers, obtained as a waste from sugar and ethanol production, were incorporated in an amount of 25wt% into a polypropylene matrix. These fibers were previously alkali treated with NaOH to improve their adherence to the composite matrix. Thermal analyses were conducted in both types of composites, with untreated fibers and with alkali treated fiber. The result indicated that the alkali treatment improves the compatibility between the bagasse fiber and the polypropylene matrix, which then provides more thermal resistance.

Impacto do co-monômero hidroxivalerato na cinética de degradação térmica dos poli(3-hidroxialcanoatos)

The aim of this work was to evaluate the impact that the content of the co-3-hydroxyvalerate monomer has on thermal degradation kinetics of P3(HB-x%HV) copolymers. Films of the copolymers with different contents of 3-hydroxyvalerate were obtained by controlled evaporation of solvent from chloroform solution (1% m/m). Thermogravimetry study was carried out in helium atmosphere, platinum pans and sample mass about 10 ± 0.3 mg. The thermal degradation kinetic study was made on isothermal conditions and non-isothermal conditions. For the two conditions of analysis, it was observed that the copolyester studied presented a defined stage of degradation in a short time interval. The analysis of thermal degradation kinetics carried out by the isoconversional methods of Friedman and Ozawa-Flynn-Wall showed that the activation energy for the process of thermal degradation is dependent on the fraction of mass conversion. Such dependence may be related to the occurrence of cleavage of covalent bonds with different bonding energies. Other characteristic could be the structural differences caused by co-monomers 3HB and 3HV. The results obtained indicate the need to control the distribution of 3HV units to improve the thermal stability of the polyesters. Improving the thermal stability, and thus the processability of these copolymers from melt, increases the possibilities of using these environmentally friendly polyesters.

Thermal Cycling Treatment and Structural Changes in Cu-Al-Ni Monocrystalline Alloys

In the present work a monocrystalline Cu-13.5Al-4Ni (wt.%) alloy with shape memory effect (SME) submitted to thermal cycling inside the critical range was investigated in terms of number of cycles and resulting structural changes. Attention was paid to the structural changes associated with reversible β1↔γ’1 martensite transformation. The monocrystalline Cu-Al-Ni alloy was produced in Russia, according to a specific technology. The structural characteristic of the alloys was studied through optical microscopy and X-ray diffraction methods using Cu-Kα radiation. Differential scanning calorimetry permitted the determination of the temperature range as well as a thermal effect due to the β1↔γ’1 martensitic reversible transformations, before and after 100, 200 and 300 thermal cycles.

Propriedades mecânicas e termomecânicas de compósitos com partículas de diamante dispersas em matriz epoxídica modificada na razão resina/endurecedor

The mechanical properties of composites with dispersed diamond particles in epoxy matrix cured with different proportions of hardener to monomer ratio, characterized by the resin/hardener ratio (phr) were studied. An investigation on the thermo-mechanical behavior of these composites was also carried out by dynamical mechanical analysis (DMA). In the present work a complete evaluation of the mechanical properties was carried in a wide interval of phr associated with possible technological applications. Composites with up to 30 wt. % of diamond particles dispersed in type DGEBA/TETA epoxy matrix were fabricated with phr ratios varying from 7 to 21. For all investigated conditions, the composite strength decreased with the amount of incorporated diamond. Matrices with phr above the stoichiometric 13 were associated with composites with better mechanical performance. The DMA results showed that the storage modulus increases with the amount of diamond particles incorporated in the composite. The values obtained for the delta tangent, allowed an evaluation of possible mechanisms that contribute to the thermal mechanical performance of these composites.