Materials Science Forum Vol. 958

Abstract: Calcium sulfate dehydrate β (CaSO₄. 0,5H₂O) is a material obtained from the calcination of gypsite (CaSO₄.2H₂O). This is a low cost ceramic material very used in building industry. The improvement of their applications is of fundamental technological interest. Polymers are an interesting alternative of reinforcement. Polyvinyl acetate (PVAc) is an addition polymer obtained by the polymerization of vinyl acetate. This polymer is well known to achieve good adhesion to cellulosic surfaces. The aim of this work was to evaluate the mechanical properties of porous plaster bodies reinforced with PVAc. Mechanical behavior was characterized by compression and bending strength. Three water / gypsum ratios: 0.5 0.6 and 0.7 were used on this work. An amount of 5% and 10% PVAc promoted increase on the mechanical properties of gypsum. Higher amounts polymer promoted further decrease of the mechanical properties.

Abstract: The Development of new materials for building industry is a necessary issue to promote sustainability. Gypsum is an important low cost material very abundant in the northeast region of Brazil. Its physical properties make it an interesting material to form composite materials. This work presents a study of gypsum reinforced with Caroá (neoglasiovia variegate) natural fibers, where different amounts of fibers (1, 2, and 3%) were added into gypsum matrix. Three different fiber sizes (5, 10, and 20mm) were used to evaluate the effect of fiber size on the properties. PVAc was added in order to enhance the interactions between matrix and fibers. Mechanical strength was characterized by compression and bending tests. The addition of 1% mass Caroá fibers leads to a slightly increase on the mechanical strength independently of fiber size.

Abstract: We study the sound absorption coefficient of rubberized mortars in response to the incorporation of 7.5%, 15% and 30% of waste-tire rubbers in place of sand at a water-to-cement mass (w/c) ratio of 0.48. We consider two different morphologies of rubber particles, namely spheroid (S) and fiber-like (F) particles. Experimental characterization was performed after 7 days of curing. The mixtures were performed by density, water absorption, void index and sound absorption. We choose the transfer function method with one microphone successively in two locations in order to obtain the sound absorption coefficient using an impedance tube. Sound absorption coefficient results indicate a slightly enhancement for 7.5% S, 15% S, 30% S and 7.5% F mixtures from 1600 Hz to 2000 Hz. The best acoustic performance is observed for 30% S and 7.5% F mixtures from 850 Hz to 2000 Hz.

Abstract: This study considered the effect of modified and unmodified bentonite clay on the thermal properties of films based on cassava starch. The bentonite clay was modified in the presence of cetyl trimethyl ammonium bromide (CTAB). The attainment of exfoliated or intercalated nanocomposite was characterized by X-ray diffraction (XRD) and Fourier transform by infrared radiation (FTIR). In XRD, it was verified that the cassava starch dispersed the modified clay in an exfoliated way and unmodified clay in an intercalated way. In the FTIR it was characterized that the cassava starch interacted more with the modified bentonite clay compared to unmodified. Finally, thermogravimetric curves showed the thermal property of the starch films concluding that the modified clay was the reinforcing material that contributed the most to the thermal stability of the cassava starch film, retarding its decomposition point, around 35oC , in relation to the pure starch film.

Abstract: During the last few decades many researchers have been interested in acoustic wave propagation in artificial periodic composites known as sonic crystals. Sonic crystals have received renewed attention because they exhibit acoustic band gaps where there are only evanescent waves. Sonic crystals consist of a periodic array of scatterers embedded in a host medium. The host medium and/or scatterers are fluids. We investigate the band structure of acoustic waves propagating in a sustainable sonic crystal composed by miriti fibers and air, regarding square and triangular lattices. Miriti fibers are extracted from buriti palm petiole (Mauritia flexuosa Mart.), which is a typical specie that grows in Amazonian region. We also study the influence of miriti fiber cross section, i.e. circular, hollow circular, square and rotated square with a 45° angle of rotation with respect to x, y axes. Plane wave expansion method is used to solve the wave equation. Acoustic band gaps are observed for all miriti fiber cross sections and lattices. The best performances of the sustainable sonic crystal are for triangular lattice, regarding circular and rotated square miriti fiber cross sections, and for square lattice with circular miriti fiber cross section. We suggest that the sustainable sonic crystal should be feasible for noise management.

Abstract: In this study, was investigated the optimization of the factors that significantly influenced the mechanical property improvement of cassava starch nanocomposites through complete factorial design 23. The factors to be analyzed were cassava starch (A), glycerol (B) and modified clay (C) contents. The clay had its surface modified by anion exchange in the presence of a quaternary ammonium salt. The factorial analysis suggested a regression model capable of predicting the optimal mechanical property of the cassava starch biofilm from the maximization of the elastic modulus. The reliability of the regression model was tested by the correlation established with the experimental data through the following statistical analyzes: Pareto graph and response surface. The response surface showed the best combination of factor configurations to achieve the best response and SEM analysis in thermoplastic cassava starch biofilms in both the best and the worst elasticity conditions was performed to visualize the standard of the structure of the biopolymeric matrix in both conditions. The sequence of the degree of statistical significance on the elastic modulus in relation to the effects investigated is therefore C> B> A> BC> AC.

Abstract: The aim of the present study is to assess the physical-mechanical properties of hydroxyapatite-titanium oxide composites used in porous scaffolds produced by the polymeric wax addition method. Mixtures composed of 50%-50%wt. (sample A), 60%-40%wt. (sample B), and 70%-30%wt. (sample C) of hydroxyapatite-titanium oxide were prepared. Subsequently, 70%vol. of each sample was combined with 30%vol. polyethylene wax. Forty-five (45) specimens per composition (12 mm diameter and 10 mm height) were prepared through uniaxial pressing. The specimens were subjected to calcination at 500°C (1°C/min) and left to rest for 1 h for polymeric wax elimination. Next, they were sintered at 1250°C, 1300°C, and 1350°C for 2 h. Physical-mechanical assays were conducted to assess apparent porosity, water absorption, specific gravity, firing linear retraction, and ultimate compression strength. As temperature increased, firing linear retraction, specific gravity, and ultimate compression strength increased in all samples, whereas water absorption and apparent porosity decreased. Sample A presented the highest densification and ultimate compression strength rates at 1350°C. Overall, the physical-mechanical characteristics of these composites made them suitable to be used as biocomposites.

Abstract: The goal of this study was to characterize the mechanical behavior of dentin, dental enamel and a nanoparticulate composite resin, used in dental restorations. This characterization was performed through the static and dynamic Vickers hardness test. As for the biological tissue assays, third included human molars were used. The nanoparticulate resinous composite was condensed into a matrix, measuring approximately 10x10x2mm. The obtained HV values were represented by hardness maps. The distribution of hardness values along the enamel and dentin structures occurred unevenly in the two hardness analyzes. For dental enamel, there were differences in hardness values when compared dynamic to static tests. This difference did not occur in dentin. It was observed that the mechanical behavior of the resinous composite resembled more the behavior of the dentin than the enamel.

Abstract: The aim of this study was to evaluate the influence of shear and micro-shear tests on adhesive resistance and on defects in restorations in human dentin. The teeth were sectioned and embedded. The dentin surface was treated with universal system adhesive and the samples were divided into two groups. In the first, composite resin pins were fixed with 1 mm diameter and in the second, pins with 2 mm. After mechanical tests the samples were taken to the SEM for analysis of fractures. Tensile strength on G1 was 16 MPa and on G2 20 MPa. The fractures occurred after shear were mostly mixed and cohesive in dentin. On micro-shear adhesive and mixed, no cohesive. It can deduce that, the diameter of the pin influenced the adhesive resistance and the type of failure. Therefore, for evaluation of adhesive strength in dentin the test indicated is micro-shear.

Abstract: EVA (poly (ethylene-co-vinyl acetate)) is a copolymer widely used in the Brazilian footwear industry, where approximately 18% of the EVA remains as waste, principally after the cutting out of insoles. EVA wastes cannot be recycled or reused for the original purpose, but it may be possible to add them to Portland cement to produce concrete for non-structural applications in constructions. This work presents an analytical technique based on the interpretation of X-ray images to assess the spatial distributions of these wastes within concrete test specimens. Evaluation was made of the feasibility of using this technique to study the incorporation of the wastes. Test specimens of concrete were produced according to Brazilian technical standard ABNT-NBR 5738, using a sand/gravel/cement ratio of 3:2:1, where EVA replaced part of the gravel content (10, 20, 50, and 70% of the total gravel volume). Analysis of front projection X-ray images of the specimens showed that the waste was homogeneously incorporated throughout the entire material, as required for concrete. The results of compressive strength tests showed that for samples containing up to 20% of EVA waste, the compression resistance remained almost unchanged, while incorporation of 50 or 70% of waste led to decreases of up to 64% in the resistance.