Scielo RSS <![CDATA[Materials Research]]> http://www.scielo.br/rss.php?pid=1516-143920120004&lang=en vol. 15 num. 4 lang. en <![CDATA[SciELO Logo]]> http://www.scielo.br/img/en/fbpelogp.gif http://www.scielo.br <![CDATA[<b>Influence of Er,Cr</b>: <b>YSGG laser on bond strength of self-adhesive resin cement</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1516-14392012000400001&lng=en&nrm=iso&tlng=en The purpose of this study was to investigate the bond strength of fiber post previously laser treated root canals. Forty single-rooted bovine teeth were endodontically treated, randomly and equally divided into two main groups according to the type of pretreatment: G1: 2.5% NaOCl (control group); and G2: Er,Cr:YSGG laser. Each group was further subdivided into 2 groups based on the category of adhesive systems/ luting materials used: a: an etch-and-rinse resin cement (Single Bond/RelyX ARC; 3M ESPE), and b: a self-adhesive resin cement (Rely X Unicem; 3M ESPE). Three 1.5 mm thick slabs were obtained per root and the push-out test was performed at a crosshead speed of 0.5 mm/min until post dislodgement occurred. Data were analyzed by ANOVA and post-hoc Tukey's test at a pre-set alpha of 0.05. Analysis of variance showed no statistically significant difference (p > 0.05) among the groups G1a (25.44 ± 2.35) and G1b (23.62 ± 3.48), G2a (11.77 ± 2.67) and G2b (9.93 ± 3.37). Fractures were observed at the interface between the dentin and the resin in all groups. The Er,Cr:YSGG laser irradiation did not influence on the bond strength of the resin cements and the etch-and-rinse resin cement had better results on bond strength than self-adhesive resin cement. <![CDATA[<b>Assessment of cumulative damage by using ultrasonic C-scan on carbon fiber/epoxy composites under thermal cycling</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1516-14392012000400002&lng=en&nrm=iso&tlng=en In recent years, structural composites manufactured by carbon fiber/epoxy laminates have been employed in large scale in aircraft industries. These structures require high strength under severe temperature changes of -56° until 80 °C. Regarding this scenario, the aim of this research was to reproduce thermal stress in the laminate plate developed by temperature changes and tracking possible cumulative damages on the laminate using ultrasonic C-scan inspection. The evaluation was based on attenuation signals and the C-scan map of the composite plate. The carbon fiber/epoxy plain weave laminate underwent temperatures of -60° to 80 °C, kept during 10 minutes and repeated for 1000, 2000, 3000 and 4000 times. After 1000 cycles, the specimens were inspected by C-scanning. A few changes in the laminate were observed using the inspection methodology only in specimens cycled 3000 times, or so. According to the found results, the used temperature range did not present enough conditions to cumulative damage in this type of laminate, which is in agreement with the macro - and micromechanical theory. <![CDATA[<b>Fracture resistance of bleached teeth restored with different procedures</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1516-14392012000400003&lng=en&nrm=iso&tlng=en This study evaluated the fracture resistance of teeth submitted to internal bleaching and restored with different non-metallic post. Eighty mandibular incisors were endodontically treated and randomly divided in 10 groups (n = 8): G1- restored with composite resin (CR), G2- CR + fiber-reinforced composite post (FRC, Everstick post, Sticktech) cemented with resin cement self-etch adhesive (RCS, Panavia F 2.0, Kuraray), G3- CR + FRC + self-adhesive resin cement (SRC, Breeze, Pentral Clinical), G4- CR+ glass fiber post (GF, Exacto Post, Angelus) + RCS, G5- CR + GF + SRC. The G6 to G10 were bleached with hydrogen peroxide (HP) and restored with the same restorative procedures used for G1 to G5, respectively. After 7 days storage in artificial saliva, the specimens were submitted to the compressive strength test (N) at 0.5 mm/min cross-head speed and the failure pattern was identified as either reparable (failure showed until 2 mm below the cement-enamel junction) or irreparable (the failure showed <2 mm or more below the cement-enamel). Data were analyzed by ANOVA and Tukey test (α = 0.05). No significant difference (p < 0.05) was found among G1 to G10. The results suggest that intracoronal bleaching did not significantly weaken the teeth and the failure patterns were predominately reparable for all groups. The non-metallic posts in these teeth did not improve fracture resistance. <![CDATA[<b>Evaluation of impact strength of polyamide 6/bentonite clay nanocomposites</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1516-14392012000400004&lng=en&nrm=iso&tlng=en Nanocomposites of polymer/clay have had much attention in recent years, particularly those developed with layered silicates due to the need of engineering materials more efficient than pure polymers for certain applications. The level of exfoliation of layered silicates in crystalline structure of polymer matrices has been studied and has been observed that it affects the crystalline behavior and the physical and mechanical properties. In this study, nanocomposites of polyamide 6 were obtained by the melt intercalation method, using a Brazilian bentonite modified with a quaternary ammonium salt. X-Ray Diffraction (XRD) results showed the incorporation of salt among the layers of clay, making it organophilic and that the nanocomposites presented exfoliated and/or partially exfoliated structures and confirmed by transmission electron microscopy (TEM). By thermogravimetry (TG), the results indicated that the presence of clay increased the thermal stability of polyamide 6. The impact properties of the nanocomposites showed inferior values in relation to the pure polyamide, in other words, decrease the toughness. <![CDATA[<b>Effective functionalization of carbon nanotubes for bisphenol F epoxy matrix composites</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1516-14392012000400005&lng=en&nrm=iso&tlng=en A brand-new type of multifunctional nanocomposites with high DC conductivity and enhanced mechanical strength was fabricated. Ionic liquid functionalized Carbon Nanotubes (CNTs-IL) were embedded into epoxy matrix with covalent bonding by the attached epoxy groups. The highest DC conductivity was 8.38 x 10-3 S.m-1 with 1.0 wt. (%) loading of CNTs-IL and the tensile strength was increased by 36.4% only at a 0.5 wt. (%) concentration. A mixing solvent was used to disperse CNTs-IL in the epoxy monomer. The dispersion and distribution of CNTs-IL in the polymer matrix were measured by utilizing both optical microscopy and scanning electron microscopy, respectively. <![CDATA[<b>Effect of rare earth ions on transition temperature in perovskite materials by on-line ultrasonic studies</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1516-14392012000400006&lng=en&nrm=iso&tlng=en On-line measurements of ultrasonic longitudinal velocity, shear velocity and longitudinal attenuation were carried out on R1-xSr xMnO3 perovskites (R = La, Pr, Nd and Sm) for different compositions of Sr, at a fundamental frequency of 5 MHz over wide range of temperatures using the through-transmission method. The observed maxima/minima in velocities and attenuation have been discussed with decrease in ionic radii and composition. As a decrease in the ionic radii of rare earth elements leads to a decrease in transition temperature (Tc), the results that are observed show that measurement is one of the best tools to explore the structural/phase transition on-line velocity in perovskite manganese materials as a function of the ionic radii of rare earth elements. <![CDATA[<b>Effect of pH-induced nanopowder deagglomeration on sintering, microstructure and dielectric properties of Ba<sub>0.77</sub>Ca<sub>0.23</sub>TiO<sub>3</sub> ceramics</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1516-14392012000400007&lng=en&nrm=iso&tlng=en Ba0.77Ca0.23TiO3 ceramics were produced in this work starting from nanopowders synthesized via a polymeric precursor method. By adjusting the pH values of the precursor solutions above 7, it was possible to prepare powders weakly aggregated and with a smaller particle size, both facts which traduced into an enhanced nanopowders' sintering process at comparatively lower temperatures. Irrespective of the initial pH value, highly-dense and second phase-free ceramics were obtained following optimal sintering parameters (temperature and time) extracted from dilatometric and density measurements. By considering these and other sintering conditions, moreover, polycrystalline materials with an average grain size varying from 0.35 to 8 mm were produced, the grain growth process involving liquid phase-assisted sintering for heat treatments achieved at 1320 °C. The study of grain size effects on the ferroelectric properties of these materials was conducted, the results being discussed in the light of previous debates, including grain size-dependent degree of tetragonal distortion in such materials, as verified in this work. <![CDATA[<b>Antilocalization effect on photo-generated carriers in semi-insulating GaAs sample</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1516-14392012000400008&lng=en&nrm=iso&tlng=en Magnetoresistance measurements were performed on an illuminated semi-insulating GaAs sample with intrinsic deep level defects. Electrical carriers were photo-generated under light excitation and positive magnetoresistance for B < 0.2 T was observed in the whole range of temperatures measured (220-315 K). Using the model developed by H. Fukuyama and K. Hoshino, we interpreted the positive magnetoresistance as mainly caused by weak antilocalization effects over hole carriers for T &gt; 240 K. The high disorder originated from the low temperature growth of the sample leads to the strong localization of carriers and gives rise to the positive magnetoresistance observed at temperatures as high as room temperature. <![CDATA[<b>Manufacturing polycrystalline pellets of natural quartz for applications in thermoluminescence dosimetry</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1516-14392012000400009&lng=en&nrm=iso&tlng=en This paper describes the manufacturing process of quartz-pellets and shows their potential use as thermoluminescence dosimeters (TLD) for those applications where low-levels of ionising radiation are present. Two batches of cold-pressed pellets were produced and their resistance were evaluated by vibration tests and weight-loss measurements. The batch manufactured with 75 × 150 µm particles showed enough resistance to be employed as TLD. The dosimetric properties of the 310 °C peak appearing in the glow curves of these pellets were characterized together with commercial TLD-100 units using γ- and X-ray beams with different energies. The uncertainties related to reproducibility and stability of the TL signal were better than 10%. The sensitivity and the linearity of the TL response of quartz-pellets were better than that measured for TLD-100 for doses ranging from 0.5 to 200 mGy. The energy dependence of the quartz-pellets was higher than that of TLD-100 but it cannot be considered a restriction to their use in clinical procedures and industrial applications. <![CDATA[<b>Crack propagation under constant amplitude loading based on an energetic parameters and fractographic analysis</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1516-14392012000400010&lng=en&nrm=iso&tlng=en The crack propagation behavior in a 2024 T351 Aluminum Alloy under constant amplitude loading has been studied. This study is complemented by quantitative microfractographic observations and energetic analysis. The obtained results under constant amplitude fatigue tests show that different crack propagation stages can be identified and correlated with the evolution of the characteristic features. In another hand, the energetic analysis shows that there is a discontinuous crack growth at low growth rates as against a cycle by cycle growth mechanism at high growth rates. <![CDATA[<b>Influence of thermal treatment on bentonite used as adsorbent for Cd, Pb, Zn retention from mono-solute and poly-solute aqueous solutions</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1516-14392012000400011&lng=en&nrm=iso&tlng=en The retentions of Zn, Cd and Pb cations by one treated bentonite up to 750 °C were analyzed. The retentions were evaluated by using mono-and poly-solute aqueous solutions of such cations. The adsorptions were carried out in batch system at room temperature. The solid/liquid ratio was 2% wt.v-1. The solids were characterized by X-ray diffraction, thermal and chemical analyses. The Zn cation from mono- or polysolute-solutions was retained in higher amount than Cd and Pb cations in similar solution types by bentonite. The retentions were effective up to 450 °C calcined bentonite, after that, the retention capacity decreased in concordance with dehydroxylation of the structure of clay minerals. <![CDATA[<b>The effect of hot multistage drawing on molecular structure and optical properties of polyethylene terephthalate fibers</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1516-14392012000400012&lng=en&nrm=iso&tlng=en In this work, mechanical and structural parameters related to the optical properties of polyethylene terephthalate (PET) fibers drawn at hot multistage have been investigated. The changes in optical parameters upon changing draw ratio are used to obtain the mechanical orientation factors <P2(cos θ)&gt; and <P4(cos θ)&gt;, various orientation functions f2(θ), f4(θ) and f6(θ), and amorphous and crystalline orientation functions (f a and f c). Also, the numbers of random links between the network junction points (N1), the average optical orientation (Fav), and the distribution function of segment ω(cos θ) were calculated. In addition, an empirical formula was suggested to correlate changes in the birefringence with the draw ratio and its constants were determined. The study demonstrated change on the molecular orientation functions and structural parameters upon hot multistage drawing. Significant variations in the characteristic properties of the drawn PET fibers were due to reorientation of the molecules caused by applied heat and external tension. <![CDATA[<b>Utilization of by-product waste silica in concrete - based materials</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1516-14392012000400013&lng=en&nrm=iso&tlng=en The usage of waste silica from AlF3 production is limited due to admixtures of fluoride in its composition. The negative effect of admixtures was eliminated by thermally activating this silica gel. After thermal activation the mineralogical composition of silica gel changes. Fluorine is binding in low-reactive compounds, which insignificant effect on the cement hydration process. The possibilities of using waste by-product silica in hardened cement paste were investigated. Silica gel could be used as additive of the hardened cement paste after thermal activation (1 hour at 800 °C temperature). It was discovered that the optimum content of thermally activated technogenic silica gel additive under the conditions explored was up to 10% of the total quantity of the cement. After 28 days of hardening, the strength of hardened cement paste increased 7 MPa when the quantity of the additive was - 10% of the total weight when compared to the strength qualities of the samples with no additives used. <![CDATA[<b>Si-TCP synthesized from "Mg-free" reagents employed as calcium phosphate cement</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1516-14392012000400014&lng=en&nrm=iso&tlng=en The influence of silicon doping on calcium phosphate cement were explored in this work. α-TCP and Si-α-TCP were prepared by solid state reaction employing "Mg-free" CaHPO4, CaCO3 and CaSiO3 as precursors. It was possible to obtain TCP powders with low contents of β phase as contaminant. Cement liquid phase was an aqueous solution containing 2.5 wt. (%) of Na2HPO4 and 1.5 wt. (%) of citric acid. The liquid-to-powder ratio was 0.6 mL.g-1. Chemical, physical and mechanical properties of the cement samples were determined by means of XRD, FTIR, XRF, compressive strength and SEM. The calcium phosphate cements obtained achieved satisfactory properties; however, Si-α-TCP presented a decrease on the rate of setting reaction. <![CDATA[<b>Full factorial design analysis of carbon nanotube polymer-cement composites</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1516-14392012000400015&lng=en&nrm=iso&tlng=en The work described in this paper is related to the effect of adding carbon nanotubes (CNT) on the mechanical properties of polymer-cement composites. A full factorial design has been performed on 160 samples to identify the contribution provided by the following factors: polymeric phase addition, CNT weight addition and water/cement ratio. The response parameters of the full factorial design were the bulk density, apparent porosity, compressive strength and elastic modulus of the polymer-cement-based nanocomposites. All the factors considered in this analysis affected significantly the bulk density and apparent porosity of the composites. The compressive strength and elastic modulus were affected primarily by the cross-interactions between polymeric phase and CNT additions, and the water/cement ratio with polymeric phase factors. <![CDATA[<b>Development of silicon solar cells and photovoltaic modules in Brazil</b>: <b>analysis of a pilot production</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1516-14392012000400016&lng=en&nrm=iso&tlng=en Brazil is a country that receives a large amount of solar radiation. Moreover, high quality quartz mines has been found in its territory and the country has well-established metallurgical grade silicon industries. However, PV technology is not used in large scale and there are no active solar cell fabs. In this context, a pilot plant to develop industrial PV technology was carried out in a Brazilian university combining education, research and industrial development. Silicon solar cell processes based on low cost chemicals and gases as well as gettering mechanisms were developed and more than 12,000 solar cells were fabricated, achieving efficiencies up to 16%, and two hundred photovoltaic modules were produced and characterized. <![CDATA[<b>Machinability study of steels in precision orthogonal cutting</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1516-14392012000400017&lng=en&nrm=iso&tlng=en The miniaturization of components and systems is advancing steadily in many areas of engineering. Consequently, micro-machining is becoming an important manufacture technology due to the increasing demand for miniaturized products in recent years. Precision machining aims the production of advanced components with high dimensional accuracy and acceptable surface integrity. This work presents an experimental study based on Merchant and Lee & Shaffer theories applied to precision radial turning of AISI D2 cold work tool and AISI 1045 medium carbon steels with uncoated carbide tools ISO grade K15. The aim of this study is to evaluate the influence of feed rate on chip compression ratio (Rc), chip deformation (ε), friction angle (ρ), shear angle (Φ), normal stress (σ) and shear stress (•) for both work materials. The results indicated that the shear angle decreased and chip deformation increased as the chip compression ratio was elevated without significant differences between both materials. Additionally, higher cutting and thrust forces and normal and shear stresses were observed for the tool steel. Finally, the Lee & Shaffer model gave shear plane angle values closer to the experimental data. <![CDATA[<b>Creep-age forming of AA7475 aluminum panels for aircraft lower wing skin application</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1516-14392012000400018&lng=en&nrm=iso&tlng=en Creep-age forming (CAF) is an interesting process for the airframe industry, as it is able to form or shape panels into smooth, but complex, curvatures. In the CAF process, the ageing cycle of the alloy is used to relax external loads imposed to the part, through creep mechanisms. Those relaxed stresses impose a new curvature to the part. At the end of the process, significant spring back (sometimes about 70%) is observed and the success in achieving the desired form depends on how the spring back can be predicted in order to compensate it by tooling changes. Most of the applications relate to simple (non stiffened) panels. The present work deals with the CAF of aluminum panels for aircraft wing skin application. CAF was performed using vacuum-bagging autoclave technique in small scale complex shape stiffened panels, machined from an AA7475 alloy plate. An analytical reference model from the literature was employed estimate the spring back effect in such panel geometry. This model that deals with simple plates was adapted to stiffened panels using a geometric simplification, resulting in a semi-empirical model. The results demonstrate that CAF is a promising process to form stiffened panels, and the spring back can be roughly estimated through a simple model and few experiments. <![CDATA[<b>Kinetic of water diffusion and color stability of a resin composite as a function of the curing tip distance</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1516-14392012000400019&lng=en&nrm=iso&tlng=en The influence of curing tip distance and storage time in the kinetics of water diffusion (water sorption-W SP, solubility-W SB, and net water uptake) and color stability of a composite were evaluated. Composite samples were polymerized at different distances (5, 10, and 15 mm) and compared to a control group (0 mm). After desiccation, the specimens were stored in distilled water to evaluate the water diffusion over a 120-day period. Net water uptake was calculated (sum of WSP and WSB). The color stability after immersion in a grape juice was compared to distilled water. Data were submitted to three-way ANOVA/Tukey's test (α = 5%). The higher distances caused higher net water uptake (p < 0.05). The immersion in the juice caused significantly higher color change as a function of curing tip distance and the time (p < 0.05). The distance of photoactivation and storage time provide the color alteration and increased net water uptake of the resin composite tested. <![CDATA[<b>Nanocomposites of polyamide 6/residual monomer with organic-modified montmorillonite and their nanofibers produced by electrospinning</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1516-14392012000400020&lng=en&nrm=iso&tlng=en Nanocomposites of an organic-modified montmorillonite (MMT) and polyamide 6 (PA6) with a residual monomer were produced by melt mixing in a torque rheometer. By wide angle X-rays diffraction (WAXD), intercalated/exfoliated structures were observed in the PA6/MMT nanocomposites with 3 and 5 wt. (%) of MMT; on the other hand, when 7 wt. (%) of MMT was added, a nanocomposite with exfoliated structures was obtained due to the predominant linking reactions between the residual monomer and the "nanoclays" organic surfactant. Solutions of these PA6/MMT nanocomposites at 15, 17 and 20 wt. (%) in formic acid were prepared. The 3 and 5 wt. (%) nanocomposites were successfully electrospun; however, electrospinning of the 7 wt. (%) nanocomposite was not possible. WAXD, scanning and transmission electron microscopy results showed that the 3 and 5 wt. (%) nanofibers with average diameter between 80-250 nm had exfoliated structures. These results indicate that the high elongational forces developed during the electrospinning process changed the initial intercalated/exfoliated structure of the nanocomposites to an exfoliated one. <![CDATA[<b>XRD, AFM, IR and TGA study of nanostructured hydroxyapatite</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1516-14392012000400021&lng=en&nrm=iso&tlng=en In this work, the synthetic hydroxyapatite (HAP) was studied using different preparation routes to decrease the crystal size and to study the temperature effect on the HAP nano-sized hydroxyapatite crystallization. X-ray diffraction (XRD) analysis indicated that all samples were composed by crystalline and amorphous phases . The sample with greater quantity of amorphous phase (40% of total mass) was studied. The nano-sized hydroxyapatite powder was heated and studied at 300, 500, 700, 900 and 1150 °C. All samples were characterized by XRD and their XRD patterns refined using the Rietveld method. The crystallites presented an anisotropic form, being larger in the [001] direction. It was observed that the crystallite size increased continuously with the heating temperature and the eccentricity of the ellipsoidal shape changed from 2.75 at 300 °C to 1.94, 1.43, 1.04 and 1.00 respectively at 500, 700, 900 and 1150 °C. In order to better characterize the morphology of the HAP the samples were also examined using atomic force microscopy (AFM), infrared spectrometry (IR) and thermogravimetric analysis (TGA). <![CDATA[<b>Effects of Sasobit<sup>®</sup> content on the rheological characteristics of unaged and aged asphalt binders at high and intermediate temperatures</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1516-14392012000400022&lng=en&nrm=iso&tlng=en This paper describes the rheological properties of PG64, PG70, and PG76 asphalt binders blended with different Sasobit® contents. The rheological properties of the Sasobit®-modified binders were characterized after being subjected to different aging conditions using the dynamic shear rheometer (DSR) and rotational viscometer (RV) according to SuperpaveTM test protocols. The results indicated that the characterization of aging in terms of the Aging Index (AI) depends on the rheological property of the asphalt binder selected for use in evaluating aging, the amount of Sasobit®, the binder type, and the temperature range. Linear relationships between failure temperatures of unaged and short-term-aged asphalt were observed for three binder types. Design charts were developed to select the appropriate Sasobit® content as a function of temperature, taking into consideration the stiffening effects of Sasobit®, using the SuperpaveTM fatigue factor and asphalt mix construction temperatures. <![CDATA[<b>The potential of bamboo in the design of polymer composites</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1516-14392012000400023&lng=en&nrm=iso&tlng=en Bamboo is an alternative sustainable material for use in product design and has been incorporated into the concepts of eco-design. Here, we investigated the mechanical properties and morphologies of low density polyethylene (LDPE)/bamboo flour (BF) composites that were modified with polyethylene-graft-maleic anhydride (PE-g-MA) and glycerol. Scanning electron microscopy (SEM) and tensile tests of the composites demonstrated poor adhesion between the filler and matrix. Contact angle measurement showed that the surface of LDPE was modified by the presence of the load. The thermal stability of the composites was studied by measuring the oxidation induction time (OIT). Preliminary bacterial penetration tests were performed using culture inoculums of E. coli and S. aureus to investigate the natural antibacterial and bacteriostatic properties attributed to bamboo. Furthermore, bamboo may have interesting antioxidant activity with potential for use in food packaging applications. <![CDATA[<b>Effect of temperature on the mechanical properties of polymer mortars</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1516-14392012000400024&lng=en&nrm=iso&tlng=en This paper presents the results of an experimental program to investigate the effect of temperature on the performance of epoxy and unsaturated polyester polymer mortars (PM). PM is a composite material in which polymeric materials are used to bond the aggregates in a fashion similar to that used in the preparation of Portland cement concrete. For this purpose, prismatic and cylindrical specimens were prepared for flexural and compressive tests, respectively, at different temperatures. Measurements of the temperature-dependent elastic modulus and the compressive and flexural strength were conducted using a thermostatic chamber attached to a universal test machine for a range of temperatures varying from room temperature to 90 ºC. The flexural and compressive strength decreases as temperature increases, especially after matrix HDT. Epoxy polymer mortars are more sensitive to temperature variation than unsaturated polyester ones. <![CDATA[<b>Influence of glass and sisal fibers on the cure kinetics of unsaturated polyester resin</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1516-14392012000400025&lng=en&nrm=iso&tlng=en The effect of grinded glass and sisal fibers (25 vol%) on the cure kinetics of composites of unsaturated polyester resin (UPR) was investigated by differential scanning calorimetry (DSC) and scanning electron microscopy (SEM). The DSC analysis was carried out at four different heating rates (5, 10, 20 and 40 °C/min), and the cure enthalpy and activation energy (Ea) were determined according to the Flynn-Wall-Ozawa (FWO) method. The results showed that increasing heating rates promoted reduced reaction times. The sisal fiber-containing composites exhibit higher activation energy values for the cure process in comparison with the neat polyester resin and the glass fiber composites. This can be due to the presence of polar groups in the sisal components, which physically interact with the polyester resin and retard the cure reaction. Hence, as sisal fiber retarded the cure reaction of the UPR resin, it is suggested that the use of natural fibers in polymer matrix composites can affect the cure kinetics of the polyester resin. <![CDATA[<b>In vitro study of cytotoxicity of orthodontic elastomeric ligatures</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1516-14392012000400026&lng=en&nrm=iso&tlng=en This study investigated the cytotoxicity of crystal-coloured orthodontic elastomeric ligatures of polyurethane. Six ligatures from distinct manufactures were divided into 6 groups of 10 elastics each: Groups P1, P2, P3, P4, P5 and P6 (Polyurethane). The cytotoxicity essay was performed using L-929 line cells, which were submitted to the cell viability test with neutral red ("dye-uptake") at time intervals of 1, 2, 3, 7 and 28 days. Analysis of variance (ANOVA) with multiple comparisons and Tukey's test were used (p < .05). There were statistical differences (p < .05) in cell viability between Groups P1, P4, P2 and P3, and Groups P5 and P6 at 1 and 2 days. All elastomeric ligatures were considered suitable for clinical use. The hypothesis was accepted, the P5 and P6 elastomers and the processing route of injection molding for these ligatures showed the lowest cell viability, due the temperature and pressure distinct in the processing of these elastomers. <![CDATA[<b>Determination of the Representative Elementary Volume for the study of sandstones and siltstones by X-Ray microtomography</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1516-14392012000400027&lng=en&nrm=iso&tlng=en X-Ray computerized microtomography (µ-CT) besides providing two-dimensional images (2-D) of the transversal sections of the sample, the biggest attraction of the methodology is the rendering of three-dimensional images (3-D), enabling a more real analysis of the porous structure of the rock. However, the reconstruction, visualization and analysis of such 3-D images are limited in computer terms. Thus, it is not always possible to reconstruct the images with the total size of the microtomographed sample. Therefore, this study aims at determining the Representative Elementary Volume (REV) in reservoir rocks concerning their porosity. In order to collect microtomographic data from reservoir rocks, a microtomograph Skyscan model 1172 was utilized for the sandstone and siltstone samples scanning. After the analysis of the graphs obtained by REV, it was concluded that the most adequate dimensions for the reconstructed volume in each analyzed sample were approximately 1400 × 1400 × 1400 µm, which are dimensions that can easily be reconstructed, visualized and analyzed. <![CDATA[<b>Carboxylated nitrile butadiene rubber/hybrid filler composites</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1516-14392012000400028&lng=en&nrm=iso&tlng=en The surface properties of the OSW and NLS are measured with the dynamic contact-angle technique. The x-ray photoelectron spectroscopy (XPS) of the OSW reveals that the OSW possesses various reactive functional groups namely hydroxyl groups (OH). Hybrid filler from NLS and OSW were incorporated into carboxylated nitrile rubber (XNBR) to produce XNBR hybrid composites. The reaction of OH groups from the OSW with COOH of the XNBR is checked by attenuated total reflectance spectra (ATR-IR) of the composites. The degree of curing ΔM (maximum torque-minimum torque) as a function of hybrid filler as derived from moving die rheometer (MDR) is reported. The stress-strain behavior of the hybrid composites as well as the dynamic mechanical thermal analysis (DMTA) is studied. Bonding quality and dispersion of the hybrid filler with and in XNBR are examined using scanning-transmission electron microscopy (STEM in SEM). <![CDATA[<b>Mechanical properties of recycled PET fibers in concrete</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1516-14392012000400029&lng=en&nrm=iso&tlng=en Fiber-reinforced concrete represents the current tendency to apply more efficient crack-resistant concrete. For instance, polyethylene terephthalate (PET) is a polyester polymer obtained from recyclable bottles; it has been widely used to produce fibers to obtain cement-based products with improved properties. Therefore, this paper reports on an experimental study of recycled-bottle-PET fiber-reinforced concrete. Fibers with lengths of 10, 15 and 20 mm and volume fractions of 0.05, 0.18 and 0.30% related to the volume of the concrete were used. Physical and mechanical characterization of the concrete was performed, including the determination of compressive strength, flexural strength, Young's modulus and fracture toughness as well as analysis using mercury intrusion porosimetry (MIP) and scanning electron microscopy (SEM). Flexure and impact tests were performed after 28 and 150 days. No significant effect of the fiber addition on the compressive strength and modulus of elasticity was observed. However, the Young's modulus was observed to decrease as the fiber volume increased. At 28 days, the concrete flexural toughness and impact resistance increased with the presence of PET fibers, except for the 0.05 vol.% sample. However, at 150 days, this improvement was no longer present due to recycled-bottle-PET fiber degradation in the alkaline concrete environment, as visualized by SEM observations. An increase in porosity also has occurred at 365 days for the fiber-reinforced concrete, as determined by MIP. <![CDATA[<b>Effects of processing parameters on microstructure and ultimate tensile strength of thixoformed AM60B magnesium alloy</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1516-14392012000400030&lng=en&nrm=iso&tlng=en The effects of processing parameters, such as the punch speed, reheating duration and reheating temperature, on microstructure and ultimate tensile strength (UTS) of thixoformed AM60B magnesium alloy have been investigated. The results indicate that low punch speed, short reheating duration or low reheating temperature often produces the defect of cold shuts or shrinkage porosities. On the contrary, gas pores can easily form. In addition, the reheating duration or temperature also has obvious effects on the primary particle size, fraction and morphology. The three parameters can significantly affect the UTS due to their effects on the formation of pores (cold shuts, shrinkage porosities and gas pores). But they can not alter the fracture path during tensile testing and the path is always along the secondarily solidified structures between the primary particles. The effect of pore amount on the UTS is lager than that of the primary particle size, fraction or morphology. In view of their effects on the microstructure compactness and the resultant UTS, the optimized parameters are reheating for 130 minutes at 610 °C and punch speed of 3 m/s. <![CDATA[<b>Thermoplastic polyurethane synthesis using POSS as a chain modifier</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1516-14392012000400031&lng=en&nrm=iso&tlng=en In this study, thermoplastic polyurethanes (TPUs) were synthesized using the one-shot process in solution. To obtain the samples n-phenylaminopropyl polyhedric oligomeric silsesquioxane (POSS) was added as a chain modifier during the synthesis in four different amounts. The samples were characterized by infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and capillary rheometry. FTIR confirm the TPU attainment due the absence of the band at ~2253 cm-1 suggesting a complete conversion of the isocyanate terminations. The TGA showed that incorporation of POSS decreased the rate of mass loss of TPU under isothermal conditions. The flexible phase showed an enhanced stability to temperature, probably due to increased phase separation between the rigid and flexible domains. The DSC showed that incorporation of 0.4 wt. (%) of POSS increased the glass transition temperature of the flexible phase. Moreover, addition of POSS modified the melting behaviour, providing samples with a higher melting enthalpy compared to neat TPU as a consequence of the formation of larger crystals. The capillary rheometry analysis revels that the POSS addition showed a clear tendency toward higher intrinsic viscosities as the amount of POSS was increased.