Effect of fiber orientation on the shear behavior of glass fiber/epoxy composites

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Processing and characterization of ablative composites used in rocket motors

The main objective of this research work was to obtain two formulations of ablative composites. These composites are also known as ablative structural composites, for applications in atmospherically severe conditions according to the high-temperature, hot gaseous products flow generated from the burning of solid propellants. The formulations were manufactured with phenolic resin reinforced with chopped carbon fiber. The composites were obtained by the hot compression molding technique. Another purpose of this work was to conduct the physical and chemical characterization of the matrix, the reinforcements and the composites. After the characterization, a nozzle divergent of each formulation was manufactured and its performance was evaluated through the rocket motor static firing test. According to the results found in this work, it was possible to observe through the characterization of the raw materials that phenolic resins showed peculiarities in their properties that differentiate one from the other, but did not exhibit significant differences in performance as a composite material for use in ablation conditions. Both composites showed good performance for use in thermal protection, confirmed by firing static tests (rocket motor). Composites made with phenolic resin and chopped carbon fiber showed that it is a material with excellent resistance to ablation process. This composite can be used to produce nozzle parts with complex geometry or shapes and low manufacturing cost.

Structural and functional characterization of barium zirconium titanate/epoxy composites

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Bacterial cellulose-hydroxyapatite composites with osteogenic growth peptide (OGP) or pentapeptide OGP on bone regeneration in critical-size calvarial defect model

This study aimed to evaluate the potential of bacterial cellulose-hydroxyapatite (BC-HA) composites associated with osteogenic growth peptide (OGP) or pentapeptide OGP(10–14) in bone regeneration in critical-size calvarial defects in mice. In this study, the BC-HA, BC-HA-OGP, and BC-HA-OGP(10–14) membranes were analyzed at 3, 7, 15, 30, 60, and 90 days. In each period, the specimens were evaluated by micro-computed tomography (µCT), descriptive histology, gene expression of bone biomarkers by qPCR and VEGFR-2 (vascular endothelial growth factor) quantification by ELISA. Three days post-operative, Runx2, Tnfrsf11b and Bglap bone biomarkers were upregulated mainly by BC-HA OGP and BC-HA OGP(10–14) membranes, suggesting an acceleration of the osteoblast differentiation/activity with the use of these biomaterials. At 60 and 90 days, a high percentage of bone formation was observed by µCT for BC-HA and BC-HA OGP(10–14) membranes. High expression of some bone biomarkers, such as Alpl, Spp1, and Tnfrsf11b, was also observed for the same membranes on days 60 and 90. In conclusion, the BC-HA membrane promoted a better bone formation in critical-size mice calvarial defects. Nevertheless, incorporation of the peptides at the concentration of 10−9 mol L−1 did not improve bone regeneration potential in the long-term.

Effect of staining agents on color change of composites

Composite resins are materials that can present color changing when exposed to pigments. Objective: The aim of this study was to evaluate, in vitro, the color changing of composites after immersion in different substances for different periods. Material and methods: Two microhybrid composite resins: Charisma (Heraeus – Kulzer) and Opallis (FGM) were used. Red wine and acai pulp were also used as immersion medium. For this study, 32 specimens with 10 mm of diameter and 2 mm of thickness were used, divided into 4 groups: Group 1 – Opallis composite immersed in red wine solution; Group 2 – Opallis composite immersed in acai berry pulp solution; Group 3 – Charisma composite immersed in red wine solution; Group 4 – Charisma composite immersed in acai berry pulp solution. The specimens were evaluated in the following time periods: T0 – baseline, T1 – 24 hours, T2 – 48 hours, T3 – 72 hours and T4 – 96 hours. For the assessment of staining, a spectrophotometer for colorimetry was used (Color Guide 45 / 0, PCB 6807 BYK-Gardner Gerestsried GmBH, Germany), and the values obtained were transferred to a computer and recorded according to CIELAB system. Results: The data were evaluated using Kruskal- Wallis non-parametric tests with the following mean values for the immersion periods of 24, 48, 72 and 96 hours, respectively: G1 – 7.35, 7.84, 9.04,10.48; G2 – 2.92, 4.15, 4.30, 4.64; G3 – 3.14, 7.35, 8.13, 8.43, G4 – 4.49, 5.99, 6.92, 6.76. Conclusion: Red wine showed a higher tendency toward altering the composite color than acai berry pulp. In addition, no significant difference was found concerning to the behavior of the two composite resins. Concerning to the immersion time periods, significant differences were only observed among the groups in the 24 hour time period.

Fluorescence Level of Composites Assessed by Computer Processing of Digital Images - ScanWhite

The human dentition is naturally translucent, opalescent and fluorescent. Differences between the level of fluorescence of tooth structure and restorative materials may result in distinct metameric properties and consequently perceptible disparate esthetic behavior, which impairs the esthetic result of the restorations, frustrating both patients and staff. In this study, we evaluated the level of fluorescence of different composites (Durafill in tones A2 (Du), Charisma in tones A2 (Ch), Venus in tone A2 (Ve), Opallis enamel and dentin in tones A2 (OPD and OPE), Point 4 in tones A2 (P4), Z100 in tones A2 ( Z1), Z250 in tones A2 (Z2), Te-Econom in tones A2 (TE), Tetric Ceram in tones A2 (TC), Tetric Ceram N in tones A1, A2, A4 (TN1, TN2, TN4), Four seasons enamel and dentin in tones A2 (and 4SD 4SE), Empress Direct enamel and dentin in tones A2 (EDE and EDD) and Brilliant in tones A2 (Br)). Cylindrical specimens were prepared, coded and photographed in a standardized manner with a Canon EOS digital camera (400 ISO, 2.8 aperture and 1/ 30 speed), in a dark environment under the action of UV light (25 W). The images were analyzed with the software ScanWhite©-DMC/Darwin systems. The results showed statistical differences between the groups (p < 0.05), and between these same groups and the average fluorescence of the dentition of young (18 to 25 years) and adults (40 to 45 years) taken as control. It can be concluded that: Composites Z100, Z250 (3M ESPE) and Point 4 (Kerr) do not match with the fluorescence of human dentition and the fluorescence of the materials was found to be affected by their own tone.

Roughness and morphology of composites: influence of type of material, fluoride solution, and time

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Effect of thermocycling on roughness of nanofill, microfill and microhybrid composites

Objective. This study aimed to investigate the surface roughness of composite resins subjected to thermal cycles procedure. Materials and methods. Two microfill, four microhybrid and four nanofill composites were used. The surface roughness (Ra) was initially measured in a profilometer using a cut-off 0f 0.25 mm, after 3000 and 10,000 thermal cycles. Data were subjected to ANOVA and Fischer's test (alpha = 0.05). Results. Overall, 3000 thermal cycles increased the surface roughness values for all materials and there was a trend in all groups to decrease the roughness after 10,000 thermal cycles. Conclusions. The composition of material, including the type of organic matrix, could be more relevant to roughness maintenance over time than the general behavior of composites based on particles fillers. The maintenance of smooth surface in resin-based composite restorations is totally dependent of organic composition of the material.

Repair of composites: Effect of laser and different surface treatments

Objectives: This study investigated the repairs of resin composite restorations after using different surface treatments.Design: Eighty four truncated cones of Filtek Z350 were prepared and thermo-cycled (20,000 cycles). Surfaces were roughened with diamond bur and etched with 37% phosphoric acid. Those cones were divided into 7 groups (N=12): 1) Prime&Bond 2.1; 2) aluminum oxide sandblasting+Prime&Bond 2.1; 3) Er:YAG laser treatment+Prime&Bond 2.1; 4) 9.6% hydrofluoric acid for 2 min-Fsilane coupling agent.; 5) silane coupling agent; 6) auto-polymerized acrylic monomer+Prime&Bond 2.1; 7) Adper Scothbond SE. Teflon device was used to fabricate inverted truncated cones of repair composite over the surface-treated. The bonded specimens were stressed to failure under tension. The data were analyzed with oneway ANOVA and Tukey tests.Results: Mean repair strengths (SD, in MPa) were, Group-2: 18.8a; Group-1: 18.7a; Group-6: 13.4ab; Group-7: 9.5bc; Group-3: 7.5bcd; Group-4: 5.2cd; Group-5: 2.6d.Conclusions: The use of diamond bur and a conventional adhesive and the use of aluminum oxide sandblasting prior to adhesive provided a simple and cost-effective solutions to composite repair. Er:YAG laser, silane alone, 9.6% hydrofluoric acid plus silane or a self-etching adhesive results in inferior composite repair strengths. (C) 2015 Elsevier Ltd. All rights reserved.

Non-conventional cement-based composites reinforced with vegetable fibers: a review of strategies to improve durability

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Electrical and Thermal study of carbon nanotubes reinforced poly (phenylene sulfide) nanostructured composites

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Vegetal fibers in polymeric composites: a review

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Monitoring the process of densification of 3D and 4D (tridirectional and tetradirectional) carbon/carbon composites

Carbon fiber reinforced carbon composites can be made by iterative liquid impregnation or gas phase carbon deposition routes. In both cases, at the final processing stage the carbon fiber is embedded in carbon matrix which results in unique properties such as low density, high thermal conductivity and thermal shock resistance, low thermal expansion and high modulus, in relation to other refractory materials. In the present study assembled three-directional and four-directional preforms, having 50% volume of pores, were densified by iterative cycles of thermoset resin impregnation followed by pyrolysis under inert atmosphere, until appropriate densities were achieved. The thermoset resin is converted in a carbon matrix during pyrolysis. The iterative manufacturing process of the carbon fiber reinforced carbon composites is evaluated by means of nondestructive techniques based on X-ray computed tomography and electrical resistivity. X-ray computed tomography gives a general mapping view of the filling pores of the preforms which impacts results of the electrical resistivity. After six processing cycles and heat treatments up to 2000?, the final densities of the three-directional and four-directional carbon fiber reinforced carbon composites were 1.16g/cm(3) and an electrical resistivity of approximate to 0.07m. The configuration of preforms, three-directional or four-directional, did not alter the densification profile, in terms of increasing density and reducing porosity during the processing cycles.

Thermal degradation and lifetime estimation of poly(ether imide)/carbon fiber composites

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Influence of water immersion and ultraviolet weathering on mechanical and viscoelastic properties of polyphenylene sulfide-carbon fiber composites

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)