The surface finish of thermally aged carbon fibre reinforced composites using E-glass as a surface barrier

This work investigated the effect of woven E-glass mass (25 g/m2, 50 g/m2, 85 g/m2, 135 g/m2) on the painted surface finish of various thermoset (EPIKOTETM RIM935, EPIKOTETM 04434, Ultratec LpTM ES300, Ultratec LpTM SPV6035) carbon fibre composite laminates, before and after aging at 95 °C for 168 h. The as-moulded laminate surfaces were evaluated using surface profilometry techniques and the painted and aged surfaces were evaluated using a wave-scan distinctness of image (DOI) instrument. It was found that the 25 g/m2 E-glass surface layer assisted with reducing the roughness of the as-moulded surfaces and the long-term waviness of the painted surfaces due to the increase in resin-richness at the surface. The EPIKOTETM 04434 resin system that contained diglycidyl ether of bisphenol F (DGEBF) epoxy had the least change in long-term waviness with thermal aging due to the rigid fluorene-based backbone in comparison to the diglycidyl ether of bisphenol A (DGEBA) systems.

Oil-spill cleanup: the influence of acetylated curaua fibers on the oil-removal capability of magnetic composites

A magnetic resin based on cardanol, furfural, and curaua fibers was prepared and characterized. The material could be used in oil-spill cleanup processes, because of its aromatic/aliphatic balance. The resin was prepared through bulk polycondensation of cardanol and furfural in the presence of curaua fibers and maghemite nanoparticles. Hydrophobicity of the curaua fibers was improved by acetylation, increasing the oil-absorbing capability of the composites. The obtained magnetic composites were studied by Fourier-transform infrared spectroscopy, X-ray diffraction, and thermogravimetric analysis. Degree of cure, magnetic force, and oil-removal capability tests were also performed. The results show that the composites possess an elevated cure degree in addition to a considerable magnetic force. The materials exhibit a good oil removal capability in the presence of a magnetic field, which is improved by the use of acetylated curaua. In the best case, the composite filled with maghemite and curaua can remove 12 parts of oil from water.

Processing and hygrothermal effects on viscoelastic behavior of glass fiber/epoxy composites

Fiber reinforced epoxy composites are used in a wide variety of applications in the aerospace field. These materials have high specific moduli, high specific strength and their properties can be tailored to application requirements. In order to screening optimum materials behavior, the effects of external environments on the mechanical properties during usage must be clearly understood. The environmental action, such as high moisture concentration, high temperatures, corrosive fluids or ultraviolet radiation (UV), can affect the performance of advanced composites during service. These factors can limit the applications of composites by deteriorating the mechanical properties over a period of time. Properties determination is attributed to the chemical and/or physical damages caused in the polymer matrix, loss of adhesion of fiber/resin interface, and/or reduction of fiber strength and stiffness. The dynamic elastic properties are important characteristics of glass fiber reinforced composites (GRFC). They control the damping behavior of composite structures and are also an ideal tool for monitoring the development of GFRC's mechanical properties during their processing or service. One of the most used tests is the vibration damping. In this work, the measurement consisted of recording the vibration decay of a rectangular plate excited by a controlled mechanism to identify the elastic and damping properties of the material under test. The frequency amplitude were measured by accelerometers and calculated by using a digital method. The present studies have been performed to explore relations between the dynamic mechanical properties, damping test and the influence of high moisture concentration of glass fiber reinforced composites (plain weave). The results show that the E' decreased with the increase in the exposed time for glass fiber/epoxy composites specimens exposed at 80 degrees C and 90% RH. The E' values found were: 26.7, 26.7, 25.4, 24.7 and 24.7 GPa for 0, 15, 30, 45 and 60 days of exposure, respectively. (c) 2005 Springer Science + Business Media, Inc.

Mechanical behavior of natural fiber composites

The use of natural fibers as reinforcement in polymeric composites for technical applications has been a research subject of scientists during the last decade. There is a great interest in the application of sisal fiber as substitutes for glass fibers, motivated by potential advantages of weight saving, lower raw material price, and ecological advantages of using green resources which are renewable and biodegradable.Castor oil, a triglyceride vegetable that has hydroxyl groups, was reacted with 4,4' diphenylmethane diisocyanate (MDI) to produce the polyurethane matrix. Woven sisal fibers were used untreated and thermal treated at 60 C for 72h, and the composites were processed by compression molding.The present work study tensile behavior at four composites: dry sisal/polyurethane, humid sisal/polyurethane, dry sisal/phenolic and humid sisal/phenolic resin. The moisture content influences of sisal fibers on the mechanical behaviors were analyzed.Experimental results showed a higher tensile strength for the sisal/phenolic composites followed by sisal/polyurethane, respectively. In this research, sisal composites were also characterized by scanning electron microscopy. (C) 2011 Published by Elsevier Ltd. Selection and/or peer-review under responsibility of ICM11

Influence of voids on the flexural resistance of the NCF/RTM6 composites

A major difficulty to achieve maximum weight savings in the manufacture of composite structural components, is the tendency of these materials have the formation of voids and cracks in the interior and surface components. In aeronautical applications, controlling the volume fraction of fibers, resins and empty the components of composite is very hard. In this work, composites of epoxy matrix RTM6 reinforced with NCF (non crimp fabric carbon) processed by resin transfer molding (RTM) were characterized for porosity (P-ap) and density (rho(ad)). We used a method based on Archimedes' principle (ASTM C830) and the technique of helium pycnometer. The porosity values were compared with those determined by acid digestion (ASTM D3171). The mechanical properties of processed composites was evaluated by testing on the performing flexural and the results were correlated with the porosity value. All techniques tested to determine void content are satisfactory. The differents results can be justified for heterogeneous void distribution on laminate and differences among techniques characteristics. (C) 2011 Published by Elsevier Ltd. Selection and/or peer-review under responsibility of ICM11

Determination of the photoinduced birefringence and of the refractive index by Brewster method of epoxy resin doped with CdS

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Effect of Artificial Aging on the Roughness and Microhardness of Sealed Composites

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

Effect of different adhesive systems on microleakage in class II composite resin restorations

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

Clinical and microbiological performance of resin-modified glass-ionomer liners after incomplete dentine caries removal

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

Streptococcus mutans Biofilm Adhesion on Composite Resin Surfaces After Different Finishing and Polishing Techniques

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

Effects of Self-Etching Adhesive Systems Used in the Dental Modelling Technique on the Cohesive Strength of Composite Resin

This study evaluated the cohesive strength of composite using self-etching adhesive systems (SE) in the lubrication of instruments between layers of composite. The specimens were made by using a Teflon (R) device. SE were used at the interface to lubricate the instruments: Group 1(G1) - control group, no lubricant was used; Group 2(G2) -Futurabond (R) M; Group 3(G3) - Optibond (R) All-In-One; Group 4(G4) - Clearfil (R) SE Bond; Group 5(G5) - Futurabond (R) NR; Group 6(G6) - Adper (R) SE Plus; Group 7(G7) - One Up Bond (R) F. Specimens were submitted to the tensile test to evaluate the cohesive strength. Data were submitted to the ANOVA and Tukey tests. ANOVA showed a value of p = 0.00. The average means (SD): G2 = 11.33(+/-3.44) a, G3 = 15.36(+/-4.06) ab, G4 = 18.9(+/-4.72) bc, G7 = 19.62(+/-4.46) bc, G5 = 21.02(+/-5.09) bc, G6 = 23.39(+/-4.17) cd, and G1 = 28.49(+/-2.89) d. All SE decreased the cohesive strength of the composite, except for Adper (R) SE Plus.

Microtensile bond strengths and scanning electron microscopic evaluation of self-adhesive and self-etch resin cements to intact and etched enamel

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

Preparation and bactericidal effect of composites based on crosslinked copolymers containing silver nanoparticles

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Adhesives with different pHs: Effect on the MTBS of chemically activated and light-activated composites to human dentin

Purpose: To evaluate the bond strength between human dentin and composites, using two light-activated single-bottle total-etch adhesive systems with different pHs combined with chemically activated and light-activated-composites. The tested hypothesis was that the dentin bond strength is not influenced by an adhesive system of low pH, combined with chemically activated or light-activated composites. Material and Method: Flat dentin surfaces of twenty-eight human third molars were allocated in 4 groups (n=7), depending on the adhesive system: (One Step Plus-OS and Prime & Bond NT-PB) and composite (light-activated Filtek Z-100 [Z100] and chemically activated Bisfil 2B [B2B]). Each adhesive system was applied on acid-etched dentin and then one of the composites was added to form a 5 mm-high resin block. The specimens were stored in tap water (37 degrees C/24 h) and sectioned into two axes, x and y. This was done with a diamond disk under coolant irrigation to obtain beams with a cross-section area of approximately 0.8 mm(2). Each specimen was then attached to a custom-made device and submitted to the microtensile test (1 mm.min(-1)). Data were analyzed using two-way ANOVA and Tukey's tests (p<0.05). Results: the anticipated hypothesis was not confirmed (p<0.0001). The bond strengths (MPa) were not statistically different between the two adhesive systems when light-activated composite was used (OS+Z100 = 24.7 +/- 7.1(a); PB+Z100 = 23.8 +/- 5.7(a)). However, with use of the chemically activated composite (B2B), PB (7.8 +/- 3.6(b) MPa) showed significantly lower dentin bond strengths than OS (32.2 +/- 7.6(a)). Conclusion: the low pH of the adhesive system can affect the bond of chemically activated composite to dentin. on the other hand, under the present conditions, the low pH did not seem to affect the bond of light-activated composites to dentin significantly.

Polymerization of photocurable commercial dental methacrylate-based composites - Photocalorimetry study

Due to their excellent aesthetics, photopolymers have been extensively used in several dentistry applications. However, several problems are reported, e.g. low mechanical and abrasion resistance, shrinkage during polymerization, etc. Properties of the final restorations are intrinsically related to the polymerization stage, which can be conveniently studied by photocalorimetry. In the present work the polymerization reaction and the filler content of different photocurable commercial dental methacrylate-based composites were studied by means of photocalorimetry and thermogravimetry, respectively. The results show that the values of curing rate, the heat of polymerization and the filler content vary significantly from one composite to another.