Key Engineering Materials Vol. 668

Abstract: The employ of vegetal fibers for textiles and composites represents a great potential in economic and social sustainable development. Some Malvaceae species are considered tropical cosmopolitans, such as from Sida genus. Several species of this genus provide excellent textile bast fibers, which are very similar in qualities to the jute textile fiber. The objective of the present study is present the physicochemical characterization of six Brazilian vegetal fibers: Sida rhombifolia L.; Sida carpinifolia L. f.; Sidastrum paniculatum (L.) Fryxell; Sida cordifolia L.; Malvastrum coromandelianum (L.) Gurck; Wissadula subpeltata (Kuntze) R.E.Fries. Respectively the two first species are from Brazilian Atlantic Forest biome and the four remaining from Brazilian Cerrado biome, despite of present in other regions of the planet. The stems of these species were retted in water at 37oC for 20 days. The fibers were tested in order to determine tensile rupture strength, tenacity, elongation, Young’s modulus, cross microscopic structure, Scanning Electronic Microscopy (SEM), regain, combustion, acid, alkali, organic solvent and cellulase effects, pH of the aqueous extract, Differential Scanning Calorimetry (DSC) and Thermogravimetric Analysis (TGA). The obtained values were compared with those from fibers of recognized applicability in the textile industry including hemp. The results are promising in terms of their employment in thermoset and thermoplastic medium resistance composites.

Abstract: To increase the durability of bamboo it is important to find an easy method to fill the micro and meso structure of the biological matrix using a nanostructural material with an anti-fungical activity. A colloidal solution of silver nanoparticle (Ag-NPs) is a dispersion of metal nanoparticle in water with a diameter between 5-100 nm. Even if the biological mechanism is not completly understood yet, Ag-NPs show a satisfactory bactericidal and antifungical activity. We present a simple and rapid production of Ag-NPs made by a sol-gel synthesis in flow mode by means of microreactor tecnology through a chemical reduction of AgNO₃ with NaBH₄ in presence of two different organic ligands: sodium/potassium tartrate and trisodium citrate. The synthesis of Ag-NPs in continuous flow compared to the batch technique allowed to reduce the time of synthesis, facilitating the reproducibility of the process and consequently obtaining NPs with more uniform physical and chemical characteristics. The microorganisms of the genus Aspergillus were used for the microbiological tests. The effect of different Ag-NPs on microbial growth was observed daily. In particular, it was shown that the response of the fungus is inversely proportional to the size of the nanoparticles, cell growth is disrupt depending on the proportion between silver and organic ligand and microbialstatic effect, especially in relation to sporulation stage was also observed.

Abstract: Sheath bamboo leaves (SBL) are potential lignocelluloses waste, aimed to produce laminated architectonic coatings. In this work was studied the surface interaction among the SBL and three types of adhesive: Polyvinyl Acetate (PVAc), Castor oil Polyurethane Adhesive bi-component (Vegetal PU), Polyester Resin unsaturated bi-component (Polyester R.); through energy surface, by measuring water absorption capacity, contact angle and digital optical microscopy. The results showed that PU vegetal decrease the water absorption capacity showing a good adhesion at SBL surfaces, in comparison with PVAc and Epoxy resin. Contact angle tests showed that castor oil based PU Resin and Epoxy resin adhesive scattering well in the surface in comparison with water based adhesive like PVAc. Apparently, in the visual and aesthetic analysis by digital optical microscopy, PVAc let see the real SBL appearance, due to low reflectance.We shall be able to publish your paper in electronic form on our web page http://www.scientific.net, if the paper format and the margins are correct.Your manuscript will be reduced by approximately 20% by the publisher. Please keep this in mind when designing your figures and tables etc.

Abstract: The necessity to restore the design specifications of a determined structure, combined with cost, weight and environmental impact reduction makes the use of high performance composite systems, involving, either synthetic or natural materials, interesting. By applying a layer of fiber reinforcement bonded with the glued laminated timber beam (Glulam) with an appropriate adhesive, a high performance composite system is obtained, resulting on a significant increase of strength and bending stiffness of the structural element that each isolated material did not have before. This paper carried out an analysis of the feasibility of use synthetic and natural fibers as alternative to structural reinforcement to laminated timber beams, made of the reforestation wood species Pinus caribea and Eucalyptus grandis that represent respectively two resistance classes of monocotyledon and dicotyledonous, exposing, through an analytical model. The numerical results obtained from the analysis of the Glulam beams reinforced with glass, carbon, Vectran^® and natural fibers such as sisal fibers, are compared among each other considering cost, weight and gain of resistance and stiffness. It is observed that for small lengths (and therefore, small cross sections), the use of Vectran® fiber is not the best option, since an equivalent resistance gain can be obtained by applying a thicker layer of glass fiber, once it possesses a lower cost and a non-significant impact on the final structure's weight. For all the other considered cases, the choice of the Vectran® fiber is very interesting, since on these situations a thicker layer of glass fiber does not provide much cost reduction and is not enough to achieve the desired strength without increasing the structure's weight significantly. Regarding the sisal fiber, it is a material that is easy to find and with a low cost in Brazil, its utilization is interesting when working with low resistance wood species. Although the gain of resistance provided by this fiber as a reinforcement material is fairly low, the desired result can be obtained by increasing the thickness of the reinforcement layer, which still keeps the cost and weight of the reinforced element much smaller than those resulting from the implementation of a thinner layer of glass fiber.

Abstract: The aim of this work was to determine the best fibrillation intensity that should be used to produce high crystalline and thermal stable microfibrillated cellulose (MFC) and nanocellulose films from C. goeldiana veneer wastes. The number of passages (cycles) of cellulose suspension tested in grinder were 10, 20, 30 and 40. Important properties to be analyzed included changes in morphology from the raw wood to the nanocellulose films, increases/decreases in cellulose crystalline index for inference on biomaterial strength, and thermal behavior changes to support conclusions on biomaterials processing and application possibilities. After chemical treatments for cellulose isolation, mechanical shearing was applied to produce cellulose nanostructures; hence nanocellulose films could be successfully produced from C. goeldiana wood wastes. Influence of more refining cycles on thermal properties, indicated higher stability for 40-cycles nanocellulose films. In general, grinder refining process decreased crystalline index of cellulose.

Abstract: Several fiber treatments can be applied to mitigate the high water absorption of vegetal fibers. Wetting and drying cycles are usually performed in the industry of paper and cellulose to reduce the volume variation of the natural fibers. This procedure stiffens the polymeric structure of the fiber-cells (process known as hornification) resulting in a higher dimensional stability. The aim of this study is to determine the effect of the hornification on the interface of natural fibers. For this purpose, cycles of wet and drying was applied on Sisal, Curaua and Jute fibers. Fiber pull-out tests were performed in embedment lengths of 25mm. Furthermore, the influence of the hornification in the fibers mechanical (under tensile loading) and microstructural (surface modifications of the fiber and changes in the fiber-cell structure) behavior were investigated. The results indicate changes on the tensile strength and strain capacity of the studied fibers, showing that morphology and chemical composition play an important role on the efficiency rate of hornification.

Abstract: Laminated bamboo is a natural composite material with cellulose fibers, parenchyma cells, and vascular bundles. The mechanical characterization of this material includes not only the determination of its strength, but also of its elastic constants. Given the anisotropic nature of the laminated material, compression tests were performed on three groups of specimens. The elastic modulus in the load direction and the Poisson's ratio were determined, and the results showed that the material's physical anisotropy causes an anisotropic mechanical behavior. The average values obtained for the elastic modulus ranged from 30044 MPa for group 1 to 265 MPa for group 2. The results of the test to determine the Poisson's ratio in compression perpendicular to the fibers, ranged from 0.013 to 0.278 whereas those obtained in compression parallel to the fibers, ranged from 0.621 to 1.506.

Abstract: The use of natural fibers has a great interest due to their damping properties, low density and moderate strength. The effect of incorporating chopped natural fibers, as disperse reinforced phase, on the dynamic or quasi-static elastic modulus of glass fiber laminates is presented. Squares of 32 cm² plain wave glass fiber prepreg with epoxy resin were used in a stacking sequence [0]4. Short length chopped (1-3 mm) natural coir fiber was placed in between of each glass fiber prepreg sheet (4) and laminates were prepared by the vacuum bag technique. The volume fraction of natural fiber was 30% (mass fraction of 10%) and samples of 254 mm length and 25.4 mm width were cut and tested at vibration conditions in a cantilever beam arrangement. The vibration frequency was measured by an accelerometer ADXL335 at z-axis, perpendicular to the sample test plane and the elastic modulus was estimated with the cantilever model. The results showed that the samples with coir fiber showed an increase in the dynamic elastic modulus value of 150 to 171% with regard to that one of glass fiber samples without fiber. Standard Test Method for Tensile Properties of Polymer Matrix Composite Materials (ASTM D3039) was also used to further characterize the thin samples (≈0.75 mm) with an Instron machine 8800, 25kN. The tensile properties obtained are lower for coir fiber samples than the ones without.

Abstract: The objective of this study was to investigate, by physical properties, the efficiency of MDP panels, compared to conventional particleboards, since MDP was considered as a raw material for the manufacture of these panels. MDP panels had the following composition: 20/60/20 face/core; a urea-formaldehyde adhesive was used, with a solids content of 55%; pH 8.42; viscosity of 420 Cp and gel time of 51 seconds. 12% of dry base resin were applied to the particles. The pressing cycle was 4 MPa, with a temperature of 160°C for a period of 8 minutes. The panels were produced with a density of 0.70g/cm3. We observed that with the exception of the physical properties of water absorption after 2 hours, the MDP showed lower physical properties (water absorption after 24 hours and thickness swelling after 2 hours and 24 hours of immersion in water) in relation to the panels conventional clusters. Thus demonstrating its superiority in relation to the physical properties of MDP compared to conventional agglomerated panels, emphasizing their use in this way.

Abstract: In recent years, there was a great offer of patented additives (enzymes) to the road market as solution to soil stabilization. However, they are many times rejected because there are no theoretical foundation to prove such uses, and also because researches themselves don’t see research opportunities. Anyway, these products has been marketed, and frequently municipalities and states waste resources by choosing for a solution that is not yet well studied. This study aims to present a methodology to solve the problems that affects the use of additives in laboratory, because his use in conventional tests do not shown efficient for these purposes. For this, it was used a portable traffic simulator, easy handling and common in pavement laboratories. It is a standardized equipment, used to assess the effect of compression and the strain characteristics of asphaltic coating layers. It was developed a set with several accessories to mold samples in the shape of tablets (380 x 50 x 10 mm), may be easily adapted to the equipment selected as simulator. The soils used for the production of the tested tablets were lateritic soils from Rio de Janeiro–RJ, and the enzymatic products were imported. A rigorous care was followed in the production of each tablet to ensure equality and, after, compare results each other. These tablets were molded and tested in order to obtain a series of experimental results, comparing the soil treated with enzymes with the soil without any kind of treatment. The study concludes, in principle, that the equipment used and the developed accessories are appropriate for this purpose and that the use of enzymes showed effective for some applications, but lacks more studies, including with the use of other types of soil to prove such effectiveness.