Avaliação de eficiência da implantação de técnica de bioengenharia de solos

O Baixo São Francisco está em constante dinâmica hidroambiental resultante das alterações promovidas na calha do rio, representadas pelos processos geomorfológicos ou por ações antrópicas como a construção das barragens que por sua vez provocou mudanças geomorfológicas resultando na aceleração de processos erosivos nas suas margens. O objetivo deste trabalho foi avaliar a implantação de técnicas de recuperação hidroambiental com uso de bioengenharia de solos na margem do rio São Francisco. A área estudada compreende um trecho do baixo curso do rio São Francisco, localizado no município de Amparo do São Francisco, no estado de Sergipe, nordeste do Brasil, onde técnica de bioengenharia de solos, como enrocamento vegetado, foi implementada no ano de 2011. Três grupos de indicadores individuais foram selecionados que juntos contribuíram para a avaliação da Recuperação da Área Degradada relacionados à qualidade do solo, como resistência do solo à penetração e Velocidade de Infiltração Básica, à recuperação da biodiversidade como banco de sementes e a regeneração natural da área por meio de indicadores como composição e cobertura linear de espécies. A metodologia empregada contempla uma avaliação dos resultados originados do uso da biotécnica a partir da identificação da contribuição da vegetação que auxilia na contenção de taludes, uma vez que a cobertura vegetal protege a superfície do solo contra ações erosivas como o vento e a água da chuva. O reforço mecânico trazido pelo sistema radicular das plantas contra cisalhamento do solo se mostrou pela menor resistência à penetração do solo e maior Taxa de infiltração. Evaluation of efficiency of the implementation of soil bioengineering techniqueA B S T R A C TThe Lower São Francisco is in constant hydro-environmental dynamics resulting from the changes promoted in the river channel, represented by geomorphological processes or by anthropic actions such as the construction of dams that in turn caused geomorphological changes resulting in the acceleration of erosive processes on its banks. The objective of this work was to evaluate the implementation of hydroenvironmental recovery techniques using soil bioengineering on the bank of the São Francisco River. The studied area comprises a stretch of the low course of the São Francisco River, located in the municipality of Amparo do São Francisco, in the state of Sergipe, northeastearn Brazil, where soil bioengineering technique, such as vegetated rockfill, was implemented in 2011. Three groups of individual indicators were selected that together contributed to the assessment of Degraded Area Recovery related to soil quality, such as soil resistance to penetration and Basic Infiltration Speed, to the recovery of biodiversity as a seed bank and the natural area regeneration through indicators such as composition and linear species coverage. The employed methodology includes an evaluation of the results from the use of biotechnology based on the identification of the vegetation contribution that helps to contain slopes, since the vegetation cover protects the soil surface against erosive actions such as wind and rainwater. The mechanical reinforcement brought by the root system against soil shear was shown by the lower resistance to soil penetration and a higher infiltration rate.Keywords: Degraded Areas Recovery, erosion, São Francisco River

Effect of Length of Cellulose Nanofibers on Mechanical Reinforcement of Polyvinyl Alcohol

Cellulose nanofibers (CNF), representing the nano-structured cellulose, have attained an extensive research attention due to their sustainability, biodegradability, nanoscale dimensions, large surface area, unique optical and mechanical performance, etc. Different lengths of CNF can lead to different extents of entanglements or network-like structures through van der Waals forces. In this study, a series of polyvinyl alcohol (PVA) composite films, reinforced with CNF of different lengths, were fabricated via conventional solvent casting technique. CNF were extracted from jute fibers by tuning the dosage of sodium hypochlorite during the TEMPO-mediated oxidation. The mechanical properties and thermal behavior were observed to be significantly improved, while the optical transparency decreased slightly (Tr. > 75%). Interestingly, the PVA/CNF20 nanocomposite films exhibited higher tensile strength of 34.22 MPa at 2 wt% filler loading than the PVA/CNF10 (32.55 MPa) while displayed higher elastic modulus of 482.75 MPa than the PVA/CNF20 films (405.80 MPa). Overall, the findings reported in this study provide a novel, simple and inexpensive approach for preparing the high-performance polymer nanocomposites with tunable mechanical properties, reinforced with an abundant and renewable material.

Two Birds with One Stone: Preparation of 4, 4-Diaminodiphenylmethane Functionalized GO@SiO2 with Mechanical Reinforcement and UV Shielding Properties and Its Application in Thermoplastic Polyurethane

This study prepared 4,4-diaminodiphenylmethane (DDM)-functionalized graphene oxide (GO)@silica dioxide (SiO2) nano-composites through amidation reaction and low-temperature precipitation. The resulting modified GO, that was DDM−GO@SiO2. The study found that DDM−GO@SiO2 showed good dispersion and compatibility with thermoplastic polyurethane (TPU) substrates. Compared with pure TPU, the tensile strength of the TPU composites increased by 41% to 94.6 MPa at only 0.5 wt% DDM−GO@SiO2. In addition, even when a small amount of DDM−GO@SiO2 was added, the UV absorption of TPU composites increased significantly, TPU composites can achieve a UV shielding efficiency of 95.21% in the UV-A region. These results show that this type of material holds great promise for the preparation of functional coatings and film materials with high strength and weather resistance.

Mechanical Reinforcement of Polyamide 6 by Cold Hydrostatic Extrusion

This paper presents the effect of severe plastic deformation obtained using the cold hydrostatic extrusion (HE) method on the mechanical and structural properties of polyamide 6 (PA6). As a result of the plastic strain, a significant increase in ultimate tensile strength and tensile modulus were observed. Tensile strength rose by almost 500%, up to the level of 508 MPa, whereas the tensile modulus rose by about 65%. Flexural modulus increase was also observed to 3230 MPa, i.e., by approx. 160%. As a result of high plastic deformation, the structure of the polyamide 6 changed significantly, as evidenced by its fibrous nature as presented in the results of the scanning electron microscopy inspection (SEM). The surface quality of products investigated was tested using profilometry.

Magnetic Field-Assisted 3D Printing of Limpet Teeth Inspired Polymer Matrix Composite With Compression Reinforcement

Lightweight and cost-effective polymer matrix composites (PMCs) with extraordinary mechanical performance will be a key to the next generation of diverse industrial applications, such as aerospace, electric automobile, and biomedical devices. Limpet teeth made of mineral-polymer composites have been proved as nature’s strongest material due to the unique hierarchical architectures of mineral fiber alignment. Here, we present an approach to build limpet teeth inspired structural materials with precise control of geometric morphologies of microstructures by magnetic field-assisted 3D printing (MF-3DP). α-Iron (III) oxide-hydroxide nanoparticles (α-FeOOHs) are aligned by the magnetic field during 3D printing and aligned α-FeOOHs (aFeOOHs) bundles are further grown to aligned goethite-based bundles (aGBs) by rapid thermal treatment after printing. The mechanical reinforcement of aGBs in PMCs can be modulated by adjusting the geometric morphology and alignment of α-FeOOHs encapsulated inside the 3D printed PMCs. In order to identify the mechanical enhancement mechanism, physics-based modeling, simulation, and tests were conducted, and the results further guided the design of bioinspired goethite-based PMCs. The correlation of the geometric morphology of self-assembled α-FeOOHs, curing characteristics of α-FeOOHs/polymer composite, and process parameters were identified to establish the optimal design of goethite-based PMCs. The 3D printed PMCs with aGBs show promising mechanical reinforcement compared with PMCs without aGBs. This study opens intriguing perspectives for designing high strength 3D printed PMCs on the basis of bioinspired architectures with customized configurations.

Mechanical and hydrodynamic analyses of helical strake-like ridges in a glass sponge

From the discovery of functionally graded laminated composites, to near-structurally optimized diagonally reinforced square lattice structures, the skeletal system of the predominantly deep-sea sponge Euplectella aspergillum has continued to inspire biologists, materials scientists and mechanical engineers. Building on these previous efforts, in the present study, we develop an integrated finite element and fluid dynamics approach for investigating structure–function relationships in the complex maze-like organization of helical ridges that surround the main skeletal tube of this species. From these investigations, we discover that not only do these ridges provide additional mechanical reinforcement, but perhaps more significantly, provide a critical hydrodynamic benefit by effectively suppressing von Kármán vortex shedding and reducing lift forcing fluctuations over a wide range of biologically relevant flow regimes. By comparing the disordered sponge ridge geometry to other more symmetrical strake-based vortex suppression systems commonly employed in infrastructure applications ranging from antennas to underwater gas and oil pipelines, we find that the unique maze-like ridge organization of E. aspergillum can completely suppress vortex shedding rather than delaying their shedding to a more downstream location, thus highlighting their potential benefit in these engineering contexts.

Nanocarbon-Based Flame Retardant Polymer Nanocomposites

In recent years, nanocarbon materials have attracted the interest of researchers due to their excellent properties. Nanocarbon-based flame retardant polymer composites have enhanced thermal stability and mechanical properties compared with traditional flame retardant composites. In this article, the unique structural features of nanocarbon-based materials and their use in flame retardant polymeric materials are initially introduced. Afterwards, the flame retardant mechanism of nanocarbon materials is described. The main discussions include material components such as graphene, carbon nanotubes, fullerene (in preparing resins), elastomers, plastics, foams, fabrics, and film–matrix materials. Furthermore, the flame retardant properties of carbon nanomaterials and their modified products are summarized. Carbon nanomaterials not only play the role of a flame retardant in composites, but also play an important role in many aspects such as mechanical reinforcement. Finally, the opportunities and challenges for future development of carbon nanomaterials in flame-retardant polymeric materials are briefly discussed.