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As one of the lightest metallic materials, magnesium is considered as a promising replacement for aluminum, titanium, and steel. However, lightweight energy-saving magnesium and magnesium alloys suffer from poor ductility (5% to 8%) due to their hexagonal closed packed crystalline structure and a limited number of easily activated independent slip systems at room temperature. This creates some challenges for magnesium and its alloys for various industrial applications. One technique to improve both strength and ductility, without any tangible weight penalty, of magnesium and its alloys is to add nanosize (less than 100 nm) reinforcements (e.g. nanoparticles) to the matrix as creat so-called magnesium nanocomposites. Various nano-reinforcing materials including oxides (Al2O3, TiO2, Y2O3, ZnO, ZrO2), carbides (SiC, B4C, TiC), nitrides (BN, AlN, TiN), borides (TiB2, SiB6, ZrB2), and carbonaceous materials (carbon nanotube and carbon nanoplatelets). The volume fraction of these nano-size reinforcing structures are normally less than 3 vol.% to avoid the clustering (agglomeration) of the nano-reinforcements which can adversely affect strength and ductility. That is, depending on the matrix (magnesium and magnesium alloys) and the nanosize reinforcement, there is an optimum volume fraction beyond which the properties (strength and ductility) would decrease. Though various aspects of the microstructure/mechanical property/manufacturing process of the magnesium nanocomposites have been studied so far, the failure and, in particular, fracture of these materials have not been yet classified properly. Investigating the fracture of magnesium nanocomposites, including the type of fracture, fracture mechanism, the effect of the nano-reinforcements on the fracture of Mg nanocomposites, enables the researchers to assess the role of nanosized reinforcement on the modes of failure and mechanical properties. This paper aims at providing a review of the fractography of compressive and tensile tests of nanocomposites Mg, classifying fractography by all kinds of reinforcement and working conditions of the Mg nanocomposite. Also, the effect of test temperature, cyclic loading, and heat treatment on the fracture of magnesium -matrix nanocomposite is discussed thoroughly. Among various nanoparticles and according to the review of the available literature, Al, Y2O3, and NiTi can significantly improve the tensile strength of the Mg matrix while ZnO and Sm2O3 reinforced nanocomposites show higher compressive yield stress.

International audience; Natural structural materials frequently consist of multimaterial nanocomposites with complex superstructure giving rise to exceptional mechanical properties, but also commonly preventing access to their synthetic reproduction. Here we present the spin-assisted layer-by-layer assembly of anisotropic wood-inspired films composed of anionic cellulose nanofibrils and cationic poly(vinyl amine) possessing a tensile strength that exceeds that of the wood from which the fibers originate. The degree of orientation of the nanofibrils was studied by atomic force microscopy and depends strongly on the distance from the center of the spun surface. The nanofibrils are preferentially aligned in the direction of the shear flow, and consequently, the mechanical properties of such films differ substantially when measured parallel and perpendicular to the fibril orientation direction. For enabling a diversity of bioinspired applications including sensing, packaging, electronics, or optics, the preparation of nanocomposite materials and devices with anisotropic physical properties requires an extreme level of control over the positioning and alignment of nanoscale objects within the matrix material.

The aim of this study was to fabricate a new kind of hybrid fabric composites with the cross-linked electrospun poly(vinyl butyral) (PVB) composite nanofibres. The experiments were performed with the 10 wt.% PVB/ethanol solution for electrospinning where the modified silica nanoparticles (mSiO(2)), the oxidised single-walled carbon nanotubes (o-SWCNT) and the o-SWCNT/mSiO(2) hybrid nanoparticles were added to the solution. The electrospun fibres were crosslinked with glutaraldehyde (GA) afterwards in order to reinforce the composite structure by bonding to the p-aramid fabrics. The chemical and thermo-mechanical properties of the hybrid fabric composites were evaluated. The greatest improvement in thermo-mechanical properties was achieved by the sample which contained the cross-linked PVB fibres with the o-SWCNT/mSiO(2) hybrid nanoparticles.

Biopolymers such as gelatin (Gel) and cellulose nanofibrils (CNF) have many of the essential requirements for being used as scaffolding materials in tissue regeneration; biocompatibility, surface chemistry, ability to generate homogeneous hydrogels and 3D structures with suitable pore size and interconnection, which allows cell colonization and proliferation. The purpose of this study was to investigate whether the mechanical behaviour of the Gel matrix can be improved by means of functionalization with cellulose nanofibrils and proper cross-linking treatments. Blending processes were developed to achieve a polymer nanocomposite incorporating the best features of both biopolymers: biomimicry of the Gel and structural reinforcement by the CNF. The designed 3D structures underline interconnected porosity achieved by freeze-drying process, improved mechanical properties and chemical stability that are tailored by CNF addition and different cross-linking approaches. In vitro evaluations reveal the preservation of the biocompatibility of Gel and its good interaction with cells by promoting cell colonization and proliferation. The results support the addition of cellulose nanofibrils to improve the mechanical behaviour of 3D porous structures suitable as scaffolding for tissue regeneration.

Made available in DSpace on 2018-11-26T17:45:10Z (GMT). No. of bitstreams: 0 Previous issue date: 2018-01-30 Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) The use of cellulose nanofibers as reinforcement may contribute for improving particle packing and decrease the crack growth rate of composites at nanoscale. Additionally, the high specific surface area of cellulose nanofibers contributes to improve the adhesion between the cement particles. Thus, the aim of this work was the study the performance of hybrid composites reinforced with 8% pulp and 1% nanofibrillated cellulose compared to composites reinforced with only 9% of pulp produced by the extrusion process. The accelerated aging process by means of 200 wet and dry cycles was carried out to assess composite degradation. In the hybrid composites the nanofibrillated cellulose improved the mechanical behavior compared to the composite without nanofiber. This improvement may be associated with greater adherence between the nanofibrils and the cement matrix. After accelerated ageing, the composites with and without nanofibers showed no reduction in mechanical performance, which is attributed to the lower alkalinity provided by the accelerated carbonation. Therefore, the nanofibrillated cellulose showed to be a promising material for use as nanoreinforcement of the extruded hybrid cement-based composites. (C) 2017 Elsevier Ltd. All rights reserved. Univ Sao Paulo, Fac Anim Sci & Food Engn, Dept Biosyst Engn, Duque de Caxias Norte St 225, BR-13630000 Pirassununga, SP, Brazil Sao Paulo State Univ, Fac Engn, Dept Mat & Technol, Ariberto Pereira da Cunha 333, BR-12516410 Guararingueta, SP, Brazil Sao Paulo State Univ, Fac Engn, Dept Mat & Technol, Ariberto Pereira da Cunha 333, BR-12516410 Guararingueta, SP, Brazil FAPESP: 2011/01128-5 FAPESP: 2012/51467-3 FAPESP: 03823/2013 FAPESP: 2015/21079-0 CAPES: 03884/2014 CNPq: 142082/2011-2

Poly(lactic acid) (PLA) was reactively blended with thermoplastic cassava starch (TPCS) and functionalized with commercial graphene (GRH) nanoplatelets in a twin-screw extruder, and films were produced by cast-film extrusion. Reactive compatibilization between PLA and TPCS phases was reached by introducing maleic anhydride and a peroxide radical during the reactive blending extrusion process. Films with improved elongation at break and toughness for neat PLA and PLA-g-TPCS reactive blends were obtained by an addition of GRH nanoplatelets. Toughness of the PLA-g-TPCS-GRH was improved by ~900% and ~500% when compared to neat PLA and PLA-g-TPCS, respectively. Crack bridging was established as the primary mechanism responsible for the improvement in the mechanical properties of PLA and PLA-g-TPCS in the presence of the nanofiller due to the high aspect ratio of GRH. Scanning electron microscopy images showed a non-uniform distribution of GRH nanoplatelets in the matrix. Transmittance of the reactive blend films decreased due to the TPCS phase. Values obtained for the reactive blends showed ~20% transmittance. PLA-GRH and PLA-g-TPCS-GRH showed a reduction of the oxygen permeability coefficient with respect to PLA of around 35% and 50%, respectively. Thermal properties, molecular structure, surface roughness, XRD pattern, electrical resistivity, and color of the films were also evaluated. Biobased and compostable reactive blend films of PLA-g-TPCS compounded with GRH nanoplatelets could be suitable for food packaging and agricultural applications. Fil: Bher, Anibal Ricardo. Universidad Nacional de San Martín; Argentina. Michigan State University; Estados Unidos. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Nordeste. Instituto de Materiales de Misiones. Universidad Nacional de Misiones. Facultad de Ciencias Exactas Químicas y Naturales. Instituto de Materiales de Misiones; Argentina Fil: Unalan, Ilke Uysal. Izmir Ekonomi Universitesi; Turquía. Michigan State University; Estados Unidos Fil: Auras, Rafael. Michigan State University; Estados Unidos Fil: Rubino, Maria. Michigan State University; Estados Unidos Fil: Schvezov, Carlos Enrique. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Nordeste. Instituto de Materiales de Misiones. Universidad Nacional de Misiones. Facultad de Ciencias Exactas Químicas y Naturales. Instituto de Materiales de Misiones; Argentina

The physical and mechanical properties of the six samples of polyurethane/p-aramid multiaxial fabric forms (Kolon fabrics) were analyzed by high speed impact tester. The samples were impregnated with 10 wt.% poly (vinyl butyral) (PVB)/ethanol solution and modified with γ-aminopropyltriethoxysilane (AMEO silane)/ethanol solution. Unmodified silica (SiO2) nanoparticles, tungsten disulfide (WS2) nanoparticles and multiwalled carbon nanotubes (MWCNT) were used as reinforcement for multiaxial Kolon fabrics. The SiO2/PVB mass fraction was 10 wt.%, while the WS2/PVB and MWCNT/PVB mass fractions were the same - 1 wt.%. The results revealed the increase of the maximal impact force and the total energy absorbed for all the samples compared to the unmodified Kolon fabric sample and the application possibilities of these materials for the antiballistic protection. Fizička i mehanička svojstva šest uzoraka poliuretan/p-aramidnih multiaksijalnih tkanina (Kolon lamina) su analizirana pomoću impakt tester uređaja. Uzorci su impregnisani sa 10 mas.% rastvorom poli (vinil butiral)(PVB)/etanol i modifikovani 2 mas.% rastvorom γ-aminopropiltrietoksisilana (AMEO silan) u etanolu. Nemodifikovane silika (SiO2) nanočestice, volfram disulfid (WS2) nanočestice i višeslojne ugljenične nanocevi (MWCNT) su korišćene kao ojačanja multiaksijalnih Kolon lamina. Maseni udeo ojačanja SiO2/PVB je bio 10 mas.%, dok su maseni udeli WS2/PVB i MWCNT/PVB bili 1 mas.%. Rezultati pokazuju povećanje maksimalne udarne sile i ukupne apsorbovane energije kod svih uzoraka u odnosu na nemodifikovani Kolon uzorak i mogućnosti primene ovih materijala za antibalističku zaštitu.