Search

The present study focuses on the effect of CNT nanofillers on the interlaminar static and fatigue crack propagation in carbon fiber reinforced composite laminates. Multi-walled carbon nanotubes (MWCNTs) were dispersed over the laminate interface through solvent spraying technique. The mode I fracture toughness and R curve behavior were determined first from DCB specimens. Then, the fatigue tests were performed at different stress ratios for laminates containing different contents of CNTs to determine the delamination growth rate da/dN from fatigue crack growth (FCG) curves. When FCG curves are expressed as a function of G, where G is the energy release rate, the growth curves are dependent on the R-ratio. It was found that the addition of CNTs enhances the delamination resistance in the initial part of FCG curves, i.e. low cyclic region. As the test progresses, the effect gradually diminishes making nanofillers ineffective. It is then shown that the FCG curves can be characterized when crack growth rates are expressed as a function of the crack‐driving force Δ κ ¯ used in the Hartman‐Schijve equation. Therefore, the present paper presents a methodology to account for the stress ratio effect to evaluate the crack growth rate for any given R-ratio and to obtain a valid, upper-bound FCG rate curves in CNT reinforced laminates that exhibit high degree of scatter. [ABSTRACT FROM AUTHOR]

The addition of nanoscale additions to magnesium (Mg) based alloys can boost mechanical characteristics without noticeably decreasing ductility. Since Mg is the lightest structural material, the Mg-based nanocomposites (NCs) with improved mechanical properties are appealing materials for lightweight structural applications. In contrast to conventional Mg-based composites, the incorporation of nano-sized reinforcing particles noticeably boosts the strength of Mg-based nanocomposites without significantly reducing the formability. The present article reviews Mg-based metal matrix nanocomposites (MMNCs) with metallic and ceramic additions, fabricated via both solid-based (sintering and powder metallurgy) and liquid-based (disintegrated melt deposition) technologies. It also reviews strengthening models and mechanisms that have been proposed to explain the improved mechanical characteristics of Mg-based alloys and nanocomposites. Further, synergistic strengthening mechanisms in Mg matrix nanocomposites and the dominant equations for quantitatively predicting mechanical properties are provided. Furthermore, this study offers an overview of the creep and fatigue behavior of Mg-based alloys and nanocomposites using both traditional (uniaxial) and depth-sensing indentation techniques. The potential applications of magnesium-based alloys and nanocomposites are also surveyed.

• Mechanical, corrosion behavior, biocompatibility and antibacterial activity of Mg-based metal matrix nanocomposites (MMNCs) are presented. • Different fabrication processes and post-processes treatments for MMNCs are reviewed and summarized. • Strengthening models and mechanisms for MMNCs have been proposed. • The latest development of MMNCs for biomedical and industrial applications is presented. • Creep and fatigue behavior of MMNCs using both traditional and depth-sensing indentation techniques are presented. The addition of nanoscale additions to magnesium (Mg) based alloys can boost mechanical characteristics without noticeably decreasing ductility. Since Mg is the lightest structural material, the Mg-based nanocomposites (NCs) with improved mechanical properties are appealing materials for lightweight structural applications. In contrast to conventional Mg-based composites, the incorporation of nano-sized reinforcing particles noticeably boosts the strength of Mg-based nanocomposites without significantly reducing the formability. The present article reviews Mg-based metal matrix nanocomposites (MMNCs) with metallic and ceramic additions, fabricated via both solid-based (sintering and powder metallurgy) and liquid-based (disintegrated melt deposition) technologies. It also reviews strengthening models and mechanisms that have been proposed to explain the improved mechanical characteristics of Mg-based alloys and nanocomposites. Further, synergistic strengthening mechanisms in Mg matrix nanocomposites and the dominant equations for quantitatively predicting mechanical properties are provided. Furthermore, this study offers an overview of the creep and fatigue behavior of Mg-based alloys and nanocomposites using both traditional (uniaxial) and depth-sensing indentation techniques. The potential applications of magnesium-based alloys and nanocomposites are also surveyed. [ABSTRACT FROM AUTHOR]

The aim of this research was to prepare a nanocomposite film based on Barhang (Plantago major L) seed mucilage. Zinc oxide (ZnO) and cellulose nanofiber (CNF) nanoparticles at the concentrations of 4 and 8% w/w were incorporated for improving the morphological, structural, thermal, water vapor permeability and mechanical properties of films. The F T -IR results confirmed the occurring of new interactions between nanoparticles and mucilage polysaccharides. XRD results indicated that the effect of ZnO on semi -crystalline structure of Barhang film is higher than the effect of CNF. The neat film has a smooth surface, but the roughness increased by addition of nanoparticles. According to TGA results, the thermal stability of films was affected by incorporation of nanoparticles, but the effect of CNF on improving the thermal stability of film was more than ZnO. The addition of nanoparticles at the concentration of 4% had no effect on the thickness of films but by increasing to 8%, the thickness increased. Moisture content and moisture absorption of films was also decreased significantly by incorporation of nanoparticles. The water vapor permeability of films was dependent on the concentration of nanoparticles and at 4%, it decreased significantly but at 8% concentration, the permeability increased again due to the aggregation of nanoparticles and their hydrophilic nature. The water contact angle of films’ surface increased by addition of ZnO but the CNF caused to decrease this value due to its hydrophilicity. The effect of CNF on improving the mechanical properties of films was better than ZnO. The CNF had the most effect on increasing tensile strength, elastic modulus and elongation to break. The effect of CNF on the improving of the barrier and mechanical properties of Barhang seed mucilage based films was more than ZnO due to its better compatibility. In general, this research indicated that the Barhang seed mucilage based film incorporated with organic and inorganic nanoreinforcements, has desired physicochemical properties and can be introduced as a suitable candidate for food packaging applications. [ABSTRACT FROM AUTHOR]

The present study is focused on the nanoreinforcement of carbon fiber reinforced polymer laminates to evaluate its effect on delamination growth in double cantilever beam specimen. Multi‐walled carbon nanotubes were sprayed on the laminate interface using air‐brush spraying technique. Three nanofiller contents of 0.05 wt.%, 0.1 wt.%, and 0.5 wt.% were examined to evaluate the mode I fracture toughness (GIC) in a double cantilever beam specimen and the results were compared with the base laminate (0.0 % carbon nanotubes). The average mode I fracture toughness of composite laminates increased from 180.6 J/m2 to 270.92 J/m2 due to the addition of 0.05 wt.% multi‐walled carbon nanotubes, and to 268.27 J/m2 for 0.1 wt.% multi‐walled carbon nanotubes. Mechanisms for the increase in GIC of the nanofiller reinforced laminates are discussed based on the experimental results and microscopic study of fractured specimen surfaces from scanning electron microscopy. Energy dissipation from carbon nanotube bridging ahead of the crack front is the major toughening mechanism resulting in improved fracture toughness. Numerical simulations of delamination growth were performed as well by using virtual crack closure technique analysis in Abaqus. The R‐curve behaviour from the experiments is implemented in the finite element modeling of delamination growth to validate the effect of nanoreinforcements. [ABSTRACT FROM AUTHOR]

Cartilage repair strategies are evolving at a fast pace with technology development. Matrices that offer multifaceted functions and a full adaption to the cartilage defect are of pivotal interest. Current cartilage repair strategies face numerous challenges, mostly related to the development of highly biomimetic materials, non-invasive injectable solutions, and adequate degradation rates. These strategies often fail due to feeble mechanical properties, the inability to sustain cell adhesion, growth, and differentiation or by underestimating other players of cartilage degeneration, such as the installed pro-inflammatory microenvironment. The integration of nanomaterials (NMs) into 3D scaffolds, hydrogels and bioinks hold great potential in the improvement of key features of materials that are currently applied in cartilage tissue engineering. NMs offer a high surface to volume ratio and their multiple applications can be explored to enhance cartilage mechanical properties, biocompatibility, cell differentiation, inflammation modulation, infection prevention and even to function as diagnostic tools or as stimuli-responsive cues in these 3D structures. In this review, we have critically reviewed the latest advances in the development of nanoenabled 3D matrices - enhanced by means of NMs - in the context of cartilage regeneration. We have provided a wide perspective of the synergistic effect of combining 3D strategies with NMs, with emphasis on the benefits brought by NMs in achieving functional and enhanced therapeutic outcomes. Cartilage is one of the most challenging tissues to treat owing to its limited self-regeneration potential. Novel strategies using nanoenabled 3D matrices have emerged from the need to design more efficient solutions for cartilage repair, that take into consideration its unique mechanical properties and can direct specific cell behaviours. Here we aim to provide a comprehensive review on the synergistic effects of 3D matrices nanoenrichment in the context of cartilage regeneration, with emphasis on the heightening brought by nanomaterials in achieving functional and enhanced therapeutic outcomes. We anticipate this review to provide a wide perspective on the past years' research on the field, demonstrating the great potential of these approaches in the treatment and diagnosis of cartilage-related disorders. [Display omitted] [ABSTRACT FROM AUTHOR]

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%–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.

A resorcinol resin/water dispersion and a rubber latex are added to 1% 2,2,6,6,‐tetramethylpyperidine‐1‐oxyl (TEMPO)‐oxidized cellulose nanofibers (TEMPO‐CNFs) dispersed in water, followed by oven drying at 40 °C for 20 h to prepare a dried TEMPO‐CNF/resorcinol resin/latex rubber (DTRL) mixture with a weight ratio of 1/0.5/3. DTRL is then added to a nitrile‐butadiene rubber (NBR) or a carboxy group‐containing NBR (X‐NBR) sheet, and the mixture is kneaded by a two‐roll mill at 20–30 °C with high shear forces. The tensile strength and Young's modulus of the crosslinked DTRL/rubber composite sheets remarkably increased from 10 and 12 MPa, respectively, for the reference sheet to 24 and 82 MPa, respectively, for the DTRL/rubber composite sheets containing ≈10 vol% TEMPO‐CNFs. Scanning electron microscopy revealed that no TEMPO‐CNF agglomerates are present in the DTRL/rubber composite sheets. The tensile properties of the composite sheets are the best when a X‐NBR sheet and NBR latex are used as the matrix rubber and latex in DTRL preparation, respectively. When water‐extracted DTRL (WDTRL, mass recovery ratio ≈94%) is used in place of DTRL, the WDTRL/rubber composite sheets show sufficient water resistance, while the tensile properties are almost the same as those of the DTRL/rubber composite sheets. [ABSTRACT FROM AUTHOR]

Packaging consumes around 40% of the total plastic production. One of the most important fields with high requirements is food packaging. Food packaging products have been commonly produced with petrol polymers, but due to environmental concerns, the market is being moved to biopolymers. Poly (lactic acid) (PLA) is the most promising biopolymer, as it is bio-based and biodegradable, and it is well established in the market. Nonetheless, its barrier properties need to be enhanced to be competitive with other polymers such as polyethylene terephthalate (PET). Nanoclays improve the barrier properties of polymeric materials if correct dispersion and exfoliation are obtained. Thus, it marks a milestone to obtain an appropriate dispersion. A predispersed methodology is proposed as a compounding process to improve the dispersion of these composites instead of common melt procedures. Afterwards, the effect of the polarity of the matrix was analyzing using polar and surface modified nanoclays with contents ranging from 2 to 8% w/w. The results showed the suitability of the predispersed and concentrated compound, technically named masterbatch, to obtain intercalated structures and the higher dispersion of polar nanoclays. Finally, the mechanical performance and sustainability of the prepared materials were simulated in a food tray, showing the best assessment of these materials and their lower fingerprint.

Graphical abstract Highlights • Achieved kinetic stabilization of a cellulose nanocrystal dispersion in a UV-curable prepolymer. • Reinforcement effects seen at CNC concentrations ≤0.5 wt% of the UV-curable coating. • 154% improvement in adhesive strength in nanocomposite coatings. • 16% increase in tensile strength in nanocomposite films. Abstract Cellulose nanocrystals (CNC) at low loading levels were shown to reinforce a photocurable coating resulting in improved adhesion. A polyether polyol containing CNC at loading levels of up to 1.8 wt% was grafted with 3-isopropenyl-α,α-dimethylbenzyl isocyanate to functionalize it with a photocurable group. The nanoparticles were kinetically stabilized in the rapidly forming prepolymer of high viscosity. Photoinitiators and a difunctional reactive diluent were added to produce optically transparent coatings and free films upon irradiation by ultraviolet (UV) light. This allowed evaluation of the effects of CNC at low loading levels in a glassy polymer matrix obtained through a rapid cure system. Incorporation of CNC nanoparticles in the polymer matrix resulted in an average improvement in adhesive strength of 154% while enhancing tensile strength by an average of 16%. The technique described could be used as a new approach to reduce adhesive failure in UV-curable coatings without sacrificing their mechanical strength. [ABSTRACT FROM AUTHOR]

Abstract A fast, facile, nonhazardous, environment-friendly, and high yield process was developed for the plasma treatment of graphite particles and the production of plasma-functionalized multilayered graphene (pf-MLG). Graphite particles (< 20 μ m) were functionalized using a subatmospheric 13.56 MHz radio frequency-excited oxygen plasma followed by liquid-phase exfoliation to produce pf-MLG with a high aspect ratio (> 2585) with < 20 graphene layers. The exfoliated graphene also exhibited high dispersibility in water after plasma functionalization without the use of surfactants. The pf-MLG nanoflakes were incorporated into a cement mixture with 0.1 and 0.5 wt% pf-MLG loading. A 56% increase in compressive strength of cement mortars was achieved for the 0.5 wt% pf-MLG after 28 days curing. This is attributed to the strong interfacial interaction between graphene and the cement matrix and the promotion of hydration. The highly scalable process of pf-MLG-reinforced cement will make a positive impact on the environment, especially in the construction industry. [ABSTRACT FROM AUTHOR]

Abstract 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. Graphical abstract Unlabelled Image Highlights • The scaffolds' biodegradability is controlled exploiting the cross-linking reactions. • The role of CNF as nano-reinforcement is confirmed and discussed. • The scaffolds' performances are tailored modifying the polymeric blends. • The scaffolds are able to promote and support cell adhesion and proliferation. [ABSTRACT FROM AUTHOR]

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.

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 (mSiO2), the oxidised single-walled carbon nanotubes (o-SWCNT) and the o-SWCNT/mSiO2 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/mSiO2 hybrid nanoparticles. [ABSTRACT FROM AUTHOR]

Matrix modification of carbon fiber reinforced polymer composites with nanoparticles is an effective way to improve its matrix dominated properties. After nanoparticle modification, understanding mechanical properties is important in structural applications, and improvement of such properties can lead to the usage in the wider fields. This study aimed to investigate experimentally static and dynamic mechanical behaviors of CaCO 3 modified epoxy/carbon fiber nanocomposites. For this, we filled various amounts of CaCO 3 nanoreinforcements into the epoxy matrix, and the nanoreinforced epoxy was used to impregnate carbon fabrics (CF) by utilizing vacuum assisted resin infusion method (VARIM). The prepared fiber reinforced nanocomposites were subjected to tensile, bending and low velocity impact loadings. As a result of all experiments, the tensile strength of CF/epoxy nanocomposites increased about 48% with the addition of 2 wt% CaCO 3 nanoreinforcement. The flexural strength enhancements were also determined as 47% for the same CaCO 3 nanoreinforcement loading. Besides, by utilizing low-velocity impact tests, we revealed that the CaCO 3 nanoparticle reinforced CF/epoxy nanocomposites exhibited higher impact performances compared to neat CF/epoxy composites. The resulting fracture morphologies were examined by electron microscopy to disclose related mechanical toughening mechanisms. Based on the morphological analysis, crack pinning, crack deflection and debonding of nanoparticles were the primary reasons leading to the improvement of toughness. The authors concluded that the addition of the CaCO 3 nanoreinforcements in CF/epoxy composites has significantly influenced the mechanical and physical properties of the nanocomposites. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Development of homogenous metal matrix nanocomposites with uniform distribution of nanoreinforcement, preserved matrix nanostructure features, and improved properties, was possible by means of innovative processing techniques. In this work, Al-SiC nanocomposites were synthesized by mechanical milling and consolidated through spark plasma sintering. Field Emission Scanning Electron Microscope (FE-SEM) with Energy Dispersive X-ray Spectroscopy (EDS) facility was used for the characterization of the extent of SiC particles’ distribution in the mechanically milled powders and spark plasma sintered samples. The change of the matrix crystallite size and lattice strain during milling and sintering was followed through X-ray diffraction (XRD). The density and hardness of the developed materials were evaluated as function of SiC content at fixed sintering conditions using a densimeter and a digital microhardness tester, respectively. It was found that milling for 24 h led to uniform distribution of SiC nanoreinforcement, reduced particle size and crystallite size of the aluminum matrix, and increased lattice strain. The presence and amount of SiC reinforcement enhanced the milling effect. The uniform distribution of SiC achieved by mechanical milling was maintained in sintered samples. Sintering led to the increase in the crystallite size of the aluminum matrix; however, it remained less than 100 nm in the composite containing 10 wt.% SiC. Density and hardness of sintered nanocomposites were reported and compared with those published in the literature.

Metal and ceramic matrix composites have been developed to enhance the stiffness and strength of metals and alloys, and improve the toughness of monolithic ceramics, respectively. It is possible to further improve their properties by using nanoreinforcement, which led to the development of metal and ceramic matrix nanocomposites, in which case, the dimension of the reinforcement is on the order of nanometer, typically less than 100 nm. However, in many cases, the properties measured experimentally remain far from those estimated theoretically. This is mainly due to the fact that the properties of nanocomposites depend not only on the properties of the individual constituents, i.e., the matrix and reinforcement as well as the interface between them, but also on the extent of nanoreinforcement dispersion. Therefore, obtaining a uniform dispersion of the nanoreinforcement in the matrix remains a key issue in the development of nanocomposites with the desired properties. The issue of nanoreinforcement dispersion was not fully addressed in review papers dedicated to processing, characterization, and properties of inorganic nanocomposites. In addition, characterization of nanoparticles dispersion, reported in literature, remains largely qualitative. The objective of this review is to provide a comprehensive description of characterization techniques used to evaluate the extent of nanoreinforcement dispersion in inorganic nanocomposites and critically review published work. Moreover, methodologies and techniques used to characterize reinforcement dispersion in conventional composites, which may be used for quantitative characterization of nanoreinforcement dispersion in nanocomposites, is also presented.

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.

The morphological, structural and thermal behavior of starch nanocrystals (SNCs) extracted from waxy maize starch through an acid hydrolysis were compared with those of starch nanoparticles (SNPs) obtained through an ultrasound treatment starting from the same waxy maize starch. The SNPs were found to be completely amorphous, slightly smaller and had no surface charge, whereas the SNCs had the expected platelet-like morphology with a negative surface charge introduced as a result of the use of sulphuric acid in the acid hydrolysis step. SNCs also showed better thermal stability than SNPs in the presence of water. As a result of their platelet-like morphology, the SNCs performed better in reinforcing a polymer film. On the other hand, SNPs reduced the transparency of the nanocomposite films to a lesser extent than the SNCs due to their smaller size. [ABSTRACT FROM AUTHOR]

The potential of enhancement of superhard steel and cast iron cutting tool performance on the basis of microstuctural modifications of the tool materials is studied. Hybrid machining tools with mixed diamond and cBN grains, as well as machining tool with composite nanomodified metallic binder are developed, and tested experimentally and numerically. It is demonstrated that both combination of diamond and cBN (hybrid structure) and nanomodification of metallic binder (with hexagonal boron nitride/hBN platelets) lead to sufficient improvement of the cast iron machining performance. The superhard tools with 25% of diamond replaced by cBN grains demonstrate 20% increased performance as compared with pure diamond machining tools, and more than two times higher performance as compared with pure cBN tools. Further, cast iron machining efficiency of the wheels modified by hBN particles was 80% more efficient compared to the tool with the original binder. Computational model of hybrid superhard tools is developed, and applied to the analysis of structure-performance relationships of the tools. [ABSTRACT FROM AUTHOR]

The potential of carbon nanotube reinforcement of metallic binders for the improvement of quality and efficiency of diamond cutting wheels is studied. The effect of multi-walled carbon nanotube (MWCNT) reinforcement on the mechanical properties i.e. hardness, Young modulus, strength and deformation behavior of copper and iron based binder for diamond cutting wheels is investigated experimentally and numerically. Computational micromechanical studies were carried out to clarify the mechanisms of the MWCNT material strengthening. It is demonstrated that the adding of MWCNTs leads to the decrease of grain size of the structural constituents of the binder, what in turn leads to the improved simultaneously hardness, Young modulus, plastic extension, bending strength and performances of the metallic binders. Comparing service properties of diamond end-cutting drill bits with and without MWCNT one observed the drastic increase of the cutting speed as a result of MWCNT reinforcement. [ABSTRACT FROM AUTHOR]

The biodegradable foamed nanocomposites were developed from the reinforcement of surface acetylated cellulose nanocrystals (ACNC) as bionanofillers and the poly(butylene succinate) (PBS) as polymeric matrix. The surface modification of high-efficiency acetylation on the cellulose nanocrystals converted the hydrophilic hydroxyl groups to hydrophobic acetyl groups, which improved the compatibility between rigid nanoparticles and polyester matrix through the similar ester groups of two components. With the introduction of 5 wt% ACNC, the specific flexural strength ( σ / ρ f ) and the specific flexural modulus ( E / ρ f ) of the foamed composites significantly increased by 75.7% and 57.2% in comparison with those of the neat PBS foamed material. Meanwhile, with the change of the ACNC concentrations, the cell size and cell density of the foamed composites can be regulated and achieved the high cell density of 1.95 × 10 5 cells/cm 3 bearing the small average cell size of 178.84 μm (5 wt% ACNC). The microstructure observation of the foamed composites indicated the moderate loading levels of rigid ACNC can serve as the reinforcing phase for the stress transfer and promote the crystallinity advancement of the foamed composites. [ABSTRACT FROM AUTHOR]

Development of homogenous metal matrix nanocomposites with uniform distribution of nanoreinforcement, preserved matrix nanostructure features, and improved properties, was possible by means of innovative processing techniques. In this work, Al-SiC nanocomposites were synthesized by mechanical milling and consolidated through spark plasma sintering. Field Emission Scanning Electron Microscope (FE-SEM) with Energy Dispersive X-ray Spectroscopy (EDS) facility was used for the characterization of the extent of SiC particles' distribution in the mechanically milled powders and spark plasma sintered samples. The change of the matrix crystallite size and lattice strain during milling and sintering was followed through X-ray diffraction (XRD). The density and hardness of the developed materials were evaluated as function of SiC content at fixed sintering conditions using a densimeter and a digital microhardness tester, respectively. It was found that milling for 24 h led to uniform distribution of SiC nanoreinforcement, reduced particle size and crystallite size of the aluminum matrix, and increased lattice strain. The presence and amount of SiC reinforcement enhanced the milling effect. The uniform distribution of SiC achieved by mechanical milling was maintained in sintered samples. Sintering led to the increase in the crystallite size of the aluminum matrix; however, it remained less than 100 nm in the composite containing 10 wt.% SiC. Density and hardness of sintered nanocomposites were reported and compared with those published in the literature. [ABSTRACT FROM AUTHOR]

Metal and ceramic matrix composites have been developed to enhance the stiffness and strength of metals and alloys, and improve the toughness of monolithic ceramics, respectively. It is possible to further improve their properties by using nanoreinforcement, which led to the development of metal and ceramic matrix nanocomposites, in which case, the dimension of the reinforcement is on the order of nanometer, typically less than 100 nm. However, in many cases, the properties measured experimentally remain far from those estimated theoretically. This is mainly due to the fact that the properties of nanocomposites depend not only on the properties of the individual constituents, i.e., the matrix and reinforcement as well as the interface between them, but also on the extent of nanoreinforcement dispersion. Therefore, obtaining a uniform dispersion of the nanoreinforcement in the matrix remains a key issue in the development of nanocomposites with the desired properties. The issue of nanoreinforcement dispersion was not fully addressed in review papers dedicated to processing, characterization, and properties of inorganic nanocomposites. In addition, characterization of nanoparticles dispersion, reported in literature, remains largely qualitative. The objective of this review is to provide a comprehensive description of characterization techniques used to evaluate the extent of nanoreinforcement dispersion in inorganic nanocomposites and critically review published work. Moreover, methodologies and techniques used to characterize reinforcement dispersion in conventional composites, which may be used for quantitative characterization of nanoreinforcement dispersion in nanocomposites, is also presented. [ABSTRACT FROM AUTHOR]

The interest in structural health monitoring of carbon fiber-reinforced polymers using electrical methods to detect damage in structures is growing because once the material is fabricated the evaluation of strain and damage is simple and feasible. In order to obtain the conductivity, the polymer matrix must be conductive and the use of nanoreinforcement seems to be the most feasible method. In this work, the behavior of nanoreinforced polymer with carbon nanotubes (CNTs) and composites with glass and carbon fibers with nanoreinforced matrices was investigated. These composites were evaluated in tensile tests by simultaneously measuring stress, strain and resistivity. During elastic deformation, a linear increase in resistance was observed and during fracture of the composite fibers, stronger and discontinuous changes in the resistivity were observed. Among other factors, the percentage of nanotubes incorporated in the matrix turned out to be an important factor in the sensitivity of the method. [ABSTRACT FROM PUBLISHER]

Extreme loads events can cause enormous human and infrastructure losses. Computer modeling is the key to reducing the high cost of dynamic monitoring and experimentation. Engineers in various fields have undertaken complicated modeling for structures under abnormal loads. However, an efficient and accurate model is necessary to more rapidly address dangerous shock problems. Composite materials have replaced metals in various applications thanks to their superior shock resistance properties. This investigation particularly relates to their usage on naval ships to achieve improved blast survivability with the additional benefit of lower cost. A relatively simple model is detailed for the approximate centerline response prediction of the specific complex case of composite materials tested in a shock tube. A modal analysis simulation of a beam is performed using gross properties as well as physical geometry and arbitrary shock. Closed form equations have been employed to derive the eigenproblem that generates mode shapes and natural frequencies, and the resulting responses are compared to experimental shock tube test results. The best outcome was generated by the simplest model consisting of a shock pressure pulse averaged in two divisions and applied over the entire beam span. For this case, the simulation and experimental responses had reasonable correlation forfra ctured E-glasslvinyl-ester composite specimens with both nanoclay and graphite platelet reinforcement. This model is also a conservative estimate for the transient test deflection range for all other specimens. [ABSTRACT FROM AUTHOR]

Abstract: Poly(rotaxan)s of poly(ethylene glycol) and α-cyclodextrines (CD) block copolymers end-capped with poly(methyl methacrylate) chains were synthesized by atom transfer radical polymerization. The synthesized copolymers were characterized by 1H NMR, 2D NOESY NMR, X-ray and Thermogravimetric analysis. Assuming a maximum relation of 2 CDs per ethyleneglycol unit, a coverage degree of 18% and 15% was achieved. X-ray analysis showed a characteristic signal around 20θ for all copolymers with an amorphous halo mainly due to inter-crystal poly(ethylene glycol) and poly(methyl methacrylate) chains. Full Molecular Dynamics of 20ns was used to simulate the crystal structure of these copolymers. A pair correlation function was used to determine the coupling between hydrogen atoms of PEG, PMMA and cyclodextrine obtained by 2D NOESY NMR. [Copyright &y& Elsevier]

In the present study, elemental and nanoAl2O3 particulate reinforced magnesium materials were synthesised using an innovative disintegrated melt deposition technique followed by hot extrusion. Microstructural characterisation of the composite samples showed retention and uniform distribution of reinforcement, grain refinement of magnesium matrix, and the presence of minimal porosity. Physical properties characterisation revealed that the addition of nanoAl2O3 particulates as reinforcement improves the dimensional stability of pure magnesium. Mechanical properties characterisation revealed that the presence of nanoAl2O3 reinforcement led to significant improvement in hardness, elastic modulus, 0·2% yield strength, UTS and ductility. The results further revealed that the combination of 0·2% yield strength, UTS, and ductility exhibited by nanoAl2O3 reinforced magnesium remained much superior even when compared to magnesium reinforced with a much higher volume percentage of micrometre size SiCp. An attempt is made in the present study to correlate the effect of nanoAl2O3 as reinforcement and its increasing amount with the microstructural, physical, and mechanical properties of magnesium. MST/6233 [ABSTRACT FROM AUTHOR]

Packaging consumes around 40% of the total plastic production. One of the most important fields with high requirements is food packaging. Food packaging products have been commonly produced with petrol polymers, but due to environmental concerns, the market is being moved to biopolymers. Poly (lactic acid) (PLA) is the most promising biopolymer, as it is bio-based and biodegradable, and it is well established in the market. Nonetheless, its barrier properties need to be enhanced to be competitive with other polymers such as polyethylene terephthalate (PET). Nanoclays improve the barrier properties of polymeric materials if correct dispersion and exfoliation are obtained. Thus, it marks a milestone to obtain an appropriate dispersion. A predispersed methodology is proposed as a compounding process to improve the dispersion of these composites instead of common melt procedures. Afterwards, the effect of the polarity of the matrix was analyzing using polar and surface modified nanoclays with contents ranging from 2 to 8% w/w. The results showed the suitability of the predispersed and concentrated compound, technically named masterbatch, to obtain intercalated structures and the higher dispersion of polar nanoclays. Finally, the mechanical performance and sustainability of the prepared materials were simulated in a food tray, showing the best assessment of these materials and their lower fingerprint. [ABSTRACT FROM AUTHOR]