Reinforcement Of Nanocomposites Research Articles

The reinforcing and characteristics of interphase as the polymer chains adsorbed on the nanoparticles in polymer nanocomposites

In this study, the adsorbed polymer chains on the nanoparticle surface are assumed as an interphase layer, which increases the reinforcing efficiency of nanoparticles in polymer nanocomposites. The interphase is taken into account to enhance the effective volume fraction of nanoparticles, which is determined by the Maxwell model for Young’s modulus of composites. Also, the modulus and strength of interphase are calculated by proper models. The interphase properties are estimated and discussed for various samples containing different nanoparticles. The present methodology gives fine agreement between the experimental results of mechanical properties and the calculations. Also, the acceptable results for interphase properties are obtained which confirm the validity of the presented models. The small nanoparticles and thick interphase significantly increase the nanocomposite reinforcement. Additionally, Young’s modulus of nanoparticles causes negligible effect on the modulus of nanocomposites in spite of the interphase properties such as thickness and interfacial area.

Mesoscale evolution of non-graphitizing pyrolytic carbon in aligned carbon nanotube carbon matrix nanocomposites

Polymer-derived pyrolytic carbons (PyCs) are highly desirable building blocks for high-strength low-density ceramic meta-materials, and reinforcement with nanofibers is of interest to address brittleness and tailor multi-functional properties. The properties of carbon nanotubes (CNTs) make them leading candidates for nanocomposite reinforcement, but how CNT confinement influences the structural evolution of the PyC matrix is unknown. Here, the influence of aligned CNT proximity interactions on nano- and mesoscale structural evolution of phenol-formaldehyde-derived PyCs is established as a function of pyrolysis temperature ( $$T_{\mathrm {p}}$$ ) using X-ray diffraction, Raman spectroscopy, and Fourier transform infrared spectroscopy. Aligned CNT PyC matrix nanocomposites are found to evolve faster at the mesoscale by plateauing in crystallite size at $$T_{\mathrm {p}}$$ $$\sim$$ 800 $$^{\circ }\hbox {C}$$ , which is more than $$200\,\,^{\circ }\hbox {C}$$ below that of unconfined PyCs. Since the aligned CNTs used here exhibit $$\sim$$ 80 nm average separations and $$\sim$$ 8 nm diameters, confinement effects are surprisingly not found to influence PyC structure on the atomic-scale at $$T_{\mathrm {p}}$$ $$\le $$ 1400 $$^{\circ }\hbox {C}$$ . Since CNT confinement could lead to anisotropic crystallite growth in PyCs synthesized below $$\sim$$ 1000 $$^{\circ }\hbox {C}$$ , and recent modeling indicates that more slender crystallites increase PyC hardness, these results inform fabrication of PyC-based meta-materials with unrivaled specific mechanical properties.

Focus on Gradientwise Control of the Surface Acetylation of Cellulose Nanocrystals to Optimize Mechanical Reinforcement for Hydrophobic Polyester-Based Nanocomposites.

Surface acetylation of cellulose nanocrystals (CNCs) imposes an important effect on CNC-related mechanical enhancement of hydrophobic polyester-based composites, of which interfacial properties still need optimization. In the present work, the surface acetylation of CNCs was adjusted as a gradient of above ca. 10%. Then, we found that the surface energy of acetylated CNCs (ACNs) decreased and thus their hydrophobicity increased as the surface acetylation degree increased. Hence, the ACNs with varied degrees of acetyl substitution (DSsurface-acetyl) values were attempted to reinforce a kind of hydrophobic polyester, poly(3-hydroxybutyrate-co-4-hydroxybutyrate) (PHB). The results indicated that a smaller discrepancy in the surface energy between the CNC surface and the PHB matrix was obtained, as the surface acetylation degree increased, and then, the affinity and interaction between the two components increased, which improved the homogeneous distribution of ACNs in the PHB matrix. Besides, in comparison to the nanocomposites filled with 15 wt % unmodified CNCs, the tensile strength of those with ACNs of 62.9% DSsurface-acetyl was 43.3% higher. This study was the first attempt to adjust the surface substitution degrees with a gradient profile for the surface modification of CNCs and prove that acetylation gradient control is an effective and facile strategy to optimize the mechanical properties.

Tensile properties and wear resistance of epoxy nanocomposites reinforced with cellulose nanofibers

Cellulose nanofibers (CNFs) were prepared from sugarcane bagasse and used as reinforcement in epoxy nanocomposites. To obtain CNFs, the cellulose was bleached with sodium chlorite, hydrothermally hydrolyzed with 5% w/v oxalic acid under pressure of 800 psi at 100 °C in a microwave reactor, and homogenized using a mechanical homogenizer. The diameters of CNFs determined from field emission scanning electron microscope (FE-SEM) vary from 8 to 86 nm. The percentage crystallinity obtained from X-ray diffractometry is 62.8%. The epoxy was mixed with the prepared CNFs and cured at room temperature for 7 days. The effects of CNFs concentrations (0, 0.5, 1.0, 3.0, 5.0 and 10.0 wt%, dry basis) on the tensile properties and scratch resistance of the nanocomposites were investigated. Young’s modulus and tensile strength increased with an increasing CNFs loading up to 3 wt %. Above that concentration the tensile elongation at break increased; this was at the rate faster than the modulus decreased. The instantaneous and healing scratch depths and thus viscoelastic recovery were determined using a micro-scratch tester. The percentage recovery values are higher for the nanocomposites than for the pure epoxy.

Fracture related mechanical properties of low and high graphene reinforcement of epoxy nanocomposites

Tensile ductility and fracture toughness of nano-reinforced epoxy resin with different types and concentrations of graphene nanoplatelets (GnPs) are investigated. GnPs types with small (2 nm) and large (15 nm) lateral size were used and for various weight percentages in order to fabricate a series of epoxy/GnPs nanocomposites. Tensile mechanical properties as well as fracture toughness (according to compact tension C(T) geometry) were experimentally assessed. The results indicate that the fracture mechanism vary according to the GnPs concentration and type used. For low filler concentrations (<0.25 wt% GnPs), an approximate 15% increase in ultimate tensile strength Rm and 12% in fracture toughness was noticed for the fine dispersion of small lateral size GnPs type. For the case of the large lateral size GnPs type, lower enhancement in Rm was observed, while fracture toughness was decreased. Reinforcement at higher concentrations (>1 wt% GnPs) revealed that the fracture mechanism altered and this was attributed to the “whitened zones” of the soft interphases of GnPs/matrix. An almost 30% increase in tensile ductility was attributed to the GnPs tilting for the fine dispersion of the small lateral size GnPs and therefore an essential loading transfer was involved. For reinforcement with extreme filler concentrations (>5 wt% GnPs) a decrease in all investigated mechanical properties was noticed and this was attributed to the particles agglomeration.

Thickness effect on the tensile and dynamic mechanical properties of graphene nanoplatelets-reinforced polymer nanocomposites

The thickness effect of graphene nanoplatelets (GNPs) on the morphology, tensile and dynamic mechanical properties of GNPs/PMMA nanocomposites has been studied. Two types of GNPs, G5 (5 nm thick) and G100 (100 nm thick), were incorporated into a poly-methyl methacrylate (PMMA) matrix, each with four weight percentages: 0.1, 0.5, 1.0 and 5.0%. After measured by tensile test and dynamic mechanical analysis, the thinner G5 was found to improve more significantly the reinforcement of nanocomposites than G100. At 5.0 wt%, the Young’s modulus of G5/PMMA was 53.6% greater than that of the pure PMMA as compared to a 26.1% increase for G100/PMMA; the ultimate tensile strength of G5/PMMA was enhanced by 25.5% compared to 3.1% for G100/PMMA; the storage modulus of G5/PMMA was improved by 84.3% compared to 54.1% for G100/PMMA. The fracture toughness of both nanocomposites improved greatly at 0.1 wt%: a 47.9% improvement for G5/PMMA compared with pure PMMA and 20.8% for G100/PMMA, and maintained at the same level up to 1.0 wt%. The advantage of G5 over G100 in terms of tensile and dynamic mechanical properties enhancement was caused by its thinness, to be related to its high specific surface area.

Reinterpretation of the mechanical reinforcement of polymer nanocomposites reinforced with cellulose nanorods

ABSTRACTThe mechanical reinforcement of nanocomposites containing nanorods‐like fillers such as cellulose nanocrystals (CNCs) is often interpreted by adapting the classical parallel–series model, assuming a simple hyperbolic dependence between the percolation threshold and aspect ratio. However, such assumptions are valid only for nanorods with high aspect ratio and often are misinterpreting the reinforcement obtained at low volume fraction of filler loading. To elucidate this intriguing scenario, we proposed a new approach and validated it by compiling and reinterpreting some of available literature that represent the experimental reinforcement with CNCs. Our approach showed better accuracy, specifically for the cases of CNC nanorods with lower aspect ratio. We conclude that this route permits a more realistic evaluation of the mechanical reinforcement, where a physical parameter accounting the polymer filler association is introduced. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 45254.

Synthesis and characterization of poly1-hexene/silica nanocomposites

SiO2 nano particles, with particle size of 12 nm, were first modified by substituting surface OH groups with O-hexyl moiety. Then, poly1-hexene/modified-SiO2 composites with various nano-SiO2 weight fractions were prepared by three different methods: in situ, solution, and melt methods and designated as PH-SiO2/Insitu, PH-SiO2/Sol and PH-SiO2/Melt, respectively. PH-SiO2/Insitu samples showed highly uniform particle dispersion up to 30 wt. % of silica while in PH-SiO2/Sol and PH-SiO2/Melt samples agglomeration of the silica nanoparticles occurred for filler contents ≥5 wt. % (i.e. 5, 10, 20 and 30 wt%). In the synthesized composites, the storage modulus significantly increased as high as 20.7 times when compared with neat poly1-hexene. Maximum decomposition temperature (Tmax) and char yield at 600 °C increased with increasing silica level. Rheological results showed that Gʹ> Gʺ over the frequency range, illustrating the elastic behavior of the composite samples. In fact, samples showed the characteristic of a non-Newtonian fluid with a strong shear thinning effect in which η* increased with increasing filler weight fraction. From the results, it can be expected that modified silica could replace silica nanoparticles in polyolefin nanocomposite reinforcement.

Hydroxyapatite reinforced inherent RGD containing silk fibroin composite scaffolds: Promising platform for bone tissue engineering

Replacement and repair of ectopic bone defects and traumatized bone tissues are done using porous scaffolds and composites. The prerequisites for such scaffolds include high mechanical strength, osseoconductivity and cytocompatibility. The present work is designed to address such requirements by fabricating a reinforced cytocompatible scaffold. Biocompatible silk protein fibroin collected from tropical non-mulberry tasar silkworm (Antheraea mylitta) is used to fabricate fibroin-hydroxyapatite (HAp) nanocomposite particles using chemical precipitation method. In situ reinforcement of fibroin-HAp nanocomposite and external deposition of HAp particles on fibroin scaffold is carried out for comparative evaluations of bio-physical and biochemical characteristics. HAp deposited fibroin scaffolds provide greater mechanical strength and cytocompatibility, when compared with fibroin-HAp nanoparticles reinforced fibroin scaffolds. Minimal immune responses of both types of composite scaffolds are observed using osteoblast-macrophage co-culture model. Nanocomposite reinforced fibroin scaffold can be tailored further to accommodate different requirements depending on bone type or bone regeneration period.

Highly redispersible sugar beet nanofibers as reinforcement in bionanocomposites

A simple method for preparing redispersible nanofibers from sugar beet residue and their use as a well-dispersed reinforcement for a polyvinyl alcohol (PVA) matrix is reported. It is known that the redispersion of dried cellulose nanofibers is difficult because of the formation of strong hydrogen bonds between the nanofibers. The results show that the properties of the initial sugar beet nanofiber suspension can be recovered without the use of chemical modification or additives with higher pectin and hemicellulose content. Undried and redispersed nanofibers with and without pectin were used as nanocomposite reinforcement with PVA. The redispersed nanofibers were as good reinforcements as the undried nanofibers. The tensile strength and elastic modulus of the nanocomposites with the redispersed sugar beet nanofibers were as good as those of the nanocomposites with undried nanofibers. Interestingly, the nanofiber dispersion in the PVA matrix was better when sugar beet nanofibers containing pectin and hemicellulose were used as reinforcements.

Novel modified nanocellulose applicable as reinforcement in high-performance nanocomposites

The influence of modification and vacuum/supercritical CO2 (scCO2) drying methods on the surface properties, morphology and thermal stability of cellulose nanocrystals (NC) was presented in this study. Introduction of reactive vinyl groups on NC surface was performed by either direct esterification with oleic acid, linseed or sunflower oil fatty acids; or by amidation of maleic acid/ethylene diamine with methyl ester of fatty acid. Obtained modified NC (m-NC) were characterized using FTIR and Raman spectroscopy; and by determination of acid, iodine and ester values. Structural analysis of m-NC showed varieties of forms, from spongy to nanostructural non-uniform layered morphology with observable agglomeration, which confirmed morphology dependence on modification/processing methods Thermogravimetry-MS spectrometry showed different thermal stability and degradation pathways of NC/m-NC. Incorporation of 1 wt% of reactive m-NC in unsaturated polyester lead to high performance nanocomposites and contributed to increase of stress at break in the range from 76 to 93%.

High-Energy Dissipation Performance in Epoxy Coatings by the Synergistic Effect of Carbon Nanotube/Block Copolymer Conjugates.

Hierarchical assembly of hard/soft nanoparticles holds great potential as reinforcements for polymer nanocomposites with tailored properties. Here, we present a facile strategy to integrate polystyrene-grafted carbon nanotubes (PSgCNT) (0.05-0.3 wt %) and poly(styrene-b-[isoprene-ran-epoxyisoprene]-b-styrene) block copolymer (10 wt %) into epoxy coatings using an ultrasound-assisted noncovalent functionalization process. The method leads to cured nanocomposites with core-shell block copolymer (BCP) nanodomains which are associated with carbon nanotubes (CNT) giving rise to CNT-BCP hybrid structures. Nanocomposite energy dissipation and reduced Young's Modulus (E*) is determined from force-distance curves by atomic force microscopy operating in the PeakForce QNM imaging mode and compared to thermosets modified with BCP and purified carbon nanotubes (pCNT). Remarkably, nanocomposites bearing PSgCNT-BCP conjugates display an increase in energy dissipation of up to 7.1-fold with respect to neat epoxy and 53% more than materials prepared with pCNT and BCP at the same CNT load (0.3 wt %), while reduced Young's Modulus shows no significant change with CNT type and increases up to 25% compared to neat epoxy E* at a CNT load of 0.3 wt %. The energy dissipation performance of nanocomposites is also reflected by the lower wear coefficients of materials with PSgCNT and BCP compared to those with pCNT and BCP, as determined by abrasion tests. Furthermore, scanning electron microscopy (SEM) images taken on wear surfaces show that materials incorporating PSgCNT and BCP exhibit much more surface deformation under shear forces in agreement with their higher ability to dissipate more energy before particle release. We propose that the synergistic effect observed in energy dissipation arises from hierarchical assembly of PSgCNT and BCP within the epoxy matrix and provides clues that the CNT-BCP interface has a significant role in the mechanisms of energy dissipation of epoxy coating modified by CNT-BCP conjugates. These findings provide a means to design epoxy-based coatings with high-energy dissipation performance.

Cellulose Nanowhiskers from Moso Bamboo Residues: Extraction and Characterization

To take full advantage of moso bamboo processing waste, bamboo cellulose nanowhiskers were isolated from bamboo residues using sulfuric acid hydrolysis. Changes in bamboo cellulose at different stages of processing, as well as the roles of acid concentrations (55 wt% and 65 wt%) and hydrolysis times (1 h to 5 h) on the characteristics of nanowhiskers were investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), thermogravimetry-Fourier transform infrared spectroscopy analysis (TGA-FTIR), synchrotron radiation wide angle X-ray scattering (WAXS), composition analysis, and Brunauer-Emmett Teller (BET) analysis. Both rod-like and network-like nanowhiskers were observed. Alkaline pretreatment removed impurities and part of the hemicellulose. Cellulose content increased to nearly 85%, and specific surface area improved as well after bleaching. Nanowhiskers had an average length of 455 nm, diameter of 12 nm, and an aspect ratio of about 37. Cellulose I was the dominant composition in bamboo cellulose; the transformation of cellulose Iα to cellulose Iβ was observed. Nanowhiskers presented greater crystallinity and crystallite size than those of cellulose without hydrolysis, but lower thermal stability. These bionanowhiskers might be used as reinforcements in nanocomposites.

Strengthening in and fracture behaviour of CNT and carbon-fibre-reinforced epoxy–matrix hybrid composite

Advanced materials such as continuous fibre-reinforced polymer matrix composites offer significant enhancements in strength and fracture resistance properties as compared with their bulk, monolithic counterparts. In the present work, mode-I (tensile) fracture behaviour of the neat epoxy (without nano- or hybrid reinforcements), nanocomposite (with amino-functionalized multi-walled carbon nanotube (MWCNT) reinforcement to neat epoxy) and hybrid composite (with amino MWCNT and carbon fibre reinforcements to neat epoxy) along with their flexural strength and interlaminar shear strength has been reported and discussed. Limited topological studies have also been conducted to understand the nature of material fracture and its dependence on the notch orientation. The results thus obtained are analysed and discussed in detail to elucidate: (i) alignment of fibre and its influence on the anisotropy in strength and fracture resistance, (ii) dependence of notch root radii on the apparent fracture toughness and concurrence to strain-controlled fracture and (iii) finally, the nature of J–R curves. The results thus obtained have revealed that the resistance to fracture is significantly increased with the addition of amino-functionalized MWCNTs and carbon fibres. In the hybrid composite, fracture resistance is greater in the longitudinal orientation of fibres than in the transverse orientation and it exhibits a significantly higher strength–fracture toughness combination.

Strong and Stiff: High-Performance Cellulose Nanocrystal/Poly(vinyl alcohol) Composite Fibers.

The mechanical properties of rodlike cellulose nanocrystals (CNCs) suggest great potential as bioderived reinforcement in (nano)composites. Poly(vinyl alcohol) (PVOH) is a useful industrial material and very compatible with CNC chemistry. High performance CNC/PVOH composite fibers were produced coaxial coagulation spinning, followed by hot-drawing. We showed that CNCs increase the alignment and crystallinity of PVOH, as well as providing direct reinforcement, leading to enhanced fiber strength and stiffness. At 40 wt % CNC loading, the strength and stiffness reached 880 MPa and 29.9 GPa, exceeding the properties of most other nanocellulose based composite fibers previously reported.

Microwave Assisted Manufacturing and Repair of Carbon Reinforced Nanocomposites

We report a composite capable of advanced manufacturing and damage repair. Microwave energy is used to induce thermal reversible polymerization of the matrix allowing for microwave assisted composite welding and repair. Composites can be bonded together in just a few minutes through microwave welding. Lap shear testing demonstrates that microwave welded composites exhibit 40% bond strength relative to composites bonded with epoxy resin. Double cantilever beam testing shows 60% recovery in delamination strength after microwave assisted composite repair. The interfacial adhesion and composite repair after microwave exposure are examined by X-ray computed tomography. The microwave processing is shown to be reproducible and consistent. The ability to perform scalable manufacturing is demonstrated by the construction of a large structure from smaller components.

Powder processing methodology for production of graphene oxide reinforced aluminium matrix composites

In this paper, the preparation and properties of reduced graphene oxide (rGO) reinforcement of aluminium matrix nanocomposites (AMCs) are presented. The commercial colloidal graphene oxide was firstly coated on the selected aluminium powder particles, and the graphene oxide was then reduced through thermal annealing process. The rGO-aluminium powder dispersions were prepared in order to provide coated aluminium particles before synthesis of the metal matrix nanocomposites. As-received pristine aluminium powder and pre-synthesised rGO-AMCs were cold compacted into disc-shaped specimens and sintered. The mechanical properties and microstructure were studied and characterised via Vickers hardness, a flexural bending test, X-ray diffraction and scanning electron microscopy. The rGO was observed to be dispersed effectively in the aluminium matrix and well consolidated within the composites. The relevant factors for the powder metallurgy process, e.g. compaction pressure, density, sintering conditions, have been elaborated and optimised. Enhancements of 32% in micro hardness of 0.3 wt.% rGO-Al composites were observed compared to the baseline pure aluminium prepared under identical experimental conditions. The graphene oxide and graphene nanosheets have proven potentially capable of realising mechanical reinforcements in aluminium matrix composites under cold compaction and sintering powder metallurgy techniques only.

The Reinforcement of Particulate-Filled Polymer Nanocomposites by Nanoparticles Aggregates

The Reinforcement of Particulate-Filled Polymer Nanocomposites by Nanoparticles Aggregates

Filler Size Effects on Reinforcement in Elastomer-Based Nanocomposites: Experimental and Simulational Insights into Physical Mechanisms

Nanocomposites consisting of polymers reinforced with filler particles are important for a wide variety of industries and processes, but although they exhibit unique viscoelastic properties and as such are widely applied in e.g. tires, the precise mechanism of their reinforcement is at best incompletely understood at present. In order to understand it at a fundamental level, and ultimately control it in practice, it is essential to determine the impact of interactions between filler particles and polymer matrix on the nanocomposite microstructure and its macroscopic dynamic mechanical properties. To this end, we performed experiments on two model systems as well as molecular dynamics simulations, aiming to determine to what extent widely used shear-distortion models of the reinforcement are applicable as well as the role played by molecular interactions on the enhancement of the mechanical properties. In both experiments and simulations a linear dependence of the reinforcement on the inverse radius of the...

Functionalization of carbon nanotubes with (3‐glycidyloxypropyl)‐trimethoxysilane: Effect of wrapping on epoxy matrix nanocomposites

ABSTRACTIn this work, multiwalled carbon nanotubes (MWCNT), after previous oxidation, are functionalized with excess (3‐glycidyloxypropyl)trimethoxysilane (GLYMO) and used as reinforcement in epoxy matrix nanocomposites. Infrared, Raman, and energy‐dispersive X‐ray spectroscopies confirm the silanization of the MWCNT, while transmission electron microscopy images show that oxidized nanotubes presented less entanglement than pristine and silanized MWCNT. Thickening of the nanotubes is also observed after silanization, suggesting that the MWCNT are wrapped by siloxane chains. Field‐emission scanning electron microscopy reveals that oxidized nanotubes are better dispersed in the matrix, providing nanocomposites with better mechanical properties than those reinforced with pristine and silanized MWCNT. On the other hand, the glass transition temperature of the nanocomposite with 0.05 wt % MWCNT‐GLYMO increased by 14 °C compared to the neat epoxy resin, suggesting a strong matrix–nanotube adhesion. The functionalization of nanotubes using an excess amount of silane can thus favor the formation of an organosiloxane coating on the MWCNT, preventing its dispersion and contributing to poor mechanical properties of epoxy nanocomposites. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 44245.