Nanofiller Loading Research Articles

Size-scale effects of silica on bis-GMA/TEGDMA based nanohybrid dental restorative composites

The present study focuses on the effect of size-scale combination of silica on the mechanical and dynamic mechanical properties of acrylate based (50% Bis-GMA and 50% TEGDMA by weight) composites with an aim to overcome the conventional problem of high-volume fraction filling of acrylate based composites, typically used in restorative dentistry. Two classes of light-cured composites based on the size-scale combination of silica (7nm+2μm; 14nm+2μm) as the filler were prepared. FTIR spectroscopy revealed functionality and interactions whereas morphological investigations concerning the state of distribution and dispersion of nano- and micro-silica has been carried out by SEM–EDX Si-dot mapping. The dynamic mechanical properties, compressive, flexural and diametral tensile strengths were characterized. Micromechanical analysis of viscoelastic storage moduli following Kerner composite model has revealed an enhancement in the reinforcement efficiency of the nanohybrid composites based on the filler size-scale combination of 14nm+2μm with 10wt.% nanofiller loading. The compressive strength of the micro-filled composite (with 2μm silica only) was found to remain comparable to that of the nanohybrid with 5wt.% of 7nm silica and 10wt.% of 14nm silica filled composites. Diametral tensile strength has been observed to be influenced by the size-scale combination and extent of nanofiller loading. The effective volume fractions in the composites validating the experimentally determined DTS were calculated following Nicolais–Narkis model. Our study demonstrates the conceptual feasibility of exploring the optimization of size-scale combinations of filler for enhancement in reinforcement efficiency by manipulating the volume fraction of filler induced immobilized polymer chains by resorting to the principle of micromechanics.

EMI shielding effectiveness of carbon based nanostructured polymeric materials: A comparative study

The microstructure, electromagnetic interference (EMI) shielding effectiveness (SE), DC electrical conductivity, AC electrical conductivity and complex permittivity of nanostructured polymeric materials filled with three different carbon nanofillers of different structures and intrinsic electrical properties were investigated. The nanofillers were multiwall carbon nanotubes (MWCNT), carbon nanofibers (CNF) and high structure carbon black (HS-CB) nanoparticles and the polymer was acrylonitrile-butadiene-styrene (ABS). In addition, the EMI SE mechanisms and the relation between the AC electrical conductivity in the X-band frequency range and the DC electrical conductivity were studied. The nanocomposites were fabricated by solution mixing and characterized by uniform dispersion of the nanofillers within the polymer matrix. It was found that, at the same nanofiller loading, the EMI SE, permittivity and electrical conductivity of the nanocomposites decreased in the following order: MWCNT>CNF>CB. MWCNT based nanocomposites exhibited the lowest electrical percolation threshold and the highest EMI SE owning to the higher aspect ratio and electrical conductivity of MWCNT compared to CNF and HS-CB. The AC conductivity in the X-band frequency range was found to be independent of frequency.

Effect of MgO nanofillers on burst release reduction from hydrogel nanocomposites

In this study, MgO nanoparticles are applied to control the initial burst release by modification of matrix structure, thereby affecting the release mechanism. The effects of MgO nanofiller loading on the in vitro release of a model drug are investigated. Surface topography and release kinetics of hydrogel nanocomposites are also studied in order to have better insight into the release mechanism. It was found that the incorporation of MgO nanofillers can significantly decrease the initial burst release. The effect of genipin (GN) on burst release was also compared with MgO nanoparticles, and it was found that the impact of MgO on burst release reduction is more obvious than GN; however, GN cross-linking caused greater final release compared to blanks and nanocomposites. To confirm the capability of nanocomposite hydrogels to reduce burst release, the release of β-carotene in Simulated Gastric Fluid and Simulated Intestinal Fluid was also carried out. Thus, the application of MgO nanoparticles seems to be a promising strategy to control burst release.

Nanowire-filled polymer composites with ultrahigh thermal conductivity

Realizing high thermal conductivity nanocomposites is a challenge because of difficulties in incorporating high fractions of uniformly dispersed nanofillers and countering low filler-matrix interfacial conductance. Here, we obviate these issues by using <3 vol. % gold nanowire fillers to obtain a 30-fold increase in polydimethylsiloxane thermal conductivity that is 6-fold higher than any nanocomposite at low nanofiller loadings and exceeds theoretical predictions. The nanowire diameter and aspect ratio are keys to obtaining cold-welded networks that enhance thermal conductivity while fostering low modulus and electrical conductivity. Such nanowire nanocomposites are attractive for many applications in electronics, packaging, and energy devices.

Property enhancement in unsaturated polyester nanocomposites by using a reactive intercalant for clay modification

AbstractPolymeric nanocomposites were synthesized from unsaturated polyester (UPE) matrix and montmorillonite (MMT) clay using an in situ free radical polymerization reaction. Organophilic MMT was obtained using a quaternary salt of coco amine as intercalant having a styryl group making it a reactive intercalant. The resultant nanocomposites were characterized via X‐ray diffraction and transmission electron microscopy. The effect of increased nanofiller loading on the thermal and mechanical properties of the nanocomposites was investigated. All the nanocomposites were found to have improved thermal and mechanical properties as compared with neat UPE matrix, resulting from the contribution of nanolayer connected intercalant‐to‐crosslinker which allows a crosslinking reaction. It was found that the partially exfoliated nanocomposite structure with an exfoliation dominant morphology was achieved when the MMT loading was 1 wt %. This nanocomposite exhibited the highest thermal stability, the best dynamic mechanical performance and the highest crosslinking density, most probably due to more homogeneous dispersion and optimum amount of styrene monomer molecules inside and outside the MMT layers at 1 wt % loading. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

Flame-Retardant Electrical Conductive Nanopolymers Based on Bisphenol F Epoxy Resin Reinforced with Nano Polyanilines

Both fibril and spherical polyaniline (PANI) nanostructures have successfully served as nanofillers for obtaining epoxy resin polymer nanocomposites (PNCs). The effects of nanofiller morphology and loading level on the mechanical properties, rheological behaviors, thermal stability, flame retardancy, electrical conductivity, and dielectric properties were systematically studied. The introduction of the PANI nanofillers was found to reduce the heat-release rate and to increase the char residue of epoxy resin. A reduced viscosity was observed in both types of PANI-epoxy resin liquid nanosuspension samples at lower loadings (1.0 wt % for PANI nanospheres; 1.0 and 3.0 wt % for PANI nanofibers), the viscosity was increased with further increases in the PANI loading for both morphologies. The dynamic storage and loss modulii were studied, together with the glass-transition temperature (T(g)) being obtained from the peak of tan δ. The critical PANI nanofiller loading for the modulus and T(g) was different, i.e., 1.0 wt % for the nanofibers and 5.0 wt % for the nanospheres. The percolation thresholds of the PANI nanostructures were identified with the dynamic mechanical property and electrical conductivity, and, because of the higher aspect ratio, nanofibers reached the percolation threshold at a lower loading (3.0 wt %) than the PANI nanospheres (5.0 wt %). The PANI nanofillers could increase the electrical conductivity, and, at the same loading, the epoxy nanocomposites with the PANI nanofibers showed lower volume resistivity than the nanocomposites with the PANI nanospheres, which were discussed with the contact resistance and percolation threshold. The tensile test indicated an improved tensile strength of the epoxy matrix with the introduction of the PANI nanospheres at a lower loading (1.0 wt %). Compared with pure epoxy, the elasticity modulus was increased for all the PNC samples. Moreover, further studies on the fracture surface revealed an enhanced toughness. Finally, the real permittivity was observed to increase with increasing the PANI loading, and the enhanced permittivity was analyzed by the interfacial polarization.

Understanding the relationship of performance with nanofiller content in the biomimetic layered nanocomposites

Montmorillonite/poly(vinyl alcohol) (MMT/PVA) nanocomposites spanning the complete range of MMT content (0-100 wt%) are prepared by simple evaporation-induced assembly. Effects of MMT content on the structure and mechanical properties of nanocomposites are systematically investigated and exhibit two important transitions at MMT contents of 30 wt% and 70 wt%. In the range of 0-30 wt%, the nanocomposites show a random structure. With the content of PVA increasing, the mechanical properties of the resultant nanocomposites were dramatically enhanced and were higher than that by prediction according to the conventional composite model. In the range of 30-70 wt%, the nanocomposites show a nacre-like layered structure with alternating MMT platelets and PVA layers, and all PVA is completely restricted by MMT platelets. The mechanical properties of nanocomposites were further improved by increasing the content of MMT, and reached the maximum value at the MMT content of 70 wt%. The 70 wt% MMT/PVA nanocomposite has a tensile strength of 219 ± 19 MPa, which is 5.5 times higher than that of a pure PVA film and surpasses nacre and reported biomimetic layered clay/PVA composites. When the MMT content is higher than 70 wt%, the layered structure is transformed to tactoids, which deteriorate mechanical properties. These results offer comprehensive understanding for developing high-performance biomimetic layered nanocomposite materials with high nanofiller loading.

Polyaniline stabilized barium titanate nanoparticles reinforced epoxy nanocomposites with high dielectric permittivity and reduced flammability

Epoxy polymer nanocomposites (PNCs) filled with both barium titanate (BaTiO3) (500 and 100 nm) and conductive polyaniline (PANI) stabilized BaTiO3 nanoparticles (NPs) have been successfully prepared. The effects of the BaTiO3 nanofiller loading level and the PANI coating on the mechanical properties, rheological behavior, thermal stability, flammability and dielectric properties were systematically studied. The viscosity study on the nanosuspensions indicates that the PANI layer on the BaTiO3 nanoparticle surface can promote the network formation of the epoxy resin. The introduction of the PANI layer was found to reduce the heat release rate and to increase the char residue of the epoxy resin. The dynamic storage and loss moduli were studied together with the glass transition temperature (Tg) obtained from the peak of tan δ, and the reduced Tg in the PNCs is associated with the enlarged free volume. The tensile test indicated an improved tensile strength of the epoxy matrix with the introduction of the BaTiO3 NPs. Compared with the cured pure epoxy, the elasticity modulus was increased for all the PNC samples. The fracture surface study revealed an enhanced toughness. Due to the ferroelectric nature of BaTiO3, the real dielectric permittivity increased with increasing the BaTiO3 nanoparticle loading. The PANI layer on the surface of BaTiO3 also enhanced the dielectric permittivity arising from the interfacial polarization formed in the PNCs.

Iron-core carbon-shell nanoparticles reinforced electrically conductive magnetic epoxy resin nanocomposites with reduced flammability

Carbon coated iron (Fe@C) nanoparticles successfully served as nanofillers for obtaining magnetic epoxy resin polymer nanocomposites (PNCs). The effects of nanofiller loading level on the rheological behaviors, thermal stability, flammability, dynamic mechanical, mechanical properties, electrical conductivity and magnetic properties were systematically studied. And the curing process of the PNCs was also studied by Fourier transform infrared spectroscopy test. A reduced viscosity was observed in the 1.0 wt% Fe@C/epoxy resin liquid suspension samples and the viscosity was increased with further increasing the Fe@C nanoparticle loading. In the TGA test, the introduction of the Fe@C nanofillers gave a lower onset decomposition temperature of the PNCs. However, a reduced flammability was observed in the PNCs due to the easier char formation from epoxy matrix induced by the Fe@C nanoparticles. The dynamic storage and loss modulii were studied together with the glass transition temperature (Tg) being obtained from the peak of tanδ. Enhanced storage modulus was observed in the PNCs with 20.0 wt% Fe@C nanoparticles. The percolation thresholds of the Fe@C nanoparticles were identified with the study of tensile strength and electrical conductivity. Due to the cavities initiated by the nanoparticles, the PNCs with 5.0 wt% Fe@C nanoparticles showed an increased tensile strength up to 60% compared with pure epoxy. The Fe@C nanofillers could efficiently increase the electrical conductivity of the epoxy matrix, and the particle chain observed in the SEM image of fracture surface indicated the formation of percolated Fe@C nanoparticles in the epoxy matrix. Finally, the Fe@C nanoparticles become magnetically harder after dispersing in epoxy due to the decreased interparticle dipolar interaction, which arises from the enlarged nanoparticle spacer distance for the single domain nanoparticles.

Synthesis of Epoxy-TiO2 Nanocomposites: A Study on Sliding Wear Behavior, Thermal and Mechanical Properties

Epoxy-based nanocomposites containing functionalized nanoscale TiO2 with 0.5%, 1%, 5%, and 10% by weight were developed. A coupling agent was employed to functionalize nano titania for better compatibility of nanoscale particles with dispersing media. Under sliding conditions, the specific wear rate and coefficient of friction were evaluated. The dispersion of fillers in the matrix was also studied using scanning electron microscopy. The wear mechanism is studied in correlation with a micrograph of the worn-out surface of nanocomposites. The various mechanical properties and thermal stability were studied and the influences of nanofiller loading on these parameters were observed.

Microstructure, electrical, and electromagnetic interference shielding properties of carbon nanotube/acrylonitrile–butadiene–styrene nanocomposites

AbstractProcessing, electrical, and electromagnetic interference (EMI) shielding behaviors of carbon nanotube (CNT)/acrylonitrile–butadiene–styrene (ABS) nanocomposites were studied as function of CNT concentration. The nanocomposites were prepared by melt mixing followed by compression molding. The selective and good level of dispersion of CNT in the styrene–acrylonitrile section of the ABS polymer was found to create conductive networks in the ABS matrix at a nanofiller loading of 0.75 wt %. At this nanofiller loading, the nanocomposite electrical conductivity was 10−5 S/m. This conductivity makes the nanocomposite suitable for electrostatic discharge protection applications. The EMI shielding effectiveness of the nanocomposites increased with the increase in nanofiller concentration. In the 100–1500 MHz frequency range, 1.1 mm thick plates made of ABS nanocomposite filled with 5 wt % CNT exhibit an EMI shielding effectiveness of 24 dB. At this shielding level, the nanocomposite is suitable for a broad range of applications. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012

Electrical treeing and the associated PD characteristics in LDPE nanocomposites

Treeing in low density polyethylene (LDPE) filled with alumina nanocomposite as well as unfilled LDPE samples stressed with 50 Hz ac voltage has been studied. The tree inception voltage was monitored for various samples with different nano-filler loadings and it is seen that there is an increase in tree inception voltage with filler loading in LDPE. Treeing pattern and tree growth duration for unfilled and nano-filled LDPE samples have also been studied. Different tree growth patterns as well as a slower tree growth with increase in filler loading in LDPE nanocomposites were observed. The observed slow propagation of tree growth with filler loading is attributed to the changes in the polymer crystalline morphology induced by the presence of nano-particles and the greater ability of the nanoparticles to resist discharge growth. SEM studies carried out to determine the morphology of unfilled and nano-filled LDPE showed an increase in lamellae packing in LDPE nanocomposites and this increased lamellar density leads to a reduction in the tree propagation rate. Partial discharge activities were also monitored during the electrical tree growth in both the unfilled and the nano-filled LDPE samples and were found to be significantly different. PD magnitude and the number of PD pulses per cycle were found to be lower with electrical tree growth duration in LDPE nanocomposites as compared to unfilled LDPE. The same trend was seen with increased filler loading also.

Rheological behavior of polypropylene nanocomposites at low concentration of surface modified carbon nanotubes

AbstractThis article reports the rheological behavior of nanocomposites of isotactic polypropylene with both unmodified multiwall carbon nanotubes (CNTs) and phenol and 1‐octadecanol (C18) functionalized CNT (f‐CNT) at 0.1, 0.25, 1.0, and 5.0 wt% of the nanofillers. The incorporation of CNT at low loadings of 0.1 and 0.25 wt% decreases the storage and loss modulus and complex viscosity of the system, especially for the case of using f‐CNT. Out of the two types of functionalizations, C18 functionalization registers the lowest modulus and viscosity and displays processing aid behavior at 0.1 wt% loading, which is believed to be due to the disruption of the polymer entanglements. As the nanofiller loading increases to 1 wt%, the disruption of polymer entanglements effect is balanced by the hydrodynamic effect and subsequently neat polypropylene (PP), and the filled PP systems show similar modulus and complex viscosity. As the nanofiller loading increases further to 5 wt%, the hydrodynamic effect becomes the dominating factor, and the modulus and the complex viscosity of the nanofilled system become greater than that of neat PP. Results suggest that the 0.1 wt% loading of C18 f‐CNT could be a useful processing aid additive for improving polypropylene processability. POLYM. ENG. SCI., 52:1868–1873, 2012. © 2012 Society of Plastics Engineers

The effect of nanoparticles on gastrointestinal release from modified κ-carrageenan nanocomposite hydrogels

In this article, silver and magnetite nanofillers were synthesized in modified κ-carrageenan hydrogels using the in situ method. The effect of metallic nanoparticles in gastro-intestinal tract (GIT) release of a model drug (methylene blue) has been investigated. The effect of nanoparticles loading and genipin cross-linking on GIT release of nanocomposite is also studied to finally provide the most suitable drug carrier system. In vitro release studies revealed that using metallic nanocomposites hydrogels in GIT studies can improve the drug release in intestine and minimize it in the stomach. It was found that cross-linking and nanofiller loading can significantly improve the targeted release. Therefore, applying metallic nanoparticles seems to be a promising strategy to develop GIT controlled drug delivery.

Exfoliated/intercalated silicate/hot styrene butadiene rubber nanocomposites: Structure–properties relationship

AbstractRubber nanocomposites based on hot styrene‐butadiene rubber (SBR) and organophilic layered silicate were prepared via mechanical mixing followed by compression molding. Varying amount of organically modified nanosilicate, 2.5, 5, 10, and 15 parts per hundred of rubber (phr), was added to the SBR matrix to examine the influence of nanosilicate on morphology and structure–property relationships. The morphology of nanocomposites was studied by X‐ray diffraction and transmission electron microscopy which reveal that the nanocomposite contained a good dispersion of intercalated/exfoliated layers through the matrix. The interaction between SBR matrix and nanofiller was studied by infrared spectroscopy. No clear evidence for the formation of new components in the rubber was found but infrared spectroscopy denoted evidence for exfoliation. The reinforcing effect of the nanosilicate was determined by mechanical testing and dynamomechanical analysis. The results indicate that the tensile properties and the storage modulus increased with increasing nanofiller loading. This suggests a strong rubber–nanosilicate interaction which is attributed to the exfoliated/intercalated structure. Thermogravimetric analysis revealed that incorporation of organoclay enhances the thermal stability of the nanocomposites. The best thermal stability was observed for nanocomposites containing 5 phr nanosilicate. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Covalent functionalization of graphene with organosilane and its use as a reinforcement in epoxy composites

Functionalized graphene nanosheets (f-GNSs) produced by chemically grafting organosilane were synthesized by a simple covalent functionalization with 3-aminopropyl triethoxysilane. The f-GNSs showed a larger thickness, but smaller width and than the un-treated graphene. The covalent functionalization of graphene with silane was favorable for their homogeneous dispersion in the polymer matrix even at a high nanofiller loading (1wt.%). The initial thermal degradation temperature of epoxy composite was increased from 314°C to 334°C, at a f-GNS content of 1wt.%. Meanwhile, the addition of 1wt.% f-GNSs increased the tensile strength and elongation to failure of epoxy resins by 45% and 133%, respectively. This is believed to be attributed to the strong interfacial interactions between f-GNSs and the epoxy resins by covalent functionalization. The experimentally determined Young’s modulus corresponded well with theoretical simulation under the hypothesis that the graphene sheets randomly dispersed in the polymer matrix.

Thermal and flammability properties of polypropylene/carbon black nanocomposites

Polypropylene/carbon black (PP/CB) nanocomposites were prepared by melt compounding to investigate the effect of nanofiller loadings on the thermal and flammability properties of PP. The obtained nanocomposites displayed not only dramatically enhanced thermal stability both under nitrogen and in air, but also improved flame retardancy to some extent. Moreover, the higher the loading level of CB, the better was the improved effect. This enhanced mechanism was attributed mainly to trapping of peroxy radicals by CB nanoparticles at elevated temperature to form a gelled-ball crosslinked network, which act as a barrier to both heat and mass transfer. The thermal-oxidation cross-linking reaction was supported by the results of rheological properties, gel measurements and FTIR analysis.

Aromatic Polyimide/MWCNT Hybrid Nanocomposites: Structure, Dynamics, and Properties

Two series of hybrid polyimide (PI)/multiwalled carbon nanotube (MWCNT) nanocomposites were prepared including COOH-functionalized or pristine nanotubes, and their structure, morphology and dynamics/mechanical properties at 20°C–500°C were studied using WAXD (Wide-angle X-ray diffraction), AFM (Atomic force microscopy), TEM (transmission electron microscopy), DSC (Differential scanning calorimetry), DMA (Dynamic mechanical analysis), CRS (creep rate spectroscopy) techniques, and stress–strain testing. The impact of nanofiller loadings of 0.125, 0.25, 0.5, or 1 wt% relative to PI was evaluated. Specific changes in the matrix morphology and different quality of nanotube dispersion in the nanocomposites with amorphous and semicrystalline matrices were determined. The best nanotube dispersion was observed in the composites with 0.5 wt% MWCNT-COOH. A peculiar high temperature dynamics, different for amorphous, and semicrystalline matrices, was revealed in these nanocomposites. The most dramatic changes in high temperature dynamics and a pronounced dynamic heterogeneity as well as substantially enhanced mechanical properties at room temperature were revealed in the case of a semicrystalline PI matrix. The results were treated in terms of the synergistic impact of nanotubes and matrix crystallites on dynamics in the intercrystalline regions of PI (“combined constrained dynamics effect”) and the peculiar interfacial dynamics.

Influence of nano-fillers on electrical treeing in epoxy insulation

This paper presents the results of a study on the effect of alumina nano-fillers on electrical tree growth in epoxy insulation. Treeing experiments were conducted at a fixed ac voltage of 15 kV, 50 Hz on unfilled epoxy samples as well as epoxy nanocomposites with different loadings of alumina nano-fillers. Time for tree inception as well as tree growth patterns were studied. The results show that there is a significant improvement in tree initiation time with the increase in nano-filler loading. Different tree growth patterns as well as slower tree growth with increasing filler loadings were observed in epoxy nanocomposites. The nature of the tree channel and the elemental composition of the material on the inner lining of the tree channels have been studied using SEM imaging and EDAX analysis respectively of the cut section of the tree channels. It has been shown that the type of bonding at the interface has an influence on the electrical tree growth pattern. The nature of the bonding at the interface between the epoxy and the nano-filler has been studied using FTIR spectrometry. Finally the influence of the interface on tree growth phenomena in nanocomposites has been explained by a physical model.

Polypyrrole metacomposites with different carbon nanostructures

Polypyrrole (PPy) nanocomposites incorporating different carbon nanostructures (CNS), including graphenes of different sizes, carbon nanofibers (CNFs) and carbon nanotubes (CNTs), have been successfully synthesized using a surface initiated polymerization (SIP) method. The effects of graphene size, loading level and surface functionality on the electrical conductivity and dielectric permittivity of their corresponding nanocomposites have been systematically studied. The electron transportation mechanism has been investigated, which follows a quasi 3-d variable range hopping (VRH) behavior in the nanocomposites. Meanwhile, CNFs and CNTs with the same loading as graphene are also comparatively studied. Scanning electron microscopy and transmission electron microscopy results indicate that the PPy coating on one-dimensional carbon nanostructures, such as CNFs and CNTs, is more smooth and uniform than that on the two-dimensional graphenes. PPy/CNTs nanocomposites exhibit the lowest resistivity, followed by the composites incorporating the smaller sized graphene without surfactant. More interestingly, a negative permittivity is found in each composite system, which can be easily controlled by adjusting the nanofiller loading, morphology and surface functionality. TGA results indicate that the thermal stability of the polymer nanocomposites (PNCs) is affected by the graphene loading rather than the different nanostructures.