Strong Reinforcement Effect Research Articles

Exploring Effects of Graphene and Carbon Nanotubes on Rheology and Flow Instability for Designing Printable Polymer Nanocomposites.

Nowadays, a strong demand exists for printable materials with multifunctionality and proper rheological properties to overcome the limitations to deposit layer-by-layer in additive extrusion. The present study discusses rheological properties related to the microstructure of hybrid poly (lactic) acid (PLA) nanocomposites filled with graphene nanoplatelets (GNP) and multiwall carbon nanotubes (MWCNT) to produce multifunctional filament for 3D printing. The alignment and slip effects of 2D-nanoplatelets in the shear-thinning flow are compared with the strong reinforcement effects of entangled 1D-nanotubes, which govern the printability of nanocomposites at high filler contents. The mechanism of reinforcement is related to the network connectivity of nanofillers and interfacial interactions. The measured shear stress by a plate-plate rheometer of PLA, 1.5% and 9% GNP/PLA and MWCNT/PLA shows an instability for high shear rates, which is expressed as shear banding. A rheological complex model consisting of the Herschel-Bulkley model and banding stress is proposed for all considered materials. On this basis, the flow in the nozzle tube of a 3D printer is studied by a simple analytical model. The flow region is separated into three different regions in the tube, which match their boundaries. The present model gives an insight into the flow structure and better explains the reasons for printing enhancement. Experimental and modeling parameters are explored in designing printable hybrid polymer nanocomposites with added functionality.

Hydrophobization of nanodiamond for polypropylene nanocomposites

Purified and de-aggregated nanodiamonds (ND) synthesized by detonation of explosives provide high surface to volume ratio and unique modification opportunities of their surface groups. In general, ND possesses polar groups, therefore, easily forms agglomerates in non-polar polymer matrix. In this study, the effects of hydrophobization of ND on the structure and the properties of polypropylene (PP) nanocomposites were investigated. Long alkyl chains of octadecyl amine (ODA) were introduced on the surface of ND with the substitution ratio of 68 %. The structural study showed that the dispersibility of ND was remarkably improved by the hydrophobization so that the PP/ND-ODA nanocomposites showed higher transparency than that of the PP/ND nanocomposites. The increased crystallinity of PP in the nanocomposites indicates that ND and ND-ODA acted as crystallization nuclei in the nanocomposites. As for the mechanical properties, the increased Young's modulus of PP/ND nanocomposites was further increased by the addition of ND-ODA. The Young's modulus of the nanocomposites with 0.5 wt% ND-ODA was 64 % higher than that of PP. The strong reinforcement effects also appeared as high heat resistances of the nanocomposites.

Elements of a compound elicit little conditioned reinforcement.

The acquisition of instrumental responding can be supported by primary reinforcers or by conditional (also known as secondary) reinforcers that themselves have an association to a primary reinforcer. While primary reinforcement has been heavily studied for the past century, the associative basis of conditioned reinforcement has received comparatively little experimental examination. Yet conditioned reinforcement has been employed as an important behavioral assay in neuroscience studies, and thus an analysis of its associative basis is called for. We evaluated the extent to which an element from a previously trained compound would facilitate conditioned reinforcement. Three groups of rats received Pavlovian conditioning with a visual-auditory compound cue followed by food. After training, a lever was made available that, when pressed, produced the same trained compound (group compound), only the auditory cue (group element), or a novel auditory cue (group control). The rats in group compound pressed the lever at a higher rate than did rats in either group element or group control, demonstrating a strong conditioned reinforcement effect only in group compound. Interestingly, there was almost no difference in responding between group element and group control. The implications of this generalization decrement in conditioned reinforcement are discussed-particularly as they relate to research in behavioral neuroscience. (PsycInfo Database Record (c) 2022 APA, all rights reserved).

The Effects of Social Media Content Created by Human Brands on Engagement: Evidence from Indian General Election 2014

With human brands or individual celebrities in fields ranging from sports to politics increasingly using social media platforms to engage with their audience, it is important to understand the key drivers of online engagement. Using Twitter data from the political domain, we show that positive and negative-toned content receive higher engagement, as measured by retweets, than mixed or neutral toned tweets. However, less popular human brands generate higher social media engagement from positive-toned content compared with more popular human brands. Therefore, we recommend that popular human brands (e.g., popular politicians or chief executive officers) keep their content objective rather than emotional. Furthermore, the tone of related brands (i.e., human brands who belong to the same political party) has a strong reinforcement effect; that is, social media engagement is higher when the tone of the focal human brand and related brands are the same and lower when the tones are different. Therefore, we prescribe that human brands actively coordinate their social media content with related brands to generate higher engagement. From human brands’ perspective, our findings recommend a comprehensive social media strategy, which takes into account the tone of content, tone of related brands’ content, and human brands’ popularity.

Development of MOF Reinforcement for Structural Stability and Toughness Enhancement of Biodegradable Bioinks.

Three-dimensional (3D) bioprinting is a technology that can precisely fabricate customized tissues and organs. Hydrogel materials that can embed living cells for use in 3D printing are called bioinks. However, there are only limited options of bioinks currently because they require the following features at once, such as printability, repetitive layer-by-layer stacking (stackability), structure stabilization, and biological properties. A polyurethane-gelatin double network hydrogel bioink was previously reported to own tunable modulus through changing the solid content, but cell viability at the high solid content is inevitably reduced. In the present study, the reinforcement effects of a metal-organic framework (MOF), zeolitic imidazolate framework-8 (ZIF-8), in the PUG bioink were evaluated. The printability, stackability, thermoresponsiveness, and shear-thinning behavior of the PUG-ZIF-8 composite hydrogels were examined. It was found that the PUG composite hydrogel containing 1250 μg/mL ZIF-8 crystals showed significant structural stability and modulus enhancement (∼2.5-fold). However, the PUG bioink containing 1250 μg/mL ZIF-8 crystals may lead to cell senescence or death. The cytocompatible concentration of ZIF-8 crystals in the bioink was about 875 μg/mL, and this concentration was much higher than the reported tolerable amount (∼50 μg/mL) of ZIF-8 for biomedical applications. The strong reinforcement effect of ZIF-8 and the drug-loading/sensing possibilities of MOFs may open new opportunities for using MOFs in 3D bioprinting applications.

Strong reinforcement effects of nanodiamond on mechanical and thermal properties of polyamide 66

In this study, polyamide 66 (PA66)/nanodiamond (ND) nanocomposites were prepared by in-situ polymerization and their chemical/physical structures and properties were investigated. Since ND was highly dispersed at the nanoscale in PA66, the nanocomposites with a low loading of ND (<0.3 wt%) exhibited high optical transparency similar to that of neat PA66. FTIR spectra revealed that the amide bond content of the nanocomposite was greater than that of neat PA66, indicating that the amide bond was formed at the interface between PA66 and ND in the process of in-situ polymerization. In terms of the mechanical properties, the Young's modulus and tensile strength considerably increased by the incorporation of ND. With the loading of only 0.5 wt% of ND, the Young's modulus and tensile strength increased by 140% and 39%, respectively. In addition, the nanocomposites showed excellent enhancement in the thermal stability as well as the thermal conductivity. The thermal decomposition temperature increased by 16 °C at an ND content of 0.5 wt%. The strong reinforcement effect of ND was assumed to be considerably greater than that of previously reported random oriented nanocarbons, related to not only the nano-dispersion and strong interfacial interaction but also the nanoconfined region at the interface.

Mechanical properties of transparent high strength biocomposites from delignified wood veneer

Transparent wood (TW) based on delignified birch veneer and thermoplastic poly(methyl methacrylate) (PMMA) is investigated by uniaxial tensile tests and full-field strain analyses based on digital image correlation techniques. TW is considered as a composite of unidirectional fibers (wood veneer) in a matrix (PMMA). Four in-plane elastic constants along the material axes are reported to enable the usage of continuum mechanics and lamination theory. Longitudinal composite strength is as high as 270 MPa at a reinforcement content of only 25 vol%. The failure behavior is interpreted based on strain field development. Strong reinforcement effects were observed from delignified birch veneer. Despite the fragility of delignified veneers, this constituent provides unexpectedly high reinforcement due to the high cellulose content and favorable stress transfer mechanisms.

Strong Reinforcement Effects in 2D Cellulose Nanofibril-Graphene Oxide (CNF-GO) Nanocomposites due to GO-Induced CNF Ordering.

Nanocomposites from native cellulose with low 2D nanoplatelet content are of interest as sustainable materials combining functional and structural performance. Cellulose nanofibril-graphene oxide (CNF-GO) nanocomposite films are prepared by a physical mixing-drying method, with focus on low GO content, the use of very large GO platelets (2-45μm) and nanostructural characterization using synchrotron x-ray source for WAXS and SAXS. These nanocomposites can be used as transparent coatings, strong films or membranes, as gas barriers or in laminated form. CNF nanofibrils with random in-plane orientation, form a continuous non-porous matrix with GO platelets oriented in-plane. GO reinforcement mechanisms in CNF are investigated, and relationships between nanostructure and suspension rheology, mechanical properties, optical transmittance and oxygen barrier properties are investigated as a function of GO content. A much higher modulus reinforcement efficency is observed than in previous polymer-GO studies. The absolute values for modulus and ultimate strength are as high as 17 GPa and 250 MPa at a GO content as small as 0.07 vol%. The remarkable reinforcement efficiency is due to improved organization of the CNF matrix; and this GO-induced mechanism is of general interest for nanostructural tailoring of CNF-2D nanoplatelet composites.

Microstructure and properties of DLC/CNx films with different CNx sublayer thicknesses

The DLC/CNx multilayer films with different CNx sublayer thicknesses were deposited on Si wafer by using magnetron sputtering technique. The microstructure and properties of the films were characterized by scanning electron microscopy (SEM), X-ray diffractometry (XRD), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, nano-indentation, scratch tests and a ball-on-disc tribometer. All the DLC/CNx films were amorphous and compact with low internal stresses and strong reinforcement effects. The content of sp3 bonds in CNx sublayer, the hardness and adhesion of the overall films decreased while the wear rate of the multilayer films increased with increasing the CNx sublayer thickness. The friction states of the multilayer films in vacuum and air were very stable. The friction coefficients of the DLC/CNx films were ~0.16 in vacuum and ~0.20 in air, and they were independent of CNx sublayer thickness. The multilayer film with CNx sublayer thickness of 0.5 nm was of a hardness of 36.9 GPa and interface adhesion of 27 N, which exhibited excellent tribological properties in vacuum and in air.

Melt-Processed Poly(Ether Ether Ketone)/Carbon Nanotubes/Montmorillonite Nanocomposites with Enhanced Mechanical and Thermomechanical Properties.

The agglomeration problem of nanofillers, for instance, carbon nanotubes (CNTs) in a poly(ether ether ketone) (PEEK) matrix, is still a challenging assignment due to the intrinsic inert nature of PEEK to organic solvents. In this work, organically modified montmorillonite (MMT) was introduced as a second filler for improving the dispersion of CNTs in the PEEK matrix and enhancing the mechanical properties, as well as reducing the cost of the materials. The nanocomposites were fabricated through melt-mixing PEEK with CNTs/MMT hybrids, which were prepared in advance by mixing CNTs with MMT in water. The introduction of MMT improved the dispersion stability of CNTs, as characterized by sedimentation and zeta potential. The CNTs/MMT hybrids were maintained in PEEK nanocomposites as demonstrated by the transmission electron microscope. The mechanical and thermomechanical measurements revealed that CNTs together with MMT had a strong reinforcement effect on the PEEK matrix, especially at high temperature, although it had a negative effect on the toughness. A maximum increase of 48.1% was achieved in storage modulus of PEEK nanocomposites with 0.5 wt% CNTs and 2 wt% MMT at 240 °C, compared to that of neat PEEK. The differential scanning calorimetry results revealed that CNTs accelerated the crystallization of the PEEK matrix while a further addition of MMT played an opposite role. The nucleation activity of the fillers was also evaluated by the Dobreva method.

Viscoelastic properties and reinforcement of non-aggregated and aggregated nanocomposites

We investigate the properties of polymer nanocomposites consisting of narrow disperse spherical nanoparticles that are coated with narrow disperse polymers. These nanoparticles can be homogeneously dispersed in a polymer matrix. The structure of the polymer-coated nanoparticles was examined by using small angle X-ray scattering (SAXS) and transmission electron microscopy (TEM), and was related to the viscoelastic properties of the nanocomposites. We observe a systematic retardation of the polymer relaxation dynamics with increasing particle loading. Nanoparticle aggregation leading to the formation of chain-like structures causes a strong reinforcement effect.

High-yield production of large aspect ratio carbon nanotubes via catalytic pyrolysis of cheap coal tar pitch

High aspect ratio (up to 5000) multi-walled carbon nanotubes (MWCNTs) were prepared on a large scale via Co-catalyzed pyrolysis of cheap coal tar pitch at 973–1273 K in an Ar-based atmosphere. Scanning Electron Microscopy and Transmission Electron Microscopy investigations revealed that as-prepared carbon nanotubes were ca. 200 μm, 40 nm and 10 nm respectively, in length, outer diameter, and wall thickness. Density functional theory calculations suggest that the in-situ reduced Co catalyst from the original cobalt nitrate precursor facilitated the cleavage of C=C and C-H bonds in adsorbed C2H4 molecules by increasing the bond length and decreasing the bond strength via donating electrons to the C atoms. The straight MWCNTs grew from/on the Co clusters through a decomposition-diffusion-penetration mechanism. The catalytic formation of high aspect ratio MWCNTs from coal tar pitch stated above can be used to improve mechanical properties of carbon-containing refractory composites. As revealed by our work, cold crushing strength and modulus of rupture of a model Al2O3-carbon refractory containing 0.75 wt% Co catalyst were respectively 26% and 34% higher than in the case of its catalyst-free counterpart, indicating the strong reinforcement effects of in-situ formed MWCNTs.

Preparation and Characterization of Microcrystalline Cellulose from Sacred Bali Bamboo as Reinforcing Filler in Seaweed-based Composite Film

Microcrystalline cellulose (MCC) isolated from cheap, fast-growing and abundant accessible Sacred Bali bamboo (Schizostachyum brachycladum) was utilized as reinforcement material in the seaweed-based composite film. Isolation of MCC was carried out by using a combination of pulping, bleaching and acid hydrolysis process. This study emphasized on the feasibility of MCC production from Sacred Bali bamboo by studying its properties using X-ray diffraction (XRD), scanning electron microscopy (SEM), fourier transform infrared spectroscopy (FTIR) and thermogravimetric analysis (TGA). The commercial-MCC (CMCC) was used as reference material. Results showed that the production yield, moisture content (MC) and fiber length of bamboo-MCC (BMCC) were 83.37±1.48 %, 4.50±0.5 %, and 0.47±0.02 mm, respectively. According to the chemical analysis by FTIR, both lignin and hemicellulose were completely removed from BMCC, and thus, improved the crystallinity (78 %) and thermal stability (≈325 °C) of BMCC. This study also revealed that MCC produced from Sacred Bali bamboo demonstrated strong mechanical reinforcement effect in the seaweed-based film. Hence, Sacred Bali bamboo-MCC could be used as reinforcement material in the polymer.

Trans crystallization behavior and strong reinforcement effect of cellulose nanocrystals on reinforced poly(butylene succinate) nanocomposites.

Biodegradable poly(butylene succinate) (PBS) nanocomposites are polymerized via in situ polymerization of succinic acid (SA) with cellulose nanocrystal (CNC)-loaded 1,4-butanediol (1,4-BD) mixtures. As reinforcement fillers, whisker-like CNCs are first dispersed in alcohol and sequentially spray-dried, before adding them to 1,4-BD. During the polymerization, the remains of sodium sulfonate in the CNC surfaces retard the polycondensation reaction, which is carefully controlled for the CNC-loaded systems. For the 0.1–1.0 wt% CNC-loaded PBS nanocomposites, it is found the nano-fillers are sufficiently dispersed to induce different crystallization behavior of the matrix polymer. The CNCs may initially act as heterogeneous nucleation sites of the molten PBS chains, during melt crystallization. In this case, most of them tend to be pushed out from the growing crystallites, which develop different nanocomposite morphologies with increasing CNC content. Among the resulting nanocomposites, the 0.1 wt% CNC-loaded system shows the highest tensile strength of 65.9 MPa, similar to that of nylon 6, as a representative engineering polymer as well as 2 fold elongation at break compared with Homo PBS. The in situ polymerized CNC-loaded PBS nanocomposites are expected to be a 100% biomass material for a virtuous cycle of biorefinery. Moreover, they demonstrate that the CNC-loaded PBS nanocomposite with a low CNC loading content can be used in various commercial applications for pollution abatement.

Enhanced robustness of evolving open systems by the bidirectionality of interactions between elements

Living organisms, ecosystems, and social systems are examples of complex systems in which robustness against inclusion of new elements is an essential feature. A recently proposed simple model has revealed a general mechanism by which such systems can become robust against inclusion of elements with totally random interactions when the elements have a moderate number of links. The interaction is, however, in many systems often intrinsically bidirectional like for mutual symbiosis and competition in ecology. This study reports the strong reinforcement effect of the bidirectionality of the interactions on the robustness of evolving systems. We show that the system with purely bidirectional interactions can grow with twofold average degree, in comparison with the purely unidirectional system. This drastic shift of the transition point comes from the reinforcement of each node, not from a change in structure of the emergent system. For systems with partially bidirectional interactions we find that the regime of the growing phase gets expanded. In the dense interaction regime, there exists an optimum proportion of bidirectional interactions for the growth rate at around 1/3. In the sparsely connected systems, small but finite fraction of bidirectional links can change the system’s behaviour from non-growing to growing.

TEST AND CALCULATION OF THE CARBON BLACK REINFORCEMENT EFFECT ON THE HYPER-ELASTIC PROPERTIES OF TIRE RUBBERS

ABSTRACT The strong reinforcement effect of filler particles on the mechanical behavior of elastomers has been well known for decades and has significantly contributed to the wide use of rubber materials in the tire industry. By using the automated grid method testing system, the quasi-static mechanical tests of three typical kinds of carbon black–filled tire rubbers with different elastomeric matrixes are carried out. Then, the influences of carbon black reinforcement on their hyper-elastic properties (the stress–strain relationship, the “S”-shaped nonlinear characteristic, and the stress level at certain stretch) are systemically discussed. The experimental data also allowed for a direct evaluation on a classical constitutive model based on the amplification of the first strain invariant. Comparison results illustrate that this model can explicitly take into account the reinforcement dependence of hyper-elasticity of tire rubbers in a certain degree. After that, the moderate finite deformation of these reinforced tire rubbers is studied using numerical investigations. For gaining the effect of particle clustering, different spatial distributions of carbon black particles (regular random dispersion and agglomerate random dispersion) in the elastomeric matrix are analyzed through the finite element simulations. The comparison of experimental and numerical results emphasizes the importance of the consideration of particle distribution and suggests that successful modeling of the material mainly requires a rational treatment of composite nature of its microstructure.

Strong nanocomposite reinforcement effects in poly(vinyl alcohol) with melanin nanoparticles

The high dispersibility of melanin NPs in the PVA was achieved by using a simple casting method. The mechanical properties remarkably increased at a low content of melanin, and was even superior to conventional carbon-based nanofillers.

Poly(vinylidene fluoride)/silica nanocomposite membranes by electrospinning

AbstractPoly(vinylidene fluoride) (PVDF)/silica nanocomposite membranes containing up to 30% silica were prepared by electrospinning using colloidal silica as the source of silica and dimethyl formamide as the solvent. The fiber morphology was observed by field emission scanning electron microscopy. The average fiber diameter is about 0.3 μm for PVDF/silica composite fibers having 10–30% silica. Silica nanoparticles were observed on all fiber surfaces with fairly good dispersion and distribution. Fourier transform infrared spectroscopy and differential scanning calorimeter were used to investigate the crystallization behavior of PVDF and showed that a mixture of α‐, β‐, and γ‐phase crystals was obtained with little content of α phase and all the PVDF/silica composite membranes have similar degree of crystallinity. Static water contact angle measurements were performed to investigate the surface wettability of the membranes. The mechanical properties were evaluated by tensile tests, showing strong reinforcement effect. The tensile modulus and tensile strength increase significantly when silica is present. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

Grammatical Constructions in Typical Developing Children: Effects of Explicit Reinforcement, Automatic Reinforcement and Parity

This study replicated and extended Wright (2006) and Whitehurst, Ironsmith, and Goldfein (1974) by examining whether preschool aged children would increase their use of passive grammatical voice rather than using the more age-appropriate active grammatical construction when the former was modeled by an adult. Results showed that 5 of the 6 participants began using the passive voice after this verbal behavior had been modeled. For 3 of the participants, this change was large. The change occurred even though the adult model explicitly rewarded the participant with praise and stickers for using the active voice, while providing no praise or stickers for using the passive form that was modeled. For 1 participant, the modeling procedure had no effect on use of the passive voice. These results indicate a strong automatic reinforcement effect of achieving parity with the grammatical structures used by adults, compared to the effects of explicit reinforcement by the adult. This might help to explain why children acquire grammatical structures prevalent in their language community apparently without explicit instruction.

Strong Nanocomposite Reinforcement Effects in Polyurethane Elastomer with Low Volume Fraction of Cellulose Nanocrystals

Polyurethane/cellulose nanocrystal nanocomposites with ultrahigh tensile strength and stain-to-failure with strongly improved modulus were prepared by adding cellulose nanocrystals (CNCs) during th ...