Nanoclay Content Research Articles

Effect of nano clay and PCE on the buildability of ultra-fine dredged sand-based 3D printing materials

The use of ultra-fine dredged sand instead of natural sand in construction 3D printing materials can significantly reduce the cost. However, ultra-fine dredged sand has fine particles and high angular morphology, which can hinder the buildability and continuous printability of construction 3D printing materials. The addition of polycarboxylate superplasticizer (PCE) can effectively solve this problem. Considering that the change of PCE (content of 0, 0.1%, 0.2%, 0.3%) content has a great influence on the printing performance of mortar, in order to make up for this deficiency, nano clay (content of 0,1%) is added to the mortar. The experimental results showed that the addition of nano clay can significantly reduce the negative effects of PCE on the yield stress and apparent viscosity of 3D printing materials (3DPM). When the content of PCE is 0.2%, the addition of 1% NAC could increase the static yield stress and viscosity growth rate of 3DPM by 111.8% and 115.3% respectively. In addition, unconfined compressive strength test, isothermal calorimetry, Mercury invasion porosity method and thermogravimetric analysis were used to characterize the hardening properties of 3DPM. The results of heat of hydration showed that the addition of nano clay reduced the hydration exothermic peak of 3DPM, but increased the total heat release. The results of pore structure analysis showed that the addition of nano clay reduced the macropore (>1000 nm) of 3DPM from 19.31% to 18.82%. Thermogravimetric analysis showed that the addition of nano clay increased the hydration products. Therefore, the compressive strength of 3DPM was kept within an acceptable range. Finally, the laboratory’s printing results indicated that the 3DPM can print up to 20 layers continuously.

Toward understanding the crystallization behavior of polypropylene‐based nanocomposites: Effect of ethylene–octene copolymer and nanoclay localization

AbstractThe crystallization properties of polypropylene (PP), a widely used polymer in industry, can be modified to overcome its mechanical limitations. In the current work, we investigated the effect of ethylene octene copolymer (EOC), blend morphology, nanoclay loading, nano‐localization, and component ratios on PP/EOC crystallization behavior in various aspects, including crystallization rate, degree of crystallinity, nucleation state, and crystalline phases. The results revealed that adding EOC with varying ratios can decrease PP crystallinity both in degree and rate due to the partial miscibility of components through grafting. Furthermore, it was found that the effect of the nanoclay on the crystallization behavior of PP is dependent on the nanoclay loading and its localization in the blend. The nanoclay, therefore, served as a nucleation agent at low nanoparticle contents, accelerating the crystallization rate regardless of the blend's microstructure. However, the crystallization rate of the blend samples at high nanoclay contents (above the rheological percolation threshold) was strongly influenced by the type of morphology. Accordingly, high nanoclay concentrations in blends with matrix‐dispersed morphologies reduced crystallization rates (increasing half‐time from 164 to 216 and 186 s), primarily because PP chains slowed down due to their interactions with nanoparticles and nanoclay hindrance. In contrast, in a blend with a co‐continues‐type morphology, the crystallization rates increased (decreasing half‐time from 624 to 270 and 236 s) due to nano‐localization at the interface and morphology transformation to the matrix‐dispersed one. The blends and nanocomposites based on PP/EOC were also investigated to determine the relationship between the crystallization behavior and mechanical properties.

Influence of hybridizing fillers on mechanical properties of foam composite panel

AbstractFoam composite panels made from hybrid fillers are materials developed to have low density with high mechanical properties. This work focuses on improving the mechanical properties of epoxy‐based foam composite panels with hybridized fillers by combining hollow glass microspheres (HGM) and nanoclay. The HGM content was varied from 1 wt.% to 3 wt.% in foam composites panel, while nanoclay content was varied from 1 wt.% to 5 wt.% in each of the HGM‐filled series of foam composites panel, these foam composite panels were fabricated using a conventional resin casting method. The mechanical properties such as tensile strength, impact strength, hardness, flexural strength of the prepared hybrid‐filled foam composite panels were determined and compared with the neat epoxy. It was found that the hybrid‐filled foam composite panels exhibited improved mechanical properties than the neat epoxy. These improved properties were because of excellent interfacial adhesion between the hybrid fillers and the matrix. The improved mechanical properties could suggest that this material may be suitable for application in industries where lightweight materials with good mechanical properties are required. This study showed a new area of synthetic foam development research by enhancing mechanical properties using hybrid‐filled.

Investigation of the Effect of Hybrid Nanofiller on the Mechanical Performance and Surface Properties of Bio-Based Polylactic Acid/Polyolefin Elastomer (PLA/POE) Blend.

Polylactic acid has stood out among bio-based polymers for its usage in the food packaging industry and biomedical fields. Through the melt mixing process, the toughened poly(lactic) acid (PLA) was prepared with polyolefin elastomer (POE), incorporated via various ratios of nanoclay and a fixed amount of nanosilver particles (AgNPs). The correlation between the compatibility and morphology, mechanical properties, and surface roughness of samples with nanoclay was studied. The calculated surface tension and melt rheology confirmed the interfacial interaction demonstrated by droplet size, impact strength, and elongation at break. Each blend sample exhibited matrix-dispersed droplets, and the size of POE droplets steadily dropped with increasing nanoclay content, corresponding to the enhanced thermodynamic affinity between PLA and POE. Scanning electron microscopy (SEM) acknowledged that the inclusion of nanoclay in the PLA/POE blend ameliorated the mechanical performance by preferable localization in the interface of used components. The optimum value of elongation at break was acquired at about 32.44%, where the incorporation of 1 wt.% nanoclay led, respectively, to 171.4% and 24% enhancement rather than the PLA/POE blend with the composition of 80/20 and the virgin PLA. Similarly, the impact strength reached 3.46 ± 0.18 kJ m-1 as the highest obtained amount, showing the proximity of 23% progress to the unfilled PLA/POE blend. Surface analysis indicated that adding nanoclay caused the augment of surface roughness from 23.78 ± 5.80 µm in the unfilled PLA/POE blend to 57.65 ± 18.2 µm in PLA/POE contained 3 wt.% nanoclay. Rheological measurements implied that organoclay resulted in the strengthening of melt viscosity as well as the rheological parameters such as storage modulus and loss modulus. Han plot further showed that the storage modulus is always higher than the loss modulus in all prepared PLA/POE nanocomposite samples, corresponding to the restriction of polymer chains mobility induced by the formation of strong molecular interaction between nanofillers and polymer chains.

Nanoclay-Reinforced Nanocomposite Nanofibers—Fundamentals and State-of-the-Art Developments

Nanoclays are layered mineral silicates, i.e., layered silicate nanosheets. Nanoclays such as montmorillonite, bentonite, kaolinite, etc., have been used as reinforcements in the nanofibers. Numerous polymers have been used to fabricate the nanofibers, including poly(vinylidene fluoride), poly(vinyl alcohol), polycaprolactone, nylon, polyurethane, poly(ethylene oxide), and others. To develop better compatibility with polymers, nanoclays have been organo-modified prior to reinforcement in the nanofiber matrices. This state-of-the-art review highlights the fundamentals, design, fabrication, and characteristics of the polymer/nanoclay nanofibers. The nanoclay filled nanocomposite nanofibers have been fabricated using electrospinning and other fiber processing techniques. The electrospinning technique has been preferred to form the nanoclay-filled nanofibers, owing to the better control of processing parameters and resulting nanofiber properties. The electrospun polymer/nanoclay nanofibers usually have fine nanoparticle dispersions, microstructures, smooth textures, and narrow diameters. The physical properties of the designed nanofibers depend upon the processing technology used, solvent, solution/melt concentration, flow rate, spinning speed, voltage, and other process parameters. Hence, this review attempts to assess a literature-driven consequence of embedding nanoclays in the polymeric nanofibers in a broad context of the application of these fibrous materials. Conclusively, to design the polymer/nanoclay nanofibers, montmorillonite nanoclay has been observed as a nanofiller in most of the studies, and, similarly, the electrospinning technique was preferred as a fabrication technique. Almost all the physical properties of the nanofibers studied revealed dependences upon the choice of the polymer matrix for nanofiber formation as well as the nanoclay contents, modification, and dispersion state. Accordingly, the nylon/nanoclay nanofibers have been investigated for nanofiller dispersion, mechanical properties, and thermal profiles. The antibacterial properties were among the prominent features of the poly(vinyl alcohol)/nanoclay nanofibers. The poly(vinylidene fluoride)/nanoclay systems were explored for the microstructure, crystallinity, and piezoelectric properties. The polycaprolactone/nanoclay nanofibers having fine microstructure were capable of forming tissue engineering scaffolds. The drug delivery and sound absorption properties were noticeable for the polyurethane/nanoclay nanofiber systems. Moreover, the poly(lactic acid)/nanoclay nanofibers were found to have prominent biodegradability and low gas permeability features. The resulting polymer/nanoclay nanocomposite nanofiber systems found potential for the technical applications of sensors, packaging, tissue engineering, and wound healing. However, thorough research efforts have been found to be desirable to find the worth of polymer/nanoclay nanofibers in several concealed technological sectors of energy, electronics, aerospace, automotives, and biomedical fields.

Optimization of Machining Parameters of Natural/Glass Fiber with Nanoclay Polymer Composite Using Response Surface Methodology

Machining processes are one of the most important finishing operations in the fabrication of composites, which contain natural fibers. However, it is difficult to attain a better fishing on the final components. Hence, an attempt has been made in the work to achieve a good surface finish in compression-molded hybrid fiber composites containing nanoclay particles by optimizing the milling parameters. Experiments were conducted by using Box–Behnken design (response surface methodology (RSM)) to optimize the milling process parameters such as spindle speed (16, 24, and 32 rpm), feed rate (0.1, 0.2, and 0.3 mm/rev.), and depth of cut (1, 1.5, 2 mm) along with different vol% of nanoclay content (3%, 6%, and 9%). The surface roughness of machined fiber composite was measured, and the most influential parameters were analyzed by analysis of variance, evaluation of signal-to-noise ratio, and mathematical models of responses were developed by RSM. The experimental results (A2B1C4D3) indicated that the feed rate is one of the most significant parameters, followed by nanoclay content, depth of cut, and spindle speed. Surface roughness was found to decrease continuously (2.18–2.08 µm) with increasing nanoclay content (up to 6%) at a certain limit and further addition of clay content (above 6%); the results were declined (2.42 µm) for the same levels of other parameters.

Nonlinear Viscoelasticity and Toughening Mechanisms in Nanoclay-PNIPAAm Double Network Hydrogels.

We investigate the mechanical properties of a magnetic temperature-sensitive hydrogel at varying concentrations of covalent and physical cross-linking. The hydrogel consists of covalently cross-linked poly(N-isopropylacrylamide) (PNIPAAm), physically interacting nanoclay particles, and magnetic ferric oxide nanoparticles. The physical nanoclay network exhibits strong viscoplastic behavior, and we find that increasing nanoclay content improves both strength and toughness in the double network materials. We investigate the behavior of the gels using a nonlinear viscoplasticity model with a modified rule of mixtures approach and attribute the observed trends to two factors: (a) the yield-stress behavior of the nanoclay network and (b) load-sharing interactions between the PNIPAAm and the nanoclay. Our findings indicate a strong correlation between the mass ratio of covalent cross-linker used and fractional percolation of the PNIPAAm network.

Electrospinning of cellulose acetate/graphene/nanoclay nanocomposite for textile wastewater filtration

In this study, electrospinning technique was used to prepare cellulose acetate (CA) and graphene oxide (GO) nanofiber composites along with nanoclay (NC) for filtration applications. For this purpose, different contents of GO and NC were added to the CA solution, and the electrospinning process was optimized to produce the finest fiber. The morphology and crystalline structures of the resulting nanofiber composites were examined by scanning electron microscopy (SEM) and X-ray diffraction (XRD), respectively. According to the obtained results, the CA (12%)/GO (1%)/NC (1%) nanofiber had the minimum mean fiber diameter and uniform diameter distribution among all electrospun fibers. TEM images showed good dispersion of the employed nanostructures (GO and NC) in the fibrous membranes. The results of the mechanical test revealed 24% improvement in the tensile strength of the nanocomposite fiber (CA/GO/NC) in comparison with CA fiber. Thermogravimetric analysis (TGA) indicated that the presence of GO and NC led to higher thermal stability than pristine polymeric fiber. XRD results confirmed the presence of both amorphous and crystalline CA in the optimized sample. The spectrophotometric analysis showed that the amount of dye absorption increased after adding GO and NC to CA. In conclusion, the produced fibrous nanocomposite can be used as a potential filter for color removal in the textile industry.

Vulcanization, compounding, thermo-mechanical properties and surface morphology of montmorillonite nanoclay based nitrile rubber nanocomposites

Remarkable importance has been bestowed upon polymer nanocomposites over the last few decades. Recently high-performance nanocomposites based on organic polymer/inorganic fillers have provided a new platform to the investigators in scientific and industrial aspects because of their unique and excellent properties. The main challenge lies in efficient dispersion and alignment of nanoclay into polymer matrix. The nanocomposites provided superior thermo-mechanical properties i.e., flexibility, light weight, good processability with comparatively low cost and several applications in field such as automobile, electrical, safety, and aerospace. The present investigation is devoted on the development of nitrile rubber nanocomposites reinforced with montmorillonite (MMT) nanoclay and other vulcanization and compounding additives like dicumyl peroxide, zinc oxide, stearic acid, di-octyl-phthalate, antioxidant, curing agents etc., and this also study investigated the effect of MMT nano-clay of loading 1, 3, 5 parts per hundred rubber (phr) on the thermo-mechanical properties and morphological aspects of nitrile rubber. Nanocomposites samples were prepared through vulcanization and compounding method using two roll mills, followed by compression moulding. The results revealed that 5 phr content of MMT nanoclay in the nitrile rubber matrix gives the highest tensile strength, tensile modulus and elongation at break according to ASTM standard and thermal stability carried out through thermal gravimetric analysis (TGA). The modification in various properties can be attributed to better interfacial adhesion between nanoclay and rubber matrixes examined by scanning electron microscopy (SEM).

Investigating the lubrication performance of vegetable oils reinforced with HNT and MMT nanoclays as green lubricant additives

Currently, technology demands a sustainable and more environmentally friendly lubricant. In addition, government regulations and recent concern about using petroleum-based lubricants have increased research on environmentally friendly lubricants such as vegetable oils. This study investigates the lubrication performance of corn and peanut oils reinforced with different concentrations of Halloysite clay nanotubes (HNTs) and Montmorillonite nanoclay (MMT) as green lubricant additives. Block-on-ring wear tests following the ASTM G-077-17 standard procedure were conducted to investigate the effect of different nanoparticle (NP) concentrations on the coefficient of friction (COF) and wear volume loss. Different surface analytical methods, including scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), and profilometry, were used to analyze the worn surfaces. Additionally, the lubrication performance of the newly developed vegetable oil-based nanolubricants was evaluated in an industrial-type application through tapping torque tests. The tribological results revealed that the coefficient of friction (COF) for the corn oil was lowered by 56% and 77% with the addition of HNT and MMT NPs, respectively, compared to corn oil without additives. Similarly, the COF for the peanut oil was lowered by 66% and 81% with the addition of HNT and MMT NPs, respectively, compared to peanut oil without additives. Moreover, the volumetric wear decreased by 78% and 75% for the corn oil and 67% and 62% for the peanut oil when using HNT and MMT NPs as lubricant additives, respectively. Therefore, based on the experimental results, the authors conclude that vegetable oils reinforced with HNT and MMT nanoclays have the potential to be used as good biodegradable nanolubricants.

Comparative performance of fused deposit modeling3D‐printedand injection molded polylactic acid/thermoplastic starch/nanoclay bio‐based nanocomposites

AbstractThe use of biodegradable polymers is a good strategy to overcome challenges induced by petroleum‐based polymers. However, in general, there exist limitations in the formulation and fabrication of biodegradable polymers to be used in the development of parts with targeted applications. The issue is more highlighted when the 3D printing of biodegradable blends needs to be addressed. This study examines the formulation and fabrication of biodegradable nano‐reinforced polymer blends to be used in fused‐filament 3D printing. The melt‐mixing method was utilized to prepare filaments and nanocomposite systems of polylactic acid (PLA)/thermoplastic starch (TPS) blends reinforced with 0–5 wt% of nanoclay. To better understand the feasibility of the formulated compound, the process–structure–property interplays in the PLA/TPS based specimens fabricated via the fused‐filament 3D printing and injection molding were investigated and compared. The findings revealed the molded specimens showed greater tensile and flexural behavior than the printed specimens, whereas the impact resistance of the printed and molded parts was comparable. It was shown that increasing nanoclay content led to the increase in the tensile strength, Young's modulus and flexural strength of the specimens regardless of the method used. The greatest tensile strength of 10.1 and 20.1 MPa was revealed at the optimized nanoclay content of 1 and 3 wt% in 3D printed and molded parts, respectively. The surface morphology demonstrated that the addition of nanoclay favorably contributed to the interfacial adhesion, confirmed by the mechanical response of the specimens. It was shown nanoclay enhanced the thermal stability and crystallinity of the specimens while reducing water absorption and biodegradability due to its barrier properties.

Effect of water-based nanoclay and ambient temperature on rheological properties of UHPC pastes

Rheological properties of ultra-high-performance concrete (UHPC) pastes significantly impact the flowability and segregation resistance of UHPC, thus are of great importance to investigate. This study investigated the coupled effect of the water-based nanoclay suspension and ambient temperatures on rheological properties of UHPC pastes. Firstly, the water-based nanoclay was proved to show good compatibility with used PCE-based HRWR. Besides, the nanoclay content varied from 0 to 0.20% and the evaluated ambient temperatures were 10 °C, 25 °C, and 35 °C. Results showed that the addition of nanoclay and elevation of ambient temperatures significantly increased plastic viscosity and dynamic yield stress of UHPC pastes. The thixotropy of UHPC pastes was also enhanced, which was quantified by a bi-linear model including initial fluctuations of static yield stress (τfloc) and thixotropy index (IA). The enhancement of rheological properties are closely related to the evolution of internal microstructure, including physical and chemical effects. The physical effects refer to the flocculation between particles: (1) the addition of nanoclay accelerated the flocculation by the electrostatic attraction forces; (2) the elevation of ambient temperatures accelerated the flocculation by promoting Brownian motions of particles. The chemical effects refer to the increased hydration reaction: (1) the nanoclay addition increased aluminates contents, thus promoting the hydration of C3A to generate ettringite; (2) the elevation of ambient temperatures increased the dissolution of C3A then promoted the hydration. More importantly, ettringite is the main hydration product to affect the rheological properties of UHPC pastes. This study revealed the coupled effect of water-based nanoclay and ambient temperature on rheology of UHPC pastes and will advance the large-scale application of the water-based nanoclay suspension.

Dynamic Fracture Resistance under Plane Strain Conditions of High-Density Polyethylene Nanoclay Composites.

Polymer nanoclay composites have received significant attention due to their substantially enhanced mechanical, thermal and barrier properties. However, the effect of these nanoclays on the dynamic fracture resistance of a polymer matrix during fast fracture events has not been documented. In this study, the effect of nanoclay addition on the rapid crack propagation (RCP) resistance of high-density polyethylene (HDPE) was investigated through the high-speed double torsion test. Results showed that the addition of 1, 3, and 5% of nanoclays improved the dynamic fracture resistance under the plane strain conditions (Gd1) of HDPE up to 65%. An increase in the storage and loss modulus, and a decrease in crystallinity and melt flow index with nanoclay content was also found. Although the presence of agglomerates can hinder the enhancement of Gd1 as it promotes agglomerate fracture and debonding, the increase in energy consumption through fibrillation and crazing promoted by the nanoclay prevails, suggesting that the nanoclay's toughening effect that has been extensively reported under quasi-static and impact tests, is also present under RCP conditions, and that the HDPE nanocomposites could be used in applications in which RCP must be prevented.

Nanocomposite of CO2-Based Polycarbonate Polyol with Highly Exfoliated Nanoclay.

Polypropylene carbonate (PPC) derived from carbon dioxide has been used as a precursor for the synthesis of polyurethane (PU). The high viscosity of the PPC is the key parameter hindering its processability during PU synthesis. Herein, a PPC nanocomposite with highly exfoliated nanoclay was prepared through a solution intercalation process. A wide range of nanoclay concentrations incorporated into the PPC were studied. The impacts of the nanoclay on the PPC were investigated in order to maintain the polymer structure while improving its physical properties. The characterizations of PPC nanocomposites showed that the highly exfoliated nanoclay contributed to a viscosity reduction, and a slight reduction in the molecular weight. The polymer degradation was indicated by the formation of cyclic propylene carbonate. The minimum or critical concentration of nanoclay was found to be between ∼0.5 and 2.0 wt %. Within this range, the polymer degradation is minimal. The PPC nanocomposites with a lower viscosity showed excellent precursors for making PU coating materials. The PU coating derived from the PPC nanocomposite has higher anticorrosive properties in comparison with the non-modified PU coating.

Effect of nanoclay and nano-calcium carbonate content on the properties of polybutylene succinate/nanoparticle composites

How nanoparticle type and content affect polybutylene succinate (PBS) properties were investigated by varying nanoclay and calcium carbonate nanoparticles (nanoCaCO3) from 0 to 15 wt%. PBS/nanoparticle composites were prepared by compounding with a co-rotating twin-screw extruder and forming them with a compression molding machine. Their mechanical properties, filler dispersion, crystallinity, and permeability were evaluated using tensile testing, energy dispersive X-ray analysis, transmission electron microscopy, differential scanning calorimetry, X-ray diffraction, and water vapor and gas permeability measurements. The results showed that adding nanoclay and nanoCaCO3 enhanced the PBS stiffness. In comparison to neat PBS, the highest tensile moduli were 46% higher at 15 wt% nanoclay and 30% higher at 15 wt% nanoCaCO3. The ultimate tensile strength (UTS) for the PBS/nanoclay composites tended to decrease as the nanoclay content increased. Nanoclay dispersion was poor in composites containing more than 5 wt% nanoclay. Surface treating the nanoCaCO3 particles with a fatty acid resulted in similar UTS values and reduced the elongation at break to 15% from 225% for the neat PBS. The decrease in ductility resulted from PBS chain scission. The nanoclay and nanoCaCO3 at low content enhanced the PBS crystallization. The nanoplatelet-shaped nanoclay led to greater agglomeration than the cubic-shaped nanoCaCO3, but the nanoclay was more effective than the nanoCaCO3. The water vapor barrier properties improved with the added nanoclay, with about a 52% reduction in water vapor permeability as compared to neat PBS. The water vapor and oxygen barrier properties of nanoclay were more effective than the nanoCaCO3.

Development of nanoclay-based nanocomposite surfaces with antibacterial properties for potential biomedical applications

Biofilm formation on biomedical implant surfaces requires bacterial adhesion, which increases the risk of infection and chronic inflammation. Since intercalation of quaternary ammonium salts (QAS) into montmorillonite (MMT) clay, known as organoclays, has been reported to increase surface broad-spectrum antibacterial properties, we aimed to develop an antibacterial surface composed of thermoplastic polyurethane (TPU) embedded with bentonite and MMT clay containing QAS to prevent initial bacterial attachment. We evaluated its potential application in reducing bacterial adhesion and enhancing bacteria-killing properties using Gram-positive Staphylococcus aureus and Gram-negative Escherichia coli. Our results demonstrated that the nanoclay-embedded TPU surfaces with QAS significantly reduced the adhesion of E. coli and S. aureus by 68.82% and 65.18%, respectively, compared to the plain TPU surfaces. Additionally, a higher nanoclay concentration coating on the surface could enhance its effectiveness, as shown by 85.34% and 82.74% reduction in E. coli and S. aureus adhesion and killing efficiency. Furthermore, we observed that nanoclay-embedded TPU surfaces had no detrimental effects on the viability of human dermal fibroblasts. Taken together, these techniques could provide novel strategies for inhibiting bacterial adhesion and supporting bacteria killing on biomedical implant surfaces, as the investigated surfaces are simple to synthesize, efficient, and cost-effective.

Highly thixotropic ultra-high-performance concrete (UHPC) as an overlay

Ultra-high-performance concrete (UHPC) is an emerging overlay material for the bridge deck rehabilitation. As a durable material, UHPC overlay can effectively extend the service life of the bridge. In this study, the highly thixotropic UHPC overlay was designed and developed to facilitate sloped overlay construction with minimum formworks. A new type of water-based and well-dispersed nanoclay suspension was utilized to enhance the thixotropy. Two indices, including initial fluctuation of yield stress (τfloc) and thixotropy index (IA), were proposed to evaluate the thixotropy of fresh UHPC. It was found that, as nanoclay contents increased from 0 to 0.20 % (by mass of binders), the initial fluctuation of yield stress (τfloc) increased from 392.7 Pa to 3290.1 Pa and the thixotropy index (IA) increased from 9.7 Pa/min to 16.4 Pa/min, representing the significant enhancement on thixotropy. The highly thixotropic UHPC overlay showed good shape stability after the placement, but showing plenty of defects on the interface. It was shown that the bond strengths between thixotropic UHPC overlay and substrate are reduced by over 30 %. To address this issue, the application of proper vibration index on highly thixotropic UHPC overlay was investigated. Results showed that the bond strength between thixotropic UHPC overlay and substrate was increased by 45 % after the optimal vibration index. The SEM observation of the interface confirmed the increased air voids for highly thixotropic UHPC overlay and the reduced air voids after optimal vibration index. This study will promote the acceptance of highly thixotropic UHPC as an overlay.

Effect of Organomontmorillonite-Cloisite® 20A Incorporation on the Structural and Drug Release Properties of Ureasil-PEO Hybrid.

This paper presents the influence of the presence of a modified organoclay, Cloisite® 20A (MMTA) on the structural and drug release properties of ureasil organic-inorganic hybrid. Sol-gel process was used to prepare the hybrid nanocomposites containing sodium diclofenac (DCF) at 5% wt. The effect of the amount of MMTA incorporated into the ureasil hybrid matrix was evaluated and characterized in depth by different techniques such as X-ray diffraction (XRD), small angle X-ray scattering (SAXS), differential scanning calorimetry (DSC), and swelling properties. The influence of MMTA on ureasil nanocomposites release profile was evaluated by in situ UV-vis. The diffraction patterns of the UPEO-MMTA nanocomposites showed a synergistic contribution effect that led to an intensity increase and narrowed the diffraction peaks, evidencing a crystallite PEO growth as a function of the modified nanoclay content. The interactions between polyether chains and the hydrogenated tallow of MMTA led to an easy intercalation process, as observed in UPEO-MMTA nanocomposites containing low (1% wt) or high (20% wt) nanoclay content. The waterway (channels) created in UPEO-MMTA nanocomposites contributed to a free volume increase in the swollen network compared to UPEO without MMTA. The hypothesis of the channels created after intercalation of the PEO phase in the interlayer of MMTA containing organoammonium ions corroborates with the XRD results, swelling studies by SAXS, and release assays. Furthermore, when these clay particles were dispersed in the polymeric matrix by an intercalation process, water uptake improvement was observed, with an increased amount of DCF release. The design of ureasil-MMTA nanocomposites containing modified nanoclay endows them with tunable properties; for example, swelling degree followed by amount of controlled drug release, opening the way for more versatile biomedical applications.

Experimental investigation of the in-plane quasi-static mechanical behaviour of additively-manufactured polyethylene terephthalate/organically modified montmorillonite nanoclay composite auxetic structures

Apart from the inherent anomalous behaviour under tensile and compressive structures, auxetic structures have shown improved energy absorption characteristics that are of prime interest to various fields of study. This is further exemplified by additive manufacturing (AM) techniques and polymer composites to tailor the shape, geometry and form of these structures. Consequently, this paper aims to characterise the in-plane compressive behaviour and negative Poisson’s ratio (NPR) of the most prominent auxetic structures fabricated additively used polymer nanocomposite materials. The study incorporates the use of glycol-modified polyethylene terephthalate (PETG) and nanocomposites of PETG filled with organically modified montmorillonite (OMMT) nanoclay particles to produce auxetic structures fabricated through fused filament fabrication (FFF). Different structures such as hexagonal re-entrant honeycomb structures, peanut-shaped honeycombs, chiral honeycomb structures and missing rib structures are characterised for their compressive performance through experimental approaches involving mechanical testing and digital image correlation (DIC). Different parameters such as the peak crushing strength, average crushing strength, NPR, specific energy absorption (SEA), and crush force efficiency (CFE) of these structures are evaluated at different strain rates/loading rates for varying concentrations of nanoclay and PETG. It is observed that higher loadings of nanoclay particles lower the compressive strength of the structures. Additionally, the NPR decreases with increasing strain rates and is also influenced by the composition and the resultant stiffness. Moreover, the geometrical parameters of the structure largely influence its strain energy absorption. The results have shown that such material-structure combinations can produce structures of high-performance capabilities suitable for aerospace applications.

Modification Effect of Nano-Clay on Mechanical Behavior of Composite Geomaterials: Cement, Nano-Silica and Coastal Soft Soil.

To study the modification effect of nano-clay and nano-SiO2 on cement-reinforced coastal soft soil, the effects of the nano-SiO2 and nano-clay on the mechanical properties of cement soil were studied through unconfined compressive and unconsolidated undrained shear tests, and the Duncan-Chang model was used to fit the test results. Results show that adding nano-clay and nano-SiO2 to cement soil improved its compressive and shear strength. The compressive strength and shear strength increased by 18-57% and 3-32%, respectively, with the increase in nano-clay content in a content range of 0-10%. Additionally, nano-clay can enhance the ductility of cement soil. Moreover, nano-clay and nano-SiO2 improve the shear strength by increasing the internal friction angle by 1°-2° and cohesion of 9-25%, and the cement-stabilized coastal soft soil enhanced by nano-SiO2 and nano-clay conforms to the Duncan-Chang model well.