Montmorillonite Clay Particles Research Articles

Experimental study of mechanical, morphological and thermal performance of bamboo-reinforced polylactic acid-based montmorillonite clay hybrid composite

Polylactic acid (PLA) is a promising, sustainable alternative to conventional petroleum-based polymers, but its mechanical and thermal properties limit its applications. This study introduces bamboo powders (BP) and montmorillonite clay particles (MMT) into the PLA matrix to prepare novel bio-based polymer hybrid composites using a unique combination of weight percentages of BP and MMT without chemical solvents through a stir casting process under optimised input parameters followed by compression moulding. Polymer hybrid composites were fabricated with different weight combinations, and their mechanical, morphological, and thermal properties were analysed. Tensile, flexural, and impact tests were performed to examine the mechanical performance, while thermogravimetric analysis and differential scanning calorimetry were used to assess thermal stability and characteristics. Microscopy observations showed a strong interaction between the bamboo, clay, and PLA matrix. The results revealed that the maximum tensile strength and modulus increased by 26.1 % and 40.8 %, respectively, with 10 wt% BP and 4 wt% clay content. Impact strength increased by 48 % with 15 wt% BP and 4 wt% clay content. Moreover, the thermal decomposition temperature, glass transition temperature (Tg), crystallisation temperature (Tc), and melting temperature (Tm) of the hybrid composites improved considerably with 10 wt% BP and 4 wt% clay content, increasing by 4 °C, 2 °C, and 8 °C, respectively. Based on the findings of this study, the controlled processing parameters were optimised to fabricate the bio-based composite with significantly improved mechanical and thermal properties. These properties make the composite suitable for various automotive and structural applications.

Impact of carrier particle surface properties on drug nanoparticle attachment

HypothesisThe stabilization and isolation to dryness of drug nanoparticles has always been a challenge for nano-medicine production. In the past, the use of montmorillonite (MMT) clay carrier particles to adsorb drug nanoparticles and maintain their high surface area to volume ratio after isolation to dryness has proven to be effective. We hypothesise that the distribution of hydrophilic and hydrophobic patches on the clay’s surface as well as its porosity/roughness, hinder the agglomeration of the drug nanoparticles to the extent that they retain their high surface area to volume ratio and display fast dissolution profiles. ExperimentsIn this work, the distribution of hydrophobicity and hydrophilicity, and the porosity/roughness, of the surface of selected silica carrier particles were varied and the impact of these variations on drug nanoparticle attachment to the carrier particle and subsequent dissolution profiles was studied. FindingsThe fastest dissolution profiles at the highest drug nanoparticle loadings were obtained with a periodic mesoporous organosilane carrier particle which had a homogeneous distribution of hydrophobic and hydrophilic surface properties. Carrier particles with rough/porous surfaces and a combination of hydrophobic and hydrophilic patches resulted in nanocomposite powders with faster dissolution behaviour than carrier particles with predominantly either a hydrophobic or hydrophilic surface, or with non-porous/smoother surfaces.

Microplastics exhibit lower carrying effects on the bioaccessibility and cytotoxicity of lead than montmorillonite clay particles

Microplastics (MPs) in the environment are always colonized by microbes, which may have implications for carrying effect of pollutants and exposure risk in organisms. We present the crucial impacts and mechanisms of microbial colonization on the bioaccessibility and toxicity of Pb(II) loaded in disposable box-derived polypropylene (PP) and polystyrene (PS) MPs and montmorillonite (MMT) clay particles. After 45 d incubation, higher biomass measured by crystal violet staining were detected in MMT (1.23) than in PP and PS (0.400 and 0.721) indicating preferential colonization of microbes in clay particles. Microbial colonization further enhanced the sorption ability toward Pb(II), but inhibited the desorption and bioaccessibility of enriched Pb(II) in zebrafish and decreased the toxicity to gastric epithelial cells in an order of MMT > PS ≈ PP. The crucial effects were mainly because microbe-colonized substrates possessed higher oxygen functional groups and specific surface area and exhibited stronger interactions with Pb(II) and digestive component (i.e., pepsin) than pure substrates. This decreased the available soluble pepsin for complexing with sorbed Pb(II). The findings highlight the role of microbial colonization in modulating the exposure risks of artificial and natural substrate-associated pollutants and suggest that the risks of MPs may be overestimated compared to clay particles.

Effect of sodium montmorillonite clay on the kinetics of CH4 hydrate - implication for energy recovery

Silty-clayey host sediments have been widely identified in naturally-occurring hydrate-bearing sediments in the South China Sea. However, the effect of clay minerals on the kinetics of CH4 hydrate (MH) formation and dissociation remains unknown and warrants further investigation. The objective of this paper is to elucidate the effect of montmorillonite (MMT) clay particles on the formation and dissociation kinetics of MH. A series of experiments involving kinetics and morphological observations were designed to investigate the kinetics of MH in MMT suspensions with mass fractions ranging from 0.1 wt% to 9.0 wt%. The experimental results reveal that MMT promotes nucleation but delays the growth kinetics of MH. The diffuse double layer (DDL) on clay minerals is quantified to explain the observed kinetic behavior. The electric field induced on the clay surface resulted in a shorter induction time. The morphology observed indicated that MH initially forms at the gas–liquid interface and develops upward along the reactor surface, resulting in the hydrate-clay stratification behavior. The upward migration of water due to hydrate growth promotes the agglomeration of MMT clay and reduces the conversion of free water to hydrate. The findings of this study are essential in understanding the mechanisms of the naturally occurring negatively-charged clay particles on the kinetics of MH. Moreover, the results have implications for the occurrence of MH in clay-rich sediments in nature and the development of energy-efficient recovery strategies from silty-clayey hydrate-bearing sediments.

Preparation, stabilisation, isolation and tableting of valsartan nanoparticles using a semi-continuous carrier particle mediated process

This work investigated the technical feasibility of preparing, stabilizing and isolating poorly water-soluble drug nanoparticles via a small-scale antisolvent precipitation process operating in semi-continuous mode. Specifically, a novel semi-continuous process was demonstrated for the carrier particle mediated production, stabilization and isolation of valsartan nanoparticles into a solid form using montmorillonite clay particles as the carrier. The semi-continuous process operated robustly for the full duration of the experiment (~16 min) and steady-state conditions were reached after ~5 min. Nanoparticles of valsartan (51 ± 1 nm) were successfully prepared, stabilized and isolated with the help of montmorillonite (MMT) or protamine functionalized montmorillonite (PA-MMT) into the dried form by this semi-continuous route. The dissolution profile of the isolated valsartan nanocomposite solids was similar to that of valsartan nanocomposite solids produced via the corresponding laboratory scale batch mode process, indicating that the product quality (principally the nanoscale particle size and solid-state form) is retained during the semi-continuous processing of the nanoparticles. Furthermore, tablets produced via direct compression of the isolated valsartan nanocomposite solids displayed a dissolution profile comparable with that of the powdered nanocomposite material. PXRD, DSC, SSNMR and dissolution studies indicate that the valsartan nanoparticles produced via this semi-continuous process were amorphous and exhibited shelf-life stability equivalent to > 10 months.

Mechanical Properties of Epoxy/Clay Composite Coatings on an X65 Steel Substrate

This paper presents the results of a combined experimental and theoretical study of the interfacial and mechanical properties of epoxy/clay composites coatings on a mild steel substrate. This was studied using nano-indentation and Brazil Disk techniques to determine the Young’s moduli, hardness values and mode mixity characteristics of the composite coatings. The Young’s moduli of the reinforced composites comprising 1, 3, and 5 wt. % of montmorillonite clay particles are shown to improve, respectively, by about 23%, 58%, and 50% while the respective hardness values increased by about 46%, 80%, and 88%, relative to those of pristine epoxy. The measured mechanical properties have also shown to compare favorably with predictions from composite theories (rule-of-mixture and shear lag theories). The interfacial toughness between X65 steel and the epoxy/clay coatings increases with increasing mode mixity. This is associated with crack-tip shielding by crack deflection and crack bridging. The trends in the measured mode-mixity dependence of the interfacial fracture toughness values are consistent with predictions from the simplified zone, normal zone, and row models (at lower mode mixity). The insights from the observations and the measured crack profiles are incorporated into zone and row models for the estimation of crack-tip shielding. The implications of the results are discussed for the design of epoxy/clay composites with attractive combinations of mechanical properties.

Microstructural and Finite Element Analysis - Assisted Nanomechanical Characterization of Maize Starch Nanocomposite Films

Biocomposite films were prepared using normal maize starch plasticized with glycerol and water and sodium montmorillonite clay particles employing the solution mixing procedure. Scanning electron microscopy (SEM), X-ray diffraction (XRD), three-dimensional profilometry and tensile along with nanoindentation tests assisted with a Finite Element Analysis (FEA) were used for the assessment of starch-based films with various percentages of nanoclay particles. XRD analysis revealed intercalation of the test specimens while their morphology was ascertained using SEM/EDX. The FEA results were compared with the experimental measurements from nanoindentation and tensile tests. A satisfactory correlation was obtained between the experimental measurements and the computational models, demonstrating FEA-assisted nanoindentation as a useful technique for assessment, showing the effect of the different nanoclay concentrations on the mechanical properties.

Modification of the zeta potential of montmorillonite to achieve high active pharmaceutical ingredient nanoparticle loading and stabilization with optimum dissolution properties

Nanoparticles (NPs) of three poorly water-soluble BCS class II active pharmaceutical ingredients (APIs) (clozapine (CLO), curcumin (CUR) and carbamazepine (CBMZ) with zeta potentials –28.5 ± 2.5, –33 ± 1.5 and –13 ± 1.5 mV respectively) were produced, stabilized and isolated into the solid state with the help of Montmorillonite (MMT) clay carrier particles. The nanoparticles of clozapine (27 nm), curcumin (170 nm) and carbamazepine (30 nm) were produced and stabilized in suspension using a reverse antisolvent precipitation technique in the presence of ‘as received’ MMT carrier particles (∼30 μm) and/or MMT carrier particles whose surface had been slightly modified with a cationic protein, protamine sulphate salt (PA). The resulting nanoparticle carrier composites were isolated directly from suspension into a solid state form by simple filtration followed by air-drying. The API dissolution rates from these dried NP-carrier composites were comparable with those of the respective stabilized API nanoparticles in suspension up to maximum CLO, CUR and CBMZ loadings of 23%, 21.8% and 33.3% (w/w) respectively, although surface modification of the MMT carrier particles with PA was needed for the CLO and CUR NP-carrier composites in order to preserve the fast API nanosuspension-like dissolution rates at higher API loadings. For both of these APIs, the optimal loading of PA on MMT was around 4 mg/g, which likely helped to limit aggregation of the API nanoparticles at the higher API loadings. Interestingly, no MMT surface modification was needed to preserve fast API dissolution rates at higher API loadings in the case of the CBMZ NP-carrier composites. This discrimination among the three APIs for carrier particle surface modification was previously observed in reported studies by our group for three other APIs, namely valsartan, fenofibrate and dalcetrapib. When examined together, the data for all six APIs suggest a general trend whereby API nanoparticles with zeta potentials more positive than around −25 mV do not require carrier particle surface modification with PA in order to preserve their fast dissolution rates from NP-carrier composites at higher API loadings. Thus, this study offers a potentially effective means of transforming poorly water soluble BCS Class II APIs into fast dissolving solid dosage NP-carrier composites, whereby the surface properties of the carrier particle can be tuned with prior knowledge of the zeta potential of the API nanoparticles.

Microstructural and Rheological Characteristics of a Water-Clay Suspension Containing Montmorillonite Clay Particles

The rheological and microstructural characteristics of water suspensions of montmorillonite clay containing solid-phase particles of sizes d ≤ 160 μm are examined. The dependences of the relative viscosity of a clay solution and the tortuosity on the volumetric content of clay are established.

Изменение сил адгезии на поверхности частиц при обработке монтмориллонитовой глины высоким давлением

Изменение сил адгезии на поверхности частиц при обработке монтмориллонитовой глины высоким давлением

Monte Carlo analysis of montmorillonite particle structures and modeling of dissolution rate reduction

The equilibrium structure of montmorillonite clay particles was calculated using Monte Carlo simulation to evaluate the long-term behavior of alteration for bentonite buffer materials in geological repositories of radioactive waste. It has been experimentally observed that the dissolution rate of montmorillonite strongly decreases as the density increases. One of the primary causes of this reduction in dissolution rate is the reduction in reactive surface area when the edges of particles are covered with other particles (physical masking). In this study, we proposed a geometrical model in which the masking area (the edge surface masked by other particles) is calculated from the edge-to-face distance of particles. The effective edge surface area (ESA) from the equilibrium structure obtained from Monte Carlo simulation was computed using the masking model. The numerical results of the effective ESA are in good agreement with the experimental measurements of the dissolution rate by atomic force microscopy in a wide range of density conditions. Moreover, we propose a prediction expression of the effective ESA of montmorillonite particles over a wide range of density conditions, which produces physically reasonable predictions.

The failure of using equilibrium adsorption of fosthiazate onto montmorillonite clay particles to predict their cotransport in porous media as revealed by batch and column studies

Adsorption of fosthiazate onto montmorillonite clay particles (MPs) and cotransport of fosthiazate and MPs in sand and soil porous media were investigated for the understanding of the influence of MPs on transport of fosthiazate in subsurface environments. The adsorption of fosthiazate onto MPs was first examined by batch experiments and described by isotherm equations. Then, column experiments were conducted to investigate cotransport of fosthiazate and MPs in sand or soil porous media. Finally, the distribution of fosthiazate between colloidal (i.e., MPs) and solution phases during their cotransport in the porous media was compared to that in the batch experiments. The isotherms for the fosthiazate adsorption were well fitted by Freundlich equilibrium model. The adsorption was endothermic and spontaneous, which was attributed to electrostatic attraction of the electronegative groups (phosphate ester) on the fosthiazate at the positively charged sites on the MPs. Almost complete breakthroughs were observed for the fosthiazate in sand porous media due to lack of positive surface charges for the adsorption. The addition of MPs did not enhance the retention of fosthiazate, i.e, by attachment of the MPs associated with fosthiazate, because the attachment rate of MPs on the sand surfaces was much greater than the adsorption rate of fosthiazate. However, the MPs remained in the pore water causing a distribution of fosthiazate between the colloidal and solution phases. Such distribution was dependent on MP concentration and collector property (i.e., sand or soil) and was different from that in batch experiments. Our study was the first to unambiguously show that the equilibrium adsorption cannot be used in transport models to predict the mobility of MP-associated organophosphorus pesticide fosthiazate due to greater attachment rate of MPs on soil collectors than adsorption rates of the pesticide on the MPs.

Selective separation of cesium contaminated clays from pristine clays by flotation

The ongoing boom of industrialization is conflicted by concerns regarding increased levels of environmental contamination, in particular the uncontrolled release of heavy metal ions and radionuclides into soils and groundwater systems. The extent of contamination can be substantial, hence ways to remediate and reduce the volume of waste for further treatment and ultimate disposal are highly desired. In the current study, flotation has been considered as an engineering solution to rapidly separate cesium contaminated clays from low-level contaminated and pristine clays. Cesium (Cs+) sorption by montmorillonite clay particles was considered over a range of ionic concentrations (0.01–500 mM), showing a multistage sorption isotherm that can be interpreted using a two-site model, which considers both interlayer ion-exchange and specific ion sorption on the clay basal planes at higher cesium concentrations. Assessment by X-ray photoelectron spectroscopy (XPS) and zeta potential confirmed the increased surface contamination with increasing Cs+ concentration, with the surface enrichment sufficiently altering the surface chemistry of the contaminated clays for them to favourably interact with the flotation collector, ethylhexadecyldimethyl-ammonium-bromide (EDAB). Within a critical concentration range of EDAB, the cesium contaminated clays were separated from pristine clays using flotation, with recovery efficiencies of ∼75% for the contaminated clays, compared to <25% for the pristine clays. When contaminated and pristine clays were blended, separation by flotation once again demonstrated excellent selectivity for the contaminated clays. The current study highlights the potential for flotation to rapidly treat contaminated clay rich soils and significantly reduce the volume of contaminated solids for further treatment or ultimate disposal.

Ice and Cryosalt Formation in Saline Microporous Clay Gels

Hydrated clay minerals that are common to Earth’s atmosphere and terrestrial and aquatic environments can form gels that host saline solutions. Using cryogenic electron microscopy and vibration spectroscopy, we show that saline gels of montmorillonite frozen at < –90 °C host elongated hexagonal ice (Ih) microcrystals embedded in a network of honeycomb micropores. Freezing segregates salts into walls of aggregated clay nanoparticles sharing face-to-face contacts. Above ∼ –50 °C, clay gels that are sufficiently dense (≫10 g/L) and flexible (Na-exchanged montmorillonite) also host the cryosalt mineral hydrohalite (NaCl·2H2O), either co-existing or entirely replacing Ih in the gels. Hydrohalite does not form in gels of low-density (<10 g/L) or rigid (Ca-exchange montmorillonite) clay particles. These results suggest that hydrohalite forms in expandable clay gels that are sufficiently dense and flexible to retain saline solutions within their walls, possibly through interparticle capillary and hydration forces...

Self-sensitization of tetracycline degradation with simulated solar light catalyzed by ZnO@montmorillonite

Zinc oxide (ZnO) nano-particles were chemically deposited onto montmorillonite (MONT) clay particles. The composite ZnO@MONT was then characterized and used as a catalyst for photo-degradation of aqueous tetracycline. Unlike earlier studies, solar simulated light can be effectively used in this work. The composite shows high efficiency as adsorbent and as a photo-degradation catalyst. Both adsorbed and dissolved tetracycline molecules undergo mineralization under the photo-catalytic conditions, and up to 94% of the contaminant gross amount is completely mineralized. Other forms of ZnO particles, commercial ZnO and synthetic ZnO particles were examined in separate experiments. The ZnO@MONT is superior to both pristine counterparts. The ability of tetracycline to sensitize the supported ZnO particles, to solar simulated light, before being photo-degraded itself, is discussed here for the first time. In addition to enhanced catalytic activity of the ZnO@MONT, the composite can be efficiently recovered and reused with no significant loss of efficiency.

Synthesis and Characterization of Silver Nanoparticles Anchored on Montmorillonite via Chemical Reduction

Montmorillonite clay particles were decorated with silver (Ag) nanoparticles by chemical reduction of Ag nitrate with sodium citrate. X-ray diffraction (XRD) and energy dispersive X-ray spectrometry (EDS) confirmed the presence of metallic Ag on the surface of montmorillonite. The average crystallite size of the Ag nanoparticles obtained from the broadening of the 111 Ag peak ranged at 13-16 nm. On the other hand, the apparent particle sizes obtained from the SEM images were about 79-128 nm, suggesting that the nanoparticles are polycrystalline and possibly agglomerated. The increase in the concentration of reducing agent produced smaller Ag nanoparticles with narrower size distribution. The antibacterial test showed that the Ag nanoparticles, with mean size of 79 nm, adsorbed on montmorillonite were able to inhibit the growth of Staphylococcus aureus (S. aureus) with an antimicrobial index of 0.4.

Chemical Signaling and Functional Activation in Colloidosome-Based Protocells.

An aqueous-based microcompartmentalized model involving the integration of partially hydrophobic Fe(III)-rich montmorillonite (FeM) clay particles as structural and catalytic building blocks for colloidosome membrane assembly, self-directed membrane remodeling, and signal-induced protocell communication is described. The clay colloidosomes exhibit size- and charge-selective permeability, and show dual catalytic functions involving spatially confined enzyme-mediated dephosphorylation and peroxidase-like membrane activity. The latter is used for the colloidosome-mediated synthesis and assembly of a temperature-responsive poly(N-isopropylacrylamide)(PNIPAM)/clay-integrated hybrid membrane. In situ PNIPAM elaboration of the membrane is coupled to a glucose oxidase (GOx)-mediated signaling pathway to establish a primitive model of chemical communication and functional activation within a synthetic "protocell community" comprising a mixed population of GOx-containing silica colloidosomes and alkaline phosphatase (ALP)-containing FeM-clay colloidosomes. Triggering the enzyme reaction in the silica colloidosomes gives a hydrogen peroxide signal that induces polymer wall formation in a coexistent population of the FeM-clay colloidosomes, which in turn generates self-regulated membrane-gated ALP-activity within the clay microcompartments. The emergence of new functionalities in inorganic colloidosomes via chemical communication between different protocell populations provides a first step toward the realization of interacting communities of synthetic functional microcompartments.

UV degradation of clay‐reinforced polypropylene nanocomposites

The aim of this work is to experimentally characterize the UV‐degradation process at both the surface and at different layers across the thickness of injection‐molded polypropylene (PP) matrix containing different amounts of nanosized montmorillonite (MMT) clay particles. These nanocomposite materials have been exposed to UV irradiations (λ = 320 nm) at different preset temperatures (25, 45, and 65°C) in the presence of oxygen and during different exposure times. The extent of such process at these layers was determined using both the FTIR spectroscopy and the wide‐angle X‐ray diffraction analyses. The micromechanical properties across the thickness have been characterized using the nanoindentation technique. The obtained results have indicated that the UV‐degradation process for the nanocomposite materials is much more intense than the one observed for the neat PP. Moreover, it has been noted that such degradation process is not uniform across the thickness of the exposed materials. Results obtained from the X‐ray analysis have shown an increase of the crystallinity of the polymer molecules at only the external surface of the exposed materials. This was confirmed using the nanoindentation test as an increase of the Young's modulus at this layer was noted. POLYM. ENG. SCI., 56:469–478, 2016. © 2016 Society of Plastics Engineers

The application of benzimidazole and zinc cations intercalated sodium montmorillonite as smart ion exchange inhibiting pigments in the epoxy ester coating

The objective of this study is to develop and characterize the active protection properties of the benzimidazole (BIA) and zinc cations (Zn2+) intercalated sodium montmorillonite clay particles in an epoxy ester coating. The corrosion protection properties of the samples were studied by an electrochemical impedance spectroscopy (EIS). Results obtained revealed that the Na+ cations presented in the galleries of clay were successfully exchanged with BIA+ and Zn2+ cations. The active corrosion protection properties of the samples were demonstrated by EIS analysis. Promising self-healing and active protection properties were demonstrated by clay particles modified with both BIA+ and Zn2+ cations.

Degradation behavior of PEO coating on AM50 magnesium alloy produced from electrolytes with clay particle addition

Amorphous plasma electrolytic oxidation (PEO) coating with sealed discharge channels can be formed in alkaline phosphate electrolyte containing montmorillonite clay particles. The effect of various concentrations of phosphate and hydroxide ions in the clay-containing electrolyte on the microstructure of the coatings was studied in the present work and correlated with the corrosion behavior. The clay particles were reactively incorporated into the coating. Single amorphous phase appears in PEO coatings produced from electrolytes containing higher concentration of phosphate. These amorphous coatings are degrading within a relatively short period in 0.5wt% NaCl solution. Electrolytes containing higher concentration of KOH tend to produce mixed PEO coatings composed of crystalline and amorphous phases. These layers demonstrate higher corrosion resistance and degradation stability. Thus, the degradation rate of PEO coatings is governed mostly by the stability of their phase composition, which might be controlled by varying electrolyte composition.