MMT Clay Research Articles

Electrical and mechanical properties of free-standing PMMA–MMT clay composites

Abstract

Isoconversional kinetic analysis of DSC data on nonisothermal crystallization: Estimation of Hoffman-Lauritzen parameters and thermal transitions in PET/MMT nanocomposites

The differential isoconversional method of Friedman is applied to non-isothermal melt crystallization DSC data to obtain effective activation energy ΔE. In comparison to neat PET, ΔE of intercalated 93A MMT clay nanocomposites (PCNs) decreased and highly dependent on the clay content. Hoffman-Lauritzen (H–L) secondary nucleation theory parameters, Kg and U* were evaluated using isoconversional approach of Vyazovkin and Sbirrazzuoli. Crystallization regime transition from regime III is observed at 190°C for neat PET, which shifted to higher temperature range 200°C–208 °C for PCNs. The Kg parameters for both regimes for PET are consistent with our isothermal experiments and reported in literature. However, the Kg values of nanocomposites are highly sensitive to the temperature dependent nucleation activity and ΔE of PET chain motion in melt and are not very much comparable with our isothermal results. Nevertheless, the observed results clearly indicate that the 93AMMT clay layers predominantly act as heterogeneous nucleating sites.

Ru-exchanged MMT Clay with Functionalized Ionic Liquid for Selective Hydrogenation of CO2 to Formic acid

Ruthenium-exchanged montmorillonite clay with different catalyst loading was easily synthesized and tested for hydrogenation of carbon dioxide to formic acid. Application of additives like triphenyl phosphine (PPh3), water and ethanol were tested during the reaction. Low catalyst loading, easy product isolation step and seven times catalyst recycling are the major outcomes of this proposed protocol.

Molecular interactions in biomineralized hydroxyapatite amino acid modified nanoclay: In silico design of bone biomaterials

A simulations driven approach to design of a novel biomaterial nanocomposite system is described in this study. Nanoclays modified with amino acids (OMMT) were used to mineralize hydroxyapatite (HAP), mimicking biomineralization. Representative models of organically modified montmorillonite clay (OMMT) and OMMT-hydroxyapatite (OMMT-HAP) were constructed using molecular dynamics and validated using X-ray Diffraction (XRD), Fourier Transforms Infrared (FTIR) spectroscopy and Transmission Electron Microscopy (TEM). Attractive interactions exist between Ca atoms of HAP and CO group of aminovaleric acid, indicating chelate formation in OMMT-HAP. Interaction energy maps describe molecular interactions among different constituents and their quantitative contributions in the OMMT and OMMT-HAP systems at both parallel and perpendicular orientations. High attractive and high repulsive interactions were found between PO43− and MMT clay as well as aminovaleric molecules in OMMT-HAP perpendicular and parallel models. Large non-bonded interactions in OMMT-HAP indicate influence of neighboring environment on PO43− in in situ HAPclay. Extensive hydrogen bonds were observed between functional hydrogen atoms of modifier and MMT clay in OMMT-HAP as compared to OMMT. Thus, HAP interacts with clay through the aminovaleric acid. This computational study provides a framework for materials design and selection for biomaterials used in tissue engineering and other areas of regenerative medicine.

Adsorption of PolyCarboxylate Poly(ethylene glycol) (PCP) esters on Montmorillonite (Mmt): Effect of exchangeable cations (Na+, Mg2+ and Ca2+) and PCP molecular structure

This study deals with the adsorption of PolyCarboxylate Poly(ethylene glycol) esters (PCP) superplasticizers on Na-, Mg- and Ca-saturated Montmorillonite (Mmt) clays. The interactions have been examined through different experimental methods: adsorption isotherms, zeta potential measurements and sedimentation experiments. It was found that PCP adsorption depends both on the architecture of PCP molecules and the nature of cation located on the interlayer exchange sites of the Montmorillonite. Whatever the PCP, a larger amount was adsorbed on Na-Mont than on Mg-Mont or Ca-Mont. This indicates the occurrence of two adsorption mechanisms: (i) a superficial adsorption via electrostatic interactions between the carboxylate groups of PCP and positively charged sites on clay surfaces, (ii) intercalation of ether units of the PCP grafts in the interlayer space by displacement of water molecules coordinated to the exchangeable cations.Furthermore, despite the weak negative values of the zeta potential, the addition of PCP promotes the stability of the suspensions which is attributed to steric repulsion acting between particles.

Bionanocomposite Obtained from Poly (lactic acid)/Biopolyethylene Blend and Clay

SummaryThe aim of this work is the development of a bionanocomposite from Poly (lactic acid)‐PLA/Biopolyethylene (PE) blend and clay. The montmorillonite (MMT) clay was organically modified with an ionic surfactant to become organophilic (OMMT). The MMT and OMMT clays were characterized by Fourier Transform Infrared Spectroscopy (FTIR) and X‐Ray Diffraction (XRD) techniques. The blends and the biocomposites were prepared by extrusion followed by injection molding and characterized by XRD, mechanical properties and Scanning Electron Microscopy (SEM). XRD and FTIR results indicated that the MMT clay was sucessfully modified becoming OMMT. XRD results also indicated that for the PLA/PE/EMA‐GMA biocomposite a bionanocomposite with an intercalated structure was obtained. SEM results showed that the addition of the OMMT clay to both PLA/PE and PLA/PE/EMA‐GMA blends led to a substantial decrease in the PE dispersed phase domains size. This decrease was more pronounced in the PLA/EMA‐GMA/OMMT bionanocomposite.

Characterization and Application of Intercalated Montmorillonite with Verapamil and its Polymethyl Methacrylate Nanocomposite in Drug Delivery

This work examined two drug delivery systems: the first system studied the adsorption of Verapamil hydrochloride drug into montmorillonite clay (MMT) by intercalation process to prepare MMT-Verapamil hybrid at different intercalating time, temperatures, pH values and initial drug concentrations. The second system includes the preparation of MMT-Verapamil hybrid combined with polymethyl methacrylate via an emulsion polymerization process to produce a novel nanocomposite material to be used in drug delivery. The polymerization process was carried out using an ultrasonic technique to achieve a biologically safe drug delivery system. Best conditions for the intercalation of verapamil hydrochloride drug into the interlayer of MMT clay were found to be at 50°C and 1 hr using pH ranges of 4–6. The prepared MMT-Verapamil hybrid and the produced MMT-verapamil-MMA nanocomposite material were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM) and thermal gravimetric analysis (TGA). The in-vitro release profile of Verapamil in the case of a drug hybrid is faster than the release in the case of a drug nanocomposite in both gastric and intestinal fluids where, in the case of gastric fluid (pH 1.2), about 40% of the loaded drug was released from the drug hybrid in the first 4 h against only 37% in 5 h in the case of drug nanocomposite. Also in the intestinal fluid (pH 7.4), the verapamil release from drug hybrid reached 68% in 5 h against only 57% was released from drug nanocomposites in 7 h.

LDPE/clay/carvacrol nanocomposites with prolonged antimicrobial activity

ABSTRACTOver the past decade there is an immense effort to develop antimicrobial packaging systems, which incorporates natural biopreservatives, such as essential oils (EOs). The highly volatile nature of EOs, which is advantageous for their efficient diffusion and mode of action, presents a major obstacle for their incorporation with polyolefins via conventional high‐temperature melt compounding and processing. This study presents a new approach to use organo‐modified montmorillonite (MMT) clays, as active carriers for carvacrol (used as a model EO), aiming to minimize its loss throughout the polymer compounding. Different MMT clays are pretreated with carvacrol, resulting in the oil molecules intercalation in between the clay galleries and enhanced carvacrol thermal stability. These hybrids are incorporated within low‐density polyethylene (LDPE) and the resulting films are characterized in terms of their nanostructure, thermal properties, and antimicrobial activity. The LDPE/(clay/carvacrol) nanocomposites exhibit excellent and prolonged antimicrobial activity againstE. colibacteria, while LDPE/carvacrol films loss their antimicrobial functions within several days. The superior antimicrobial behavior is ascribed to the significantly higher carvacrol content and its enhanced thermal stability within the films. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci.2015,132, 41261.

Organic–Inorganic Composite Films Based on Modified Hemicelluloses with Clay Nanoplatelets

Special challenges and opportunities are present with organic–inorganic composite films with respect to potential applications. The quaternized hemicelluloses (QH) were prepared by etherification of hemicelluloses with ETA under alkaline conditions. The structure of QH was determined by FT-IR and 1H NMR. The biocomposite films were prepared based on QH and montmorillonite (MMT) by a vacuum-filtrated technique. Positively charged QH was paired with exfoliated anionic MMT clay nanoplatelets via electrostatic reaction during the paper-making process. Different ratios of hemicelluloses to clay for the preparation of films were employed. The morphology and structure of the films were characterized by SEM, AFM, FT-IR, and XRD. The thermal properties of the films were explored by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC), which suggested that the thermal properties were improved by the addition of clay nanoplatelets, whereas the optical transparency of the film decreased with the increment of clay contents. The proper proportion of QH and MMT among the three films was 1:1 based on the results of the thermal and UV–vis transparency properties of films. All of these results suggested that the composite films could be used in areas of application in the coating and packaging fields.

A novel biomimetic catalyst templated by montmorillonite clay for degradation of 2,4,6-trichlorophenol

Abstract In this study, a novel biomimetic catalyst was synthesized by intercalating hemin, which is the active center of peroxidase, into montmorillonite (MMT) clay mineral. Our results showed that the amount of hemin adsorbed on MMT was strongly affected by the fraction of cosolvent and the exchangeable cation. At methanol/water mixture of 70:30, over 9% (w/w) of hemin could be loaded on Cu 2+ exchanged MMT (Cu-MMT), which was the highest loading of hemin on various supports reported in the literature. Both infrared spectra and theoretical calculations supported that hemin could strongly interact with exchangeable Cu 2+ ion located in MMT interlayer. The constrained environment in clay interlayer would act as a unique matrix to prevent the dimerization of hemin molecule and preserve its reactivity. The newly formed hemin–Cu-MMT bioconjugate showed superior reactivity and high thermal stability as indicated by the degradation of 2,4,6-trichlorophenol compared to free hemin in aqueous solution, and the reactivity was linearly proportional to the amount of hemin loaded on clay and the substrate concentrations. MMT clay is widely distributed in the environment and inexpensive, hence offering the potential for in situ and ex situ remediation of many persistent contaminants in surface/subsurface soils utilizing hemin–Cu-MMT bioconjugate.

Gluten Biopolymer and Nanoclay-Derived Structures in Wheat Gluten–Urea–Clay Composites: Relation to Barrier and Mechanical Properties

Here, we investigated the structure of natural montmorillonite (MMT) and modified Cloisite C15A (MMT pre-intercalated with a dimethyl-dehydrogenated tallow quaternary ammonium surfactant) nanoclays in the wheat gluten–urea matrix in order to obtain a nanocomposite with improved barrier and mechanical properties. Small-angle X-ray scattering indicated that the characteristic hexagonal closed packed structure of the wheat gluten–urea matrix was not found in the C15A system and existed only in the 3 and 5 wt % MMT composites. SAXS/WAXS, TGA, and water vapor/oxygen barrier properties indicated that the dispersion of the C15A clay was somewhat better than the natural MMT clay. Confocal laser scanning microscopy showed MMT clay clusters and C15A clay particles dispersed in the protein matrix, and these were preferentially oriented in the extrusion direction only at 5 wt % of the C15 clay. The water vapor/oxygen barrier properties were improved with the presence of clay. Independent of the clay content used, the stiffness decreased and the extensibility increased in the presence of C15A due to the surfactant induced changes on the protein. The opposite “more expected” clay effect (increasing stiffness and decreasing extensibility) was observed for the MMT composites.

Stability of chitosan/montmorillonite nanohybrid towards enzymatic degradation on grafting with poly(lactic acid)

Enzymatic degradation of nanohybrid based on intercalation of chitosan (CS) within the galleries of montmorillonite (MMT) clay and grafted with poly(lactic acid) (PLA) was studied using esterase enzyme in phosphate buffered solution. Chitosan was first intercalated between the galleries of natural unmodified sodium MMT clay and subsequently grafted with PLA to prepare nanohybrids of CS-g-PLA/MMT. The prepared membranes were characterised by X-ray diffraction, transmission electron microscopy and NMR spectroscopy. The specimens were then subjected to enzymatic degradation to understand the effect of copolymerisation with PLA and the effect of incorporation of MMT in the CS matrix. The presence of MMT clay provided stability towards degradation of polymer matrix because of nanoscale dispersibility, thereby acting as a barrier towards the permeation of water molecules to induce hydrolysis of PLA. Similarly, the grafting of CS with crystalline PLA stabilised the CS matrix towards degradation, rendering it suitable for tissue engineering applications.

Photodegradation of some low‐density polyethylene–montmorillonite nanocomposites containing an oligomeric compatibilizer

ABSTRACTThe photo‐oxidation behavior at the exposed surfaces of maleated low‐density polyethylene [LDPE poly(ethylene‐co‐butylacrylate‐co‐maleic anhydride) (PEBAMA)] and montmorillonite (MMT) composites was studied using attenuated total reflection Fourier transform infrared spectroscopy, X‐ray diffraction (XRD), transmission electron microscopy (TEM), and mechanical testing. Two different MMT clays were used with the maleated polyethylene, an unmodified clay, MMT, and an organically modified montmorillonite (OMMT) clay which was significantly exfoliated in the composite. The morphologies of sample films were examined by XRD and TEM. The results were explained in terms of the effect of the compatibilizing agent PEBAMA on the clay dispersion. It was found that the OMMT particles were exfoliated in the polymer matrix in the presence of the PEBAMA, whereas the MMT clay particles were agglomerated in this matrix. Both mechanical and spectroscopic analyses showed that the rates of photo oxidative degradation of the LDPE‐PEBAMA–OMMT were higher than those for LDPE and LDPE‐PEBAMA–MMT. The acceleration of the photo‐oxidative degradation for LDPE‐PEBAMA–OMMT is attributed to the effects of the compatibilizer and the organic modifier in the composite. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40788.

Functional copolymer/organo-MMT nanoarchitectures. XIX. Nanofabrication and characterization of poly(MA-alt -1-octadecene)-g -PLA layered silicate nanocomposites with nanoporous core-shell morphology

Novel bioengineering functional copolymer-g-biopolymer-based layered silicate nanocomposites were fabricated by catalytic interlamellar bulk graft copolymerization of L-lactic acid (LA) monomer onto alternating copolymer of maleic anhydride (MA) with 1-octadecene as a reactive matrix polymer in the presence of preintercalated LA…organo-MMT clay (reactive ODA-MMT and non-reactive DMDA-MMT) complexes as nanofillers and tin(oct)2 as a catalyst under vacuum at 80°C. To characterize the functional copolymer layered silicate nanocomposites and understand the mechanism of in situ processing, interfacial interactions and nanostructure formation in these nanosystems, we have utilized a combination of variuous methods such as FT-IR spectroscopy, X-ray diffraction (XRD), dynamic mechanical (DMA), thermal (DSC and TGA-DTG), SEM and TEM morphology. It was found that in situ graft copolymerization occurred through the following steps: (i) esterification of anhydride units of copolymer with LA; (ii) intercalation of LA between silicate galleries; (iii) intercalation of matrix copolymer into silicate layers through in situ amidization of anhydride units with octadecyl amine intercalant; and (iv) interlamellar graft copolymerization via in situ intercalating/exfoliating processing. The main properties and observed micro- and nanoporous surface and internal core–shell morphology of the nanocomposites significantly depend on the origin of MMT clays and type of in situ processing (ion exchanging, amidization reaction, strong H-bonding and self-organized hydrophobic/hydrophilic interfacial interactions). This developed approach can be applied to a wide range of anhydride-containing copolymers such as random, alternating and graft copolymers of MA to synthesize new generation of polymer-g-biopolymer silicate layered nanocomposites and nanofibers for nanoengineering and nanomedicine applications. Copyright © 2014 John Wiley & Sons, Ltd.

Improved photocatalytic activity of CdSe-nanocomposites: Effect of Montmorillonite support towards efficient removal of Indigo Carmine

To ascertain the contribution of adsorptive capacity of Montmorillonite (MMT) towards photocatalytic process, CdSe-MMT nanocomposites are explored for adsorptive removal of Indigo Carmine (IC). The nanocomposites are prepared via two approaches: (a) in-situ formation and (b) wet impregnation of CdSe onto MMT support. XRD analysis of composites suggested the proper dispersion of CdSe nanoparticles in MMT clay matrix with spherical morphology of 5–10nm sized CdSe nanoparticles. These nanocomposites are employed for photocatalytic degradation of IC under visible light at various IC concentrations and different amount of catalyst. Kinetics of IC is found to be of pseudo-second order with 10% in-situ and 50% loaded nanocomposites exhibiting better photocatalytic activity at 1.0gL−1 catalyst and 100mgL−1of IC. Dynamics of its adsorptive removal on the composite surface evaluated by employing error estimation tools clearly suggest that Redlich–Peterson and Flory–Huggins adsorption isotherms effectively describe the multi-layer process. It is observed that spontaneous, exothermic chemisorption process occurring on the surface indeed enhances photocatalytic activity. Moreover, such a feature is also found to be associated with diffusion of IC within mesoporous structure of MMT that subsequently favors pore-diffusion controlled adsorption process. IR spectral analysis demonstrated that IC molecule is degraded on the catalyst surface. Light or oxygenated species induced photocorrosion of CdSe is suppressed due to its composite formation with MMT that results in 620ppm removal of IC during successive cycles; a feature ascribed as improved photocatalytic activity for CdSe nanoparticles.

Synthesis and Characterization of Poly (Vinyl Acetate)/MMT Nanocomposite Flame Retardant

Current environmental benign and flame retardant poly (vinyl acetate) (PVAc)/montmorillonite (MMT) clay nanocomposites were prepared by emulsifier free emulsion technique in microwave (MW) oven. MMT clay was incorporated as additional filler in PVAc/MMT nanocomposites to improve the homogeneity of the ‘physical’ barrier, since clay produces silicon-oxy-carbide (Si-O-C) char on heating. The fine dispersion of the MMT and the interactions between PVAc and clay created significant improvement of the flame retardancy which has been evaluated using cone calorimeter. The presence of clay in PVAc/MMT nanocomposites was characterized with infrared (IR), X-ray diffraction (XRD) and transmission electron microscopy (TEM). The fire retardancy of PVAc/MMT nanocomposites caused by the formation of Si-O-C char was characterized by scanning electron microscopy (SEM). The biodegradation property was tested by activated sludge water via water absorbency and was further confirmed from SEM for its better commercialization and ecofriendly nature.

Accelerated Weatherability of the Low‐Density Polyethylene Nanocomposites with Silica, Clay, and Zinc Oxide

Nanocomposites based on low‐density polyethylene (LDPE) with MMT clay, nanosilica, and nanoscale zinc oxide (at 5 wt.%) were prepared by melt processing and evaluated for durability using laboratory accelerated weathering. The changes in tensile properties of the nanocomposites with the duration of exposure were compared to data from natural weathering outdoors. The enhancement of degradation rates of the LDPE matrix by the presence of nanofillers in accelerated weathering is reported.

Nanofibrillated cellulose, poly(vinyl alcohol), montmorillonite clay hybrid nanocomposites with superior barrier and thermomechanical properties

Nanocomposites of poly(vinyl alcohol) (PVA), nanofibrillated cellulose (NFC), and montmorillonite (MMT) clay were prepared via solvent casting. In addition to investigating the effect of clay loading, PVA matrices crosslinked with poly(acrylic acid) (PAA) were prepared and compared with linear (noncrosslinked) PVA nanocomposites. 13C NMR and infrared spectroscopy confirmed the presence of crosslinks. Scanning electron microscopy revealed effective NFC and MMT clay dispersion throughout the nanocomposites, while X-ray diffraction highlighted the effectiveness of PAA to encourage clay dispersion. MMT clay provided a barrier against the diffusion of water and oxygen (molecules) through the nanocomposite films. Permeability and adsorption were further reduced by crosslinking, while oxygen barrier properties were remarkably enhanced at elevated relative humidities. Thermal stability of the PVA segments was strengthened by the presence of MMT clay and crosslinks. MMT clay–reinforced PVA and NFC within the films, increasing the Young's modulus, tensile strength, and glass transition temperature. Crosslinking further enhanced the thermomechanical properties by imparting physical restraints on polymer chain segments, providing elasticity, and ductility. The hybrid films were successfully reinforced at elevated humidities, with nanocomposites displaying enhanced storage moduli and near-complete recovery. POLYM. COMPOS., 35:1117–1131, 2014. © 2013 Society of Plastics Engineers

Polynorbornene/MMT nanocomposites via surface-initiated ROMP: synthesis, characterization, and dielectric and thermal properties

Exfoliated polynorbornene (PNBN)/montmorillonite (MMT) nanocomposites were synthesized for the first time by the surface-initiated ring-opening metathesis polymerization. PNBN is one of the challenging materials in low dielectric films for packaging applications in electric–electronic industries. This is the first example of in situ polymerization of NBN within the catalyst intercalated montmorillonite layers using ROMP in different clay loading degrees. The Na–MMT clay was modified with a Quaternary ammonium salt containing ruthenium complex as a suitable catalyst and intercalant as well. Powder X-ray diffraction spectroscopy and transmission electron microscopy analysis indicated that the resultant nanocomposites exhibited exfoliated morphologies with homogeneous clay platelet distribution. Nanocomposite materials were obtained with high thermal degradation temperature and low dielectric constant when compared with pure PNBN. The dielectric constants decreased with the increase in the clay content.

Synthesis, characterization and dielectric properties of polynorbornadiene–clay nanocomposites by ROMP using intercalated Ruthenium catalyst

Polynorbornadiene clay nanocomposites were prepared for the first time by the ring opening metathesis polymerization (ROMP) using modified montmorillonite and polynorbornadiene the latter of which is used commonly in electric–electronic industry. The Na–MMT clay was modified by a quaternary ammonium salt containing Ruthenium complex as a suitable catalyst and intercalant as well. The norbornadiene monomers were polymerized within the modified montmorillonite layers by in-situ polymerization method in different clay loading degrees. Intercalation ability of the Ru catalyst and partially exfoliated nanocomposite structure were proved by powder X-ray Diffraction (XRD) Spectroscopy and Transmission Electron Microscopy (TEM) methods. The nanocomposite materials with high thermal degradation temperature and low dielectric constant compared to the pure polynorbornadiene were obtained. The dielectric constants decreased with the increase of the clay content.