MMT Layers Research Articles

Heterogeneous Ultrathin Films of Poly(vinyl alcohol)/Layered Double Hydroxide and Montmorillonite Nanosheets via Layer-by-Layer Assembly

In this paper, Co-Al layered double hydroxide (LDH) and montmorillonite (MMT) have been exfoliated into charged single layers in the solvent of formamide and water, respectively. The structures of individual layers of LDH and MMT were characterized by X-ray diffraction (XRD) and atomic force microscopy (AFM). The delamination mechanisms of LDH and MMT were also discussed. Furthermore, heterogeneous ultrathin films of poly(vinyl alcohol) (PVA)/charged inorganic nanosheets, (PVA/MMT/PVA/LDH)(n), were fabricated by layer-by-layer (LBL) assembly via hydrogen bonding. The LBL assembly process was monitored by UV-vis spectroscopy, and the structures of the heterogeneous ultrathin films were analyzed by XRD.

Gas‐Phase Polymerization with Transition Metal Catalysts Supported on Montmorillonite – A Particle Morphological Study

AbstractThis investigation focuses on the mechanism of particle fragmentation and growth when clay‐supported metallocene catalysts are used to polymerize ethylene in gas‐phase reactors. We supported bis(cyclopentadienyl)‐zirconium dichloride (Cp2ZrCl2) on montmorillonite (MMT) pretreated with triisobutylaluminum and 10‐undecence‐1‐ol to produce in‐situ polyethylene‐clay nanocomposites. During gas phase polymerization, the MMT layers were exfoliated by the growing polymer chains, starting from the openings of the clay galleries. After microtoming, the cross‐section of the fragmented MMT particles showed bundles of distorted silicate layer stacks, proving that exfoliation took place during polymerization, producing an in‐situ polyethylene‐clay nanocomposite. Calculations of d‐spacing by transmission electron microscopy (TEM) matched those measured by X‐ray diffraction (XRD) analysis.

Preparation and properties of polyethylene/montmorillonite nanocomposites formed via ethylene copolymerization

AbstractBACKGROUND: In situ formation of polyethylene/clay nanocomposites is one of the prevalent preparation methods that include also solution blending and melt blending with regard to process simplification, economy in cost, environment protection and marked improvement in the mechanical properties of the polymeric matrix. In the work reported here, the preparation of linear low‐density polyethylene (LLDPE) and fabrication of polymer/clay nanocomposites were combined into a facile route by immobilizing pre‐catalysts for ethylene oligomerization on montmorillonite (MMT).RESULTS: [(2‐ArNC(Me))2C5H3N]FeCl2 (Ar = 2,4‐Me2(C6H3)) was supported on MMT treated using three different methods. The MMT‐supported iron complex together with metallocene compound rac‐Et(Ind)2ZrCl2 catalyzed ethylene to LLDPE/MMT nanocomposites upon activation with methylaluminoxane. The oligomer that was formed between layers of MMT promoted further exfoliation of MMT layers. The LLDPE/MMT nanocomposites were highly stable upon heating. Detailed scanning electron microscopy analysis revealed that the marked improvement in impact strength of the LLDPE/MMT nanocomposites originated from the dispersed MMT layers which underwent cavitation upon impact and caused plastic deformation to absorb most of the impact energy. In general, the mechanical properties of the LLDPE/MMT nanocomposites were improved as a result of the uniform dispersion of MMT layers in the LLDPE matrix.CONCLUSION: The use of the MMT‐supported iron‐based diimine complex together with metallocene led to ethylene copolymerization between layers of MMT to form LLDPE/MMT nanocomposites. The introduction of exfoliated MMT layers greatly improved the thermal stability and mechanical properties of LLDPE. Copyright © 2009 Society of Chemical Industry

Influence of montmorillonite treatment and montmorillonite dispersion state on the crystallization behavior of poly(ethylene terephthalate)/montmorillonite nanocomposites

AbstractTiO2/SiO2 sol was intercalated into montmorillonite (MMT), which was pretreated with polyvinylpyrrolidone (PVP). A series of poly(ethylene terephthalate) (PET)/MMT hybrids were prepared using the obtained MMT as polycondensation catalysts. X‐ray diffraction (XRD) results proved that MMT dispersion states could be controlled by the amount of TiO2/SiO2 sol that was incorporated into MMT, ranging from agglomeration to exfoliation. The crystallization behavior of PET/MMT composites synthesized in this study was characterized by differential scanning calorimeter (DSC), polarized optical microscope (POM) and scanning electron microscopy (SEM) to clarify the effects of clay treatment and its dispersion state on the crystallization behavior of the PET substrate. The results indicated that MMT treated with less PVP would retain relatively higher nucleation efficiency while when MMT containing more PVP, the nucleation effect of MMT became weaker. If MMT formed big grains within PET substrate, the disturbance of the growing crystals was negligible; but the exfoliation of MMT layers would greatly magnify the spatial constraint which would slow down the crystallization process of PET matrix. For certain exfoliated PET/MMT composites, the crystallization rate was even lower than that of pure PET though clay content was low. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

Electrospinning and characterization of poly(vinyl alcohol)/chitosan oligosaccharide/clay nanocomposite nanofibers in aqueous solutions

Submicron fibers of the composite of poly(vinyl alcohol) (PVA), chitosan oligosaccharide [COS, (1→4)2-amino-2-deoxy-β-d-glucose], and montmorillonite clay (MMT) were prepared using electrospinning method with aqueous solutions. Scanning electron microscopy, transmission electron microscopy (TEM), X-ray diffraction (XRD), thermal gravimetric analyzer, and tensile strength testing machine (Zwick) were utilized to characterize the PVA/COS/MMT nanofiber mats morphology and properties. The PVA/COS ratio and MMT concentration play important roles in nanofiber mat properties. XRD and TEM data demonstrated that exfoliated MMT layers were well-distributed within nanofiber. It was also found that the mechanical property and thermal stability were increased with COS and MMT contents.

Preparation and characterization of electrospun pullulan/montmorillonite nanofiber mats in aqueous solution

Pullulan (PULL)/montmorillonite clay (MMT) nanofiber blend mats with various weight ratios have been fabricated by the electrospinning technique in aqueous solution. The PULL/MMT nanofiber mats are characterized by X-ray diffraction (XRD), differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA), field-emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), Fourier transform infrared (FT-IR) and mechanical measurements. The study shows that the introduction of MMT results in improvement in tensile strength, and thermal stability of the PULL matrix. XRD patterns and TEM micrographs suggest the coexistence of intercalated MMT layers over the studied MMT contents. XRD analyses also reveal an increase of the crystallinity of the blend nanofiber mats with addition of MMT fillers. Moreover, FT-IR divulges that there might be possible interaction occurred between the MMT clay and PULL matrix.

Electrospinning fabrication and characterization of poly(vinyl alcohol)/montmorillonite nanofiber mats

AbstractPoly(vinyl alcohol) (PVA)/montmorillonite clay (MMT) nanofiber mats have been fabricated by the electrospinning technique. The PVA/MMT nanofiber mats were characterized by X‐ray diffraction (XRD), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), Fourier transform infrared (FTIR), and mechanical measurements. The study showed that the introduction of MMT results in improvement in tensile strength, and thermal stability of the PVA matrix. XRD patterns and SEM micrographs suggest the coexistence of exfoliated MMT layers over the studied MMT contents. FTIR revealed that there might be possible interaction occurred between the MMT clay and PVA matrix. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

Characterization of poly(vinylidene fluoride)/Na+‐MMT composites: An investigation into the β‐crystalline nucleation effect of Na+‐MMT

AbstractPoly(vinylidene fluoride)(PVDF)/Na+‐MMT composites have been successfully prepared utilizing sodium montmorillonite (Na+‐MMT) via N,N‐dimethylformamide (DMF) solution mixing. The dispersion of Na+‐MMT layers in composites were investigated by transmission electron microscopy (TEM) and X‐ray diffraction (XRD). The effect of adding Na+‐MMT on crystallization behavior of PVDF was specifically studied. The β‐crystalline nucleation effect of Na+‐MMT was investigated and confirmed by differential scanning calorimetry (DSC), XRD, and Fourier transform infrared (FTIR) results. The interaction between PVDF and the surface of Na+‐MMT layers in DMF solution was confirmed by UV‐Vis absorbency. The effect of adding Na+‐MMT on rheological and electrical properties of PVDF/Na+‐MMT composites were also determined. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 903–911, 2009

Crystalline β‐structure of PHBV grown epitaxially on silicate layers of MMT

AbstractThe poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) (PHBV)/montmorillonite(MMT) nanocomposites were investigated by wide‐angle X‐ray scattering (WAXS). The aim of the investigation was solution intercalation of MMT with PHBV. Beside the usual orthorhombic unit cell, a stable pseudohexagonal β‐structure of PHBV was obtained. Well known β‐structure has one common WAXS reflection (d = 0.480 nm), which corresponds to the mean distance of PHBV chains in the pseudohexagonal structure. The new β‐structure has two diffraction peaks in the WAXS pattern. It is a three‐dimensionally ordered crystalline structure oriented in parallel with the silica layers of MMT. The new polymorphic form is supposed to be growing on the layers of MMT. Its layers serve as primary nucleation centers for epitaxial growth of the β‐structure. After annealing, this polymorphic form of PHBV disappears and it is transformed into the more stable α‐form leading to an enhanced total crystallinity of the polymer comprised in the nanocomposite. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 751–755, 2009

Electrospinning and characterization of medium-molecular-weight poly(vinyl alcohol)/high-molecular-weight poly(vinyl alcohol)/montmorillonite nanofibers

Submicron fibers of medium-molecular-weight poly(vinyl alcohol) (MMW-PVA), high-molecular-weight poly(vinyl alcohol) (HMW-PVA), and montmorillonite clay (MMT) in aqueous solutions were prepared by electrospinning technique. The effect of HMW-PVA and MMT on the morphology and mechanical properties of the MMW-PVA/HMW-PVA/MMT nanofibers were investigated for the first time. Scanning electron microscopy, viscometer, tensile strength testing machine, thermal gravimetric analyzer (TGA), and transmission electron microscopy (TEM) were utilized to characterize the PVA/MMT nanofibers morphology and properties. The MMW-PVA/HMW-PVA ratios and MMT concentration played important roles in nanofiber's properties. TEM data demonstrated that exfoliated MMT layers were well distributed within nanofibers. It was also found that the mechanical property and thermal stability were increased with HMW-PVA and MMT contents.

PAN‐based fibers modified with two‐component ceramic nanoparticles

AbstractThe authors determined conditions for manufacturing PAN precursor fibers containing a system of two nanoadditives, montmorillonite (MMT), and hydroxyapatite (HAp) in their structure. The PAN precursor fibers thus obtained are characterized by a tenacity of more than 30 cN/tex and a total volume of pores at the level of 0.29 cm3/g. Furthermore, it was found that the use of nanoadditives entails the remodeling of the paracrystalline structure of PAN fibers into a strictly crystalline one. This is accompanied by a decrease in spacing between MMT layers combined with their partial exfoliation. The fibers thus obtained, after being carbonized, will be used for medical applications. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

Microemulsion Polymerized Polyaniline/Montmorillonite Nanocomposite and Its Electrorheology

Conducting polyaniline (PANI) and inorganic Na+-Montmorillonite (Na+-MMT) nanocomposite material was prepared via a microemulsion polymerization method. To observe the morphology of the as-synthesized PANI/Na+-MMT nanocomposite, SEM images were employed. D-spacing of the PANI/Na+-MMT nanocomposite obtained from the XRD was found to become wider than that of pure Na+-MMT particles due to the successful intercalation of PANI into Na+-MMT layers. The fabricated PANI/Na+-MMT nanocomposite based electrorheological (ER) fluid was prepared by dispersing the particles in insulating silicone oil. Dynamic mechanical properties of the ER fluid were investigated via an oscillatory testing method using a vertical oscillation rheometer under an applied electric field, showing typical ER behavior.

Crystallization behavior of poly(vinylidene fluoride)/montmorillonite nanocomposite

AbstractThe crystallization behavior of poly(vinylidene fluoride)/montmorillonite (PVDF/MMT) nanocomposite was investigated by using differential scanning calorimeter (DSC), polarizing optical microscope (POM), and X‐ray diffraction. The results showed that the crystallization behavior of PVDF was changed by adding MMT in PVDF matrix. The MMT layers in PVDF acted as effective nucleation agents. It is observed that the crystallization temperature of PVDF/MMT nanocomposite was higher than that of PVDF at various cooling rates. The value of half‐time of crystallization showed that the crystallization rate of PVDF/MMT nanocomposite was faster than that of PVDF at a given cooling rate. The addition of MMT hindered the growth of spherulite. Nonisothermal crystallization data was analyzed using Avrami, Ozawa, and Jeziorny method. The Jeziorny method successfully described the nonisothermal crystallization behaviors of PVDF/MMT nanocomposite. The MMT loading was favorable to produce the piezoelectric β phase in the PVDF matrix. The α phase coexisted with the β phase in the PVDF/MMT nanocomposite. For this polymorphic structure, a possible explanation was proposed based on the variable temperature X‐ray diffraction, DSC, and POM experiments. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers

PREPARATION AND CHARACTERIZATION OF SOY PROTEIN ISOLATE (SPI)/MONTMORILLONITE (MMT) BIONANOCOMPOSITES

The bionanocomposites of soy protein isolate (SPI)/montmorillonite (MMT) have been prepared successfully via simple melt mixing, in which MMT was used as nanofiller and glycerol was used as plasticizer. Their structures and properties were characterized with X-ray diffraction (XRD), differential scanning calorimetry (DSC), scanning electron microscopy (SEM), thermogravimetric analysis and tensile testing. XRD, TEM and SEM results indicated that the MMT layers could be easily intercalated by the SPI matrix even by simple melt processing. The exfoliated MMT layers were randomly dispersed in the protein matrix as MMT content was low (less than 5 wt%), an incomplete exfoliation was evident from SEM results, and some primary particles were observed as the MMT content was high (from 5 wt% to 9 wt%). A significant improvement of the mechanical strength and thermal stability of SPI/MMT nanocomposites has been achieved. Our work suggests that simple melt processing is an efficient way to prepare SPI/MMT nanocomposites with exfoliated structure.

Influence of montmorillonite nano-dispersion on polystyrene photo-oxidation

UV photo-oxidative degradation of polystyrene/montmorillonite nanocomposites (PS/o-MMTs) and microcomposite (PS/Na/MMT), obtained via in situ bulk polymerization, has been studied in accelerated conditions. Imidazolium or standard alkylammonium surfactants were used to modify MMT. The chemical modification resulting from photo-oxidation has been followed using infrared spectroscopy (FT-IR). The rate of photo-oxidation of PS/o-MMT and PS/Na/MMT was faster than that of pristine PS. The results suggest that the photo-oxidative instability could be related to the degree of exfoliation and then to the presence of catalytic active sites on the MMT layer surface.

Delivery systems for some biologically active 1,2,4‐triazine derivatives: synthesis and release

AbstractTriazine‐loaded polymer microparticles composed of cross‐linked polymethylmethacrylate (PMMA) have been prepared. A series of PMMA cross‐linked polymers were prepared from methylmethacrylate (MMA) and divinylbenzene (DVB) by suspension polymerization using different percentages of solvents and cross‐linkers. Biologically active compounds including 4‐amino‐6‐substituted‐3‐thioxo‐3,4‐dihydro‐2H‐5‐oxo (or thioxo)‐1,2,4‐triazines (I–IV) were prepared and reacted with PMMA. Since optimization of the polymer delivery system is required to improve clinical applications, the effect of surface area, cross‐linker percentage on the loading, and release of triazines were studied. Alkaline conditions seem to favorably affect triazine release. Triazine hydrochlorides were ion exchanged with sodium montmorillonite (Na‐MMT). X‐ray diffraction (XRD) analysis confirms the intercalation of triazines between the layers of MMT. The presence of mineral domains with an average size of 33 nm was observed by transmission electron microscopy (TEM). The release of triazine compounds is more controllable in intercalated layered silicates. Copyright © 2008 John Wiley & Sons, Ltd.

In situ intercalative polymerization of conducting polypyrrole/montmorillonite nanocomposites

AbstractConducting polypyrrole (PPy)‐montmorillonite (MMT) clay nanocomposites have been synthesized by the in situ intercalative polymerization method. The PPy‐MMT nanocomposites are characterized by field‐emission scanning electron microscopy (FE‐SEM), transmission electron microscopy (TEM), X‐ray diffraction (XRD), ultraviolet–visible (UV–vis) spectroscopy, thermogravimetric analysis (TGA), and Fourier‐transform infrared (FTIR) spectroscopy. XRD patterns show that after polymerization by the in situ intercalative method with ammonium persulfate and 1 M HCl, an increase in the basal spacing from 1.2 to 1.9 nm was observed, signifying that PPy is synthesized between the interlayer spaces of MMT. TEM and SEM micrographs suggest that the coexistence of intercalated MMT layers with the PPy macromolecules. FTIR reveals that there might be possible interfacial interactions present between the MMT clay and PPy matrix. The study also shows that the introduction of MMT clay results in thermal stability improvement of the PPy. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 2279–2285, 2008

Preparation and friction properties of PBT/MMT composites

AbstractPoly(butylene terephthalate)/clay composites were prepared by direct melt compounding. Two structures were formed as confirmed by XRD and transmission electron microscopy. The presence of MMT layers does not change the crystal structure and the degree of crystallinity of PBT matrix. The tribological behaviors of neat PBT and PBT/clay composites were studied by the means of a pin‐on‐disk apparatus. It was found that the intercalation of organoclay could help reduce the friction coefficient and the specific wear rate of PBT, while the addition of natural clay was harmful to the friction coefficient and wear resistance of the polymer matrix. The different tribological behaviors of the composites are due to their different morphologies and the difference in the interfacial adhesion between the matrix and the clay platelets. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers

Visible light induced TiO2 pillared MMT photocatalyst coupling-doped with S and N

Visible light induced titanium dioxide (TiO2) pillared montmorillonite clay (MMT) photocatalyst coupling-doped with S and N elements was prepared by the two-step adsorption method. The photocatalyst was characterized by X-ray photoelectron spectroscopy (XPS) and ultraviolet-visible (UV-vis) absorption spectroscopy. The photocatalysic efficacy of the prepared photocatalyst for degrading gaseous formaldehyde was evaluated under visible light irradiation. The degrading rate of gaseous formaldehyde is nearly 85% in 300 min visible light irradiation. The results demonstrate that the much higher visible light photocatalytic activity of the photocatalyst is due to the synergistic effects of coupling-doping of S and N elements to TiO2, extensive specific surface area of MMT and quantum sized efficacy between layers of MMT.

Thermal stability and ablation properties of silicone rubber composites

AbstractEffects of incorporation of clay and carbon fiber (CF) into a high temperature vulcanized (HTV) silicone rubber, i.e., poly(dimethylsiloxane) (PDMS) containing vinyl groups, on its thermal stability and ablation properties were explored through thermogravimetric analyses (TGA) and oxy‐acetylene torch tests. Natural clay, sodium montmorillonite (MMT), was modified with a silane compound bearing tetra sulfide (TS) groups to prepare MMTS4: the TS groups may react with the vinyl groups of HTV and enhance the interfacial interaction between the clay and HTV. MMTS4 layers were better dispersed than MMT layers in the respective composites with exfoliated/intercalated coexisting morphology. According to TGA results and to the insulation index, the HTV/MMTS4 composite was more thermally stable than HTV/MMT. However, addition of CF to the composites lowered their thermal stability, because of the high thermal conductivity of CF. The time elapsed for the composite specimen, loaded with a constant weight, to break off after the oxy‐acetylene flame bursts onto the surface of the specimen was employed as an index for an integrated assessment of the ablation properties, simultaneously taking into consideration the mechanical strength of the char and the rate of decomposition. The elapsed time increased in the order of: HTV < HTV/CF ≈ HTV/MMTS4 < HTV/CF/MMTS4 ≈ HTV/MMT < HTV/CF/MMT. This order was different from the increasing order of the thermal stability determined by TGA results and the insulation index. The decreased degree of crosslinking of the composites with MMTS4 compared with that of the composite with MMT may be unfavorable for the formation of a mechanically strong char and could lead to early rupture of the HTV/MMTS4 specimen. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008