Organically Modified Layered Silicate Research Articles

Luminescence of a laser dye in organically-modified layered silicate pigments

The main focus of the present work was the development of pigments based on layered nanomaterials exhibiting luminescent properties. Two layered silicates, montmorillonite (Mt) and saponite (Sap), differing in their cation exchange capacity (CEC), were modified with cationic organic surfactants (tetraoctylammonium and tetraoctylphosphonium) in various amounts relative to the CEC (25–100%) and with a laser dye, rhodamine 6G (R6G), with dye/silicate ratios of 0.001–0.08 mmol g−1. The photoluminescence and its dependence on the surfactant amount, dye concentration, and the layered silicate type were evaluated. Modification by the surfactants played a key role and caused an increase in fluorescence, particularly for Mt, whose hybrids were non-active without the modification. The intensity increased significantly even for samples modified with amounts of surfactants equal to 25% of the CEC values. Dye concentrations above 0.02 mmol g−1 caused a diminishing of the fluorescence intensities due to the formation of non-luminescent molecular aggregates of the dye. Advanced chemometric and statistical analysis was applied for better differentiation of the components in fluorescence spectra. By selecting suitable organic cation and dye components, it was possible to prepare pigments exhibiting high fluorescence and at (for R6G) unusually long wavelengths, approaching the near-infrared region (650–700 nm).

Effects of additives of organically modified montmorillonite and Octosilicate in a silica reinforced tire tread mixture

Dual filler networks of spherical and layered particles on the example of elastomer-reinforcement with silica, doped with a small quantity of organically-modified layered silicates (Octosilicate or montmorillonite) in the mass ratio of 80 to 3 were investigated, as well as the influence of the organic-modifier on the mechanical properties of the rubber composites. Synergies with interesting mechanical properties for technical rubber applications were found, but surprisingly only for the system that contains organically modified octosilicate, attributed to a higher extent of exfoliation/intercalation and related to a higher and more homogeneous surface modification than for organically modified montmoriilonite under the chosen experimental conditions. Shear modulus measurements on concentration series' allowed the determination of scaling exponents for the reinforcement that are well described by the cluster-cluster aggregation model. This also suggests integration of the relatively large layers of montmorillonite or Octosilicate during the early stages of the flocculation process because of the increased collision probability of particles of different sizes over particles of same size.

Dispersion of Organically Modified Layered Silicates in Melt Blended Poly(Lactic Acid) Composites: Effects of Cation Head Groups and Oxygenated Alkyl Chains

Extruded organically modified layered silicate (OMLS) - poly(lactic acid) (PLA) composites exhibit a mixed intercalated/exfoliated morphology. To explore effects of surfactant hydrophobicity and polarity on the quality of dispersion, a series of OMLS were prepared from quaternary ammonium, phosphonium, and imidazolium salts, including some synthesized hexadecanoic acid containing ionic liquids. The alkyl chains were modified to include aromatic and oxygen moieties while keeping the same long alkyl chain length. Nile Blue was co-exchanged to add a fluorescent tag to the layered silicates. The effectiveness of this technique for PLA and different Nile Blue salts were assessed. Degree of exfoliation was monitored using x-ray diffraction and fluorescence spectroscopy. Thermal characteristics of the new OMLS were measured.

Morphology and rheological behavior of polylactic acid/clay nanocomposites

AbstractThe investigated rheological properties of polylactic acid (PLA)/clay nanocomposite are important to understand the effect of organically modified layered silicates (OMLS) (clay) on processing as well as the change in viscoelastic properties due to polymer filler interaction. The time sweep result revealed that the thermal stability improved with addition of nanoclay due to the formation of percolating network structure. It was also supported by multi wave ramp test. The frequency sweep analysis showed that the dynamic moduli increased with addition of nanoclay. Viscoelastic spectra (DMTA) showed an increase of the storage and loss moduli with the increase in the clay content. Wide angle X‐ray diffraction (WAXD) and transmission electron microscopy (TEM) were used to determine the degree of intercalation, or exfoliation and nanostructure level of clay dispersion on PLA nanocomposites. XRD data demonstrated complete exfoliation at lower nanoclay content. On increasing the nanoclay content, exfoliated and partially intercalated structures were obtained. POLYM. ENG. SCI., 2012. © 2011 Society of Plastics Engineers

Effect of organically modified layered silicate nanoclay on the dynamic viscoelastic properties of thermoplastic polyurethane nanocomposites

Different formulations of organically modified layered silicate (OMLS) clay based medical grade thermoplastic polyurethane (TPU) nanocomposites were successfully prepared via melt blending followed by compression molding. The effect of incorporation of nanoclay on the spherulitic morphology of the TPU matrix was studied with a polarizing optical microscope (POM). The exfoliation/intercalation of organoclay was attributed to the TPU–organoclay interaction and shear stress during melt mixing. The effects of clay content and degree of clay dispersion on the rheological properties of nanocomposites were studied using a rubber process analyzer (RPA) with the help of dynamic strain, frequency, and temperature sweeps. The dynamic rheological studies show that the complex viscosity ( η*) and dynamic storage modulus ( G′) of pristine TPU increased significantly with the incorporation of organoclay loading, which is attributed to the formation of an interphase between soft and hard segments of the TPU matrix and effective dispersion of the organoclay.

PA66/PA12/clay based nanocomposites: morphology and physical properties

The structure and the physical properties of several polyamide 66 (PA66)/polyamide 12 (PA12) blends containing different amounts of the two polymers and obtained by melt-blending have been investigated. A low amount of organically-modified layered silicate (OMLS, 4 wt%) has also been introduced in order to further improve the physical properties and, in particular, to evaluate its effect on the blends' structure and components' miscibility. The microstructure and morphology of all the composites were analyzed by means of X-Ray diffraction (WAXD), transmission electron microscopy (TEM), and high resolution scanning electron microscopy (SEM), while the macroscopic scale properties (mechanical behavior and water adsorption) were assessed in order to investigate and understand the materials' structure–properties relationships. The partial miscibility of PA66 and PA12, with phase separation depending on blend composition, has been confirmed. The results also underlined the possibility to tailor the behavior of polymer blends in terms of mechanical water adsorption properties by varying the amount of PA12, added to PA66 with and without the addition of the OLMS. The effectiveness of the clay in modifying the components' miscibility as well as its tendency to segregate preferentially within separate PA66 domains have been assessed. WAXD results showed opposite effects of PA12 and clay on the crystallization behavior of PA66, an aspect that has also been deepened in another paper by the same authors discussing the results of the complete thermal characterization. Copyright © 2010 John Wiley & Sons, Ltd.

SBR/organoclay nanocomposites for the application on tire tread compounds

N,N-dimethyldodecylamine (tertiary amine)-modified MMT (DDA-MMT) was prepared as an organically modified layered silicate (OLS), after which styrene-butadiene rubber (SBR) nanocomposites reinforced with the OLS were manufactured via the latex method. The layer distance of the OLS and the morphology of the nanocomposites were characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). By increasing the amount ofN,N-dimethyldodecylamine (DDA) up to 2.5 g, the maximum values of torque, tensile strength and wear resistance of the SBR nanocomposites were increased due to the increased dispersion of the silicate layers in the rubber matrix and the increased crosslinking of the SBR nanocomposites by DDA itself. When SBR nanocomposites were manufactured by using the ternary filler system (carbon black/silica/OLS) to improve their dynamic properties as a tire tread compound, the tan δ (at 0 °C and 60 °C) property of the compounds was improved by using metal stearates instead of stearic acid. The mechanical properties and wear resistance were increased by direct substitution of calcium stearate for stearic acid because the filler-rubber interaction was increased by the strong ionic effect between the calcium cation and silicates with anionic surface. However, as the amount of calcium stearate was further increased above 0.5 phr, the mechanical properties and wear resistance were degraded due to the lubrication effect of the excessive amount of calcium stearate. Consequently, the SBR/organoclay nanocomposites that used carbon black, silica, and organoclay as their ternary filler system showed excellent dynamic properties, mechanical properties and wear resistance as a tire tread compound for passenger cars when 0.5 phr of calcium stearate was substituted for the conventionally used stearic acid.

Improving the exfoliation of layered silicate in a poly(ethylene terephthalate) matrix using supercritical carbon dioxide

AbstractA technique for improving the exfoliation of organically modified layered silicate (OMLS) in a poly(ethylene terephthalate) (PET) matrix using super critical carbon dioxide (scCO2) is compared to traditional direct melt blending. The process relies on the rapid expansion of a scCO2/OMLS mixture directly into the second stage of a single screw extruder where the clay and scCO2 mixture is subsequently melt blended with the PET matrix. The simple, environmentally benign process results in a more highly delaminated system than traditional direct melt compounding. X‐ray diffraction analysis is used to reveal improved clay morphologies and the resulting mechanical properties are examined. Rheology is used as a tool to draw conclusions about the effect that scCO2 has on reducing PET matrix degradation during processing. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers

New Insight into Biodegradation of Polylactide (PLA)/Clay Nanocomposites Using Molecular Ecological Techniques

Novel molecular ecological techniques were used to study changes in microbial community structure and population during degradation of polylactide (PLA)/organically modified layered silicates (OMLS) nanocomposites. Cloned gene sequences belonging to members of the phyla Actinobacteria and Ascomycota comprized the most dominant groups of microorganisms during biodegradation of PLA/OMLS nanocomposites. Due to their numerical abundance, members of these microbial groups are likely to play an important role during biodegradation process. This paper presents new insights into the biodegradability of PLA/OMLS nanocomposites and highlights the importance of using novel molecular ecological techniques for in situ identification of new microorganisms involved in biodegradation of polymeric materials.

Cross‐linked and uncross‐linked biodegradable nanocomposites. I. Nonisothermal crystallization kinetics and gas permeability

AbstractVarious nanocomposites of poly(butylene succinates) (PBS) with different ratios of organically modified layered silicates (OMLS) were prepared. Moreover, such PBS nanocomposites cross‐linked by dicumyl peroxide (DCP) were also prepared in this work. Effects of cross‐linking and OMLS on nonisothermal crystallization kinetics and the gas permeability of PBS samples were investigated further. WAXD indicates that the layers of clay were intercalated by the modifiers, and that the interlayer distance of OMLS in the nanocomposites could be expanded to about 2.96 nm. The results of DSC analysis revealed that the crystallization temperatures of nanocomposites shifted to the lower temperature with the increase of OMLS content. With the addition of OMLS, crystallinity was decreased, whereas the half‐life of crystallization was increased. On the other hand, even the cross‐linked effects also increased the half‐life of crystallization of the materials, but did not necessarily decrease crystallinity in all cases. Moreover, the PBS/OMLS nanocomposites showed a 23.87–46.64% decrease in permeability of oxygen when compared with the pristine PBS sample. Yet, the cross‐linked nanocomposites exhibited decrements of 6.38–39.53%. This indicates that the gas permeability of PBS was more effectively depressed by the addition of OMLS than by the cross‐linking reaction. The cross‐linked structure of polymer seemed not to be very effective in decreasing the gas permeability of PBS. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

Enzymatic degradation kinetics of poly(butylene succinate) nanocomposites

In this work, poly(butylene succinates) (PBS)/organically modified layered silicates (OMLS) composites were prepared by solution blending. The degradability of PBS, PBS/layered silicates and PBS/OMLS nanocomposites have been investigated using enzymatic degradation method. Effects of layered silicates and OMLS contents on the degradation behavior of PBS were explored. The results reveal that the degradability of the composites was both enhanced by the addition of layered silicates or OMLS as compared to the pristine PBS sample. The calculated data based on the autocatalytic model show that the degradation kinetics of PBS/layered silicates composites is the chain scission process with the following autocatalytic reactions, which is very similar to that of pure PBS matrix. On the other hand, the surface-catalyzed reaction model may be more suitable to describe the degradation behavior of the PBS/OMLS nanocomposite. Moreover, the results show that rate-controlling step of the degradation reaction for PBS/OMLS nanocomposite is more probable to be the desorption step.

Effect of Organoclay on the Orientation and Thermal Properties of Liquid‐Crystalline

AbstractThe preparation and thermal and thermo‐mechanical properties of nanocomposites based on liquid‐crystalline polymers (LCP) and organically‐modified layered silicate (OMLS) is described. From XRD patterns, very little smectic ordering is present in the pure LCP; in the nanocomposites, the polymer chains tended to orient in the direction of the dispersed clay layers. According to the DSC results, during first heating, the first melting peak represents the crystalline to nematic transition and, after that, a broader isotropization takes place. Although TGA of the samples showed a single‐step decomposition through chain scission under an inert atmosphere, in air the nanocomposites underwent a two‐step process, with onset of degradation at a higher temperature. The first step is mainly due to chain scission and the second is due to oxidative reactions.magnified image

ABS/clay nanocomposites obtained by a solution technique: Influence of clay organic modifiers

Acrylonitrile-butadiene-styrene (ABS) polymer/clay nanocomposites were produced using an intercalation–adsorption technique from polymer in solution: polymer/clay suspensions were subjected to ultrasonic processing to increase the effectiveness of mixing. Several kinds of organically modified layered silicates (OMLS) were used to understand the influence of the surfactant nature on the intercalation–exfoliation mechanism. We show that only imidazolium-treated montmorillonite (DMHDIM-MMT) is stable at the processing temperature of 200 °C, used for hot-pressing, whereas alkyl-ammonium modified clays show significant degradation. The morphology of ABS based polymer nanocomposites prepared in this work was characterized by means of wide angle X-ray diffraction (WAXD) and transmission electron microscopy (TEM). Dynamic-mechanical analysis (DMA) was used to determine the storage modulus and damping coefficient as a function of temperature, and to investigate the correlations between mechanical properties and morphology of the nanocomposites. The thermal stability was assessed by means of thermogravimetric analysis (TGA). DMA and TGA show that the nanocomposites based on imidazolium-modified clay out-perform the nanocomposites based on quaternary-ammonium-modified clays in terms of mechanical properties and thermal stability.

Influence of nanofillers on thermal insulating properties of polyurethane nanocomposites foams

AbstractThe effect of several nanofillers on thermal insulating properties of polyurethane rigid foams (PUR) was analyzed. The nanofillers used differ for chemical nature and aspect ratio. We used both pristine and organically‐modified layered silicates (OMLS) and inorganic spherical nanopowders. The fillers were first dispersed in the polyol component through use of sonication; then doped polyol was mixed with isocyanate. The effect of polyol viscosity and nature (polyether or polyester) on the degree of the dispersion of the filler was also taken into account. The results obtained showed that the chemical nature and viscosity of polyols as well as the kind of compatibilization of the filler play a very important role in favoring the filler dispersion on a nanometer scale; the aspect ratio of the filler is instead not so important. When a good degree of dispersion is achieved, the thermal insulating properties of the foam can be slightly enhanced, as the fillers may act as nucleating agents. Some drawbacks were also found in using nanofillers: the fillers may bring in some cases an increase of the open cell content making the diffusion rate of the blowing agents faster thus leading to a worsening of thermal insulating properties during time. POLYM. ENG. SCI., 47:1351–1358, 2007. © 2007 Society of Plastics Engineers

Biodegradable nanocomposites based on poly(butylene succinate)/organoclay

In this work, we try to incorporate the inorganic system into the biodegradable polymers to compose an organic/inorganic polymer hybrid. Various nanocomposites of poly(butylene succinates) (PBS) with different ratios of organically modified layered silicates (OMLS) prepared by solution blending were investigated. The OMLS used for the preparation of nanocomposites were functionalized ammonium salts modified montmorillonite. The effects of OMLS on the nanocomposites were investigated by XRD, TEM, DMA and TGA in the aspect of the d-spacing of clay, mechanical and thermal properties. Interestingly, all these nanocomposites exhibited improved properties when compared with the pristine PBS sample. XRD indicates that the layers of clay were intercalated by the modifiers, and the interlayer distance of organoclay in the nanocomposites could be extended to about 29.4 A. Moreover, the thermal stability of the nanocomposites was enhanced by the addition of organoclay via TGA study, closely related to the organoclay content in the PBS matrix. DMA data shows that the storage and loss moduli were concurrently enhanced by the addition of organoclay as compared to the pristine PBS sample. Moreover, the glass transition temperatures also increased about 5 to 20 °C (from DMA, peak of tanδ) for the various organoclay-containing samples. The enhanced mechanical and thermal properties can be achieved from these organoclay modified-nanocomposites.

Newly developed nanocomposites from cellulose acetate/layered silicate/poly(ε-caprolactone): Synthesis and morphological characterization

New biodegradable cellulose acetate/layered silicate grafted poly(e-caprolactone) [(CA/layered silicate)-g-PCL] nanocomposites were prepared by in situ polymerization of e-caprolactone in the presence of cellulose acetate (CA) and organically modified layered silicate (OMLS). The structures of the resulting composites were investigated. X-ray diffractometry was carried out to survey general structural features of (CA/OMLS)-g-PCL nanocomposites, and revealed that OMLSs having hydroxyl groups in the organic modifiers greatly altered the layered silicate structure by monomer intercalation and successive exfoliation through its polymerization. Two of the representative cases were characterized by wide-angle and small-angle X-ray scattering analyses with a synchrotron source. The morphology of these nanocomposites was further examined by transmission electron microscopy. When SPN, one of OMLSs having one hydroxyl group in its modifier, was used, the silicate layers could not be dispersed thoroughly, but existed as aggregates consisting of several silicate layers. Among them, the crystal growth of PCL developed by transcrystallization, where the crystal growth was restricted in the confined space. When Cloisite 30B, having two hydroxyl groups within the modifier, was used, the silicate layers forming the clay were dispersed completely in the composite and random orientation of the OMLS was observed.

Application of mean-field model of polymer melt intercalation in organo-silicates for nanocomposites

The mean-field, lattice-based model of polymer melt intercalation in organically-modified layered silicates (OLS) originally developed by Vaia and Giannelis was applied for different polymers such as poly(methyl methacrylate) (PMMA), polypropylene (PP), and poly(ethylene oxide) (PEO). The nature of each polymer controls significantly the intercalation of the system. The internal energy change caused by the interaction of polymer, surfactant and clay is the strongest factor in determining the equilibrium structure of the nanocomposite system.

Microstructural Origin of Strength and Toughness of Epoxy Nanocomposites

Nanocomposites of a bifunctional epoxy resin are synthesized and evaluated. Organically modified layered silicate (OLS) particles (4% by weight) and multiwalled carbon nanotubes (MWNT) (1% by weight) are used as reinforcements. Thermal and viscoelastic characterization of the two composites are performed and compared with the neat resin. Tensile tests are conducted on multiple identical unnotched and notched specimens to evaluate the overloading and fracture behavior of the nanocomposites. In comparison with the neat bifunctional epoxy, it is found that the 1% MWNT reinforcement increased the ultimate strength and strain to failure by about 139 and 158%, respectively. In comparison, the OLS has increased the ultimate strength and strain by about 30 and 20%, respectively. In comparison with the neat resin, there is a 170% increase in the fracture toughness of the MWNT composites and only 17% in the case of the OLS composites. Fracture surface analysis revealed the various mechanisms by which the MWNT composites acquire their superior strength and toughness in comparison with the neat resin.

Novel biobased nanocomposites from functionalized vegetable oil and organically-modified layered silicate clay

The new biobased nanocomposites are processed from anhydride-cured epoxidized linseed oil (ELO)/ or octyl epoxide linseedate (OEL)/diglycidyl ether of bisphenol F (DGEBF) epoxy matrix and organomontmorillonite clay. The selection of anhydride curing agent and biobased epoxy resulted in an excellent combination to provide an epoxy matrix having high elastic modulus, high glass transition temperature, and high heat distortion temperature (HDT), with higher amounts of functionalized vegetable oil (FVO), compared with amine-cured biobased epoxy. The sonication technique was utilized to process the organically-modified clay nanoplatelets in the glassy biobased epoxy network resulting in nanocomposites where the clay nanoplatelets are almost completely exfoliated and homogeneously dispersed in the epoxy network. The processed exfoliated clay nanocomposites showed higher storage modulus compared with the neat epoxy containing the same amount of FVO. Therefore, the lost storage modulus with larger amount of FVO can be regained with exfoliated clay nanoreinforcement.

Tuning Polymer Nanocomposite Morphology: AC Electric Field Manipulation of Epoxy–Montmorillonite (Clay) Suspensions

AC electric field alignment (see Figure) offers a route to composite films with unusual physical properties, in numerous geometries and applicable to a wide range of organically modified layered silicates. Exchangeable organic cations on the aluminosilicate surface are suspected to cause the induced dipole. Orientational, compositional, and translational control of nanoparticles, paralleling efforts in electric field‐trapping and traveling wave applications, could be achieved.