Layered Silicate Montmorillonite Research Articles

Influence of modified biopolymers on thermal properties and biodegradation processes of carboxylated nitrile-butadiene (XNBR) nanocomposities

The presented study includes a comparison of the effect of fillers used in carboxylated nitrile butadiene rubber XNBR on the properties of the obtained polymer materials. Fillers used in this study originated from the tanning industry waste: cattle hair keratin, enzymatic hydrolyzate of cattle hair keratin and condensate of enzymatic hydrolyzate of cattle hair keratin. The use of commonly found in nature phyllosilicates allows to obtain nanocomposites. That is why in the presented study we used different mass fraction of layered silicate—montmorillonite. The dispersion of silicates in polymer matrices can be influenced by their physical and chemical modifications that lead to changes in the properties of the polymer matrices themselves. In the presented study the kinetics of vulcanization of elastomer blends was investigated, and the obtained XNBR rubber vulcanizates were analyzed for mechanical, optical, rheological, thermal analysis and their resistance to accelerated thermo-oxidative aging (S) and susceptibility to biodegrade were tested. The produced elastomer composites may be used in the rubber industry in the assortment of various types of washers, elastomer seals or conveyor belts—materials that often work under elevated temperature conditions. Therefore, it seems advisable to understand the thermal properties of this type of materials, eg for suitability in real conditions. Therefore, Thermogravimetry (TG), Differential Scanning Calorimetry (DSC), Oxygen Index (IO) analyzes have been carried out, showing that different mechanisms of decomposition occur in layers of fiber-enriched polymer composites than unrecoverable ones. The modified keratin also slightly decreases the glass transition temperature. In addition, the presence of a modified keratin in the XNBR elastomer structure increases the composites compliance with the biodegradation process.

Influence of the Chemical Nature and Structural Characteristics of Nanofillers on the Mechanism of Polyethylene Pyrolysis

The influence of different types of nanofillers on the mechanism of polyethylene thermal degradation is studied. The composition of the products of pyrolysis of composite material was evaluated using gas chromatography–mass spectrometry (GC–MS). It has been found that incorporating carbon nanofillers (carbon nanotubes, graphite nanoplates, and reduced graphite oxide) into polyethylene leads to increase in the fraction of heavy hydrocarbons of the pyrolysis products. The varying influence of carbon fillers on the pyrolysis process is explained in terms of the surface defectiveness of the fillers and their specific effect on the segmental mobility of the polyethylene macroradicals within the framework of the previously proposed theory. The use of montmorillonite-layered silicate as a filler leads to a qualitative change in the composition of pyrolysis products, which is caused by the presence of catalytic acid sites and the ionic character of the polyethylene thermal degradation mechanism.

Thermoplastic Vulcanizates Filled with а Layered Silicate

Oil-resistant and thermoformed thermoplastic vulcanizates based on butadiene-nitrile rubber and polypropylene were obtained, containing a layered silicate montmorillonite as a filler. The structural characteristics of composites based on thermoplastic vulcanizates were studied using the methods of fractal analysis. It has been established that the value of the static flexibility of the polymer chain of a thermoplastic vulcanizate containing montmorillonite exceeds the static flexibility of the polymer chain of an unfilled thermoplastic vulcanizate. It is shown that the introduction of montmorillonite in the amount of 1-3 pbw in thermoplastic vulcanizates leads to improved performance characteristics of the obtained composites.

PVA Nanofibers Including Biopolymer-grafted Copolymer for Potential Biomedical Applications

Multifunctional nanofibers were fabricated by electrospinning of polyvinyl alcohol/octadecylamine montmorillonite layered silicate nanocomposite as a matrix polymer and amphiphilic copolymer-g-biopolymer (polylactic acid, PLA) as a biocompatible partner polymer. Crystal structure of the nanofibers significantly changed due to in situ phase separation processing via different chemical and physical interfacial interactions. Relative high thermal stability, high first melting and low crystallinity were observed for the matrix/polymer nanofibers. Nanofibers exhibit low cytotoxicity and necrotic effect for MC3T3-E1 preosteoblast cells.

Viscoelasticity and Dynamics of Confined Polyelectrolyte/Layered Silicate Nanocomposites: The Influence of Intercalation and Exfoliation

AbstractThe influence of different confinement regimes on the linear viscoelastic properties of a polyelectrolyte, the protonated poly‐[(dimethylamino) ethyl methacrylate] (PDMAEMAH), is investigated. PDMAEMAH is reinforced with the layered silicate montmorillonite (MMT). Neat MMT and MMT treated with sulfobetaine and ammonia‐based surfactants (MMT/SB and MMT/NH, respectively) are utilized. Transmission electron microscopy and X‐ray scattering show that MMT and MMT/NH produce intercalated morphology, whereas MMT/SB produces an exfoliated morphology. Thus, the polyelectrolyte is under different confinement regimes. The confinement produces the increase of glass transition temperature Tg; however, the increase is larger for the (highly confined) intercalated morphology. Master curves are constructed applying time–temperature superposition. Strikingly, the viscoelastic spectra evidence that the intercalated morphology produces twofold increase of rubber‐like modulus, whereas the exfoliated morphology produces over fourfold reduction of rubber‐like modulus, both at 3 wt% clay concentration. The reduction of rubber‐like modulus suggests that an exfoliated morphology produces disruption of the entanglement density. Analysis in the segmental relaxation regime shows that the intercalated morphology induces longer relaxation times, that is, more dynamics retardation, in correlation with the increase of glass transition temperature. This research paves the road for better understanding of viscoelastic behavior and dynamics of molten polyelectrolytes under confinement.

Organoclay hybrid materials as precursors of porous ZnO/silica-clay heterostructures for photocatalytic applications.

In this study, ZnO/SiO2-clay heterostructures were successfully synthesized by a facile two-step process applied to two types of clays: montmorillonite layered silicate and sepiolite microfibrous clay mineral. In the first step, intermediate silica–organoclay hybrid heterostructures were prepared following a colloidal route based on the controlled hydrolysis of tetramethoxysilane in the presence of the starting organoclay. Later on, pre-formed ZnO nanoparticles (NP) dispersed in 2-propanol were incorporated under ultrasound irradiation to the silica–organoclay hybrid heterostructures dispersed in 2-propanol, and finally, the resulting solids were calcinated to eliminate the organic matter and to produce ZnO nanoparticles (NP) homogeneously assembled to the clay–SiO2 framework. In the case of montmorillonite the resulting materials were identified as delaminated clays of ZnO/SiO2-clay composition, whereas for sepiolite, the resulting heterostructure is constituted by the assembling of ZnO NP to the sepiolite–silica substrate only affecting the external surface of the clay. The structural and morphological features of the prepared heterostructures were characterized by diverse physico-chemical techniques (such as XRD, FTIR, TEM, FE-SEM). The efficiency of these new porous ZnO/SiO2-clay heterostructures as potential photocatalysts in the degradation of organic dyes and the removal of pharmaceutical drugs in water solution was tested using methylene blue and ibuprofen compounds, respectively, as model of pollutants.

Design and preparation of natural layered silicate/bio-based elastomer nanocomposites with improved dispersion and interfacial interaction

Green nanocomposites consisting of bio-based poly(dibutyl itaconate-ter-isoprene-ter-4-vinylpyridine) (PDBIIVP) elastomers with different 4-vinylpyridine (4-VP) contents and natural layered silicate montmorillonite (MMT) were prepared by a green latex co-coagulation method. The effects of the pyridine groups on the interfacial interaction, morphology, and performance of the nanocomposites were investigated. Ionic bonding interfaces, which were confirmed by X-ray photoelectron spectroscopy, were introduced to the nanocomposites through the electrostatic attraction between the protonated pyridine groups of the modified elastomers and the electronegative MMT during the co-coagulation of PDBIIVP latex and MMT aqueous suspension with hydrochloric acid. The dispersion of MMT and the interfacial interaction between PDBIIVP and MMT were improved remarkably, as demonstrated by X-ray diffraction, transmission electron microscopy, rubber process analyzer (RPA) results and swelling tests. The mechanical and gas barrier properties of PDBIIVP improved markedly with increasing 4-VP content. For the PDBIIVP with 7.0 wt% 4-VP, the addition of 10 phr of MMT increased the tensile strength by 730% and reduced the gas permeability by 71%.

Water vapour permeability of poly(lactic acid) nanocomposites

A series of poly(lactic acid) (PLA) nanocomposites containing from 1 up to 6wt% of montmorillonite layered silicate were prepared by melt compounding followed by compression moulding. The morphology of the nanocomposites was investigated using transmission electron microscopy (TEM) and wide-angle X-ray diffraction (WAXD) and it was confirmed that the nanocomposite structures were intercalated. The average aspect ratio of the compounded nanoclay was found to be 50. Water vapour transmission rates (WVTR) through the films were measured at 38°C and at a relative humidity of 90%. It was found that the measured values of WVTR decreased with increasing nanoclay content up to a value of 5wt% and the results gave good agreement with predictions from the Nielsen ‘tortuous path’ model.

SAXS investigation of structure–property relationship of polypropylene/montmorillonite composites during load cycling

Polypropylene (PP) can hardly be reinforced by the layered silicate montmorillonite (MMT), but the material fatigue appears somewhat reduced. The probable reason is amplified competitive nucleation of the PP by MMT component. Utilizing small‐angle X‐ray scattering (SAXS) from synchrotron, we investigate the nanostructure evolution of the PP in straining experiments from neat PP and compatibilized composite materials. The compatibilizer is a styrene–ethylene/butylene–styrene copolymer (SEBS). Oriented injection‐molded test bars are studied.The discrete SAXS probes variations of sizes and distances among those crystalline domains that are not placed at random. Crystallite dimensions and distances are documented for modeling purposes. The nanoscopic strain is computed from the distance variation and compared with the macroscopic strain. Differences between macroscopic and nanoscopic strain are observed. They require postulating regions with statistical placement of crystallites (poorly arranged region, PAR) in addition to the SAXS‐probed well‐arranged semi‐crystalline entities (WAE). The extensibility of WAEs must be different from that of the PARs. In neat PP, the observed WAEs are well developed and stronger than the PARs. In the composites, the WAEs are made from thin and less extended crystalline domains. They are weaker than the PARs that appear reinforced. Thus, enclosing each MMT layer a PAR is formed, and the WAEs generated farther away remain imperfect. Consequently, in the composites, the narrow crystalline domains from the WAEs do not break into even smaller pieces, and the fatigue of the composites is lower than that of the neat PP. Copyright © 2013 John Wiley & Sons, Ltd.

Effect of polysulfone modification techniques on the properties of polymer-silicate nanocomposites

An effect of different methods of structural modification of the heat-resistant amorphous polysulfone with layered silicate montmorillonite on the properties of the resulting polymer-silicate nanocomposites has been studied. Comparative evaluation of the technological, physical, mechanical, thermal, and rheological properties of the nanocomposites has been performed.

Thermal and Mechanical Effects in Polystyrene-Montmorillonite Nanocomposite Foams

Nanocomposite polystyrene (PS) foams based on montmorillonite layered silicate (MLS) as nanofillers were prepared using in-situ polymerization of styrene. These nanocomposites were characterized for their thermal and mechanical properties using differential scanning calorimetry (DSC), x-ray diffraction (XRD), dynamic mechanical analyzer (DMA) and scanning electron microscope (SEM). Foamed sample microscopy revealed that the cell size reduced with the increasing amount of nanofiller. The mechanical properties showed a significant increase.

Maleated amorphous ethylene propylene compatibilized polyethylene nanocomposites: Room temperature nonlinear creep response

AbstractNonlinear creep of polyethylene and its nanocomposites remains an area of significant interest. Maleated polyethylene is often used as a compatibilizer to ensure enhanced dispersion. This article investigates blown films of linear low‐density polyethylene and its nanocomposites with montmorillonite‐layered silicate (MLS). An amorphous ethylene propylene copolymer grafted maleic anhydride (amEP) was added to enhance the interaction between the PE and the MLS. Tensile results indicate that the addition of amEP and MLS separately and together produces a synergistic effect on the mechanical properties of the neat PE. Nonlinear creep was analyzed by examining creep and recovery of the films with a Burger model and the Kohlrausch‐Williams‐Watts relation. A consistent decrease in unrecoverable plastic strain was obtained in the nanocomposite samples. A decreased retardation time associated with MLS presence was determined. POLYM. ENG. SCI., 50:1620–1632, 2010. © 2010 Society of Plastics Engineers

Separating stress and time dependent effects in the temperature dependent creep of polyethylene nanocomposites

AbstractThe nonlinear time dependent creep of linear‐low density polyethylene (LLDPE) reinforced with montmorillonite layered silicate was investigated. A previous study related the time/stress dependence of creep compliance of the material at room temperature using the Burger and Kohlrausch‐Williams‐Watts models. Using both the creep and recovery compliance curves, we employ the Schapery formulation to study the relationship between deformation, time, stress, and temperature of LLDPE nanocomposites. Smooth mastercurves are constructed using time–temperature–stress superposition principles. The stress and temperature‐related creep constants and shift factors were determined for the material using the Schapery nonlinear viscoelastic equation. The prediction results confirm the enhanced creep resistance of nanofillers even at extended time scales and low temperatures. POLYM. ENG. SCI., 50:1646–1657, 2010. © 2010 Society of Plastics Engineers

Ethylene maleated amorphous propylene compatibilized polyethylene nanocomposites: Stress and temperature effects on nonlinear creep

AbstractThe effects of stress and temperature on the nonlinear creep behavior of linear low‐density polyethylene (LLDPE) nanocomposites reinforced with montmorillonite‐layered silicate (MLS) nanoclay and compatibilized with an amorphous maleated ethylene copolymer (amEP) is investigated. To study the effect of stress on the creep resistance of these materials, creep tests were conducted at different stress levels (10, 25, and 50% yield stress). The effect of temperature was examined by analyzing the creep and recovery of the films at temperatures in the range of −100 to 25°C. The individual creep compliance curves for each stress level and temperature were fitted to both the Burgers model and the Kohlrausch‐Williams‐Watts (KWW) function. The results indicate that modification of the polyethylene results in a suppression of relaxation times but the temperature trends are reversed below the β transition temperature. Filled systems exhibited a distribution in relaxation times whose trend matched the relaxation time trends in both Burger and KWW models. POLYM. ENG. SCI., 50:1633–1645, 2010. © 2010 Society of Plastics Engineers

Effect of layered silicate nanoclay on the properties of silane crosslinked linear low-density polyethylene (LLDPE)

In the present work, the effect of pristine layered silicate montmorillonite (MMT) nanoclay on the properties of silane-crosslinked LLDPE prepared by melt compounding is investigated. The effect of the sequence of feeding additives (nanoclay and grafting agent) into the mixer on gel content, thermal and mechanical properties were studied. Results demonstrate that the sequence of feeding additives influences the final properties of nanocomposites. For samples prepared by first grafting of silane on LLDPE followed by incorporation of nanoclay into the polymer matrix, the gel content and the rate of crosslinking increased, while the elongation at break decreased. For samples prepared by first mixing nanoclay into the LLDPE matrix followed by the grafting reaction, the rate of crosslinking and the tensile properties did not change significantly. The gel content increased with increasing content of nanoclay for both process routes due to an enhanced permeation of water molecules into the polymer matrix in the presence of polar montmorillonite particles. Wide angle X-ray scattering (WAXS) results proved the intercalation/partial exfoliation morphology of nanoclay in the silane-grafted LLDPE matrix. Differential scanning calorimetry (DSC) data showed multiple melting behaviour for crosslinked samples which is indicative for different crystalline structures of the sol and gel part of the LLDPE matrix.

Co-extrusion of multilayer poly(m-xylylene adipimide) nanocomposite films for high oxygen barrier packaging applications

Multilayer packaging films incorporating a montmorillonite layered silicate (MLS)/poly(m-xylylene adipimide) (MXD6) nanocomposite as the oxygen barrier layer and low-density polyethylene (LDPE) as the moisture resistant layer were produced through the co-extrusion process at the laboratory and pilot scale level. Extrusion screw speeds were varied from 30 to 130 rpm in order to produce samples with varying layer thicknesses. The multilayer film structure was scaled up from the laboratory scale to the pilot-level scale based on oxygen transmission data obtained from the laboratory-scale process parameters. Laboratory-scale film results indicated that the film which demonstrated an optimal oxygen transmission rate (OTR) of 0.3 cm 3/(m 2 day) at 60%RH and water vapor transmission rate (WvTR) of 1.4 g/(m 2 day) at 90%RH had a structure that contained a core barrier film layer of nanocomposite MXD6 that makes up roughly 34% of the total film thickness, with the remainder of the film material consisting of maleic anhydride grafted polyolefin tie layers and LDPE skin layers. The OTR of the films changed as the relative humidity of the test environment was varied from 0 to 90%. However, for the pilot-scale trial it was necessary to reduce the target thickness of the core nylon barrier layer to 22% due to layer-to-layer melt flow instabilities that occurred during processing. The barrier properties of the multi-layer co-extruded films were highly dependant on overall film thickness. The highest performing oxygen barrier pilot-scale film had an OTR of 0.3 cm 3/(m 2 day) (60%RH) and a WvTR of 2.4 g/(m 2 day) (90%RH) with a core nylon layer of 1.5 mil and a total thickness of 7.7 mil. Correlation of the layer thicknesses to the barrier and mechanical properties of the pilot-scale multilayer films indicated that an increased nanocomposite core layer thickness improved the oxygen barrier performance and decreased film elongation while improving the tear resistance of the films.

Gelatin-Clay Bio-Nanocomposites: Structural and Functional Properties as Advanced Materials

Clay minerals such as the layered silicates montmorillonite and vermiculite, as well as the fibrous clay sepiolite, and a layered double hydroxide ([Zn2Al(OH)6]Cl.nH2O) have been used to prepare gelatin-clay micro- and nano-composites. This biopolymer can be assembled to those inorganic solids through interactions at the nanometric range, but only in the case of montmorillonite intercalation of gelatin takes place. One of the most salient features of the resulting bio-nanocomposites is the possibility to be processed as homogeneous thin films provided of good mechanical properties and transparency. The Young's modulus of gelatin-sepiolite bio-nanocomposites may increase by a factor of 2.5 with respect to neat gelatin. The incorporation of pH indicator dyes to the montmorillonite bio-nanocomposite films allows their application for optical pH sensing.

Ablation mechanism of polymer layered silicate nanocomposite heat shield

Recent advances in polymer layered silicate nanocomposites especially improve flammability resistance; encourage the examination of this unique class of evolving materials as potential ablatives. Polymer layered silicate nanocomposites show excellent potential as ablative heat shields. Determining the thermal diffusivity together with the mass and energy transfer is an important problem encountered in design of heat shield system which pyrolyses and ablates at high temperature. The aim of this work is to give information on the influence of the experimental conditions to the estimated effective thermal diffusivity of ablative nanocomposite and composite materials. Here, we present the inverse solution to estimate the parameter used to identify the effective thermal diffusivity of resol type phenolic resin-asbestos cloth montmorillonite layered silicate nanocomposite and its composite counterpart. The experimental setup consists of a standard oxyacetylene flame test. The transient temperature measurements, taken from the top surface and through the thickness of the samples, are used in the inverse analysis to estimate the change of the effective thermal diffusivity. The results of this work clarify the mechanism of the ablation and thermal diffusivity of the layered silicate nanocomposite heat shields due to the high temperature degradation in comparison with its composite counterpart.

Nanoalloy Based on Clays: Intercalated‐Exfoliated Layered Silicate in High Performance Elastomer

A novel method is described for the preparation of nanocomposites comprising a high performance rubber for tire application and layered silicates clay. In this work nanocomposites of solution‐styrene butadiene rubber (S‐SBR) with montmorillonite layered silicate were prepared with carboxylated nitrile rubber (XNBR), a polar rubber, as a compatibilizer. A sufficient amount of organomodified layered silicate was loaded in carboxylated nitrile rubber (XNBR) and this compound was blended as a master batch in the S‐SBR. Mixed intercalated/exfoliated morphologies in the nanocomposite are evinced by X‐ray diffraction measurements and transmission electron microscopy. Dynamic mechanical analysis also supports the compatibility of the composites. A good dispersion of the layered silicate in the S‐SBR matrix was reflected from the physical properties of the nanocomposites, especially in terms of tensile strength and high elongation properties.

Supported Zr‐and Hf‐cene Catalysts for Propylene Polymerization

AbstractThe supported metallocene catalysts were obtained on the layered silicate montmorillonite (MMT), using AlMe3 and AliBu3 for synthesis of alkylaluminoxane directly on a support surface, followed by metallocene supporting. It was shown that the MMT‐H2O/AliBu3 forms with ansa‐Zr‐cenes of C1 and C2‐symmetry the significantly more active supported metal‐alkyl complexes in propene polymerization, than MMT‐H2O/AlMe3. The MMT‐H2O/AliBu3 is the effective activator of the ansa‐Hf‐cenes, in contrast to MAO and MMT‐H2O/AlMe3, giving the high active supported catalysts for synthesis of isotactic and elastic polypropene. The character of influence of metallocene fixation on support on the isotactic pentad [mmmm] content in polymer, compared to homogeneous analogues, depends on the metallocene nature. The introduction of borate Ph3CB(C6F5)4 in the case of both Zr‐cene and Hf‐cene catalysts increases significantly the activity at the reduced ratio of Al/Zr, Hf (100–500 instead of 2000–3000) and stabilizes the catalytic complexes.