Pristine Clay Research Articles

Steam reforming of methanol over Cu/ZnO/Al2O3 modified with hydrotalcites

Dilution of a commercial Cu/ZnO/Al 2 O 3 (CZA) catalyst by well-crystallized MgAl hydrotalcite nitrate (HTNO 3 ) and chloride (HTCl) resulted in the formation of the modified samples CZA–HTN and CZA–HTCl, respectively. The samples were characterized by N 2 sorption and XRD measurements. The structures of the CZA–HT materials proved to be more compact than those of the pristine clays. The modified samples were investigated as catalysts for the steam reforming of methanol under steady state conditions. The catalytic activity and the long-term stability of CZA–HT were found to depend strongly on the nature of the interlamellar anion of HT. CZA–HTN exhibited a marked catalytic activity and an enhanced thermal stability. It was pointed out that dilution with HTNO 3 improved the catalytic performance of CZA by increasing the methanol conversion and decreasing the CO production. The moderate increase in the methanol conversion for CZA–HTN during time-on-stream was attributed to partial delamination of the HT structure under SRM conditions. The application of an enhanced H 2 O:MeOH ratio of 1.3 for CZA–HTN was found to decrease both the methanol conversion and the CO formation to an appreciable extent.

Fabrication of pre-exfoliated clay masterbatch via exfoliation-adsorption of polystyrene nanobeads

The approach studied in the present work produced an exfoliated state of clay layers via confinement of the charged nano-sized polystyrene (PS) beads within the gallery of swollen pristine clay. It was demonstrated that adsorption of the polymer nanobeads dramatically promotes expansion of the clay gallery. A comparative study of incorporation was conducted by employing organo-modified clay along with two different colloid polymer systems: electrostatically stabilized PS nanobeads and cationic monomer-grafted PS nanobeads. The mechanism of adsorption of the monomer-grafted polymer beads onto clay via cationic exchange between the alkyl ammonium group of the polymer nanobeads and the interlayer sodium cation of the layered silicate was verified by using several techniques. As distinct from the polymer nanobeads formed using conventional miniemulsion polymerization method, competitive adsorption of stabilizing surfactant molecules was be prevented by grafting the surface functional groups into the polymer chain, thereby supporting the observed effective adsorption of the polymer beads. The presence of surface functional groups that support the establishment of strong polymer-clay interactions was suggested to improve the compatibility of the clay with the polymer matrix and eventually play a crucial role in the performance of the final nanocomposites.

Influence of compatibilizer degradation on formation and properties of PA6/organoclay nanocomposites

Nanocomposites based on polyamide 6 (PA6) and commercial layered silicates have been prepared by both in situ polymerization and melt compounding. The main aim of the present work has been centred on compatibilizer degradation, caused by the preparation conditions, in terms of nanocomposite end features. Two montmorillonite (MMT)-type, organically-modified clays (OMLS), namely Cloisite 30B ® and Nanofil 784 ®, and a sodium MMT (Cloisite Na ®) have been studied. Thermal properties of the layered silicates have been evaluated by TGA, IR, WAXD and pyrolysis–gas–mass. In order to better assess the influence of high temperature processes on clay modifications, a thermal treatment which mimics the conditions used during the in situ polymerization (4 h at 250 °C) has been applied on layered silicates. The above treatment, besides the elimination of absorbed water from all the clays, turned out to prove noteworthy differences in compatibilizer modification for the two organoclays. Indeed, in the case of Closite 30B ® only a removal of organic molecules outside the silicate galleries and a likely reorganization of those present inside the galleries have been detected, while a relevant chemical modification of Nanofil 784 ® compatibilizer has been conversely found. As far as nanocomposite characteristics are concerned, the latter have been found to depend on both the preparation method and clay type. In the case of in situ polymerization, also thermally-treated layered silicates, coded (T), have been used, in order to put more clearly in evidence the role of compatibilizer decomposition on nanocomposite formation and properties. Indeed, nanocomposite samples containing Closite 30B ®(T) have been found to be completely exfoliated, while the same thermal treatment seems to make worse the properties of those based on Nanofil 784 ®(T). Furthermore, with respect to nanocomposites based on pristine clays, samples containing thermally-treated silicates turned out to be different in terms of both molecular mass and crystal structure of the polymer matrix. Namely, PA6 γ-form seems to be promoted for all nanocomposites prepared in such a way, probably because of water removal at high temperature, which makes –OH groups of the layered silicate more free to interact with polyamide chains, thus causing a restriction of their mobility.

Polymer-based nanocomposites: Overview, applications and perspectives

Polyamide 6 and pristine montmorillonite have been melt blended in an extruder and water was injected into the melt in order to produce polyamide-based nanocomposites. The pristine clay was found to be exfoliated and dispersed homogenously in the polyamide. A mechanism explaining the formation of such nanocomposites is presented. Concentrated systems were achieved and redispersed in polypropylene by reactive processing. It is shown that, by this way, polyamide acts as a “primary” compatibiliser, with the maleic anhydride modified polyolefin playing the role of a “secondary” compatibiliser.

Mechanistic examination of pre-exfoliating confinement of surface-active polystyrene nanobeads within pristine clay

Hydrophobic polymer (PS) nanoparticles preformed through an emulsifier-free emulsion polymerization method were successfully incorporated into a gallery of pristine sodium montmorillonite via interfacial cation exchange. The polymer beads confined between clay nanosheets were capable of (1) preventing the silicate layers from restacking and (2) maintaining the exfoliated state of clay. The increase in the abundance of surface groups promoted adsorption of the nanobeads onto the silicate surface and eventually led to the establishment of strong polymer–clay interactions. These findings suggest that, on the basis of the obtained pre-exfoliated clay masterbatch, the presence of strong polymer–clay interactions could improve the mechanical performance of nanocomposites.

Epoxy−Clay Fabric Film Composites with Unprecedented Oxygen-Barrier Properties

A new barrier-film chemistry is described in which two materials, namely a clay fabric film and a polymer, are combined to form a composite with gas-barrier properties that are far superior to those of the parent end members. Homoionic inorganic smectite clay fabric films of sodium montmorillonite and synthetic lithium fluorohectorite were cast in self-supported film form, impregnated with liquid epoxy resin and amine curing agent, and then cured to form the final epoxy−clay fabric film composite. The oxygen permeabilities of the epoxy−clay fabric film composites were lower by 2−3 orders of magnitude in comparison to that of the pristine polymer and by 3−4 orders of magnitude in comparison to that of the pristine clay film. This unprecedented reduction in oxygen permeability was attributed in part to the high volume fraction (∼77%) of highly aligned and nonswellable clay nanolayers in the fabric film and to the polymer filling of voids formed between imperfectly tiled clay platelet edges in the film. Mixed organic−inorganic ion-exchange forms of clay fabric films made through ion-exchange reactions of inorganic clay films form a heterostructure in which the outer regions of the film contain a swellable organoclay phase and the interior regions retain the nonswellable inorganic clay barrier phase. The modulus and glass-transition temperature of the polymer phase is not compromised upon formation of the clay fabric film composites.

Removal of basic dye from water onto pristine and HCl-activated montmorillonite in fixed beds

The removal of a basic dye from water onto pristine montmorillonite and HCl-activated montmorillonites in fixed beds was investigated. Experiments were carried out as a function of liquid flow rate, influent dye concentration, and column length. The adsorption capacity of basic dye onto pristine clay could be largely improved when the clay is activated by HCl. The mathematical models that involve two parameters of standard deviation (σ) and the time ( t 0) were tested to fit the measured breakthrough curves of basic dye in fixed beds. A macroscopic model developed by Hutchins and kinetic studies were fitted to calculate the adsorption capacity in fixed beds. It is indicated that the predominating step of mass transfer for the adsorption system was diffusion of stagnating liquid-film for pristine clay, but intraparticle diffusion for HCl-activated clay. In addition, the application of the mathematical models is discussed.

Nanocomposites based on polyethylene and Mg–Al layered double hydroxide: characterisation of modified clay, morphological and rheological analysis of nanocomposites

Magnesium and aluminium based layered double hydroxide (Mg–Al LDH) after modification with anionic surfactant has been used as nanoclay to prepare polyethylene based nanocomposites using the melt mixing technique. The modified Mg–Al LDH has interlayer separation about four times higher than the unmodified clay and also low surface tension. The modified clay also possesses similar platelet type particle morphology like pristine clay. X-ray diffraction and electron microscopic analyses reveal that the nanocomposites are mainly exfoliated/intercalated type characterised by the presence of hierarchy of clay particle morphology in the matrix. The dispersed particle forms aggregates or localised domains of network structure. As a result, response to steady shear is characterised by the presence of stress overshoot at the start-up flows, especially at higher LDH concentrations. The rheological analysis shows that the dispersed LDH particles caused deviation of linear viscoelastic response of the melt from that of the unfilled polyethylene.

Organo clay mineral–melted polyolefin nanocomposites Effect of surfactant/CEC ratio

Abstract Clay mineral–polymer nanocomposites are prepared by dispersing solid organo clay minerals in two different melted polyolefin matrices, namely polyethylene (PE) and ethylene vinyl acetate (EVA). The organo clay minerals are prepared by adding different amounts of surfactant corresponding to the CEC of the pristine clay mineral. The characteristics of the organo clay minerals are obtained by XRD, IR spectroscopy, TGA, and swelling volume measurements. The amount of added surfactant has a direct effect on the interlayer separation and organophilicity–hydrophilicity balance of the clay mineral, evidencing a particular behavior transition about OMt1.2 The intercalation of PE is found to be dependent on the interlayer distance of the organo clay minerals while EVA intercalates in the organo clay minerals whatever the amount of surfactant (> 0.5CEC), leading to the same interlayer spacing (4 nm). The polymer intercalation is more homogeneous in clay minerals having high surfactant loading corresponding to 1.5 and 2 CEC. Cone calorimeter results of the studied nanocomposites show a PHRR reduction of 32% for PE–OMt1.5 and of 47% for EVA–OMt1. For both polymers, the best compromise between mechanical and thermal properties, is obtained for organoclay filler obtained with an amount of added surfactant in a range 1–1.5 CEC.

Nanocomposites from Untreated Clay : A Myth ?

AbstractPolyamide 6 and pristine montmorillonite have been melt blended in an extruder and water was injected into the melt in order to produce nanocomposites. The pristine clay was found to be exfoliated and dispersed homogenously in the nanocomposites. A mechanism explaining the formation of such nanocomposites is presented.

Improvement of adhesive properties of rubbery epoxy using organoclay

The effect of incorporation of pristine montmorillonite clay and the corresponding organoclay into rubbery epoxy matrix on its adhesive properties has been investigated. Rubbery epoxy is of particular interest because of its potential for vibration damping applications. It was found that a significant improvement in adhesive properties occurred as a result of incorporation of organoclay, unlike pristine montmorillonite clay. The improvement is attributed to the reinforcing effect as observed from tensile testing. The reinforcing effect has been explained in terms of a better compatibility and the intercalation of polymer chains into clay galleries.

A Colloidal Route for Delamination of Layered Solids: Novel Porous‐Clay Nanocomposites

AbstractUnder soft conditions, it is possible to cause the irreversible delamination of organoclays (long‐chain alkylammonium cation‐exchanged smectites, and vermiculite‐layered silicate derivatives) via a sol–gel process that involves alkoxysilanes (e.g., tetraethoxysilane) and that finally gives silica–clay heteromaterials. These intermediate silica–organoclay nanocomposites facilitate the diffusion of the alkoxides which, in the presence of water, are hydrolyzed and subsequently polymerized. This process is a heterocoagulation that gives homogeneous gels in which the order in the layer stacking of clays is partially or completely lost, depending on the nature of the layered silicate. After calcination to eliminate the organic moiety, that is, the alkylammonium chains, the gel is irreversibly transformed into a silica–clay material in which the silicate layers are fully separated by the silica network generated by the alkoxide. The resulting solids are inorganic–inorganic nanocomposites which could be compared to polymer–clay nanocomposites, but in the present case the inorganic silica network is the continuous phase and the individual layers the corresponding disperse phase of the nanocomposite. These materials are solids of high specific surface area (> 400 m2 g–1), which exhibit micro‐ and mesoporosity, and also have properties inherent to both components, the pristine clay (e.g., a cation‐exchange capacity) and the silica network (e.g., an ability to be functionalized).

Morphology and thermal stability of BR/clay composites prepared by a new method

AbstractA new potential preparation method named in situ organic modification was used to prepare intercalated polybutadiene rubber (BR)/clay/dimethyl dihydrogenated tallow ammonium chloride (DDAC) composites. That is, BR, pristine clay, and intercalatant DDAC were directly mixed in a Haake rheometer without pretreating the pristine clay with the intercalatant. The morphology of the BR/clay composites was investigated by means of X‐ray diffraction and scanning electron microscopy. The thermal stability of the BR/clay composites was analyzed by thermogravimetric analysis (TGA). The dispersion of clay particles in the BR/clay/DDAC composites is much better than that in the BR/pristine clay and similar to that in the BR/organoclay DK4 (modified with DDAC) composites. BR/clay/DDAC composites have much higher thermal stability than the gum BR, BR/pristine clay, and BR/DK4 composites. The clay/intercalatant ratio has little influence on the thermal stability of the BR/clay/DDAC composites, while clay content has a significant effect on their thermal stability. The enhanced thermal stability of the BR/clay/DDAC composites is related to the dispersion state of clay particles in BR. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 905–913, 2006

Study on nanodispersion of PI/clay nanocomposite by temporal analyses

The detail of nanoscaled dispersive behavior for layered clay in polyimide was first illustrated using temporal analyses. The layered structure of pristine clay remained in the poly(amic acid) and polyimide matrixes almost throughout curing process. However, the clay was mutilated by polymer chain motion during the process (cluster size reduced from ∼700 to ∼298 nm). On the other hand, organo-clay modified with octadecyldimethyl (3-trimethoxysilylpropyl) ammonium chloride initially exfoliated in the poly(amic acid) solution ( d-spacing >42 nm). At room temperature ∼200 °C, the layered structure of the clay recovered due to loss of solvent and poly(amic acid) chains intercalating into the organo-clay interlayer ( d ∼ 3.49 nm). After polyimide fully formed at 350 °C, organo-clay d-spacing decreased to ∼2.27 nm. The reduction of d-spacing was ascribed to some of the polyimide molecular chains being squeezed out of the organo-clay interlayer since hydrogen bonds between the organo-clay and poly(amic acid) molecules diminished. The change in organo-clay cluster size behaved like pristine clay, finally decreasing to ∼367 nm after polyimide formed completely. The relatively large size of the organo-clay clusters in polyimide was ascribed to the confinement effect of polymer chain motion by organo-clay since the chains were frozen in the organo-clay interlayer.

Clay exfoliation and organic modification on wear of nylon 6 nanocomposites processed by different routes

The role of nanoclay on the wear characteristics of nylon 6 nanocomposites processed via different routes is examined in this paper. Pristine clay and organoclay were used in melt-extrusion with the matrix resulting in a largely aggregated and a highly exfoliated morphology, respectively. High exfoliation of pristine clay was also achieved by a water-assist process in melt compounding. Nylon 6/pristine clay composite had the worst wear resistance due to the large aggregated clay particles. For the two nylon 6/exfoliated clay nanocomposites, the one with the organically modified clay outperformed that with the pristine clay exfoliated by water. Detailed study on the wear track and subsurface below of the nylon 6/clay composites using both transmission and scanning electron microscopy provided new insight into the differences in their deformation and damage mechanisms. It was revealed that the interfacial adhesion of clay to matrix, and not the exfoliated morphology of clay, played a critical role in wear. However, exfoliated clay morphology is preferred to aggregate morphology. Hence, the superior wear-performance of nylon 6/organoclay nanocomposite is brought about by a combined effect of fine dispersion of clay platelets in nylon 6, high interfacial interaction between nylon 6 and clay layers, and effective constraint on surrounding nylon 6 material exerted by the clay platelets.

Montmorillonite−Poly(ethylene oxide) Nanocomposites: Interlayer Alkali Metal Behavior

Clay-PEO nanocomposites can have large electrical conductivities that make them potential electrolyte materials for rechargeable lithium batteries, but the origin of these large conductivities, especially for Li-containing materials, is poorly understood. This paper presents X-ray diffraction (XRD), TGA-DTA, and (7)Li and (23)Na NMR data for PEO nanocomposites made with natural (SWy-1) and synthetic (MNTS) montmorillonite clays that provide new insight into interlayer structure. An increase in basal d(001)-spacings demonstrates successful intercalation of PEO in all samples, and X-ray line narrowing shows that this intercalation improves the layer stacking order. The basal spacings of 17.9-19.4 A are consistent with a helical or bilayer structure of PEO in the interlayer. TGA-DTA provides quantitative results for the hydration state of the nanocomposites, demonstrates PEO intercalation, and shows that the composites prepared from the synthetic montmorillonite are less stable than those made with SWy-1. (7)Li NMR shows that the nearest neighbor hydration state of Li(+) is unaffected by PEO intercalation and suggests weak interaction of Li(+) with PEO. (23)Na NMR shows that PEO intercalation results in the conversion of the multiple Na(+) hydration states observed for the pristine clay into inner sphere sites most likely formed through coordination with the basal oxygens of the clay. These differences between lithium and sodium suggested that tighter binding of the Na to the clay may be the origin of the conductivity of Li-montmorillonite-PEO nanocomposites being as much as 2 orders of magnitude larger than those of Na-montmorillonite-PEO nanocomposites. The results confirm the idea that polymer oxygen atoms do not participate in sequestering the exchangeable cations and agree with the jump process for cation migration advanced by Kuppa and Manias (Kuppa, V.; Manias, E. Chem. Mater. 2002, 14, 2171).

Flame retardant mechanism of polymer/clay nanocomposites based on polypropylene

The combustion behavior and thermal-oxidative degradation of polypropylene/clay nanocomposite has been studied in this paper. The influence of compatibilizer, alkylammonium, organoclay, protonic clay and pristine clay is considered, respectively. The decrease of heat release rate (HRR) is mainly due to the delay of thermal-oxidative decomposition of the composites. The active sites on clay layers can catalyze the initial decomposition and the ignition of the composites. On the other hand, the active sites can catalyze the formation of a protective coating char on the samples. Moreover, the active sites can catalyze the dehydrogenation and crosslinking of polymer chains. Accordingly, the thermal-oxidative stability is increased and HRR is decreased.

New method for preparing polybutadiene rubber/clay composites

AbstractPolybutadiene rubber (BR)/clay/dimethyl dihydrogenatetallow ammonium chloride (DDAC) composites were prepared by a new preparation method named in situ organic modification. That is, BR, pristine clay, and quaternary ammonium salt were directly melt‐mixed without the usual pretreatment of the pristine clay with an intercalatant. BR/pristine clay, BR/organoclay DK4 (modified with DDAC), and BR/clay/DDAC composites were analyzed with X‐ray diffraction, scanning electron microscopy, and thermogravimetric analysis. The vulcanization characteristics and mechanical properties of the BR/pristine clay, BR/DK4, and BR/clay/DDAC composites were investigated. Finally, the effects of the processing conditions, clay/DDAC ratio, and clay content on the structure and properties of the BR/clay/DDAC composites were investigated. The results showed that intercalated BR/clay/DDAC composites were prepared. Organoclay DK4 and clay/DDAC effectively accelerated the vulcanization reaction of BR, which was attributed to the existence of the intercalatant used to modify the clay. The tensile strength, elongation at break, and tear strength of the BR/clay/DDAC vulcanizates were greatly improved in comparison with those of gum BR and BR/pristine clay vulcanizates but were somewhat lower than those of BR/DK4 vulcanizates. The dispersion of clay particles in the BR/clay/DDAC and BR/DK4 composites was much better than that in the BR/pristine clay composite. The temperature at the thermal degradation peak of the BR/clay/DDAC composite obviously increased in comparison with those of the gum BR, BR/clay and BR/DK4 composites. The mixing temperature and rotor speed had remarkable effects on the structure and properties of the BR/clay/DDAC composite. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 227–237, 2005

Morphology, mechanical and optical properties of transparent BR/clay nanocomposites

In this paper, transparent high cis-1,4-polybutadiene (BR)/clay nanocomposites were prepared by directly blending BR, organoclay DK4 (a clay modified with about 40% dimethyl dihydrogenated tallow ammonium chloride (DDAC)) and dicumyl peroxide (DCP). The effects of DCP and DK4 contents on mechanical and optical properties of BR/clay nanocomposites were investigated. The microstructure of these nanocomposites was characterized by wide-angle X-ray diffraction (XRD), transmission electron microscopy (TEM) and scanning electron microscopy (SEM). The dispersion dimension of clay particles in BR was quantitatively analyzed by small angle X-ray scattering (SAXS) and intercalated BR/DK4 nanocomposites with typical sandwich structure were prepared. The dispersion of DK4 particles in BR is more uniform than that of pristine clay. The DK4 particles become aggregated in BR with increasing DK4 content. BR/pristine clay composite is opaque due to the poor dispersion of clay particles in BR. However, the BR/DK4 nanocomposites are transparent due to the better dispersion of organoclay DK4. The light transmission of BR/DK4 nanocomposite shows a slight decrease with increasing DCP content. This is attributed to the development of permanent structural inhomogeneities. The transmission decreases while the haze increases with increasing DK4 content when DK4 content exceeds 5 phr. This phenomenon can be attributed to the aggregation of clay particles. The reinforcing effect of DK4 is much better than that of pristine clay in BR matrix. The properties of BR/DK4 and BR/pristine clay composites depend greatly on their microstructure.

Properties of polyethylene-layered silicate nanocomposites prepared by melt intercalation with a PP-g-MA compatibilizer

Polyethylene (PE)/clay nanocomposites were synthesized by melt-intercalation using either PP-g-MA or PE-g-MA as a compatibilizer. The pristine clay was first modified with a swelling agent (octadecylamine) in solution to obtain an organophilic clay before being melt blended with a compatibilizer: PP-g-MA or PE-g-MA. Finally, these compounds were melt intercalated with PE to synthesis the PE/clay nanocomposite. The materials were characterized using X-RD, TEM, SEM, and TGA. The physical properties were observed with DMA and tension tests. Permeability tests of the PE/clay nanocomposites were also performed. The clays in PE/clay nanocomposites with the compatibilizer PP-g-MA were better exfoliated. The mechanical and gas barrier properties improved as the clay content increased.