Orientation Of Clay Platelets Research Articles

Shale anisotropic rock-physics model incorporating the effect of compaction and nonplate mixtures on clay preferred orientation

Compared with other sedimentary rocks, the strong elastic anisotropy of shale is extremely prominent, which is mainly caused by the preferred orientation and platy nature of its clay minerals. Especially in seismic reservoir characterization, a suitable and correct estimation of the shale elastic anisotropy can improve the accuracy of the shale seismic inversion and prediction. Due to the long-term compaction of shale and the rearrangement of minerals, its microstructure and macrostructure are more complex, resulting in obvious anisotropic characteristics of shale. Existing methods do not incorporate the impact of nonplate particles on clay platelets, or indirectly incorporate it through empirical formulas, resulting in poor applicability and errors in the rock-physics models. To reveal the main causes of the anisotropy of clay minerals, a theoretical model incorporating the effect of compaction and nonplate particles on the preferred orientation of clay platelets is developed using experimental data and electronic scanning results. Based on theoretical analysis, an orientation distribution function (ODF) based on the effect of compaction and nonplate particles is derived, which not only incorporates the influence of compaction but also further incorporates the effect of other nonplate particles, such as quartz, which makes the established shale anisotropic rock-physics model more reasonable and accurate. Then, an improved anisotropic shale rock-physics model is developed using the compaction and nonplate particles-based ODF. The prediction results indicate that the presence of nonplate particles has an inhibitory effect on the preferred orientation of clay platelets, which is verified by the measured experimental data and indicates that our method is reliable and effective.

Clay platelet orientation inside self-standing beidellite clay films: Effect of silica nanospheres and link with macroscopic mechanical resistance

Clay minerals and silica are essential components of soil. Understanding the multi-scale structure of a simple model system formed of (negatively charged) beidellite clay nanoplatelets and silica nanospheres is a first step in understanding the complex structure of soil. Due to their strong shape anisotropy, clay nanoplatelets exhibit preferential orientation at the microscopic level, both in aqueous dispersions and in dry deposits. Adding spherical colloids into the system changes the clay platelet organization. These changes are studied here for the case of self-standing clay films, using a small angle X-ray scattering (SAXS) beamline, equipped with a goniometer and a rotating device. We investigated orientation of clay nanoplatelets as a function of the nanoplatelet and nanosphere sizes, their surface charge and sphere/platelet number ratio. Two methodologies are developed to calculate the nanoplatelet order parameter 〈P2〉: (a) background contribution is subtracted from the azimuthal profile curve at a given wavevector q and (b) isotropic contribution is subtracted directly at the level of the 2D SAXS images. Smaller clay nanoplatelets (∼200 nm in lateral size) exhibit a better orientation than larger platelets (> ∼300 nm). Adding small positively and negatively charged nanospheres (diameter ∼ 30 nm) destroys the high degree of orientation of small clay platelets. Large spheres (diameter similar to the nanoplatelet size, ∼300 nm) destroy orientation for both types of clay platelets. A simple tensile strength setup allows to measure the breaking stress of the self-standing films to make the link between microscopic and macroscopic structure. Films of small clay platelets without spheres were mechanically the most resistant. Films with added positively charged spheres were stiffer than films with negatively charged spheres. The methodology presented here opens perspectives for the study of structure and mechanical response of clay deposits.

Micromechanics-based rock-physics model for inorganic shale

The full set of transversely isotropic elastic stiffness constants of inorganic shale (mudrock with total organic carbon less than 1.5%) can be successfully modeled and, therefore, predicted based on the mineral composition, mineral stiffnesses, clay platelet orientation distribution function, and microgeometry of the pore space. A fundamentally novel concept drawing from the Maxwell homogenization scheme allows a zero-porosity mineral matrix of the mudrock to be expressed as a polycrystal of variable composition and clay mineral alignment. Introduction of the brine-saturated pore space allows us to account for realistic 3D pore types and their combinations as well as elastic interactions, opening the way for better integration of rock physics and geomechanics with modern petrographic investigations and better shale velocity/anisotropy prediction as a function of diagenetic porosity reduction. We were able to calibrate the model using a limited subset of high-quality ultrasonic measurements on shale and constrain main pore geometries such as tetrahedra and irregular spheroids, often reported in modern scanning electron microscopy images. The model is then used to constrain the anisotropy tensor elements of illite-dominated clay, impossible to measure directly, and explore the main compositional and microstructural controls on the anisotropic elasticity of inorganic shale, including the most troublesome [Formula: see text] stiffness and its derivative — the anisotropy parameter [Formula: see text], which is of paramount importance in quantitative seismic interpretation.

Elastic Anisotropy Modeling of Organic-Rich Lower Gondwana Shale in Eastern India

Analysis of cores from the Lower Gondwana basin in eastern India confirms the presence of abundant organic matter, indicating a high shale gas prospective zone. Shale is intrinsically (transversely) anisotropic due to the preferential orientation of anisotropic clay platelets depending on the geological processes of deposition. Such anisotropy needs to be incorporated in modeling for an accurate explanation of observed seismic anisotropy in shale. Combined anisotropic formulations of self-consistent approximation (SCA) and differential effective medium (DEM) theory is the most suitable among existing theories to deal with the complex microstructure of shale. We start by predicting the bulk and rigidity moduli of clay mineral aggregates as 21 GPa and 10 GPa from our model, which are difficult to measure in the laboratory due to the small crystal size of clay. A concept of host medium (HM) is presented here, which is constituted of clay mineral aggregates, kerogen, and unconnected pores. Other minerals are added in the biconnected composite constituted of HM and connected pores filled with water. An orientation distribution function (ODF) of clay particles is determined using the combined SCA-DEM theory from the observed ultrasonic velocity measurements. Our model shows strong intrinsic anisotropy at the shallow depth that decreases with depth because of the changes in the microstructure of the shale. The P-velocity predicted from our model, widely used Biot–Gassmann theory (BGT) and Biot–Gassmann theory modified by Lee (BGTL) match well with the measured data where P-wave anisotropy is insignificant. We also predict from our model the volume of kerogen and total organic carbon as 26–43% and 6–8%, respectively.

Anisotropic phase-separated morphology of polymer blends directed by electrically pre-oriented clay platelets.

We describe a general pathway to prepare an anisotropic phase-separated polystyrene (PS) - poly(vinyl methyl ether) (PVME) blend morphology by using electrically pre-orientated clay platelets. The clay platelets were oriented in a PS/PVME blend by means of an externally applied AC electric field while the blend is in one phase. Following orientation step, phase separation of the blends was induced by a temperature jump above their lower critical solution temperature (LCST) in the presence of the oriented clay platelets. In this process, an early stage co-continuous PS/PVME morphology coarsened and turned anisotropic phase-separated morphology parallel to the direction defined by clay planes oriented by AC electric field. The degree of anisotropy of PS/PVME phase-separated morphology was characterized by image analysis and that was found to be linearly proportional to the degree of orientation of clay platelets obtained by a 2D Wide Angle X-ray Scattering (WAXS). Transmission Electron Microscope (TEM) image of the blend morphology revealed that clay platelets oriented to AC field direction were located in a PVME phase. The electrically ordered column structures of clay platelets in the PVME phase yielded anisotropic PS diffusion during the phase separation. This process provides a unique new way to develop directionally organized phase-separated morphology from partially miscible binary blends using nanoparticles in combination with an external electric field.

A general orientation distribution function for clay-rich media

The role of the preferential orientation of clay platelets on the properties of a wide range of natural and engineered clay-rich media is well established. However, a reference function for describing the orientation of clay platelets in these different materials is still lacking. Here, we conducted a systematic study on a large panel of laboratory-made samples, including different clay types or preparation methods. By analyzing the orientation distribution functions obtained by X-ray scattering, we identified a unique signature for the preferred orientation of clay platelets and determined an associated reference orientation function using the maximum-entropy method. This new orientation distribution function is validated for a large set of engineered clay materials and for representative natural clay-rich rocks. This reference function has many potential applications where consideration of preferred orientation is required, including better long-term prediction of water and solute transfer or improved designs for new generations of innovative materials.

Porosity‐Permeability Relationships in Mudstone from Pore‐Scale Fluid Flow Simulations using the Lattice Boltzmann Method

AbstractWe model mudstone permeability during consolidation and grain rotation, and during fluid injection by simulating porous media flow using the lattice Boltzmann method. We define the mudstone structure using clay platelet thickness, aspect ratio, orientation, and pore widths. Over the representative range of clay platelet lengths (0.1–3 μm), aspect ratios (length/thickness = 20–50), and porosities (ϕ = 0.07–0.80) our permeability results match mudstone datasets well. Homogenous kaolinite and smectite models document a log linear decline in vertical permeability from 8.31 × 10−15–6.84 × 10−17 m2 at ϕ = 0.76–0.80 to 6.33 × 10−19–1.30 × 10−23 m2 at ϕ = 0.14–0.16, showing good correlation with experimental data (R2 = 0.42 and 0.56).We employ our methodology to predict the permeability of two natural mudstone samples composed of smectite, illite, and chlorite grains. Over ϕ = 0.32–0.58, the permeability trends of two models replicating the mineralogical composition of the natural mudstone samples match experimental datasets well (R2 = 0.78 and 0.74). We extend our methodology to evaluate how vertical permeability might evolve during microfracture network growth or macrofracture propagation upon fluid injection in compacted mudstone. Fluid injection results in a permeability increase from 1.02 × 10−20 m2 at ϕ = 0.07 to 2.07 × 10−16 m2 at ϕ = 0.29 for growth of a microfracture network, and from 1.02 × 10−20 m2 at ϕ = 0.07 to 1.23 × 10−16 m2 at ϕ = 0.32 for macrofracture propagation. Our results suggest that a distributed microfracture network results in greater permeability during fluid injection in compacted mudstones (ϕ = 0.07–0.32) in comparison to a wide macrofracture. Our modeling approach provides a simple means to estimate permeability during burial and compaction or fluid injection based on knowledge of porosity and mineralogy.

Tuning the mechanical and dielectric properties of clay‐containing thermoplastic elastomer nanocomposites

In this study, the mechanical strength and the AC short term breakdown strength of polystyrene‐b‐poly(ethylene‐co‐butylene)‐b‐polystyrene (SEBS) thermoplastic elastomer clay‐containing nanocomposites have been investigated as function of their morphologies. The SEBS/clay nanocomposites with tailored morphologies were prepared previously by different processing techniques. They featured different orientations of clay platelets as well as polystyrene (PS) block nanodomains, namely: isotropic, oriented, and partially oriented morphologies. In unfilled SEBS matrices, the mechanical strength was mainly tuned by the orientation of PS block nanodomains. A good correlation between the dielectric breakdown strength and the mechanical stiffness was observed overall: the higher the mechanical strength was, the higher the breakdown strength was. In the nanocomposites, the orientation of clay platelets as well as the degree of order and the characteristic sizes of the block copolymer domains were seen to affect strongly the breakdown strength behavior in addition to the mechanical strength. In particular, the partially oriented morphology achieved by film blowing extrusion exhibited the maximum increase of the breakdown strength by 25% with optimized mechanical stiffness evaluated between that of the oriented morphology as a lower limit and that of the isotropic morphology as an upper limit. POLYM. ENG. SCI., 58:E174–E181, 2018. © 2018 Society of Plastics Engineers

Understanding anisotropic mechanical properties of shales at different length scales: In situ micropillar compression combined with finite element calculations

AbstractFrom microstructural observations and experimental work it is known that shales consist of a mechanically weak porous fine‐grained clay matrix with embedded and mechanically strong silt/sand grains. Thereby, the respective contents of weak and strong constituents control bulk mechanical properties. In addition, the clay matrix is characterized by a preferred orientation of clay platelets, which are a major control on the bulk anisotropy of shales. To date, little is known about the micromechanical properties of the fine‐grained porous clay matrix, which is particularly true in case of its micromechanical anisotropy. Such information can, however, only be assessed on the microscale. Therefore, the drained micromechanical properties parallel and perpendicular to bedding were investigated by means of compressing micropillars with a flat punch indenter in a scanning electron microscope. Microscopic failure mechanism was found to be anisotropic: (i) in case loading was parallel to bedding it occurred by a combination of localized shearing, kinking/buckling of elongated clay aggregates, and bedding parallel splitting and (ii) for loading perpendicular to bedding failure occurred mainly by localized shearing. The measured stiffness of the drained porous clay matrix perpendicular (Ev) and parallel (Eh) to bedding was about 8 GPa and 30 GPa, respectively. Using these stiffness values as input in voxel‐based finite element modeling and in combination with realistic microstructures, which are characterized with different contents of “soft” and “hard” constituents, revealed that the measured high microscale anisotropy Eh/Ev = 3.75 is crucial in understanding the bulk anisotropy of clay rocks.

Uniaxial and plane orientations of clay platelets in nanocomposite gels with different compositions during stretching and recovery

Changes in the birefringence (ΔnNC) of nanocomposite (NC) gels upon stretching and recovery were investigated for gels comprising a poly(N-isopropylacrylamide)−clay network structure. Irrespective of the composition of the NC gels, a change in the birefringence appeared upon stretching; ΔnNC varied greatly depending on the clay and water contents (Cclay and Cw, respectively) of the gels and the stretching ratio. The NC gels with low Cclay gave rise to unique ΔnNC vs. strain curves with a maximum ΔnNC. For samples with higher Cclay, the variation of ΔnNCs observed in the edge- and through-directions, which is attributed to plane-orientation of the clay platelets, increased with increasing Cclay. This was confirmed by scanning electron microscopy observation, and the percentage plane-orientation was evaluated from the ΔnNC data. On recovery of the strain, the plane-oriented clay platelets underwent minimal reversion to the original state, although most of the PNIPA chains reverted to the random conformation. The effects of Cw on the ΔnNC–strain curves were also clarified.

Compaction of quartz-kaolinite mixtures: The influence of the pore fluid composition on the development of their microstructure and elastic anisotropy

Shales play important roles in sedimentary basins, acting as both seals and reservoir rocks, and knowledge of their anisotropic velocity trends is of practical importance for correct seismic image processing and inversion, and for seismic to well tie. Whereas velocity-depth trends are extensively studied for conventional reservoirs and critical factors that control their compaction are well understood, little work has been done on shales. Compaction trends of shaly formations are controlled by a number of parameters such as clay mineralogy, silt fraction and depositional environment. This large number of parameters, which are difficult if not impossible to control in naturally deposited shales, make the study of shale compaction a statistically complex, multivariate and non-unique problem. In such a situation, laboratory experiments that allow precise planning of mixture mineralogy and chemical compositions of pore fluids as well as an accurate control of microstructural changes seems to be an attractive alternative.In this work, we have conducted two sets of compaction experiments on quartz-kaolinite mixtures with 100%, 75% and 60% of kaolinite powders (dry weight). In the first set, the use of a KCl brine solution to saturate the mixtures has led to the aggregation of the existing clay particles with each other and with silt particles. In the other set, the mixtures have been treated with a dispersant to separate existing clay aggregates into individual platelets. The mixtures have been further compacted in an oedometric cell at uniaxial stresses up to 30 MPa. Compressional (in vertical and horizontal directions) and shear (in vertical direction) ultrasonic wave velocities have been measured during these compaction experiments and the P-wave anisotropy has been estimated. The effect of the chemical composition of the pore fluid on shale microstructure has been studied using the micro-CT and SEM image analysis. Neutron diffraction experiments have been conducted to understand the orientation of clay platelets at the final stage of the compaction.Our research shows that the chemical composition of pore fluid significantly affects the microstructure of the clay component and via this the elastic properties of the artificial shales. The samples with the dispersed clay microstructure (DCM) have shown larger elastic anisotropies at the same porosity and significantly larger anisotropies at the same stress. The dispersed clay platelets have orientated preferably parallel to bedding plane while the clay platelets in the samples with the aggregated clay microstructure (ACM) show a wider angle distribution in the absence of quartz particles (100% kaolinite samples). In the case of 40% of quartz fraction though, the clay particles are more aligned in the ACM sample than in the DCM one.

Structural iron in dioctahedral and trioctahedral smectites: a polarized XAS study

The chemical form of structural Fe in smectites influences many physicochemical properties of these clay minerals. Powder EXAFS data for structural Fe in smectites have been reported; however, the preferred orientation of clay platelets with respect to the X-ray beam may lead to erroneous conclusions on the local chemical environment. Dioctahedral montmorillonite and for the first time trioctahedral hectorite were prepared as textured samples, and the Fe local environment was probed by analysis of the X-ray absorption pre-edge peaks at the magic angle and by polarized EXAFS (P-EXAFS) spectroscopy. Compared to powder measurements, overlapping contributions from shells with distinct orientations can be filtered more easily by P-EXAFS, thus decreasing uncertainties on structural parameters. The pre-edge spectrum of montmorillonite is similar to spectra commonly reported for dioctahedral smectites. In contrast, the pre-edge spectrum of hectorite is notably distinct and hints to either differences in the site symmetry and/or in covalence. In both smectites, Fe is surrounded by a first O shell at a distance consistent with sixfold-coordinated Fe(III), suggesting that Fe(III) is located in the smectite octahedral sheet. This is corroborated by the distances and orientations of neighboring cationic shells, such as in-plane (Mg, Al) and out-of-plane Si shells. For montmorillonite, the results indicate Fe substitution for Al/Mg in the octahedral sheet, and a number of Fe neighbors consistent with random distribution in the octahedral sheet. For hectorite, results indicate a slight tendency for Fe atoms to form pairs in octahedral sheets; however, low numbers of neighboring cations were obtained, presumably a consequence of the presence of vacancies and/or Li in the vicinity of Fe, or of the coexistence of Fe and Mg neighbors with mutually canceling EXAFS waves. Consistent with pre-edge data, the coordination numbers can also indicate some incoherency in Fe-cation interatomic distances in hectorite as a consequence of site distortion. These results suggest that Fe3+ in hectorite locally distorts the structure of the trioctahedral phyllosilicate and tends to aggregate charge-deficient (i.e., vacant or Li+-containing) octahedral sites.

Impact of sand content on solute diffusion in Opalinus Clay

The mesostructure (micro to millimeter scale) of clay rocks was considered as a two-component mixture consisting of impermeable non-clayey sand grains embedded in a permeable clay matrix. Provided that representative diffusion properties can be defined, the clay matrix can be treated as a continuum. Under these conditions diffusion at larger scales will depend on geometric properties of the mesostructure. The objective of this study, then, is to analyze geometric parameters, which control diffusion at larger scales. In a first step a set of different clay matrix mesostructures were reconstructed on the base of synchotron X-ray computed microtomography applied to clay rock samples from northern Switzerland (e.g. Opalinus Clay). In a second step mesostructural effects on diffusion were quantified by applying diffusion simulations to reconstructed mesostructures. Further analysis revealed that constrictivity is the most dominant parameter, which controls diffusion on the millimeter scale in Opalinus Clay. Regarding diffusion, the mesostructure of the clay matrix is near isotropic. Hence, the reason for anisotropic diffusion in Opalinus Clay must be searched on the nanometer to micrometer scale and it is caused by anisotropic pore path tortuosity related to shape preferred orientation of clay platelets.

Dissipative properties and chain evolution of highly strained nanocomposite hydrogel

The dissipative property is crucial to the toughness and recovery of hydrogels. In our investigation, systematic uniaxial tension tests were conducted to evaluate the dissipative properties of poly (N-isopropylacrylamide) nanocomposite hydrogels. Two dissipative mechanisms are presented for both small and large stretches. Before yielding, most dissipation results from the orientation of clay platelets along the tensile direction; after yielding, polymer chains peel off from clay platelets to induce hysteresis. For the first time, a quadratic power law between the hysteresis work and the maximum stretch is obtained. The hysteresis work is irrelevant to the detailed loading history. When the hydrogel is unloaded to a critical displacement, polymer chains can re-adsorb to the surfaces of clay platelets. The quantity of re-ruptured physical bonds is proportional to the product of re-adsorption ratio and that of initially ruptured bonds. These results may be useful for the toughening design of hydrogels.

Molecular adhesion at clay nanocomposite interfaces depends on counterion hydration-molecular dynamics simulation of montmorillonite/xyloglucan.

Nacre-mimetic clay/polymer nanocomposites with clay platelet orientation parallel to the film surface show interesting gas barrier and mechanical properties. In moist conditions, interfacial adhesion is lowered and mechanical properties are reduced. Molecular dynamic simulations (MD) have been performed to investigate the effects of counterions on molecular adhesion at montmorillonite clay (Mnt)-xyloglucan (XG) interfaces. We focus on the role of monovalent cations K(+), Na(+), and Li(+) and the divalent cation Ca(2+) for mediating and stabilizing the Mnt/XG complex formation. The conformation of adsorbed XG is strongly influenced by the choice of counterion and so is the simulated work of adhesion. Free energy profiles that are used to estimate molecular adhesion show stronger interaction between XG and clay in the monovalent cation system than in divalent cation system, following a decreasing order of K-Mnt, Na-Mnt, Li-Mnt, and Ca-Mnt. The Mnt clay hydrates differently in the presence of different counterions, leading to a chemical potential of water that is highest in the case of K-Mnt, followed by Na-Mnt and Li-Mnt, and lowest in the case of Ca-Mnt. This means that water is most easily displaced from the interface in the case of K-Mnt, which contributes to the relatively high work of adhesion. In all systems, the penalty of replacing polymer with water at the interface gives a positive contribution to the work of adhesion of between 19 and 35%. Our work confirms the important role of counterions in mediating the adsorption of biopolymer XG to Mnt clays and predicts potassium or sodium as the best choice of counterions for a Mnt-based biocomposite design.

Characterization of clay platelet orientation in polylactide–montmorillonite nanocomposite films by X-ray pole figures

The film samples of polylactide/montmorillonite (PLA/MMT) nanocomposite were formed by compression molding, film extrusion or melt blowing. The orientation of the single-layer platelets of fully exfoliated MMT was probed in these films with X-ray diffraction utilizing analysis of 2-D WAXS patterns and the pole figure technique. The reflections of the (020) and (210) crystallographic planes of MMT, both perpendicular to the plane of the platelet, were studied.It was found that the texture of MMT created upon processing is the (100) planar texture, i.e. with MMT platelets oriented preferentially parallel to the film plane. That texture becomes significantly stronger and sharper with increasing shear deformation, according to the following order: compression molding→extrusion→blow molding. At the blow ratio of 7 the maximum of MMT orientation distribution reaches value of 8m.r.d. and the estimated Hermans orientation factor of the platelet normal with respect to the film normal, is very high, f001=0.96.The results obtained by X-ray pole figure technique were verified positively by direct TEM observations.

A combined experimental and theoretical approach to establish the relationship between shear force and clay platelet delamination in melt-processed polypropylene nanocomposites

In this article, a combined experimental and theoretical approach has been proposed to establish a relationship between the required shear force and the degree of delamination of clay tactoids during the melt-processing of polymer nanocomposites. Polypropylene (PP) was selected as a model polymer, and nanocomposites of PP with organically modified clay were prepared by a master batch dilution technique in a twin-screw extruder. The effect of PP throughput during the dilution of the master batch on the dispersion and orientation of clay platelets were studied in detail. Powder X-ray diffraction, small and wide angle X-ray scattering and high resolution transmission electron microscopy were used to study the structure and morphology of the obtained nanocomposites. The results showed that a lower feeding rate led to the orientation of clay platelets almost in the direction of extrusion. The adhesive force and the interaction energy between the clay platelets were theoretically calculated using the Hamaker approach. The analysis showed that the peeling mechanism is a practical explanation for the delamination of clay platelets during melt extrusion and that the dimensions of the clay platelet tactoids play an important role in the peeling due to the shear stress.

Structure and properties of polypropylene-nanoclay composites

The structure, morphology and mechanical properties of polypropylene-nanoclay composites containing 1 to15 wt.% nanoclay was investigated. Combination of wide-angle x-ray diffraction (WAXD) and transmission electron microscopy (TEM) was used to determine nanocomposite morphology. Mixture of intercalated and exfoliated morphology was observed for all the samples. Samples with 1 to 5 wt.% clay showed shear induced orientation of clay platelets in the surface region of the molded bars. Glass transition temperature slightly decreased due to the plasticizing effect of additives. At higher weight percentage reinforcement (10–15 wt.%), up to 67 % improvement in tensile modulus is observed. Breaking energy was significantly improved for samples with up to 2 wt.% nanoclay additives. With further increase in nanoclay weight percentage, failure mode shifted from ductile to brittle. Increase in exclusion of clay additives at the boundary of spherulites and segregation of clay platelets were observed for samples with higher weight percentage of clay additives.

Orientation Effect of Clay Platelets in Transfer Molded Polymer Nanocomposites

Transfer molding has been increasingly used to process polymer composites with various shaped nanoparticles, including platelet type nanoparticles. Platelet nanoparticles exhibit high aspect ratios (length to thickness); therefore their distributions in polymer matrix can be greatly affected by the flow trajectories in the mold. In present study, the clay platelet-polyethylene nanocomposite was prepared by transfer molding. The orientation of clay platelets developed during molding process was analyzed and measured with wide angle X-ray diffraction. Due to large velocity and shear stress gradients in the mold, the platelets caught in surface regions were rotated towards the flow direction and formed the oriented morphologies. With weaker shear stresses at the central region, the platelets were mostly randomly distributed. The shear stresses may be amplified locally at regions near the mold walls, which can further lead to or accelerate the orientations of clay particles. The orientation distribution was found to depend upon the clay fraction and sample size. The oriented platelets can be re-randomized through the annealing process. The orientation of clay platelets enhanced the orientation of polyethylene lamellae and caused shear band formation in composites when deformed.

Bioinspired and Highly Oriented Clay Nanocomposites with a Xyloglucan Biopolymer Matrix: Extending the Range of Mechanical and Barrier Properties

The development of clay bionanocomposites requires processing routes with nanostructural control. Moreover, moisture durability is a concern with water-soluble biopolymers. Here, oriented bionanocomposite coatings with strong in-plane orientation of clay platelets are for the first time prepared by continuous water-based processing. Montmorillonite (MTM) and a "new" unmodified biological polymer (xyloglucan (XG)) are combined. The resulting nanocomposites are characterized by FE-SEM, TEM, and XRD. XG adsorption on MTM is measured by quartz crystal microbalance analysis. Mechanical and gas barrier properties are measured, also at high relative humidity. The reinforcement effects are modeled. XG dimensions in composites are estimated using atomistic simulations. The nanostructure shows highly oriented and intercalated clay platelets. The reinforcement efficiency and effects on barrier properties are remarkable and are likely to be due to highly oriented and well-dispersed MTM and strong XG-MTM interactions. Properties are well preserved in humid conditions and the reasons for this are discussed.