Synthesis and Rheology of Intercalated Polystyrene/Na+‐Montmorillonite Nanocomposites

Polystyrene (PS)/clay nanocomposites were synthesized by the emulsion polymerization of styrene in the presence of sodium ion‐exchanged montmorillonite (Na⁺‐MMT), demonstrating that the strongly hydrophobic PS was intercalated into the hydrophilic silicate layers. The nanocomposites were examined by means of X‐ray diffraction, transmission electron microscopy, thermogravimetric analysis. The rheological properties of the PS/Na⁺‐MMT nanocomposites were also studied to exhibit more pronounced shear thinning behavior with increasing clay content.     

Molecular Dynamics Simulation of the Fracture in Polymer‐Exfoliated Layered Silicate Nanocomposites

Summary: The MD technique was used to investigate the fracture behavior in fully exfoliated layered silicate (nanoplatelet)‐polymer nanocomposites. MD results reveal that the addition of the nanoplatelets can improve the fracture strength of polymers. The interactions between the surface of the nanoplatelets and the segments of the polymer, and the relaxation time of polymer chains have significant influences on the fracture strength of the polymer. For polymers with T_g below room temperature, such as polyurethane, or close to room temperature, such as nylon, the nanoplatelets are always working for the enhancement of the mechanical properties. However, for polymers with T_g above room temperature, such as epoxy and polystyrene, the addition of the nanoplatelets is not working well for toughening these polymers. If the nanoplatelets are to enhance the mechanical properties of these polymers, it is necessary to build up a stress relaxation interface between the polymer and the nanoplatelet in order to reduce the effect of the difference between the relaxation time of nanofillers and that of polymers.

Force per area versus distance curves as a function of the difference of the relaxation times of the nanoplatelets and polymer chains.     

Isotactic Poly(propylene)/Monoalkylimidazolium‐Modified Montmorillonite Nanocomposites: Preparation by Intercalative Polymerization and Thermal Stability Study

Summary: Poly(propylene)/monoalkylimidazolium‐modified montmorillonite (PP/IMMT) nanocomposites were prepared by in situ intercalative polymerization of propylene with TiCl₄/MgCl₂/MMT catalyst. The PP synthesized possessed high isotacticity and molecular weight. Both wide‐angle X‐ray diffraction (XRD) and transmission electron microscopy (TEM) examinations evidenced the nanocomposite formation with exfoliated MMT homogeneously distributed in the PP matrix. A thermal stability study revealed that the nanocomposites possess good thermal stability.

X‐ray diffraction patterns of PP/IMMT (MMT = 2.2 wt.‐%) nanocomposite before and after processing.     

Exfoliated Polylactide/Clay Nanocomposites by In‐Situ Coordination–Insertion Polymerization

Poly(L ‐lactide)/layered aluminosilicate nanocomposites were synthesized in bulk by ring‐opening polymerization in the presence of two organo‐modified montmorillonites. When the organo‐modifier consisted of an ammonium cation bearing primary hydroxyl groups, polymerization was initiated by the alcohol functions after adequate activation. The growing polymer chains were directly “grafted” onto the clay surface through the hydroxyl‐functionalized ammonium cations yielding exfoliated nanocomposites with enhanced thermal stability.

TEM image of a fully exfoliated Cloisite®30B‐based nanocomposite, showing delamination of the silicate layers.     

聚氨酯基层状硅酸盐纳米复合物研究进展

具有优良综合性能的聚合物基层状硅酸盐纳米复合物是当前材料科学研究的重要方向。本文介绍了以聚氨酯材料为基质的聚合物基层状硅酸盐纳米复合物的制备技术、表征手段、物理化学性能以及结构形态,对该复合材料的工业开发前景、国内外研究现状以及发展趋势进行了分析。     

Polymer Layered Silicate/Carbon Nanotube Nanocomposites: Morphological and Rheological Properties

Morphological and rheological properties of new ternary nanocomposites based on ethylene vinyl acetate copolymers (EVA), commercial organo-modified clays (organoclays) and purified multi-walled carbon nanotubes (MWNTs), prepared via direct melt blending, have been evaluated. For sake of comparison, the corresponding binary compositions, i.e., EVA filled with either organoclays or MWNTs, have been investigated as well. While extensive exfoliation can be observed for binary EVA/clay nanocomposites, the addition of MWNTs appears to limit clay exfoliation. Rheological properties show that both clay and MWNTs increase the elastic modulus of the nanocomposites, reflecting the high degree of nanoparticle interconnectivity that can be found in these materials.     

The Rapid Exfoliation and Subsequent Restacking of Layered Titanates Driven by an Acid–Base Reaction

Two‐dimensional (2D) (hydro)oxide materials, that is, nanosheets, enable the preparation of advanced 2D materials and devices. The general synthesis route of nanosheets involves exfoliating layered metal (hydro)oxide crystals. This exfoliation process is considered to be time‐consuming, hindering their industrial‐scale production. Based on in situ exfoliation studies on the protonated layered titanate H_1.07Ti_1.73O₄?H₂O (HTO), it is now shown that ion intercalation‐assisted exfoliation driven by chemical reaction provides a viable and fast route to isolated nanosheets. Contrary to the general expectation, data indicate that direct exfoliation of HTO occurs within seconds after mixing of the reactants, instead of proceeding via a swollen state as previously thought. These findings reveal that ion intercalation‐assisted exfoliation driven by chemical reaction is a promising exfoliation route for large‐scale synthesis.     

Polyethylene/Clay Nanocomposite by In‐Situ Exfoliation of Montmorillonite During Ziegler‐Natta Polymerization of Ethylene

Complete exfoliation of montmorillonite during Ti‐based Ziegler‐Natta polymerization of ethylene has been successfully carried out by using montmorillonite (MMT‐OH) modified with intercalation agents containing hydroxyl groups. Hydroxyl groups in intercalation agents offer facile reactive sites for anchoring catalysts in between silicate layers. Comparison of exfoliation characteristics between MMT‐OH and non‐intercalated montmorillonite showed that the feasibility of exfoliation during ethylene polymerization was highly dependent on the catalyst fixation method.     

Synthesis and Characterization of Conductive Polypyrrole/Montmorillonite Nanocomposites via One-pot Emulsion Polymerization

A series of electrically conductive polypyrrole/clay nanocomposites were synthesized in this work by using one-pot emulsion oxidative polymerization of pyrrole in the presence of unmodified clay and using DBSNa as the surfactant. The effect of surfactant on the morphological and electrical properties of PPy also were investigated and discussed in some extent. Electrical conductivity of the samples was measured by using samples in which the conductive materials was sandwiched between two Ni electrodes at room temperature. PPy/MMT nanocomposites were characterized by using XRD, TEM, TGA and DSC means of investigation. Intercalated structures were determined for the nanocomposites as confirmed by XRD and TEM studies. Electrical conductivity of the nanocomposites was measured to be dependent to the clay content, and the methods of preparation. Measurement also showed that polymerization of pyrrole monomers pre-intercalated between the clay gallery spaces of the clay led to higher conductivity for the nanocomposite in the same level of clay content. Thermal property measurements showed a lower thermal decomposition rate for the PPy/MMT nanocomposites with respect to the PPy.     

FTIR法研究乙酸酚醛酯固化邻甲酚环氧树脂的反应动力学

用ＦＴＩＲ原位测量技术研究了乙酸酚醛酯与邻甲酚环氧树脂在２－甲基咪唑存在下进行恒温固化反应的动力学，测定了固化反应的动力学参数，研究结果表明，固化反应是按照一级固化反应动力学进行的，根据羰基峰在固化反应前后的变化对固化反尖机理进行了初步探讨。     

Single‐Step Exfoliation and Covalent Functionalization of MoS2 Nanosheets by an Organosulfur Reaction

A simple approach to exfoliate and functionalize MoS₂ in a single‐step is described, which combines the dispersion of MoS₂ in polybutadiene solution and ultrasonication processes. The great advantage of this process is that a colloidal stability of MoS₂ in nonpolar solvent is achieved by chemically bonding polybutadiene on the perimeter edge sites of MoS₂ sheets. In addition, elastomeric nanocomposite has been prepared with singular mechanical properties using functionalized MoS₂ as nanofiller in a polybutadiene matrix with a subsequent vulcanization reaction.     

Morphology and Linear Viscoelasticity of Poly[ethylene‐co‐(1‐octene)]/Layered Silicate Nanocomposites

Poly[ethylene‐co‐(1‐octene)] nanocomposites with different microstructures were prepared with two kinds of organoclay by melt intercalation. X‐ray diffraction and transmission electron microscopy were used to characterize the morphology of the composites. Linear storage moduli of the composites in the melt state were found to increase greatly with increasing the extent of dispersion of silicate layers and showed an obvious sensitivity to the morphologies of the composites.     

A New Strategy to Exfoliate Silicone Rubber/Clay Nanocomposites

Summary: A new strategy was developed to prepare disorderly exfoliated nanocomposites, in which a soft siloxane surfactant with a weight‐average molecular weight ( ) of 1 900 was adopted to modify the clay. The modified clay slurry was then mixed with silicone rubber by hand, and exfoliation was achieved. The proposed mechanism thereof was verified by TEM and XRD. The physical entanglement of the soft siloxane surfactant plays a vital role in the diffusion and intercalation of the matrix molecules during the compounding of the slurry‐polymer mixture. This simple method is applicable to other silicone‐based materials reinforced by clay.

TEM micrograph of silicone rubber/clay‐sil nanocomposite.     

Poly(propylene)/PET/Undecyl Ammonium Montmorillonite Nanocomposites. Synthesis and Characterization

A natural bentonite rich in calcium montmorillonite (CaMMT) was initially purified and ion-exchanged to obtain sodium montmorillonite (NaMMT). Both clays were organophillised by cationic exchange reaction with undecyl-ammonium chloride, and characterized. Isotactic poly(propylene) (PP) was melt-compounded with both the unmodified and the organophilic montmorillonites. The hybrids produced have been characterized structurally, thermally and mechanically. Maleic anhydride-grafted PP (MAH-g-PP) was used as compatibilizer in some of the formulations. Homologous series of hybrids were also synthesized employing blends of PP/PET and compared with those of the pure PP to investigate possible beneficial effects due to the presence of small amounts of PET on the microstructure and properties of this kind of materials. The analysis of the results indicates some extension of both macromolecules intercalation and clay particles exfoliation in the hybrids prepared with the organophilic montmorillonite. The hybrids prepared with compatibilized PET/PP blends were found to have a better nanostructure.     

The Aspect Ratio and Gas Permeation in Polymer‐Layered Silicate Nanocomposites

Summary: Organophilized montmorillonite‐epoxy and ‐polyurethane nanocomposites, useful for packaging applications, were prepared and their oxygen permeability was measured. The composite morphology was mixed, exfoliated and intercalated, as shown by wide‐angle X‐ray diffraction (WAXRD) and transmission electron microscopy (TEM). The gas‐barrier performance of the polyurethane composites was better than that of the epoxy composites due to more exfoliation. The average aspect ratio of the montmorillonite platelets in the nanocomposites could be estimated from the reduction in permeability by a numerical finite element approach.

A computer model comprising 50 randomly distributed and oriented round platelets with an aspect ratio of 50 at 3 vol.‐% loading, periodic boundary conditions applied.     

TPEV/Layered Silicate Nanocomposites with Dynamic Vulcanizing Process

Thermoplastic Elastomer Vulcanizates (TPEV) prepared by dynamic vulcanizing process, is a material which has both the properties of a vulcanized rubber (elasticity) and thermoplastics (processibility). TPEV is cost effective for its good processibility and eco-friendly for its recyclability. TPEV/layered silicate nanocomposites can give a greater advantage of weight reduction which is a key issue in automotive industry because of fuel efficiency. Applying TPEV/layered silicate nanocomposites, the amount of reinforcement mineral filler can be reduced greatly compared to general TPEV which is reinforced by talc or kaolin clay. The mechanical strengths of TPEV/layered silicate nanocomposites using small amounts of MMT is similar to those of general TPEV using larger amounts of general filler. Various evaluations such as degree of crosslinking, degree of filler dispersion (XRD and TEM), surface hardness and tensile properties were carried out for the TPEV/layered silicate nanocomposites.     

Morphology and Thermal Characteristics of Polyethylene Nanocomposites Made Using Montmorillonite‐Supported Cp2ZrCl2 and Ni‐Diimine Precatalysts

Bis(cyclopentadienyl)‐zirconium dichloride (Cp₂ZrCl₂) and (1,4‐bis(2,6‐diisopropylphenyl)‐acenaphthenediimine) dichloronickel (Ni‐diimine) were supported on montmorillonite (MMT) pretreated with triisobutylaluminum and 10‐undecence‐1‐ol to produce in situ polyethylene–clay nanocomposites in a gas‐phase reactor. The development of the nanocomposite morphology was investigated with transmission electron microscopy (TEM), scanning electron microscopy (SEM), and X‐ray diffraction (XRD) analysis. During polymerization, the MMT layers were partially exfoliated by the growing polymer chains, starting from the openings of the clay galleries, but intercalation and exfoliation occurred only to a certain extent. The thermal properties of the nanocomposites we also analyzed by differential scanning calorimetry (DSC).

     

The Role of Oxidation in the Migration Mechanism of Layered Silicate in Poly(propylene) Nanocomposites

Summary: Evidence of clay migration from the core to the surface of poly(propylene)/montmorillonite nanocomposites is provided. A three‐ to fivefold increase in the clay concentration of the surface is obtained during isothermal heating in oxidative atmosphere. The mechanism of migration is investigated by means of attenuated total reflectance Fourier transform infrared spectrometry. It is shown that oxygen plays a fundamental role in the migration mechanism.

ρ_Si versus c for the annealed samples.     

Synthesis of Layered Hydroxide Zinc m‐Aminobenzoate Compounds and Their Exfoliation Reactions

Two types of layered hydroxide zinc m‐aminobenzoate compounds with structures of layered basic metal salt (LBMS) were prepared by the reaction of zinc hydroxide with m‐aminobenzoic acid solution in the temperature range of 40–120°C. The formation reactions, structures, chemical compositions, and exfoliation reactions of the layered compounds in alcohol solvents were investigated by XRD, TG‐DTA, SEM, and TEM. One layered phase with a basal spacing of 1.08 nm has a α‐Ni(OH)₂‐like structure, and its chemical formula can be written as Zn(OH)_0.67(m‐NH₂C₆H₄COO)_1.33. This phase has strip‐like particle morphology and cannot be exfoliated into its nanosheets in alcohol solvents. The other layered phase with a basal spacing of 2.66 nm has a zinc hydroxide‐nitrate‐like structure, and can be exfoliated in alcohol solvents.     

Facile and Scalable Synthesis of Silicon‐Based Nanocomposites with Slitlike Nanopores: A Solid‐State Exfoliation Reaction Using Layered CaSi2

Silicon‐based nanocomposites with slitlike nanopores were prepared by heating a mixture of layered CaSi₂ and NiCl₂. The formation mechanism is based on a solid‐state exfoliation reaction wherein the formation of CaCl₂ promotes the extraction of Ca from CaSi₂, thereby exfoliating the layered structure. The nanocomposites showed anode capacity for lithium ion batteries up to 804 mA h g^?1.