The effect of the physicomechanical characteristics of the polymer matrix and structure of a filler on the stress-strain behavior of polymer-montmorrilonite nanocomposites

The stress-strain behavior of PE-Na⁺-montmorillonite nanocomposites is studied. The stress-strain characteristics of the composites are shown to be controlled by the structure of their nanofiller, which is formed upon melt mixing of the polymer and layered silicate (intercalated or exfoliated), the profile of the stress-strain curve of PE matrix, and the fracture mechanism (either adhesive or cohesive). In nanocomposites with a strong adhesive bonding between matrix and clay particles (under cohesive fracture), both the modulus and yield point are found to be markedly increased. In the case of adhesive fracture, mechanical characteristics are less improved due to debonding between matrix and filler results. For nanocomposites, experimental stress-strain characteristics are compared with theoretical estimates calculated according to the models proposed for predicting the characteristics of filled thermoplastic polymers. In some cases, experimental values of modulus and elongation at break appear to differ appreciably from theoretical estimates. The applied models should take into account the orientation of anisodiametric inclusions in a polymer matrix and the character of separation in the composite (adhesive or cohesive).     

Diffusion behavior in polymer–clay nanocomposites

This paper reviews our previous studies on the diffusion behavior in polymers clay nanocomposites. A geometric model for predicting the effective diffusivity through this type of systems as a function of clay sheets orientation, volume fraction, polymer clay interaction, and aspect ratio is proposed. Model predictions are compared to the effective diffusivity generated using random walk simulations as well as with predictions obtained from already existing theoretical models. Fair agreement is found between the model prediction and the results of numerical simulations. With respect to the already existing theoretical models, the present mathematical derivation seems more adequate to describe diffusion behavior in conventional nanocomposites systems (i.e. when fillers present very low values of volume to surface ratio). Experimental diffusion tests are discussed and interpreted with the aid of the proposed model. In addition to the aspect ratio and clay concentration, the polymer clay interactions as well as the sheets orientation are the factors controlling the barrier properties of polymer‐layered silicate nanocomposites. Good agreement was found in the case of samples containing exfoliated clay, whereas the model fails in the case of micro‐composites, in which the inorganic lamellae are agglomerated in clusters. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 265–274, 2006     

Polymorphic behavior in syndiotactic polystyrene/clay nanocomposites

X‐ray diffraction methods were used in an investigation of the structural changes in syndiotactic polystyrene (sPS)/clay nanocomposites. sPS/clay was prepared by the intercalation of sPS polymer into layered montmorillonite. Both X‐ray diffraction data and transmission electron microscopy micrographs of sPS/clay nanocomposites indicated that most of the swellable silicate layers were exfoliated and randomly dispersed in the sPS matrix. The X‐ray diffraction data also showed the presence of polymorphism in the sPS/clay nanocomposites. This polymorphic behavior was strongly dependent on the thermal history of the sPS/clay nanocomposites from the melt and on the content of clay in the sPS/clay nanocomposites. Quenching from the melt induced crystallization into the α‐crystalline form, and the addition of montmorillonite probably increased heterophase nucleation of the α‐crystalline form. The effect of the melt crystallization of sPS and sPS/clay nanocomposites at different temperatures on the crystalline phases was also examined. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 736–746, 2002     

Investigation of the effects of silicate modification on polymer‐layered silicate nanocomposite morphology

The morphological behavior of a series of polymer‐layered silicate nanocomposites (PLSNs) has been investigated. The goal was to probe the effect of “textured” silicate surfaces on PLSN morphology. The nanocomposites were fabricated by mixing montmorillonite clay that was carefully modified with tailor‐made polystyrene (PS) surfactants into a PS homopolymer matrix, where the chemical similarity of the matrix polymer and surfactants assures complete miscibility of surfactant and homopolymer. To examine the effect of silicate surface “texture,” clay was modified with combinations of long and short surfactants. The samples were then direct melt annealed to allow the equilibrium morphology to develop, and characterized by small‐angle X‐ray scattering. Based on the implications of the Balazs model and other work on the wetting behavior of polymer melts with longer surfactants and textured surfaces we expected that the intercalation of the homopolymer matrix material into the modified clay would be promoted. Extensive characterization of both the modified clays as well as the resultant nanocomposites clearly show that the modified clays exhibit a high degree of order, but also that only phase‐separated morphologies are formed in the corresponding nanocomposites. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 4075–4083, 2004     

Functional copolymer/organo‐MMT nanoarchitectures. XIX. Nanofabrication and characterization of poly(MA‐alt‐1‐octadecene)‐g‐PLA layered silicate nanocomposites with nanoporous core–shell morphology

Novel bioengineering functional copolymer‐g‐biopolymer‐based layered silicate nanocomposites were fabricated by catalytic interlamellar bulk graft copolymerization of L‐lactic acid (LA) monomer onto alternating copolymer of maleic anhydride (MA) with 1‐octadecene as a reactive matrix polymer in the presence of preintercalated LA…organo‐MMT clay (reactive ODA‐MMT and non‐reactive DMDA‐MMT) complexes as nanofillers and tin(oct)₂ as a catalyst under vacuum at 80°C. To characterize the functional copolymer layered silicate nanocomposites and understand the mechanism of in situ processing, interfacial interactions and nanostructure formation in these nanosystems, we have utilized a combination of variuous methods such as FT‐IR spectroscopy, X‐ray diffraction (XRD), dynamic mechanical (DMA), thermal (DSC and TGA‐DTG), SEM and TEM morphology. It was found that in situ graft copolymerization occurred through the following steps: (i) esterification of anhydride units of copolymer with LA; (ii) intercalation of LA between silicate galleries; (iii) intercalation of matrix copolymer into silicate layers through in situ amidization of anhydride units with octadecyl amine intercalant; and (iv) interlamellar graft copolymerization via in situ intercalating/exfoliating processing. The main properties and observed micro‐ and nanoporous surface and internal core–shell morphology of the nanocomposites significantly depend on the origin of MMT clays and type of in situ processing (ion exchanging, amidization reaction, strong H‐bonding and self‐organized hydrophobic/hydrophilic interfacial interactions). This developed approach can be applied to a wide range of anhydride‐containing copolymers such as random, alternating and graft copolymers of MA to synthesize new generation of polymer‐g‐biopolymer silicate layered nanocomposites and nanofibers for nanoengineering and nanomedicine applications. Copyright © 2014 John Wiley & Sons, Ltd.     

Synthesis of polystyrene/polybutylacrylate/layered silicate nanocomposites in aqueous medium

Synthesis of nanocomposites based on polystyrene/polybutylacrylate with layered silicates using emulsion polymerization procedure in aqueous medium allowed obtaining stable nanolatexes with sodium dodecyl sulfate as surfactant. Monomer and layered silicate nature influences the average diameter of the particles and the zeta potential appeared on the particle-disperse medium interface, as it was shown by dynamic light scattering analyses. In order to evidence the layered silicate structure, two structural evaluation methods were used. A new approach was used based on Fourier transform infrared analyses as a method to asses the clay delamination. The method was followed in conjunction with X-ray diffraction patterns and showed the pronounced delamination of the clay in the polymer matrix. The thermal stability was investigated by thermogravimetric analyses and the morphologies in solid state observed by environmental scanning electron microscope measurements.     

聚合物/层状硅酸盐纳米复合材料的环境稳定性

过去的十多年里，聚合物／层状硅酸盐纳米复合材料在制备、结构与性能方面的研究取得了长足的进步。一些聚合物基的纳米复合材料已实现工业生产，在汽车、家电和包装等领域得到应用。环境稳定性是聚合物材料应用的一个重要方面。本文从材料的耐候性、耐热性和阻燃性能的角度出发，评述了近年来聚合物／层状硅酸盐纳米复合材料在紫外光降解、热降解和燃烧性能方面的研究进展，以期对纳米复合材料的基础研究及应用开发有所裨益。     

Study on elastic modulus of crosslinked polyurethane/organoclay nanocomposites

In this paper, two polyurethane/clay nanocomposite systems with crosslinked structure were synthesized via in situ polymerization of a polyether‐ as well as a polyester‐based prepolymer with methylene‐bis‐ortho‐chloroanilline (MOCA). Two types of modified clays with different organic modifiers were used in order to see the effect of compatibility between polymer matrix and clays on elastic modulus of nanocomposites. The morphology and the dispersion of clay layers in polyurethanes have been characterized by X‐ray diffraction (XRD) and microscopic techniques. The changes of elastic modulus of nanocomposites with clay content were examined and compared with those predicted by some conventional composite models. The results showed a reasonable fitting of experimental and theoretical values only at very low clay contents. As the clay content exceeds 1.5 wt% in this system, a reduction in elastic modulus was experimentally observed due to insufficient dispersion degree of silicate layers throughout the crosslinked matrix. This behavior was not predicted with the conventional composite theories. A new model on the basis of Wu model was then developed in order to predict the reduction of elastic modulus at various clay contents in crosslinked PU matrix. This model fitted reasonably the experimental results. Copyright © 2010 John Wiley & Sons, Ltd.     

Isothermal crystallization of layered silicate/starch-polycaprolactone blend nanocomposites

The isothermal crystallization behavior of layered silicate/starch-polycaprolactone blend nanocomposites was studied by means of differential scanning calorimetry (DSC) measurements. The theoretical melting point was higher for the matrix than for nanocomposites. At low clay concentration, the induction time decreased and the overall crystallization rate increased acting as nucleating agent whereas at higher concentrations became retardants. Classical Avrami equation was used to analyze the crystallization kinetic of these materials. n values suggested that clay not only affected the crystallization rate but also influenced the mechanism of crystals growth. An Arrhenius type equation was used for the rate constant (k). Models correctly reproduced the experimental data.     

Characterization of polypropylene (PP) nanocomposites for industrial applications

This study aims in the examination of a new class of materials named polymer layered silicate nanocomposites. In our case, composites are usually combinations of polypropylene matrix with solid mineral reinforcements named silicates (e,g. montmorillonite, a natural clay). In this study, two complementary techniques used to characterize nanocomposites. Fourier transform infrared spectroscopy (FT-IR) both in transmission and attenuated total reflectance (ATR) modes combined with X-ray photoelectron spectroscopy (XPS).     

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.     

Rheological Behavior and Wear Abrasion Resistance of Polyethylene Oxide/Laponite Nanocomposites

Polymer/layered silicate nanocomposite thin films were developed as clear, transparent coatings. Laponite‐S, which is a synthetic layered clay, was dispersed in a polyethylene oxide matrix and solution cast onto glass slides for further testing. Rheological properties, wear abrasion resistance, and scratch resistance were tested for each sample to examine the nanoparticle dispersion effects on the materials' properties. In this study, we identify and characterize the materials to be used, establish the appropriate conditions for the preparation of polymer/Laponite nanocomposite dispersions, illustrate methods for the development of PEO/Laponite‐S films, and characterize the films. Results on the rheological behavior of PEO‐silicate nanocomposites as a function of Laponite solids loading and PEO concentration, as well as some preliminary wear abrasion properties of the films are presented in this study.     

Biodegradable Polylactide and Its Nanocomposites: Opening a New Dimension for Plastics and Composites

The academic and industrial aspects of the preparation, characterization, mechanical and materials properties, crystallization behavior, melt rheology, and foam processing of pure polylactide (PLA) and PLA/layered silicate nanocomposites are described in this feature article. Recently, these materials have attracted considerable interest in polymer science research. PLA is linear aliphatic thermoplastic polyester and is made from agricultural products. Hectorite and montmorillonite are among the most commonly used smectite‐type layered silicates for the preparation of nanocomposites. Smectites are a valuable mineral class for industrial applications because of their high cation exchange capacities, surface area, surface reactivity, adsorptive properties, and, in the case of hectorite, high viscosity, and transparency in solution. In their pristine form, they are hydrophilic in nature, and this property makes them very difficult to disperse into a polymer matrix. The most common way to overcome this difficulty is to replace interlayer cations with quaternized ammonium or phosphonium cations, preferably with long alkyl chains. In general, polymer/layered silicate nanocomposites are of three different types: (1) intercalated nanocomposites, in which insertion of polymer chains into the layered silicate structure occurs in a crystallographically regular fashion, regardless of polymer to layered silicate ratio, with a repeat distance of few nanometer; (2) flocculated nanocomposites, in which intercalated and stacked silicate layers are sometimes flocculated due to the hydroxylated edge–edge interactions between the silicate layers; (3) exfoliated nanocomposites, in which individual silicate layers are uniformly distributed in the polymer matrix by average distances that totally depend on the layered silicate loading. This new family of composite materials frequently exhibits remarkable improvements in its material properties when compared with those of virgin PLA. Improved properties can include a high storage modulus both in the solid and melt states, increased flexural properties, a decrease in gas permeability, increased heat distortion temperature, an increase in the rate of biodegradability of pure PLA, and so forth.

Illustration of the biodegradability of PLA and various nanocomposites.     

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.     

Poly(1‐butene)/clay nanocomposites: Preparation and properties

The preparation and properties of poly(1‐butene) (PB)/clay nanocomposites are described for the first time. Nanocomposites were prepared with the melt‐intercalation technique, using organically modified clay. The X‐ray diffraction patterns portrayed well‐defined diffraction peaks at higher d‐spacing than pristine clay, confirming the intercalation of polymer in silicate layers. Because PB exhibits time‐dependent polymorphism, the effect of clay on the phase transformation of PB was examined with thermal analysis. The phase transformation from a metastable tetragonal form to a stable hexagonal form was enhanced because of incorporation of layered silicates in the polymer matrix. The nanocomposites exhibited about a 40–140% increase in storage modulus depending on the clay content and significantly lower coefficient of thermal expansion. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 1014–1021, 2003     

Investigating the effect of nanolayered silicates on blend segmental dynamics and minor component relaxation behavior in poly(ethylene oxide)/poly(methyl methacrylate) miscible blends

Polymer–silicate nanocomposites based on poly (ethylene oxide), PEO, poly(methyl methacrylate), PMMA, and sodium montmorillonite clay were fabricated and characterized to investigate the effect of nanolayered silicates on segmental dynamics of PEO/PMMA blends. X‐ray results indicate the formation of an exfoliated morphology in the nanocomposites. At low silicate contents, an enhancement in segmental dynamics of blend nanocomposites and also PEO, minor component in blend, is observed at temperature region below blend glass transition. This result can be attributed to the improvement of the confinement effect of rigid PMMA matrix on the PEO chains by introducing a low amount of layered silicates. On the other hand, at high silicate contents, an enhancement in segmental dynamics of blend nanocomposites and PEO is observed at temperature region above blend glass transition. This behavior could be interpreted based on the reduction of monomeric friction between two polymer components, which can facilitate segmental motions of blend components in nanocomposite systems. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011     

熔体插层聚合物/粘土纳米复合材料

对国内外熔体插层法制备聚合物／粘土纳米复合材料(PCN)的研究进展进行了综述。介绍了影响PCN结构形态的各种因素；对熔体插层法制备PCN的热力学、动力学研究进行了总结；详细讨论了熔体插层的机理研究及理论模型。并对熔体插层法制备PCN提出了展望。     

Biodegradable Nanocomposites Based on the Polyester Poly(3‐hydroxybutyrate‐co‐3‐hydroxyhexanoate) and Layered Silicate or Expanded Graphite

Novel nanocomposites based on the biodegradable polymer poly(3‐hydroxybutyrate‐co‐3‐hydroxyhexanoate) (PHBHx) and layered fillers, specifically layered silicate (clay25A) and expanded graphite (EG), were prepared by melt intercalation. The dispersion of the fillers in the PHBHx was characterized by wide‐angle X‐ray diffraction (WAXD) and transmission electron microscopy (TEM). The effects of the fillers on the polymer structure, thermal stability and mechanical properties of the nanocomposites were also studied, by differential scanning calorimetry, thermogravimetric analysis, and strain‐stress measurements in elongation, respectively. The WAXD and TEM results showed that the clay25A and EG was exfoliated into well‐dispersed sheets in the polymer matrix, especially when the filler concentration were relatively low. This gave rise to considerable improvements in Young's modulus, and resulted in increases in the thermal degradation. It should be possible to convert the EG dispersions obtained thus far to ones yielding filler‐filler networks that show electrical conductivity.