Layered Silicate Nanocomposites Research Articles

Extensibility of EVA Based Nanocomposites

The structure and deformation characteristics of ethylene-vinyl acetate (EVA)-layered silicate nanocomposites were studied using steady shear and extensional rheology. EVAs with VA contents of 18% and 28% by weight and a commercially modified montmorillonite clay were melt compounded in a twin-screw extruder. Nanocomposites of 2.5%, 5% and 7.5% by weight were produced. WAXS measurements have revealed that EVA chains had intercalated into the silicate layers and expanded the interlayer distance. TEM showed that the morphologies of the nanocomposites were of mixed intercalated/exfoliated. The nanocomposites exhibited an increase in steady shear viscosities compared to the unfilled EVA polymers. At high loading there was a possibility of yield stress owing to network structures. Elasticity of the nanocomposites was compared using first normal stress difference-shear stress plots and the modified Cole-Cole plots, with both methods showing contradictory results. Melt strengths of both EVAs were enhanced with the addition of silicate fillers; however, this was at the expense of the materials' extensibility. Addition of silicate fillers also brought with it flow instabilities like draw resonance and ductile failure, both of which lead to limitations in polymer processing.

Poly(ethylene 2,6-naphthalate)/layered silicate nanocomposites: fabrication, crystallization behavior and properties

In this study, poly(ethylene 2,6-naphthalate) (PEN)/layered silicate nanocomposites (PLSNs) were successfully prepared by the intercalation of PEN polymer into organically-modified layered montmorillonite through the melt blending process. Both X-ray diffraction data and transmission electron microscopy images of PEN/layered silicate nanocomposites indicate most of the swellable silicate layers were exfoliated and randomly dispersed into the PEN matrix. Mechanical and barrier properties of the fabricated nanocomposites performed by dynamic mechanical analysis and permeability analysis show significant improvements in the storage modulus and water permeability when compared to neat PEN. Differential scanning calorimeter (DSC) was used to investigate the isothermal crystallization behavior and melting behavior of PLSNs. DSC isothermal results revealed that the crystal growth process of PEN and PLSNs are a three-dimensional spherulitic growth. The activation energy of PEN increases with increasing content of layered silicates. The result indicates that the addition of layered silicate into PEN reduces the transportation ability of polymer chains during crystallization processes.

Preparation of ABS/montmorillonite nanocomposite using a solvent/non-solvent method

Polymer layered silicate nanocomposites have been studied for many years and due to their distinguished properties and applications, it is still the subject of many research programs. There are different methods of preparation, with the melt intercalation method as the mostly used method. Due to the thermal destructive effects of melt mixing on the polymer chains there are currently efforts to develop some new methods of preparation. A solvent/non-solvent method has been developed in this study for the preparation of ABS/clay nanocomposites. ABS nanocomposite is precipitated after addition of ethanol (non-solvent) containing organic modified montmorillonite from a THF solution while it is stirring. A kind of mixing system known as homogenizer has been used in this work. The final product has been determined having an intercalated structure with a uniform interlayer spacing of the silicate layers. The ABS nanocomposites prepared in this work has been studied by X-ray diffraction, FTIR, transmission electron microscope and thermogravimetric analysis. The effect of using homogenizer on the characteristics of the nanocomposites also has been investigated and discussed in several parts of the present work.

Electrospinning of poly(MMA- co-MAA) copolymers and their layered silicate nanocomposites for improved thermal properties

Copolymers consisting of methyl methacrylate (MMA) and methacrylic acid (MAA) and their layered silicate nanocomposites were electrospun to form fibers with diameters in the sub-micron range. The presence of MAA increased the T g and thermal stability of the copolymers through formation of anhydrides upon heating. Fibers of uniform diameters were obtained for the poly(MMA- co-MAA) copolymers and nanocomposites containing montmorillonite (MMT), while protrusions were observed on the electrospun fibers from nanocomposites containing fluorohectorite (FH). The electrospinnability of copolymer solutions and nanocomposite dispersions predicted based on both rheological analyses and conductivity measurements correlates well with the experimental electrospinning observations. Dispersion of clays within the nanocomposites improved the electrospinnability of the nanocomposite dispersions. MMT is predominantly exfoliated and well distributed within the fiber and oriented along the fiber axis. Char formation was observed when the MMT-containing fibers were heated above the decomposition temperature, indicating a potential for reduced flammability and increased self-extinguishing properties, whereas the FH-containing materials disintegrated into either film or powder form.

Photo-oxidative degradation of polypropylene/montmorillonite nanocomposites

The photo-oxidative behavior of the polypropylene (PP)/montmorillonite (MMT) nanocomposites and microcomposites has been investigated upon ultraviolet exposure using the technique of infrared spectroscopy. The rate of photo-oxidative degradation of PP/MMT nanocomposites is much faster than that of pure PP. The influence of pristine MMT, alkylammonium and compatibilizer were investigated, respectively. All these components can catalyze the photo-oxidation of PP matrix, in which the influence of compatibilizer and pristine MMT is primary. Moreover, the dispersion state of the clay particles in the polymer matrices has a little influence on the photo-oxidative degradation of polymer matrix. Consequently, an integrated catalysis mechanism of the photo-oxidative degradation of PP clay nanocomposite is proposed. It would provide benefit direction for the preparation and usage of polymer layered silicate nanocomposites (PLSN).

Rheological investigation of the melt state elastic and yield properties of a polyamide-12 layered silicate nanocomposite

The dynamic and steady shear flow properties of a polyamide-12 melt layered silicate nanocomposite were studied as a function of the silicate volume fraction ϕ. In the dilute regime, the results were discussed in terms of intrinsic viscosity. Above a volume fraction threshold ϕp∼1.5%, and below a critical strain γc, the storage and loss moduli were shown to exhibit a low-frequency plateau, G0′ and G0″, and the flow curve was shown to exhibit an apparent yield stress τy. The study of G0′,γc, and τy as a function of ϕ showed that the energy needed for removing connectivity on a mesoscale did not depend on the silicate loading. These original properties were attributed to the existence, in the quiescent state, of mesoscopic domains composed of correlated silicate layers. Moreover, the steady shear response of all samples at solid volume fractions above ϕp showed the existence of a critical shear rate ∼1s−1, separating a behavior governed by the networked domains from a behavior dominated by the polymer matrix.

Three-Dimensional Structure of the Zone-Drawn Film of the Nylon-6/Layered Silicate Nanocomposites

Semicrystalline polymer/layered silicate nanocomposites exhibit a unique three-dimensional structure associated with the high-aspect ratio constituents (layered silicates and polymer crystallites), which is sensitive to shear and deformation history. Beginning from quenched biaxially extruded films of nylon-6/ montmorillonite nanocomposites, the impact of elevated temperature uniaxial drawing on the orientation of the layered silicate and crystallites, crystalline polymorphism, and layered silicate buckling was studied using X-ray and transmission electron microcopy. The quenched biaxially protruded films exhibited a uniplanar crystalline texture with the b-axis of the dominate γ-form oriented toward the normal to the film surface and the surface of the layered silicate oriented parallel to the film surface. Small-angle scattering features suggest that the lamellar of the γ-form is within the proximity of the layered silicate and has a fringed micelle structure. Upon uniaxial drawing, α-crystallites developed with a lamellar regularity of ∼15 nm along the draw direction, comparable to previous studies on pure nylon-6 fibers. The newly formed α-form exhibited a uniaxial texture with the b-axis parallel to the draw direction. This suggests that the α-form crystallized during the drawing of the film and does not have an orientation correlation with the layered silicate. Finally, the layered silicate within the zone-drawn film buckled perpendicular to the draw direction, analogous to failure of a uniaxially strained sheet of paper. The failure mode appears to occur for a collection of parallel aluminosilicate layers (2−4) and not individually. Recognition of the structural changes of the layered silicate and crystalline regions in response to uniaxial deformation of planar oriented films is critical to ascertaining the local transport properties of shaped layered silicate nanocomposite parts.

Fabrication and characterization of biodegradable poly(lactic acid)/layered silicate nanocomposites

In this study biocompatible/biodegradable poly(lactic acid) (PLA)/layered silicate nanocomposites (PLSNs) were successfully prepared by the intercalation of PLA polymer into organically modified layered silicate through the solution mixing process. Both X-ray diffraction data and transmission electron microscopy images of PLSNs indicate most of the swellable silicate layers were disorderedly intercalated into the PLA matrix. Mechanical properties of the 0.1 wt% silicate-containing fabricated nanocomposites performed by dynamic mechanical analysis have significant improvements in the storage modulus when compared to that of neat PLA matrix. Adding more layered silicates into PLA matrix induced a decrease in the mechanical properties of PLSNs, probably due to the presence of a large dimension of porosity in the fabricated nanocomposites. POLYM. ENG. SCI., 45: 1615–1621, 2005. © 2005 Society of Plastics Engineers

Rheological and Structural Investigation of Layered Silicate Nanocomposites Based on Polyamide or Polyethylene: Influence of Processing Conditions and Volume Fraction Effects

AbstractOrganoclay polymer nanocomposites offer improved material properties at very low filler loadings making them of immediate interest for industrial applications. In this study two matrices are used : a polar polymer, PA12, and a non polar polymer, LLDPE. Many articles focused on the importance of the chemistry used to modify the surface of the clay. Numerous papers studied the influence of the compatibilizing agent necessary to obtain intercalated structure, when the matrix is non polar. This paper demonstrates the importance of the way the clay was melt processed into the thermoplastic matrix. Layered silicate nanocomposites based on PA12 or LLDPE were characterized by X‐ray diffraction, transmission electron microscopy and rheological tests. The influence of volume fraction on rheological and structural properties is also investigated.

Polylactide/montmorillonite nanocomposites: study of the hydrolytic degradation

Hydrolytic degradation of polymer layered silicate nanocomposites based on polylactide matrix (PLA) and (organo-modified) montmorillonites was investigated in phosphate buffer solution for more than five months. While natural unmodified montmorillonite-Na + led to the formation of a microcomposite, mainly intercalated nanocomposites were prepared by melt blending PLA with 3 wt% of montmorillonite organo-modified either by 2-ethylhexyl (hydrogenated tallowalkyl) ammonium cations (Cloisite ®25A) or by bis-(2-hydroxyethyl) methyl tallowalkyl ammonium cations (Cloisite ®30B). The evolution of molecular weight of the matrix as well as its crystallinity with the hydrolysis time has been recorded by size exclusion chromatography (SEC) and differential scanning calorimetry (DSC), respectively. Thermogravimetric analyses (TGA) performed on the microcomposite based on Cloisite ®Na + has shown that the thermal stability of the materials decreased proportionally to the decreasing PLA molecular weight along the hydrolysis time. Moreover, in parallel to the morphology of the composites, the relative hydrophilicity of the clay layers has been shown to play a key role in the hydrolytic degradation of the PLA chains.

A Constitutive Analysis of Extensional Flow of EVA Nanocomposites

Abstract Linear and nonlinear oscillatory and extensional flow was studied for polymer layered silicate nanocomposites of organically modified bentonite in ethylene-vinyl acetate copolymer with 18 wt.% of vinyl acetate (EVA18). It was found that the rheological properties of EVA18 nanocomposites were distinctly different from the pure copolymer. The elastic response at low frequencies was significantly enhanced in comparison to that of pure EVA18. The linear to nonlinear transition for stress relaxation measurements and the damping function were examined. The relaxation spectrum was shifted toward the longer relaxation time scales for EVA18 nanocomposites, while the dependence of the damping for EVA18 nanocomposites was much stronger than that of the EVA18. In contrast, the uniaxial extensional viscosity of EVA18 nanocomposites gave weaker strain-hardening properties. The prediction of strain-hardening behaviour for EVA18 and EVA18 nanocomposites through relaxation spectrum and the damping function based on Kaye-Bernstein-Kearsley-Zapas (K-BKZ) model is discussed. A simplified estimation of the nonlinear material parameter ß in the K-BKZ model is proposed to predict more accurately the extensional viscosity for EVA18 and EVA18 nanocomposites. Experimental data and detailed predictions are also presented in this paper.

A study on phase morphology and surface properties of polyurethane/organoclay nanocomposite

In this study, polyurethane/organically modified layered silicate (organoclay) nanocomposites were prepared through in situ polymerization in the presence of organoclay. Phase morphology of the polyurethane/organoclay nanocomposite was investigated by small-angle X-ray scattering (SAXS) and atomic force microscopy (AFM). The results suggest that the inter-domain repeat distance decreased with the introduction of organoclay. The organoclay has a more significant effect on the inter-domain repeat distance at a low hard segment content. Also with the increase of the hard segment, the inter-domain repeat distance and domain size increased markedly. The size of hard domain of the polyurethane was found to be in the range of 12–32 nm in this case, and it keeps nearly unchanged with the clay content. It is suggested by AFM phase imaging technique that the hard domain can self-organize further to form spherical aggregates. The introduction of clay into the polyurethane matrix resulted in the decrease in the size of the spherical aggregates from ∼800 nm to ∼500 nm, indicating clay has an important effect on the aggregation behavior of hard domains. The effect of clay on the surface energy was examined by means of AFM and goniometry techniques. The results obtained by two methods are consistent, i.e., with the increase of clay content, the surface energy decreased due to the effect of organic modifier.

Preparation and characterization of polypropylene/layered silicate nanocomposites using an antioxidant

Polypropylene (PP)/layered silicate nanocomposites were prepared via simple melt mixing of three components, PP, layered silicates modified with octadecylamine (C18-MMT) and antioxidant, to investigate the role of antioxidant. TEM and X-ray scattering results confirmed the intercalated state of silicates in PP/layered silicate nanocomposites with antioxidant. In rheological and mechanical study, the nanocomposites with antioxidant showed higher properties than those of the unfilled PP. The nanocomposite with 5wt% C18-MMT and 0.5phr antioxidant exhibited about 1.4 times higher tensile modulus and 1.3 times higher storage modulus than the unfilled PP. However, PP/C18-MMT without antioxidant showed lower rheological values owing to the thermal decomposition of PP and the poor compatibility between PP and C18-MMT. It could be concluded that antioxidants played an important role in enhancing the compatibility between PP and C18-MMT. According to the real time X-ray diffraction, the nanocomposite showed the weak ordering of PP crystals than the unfilled PP in the load-extension plateau region of elongation.

X-ray diffraction detection of compliance in polyurethane – organoclay nanocomposites

High performance polyurethane elastomer – organically modified layered silicate (organoclay) nanocomposites based on poly(propylene glycol), 4,4′-methylene bis(cyclohexyl isocyanate), 1,4-butandiol and organoclay have been prepared. The tensile strengths and strains at break of these polyurethane elastomer nanocomposites increased by more than 150% related to the unfilled polyurethane. The fatigue properties were also very significantly improved. The existence of a 'nano-spring' in the polyurethane – organically modified layered silicate nanocomposites has been found for the first time. During stretching, the separation of the clay interlayers intercalated by polyurethane chains increased. When the stretching force was removed, the interlayer spacing returned to the original value under elastic deformation of the polyurethane sample. This finding has been used to understand why the fatigue life of polyurethane incorporated with the clay is significantly enhanced. The new understanding can be applied to the design of important new damping materials.

Analysis of viscoelastic behavior and dynamic mechanical relaxation of copolyester based layered silicate nanocomposites using Havriliak–Negami model

AbstractThe solid‐state viscoelastic properties are examined for intercalated nanocomposites based on a copolyester and (2‐ethyl‐hexyl)dimethyl hydrogenated‐tallow ammonium montmorillonite. The nanocomposites are prepared via the direct melt intercalation technique using a conventional twin‐screw extruder. Dynamic mechanical thermal analysis of the nanocomposites is conducted using two different test setups. The dynamic mechanical relaxation spectra show an increase in the storage modulus of the nanocomposite over the entire temperature range under study as compared to the pristine polymer (except in the transition region from 70 to 80 °C). These results are analyzed using the empirical Havriliak–Negami (HN) equation. The four temperature independent HN parameters (α, β, E0, and E∞) and one temperature dependent parameter (τ, the relaxation time) are determined by solving the HN equation for each temperature over the range of temperatures. The calculated moduli results fit well with the experimental values of the relaxation spectra for the nanocomposites. This study shows that the HN model can be applied to polymer layered silicate nanocomposites, and it can be used to predict their dynamic mechanical properties over a wide range of temperatures and frequencies a priori. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 2657–2666, 2004

Styrene-acrylonitrile (SAN) layered silicate nanocomposites prepared by melt compounding

Poly(styrene-co-acrylonitrile) (SAN) nanocomposites were successfully made by melt compounding and exhibited improved thermal stability and reduced flammability. The organoclays used in these nanocomposites were based upon fluorinated synthetic mica (FSM) or montmorillonite (MMT). Four different organic treatments were used on the clay surface to study the effect of organic treatment on clay dispersion: dimethyl, bis(hydrogenated tallow) ammonium (DMHTA), methyl tallow bis-2-hydroxyethyl ammonium (MTBHA), triphenyl, n-hexadecyl phosphonium (TPHDP), and 1,2-dimethyl-3- n-hexadecyl imidazolium (DMHDI). Along with studying the effect of clay organic treatment on the nanocomposite formation and flammability, the effect of acrylonitrile content in the SAN on nanocomposite formation and flammability was also studied. The overall findings suggest that dispersion of clay into SAN is rather facile, but certain combinations of organic treatment and clay type resulted in microcomposites rather than nanocomposites. Flammability of these materials was measured by pulse-combustion flow calorimetry (PCFC), also known as micro-cone calorimetry.

Effects of annealing (solid and melt) on the time evolution of polymorphic structure of PA6/silicate nanocomposites

The effects of annealing including solid-state annealing (190 °C) and melt-state annealing (230 and 250 °C) on the polymorphic behavior and thermal property of polyamide 6 (PA6)/layered-silicate nanocomposites (PA6LSN) have been investigated as a function of annealing time using Modulated Differential Scanning Calorimetry (MDSC) and wide angle X-ray diffraction. For comparison, thermal behavior and polymorphism of pure PA6 were also studied. It was demonstrated that PA6LSN and PA6 exhibited a similar polymorphic behavior when they were annealed in the solid state for different time duration. As the annealing temperature was elevated to 230 and 250 °C, significant differences in thermal behavior and polymorphism between PA6LSN and PA6 could be found. For example, the γ phase became the absolutely dominating for PA6LSN, while the α crystal was the most predominant phase in neat PA6. Moreover, a new endothermic peak is observed around 235 °C in all PA6LSN MDSC scans, which might be related to the melting of PA6 lamellae formed in the confined environment on the surface of the nano-silicate.

Physical properties of poly(ε‐caprolactone) layered silicate nanocomposites prepared by controlled grafting polymerization

AbstractPoly(ε‐caprolactone) (PCL) chains grafted onto montmorillonite modified by a mixture of nonfunctional ammonium salts and ammonium‐bearing hydroxyl groups were prepared. The clay content was fixed to 3 wt %, whereas the hydroxyl functionality was 25, 50, 75, and 100%, obtaining an intercalated or exfoliated system. The transport properties of water and dichloromethane vapors and the mechanical properties were investigated. The mechanical and dynamic mechanical analyses showed improvement of the nanocomposite elastic modulus in a wide temperature range. Interestingly, for the higher hydroxyl contents (50, 75, and 100%), the decrease of modulus at higher temperature, due to the PCL crystalline melting, did not lead to the loss of mechanical consistence of the samples. Consequently, they revealed a measurable modulus up to 120 °C, a much higher temperature with respect to pure PCL. Water sorption was investigated in the entire activity range, and a lower sorption was observed on increasing the hydroxyl content, up to the sample with 100% hydroxyl content, which turned to be completely impermeable, even in liquid water. The sample with 75% hydroxyl content showed a threshold activity (a = 0.4) below which it was impermeable to water vapor. Also, the diffusion parameters decreased when the hydroxyl content increased, up to the 100% sample, which showed zero diffusion. The diffusion parameters of an organic vapor, dichloromethane, also exhibited a decreasing value on increasing the hydroxyl content in the nanocomposites. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 1466–1475, 2004

Synthesis of resol–layered silicate nanocomposites by reaction exfoliation with acid‐modified montmorillonite

AbstractResol–layered silicate nanocomposites were prepared by the intercalative polymerization of phenol and formaldehyde in the presence of acid‐modified montmorillonite (HMMT). The nanocomposites were studied by means of X‐ray diffraction, scanning electron microscopy, transmission electron microscopy, dynamic mechanical analysis (DMA), and rheological measurements. The exfoliation of HMMT was promoted by the intragallery reactions catalyzed by protons in the galleries of the clay, whereas the extragallery polymerization catalyzed by ammonia went on simultaneously. The nanocomposites showed higher glass‐transition temperatures in the DMA diagram compared with the resol counterparts. The impact strength was improved significantly by the incorporation of the clay. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 791–797, 2004

Characterization of polypropylene (PP) nanocomposites for industrial applications

AbstractThis 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).