Silicate Nanocomposites Research Articles

Variable‐temperature Fourier transform infrared studies of matrix–nanofiller interactions in amorphous polyamide/layered silicate nanocomposites

AbstractVariable‐temperature Fourier transform infrared spectroscopy was used to investigate matrix–nanofiller interactions in amorphous semiaromatic polyamide/layered silicate nanocomposites prepared by melt intercalation. The types of polymer–nanofiller interactions were found to be strongly dependent on the nature of the polymer matrix and the surfactant‐modified layered silicate. Improved compatibility resulted when hydrogen‐bonding interactions occurred between the surfactant and polymer chains. The presence of surfactants with phenyl groups also led to a more stable molecular structure of the polymer matrix because of the enhanced resonance effect between aromatic groups. SiO stretching vibrations in the layered silicate shifted to lower wavenumbers with increasing temperature; this indicated the presence of weaker polymer‐layered silicate interactions. The results of this study demonstrate that for the polymer nanocomposites prepared by melting intercalation, more important interfacial interactions existed between the polymer and the surfactant. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Long-term AC Electrical Treeing Behaviors of Epoxy/Layered Silicate Nanocomposites Prepared by a 3-Roll Mill

Long-term AC Electrical Treeing Behaviors of Epoxy/Layered Silicate Nanocomposites Prepared by a 3-Roll Mill

PBAT based nanocomposites for medical and industrial applications

Poly(butylene adipate-co-terephthalate) (PBAT) based nanocomposites were prepared by melt blending PBAT with 5 and 10wt.% of clay nanoparticles (unmodified and modified montmorillonites, unmodified and modified fluoro-hectorites, and unmodified sepiolites). All nanocomposites showed a good level of clay distribution and dispersion into PBAT, especially nanocomposites with high clay chemical affinity with the polymer matrix. DSC results showed that addition of layered silicates slightly hindered kinetics and extent of crystallization of PBAT; however, sepiolite particles were able to promote polymer crystallization kinetics and the transformation of the PBAT crystal structure to a more ordered form.Similar increases in the thermal stability of PBAT in nitrogen and air were obtained upon addition of all clays, due to a barrier effect of the clays toward polymer decomposition product ablation.Preliminary biocompatibility tests indicated that PBAT based materials with 10% clay content have good biological safety and display almost no cytotoxicity.The addition of all nanofillers increased the hardness of PBAT matrix. The DMA analysis showed that all nanocomposites presented higher E′ values than neat PBAT, indicating that addition of clays improved the mechanical properties of PBAT. For layered silicate nanocomposites, the main influencing factors on the thermo-mechanical properties appeared to be the aspect ratio and dispersion of clay nanoplatelets, rather than polymer/clay chemical affinity. The highest E′ values of sepiolite based nanocomposites make this nanoparticle the most attractive material for tissue engineering and environmental industrial applications.

Muscovite-MWCNT hybrid as a potential filler for layered silicate nanocomposite

Hybridizing multiwalled carbon nanotube (MWCNT) with clay created a new class of functional materials especially for producing polymer layered silicate nanocomposite. The hybrid MWCNT/muscovite compound was produced using chemical vapor deposition (CVD) technique. It is rare to be found that the clay material such as muscovite to be used as a supporting material for MWCNT synthesis. X-ray Diffraction (XRD) and high resolution transmission electron microscope (HRTEM) were used to characterize the hybrid compound. XRD analysis revealed the existence of carbon element among several clay elements of muscovite clay confirming the deposition of CNT. Microstructural analysis using HRTEM further showed that MWCNT was successfully grown on the surface of muscovite particles.

Crystallinity and Crystallization Kinetics in Poly(Ethylene Oxide)/Layered Silicate Nanocomposites

Polymer materials are often filled with inorganic compounds in order to improve their properties [. The optimization of the properties is mostly achieved when the dimensions of the additive is in the nanometer range, producing a nanocomposite. Of particular interest among different organic / inorganic nanohybrids are polymer / layered silicate nanocomposites, which constitute a relatively new class of materials that has attracted growing scientific and technological interest due to the unique improvement of properties like strength, stiffness, scratch resistance, thermal and oxidative stability, gas permeability, flammability and biodegradability. These improved properties make them candidates for a number of potential applications in many industrial sectors like, for example, automotive, aerospace, electronics and biotechnology.

Supercritical CO2 as an exfoliating aid for nanocomposite preparation: Comparison of different processing methodologies

AbstractThis article examines several new methods for compounding nanocomposite materials by twin screw extrusion that use supercritical CO2 as a processing aid to produce more highly exfoliated polyolefin‐layered silicate nanocomposites than conventional melt intercalation. These methods varied the manner in which the plasticizing behavior of CO2 influences the surfactant of an organoclay, the compatibilizer, and the matrix during preparation of a polyolefin nanocomposite. The results have shown that targeting CO2 to the organoclay‐compatibilizer interface can improve the extent of intercalation. However, reduced performance was observed when CO2 was introduced predominantly to the matrix or neat organoclay. In general, the different techniques of addition for CO2 did bring about greater structural changes to the organoclay, but the stiffness of the resulting materials was lower than simply following a conventional melt intercalation approach. POLYM. ENG. SCI., 2012. © 2012 Society of Plastics Engineers

Different crystallization mechanisms in polypropylene–nanoclay nanocomposite with different weight percentage of nanoclay additives

Abstract

New Progress on Rectorite/Polymer Nanocomposites

Rectorite is a kind of layered silicate originated from Hubei province; it has unique structure character- istic albeit with the structure and characteristic much like those of montmorillonite. Rectorite is a regularly inter- stratified clay mineral with alternate pairs of dioctahedral mica-like layer (nonexpansible) and dioctahedral mont- morillonite-like layer (expansible) in 1:1 ratio. In recent years, rectorite has been widely used in the preparation of polymer/layered silicate nanocomposite. This paper introduced the structure and surface modification of rectorite and the structure and preparation method of rectorite/polymer nanocomposite. In particular, the new results of chitosan- based rectorite nanocomposite were summarized. The researchers prepared a series of chitosan-based rectorite nanocomposites via simple solution intercalation, although the rectorite content in these studies was higher than that of other reports, rectorite still dispersed well in the chitosan matrix, there were hydrogen-bonding and electrostatic interactions between rectorite and chitosan. Moreover, the researchers studied antimicrobial activity and mechanism, adsorption capacity, drug-controlled release behavior, gene transfection capacity and structure-property relationship of chitosan-based rectorite nanocomposites. In addition, the films, microsphere and nanoparticles of chitosan-based rectorite nanocomposites were prepared and their properties such as mechanical property, barrier ability, antiultra- violet capacity, thermal stability were studied. At last, the future research of rectorite/polymer nanocomposite was expected.

Isothermal melt crystallization behavior of neat poly(l-lactide) (PLLA) and PLLA/organically modified layered silicate (OMLS) nanocomposite studied by two-dimensional (2D) correlation spectroscopy

Isothermal melt crystallization behavior of neat poly(l-lactide) (PLLA) and PLLA/organically modified layered silicate (OMLS) nanocomposite was studied by using time-dependent infrared (IR) spectroscopy and transmission electron microscopy (TEM). Sets of time-dependent IR spectra reflecting the crystallization from the melt of the neat PLLA and PLLA/OMLS nanocomposite were collected at 105°C. Fine details of the crystallization behaviors were analyzed by two-dimensional (2D) correlation spectroscopy, and significant differences in the crystallization behaviors depending on the presence of OMLS were revealed. Namely, it was found that the crystalline lamellae of the PLLA nanocomposite grow along the layered silicate, while the orientation of the neat PLLA resulted in more disordered orientation because of the absence of the OMLS. The result derived from the 2D correlation analysis of the time-dependent IR spectra of PLLA samples showed good agreement with corresponding TEM images.

Nanoclay dispersion in a miscible blend: an assessment through rheological analysis

In this study, miscible polymer blend nanocom- posite of Poly(ethylene oxide)/Poly(methyl methacrylate), (PEO/PMMA), with sodium montmorillonite (Na + -MMT) clay were prepared at a constant concentration of nanopar- ticles via different solution intercalation methods. The re- sultant nanocomposites possess different structure and dispersion of Na + -MMT clays which are assessed through a combination of transmission electron microscopy (TEM) and X-ray diffraction (XRD). The rheology of the neat blend and two different layered silicate nanocomposites were in- vestigated using linear viscoelastic measurements with a parallel plate rheometry at small strain amplitudes. It was found that regardless of the extent of dispersion, the storage and loss modulus increased by incorporating the nanopar- ticles into the matrix of PEO/PMMA. Moreover, at low frequencies the rheological response of the nanocomposite in which layered silicates benefit from a better dispersion becomes relatively invariant with frequency and represents a mediocre solid-like behavior in comparison to the nano- composite in which the nanoparticles are intercalated or agglomerated.

Modeling stiffness of nanolayered silicate‐modified polyamide 6 via FEM micromechanical modeling and analytical composite models

AbstractIn this work, numerical and analytical models are chosen to study reinforcement effect of nanolayered silicate modified polyamide 6 (PA 6) composites at ambient temperature. A numerical self‐consistent unit cell model in conjunction with finite element method is applied to predict the stiffness of this polymer nanocomposite, which has been successfully applied for simulating mechanical behavior of metal matrix composites. In this work, a rectangular inclusion (layered silicate) is surrounded by PA 6 polymer matrix, which is again embedded in the PA 6/layered silicate nanocomposite. The stiffness of the composite is determined iteratively in a self‐consistent manner. For comparison, two analytical composite models (Halpin–Tsai model and Tangdon–Weng model) are implemented to evaluate the stiffness of this nanocomposite via calculations performed within MATLAB. In the modeling volume fraction, aspect ratio, exfoliation and orientation of the nanolayered silicate are taken into account. It is demonstrated that the numerical approach using the self‐consistent embedded cell model coincides well with experimental results of the stiffness of the composite. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Nanocomposites Based on Layered Silicates and Epoxy Resins: Measurement of Clay Dispersion and Exfoliation using TEM, Solid-State NMR, and X-ray Diffraction Methods

In an epoxy/layered silicate nanocomposite containing different organically modified layered silicats, the effect of various organic modifications and the layered silicate content on the layer distances are investigated by transmission electron microscopy (TEM), X-ray diffraction (XRD) measurements, and 1H solid-state NMR. TEM micrographs were evaluated using a semi-quantitative method. The effect of paramagnetic impurities present in the clay is used to obtain overall sample information related to the degree of exfoliation by 1H solid-state NMR. A new model for determination of the degree of exfoliation by proton longitudinal relaxation rate measurements is developed.

Elastomeric epoxy nanocomposites: Nanostructure and properties

In polymer layered silicate nanocomposites, significant differences have been reported between the effects of the nano-reinforcement on rigid and elastomeric nanocomposites. In this paper, we have studied elastomeric nanocomposites based upon DGEBA epoxy resin filled with montmorillonite (MMT) and cured with a long-chain polyoxypropylene diamine, for comparison with analogous rigid nanocomposites. Ultrasonic mixing was used to disperse the MMT in the matrix to improve homogeneity and decrease the agglomerate size. Two different methods of nanocomposite preparation were used in which the MMT was first swollen with either the curing agent or the epoxy before the addition of, respectively, DGEBA or diamine. A better dispersion of the nanoclay in the matrix and a greater amount of intercalation occurred when the MMT was first swollen with the diamine. The effect of MMT concentrations up to 8wt.% on the mechanical behaviour of the epoxy/MMT nanocomposites was investigated. It was found that the addition of MMT increased the tensile strength and modulus, although SAXS and TEM indicated that a significant fraction of the clay layers were not exfoliated. Nevertheless, the addition of the clay resulted in changes in the fracture surfaces, as indicated by SEM, consistent with the tensile results and indicative of toughening.

Polylactide (PLA)-clay nanocomposites prepared by melt compounding in the presence of a chain extender

Polylactide-layered silicate nanocomposites with and without a chain extender were prepared by melt mixing using a twin-screw extruder. An organo-modified clay, Cloisite® 30B, and a chain extender Joncryl®-ADR 4368F were employed in this study. The effect of the chain extender and processing conditions on the properties of the PLA-clay nanocomposites were investigated for different strategies of mixing. The resulting nanocomposites were characterized by X-ray diffraction (XRD), while their morphology was observed by SEM and TEM. The incorporation of the chain extender could enhance the degree of clay dispersion provided that it is judiciously added to the nanocomposite. The corresponding results revealed that the Joncryl-based nanocomposites, where nanoclay platelets were well-dispersed, exhibited a significantly reduced permeability as compared to others. The mechanical properties of the neat PLA, the PLA and Joncryl-based nanocomposites were also examined. The increased molecular weight in Joncryl-based nanocomposites caused a significant increase in the modulus, drawability and toughness of the samples.

An Amphiphilic Acrylic Copolymer/Montmorillonite Nanocomposite

A bi-component copolymer/layered silicate nanocomposite was synthesized by way of a two-stage radical copolymerization of emulsion intercalation and solution intercalation, using acrylates, methacrylic acid and acrylamide as monomers. The water-based product was designed with a structure of a hydrophobic copolymer dispersed in an aqueous copolymer solution to meet needs of warp sizing agents on adhesiveness to hydrophobic and/or hydrophilic fibers, appropriate glass transition temperature, as well as water-solubility. XRD patterns for the product films showed an exfoliated structure of montmorillonite (MMT) in the part of soluble acrylic copolymer as the MMT content equal to or less than 7%, while in the part of emulsion copolymer alone or the product as a whole, the MMT showed an intercalated structure. Determination of DSC indicated that chemical bondings occured between the hydrophobic and hydrophilic components, which guaranteed storage stability of the system and water-solubility of the sizing film, and that there were threeTgs corresponding to the emulsion copolymer, solution copolymer and the interfacial copolymer between the two phases. All theTgs increased with increasing content of the MMT in the composites.

The Effect of Ultrasonic Treatment on Thermal Stability of the Cured Epoxy/Layered Silicate Nanocomposite

The effect of ultrasonic treatment on thermal stability of binary systems containing epoxy and organic chemically modified montmorillonite (Cloisite 30B) was studied. Differential scanning calorimetry (DSC), thermal gravimetric analysis (TGA), transmission electron microscopy (TEM), and wide angle X-ray diffraction (WAXD) analysis were utilized. The mixing of epoxy and Cloisite 30B nanocomposites was performed by mechanical stirring, followed by 1 or 3-hour ultrasonic treatment, and polyetheramine as the curing agent. Both XRD and TEM analyses confirmed that the intercalation of Cloisite 30B was achieved. Thed0spacings for silicate in cured sample prepared at 1- and 3-hour duration of ultrasonic treatment were about 21 and 18 Å, respectively. This shows that shorter duration or ultrasonic treatment may be preferable to achieve higherd0spacing of clay. This may be attributed to the increase in viscosity as homopolymerization process occurred, which restricts silicate dispersion. The 1-hour sonicated samples seem to be more thermally stable during the glass transition, but less stable during thermal decomposition process.

Preparation and Characterization of Activated Sericite Modified by Fluorosilicate

The structure of sericite is stable, and it is hard to prepare polymer layered silicate nanocomposites (PLSN). Therefore, structural modification was employed to activate sericite to reduce the layer charger. The thermal treated sericite (S1) was prepared by thermal modification at 800 for one hour. Then, the resulting product was modified with sodium fluorosilicate, whose effect was characterized by X-ray diffraction (XRD) analysis. The dissolving-out amount of Al3+ of salt-treated product (S2) reached circa 2.55 mg/g at the optimal processing conditions. CEC of S2 was increased to 10.52 meq/100g compared with that of original sericite (4.94 meq/100g). The results of XRD analysis indicated that mica-type phase persisted after salt modification with sodium fluosilicate.

Effect of Compatibilizer on Properties of Polypropylene Layered Silicate Nanocomposite

Polypropylene layered silicate nanocomposites based on muscovite clay were prepared via melt compounding using Thermo Haake internal mixer. Muscovite was organically modified with cetyltrimethylammonium bromide (CTAB). Poly(propylene-g-maleic anhydride) copolymer (PP-g-MAH) and polypropylene-methyl polyhedral oligomeric silsesquioxane (PP-POSS) were used as a compatibilizer in the nanocomposite system at concentration of 3.0 wt% based on muscovite content. Consequently effect of compatibilizer on the mechanical properties of the nano–composites was characterized. It was found that the PP-g-MAH compatibiliser possess better overall mechanical properties than the nanocomposites with PP-POSS compatibilizer. The reason was partly due to better adhesion provided by compatibilization effect of PP-g-MAH than PP-POSS as exhibited in scanning electron micrographs.

Influence of cure conditions on properties of resol/layered silicate nanocomposites

AbstractThe effects on clay exfoliation of organic modification of montmorillonite (MMT) and the nature of the catalyst used during the synthesis and curing of a MMT modified phenolic resol resin were investigated. The impact on the final properties of other parameters such as reactivity ratio and temperature of condensation were also analyzed in order to optimize the conditions to prepare a customized organoclay‐based nanocomposite. Nanocomposites were analyzed by means of wide angle X‐ray scattering (WAXS), optical microscopy (TOM), and atomic force microscopy (AFM) techniques. The formation of either intercalated or quasi‐exfoliated structure was assessed in some systems. Thermal and mechanical properties of the cured composites were evaluated and correlated to their morphologies. More homogenous clay dispersion was achieved for composites prepared with aminoacid‐modified MMT, triethylamine (TEA) as catalyst, formaldehyde/phenol molar ratio (F/P) 2.0, and curing at 80°C. POLYM. ENG. SCI., 2012. © 2011 Society of Plastics Engineers

Predictive modeling of creep in polymer/layered silicate nanocomposites

A predictive creep model is developed which uses the properties of matrix and reinforcement to predict the creep of polymer/layered silicate nanocomposites. Up to this point, primarily empirical creep models such as Findley and Burgers models have been used for creep of polymer/clay nanocomposites. The proposed creep model is based on the elastic-viscoelastic correspondence principle and a stiffness model of these nanocomposites. Also, the added stiffness of polymeric matrix due to the constraining effect of layered silicates on polymer chains in the nanocomposite is considered by a parameter termed constraint factor. The results of the proposed model show good agreement with experimental creep data for different clay contents, stresses and temperatures. Comparing the model predictions with experimental data, a logical relationship between the method of processing and the constraint factor is discovered which shows that in-situ polymerization can be more efficient for improving creep resistance of polymer/layered silicate nanocomposites relative to melt processing.