Layered Silicate Nanocomposites Research Articles

Hybrid technology for the preparation of PMMA/Laponite® nanocomposites

Homogeneous poly(methyl methacrylate) nanocomposites were produced with a hybrid technology from Laponite® grafted with PMMA. The reinforcement was prepared by attaching PMMA chains to the surface of the silicate in in situ intercalative polymerization, then it was homogenized with PMMA in an internal mixer. Composites were prepared containing reinforcements with different lengths of the attached polymer chains. The structure of the composites was studied by scanning and transmission electron microscopy and X-ray diffraction, while their properties by DSC and tensile testing. Complete exfoliation was not achieved; the composites contained several individual silicate layers but mostly particles and/or tactoids of less than 200 nm size independently of the length of the attached polymer chains. The tactoids retained their ordered structure, although the arrangement of the layers was not very regular. The reinforcing effect of the grafted silicate was moderate and the properties of the composites were not as good as expected. However, larger molecular weight of the attached PMMA chains resulted in larger reinforcement and better properties. The strong interaction of the grafted chains and the silicate surface hindered the formation of entanglements between chains attached to the surface and the matrix polymer, and limited stress transfer as well. Other ways must be found in order to exploit the potentials of layered silicate nanocomposites as structural materials.

UV-curable polyimide/layered silicate films with improved barrier properties for the protection of semiconductor chips

Polyimide/layered silicate films can be used to protect semiconductor chips against gas and moisture permeation to prevent corrosion followed by failure of the electronic chip. The layered silicates in these films are used as barrier pigment to extend the diffusion pathway and to improve the barrier properties. However, the exfoliation of the silicates has an essential impact on the quality of the barrier. Films prepared from polyimide matrix with layered silicates were investigated as well as the distribution and orientation of silicate particles in the UV-cured film and the correlative mechanisms while hardening. The films were characterized by a variety of methods including SEM, FTIR, TGA, water vapor diffusion (WVD) and oxygen permeation measurement. The prepared films using polyimide / layered silicates nanocomposites showed a reduction of WVD and oxygen permeation of 30% and 80%, respectively. Results demonstrated that polyimide/layered silicate nanocomposite could be used as barrier coating to reduce the permeation of moisture and gases.

Tuning the Mechanical Properties of Poly(Methyl Acrylate) via Surface‐Functionalized Montmorillonite Nanosheets

AbstractPolymer layered silicate nanocomposites (PLSNs) made of montmorillonite (MMT) nanosheets and poly(methyl acrylate) (PMA) are synthesized and systematically characterized. MMT is first modified with a surface‐bound monomer and then functionalized with PMA via radical addition–fragmentation chain transfer (RAFT) polymerization using a grafting through approach. PMA‐modified MMT nanosheets with grafted polymer chains of variable length are obtained. The successful surface modification is demonstrated by near‐field scanning optical microscopy, thermogravimetric analysis, attenuated total reflection Fourier transform infrared spectroscopy, small‐angle X‐ray scattering, and size‐exclusion chromatography. The mechanical properties of various nanocomposites are evaluated via tensile testing. It can be shown that the mechanical properties (Young's modulus, tensile strength, toughness, and ductility) of these PLSNs can be fully controlled by using two major strategies, i.e., by the variation of the overall content of polymer‐modified MMT and by the variation of the chain length of the surface‐grafted polymer.

Study of the Effect of Organoclay on the Structure of Cable PVC Compound

The effect of the organoclay content in polyvinyl chloride plasticate on the features of the supramolecular structure and properties of the layered silicate nanocomposite was studied. X-ray diffraction studies showed that with an increase in the number of layered silicate nanofiller, the nanocomposite structure goes from intercalated to exfoliate. Using a combination of scanning and atomic force electron microscopy methods, it has been shown that when organomodified montmorillonite is introduced into polyvinyl chloride plastic compound, montmorillonite nanoparticles act as crystallization nuclei and along with the preservation of “old” supramolecular structures in the melt, “new” supramolecular formations appear. When studying the dependence of tensile strength of nanocomposite polyvinyl chloride on the content of nanofiller, it was found that the maximum strength of the nanocomposite is achieved at a 5-7 % organoclay concentration.

XLPE – layered silicate nanocomposites for high voltage insulation applications: dielectric characteristics, treeing behaviour and mechanical properties

The study presented here investigates the performance of nano-reinforced cross-linked polyethylene (XLPE) for high-voltage insulation applications with particular focus on dielectric characteristics, treeing behaviour and mechanical properties. The nanocomposites with varying content of organo-modified layered silicate (nanoclay) were prepared by melt mixing of polyethylene, cross-linking agent and nanoclay. X-ray diffraction and atomic force microscopy studies showed that layered silicates were uniformly dispersed with exfoliation in XLPE matrix up to 5 wt% nanoclay content with formation of intercalated structures with slight agglomeration at higher nanofiller content. The dielectric loss, relative permittivity and dielectric strength of the nanocomposites increased with increasing nanoclay content, which was attributed to the inherent properties of XLPE and nanoclay, nanofiller dispersion and interfacial polarisation. The effect of frequency on the dielectric properties was also investigated. Incorporation of nanoclay in XLPE altered the electric field stress distribution in the material and consequently retarded water tree growth. The electric field distribution and the probability of water tree growth were studied by finite element method. Additionally, mechanical properties of the nanocomposite viz. tensile strength and modulus were also enhanced. The changes in the properties were correlated to the morphology of the nanocomposites, as well as polymer filler interactions.

PVA Nanofibers Including Biopolymer-grafted Copolymer for Potential Biomedical Applications

Multifunctional nanofibers were fabricated by electrospinning of polyvinyl alcohol/octadecylamine montmorillonite layered silicate nanocomposite as a matrix polymer and amphiphilic copolymer-g-biopolymer (polylactic acid, PLA) as a biocompatible partner polymer. Crystal structure of the nanofibers significantly changed due to in situ phase separation processing via different chemical and physical interfacial interactions. Relative high thermal stability, high first melting and low crystallinity were observed for the matrix/polymer nanofibers. Nanofibers exhibit low cytotoxicity and necrotic effect for MC3T3-E1 preosteoblast cells.

Organo-modified layered silicate nanocomposites of EPDM–chlorobutyl rubber blends for enhanced performance in γ radiation and hydrocarbon environment

In this work, blends of ethylene propylene diene monomer rubber and chlorobutyl rubber were reinforced with organo-modified layered silicate (nanoclay) to enhance their performance in radiation as well as hydrocarbons environments. The mechanical properties of the nanocomposites increased (up to 57%) and solvent transport coefficients decreased (by 30%) with increasing nanoclay content. The enhancement in properties was attributed to the dispersion of nanoclay platelets in the ethylene propylene diene monomer–chlorobutyl rubber blends and the chemical interaction between nanoclay and the polymer which were confirmed by morphological and spectroscopic analysis, respectively. The effect of nanofiller content on the mechanical properties, solvent uptake and thermal degradation of blends exposed to gamma radiation was investigated by irradiating the nanocomposites with gamma rays for cumulative doses of 0.5, 1 and 2 MGy. The ethylene propylene diene monomer–chlorobutyl rubber nanocomposites with 5 phr nanoclay had the best retention of mechanical properties and solvent sorption coefficients on exposure to radiation. Depending on the dose of cumulative radiation exposure, chain scission and/or crosslinking occurred in the nanocomposites, resulting in varying degrees of changes in properties.

Design and Fabrication of Polymer Layered Silicate Nanocomposites for Water Purification

ABSTRACTZeolite and cellulose-acetate nanocomposites were fabricated in this study using a combination of melt blending and solution mixing. The nanocomposites were optimized for heavy metal adsorption using spiked lead and cadmium solutions. Fourier Transform Infrared Spectroscopy, Scanning Electron Microscopy and Powder X-Ray diffraction crystallography were used for physical characterization. Fourier Transform Infrared spectra showed a reduction of the hydroxyl peak for cellulose acetate and that of the residual silanol group for zeolites symbolizing bonding during nanocomposite formation. Scanning Electron Microscope results showed an increase in voids with zeolite loading in the nanocomposites, a useful characteristic of good adsorbents. Powder X-ray diffraction crystallography results showed a reduction in 2 theta values for the nanocomposites due to penetration of the polymer into the silicate lattice e.g. zeolite 2 theta peak at 7.44°reduced to 7.09°in the nanocomposites signifying an increase in crystal lattice d- spacing from 1.188 nm to 1.247 nm. The nanocomposites adsorbed a maximum of 97.20% lead ions and 85.06% cadmium ions from solution.

DC electrorheological response of polyethylene/organically modified layered silicate nanocomposites

The present work reports the electrorheological (ER) response of high-density polyethylene (HDPE)/organically modified silicate layers nanocomposites based on four commercially available HDPE matrices. Two single-site catalyzed bimodal resins, one single-site catalyzed unimodal resin and one Ziegler–Natta catalyzed unimodal resin are studied. It is revealed that the distinct separation of the two modes of the bimodal HDPE resins significantly enhances the ER response. It is proposed that the slower structural relaxation modes introduced by higher molecular weight species in the bimodal HDPE matrices enhance the ER response of the nanocomposites. This is ascribed to the longer induction time for leaking current density, which is an indicator of mobility and release of immobilized cationic surfactants at the silicate layers surface induced by field exposure. It is found that the screening effect of prematurely released cationic surfactants leads to a weaker ER response in nanocomposites whose matrices have faster relaxation modes. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017

Characterization of layered silicate-reinforced blends of thermoplastic starch (TPS) and poly(butylene adipate-co-terephthalate)

A two-step melt blending procedure was used to produce binary systems composed of thermoplastic starch (TPS) and poly(butylene adipate-co-terephthalate) (PBAT). To improve the properties of the blends, two different layered silicates, viz. bentonite (BT) and organically modified montmorillonite (oMMT) were incorporated. First, TPS and its layered silicate nanocomposites were prepared via extrusion compounding during which starch was plasticized with glycerol and water. In the second step, PBAT was added to TPS/layered silicate to produce blends in a batch-type mixer. Mechanical and thermal properties were determined. The blends showed acceptable ductility over 50wt.% PBAT content, although at the cost of strength and stiffness. By contrast to oMMT the BT became intercalated in TPS and TPS/PBAT blends. The reinforcing effect of BT and oMMT was most prominent for the glassy states of both TPS and TPS/PBAT blends. Thermal, and thermooxidative properties were not significantly affected by the presence of layered silicates.

In situ monitoring by DSC and modeling of curing of vinyl polysiloxanes in layered silicate nanocomposites

The study of curing mechanism and the related kinetics in montmorillonite/vinyl-terminated polysiloxane nanocomposites was carried out. Commercially unmodified montmorillonite, as well as two different types of organically modified products, under the trade names: Nanofil 116, Cloisite 20A and Cloisite 30B, respectively, was used as the reinforcing nanofillers. The vulcanization reaction was followed by isothermal and non-isothermal differential scanning calorimetry analysis. The Cloisite 20A/PDMS systems showed increased reaction rate at the early stages of cross-linking, followed by a retardation of the rate and extension of curing time, with respect to the pure PDMS. On the other hand, Cloisite 30B decreases the curing rate of PDMS during the whole process, whereas a significant increase in this parameter was recorded in the case of unmodified clay/PDMS nanocomposites. This diversity of the effect of various types of fillers was attributed to physicochemical interactions between the cross-linking system and organoclay particles mainly due to their surface chemistry. In an attempt to further evaluate the obtained results, it was found that the autocatalytic model shows good fitting with the experimental data.

Lipid‐derived monomer and corresponding bio‐based nanocomposites

AbstractFatty acid based monomer and corresponding hybrid polymer layered silicate nanocomposites have successfully been prepared by using in situ polymerizations. The hybrid materials were prepared by adding different ratios of nanoclay during free radical homopolymerization of 2‐(acryloyloxy)ethyl stearate (AOES) monomer and copolymerization of AOES with styrene. AOES monomer was synthesized by treating stearic acid with 2‐hydroxyethyl acrylate. The formation of AOES monomer, homopolymer and copolymer was confirmed by 1H NMR spectroscopic analysis. Further analysis and characterization of the nanocomposites were carried out by XRD, transmission electron microscopy, AFM and attenuated total reflectance Fourier transform infrared spectroscopy. TGA of the polymer nanocomposites was also carried out to evaluate their thermal stability, while flammability tests were conducted to investigate the effect of layered silicate on flame retardancy. Nanofiller addition into the polymer matrix substantially improved the thermal properties and fire retardancy of the composites. © 2016 Society of Chemical Industry

Influence of Conducting Polymer as Filler and Matrix on the Spectral, Morphological and Fluorescent Properties of Sonochemically Intercalated poly(o-phenylenediamine)/Montmorillonite Nanocomposites.

Nanocomposites consisting of spatially confined polymeric chains are of great interest due to their application in optoelectronic and photonics devices. Polymer layered silicate nanocomposites have attracted much attention in industry as well as academia owing to their remarkable physical and chemical properties as compared to conventional polymer nanocomposites. In present study, comparative investigation of the in-situ polymerization of poly(ophenylenediamine) intercalated montmorillonite has been done via two methods i.e using poly(o-phenylenediamine) as filler for MMT in one case and as matrix in the other. Intercalation and in-situ polymerization was confirmed by FT-IR, UV-Visible spectroscopy and XRD studies. TEM and optical microscopy studies confirmed the self-assembled morphology of nanocomposites while the fluorescence properties revealed that controlled emission could be achieved by confining poly(o-phenylenediamine) in MMT galleries. Intercalation and in-situ polymerization of o-phenylenediamine within MMT was successfully carried out using sonochemical technique. The growth of conducting polymers in the interlayer region of the clays has been shown to dramatically improve the properties of conducting polymers. Also, the loading of the polymer in the MMT has shown to influence the optical properties of the nanocomposite. IR spectra and XRD analysis confirmed the intercalation of POPD and its polymerization within the clay galleries. UV spectra revealed the doped state of POPD within clay galleries. Highest oscillator strength of 0.0137 was observed for POPD:MMT-1:0.25. Spherical self-assembled morphology was attained for POPD:MMT-1:0.25. XRD revealed major shift of 82.5 Å for the nanocomposite POPD:MMT-1:1, POPD:MMT-1:0.5 and MMT:POPD-1:0.25. Blue shift of 20 nm was noticed in the fluorescence spectra of POPD:MMT-1:0.25 and POPD:MMT-1:0.5 which was correlated to the intense interaction between NH of POPD with SiO of MMT. Highest quantum yield of 0.345 was achieved in case of POPD:MMT-1:0.25. The gallery confinement was found to control the optical as well as morphological characteristics of the nanocomposite. The controlled growth of POPD chains and their minimum aggregation resulted in the formation of self-assembled morphology. Thus, by choosing the optimum filler loading and by controlling its interaction with the matrix, nanocomposites with controlled architecture can be designed. It can be concluded that intercalation and exfoliation of nanocomposites largely depends on the experimental conditions such as type of conducting monomer, clay and organic modifier etc. The preparation technique and processing conditions influence the overall properties of the nanocomposites. Thus, by choosing the optimum filler loading and by controlling its interaction with the matrix, nanocomposites with controlled architecture can be designed. Few relevant patents to the topic have been reviewed and cited.

Fabrication and characterization of novel starch-grafted poly l-lactic acid/montmorillonite organoclay nanocomposites

In this work, poly(l-lactic acid)-g-starch layered silicate nanocomposites (NCs) (PLLA-g-starch/MMT) were fabricated by intercalative bulk graft copolymerization of LA with starch, in the presence of either stannous octoate acting as a catalyst or LA-MMT organoclay acting as a cocatalyst-nanofiller. This procedure was performed inside a custom vacuum micro-reactor. To better understand the graft copolymerization mechanism, in situ processing types, interfacial interactions and nanostructure formation of PLLA-g-starch/MMT NCs, methods such as FT-IR, XRD, 1H NMR, 13C CP/MAS-NMR, DSC/TGA, TEM and SEM were utilized. The morphology and thermal behaviors of nanocomposites were found to be strongly dependent on the loading mass fraction of LA-MMT within the nanocomposite structure and the type of in situ processing such as interfacial, physical and chemical interactions. Preintercalated LA-MMT organoclay exhibited dual functions. It demonstrated the ability to act as a catalyst, essentially accelerating in situ graft copolymerization via esterification of LA carboxyl groups with hydroxyl groups of starch macromolecules, whilst also acting as a nananofiller-compatibilizer.

Development of nanocomposites based on organically modified montmorillonite and plasticized PVC with improved barrier properties

ABSTRACTMontmorillonite (MMT) was organically modified with tributyl citrate (TBC). Organoclays (OMMTs) were processed with diisononyl phthalate (DINP)‐plasticized polyvinyl chloride (PVC) to form polymer nanocomposites. The produced composite materials showed a contradictory change in properties to that expected of a layered silicate nanocomposite, with a decreased E‐modulus and increased gas permeability compared with a material without OMMT. It was experimentally shown that the TBC modifier was extracted from the OMMT and was dispersed in the PVC/DINP matrix, whereupon the OMMT collapsed and formed micrometer‐sized agglomerates. Further investigation revealed that TBC has a significant effect on the gas permeability and the E‐modulus, even at low additions to a DINP‐plasticized PVC. A PVC nanocomposite with the TBC acting as both the OM for MMT and as the primary plasticizer was produced. This material showed a significantly increased E‐modulus as well as a decrease in gas permeability, confirming that it is possible to develop a nanocomposite based on plasticized PVC, if both the organo‐modification of the MMT and the formulation of the matrix are carefully selected. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 42876.

A benzimidazole-based conducting polymer and a PMMA–clay nanocomposite containing biosensor platform for glucose sensing

Development of materials composed of polymer–clay nanocomposites (PCN) and conducting polymers attracts great interest and preferred in various applications. Hereby, polymethylmethacrylate (PMMA) layered silicate nanocomposites were prepared by in-situ suspension polymerization by grafting PMMA with laponite using a suitable grafting agent. The properties of the as-synthesized PCN materials are characterized by differential scanning calorimetry (DSC), thermal gravimetry analysis (TGA) and gel permeation chromatography (GPC). A conducting polymer; poly(4-(2,3-dihydrothieno[3,4-b][1,4]dioxin-5-yl)-7-(2,3-dihydrothieno[3,4-b][1,4]dioxin-7-yl)-2-benzyl-1H-benzo[d]imidazole) (poly(BIPE)) and a PMMA–clay nanocomposite with 2-(methacryloyloxy) ethyltrimethylammonium chloride (MTMA) modifier were examined as a platform for biomolecule deposition. Glucose oxidase (GOx, β-d-glucose: oxygen-1-oxidoreductase, EC 1.1.3.4) was chosen as the model enzyme to prepare a scaffold for glucose sensing. Three different sensing strategies; PCN/GOx, poly(BIPE)/GOx and PCN/poly(BIPE)/GOx were analyzed and their biosensor performances were discussed. Surface morphology of the modified electrodes was characterized by scanning electron microscopy (SEM) technique. Electrochemical responses of the enzyme electrodes were monitored at −0.7V vs. Ag reference electrode by monitoring oxygen consumption in the presence of glucose. After optimum conditions were determined, kinetic and analytical parameters; KMapp, Imax, LOD and sensitivity were investigated for each sensing platform.

Poly(lactic acid)–layered silicate nanocomposites: The effects of modifier and compatibilizer on the morphology and mechanical properties

ABSTRACTPoly(lactic acid) (PLA) based nanocomposites were prepared to investigate the effects of types of nanoclays. Five different organically modified nanoclays (Cloisites®15A, 25A, and 30B, and Nanofils®5 and 8) were used. Two rubbery compatibilizers, ethylene‐glycidyl methacrylate (E‐GMA) and ethylene‐butyl acrylate‐maleic anhydride, were used in the nanocomposites as compatibilizer‐impact modifier. The degree of clay dispersion, the chemical compatibility between the polymer matrix and the compatibilizers, and changes in the morphology and mechanical properties of the nanocomposites were investigated. The mechanical properties and the morphological studies showed that the interactions between the different compatibilizers and PLA resulted in different structures and properties; such that the dispersion of clay, droplet size of the compatibilizer, and tensile properties were distinctly dependent on the type of the compatibilizer. Compatibility between C25A, C30B, and E‐GMA resulted in the best level of dispersion, leading to the highest tensile modulus and toughness among the compositions studied. In the mentioned nanocomposites, a network structure was formed owing to the high reactivity of the epoxide group of GMA towards the PLA end groups resulting in high impact toughness. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 42553.

Polyamide 11/Clay Nanocomposite Using Polyhedral Oligomeric Silsesquioxane Surfactants

This paper reports polyamide 11 (PA11)/layered silicate (clay) nanocomposite using polyhedral oligomeric silsesquioxane (POSS) surfactants. POSS functionalized with amino, ammonium and guanidinium groups were synthesized and used to facilitate the intercalation of polymer chains between silicate layers thereby to improve the dispersion of clay in polymer matrix. Nanocomposites from the blends of POSS-modified clay and PA11 were thus formulated via melting compounding and their mechanical and physical properties were characterized.

Layered silicate nanocomposites based on recycled PET

Layered silicate nanocomposites based on recycled PET

Panoptically exfoliated morphology of chlorinated polyethylene (CPE)/ethylene methacrylate copolymer (EMA)/layered silicate nanocomposites by novel in situ covalent modification using poly(ε-caprolactone)

Exfoliated morphology of covalently modified Cloisite 20A and 30B leading to phenomenal mechanical and thermal properties of C60E40/layered silicates.