Effects of modified Clay on the morphology and thermal stability of PMMA/clay nanocomposites

The potential to improve the mechanical, thermal, and optical properties of poly(methyl methacrylate) (PMMA)/clay nanocomposites prepared with clay containing an organic modifier was investigated. Pristine sodium montmorillonite clay was modified using cocoamphodipropionate, which absorbs UVB in the 280–320 nm range, via ion exchange to enhance the compatibility between the clay platelets and the methyl methacrylate polymer matrix. PMMA/clay nanocomposites were synthesized via in situ free-radical polymerization. Three types of clay with various cation-exchange capacities (CEC) were used as inorganic layered materials in these organic–inorganic hybrid nanocomposites: CL42, CL120, and CL88 with CEC values of 116, 168, and 200 meq/100 g of clay, respectively. We characterized the effects of the organoclay dispersion on UV resistance, effectiveness as an O₂ gas barrier, thermal stability, and mechanical properties of PMMA/clay nanocomposites. Gas permeability analysis demonstrated the excellent gas barrier properties of the nanocomposites, consistent with the intercalated or exfoliated morphologies observed. The optical properties were assessed using UV–Visible spectroscopy, which revealed that these materials have good optical clarity, UV resistance, and scratch resistance. The effect of the dispersion capability of organoclay on the thermal properties of PMMA/clay nanocomposites was investigated by thermogravimetric analysis and differential scanning calorimetry; these analyses revealed excellent thermal stability of some of the modified clay nanocomposites.     

Studying the corrosion resistance and hydrolytic degradation of an epoxy coating containing ZnO nanoparticles

Epoxy nanocomposites containing different contents of Nano-ZnO particles were prepared. The nanocomposites were exposed to 3.5 wt% NaCl solution up to 60 days. Mechanical properties of the nanocomposites (before and after exposure to NaCl solution) were studied by dynamic mechanical thermal analysis (DMTA) and nano-indentation techniques. Fourier transform infrared spectroscopy (FTIR) was utilized to investigate hydrolytic degradation of coatings. Corrosion resistance of the composites was studied by an electrochemical impedance spectroscopy (EIS). Results showed that blank sample was severely deteriorated after exposure to corrosive electrolyte. Corrosion resistance of the epoxy coating was significantly improved using nanoparticles. The cross-linking density and indentation hardness of the blank sample were significantly decreased after exposure to corrosive electrolyte. Results showed that nanoparticles could significantly improve coating resistance against hydrolytic degradation. Results revealed that decrease in cross-linking density and indentation hardness of the epoxy coatings containing 3.5 and 5 wt% nanoparticles were not significant. Decrease in adhesion loss was also obtained using nanoparticles.     

Mechanical properties and water uptake of epoxy–clay nanocomposites containing different clay loadings

Nanocomposites based on diglycidyl ether of bisphenol A (DGEBA) epoxy reinforced with 1–10 wt% I.30E nanoclay were fabricated using high shear mixing technique and characterized to determine the effects of clay loading on their mechanical, thermal, and water uptake properties. The XRD and TEM analyses revealed that the structures of the resultant nanocomposites were a combination of disordered intercalated and exfoliated morphologies. Tensile strength increased for nanocomposite containing 1 % clay loading and decreased for higher nanoclay loading. Unlike strength, the stiffness increased almost linearly with clay loading, showing 46 % improvement in modulus of elasticity for nanocomposites containing 5 % of nanoclay. Water uptake measurements indicated enhancement in the barrier properties of epoxy matrix as nanoclay loading increased from 1 up to 5 wt%.     

Preparation and characterization of poly(methyl methacrylate)-clay nanocomposites via melt intercalation: Effect of organoclay on thermal, mechanical and flammability properties

The PMMA nanocomposites were prepared by melt processing method. The influence of organoclay loading on extent of intercalation, thermal, mechanical and flammability properties of poly(methyl methacrylate) (PMMA)-clay nanocomposites were studied. Three different organoclay modifiers with varying hydrophobicity (single tallow vs. ditallow) were investigated. The nanocomposites were characterized by using wide angle X-ray diffraction, transmission electron microscopy, thermogravimetric analysis, differential scanning calorimetry (DSC), and tensile tests. The intercalation of polymer chain within the silicate galleries was confirmed by WAXD and TEM. Mechanical properties such as tensile modulus (E), tensile strength, percentage elongation at break and impact strength were determined for nanocomposites at various clay loadings. Overall thermal stability of nanocomposites increased by 16-17 °C. The enhancement in T_g of nanocomposite is merely by 2-4 °C. The incorporation of maleic anhydride as compatibilizer further enhanced all the properties indicating improved interface between PMMA and clay. The flammability characteristics were studied by determining the rate of burning and LOI.     

Mechanical and thermal behavior of non-crimp glass fiber reinforced layered clay/epoxy nanocomposites

Mechanical and thermal properties of non-crimp glass fiber reinforced clay/epoxy nanocomposites were investigated. Clay/epoxy nanocomposite systems were prepared to use as the matrix material for composite laminates. X-ray diffraction results obtained from natural and modified clays indicated that intergallery spacing of the layered clay increases with surface treatment. Tensile tests indicated that clay loading has minor effect on the tensile properties. Flexural properties of laminates were improved by clay addition due to the improved interface between glass fibers and epoxy. Differential scanning calorimetry (DSC) results showed that the modified clay particles affected the glass transition temperatures (T_g) of the nanocomposites. Incorporation of surface treated clay particles increased the dynamic mechanical properties of nanocomposite laminates. It was found that the flame resistance of composites was improved significantly by clay addition into the epoxy matrix.     

Effect of NiLaxFe2−xO4 nanoparticles on the thermal and coating properties of epoxy resin composites

Epoxy resin has been modified with Ni–La–Fe–O nanoparticles in the form of NiLa_xFe_2−xO₄/epoxy nanocomposites to improve their coating properties. The new composites of different x composition (x = 0.00, 0.50, 1.00, 1.50 and 2.00) were synthesized in situ while epoxy resin was prepared by using a simple solution method with ultrasonic assistance. The new nanocomposites were characterized by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction analysis (XRD), thermogravemetric analysis (TGA) and scanning electron microscopy (SEM). The thermal degradation showed a more complicated behavior in the presence of Ni–Fe–La–O as shown by the presence of two maxima in the 300–475 °C temperature range. Reinforced composites with nanoparticles showed enhanced compressive coating properties. Ni–Fe formulations showed great promise to improve epoxy coating due to their higher barrier properties and ionic charge transfer resistance.     

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 10 wt.% 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.     

Effect of metal coating of reinforcements on the microstructure and mechanical properties of Al-Al2O3 nanocomposites

The effects of various methods of reinforcement modification on the microstructure and mechanical properties of Al–Al₂O₃ nanocomposites were investigated. Alumina nanoparticles were modified by electroless deposition of Cu, Ni and Co. Subsequently, aluminium matrix nanocomposites reinforced with uncoated and coated nanoparticles were produced by the stir casting method. The results of microstructural analysis showed improved wettability of coated nanoparticles in the molten aluminium alloy. Furthermore, coated nanoparticles exhibited a more desirable interface with the matrix and were homogenously distributed within it. The mechanical properties of the nanocomposites were improving significantly when coated nanoparticles were used as reinforcements. Among the reinforcement modification methods, Ni-coating was recognised as being more effective for improving the mechanical properties of Al–Al₂O₃ nanocomposites.     

Preparation and magnetic characterization of core–shell structure stainless steel/silica nanoparticles

SiO₂-coated martensite stainless steel nanoparticles were prepared using wire electrical explosion technique combined with sol–gel technique, and their structural and magnetic properties were studied. The coating silica on stainless steel nanoparticles was based on the use of silane coupling agent 3-mercaptopropyltrimethoxysilane (HS-(CH₂)₃Si(OCH₃)₃, MPTS) as a primer to render the stainless steel surface vitreophilic, thus rendering stainless steel surface compatible with silica. The control over the silica coating layer thickness can be achieved by varying the reaction time. For stainless steel nanoparticles, their saturation and remnant magnetizations decreased upon silica coating, and their saturation magnetizations obviously decreased with increasing the thickness of SiO₂ coating layer. These stainless steel/silica core–shell nanoparticles can be utilized as precursors for making property-tunable magnetic nanoparticles, thin films, and multilayered core–shell structure nanocomposites.     

A study on montmorillonite/polyethylene nanocomposite extrusion‐coated paperboard

Extrusion coating was used to obtain montmorillonite/polyethylene‐coated paperboard. The coating was prepared from a master batch containing maleated polyethylene, low‐density polyethylene and 32 wt.% polyvinylpyrrolidone‐surface‐modified montmorillonite clay, which was blended with different amounts of low‐density polyethylene to yield composites with 4 wt.% and 8.3 wt.% montmorillonite. X‐ray diffraction revealed that the clay stacks in the coating were more extensively intercalated than in the original surface‐modified clay. Transmission electron microscopy showed that the clay stacks were, to a large extent, separated by the high shear forces during extrusion into smaller evenly distributed entities. This was, unfortunately, achieved at the expense of the formation of a great many voids and pinholes, as revealed by transmission electron microscopy and dye staining. This had strong negative effects on the oxygen barrier properties but only a modest effect on the water vapour permeability. Tensile tests showed that the coating was always ductile and that the coating–paperboard adhesion decreased with increasing clay content. The creasability was good and unaffected by the presence of the filler in the coating. Thermogravimetry showed that the degradation temperature in air of the filled coatings were of the order of 10°C higher than that of unfilled polyethylene. Copyright © 2004 John Wiley & Sons, Ltd.     

Organophosphorus and DGEBA resins containing clay nanocomposites: flame retardant,thermal, and mechanical properties

Flame-retardant nanocomposites were prepared from diglycidylphenylphosphate (DGPP) and modified montmorillonite (MMT) clay blended with DGEBA in different ratio. T _g of all formulations increased with increasing clay content in the respective series while decreasing with increasing DGPP content. The TGA, LOI, and UL-94 data of all nanocomposites indicated that the materials were thermally stable with high flame retardancy resulting from synergetic effect of phosphorus and inorganic clay. The XRD analysis of the nanocomposites with 1 and 2% of clay indicated the intercalation of clay while rest of the samples displayed exfoliation at high clay content. As compared to neat epoxy system, a maximum increase of 59.3, 45.5, and 93% of tensile, flexural, and impact strengths were observed for the prepared nanocomposites. The SEM analysis of the failure surfaces of all DGPP containing samples showed rough with ridge patterns and river markings on the fracture surface that serves in improving the mechanical properties.     

Fracture toughness of zirconia nanoparticle-filled dental composites

The fracture toughness of dental composites containing zirconia nanoparticles dispersed in a bisphenol A glycol dimethacrylate-based monomer blend (GTE) was studied for several yttria contents. Three-point bend test bars with and without a notch were tested at ambient temperature to determine elastic modulus, flexure strength, and fracture toughness. The ZrO₂ nanoparticles increased the fracture toughness of the nanocomposites compared to previous results for the matrix and Schott glass-filled nanocomposites. X-ray diffraction analyses revealed mostly tetragonal ZrO₂ in the nanocomposites before and after testing, in agreement with a theoretical analysis. The enhancement in fracture toughness in ZrO₂-filled nanocomposites was caused mainly by the higher values of particle toughness and interface toughness in GTE/ZrO₂ compared to those of GTE/Schott glass nanocomposites.     

Studies on the oxygen barrier and mechanical properties of low density polyethylene/organoclay nanocomposite films in the presence of ethylene vinyl acetate copolymer as a new type of compatibilizer

Nanocomposite films based on low density polyethylene (LDPE), containing of 2, 3, and 4 wt.% organoclay (OC) and ethylene vinyl acetate (EVA) copolymer as a new compatibilizer were prepared and characterized using rheological tests, X-ray diffraction, differential scanning calorimetry, oxygen permeation measurements, and tensile tests. There was no exfoliation or intercalation of the clay layers in the absence of EVA, while an obvious increase in d-spacing was observed when the samples were prepared with EVA present. This issue was reflected in the properties of nanocomposites. The oxygen barrier properties of the LDPE/EVA/OC film were significantly better than those of the LDPE/OC film. The average aspect ratio of clay platelets in nanocomposites was determined from permeability measurements and using Lape–Cussler model. In addition to barrier properties, the LDPE/EVA/OC film also had better elastic modulus than their counterparts without EVA. The modulus reinforcement of nanocomposites was studied using Halpin–Tsai equations, which are universally used for composites reinforced by flake-like or rod-like fillers.     

The role of epoxy matrix occlusions within BaTiO3 nanoparticles on the dielectric properties of functionalized BaTiO3/epoxy nanocomposites

In this work, the effects of controlled nanoparticles aggregations of barium titanate (BaTiO₃) on the dielectric properties of epoxy nanocomposites are investigated in detail with respect to different experimental parameters like frequency, ceramic content and temperature. Dispersing silanized BaTiO₃ nanopowder under ultrasonic and stir, nanocomposites of epoxy-amine matrix with different morphologies are obtained. The nanoparticles silane functionalization containing amine end groups effectively improve the compatibility of the nano-BaTiO₃ and the epoxy matrix. Storage modulus, glass transition temperature, tensile and flexural properties of nanocomposites and dielectric properties are increased until 10% by weight of nano-BaTiO₃ loading, well dispersed in the matrix. Above 10 wt.% of nano-BaTiO₃, scanning electronic microscopy and thermal analysis showed that agglomeration of nanoparticles occurs. Rheological and mechanical nanocomposites properties were evaluated and matrix occlusion behaviors were identified. In light of the specific behavior of the occluded polymer, the dielectric properties, especially dielectric loss are discussed.     

Effect of Nano Clay on Corrosion Protection of Zinc-rich Epoxy Coatings on Steel 37

Epoxy zinc rich coatings containing clay nanoparticles were prepared and the effect of clay content on the cathodic protection performance of the coatings was evaluated by electrochemical impedance spectroscopy(EIS) and immersion test. Open circuit potential(OCP) measurements and immersion tests were also carried out to better understand the behavior of zinc rich coating. EIS and OCP measurements showed that addition of 1 wt% clay improved the cathodic protection duration and sacrificial properties of the epoxy zinc rich coating. Transmission electron microscopy(TEM) photographs confirmed that clay nanoparticles were successfully dispersed in the coating matrix loaded with 1 wt% clay. Immersion test results indicated that addition of 1 wt% clay nanoparticles in zinc rich epoxy coatings increased the cathodic protection ability of coatings.     

Preparation and characterization of nickel/zinc sulphide: Bifunctional magnetic-optical nanocomposites

Nickel nanoparticles coated with zinc sulphide can form complex spherical with a core–shell structure. This coating process was based on mercaptoacetic acid (HSCH₂COOH) as a primer to render the nickel surface vitreophilic, thus it renders nickel surface compatible with ZnS. The morphology, structure, chemical composition, optical properties and magnetic properties of the product were investigated by using various techniques, including transmission electron microscopy (TEM), X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDS), photoluminescence (PL) spectroscope and vibrating sample magnetometer (VSM). It was found that the Ni/ZnS nanocomposites exhibited both magnetic and photoluminescent properties.     

Polyethylene organo-clay nanocomposites: the role of the interface chemistry on the extent of clay intercalation/exfoliation

High density polyethylene (HDPE)/clay nanocomposites have been prepared using three different functionalized polyethylene compatibilizers: an ethylene/vinyl acetate copolymer, a polyethylene grafted with maleic anhydride functions and a (styrene-b-ethylene/butylene-b-styrene) block copolymer. The nanocomposites were prepared via two different routes: (1) the dispersion in HDPE of a masterbatch prepared from the compatibilizer and the clay or (2) the direct melt blending of the three components. For each compatibilizer, essentially intercalated nanocomposites were formed as determined by X-ray diffraction and transmission electron microscopy. With the ethylene/vinyl acetate copolymer, a significant delamination of the intercalated clay in thin stacks was observed. This dispersion of thin intercalated stacks within the polymer matrix allowed increasing significantly the stiffness and the flame resistance of the nanocomposite. A positive effect of shear rate and blending time has also been put into evidence, especially for the process based on the masterbatch preparation, improving both the formation of thin stacks of intercalated clay and the mechanical properties and the flame resistance of the formed nanocomposites.     

Improvement of epoxy resin properties by incorporation of TiO2 nanoparticles surface modified with gallic acid esters

Epoxy resin/titanium dioxide (epoxy/TiO₂) nanocomposites were obtained by incorporation of TiO₂ nanoparticles surface modified with gallic acid esters in epoxy resin. TiO₂ nanoparticles were obtained by acid catalyzed hydrolysis of titanium isopropoxide and their structural characterization was performed by X-ray diffraction and transmission electron microscopy. Three gallic acid esters, having different hydrophobic part, were used for surface modification of the synthesized TiO₂ nanoparticles: propyl, hexyl and lauryl gallate. The gallate chemisorption onto surface of TiO₂ nanoparticles was confirmed by Fourier transform infrared and ultraviolet–visible spectroscopy, while the amount of surface-bonded gallates was determined using thermogravimetric analysis. The influence of the surface modified TiO₂ nanoparticles, as well as the length of hydrophobic part of the gallate used for surface modification of TiO₂ nanoparticles, on glass transition temperature, barrier, dielectric and anticorrosive properties of epoxy resin was investigated by differential scanning calorimetry, water vapor transmission test, dielectric spectroscopy, electrochemical impedance spectroscopy and polarization measurements. Incorporation of surface modified TiO₂ nanoparticles in epoxy resin caused increase of glass transition temperature and decrease of the water vapor permeability of epoxy resin. The water vapor transmission rate of epoxy/TiO₂ nanocomposites was reduced with increasing hydrophobic part chain length of gallate ligand. Dielectric constant of examined nanocomposites was influenced by gallate used for the modification of TiO₂ nanoparticles. The nanocomposites have better anticorrosive properties than pure epoxy resin, because the surface modified TiO₂ nanoparticles react as oxygen scavengers, which inhibit steel corrosion by cathodic mechanism.     

Biodegradable polyurethane nanocomposites containing dexamethasone for ocular route

The treatment of posterior segment ocular diseases, such as uveitis, by using eye drops and oral drugs is usually not effective due to the body's natural barriers to drug penetration. In this study, ocular implants to treat uveitis were synthesized by incorporating dexamethasone acetate, an important type of corticoid used in the treatment of some uveitis, into a biodegradable polyurethane containi clay nanoparticles. Biodegradable polyurethane nanocomposites having poly(caprolactone) oligomers as soft segments were obtained by delaminating clay particles within a polyurethane aqueous dispersion. The drug was incorporated into the polymer by dispersing it in the waterborne polyurethane followed by a drying step. Nanoparticles derived from clay were demonstrated to be able to tailor the mechanical properties of polyurethanes to achieve values that can match the properties of ocular soft tissues. Infrared spectra (FTIR) showed that the presence of clay particles was able to change the microphase separation process typical of polyurethanes. X-ray diffraction and small angle x-ray scattering (SAXS) results were explored to show that the incorporation of both dexamethasone acetate and nanocomponents derived from clay led to a less defined two-phase polyurethane. The presence of clay nanoparticles increased the rate of drug release measured in vitro. Human retinal pigment epithelial cells (ARPE-19) were cultured in contact with polyurethanes and polyurethane nanocomposites, and the viability of them (evaluated by using MTT assay after 7 days) showed that no toxic components were released from polyurethanes containing no drugs during the test.     

Nanocomposites of poly(ε-caprolactone) doped with titanium species

Organic–inorganic hybrid nanocomposites were prepared via in situ sol–gel process. The organic phase is a biodegradable polymer, poly(ε-caprolactone) (PCL), while the tetrabutyl titanate (TBT, Ti(OBu)₄) was used as inorganic precursor. Synthesis parameters like acidity medium and precursor amount were investigated in order to assess their influence on hybrid properties. The obtained nanocomposites were characterised by thermal analysis, spectroscopic techniques, transmission electronic microscopy (TEM) and X-ray diffraction to gather information on the structure of the nanocomposites. Mechanical properties and biodegradability were also evaluated. A reaction mechanism based on Fourier transform infrared spectroscopy and NMR results was proposed using methyl acetate as model compound. TEM micrographs of the nanocomposites show a fine good nanoparticles dispersion. Acidic conditions and 10 wt% of precursor lead to a nanocomposite with higher mechanical properties and biodegradability than PCL.