Epoxy-Layered Silicate Nanocomposites and Their Gas Permeation Properties

Preparation of Polyanionic Cellulosic Microparticles with Antioxidant Capacity by Introducing Sulphurous Acid Groups onto Cellulose

In this work, we presented a facile pathway to fabricate polyanionic cellulosic microparticles by selective oxidation with sodium periodate firstly, followed by grafting sodium bisulfite to the 2,3-dialdehyde cellulose particles. The obtained polyanionic cellulosic microparticles with the particle size of 2-4 μm had increased stability in water, and it had pH responsiveness. Moreover, the polyanionic cellulosic microparticles had excellent film-forming property, and the tensile strength of the film formed from pristine cellulose particles was about 40 MPa, and it increased to 64 MPa for the film formed from SRC-50 particles. Furthermore, the polyanionic cellulosic microparticles had certain reduction ability, and it could be used as coating to cover the surface of fruits or vegetables, and it could prevent the discoloration of the fresh-cut potato. The cellulose based particle coating with excellent antibrowning capacity, biocompatible, and environmentally friendly characteristics would be attractive for the applications in packaging material for food preservation.

Preparation of Montmorillonite Nanosheets through Freezing/Thawing and Ultrasonic Exfoliation

The exfoliation of layered montmorillonite (MMT) into mono- or few-layer sheets is of significance for both fundamental studies and potential applications. In this report, exfoliated MMT nanosheets with different aspect ratios have been prepared via a new freezing/thawing-ultrasonic exfoliation method. Freezing/thawing processing can exfoliate MMT tactoids with low efficiency while virtually retaining the original lateral size. The ultrasonic method has better exfoliation efficiency but tends to damage the nanosheets. By combining them and reasonably controlling the cycle index of freezing/thawing and ultrasonic power, the MMT nanosheets with different aspect ratios have been prepared efficiently. Such a unique exfoliation method has broad applicability for layered materials to produce monolayer nanosheets on a large scale.

DISPERSION OF NANOCLAY IN 1,4-POLYBUTADIENE

Two approaches to obtaining better dispersion of organo-modified nanoclay in high-molecular weight polybutadiene were assessed: (1) chemical modification of the polymer to increase its affinity for the silicate layers and (2) increasing the stretching component of the flow field used to mix the materials. As expected, the degree of dispersion, that is, the extent of intercalation of the polymer into the clay galleries and amount of exfoliation of the clay layers, increased with closer matching of the respective solubility parameters of the components. The efficiency of mechanical mixing was greater for flow fields dominated by stretching (extensional flow); less mix energy had to be expended to achieve a given level of reinforcement. However, without sufficient affinity of the polymer for the clay, complete exfoliation could not be obtained solely by mixing. Nevertheless, incomplete dispersion of the nanoclay still yields more than 40-fold increases in viscosity with 5% clay.

Development of Clay-Based Films

Phyllosilicate (clay) is used as a filler to improve the thermal stability and gas barrier properties of plastic films. However, few film preparation trials used clays as the main component. Many researchers have studied clay-based films (CBFs) that are heat-resistant and have high gas barrier properties against various gases (such as oxygen, water vapor, and hydrogen) over a wide range of temperatures. An organic binder improves the film toughness, but increases gas permeation. CBFs are obtained by solution casting and show excellent incombustibility and electrical insulation. Moreover, transparent films, e. g. for optoelectronic applications, can be prepared using synthetic clay, which does not contain colored impurities. The water vapor barrier properties of CBFs were achieved using reduced-charge smectite. Applications of CBF materials include food packaging, solar cell back sheets, hydrogen tanks, gaskets, water vapor barrier display films, substrates for printed electronics, thermal insulation, and electric insulation. Recent achievements in the field and future prospects are discussed.

Spray-coated epoxy barrier films containing high aspect ratio functionalized graphene nanosheets

Epoxy nanocomposite spray-coatings containing large aspect ratio modified graphene (MG) were successfully prepared in a facile manner.

Gas barrier properties of polymer/clay nanocomposites

The state-of-the-art progress on the use of clay for the gas barrier properties of polymer nanocomposites have been summarized.

Polystyrene/Phosphonium Organoclay Nanocomposites by Melt Compounding

Polystyrene-montmorillonite nanocomposites were prepared by melt compounding, using several ammonium and phosphonium organoclays. Melt processing was carried out in a twin screw extrusion system, specially modified to produce improved dispersion and longer residence time. The effect of molecular weight of polystyrene on clay dispersion and property enhancement was evaluated. Nanocomposite structure was characterized by wide angle x-ray diffraction (WAXD) and transmission electron microscopy (TEM). Thermal stability and mechanical and barrier properties were also determined. The quality of dispersion of organically modified montmorillonite depended on the molecular weight of the polystyrene resin. Barrier properties were measured and compared to predictions of permeability models available in the literature. Clay dispersion and property enhancement were explained in relation to the surface characteristics of the organoclays, and the work of adhesion at the polystyrene-clay interface was correlated with the tensile modulus of the nanocomposites.

Effect of Attapulgite Nanorods and Calcium Sulfate Microwhiskers on the Reaction-Induced Phase Separation of Epoxy/PES Blends

The influence of two kinds of mesoscale inorganic rod fillers, nanoscale attapulgite and micron-sized CaSO4whisker, on the reaction-induced phase separation of epoxy/aromatic amine/poly- (ether sulfone) (PES) blends has been investigated by optical microscopy (OM), scanning electron microscopy (SEM), and time resolved light scattering (TRLS). By varying the PES concentration and curing temperature, we found that the incorporation of attapulgite and CaSO4had dramatic impact on the phase separation process and the final phase morphology of blends. In blends at higher content than critical concentration, the process of phase separation was retarded by the incorporation of nanoscale fillers but accelerated by that of the micron-sized fillers, mainly due to the enhanced viscoelastic effect and the preferential wettable effect, respectively. Meanwhile both mesoscale fillers could change the cocontinuous phase structure of blends with lower PES content than critical concentration into PES-rich dispersed structure due to the surface affinity of fillers to epoxy matrix.

High strength, flexible and transparent nanofibrillated cellulose-nanoclay biohybrid films with tunable oxygen and water vapor permeability

A novel, technically and economically benign procedure to combine vermiculite nanoplatelets with nanocellulose fibre dispersions into functional biohybrid films is presented. Nanocellulose fibres of 20 nm diameters and several micrometers in length are mixed with high aspect ratio exfoliated vermiculite nanoplatelets through high-pressure homogenization. The resulting hybrid films obtained after solvent evaporation are stiff (tensile modulus of 17.3 GPa), strong (strength up to 257 MPa), and transparent. Scanning electron microscopy (SEM) shows that the hybrid films consist of stratified nacre-like layers with a homogenous distribution of nanoplatelets within the nanocellulose matrix. The oxygen barrier properties of the biohybrid films outperform commercial packaging materials and pure nanocellulose films showing an oxygen permeability of 0.07 cm(3) μm m(-2) d(-1) kPa(-1) at 50% relative humidity. The oxygen permeability of the hybrid films can be tuned by adjusting the composition of the films. Furthermore, the water vapor barrier properties of the biohybrid films were also significantly improved by the addition of nanoclay. The unique combination of excellent oxygen barrier behavior and optical transparency suggests the potential of these biohybrid materials as an alternative in flexible packaging of oxygen sensitive devices such as thin-film transistors or organic light-emitting diode displays, gas storage applications and as barrier coatings/laminations in large volume packaging applications.

Influence of clay concentration on the gas barrier of clay-polymer nanobrick wall thin film assemblies

The influence of the clay deposition suspension concentration on gas barrier thin films of sodium montmorillonite (MMT) clay and branched polyethylenimine (PEI), created via layer-by-layer assembly, was investigated. Films grown with MMT suspension concentrations ranging from 0.05 to 2.0 wt % were analyzed for their growth as a function of deposited polymer-clay bilayers (BL) and their thickness, clay concentration, transparency, nanostructure, and oxygen barrier as a function of the suspension concentration. The film thickness doubles and the visible light transmission decreases less than 5% as a function of MMT concentration for 20-BL films. Atomic force and transmission electron microscope images reveal a highly aligned nanobrick wall structure, with quartz crystal microbalance measurements revealing a slight increase in the film clay concentration as the MMT suspension concentration increases. The oxygen transmission rate (OTR) through these 20-BL composites, deposited on a 179 μm poly(ethylene terephthalate) film, decreases exponentially as a function of the MMT clay concentration. A 24-BL film created with 2.0 wt % MMT has an OTR below the detection limit of commercial instrumentation (<0.005 cc/m(2)·day·atm). This study demonstrates an optimal clay suspension concentration to use when creating LbL barrier films, which minimizes deposition steps and the overall processing time.

Exploring the structure of inter-platelet galleries in organically modified montmorillonite using the small-angle X-ray scattering interface distribution function approach

Small-angle X-ray scattering interface distribution function (IDF) analysis is successfully applied to evaluate the two- and three-phase inter-platelet gallery structure in synthetic montmorillonite (MMT) modified with a mixture of chemically grafted and physically adsorbed chains of a typical organic modifier, octadecyl trimethyl ammonium bromide. Two distinctly different states of adsorbed chains in the inter-platelet galleries are identified. The first one corresponds to a fully cation-exchanged structure with an inter-platelet distance of about 21 Å. In this case the organic modifier is in a liquid-like state, and the system does not exhibit any structural or thermal transitions between ambient temperature and 433 K. When the number of adsorbed chains exceeds the cation-exchange capacity of the MMT platelets the inter-platelet spacing is increased to 43 Å. In this case, the variable-temperature IDFs reveal partially crystalline order in the inter-platelet galleries, which vanishes at the melting point of the alkyl tails confined in the galleries.

Super gas barrier of transparent polymer-clay multilayer ultrathin films

Flexible and transparent polymeric "superbarrier" packaging materials have become increasingly important in recent years. Layer-by-layer assembly offers a facile technique for the fabrication of layered, polymer-clay superbarrier thin films. At only 51 nm thick, these nanocomposite thin films, comprised of 12 polymer and 4 clay layers, exhibit an oxygen permeability orders of magnitude lower than EVOH and SiOx. Coupling high flexibility, transparency, and barrier protection, these films are good candidates for a variety packaging applications.

Polymer Nanocomposites in Emulsion and Suspension: an Overview

Polymer nanocomposites have been a subject of intense research in the recent yeas. By nanoscale dispersion of inorganic fillers in the polymer matrices, significant enhancements in the properties of the materials have been achieved at very low filler volume fractions. Different modes of nanocomposite synthesis have been developed in the recent years which include template synthesis, in-situ polymerization, melt intercalation and polymer or prepolymer adsorption from solution. The last methodology also covers emulsion and suspension polymerization techniques for the synthesis of nanocomposites. These emulsion and suspension modes of polymer nanocomposite synthesis have the advantage that the polymerization is carried out in the presence of water which does not allow buildup of viscosity and the heat dissipation from the system is also easily achieved. The potential thermal damage to the polymer and the organic modification usually encountered in the melt intercalation is also avoided in the case of emulsion and suspension polymerization. Different polymer systems have been reported like polystyrene, polyurethanes, epoxy, poly(methyl methacrylate), poly(N-isopropylacrylamide), poly(butyl acrylate) etc. Specific synthetic methodologies like surfactant free polymerization, controlled living polymerization etc. have also been reported to successfully achieve nanocomposites with superior properties than the pure polymers. Majority of the studies bring home the conclusion that the amount of clay as well as surface modification present on clay surface significantly affect the microstructure and properties of the nanocomposite particles. Apart from clay as filler, many studies also have used the spherical inorganic particles as reinforcements.

Polymer Layered Silicate Nanocomposites: A Review

This review aims to present recent advances in the synthesis and structure characterization as well as the properties of polymer layered silicate nanocomposites. The advent of polymer layered silicate nanocomposites has revolutionized research into polymer composite materials. Nanocomposites are organic-inorganic hybrid materials in which at least one dimension of the filler is less than 100 nm. A number of synthesis routes have been developed in the recent years to prepare these materials, which include intercalation of polymers or pre-polymers from solution, in-situ polymerization, melt intercalation etc. The nanocomposites where the filler platelets can be dispersed in the polymer at the nanometer scale owing to the specific filler surface modifications, exhibit significant improvement in the composite properties, which include enhanced mechanical strength, gas barrier, thermal stability, flame retardancy etc. Only a small amount of filler is generally required for the enhancement in the properties, which helps the composite materials retain transparency and low density.

A critical appraisal of polymer-clay nanocomposites

The surge of interest in and scientific publications on the structure and properties of nanocomposites has made it rather difficult for the novice to comprehend the physical structure of these new materials and the relationship between their properties and those of the conventional range of composite materials. Some of the questions that arise are: How should the reinforcement volume fraction be calculated? How can the clay gallery contents be assessed? How can the ratio of intercalate to exfoliate be found? Does polymerization occur in the clay galleries? How is the crystallinity of semi-crystalline polymers affected by intercalation? What role do the mobilities of adsorbed molecules and clay platelets have? How much information can conventional X-ray diffraction offer? What is the thermodynamic driving force for intercalation and exfoliation? What is the elastic modulus of clay platelets? The growth of computer simulation techniques applied to clay materials has been rapid, with insight gained into the structure, dynamics and reactivity of polymer-clay systems. However these techniques operate on the basis of approximations, which may not be clear to the non-specialist. This critical review attempts to assess these issues from the viewpoint of traditional composites thereby embedding these new materials in a wider context to which conventional composite theory can be applied. (210 references).

Esterification reactions on the surface of layered silicate clay platelets

Montmorillonite platelets were modified with ammonium ions of different chemical architectures in order to study the effect of ammonium ions on the extent of surface reactions with long chain fatty acids. Varying number of hydroxyl groups and the presence of octadecyl chains in the ammonium modifications were the attributes studied. The outcome of the surface esterification was analyzed by thermogravimetric studies, IR spectroscopy and wide angle X-ray diffraction. The extent of surface reaction was observed to be extremely dependent on the chemical architecture of the ammonium ion attached to the surface. Different resulting interlayer polarity and swelling of the modified clay in the solvent owing to the solvent-modification interactions led to different extents of surface esterification. In general, it was observed that increasing the number of hydroxyl groups in combination with the octadecyl chain present in the modification was successful in generating high density brushes on the clay surface which also was responsible for achieving higher basal plane spacing of the montmorillonite platelets owing to the reduction of electrostatic interactions holding them.