Bio-based polymer nanocomposites based on nylon 11 and WS2 inorganic nanotubes

Tungsten disulphide nanotubes (INT-WS2) have been successfully dispersed in a bio-based polyamide matrix (nylon 11) by conventional melt processing. The effect of INT-WS2 content on the morphology, thermal stability, crystallization behaviour and dynamic mechanical properties is investigated. The results indicate that these inorganic nanotubes can be efficiently incorporated into the bio-based polymer matrix without the need for modifiers or surfactants. Additionally, it is found that the non-isothermal crystallization behaviour of nylon 11/INT-WS2 depends on both the cooling rate and INT-WS2 concentration. In particular, crystallization kinetics results demonstrate that the nucleating activity of INTs plays a dominant role in accelerating the crystallization of nylon 11. This fact leads to the appearance of the more-disordered phase at higher temperature. More significantly, it was shown that these INT-WS2 nanocomposites can facilitate a good processability and cost efficiency, and will be of interest for many eco-friendly and medical applications.

Fluctuating silicate:nitrate ratios and coastal plankton food webs

Marine diatoms require dissolved silicate to form an external shell, and their growth becomes Si-limited when the atomic ratio of silicate to dissolved inorganic nitrogen (Si:DIN) approaches 1:1, also known as the “Redfield ratio.” Fundamental changes in the diatom-to-zooplankton-to-higher trophic level food web should occur when this ratio falls below 1:1 and the proportion of diatoms in the phytoplankton community is reduced. We quantitatively substantiate these predictions by using a variety of data from the Mississippi River continental shelf, a system in which the Si:DIN loading ratio has declined from around 3:1 to 1:1 during this century because of land-use practices in the watershed. We suggest that, on this shelf, when the Si:DIN ratio in the river decreases to less than 1:1, then (i) copepod abundance changes from >75% to <30% of the total mesozooplankton, (ii) zooplankton fecal pellets become a minor component of the in situ primary production consumed, and (iii) bottom-water oxygen consumption rates become less dependent on relatively fast-sinking (diatom-rich) organic matter packaged mostly as zooplankton fecal pellets. This coastal ecosystem appears to be a pelagic food web dynamically poised to be either a food web composed of diatoms and copepods or one with potentially disruptive harmful algal blooms. The system is directed between these two ecosystem states by Mississippi River water quality, which is determined by land-use practices far inland.

Constraints on nebular dynamics and chemistry based on observations of annealed magnesium silicate grains in comets and in disks surrounding Herbig Ae/Be stars

Understanding dynamic conditions in the Solar Nebula is the key to prediction of the material to be found in comets. We suggest that a dynamic, large-scale circulation pattern brings processed dust and gas from the inner nebula back out into the region of cometesimal formation—extending possibly hundreds of astronomical units (AU) from the sun—and that the composition of comets is determined by a chemical reaction network closely coupled to the dynamic transport of dust and gas in the system. This scenario is supported by laboratory studies of Mg silicates and the astronomical data for comets and for protoplanetary disks associated with young stars, which demonstrate that annealing of nebular silicates must occur in conjunction with a large-scale circulation. Mass recycling of dust should have a significant effect on the chemical kinetics of the outer nebula by introducing reduced, gas-phase species produced in the higher temperature and pressure environment of the inner nebula, along with freshly processed grains with “clean” catalytic surfaces to the region of cometesimal formation. Because comets probably form throughout the lifetime of the Solar Nebula and processed (crystalline) grains are not immediately available for incorporation into the first generation of comets, an increasing fraction of dust incorporated into a growing comet should be crystalline olivine and this fraction can serve as a crude chronometer of the relative ages of comets. The formation and evolution of key organic and biogenic molecules in comets are potentially of great consequence to astrobiology.

Influence of thymol and silver nanoparticles on the degradation of poly(lactic acid) based nanocomposites: thermal and morphological properties

Biopolymers, such as poly(lactic acid) (PLA), have been proposed as environmentally-friendly alternatives in applications such as food packaging. In this work, silver nanoparticles and thymol were used as active additives in PLA matrices, combining the antibacterial activity of silver with the antioxidant performance of thymol. The combined action of both additives influenced PLA thermal degradation in ternary systems. DSC results showed that the addition of thymol resulted in a clear decrease of the glass transition temperature (Tg) of PLA, suggesting its plasticizing effect in PLA matrices. Slight modifications in mechanical properties of dog-bone bars were also observed after the addition of the active components, especially in the elastic modulus. FESEM analyses showed the good distribution of active additives through the PLA matrix, obtaining homogenous surfaces and highlighting the presence of silver nanoparticles successfully embedded into the bulk matrix. Degradation of these PLA-based nanocomposites with thymol and silver nanoparticles in composting conditions indicated that the inherent biodegradable character of this biopolymer was improved after this modification. The obtained nanocomposites showed suitable properties to be used as biodegradable active-food packaging systems with antioxidant and antimicrobial effects.

Characterization of Poly(ε-caprolactone)-Based Nanocomposites Containing Hydroxytyrosol for Active Food Packaging

Antioxidant nano-biocomposites based on poly(ε-caprolactone) (PCL) were prepared by incorporating hydroxytyrosol (HT) and a commercial montmorillonite, Cloisite®30B (C30B), at different concentrations. A full structural, thermal, mechanical and functional characterization of the developed nano-biocomposites was carried out. The presence of the nanoclay and HT increased PCL crystallinity, whereas some decrease in thermal stability was observed. TEM analyses corroborated the good dispersion of C30B into the PCL macromolecular structure as already asserted by XRD tests, since no large aggregates were observed. A reduction in oxygen permeability and increase in elastic modulus were obtained for films containing the nanoclay. Finally, the presence of the nanoclay produced a decrease in the HT release from films due to some interaction between HT and C30B. Results proved that these nano-biocomposites can be an interesting and environmentally-friendly alternative for active food packaging applications with antioxidant performance.

Effect of the intercalated cation-exchanged on the properties of nanocomposites prepared by 2-aminobenzene sulfonic acid with aniline and montmorillonite

Polymer/montmorillonite nanocomposites were prepared. Intercalation of 2-aminobenzene sulfonic acid with aniline monomers into montmorillonite modified by cation was followed by subsequent oxidative polymerization of monomers in the interlayer spacing. The clay was prepared by cation exchange process between sodium cation in (M–Na) and copper cation (M–Cu). XRD analyses show the manifestation of a basal spacing (d-spacing) for M–Cu changes depending on the inorganic cation and the polymer intercalated in the M–Cu structure. TGA analyses reveal that polymer/M–Cu composites is less stable than M–Cu. The conductivity of the composites is found to be 103 times higher than that for M–Cu. The microscopic examinations including TEM picture of the nanocomposite demonstrated an entirely different and more compatible morphology. Remarkable differences in the properties of the polymers have also been observed by UV–Vis and FTIR, suggesting that the polymer produced with presence of aniline has a higher degree of branching. The electrochemical behavior of the polymers extracted from the nanocomposites has been studied by cyclic voltammetry which indicates the electroactive effect of nanocomposite gradually increased with aniline in the polymer chain.

Electrocatalytic Performance of SiO2-SWCNT Nanocomposites Prepared by Electroassisted Deposition

Composite materials made of porous SiO2 matrices filled with single-walled carbon nanotubes (SWCNTs) were deposited on electrodes by an electroassisted deposition method. The synthesized materials were characterized by several techniques, showing that porous silica prevents the aggregation of SWCNT on the electrodes, as could be observed by transmission electron microscopy and Raman spectroscopy. Different redox probes were employed to test their electrochemical sensing properties. The silica layer allows the permeation of the redox probes to the electrode surface and improves the electrochemical reversibility indicating an electrocatalytic effect by the incorporation of dispersed SWCNT into the silica films.

Polyaniline/Montmorillonite Nanocomposites Obtained by In Situ Intercalation and Oxidative Polymerization in Cationic Modified-Clay (Sodium, Copper and Iron)

Polyaniline/montmorillonite nanocomposites (PANI/M) were obtained by intercalation of aniline monomer into M modified with different cations and subsequent oxidative polymerization of the aniline. The modified-clay was prepared by ion exchange of sodium, copper and iron cations in the clay (Na–M, Cu–M and Fe–M respectively). Infrared spectroscopy confirms the electrostatic interaction between the oxidized PANI and the negatively charged surface of the clay. X-ray diffraction analysis provides structural information of the prepared materials. The nanocomposites were characterized by transmission electron microscopy and their thermal degradation was investigated by thermogravimetric analysis. The weight loss suggests that the PANI chains in the nanocomposites have higher thermal stability than pure PANI. The electrical conductivity of the nanocomposites increased between 12 and 24 times with respect to the pure M and this increase was dependent on the cation-modification. The electrochemical behavior of the polymers extracted from the nanocomposites was studied by cyclic voltammetry and a good electrochemical response was observed.

Clay-supported graphene materials: application to hydrogen storage

The present work refers to clay–graphene nanomaterials prepared by a green way using caramel from sucrose and two types of natural clays (montmorillonite and sepiolite) as precursors, with the aim of evaluating their potential use in hydrogen storage. The impregnation of the clay substrates by caramel in aqueous media, followed by a thermal treatment in the absence of oxygen of these clay–caramel intermediates gives rise to graphene-like materials, which remain strongly bound to the silicate support. The nature of the resulting materials was characterized by different techniques such as XRD, Raman spectroscopy and TEM, as well as by adsorption isotherms of N2, CO2 and H2O. These carbon–clay nanocomposites can act as adsorbents for hydrogen storage, achieving, at 298 K and 20 MPa, over 0.1 wt% of hydrogen adsorption excess related to the total mass of the system, and a maximum value close to 0.4 wt% of hydrogen specifically related to the carbon mass. The very high isosteric heat for hydrogen sorption determined from adsorption isotherms at different temperatures (14.5 kJ mol−1) fits well with the theoretical values available for hydrogen storage on materials that show a strong stabilization of the H2 molecule upon adsorption.

The influence of surfactant loading level in a montmorillonite on the thermal, mechanical and rheological properties of EVA nanocomposites

In this work, montmorillonite (Mt) has been organically modified with ethyl hexadecyl dimethyl ammonium (EHDDMA) in 20, 50, 80 and 100% of the nominal exchange capacity (CEC) of the Mt. A full characterization of the organo-montmorillonite (OMt) obtained has been made, including thermal analysis, X-Ray Diffraction, elemental analysis CHN and nitrogen adsorption. According to the results, 12% in mass of the surfactant added is strongly retained by the Mt. When the mass percentage of EHDDMA exchanged in the OMt is increased up to this level, the interactions OMt–EHDDMA are steeply reduced depending on the EHDDMA content. Clay polymer nanocomposites (CPN) were prepared by melt mixing of EVA and different loads of OMt. The CPN were compress molded to obtain 1 mm thick sheets, which have been characterized according to their mechanical, thermal and rheological behaviors. The major changes in the structure of the OMt are obtained for low contents of EHDDMA. Nevertheless, the CPN containing OMt exchanged at 20 and 50% of the CEC show relatively low effect of the EHDDMA while the mechanical response and rheological behavior of CPN with OMt modified at 80 and 100% of the CEC are much more pronounced.

Processing and Characterization of Nano-biocomposites Based on Mater-Bi® with Layered Silicates

The development of new nano-biocomposites has been one of the main research areas of interest in polymer science in recent years, since they can combine the intrinsic biodegradable nature of matrices with the ability to modify their properties by the addition of selected nano-reinforcements. In this work, the addition of mineral nanoclays (montmorillonites and sepiolites) to a commercial starch-based matrix is proposed. A complete study on their processing by melt-intercalation techniques and further evaluation of the main properties of nano-biocomposites has been carried out. The results reported show an important influence of the nano-biocomposites morphology on their final properties. In particular, the rheological and viscoelastic characteristics of these systems are very sensitive to the dispersion level of the nanofiller, but it is possible to assess that the material processing behaviour is not compromised by the presence of these nano-reinforcements. In general, both nanofillers had a positive influence in the materials final properties. Mechanical performance shows improvements in terms of elastic modulus, without important limitations in terms of ductility. Thermal properties are improved in terms of residual mass after degradation and low improvements are also observed in terms of oxygen barrier properties.

Development of exfoliated layered stannosilicate for hydrogen adsorption

The use of hydrogen as an energy vector leads to the development of materials with high hydrogen adsorption capacity. In this work, a new layered stannosilicate, UZAR-S3, is synthesized and delaminated, producing UZAR-S4. UZAR-S3, with the empirical formula Na4SnSi5O14·3.5H2O and lamellar morphology, is a layered stannosilicate built from SnO6 and SiO4 polyhedra. The delamination process used here comprises three stages: protonation with acetic acid, swelling with nonylamine and the delamination itself with an HCl/H2O/ethanol solution. UZAR-S4 is composed of sheets a few nanometers thick with a high aspect ratio and a surface area of 236 m2/g, twenty times higher than that of UZAR-S3. At −196 °C for UZAR-S4, H2 adsorption reached remarkable values of 3.7 and 4.2 wt% for 10 and 40 bar, respectively, the latter value giving a high volumetric H2 storage capacity of 26.2 g of H2/L.

Synthesis, Characterization and Conducting Properties of Nanocomposites of Intercalated 2-Aminophenol with Aniline in Sodium-Montmorillonite

A simple method was used to synthesize poly(2-aminophenol), poly(2-aminophenol-co-Aniline) and polyaniline nanocomposites with sodium-montmorillonite (Na-M) using in situ intercalative oxidative polymerization. Morphology and thermal properties of the synthesized nanocomposites were examined by transmission electron microscopy (TEM) and thermogravimetric analysis. The thermal analysis shows an improved thermal stability of the nanocomposites in comparison with the pure poly(2-aminophenol). The intercalation of polymers into the clay layers was confirmed by X-ray diffraction studies, TEM images and FTIR spectroscopy. In addition, the room temperature conductivity values of these nanocomposites varied between 8.21 × 10−5 and 6.76 × 10−4 S cm−1. The electrochemical behavior of the polymers extracted from the nanocomposites, has been analyzed by cyclic voltammetry. Good electrochemical response has been observed for polymer films; the observed redox processes indicate that the polymerization into Na-M produces electroactive polymers.

Characterisation of montmorillonites simultaneously modified with an organic dye and an ammonium salt at different dye/salt ratios. Properties of these modified montmorillonites EVA nanocomposites

In this work, a sodium montmorillonite (Na+-Mt) was modified with two molecules simultaneously, an organic dye, methylene blue (MB), and ethyl hexadecyl dimethyl ammonium (EHDDMA). The synthesised organo-montmorillonites (OMt) combining different proportions of the two molecules were thoroughly characterised and mixed with ethylene vinyl acetate copolymer (EVA) in order to check the ability of these OMt as pigments and reinforcing additives. The synthesised OMt combining both surfactants, MB and EHDDMA, present higher interlayer distances than those with only MB, which were employed in previous works as nanopigments. When these OMt were incorporated in the EVA matrix, the obtained clay polymer nanocomposites (CPN) showed a high exfoliation degree of the OMt in the polymer, in such a way that at 80% of the cationic exchange capacity (CEC) of the Mt exchanged with EHDDMA, most of the OMt was exfoliated. Moreover, all the obtained CPN showed an increase in the Young's Moduli compared to the EVA reference, and especially those containing higher amounts of MB. The thermal stability of the CPN also increases with the MB content, compared to other CPN including conventional surfactants. The hiding power and colouring power achieved in the CPN are higher even with a much lower load of MB when EHDDMA is exchanged in the Mt.

Characterization and electrochemical properties of conducting nanocomposites synthesized from p-anisidine and aniline with titanium carbide by chemical oxidative method

A novel polymer/TiC nanocomposites “PPA/TiC, poly(PA-co-ANI)/TiC and PANI/TiC” was successfully synthesized by chemical oxidation polymerization at room temperature using p-anisidine and/or aniline monomers and titanium carbide (TiC) in the presence of hydrochloric acid as a dopant with ammonium persulfate as oxidant. These nanocomposites obtained were characterized by Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS), and thermogravimetric analysis (TGA). XRD indicated the presence of interactions between polymers and TiC nanoparticle and the TGA revealed that the TiC nanoparticles improve the thermal stability of the polymers. The electrical conductivity of nanocomposites is in the range of 0.079–0.91 S cm−1. The electrochemical behavior of the polymers extracted from the nanocomposites has been analyzed by cyclic voltammetry. Good electrochemical response has been observed for polymer films; the observed redox processes indicate that the polymerisation on TiC nanoparticles produces electroactive polymers. These nanocomposite microspheres can potentially used in commercial applications as fillers for antistatic and anticorrosion coatings.