Controlled Rate Thermal Analysis and Differential Scanning Calorimetry of Sepiolites and Palygorskites

A series of sepiolites, palygorskites and "Rocky Mountain Leather" clay minerals have been analysed by controlled rate thermal analysis and differential scanning calorimetry. Eight weight loss steps are observed and are structure and composition dependent. Three dehydration steps and five dehydroxylation steps are observed. The mass spectrometric curve mimicked the differential thermogravimetric (DTGA) curve enabling the detailed determination of the dehydration and dehydroxylation step

Anisotropy in nanocellular polymers promoted by the addition of needle‐like sepiolites

This work presents a new strategy for obtaining nanocellular materials with high anisotropy ratios by means of the addition of needle‐like nanoparticles. Nanocellular polymers are of great interest due to their outstanding properties, whereas anisotropic structures allow the realization of improved thermal and mechanical properties in certain directions. Nanocomposites based on poly(methyl methacrylate) (PMMA) with nanometric sepiolites are generated by extrusion. From the extruded filaments, cellular materials are produced using a two‐step gas dissolution foaming method. The effect of adding various types and contents of sepiolites is investigated. As a result of the extrusion process, the needle‐like sepiolites are aligned in the machine direction in the solid nanocomposites. Regarding the cellular materials, the addition of sepiolites allows one to obtain anisotropic nanocellular polymers with cell sizes of 150 to 420 nm and cell nucleation densities of 1013–1014 nuclei cm−3 and presenting anisotropy ratios ranging from 1.38 to 2.15, the extrusion direction being the direction of the anisotropy. To explain the appearance of anisotropy, a mechanism based on cell coalescence is proposed and discussed. In addition, it is shown that it is possible to control the anisotropy ratio of the PMMA/sepiolite nanocellular polymers by changing the amount of well‐dispersed sepiolites in the solid nanocomposites

Filling of mater-BI with nanoclays to enhance the biofilm rigidity

We investigated the efficacy of several nanoclays (halloysite, sepiolite and laponite) as nanofillers for Mater-Bi, which is a commercial bioplastic extensively used within food packaging applications. The preparation of Mater-Bi/nanoclay nanocomposite films was easily achieved by means of the solvent casting method from dichloroethane. The prepared bio-nanocomposites were characterized by dynamic mechanical analysis (DMA) in order to explore the effect of the addition of the nanoclays on the mechanical behavior of the Mater-Bi-based films. Tensile tests found that filling Mater-Bi with halloysite induced the most significant improvement of the mechanical performances under traction force, while DMA measurements under the oscillatory regime showed that the polymer glass transition was not affected by the addition of the nanoclay. The tensile properties of the Mater-Bi/halloysite nanotube (HNT) films were competitive compared to those of traditional petroleum plastics in terms of the elastic modulus and stress at the breaking point. Both the mechanical response to the temperature and the tensile properties make the bio-nanocomposites appropriate for food packaging and smart coating purposes. Here, we report a preliminary study of the development of sustainable hybrid materials that could be employed in numerous industrial and technological applications within materials science and pharmaceutics

Odor reduction and mechanical properties of natural rubber latex/sepiolite films

The bacterial action on non-rubber components and thermal degradation lead to offensive odor in natural rubber. This study aims to investigate the odor reduction, mechanical and morphological properties of the natural rubber latex (NRL)/sepiolite films with sepiolite from Tolsa (sepiolite-T), and sepiolite from China (sepiolite-C). The NRL/sepiolite films were prepared by heating of the NRL and curatives with various sepiolite content, from 0 to 2.0 parts per hundred rubber (phr), in a water bath at 70 ±1 °C. Then, casting the prevulcanized latex onto the glass mold. The results of nitrogen adsorption-desorption isotherms and pore size distribution show that sepiolite-T is a mesoporous material with high specific surface area (Sb e t ) and total pore volume, while sepiolite-C is a macroporous material with low Sb e t and total pore volume. The presence of volatile organic compounds (VOCs) included volatile fatty acids, alcohol, amide, hydrocarbon, terpene, and piperidines in neat NRL films and NRL/sepiolite films has been confirmed by using gas chromatography-mass spectrometry. The results show that the mesoporous sepiolite-T adsorbed more odorous VOCs compared to macroporous sepiolite-C in the neat NRL films. The result of dynamic olfactometry analysis also shows a negative correlation between odor concentration and the sepiolite content. Besides that, the odor concentration of NRL/sepiolite-T samples was much lower than NRL/sepiolite-C samples and the lowest odor concentration was achieved by adding 2.0 phr sepiolite-T (T2.0). The addition of 2.0 phr sepiolite in NRL/sepiolite-T and NRL/sepiolite-C reduced the odor concentration of NRL films by 69.1% and 59.4%, respectively. The morphological studies of NRL/sepiolite films reveal that the defects including sepiolite agglomerate, free volume and sepiolite pull-out were evident in NRL/sepiolite films. It was found that the tendency of defects formation increased with sepiolite content and consequently led to a decrease in tensile strength of NRL/sepiolite films. The rubber/sepiolite interaction in NRL/sepiolite-C films was proven by the ratio of the volume fraction of rubber in unfilled rubber sample to the volume fraction of rubber in a filled rubber sample (Vr/Vf). Therefore, NRL/sepiolite-C films demonstrated a higher tensile strength than NRL/sepiolite-T films. The increase in modulus at 300% elongation (M300) and decrease in elongation at break of NRL/sepiolite films show that the sepiolite provided stiffness to NRL/sepiolite films. The tear strength of NRL/sepiolite-T films was found to increase with sepiolite-T content due to the improvement of crack propagation resistance conferred by sepiolite-T. However, no significant changes of tear strength have been noticed in NRL/sepiolite-C films. Thus it can be concluded that sepiolite-T is a promising deodorizer for NRL films due to its higher odorous VOCs adsorption potentials. However, the high stiffness of the NRL/sepiolite films may not be appropriate for the thin rubber products except T0.5 and T1.0, which has the high elongation at break and low M300

Multicomponent bionanocomposites based on clay nanoarchitectures for electrochemical devices

Based on the unique ability of defibrillated sepiolite (SEP) to form stable and homogeneous colloidal dispersions of diverse types of nanoparticles in aqueous media under ultrasonication, multicomponent conductive nanoarchitectured materials integrating halloysite nanotubes (HNTs), graphene nanoplatelets (GNPs) and chitosan (CHI) have been developed. The resulting nanohybrid suspensions could be easily formed into films or foams, where each individual component plays a critical role in the biocomposite: HNTs act as nanocontainers for bioactive species, GNPs provide electrical conductivity (enhanced by doping with MWCNTs) and, the CHI polymer matrix introduces mechanical and membrane properties that are of key significance for the development of electrochemical devices. The resulting characteristics allow for a possible application of these active elements as integrated multicomponent materials for advanced electrochemical devices such as biosensors and enzymatic biofuel cells. This strategy can be regarded as an "a la carte" menu, where the selection of the nanocomponents exhibiting different properties will determine a functional set of predetermined utility with SEP maintaining stable colloidal dispersions of different nanoparticles and polymers in water

Diffusion Of Indigo Molecules Inside The Palygorskite Clay Channels

The search for durable dyes led several past civilizations to develop artificial pigments. Maya Blue (MB), manufactured in pre-Columbian Mesoamerica, is one of the best known examples of an organic-inorganic hybrid material. Its durability is due to the unique association of indigo molecule and palygorskite, a particular fibrous clay occurring in Yucatan. Despite 50 years of sustained interest, the microscopic structure of MB and its relation to the durability remain open questions. Combining new thermogravimetric and synchrotron X-ray diffraction analyses, we show that indigo molecules can diffuse into the channel of the palygorskite during the heating process, replacing zeolitic water and stabilizing the room temperature phases of the clay

Synthesis, characterization and photocatalytic activity of TiO2 supported natural palygorskite microfibers

This study deals with the synthesis of TiO2 supported Moroccan palygorskite fibers and their use as photocatalyst for the removal of Orange G pollutant from wastewater. The TiO2-palygorskite nanocomposite synthesis was accomplished according to a colloidal route involving a cationic surfactant as template (hexadecyltrimethylammonium bromide) assuring hence organophilic environment for the formation of TiO2 nanoparticles. The clay minerals samples were characterized before and after functionalization with TiO2. Anatase crystallizes above ca. 450 °C and remarkably remains stable up to 900 °C. In contrast, pure TiO2 xerogel obtained from titanium tetraisopropoxide (TTIP) showed before calcination a nanocrystalline structure of anatase. By increasing the temperature, anatase readily transforms into rutile beyond 600 °C. The remarkable stability at high temperature of anatase particles immobilized onto palygorskite microfibers was due to the hindrance of particles growth by sintering. Homogeneous monodisperse distribution of anatase particles with an average size of 8 nm was found by TEM and XRD onto palygorskite fibers. This anatase particle size remains below the nucleus critical size (ca. 11 nm) required for anatase–rutile transition. The TiO2 supported palygorskite sample annealed in air at 600 °C for 1 h exhibits the highest photocatalytic activity towards the degradation of Orange G compared to nanocomposite samples prepared under different conditions as well as pure TiO2 powders obtained from the xerogel route or commercially available as Degussa P25

Controlling the dynamic percolation of carbon nanotube based conductive polymer composites by addition of secondary nanofillers: The effect on electrical conductivity and tuneable sensing behaviour

In this paper, the electrical properties of ternary nanocomposites based on thermoplastic polyurethane (TPU) and multi-walled carbon nanotubes (MWCNTs) are studied. In particular two nanofillers - differing in shape and electrical properties - are used in conjunction with MWCNTs: an electrically conductive CB and an insulating needle-like nanoclay, sepiolite. The ternary nanocomposites were manufactured in a number of forms (extruded pellets, filaments and compression moulded films) and their morphological and electrical properties characterised as function of time and temperature. The presence of both secondary nanofillers is found to affect the formation of a percolating network of MWCNTs in TPU, inducing a reduced percolation threshold and tuneable strain sensing ability. These ternary nanocomposites can find application as conductive and multi-functional materials for flexible electronics, sensing films and fibres in smart textiles. (c) 2012 Elsevier Ltd. All rights reserved