Nanostructure of montmorillonite barrier layers: A new insight into the mechanism of flammability reduction in polymer nanocomposites

This study describes the mechanism of flammability reduction in flame-retarded polymer matrix organo-montmorillonite reinforced nanocomposites. Morphologies of untested polymer nanocomposites and char residues formed by combustion in the mass loss calorimeter are characterized by XRD and TEM techniques. It is postulated that a combination of well-dispersed montmorillonite platelets and flame retardants in the polymer matrix provides nano-structured char formation. Initial montmorillonite dispersion in flame-retarded nanocomposites is found to be a major controlling factor on formed char nanostructures. An initially intercalated structure is invariantly converted to complete montmorillonite collapse whereas an initially exfoliated structure transforms to nano-structured chars demonstrating retained exfoliation or a new state of intercalation via incomplete collapse of montmorillonite layers. It is proposed that nano-structured char formation is the effective mechanism of flammability reduction, i.e. reduction in rate of heat release during combustion, in flame-retarded polymer nanocomposites.     

Novel polycarbonate-based polyurethane elastomers: Composition–property relationship

Novel all-aliphatic polycarbonate-based polyurethane (PC-PU) elastomers, as well as PC-PU nanocomposites filled with organic-modified clays were synthesized, characterized and studied. It was found that they have very attractive mechanical properties (e.g., elongation at break between 600% and 800%). The prepared PC-PUs possess a distinctly segmented structure, which is the key prerequisite for their behavior as strong physical rubbery networks. All synthesized materials melt at elevated temperatures (between 110 and 200 °C) and hence can be processed like normal thermoplastics. The dispersion of the clay nanofiller was achieved by its one day swelling in the alcohol and a brief successive stirring. This procedure is very successful and leads to a partial exfoliation of the clay (documented by X-ray diffraction and TEM). The best nanocomposites with very good tensile properties, particularly with significantly increased moduli were obtained using the bentonite nanofiller. The study shows that the nanofiller interacts strongly with the hard domains and influences their melting temperature (DMTA and DSC), but it does not affect the glass transition temperature of soft domains. While Cloisite 15A was found to interact preferentially with the hard domains, the organic modified bentonite shows a strong interaction with both soft and hard segments, behaving as a blending agent. Hard domains in neat matrices, formed by hydrogen bonding of hard segments, were practically invisible by X-ray or TEM, but were successfully detected by AFM. Besides excellent mechanical properties, the prepared elastomers and their nanocomposites showed an interesting phase behavior (which was studied by combining DMTA and modulated DSC).     

含水玻璃夹层状硅酸盐的合成与XRD表征

120℃时膨润土、高岭土分别用水玻璃固化，固化物晶形仍以蒙脱石、高岭石结构为主，且蒙脱石可包含更多的水玻璃成分，其固化机理为水玻璃加强了这些硅酸盐的层间作用力，讨论了新型夹层物质形成的可能。     

Preparation and characterization of exfoliated polystyrene/clay nanocomposites using a cationic radical initiator-MMT hybrid

The exfoliated polystyrene (PS)/clay nanocomposites were prepared via in situ polymerization using a cationic radical initiator-intercalated montmorillonite hybrid. The exfoliated structure resulted from the predominant intra-gallery polymerization over the extra-gallery polymerization owing to the anchored radical initiator inside the clay galleries. Several critical properties of the nanocomposites such as the initial thermal degradation temperature, glass transition temperature, storage modulus, Young’s modulus, and tensile strength were estimated and compared with earlier reported literature values. The improvements in such properties were either comparable or much greater than the reported literature values, mainly due to the efficient exfoliation and dispersion of the clay in the PS matrix.     

Polyethylene and polypropylene nanocomposites based upon an oligomerically modified clay

Montmorillonite clay was modified with an oligomeric surfactant, which was then melt blended with polyethylene and polypropylene in a Brabender mixer. The morphology was characterized by X-ray diffraction and transmission electron microscopy, while thermal stability was evaluated from thermogravimetric analysis and the fire properties by cone calorimetry. The nanocomposites are best described as mixed immiscible/intercalated/delaminated systems and the reduction in peak heat release rate is about 40% at 5% inorganic clay loading.     

Preparation and characterization of chitosan-clay nanocomposites with antimicrobial activity

Chitosan-montmorillonite nanocomposites were prepared by an ion exchange reaction between water soluble oligomeric chitosan and a Na⁺-montmorillonite. The chitosan-montmorillonite nanocomposites were rapidly prepared within 1 h due to the high affinity between the chitosan and the montmorillonite clay host. The basal spacings of the composites were in a range of 14.5-19.6 Å depending on the mixing ratio of chitosan to clay. According to the thermogravimetric analysis (TG) and powder X-ray diffraction analysis the thermal stability of chitosan was remarkably improved in the interlayer space due to the strong electrostatic interaction of cationic chitosan molecules with anionic silicate layers. From the antimicrobial activity test it was found that the nanocomposites showed a synergistic effect in the antimicrobial activity against to Escherichia coli and Staphylococcus aureus.     

The growth of carbon nanotubes on montmorillonite and zeolite (clinoptilolite)

Synthesis of carbon nanotubes described in the present work is based on activation of methane in a hot filament CVD reactor and subsequent creation of nanostructures on a catalyst pre-treated polished surface of silicon. An essential step of the synthesis is the use of natural minerals as catalysts. We have studied the catalyst parameters, the way of its application and the amount of Fe³⁺ cations on the surface of aluminosilicates on the quality of the grown nanotube layers. The growth of carbon nanotubes catalyzed by montmorillonite and zeolite (clinoptilolite) was confirmed by scanning electron microscopy and Raman spectroscopy.     

A green and efficient oxidation of benzylic alcohols using H2O2 catalyzed by montmorillonite K-10 supported CoCl2

Primary and secondary benzylic alcohols were oxidized to the corresponding carbonyl compounds in good to high yields by environmentally friendly and green oxidant, H2O2 catalyzed by montmorillonite K-10 supported cobalt（Ⅱ） chloride.     

Aflatoxin B(1) adsorption by natural and copper modified montmorillonite

Adsorption of aflatoxin B(1) (AFB1) by natural montmorillonite (MONT) and montmorillonite modified with copper ions (Cu-MONT) was investigated. Both MONTs were characterized using the X-ray powder diffraction (XRPD) analysis, thermal analysis (DTA/TGA) and scanning electron miscroscopy/electron dispersive spectroscopy (SEM/EDS). The results of XRPD and SEM/EDS analyses of Cu-MONT suggested partial ion exchange of native inorganic cations in MONT with copper occurred. Investigation of AFB1 adsorption by MONT and Cu-MONT, at pH 3, 7 or 9, showed that adsorption of this toxin by both MONTs was high (over 93%). Since AFB1 is nonionizable, no differences in AFB1 adsorption by both MONTs, at different pHs, were observed, as expected. Futhermore, it was determined that adsorption of AFB1 by both MONTs followed a non-linear (Langmuir) type of isotherm, at pH 3. The calculated maximum adsorbed amounts of AFB1 by MONT (40.982mg/g) and Cu-MONT (66.225mg/g), derived from Langmuir plots of isotherms, indicate that Cu-MONT was much effective in adsorbing AFB1. Since, the main cation in an exchangeable position in MONT is calcium, and in Cu-MONT both calcium and copper, the fact that ion exchange of inorganic cations in MONT with copper increases adsorption of AFB1 suggests that additional interactions between AFB1 and copper ions in Cu-MONT caused greater adsorption.     

Adsorption behavior of Pb(II) on montmorillonite

The present work investigated the adsorption and desorption behaviors of Pb(II) on montmorillonite. The adsorption experiments were carried out using batch process. The results show that the adsorption is dependent on the pH value of the medium, and the uptake of Pb(II) increases with the pH increasing in the pH range of 2.0–10.0. The adsorption kinetics is in better agreement with pseudo-second order kinetics, and the adsorption data is a good fit with Langmuir isotherm. The presence of EDTA may result in a decrease of the amount of Pb(II) adsorbed. The presence of electrolyte and EDTA may enhance the desorption of Pb(II) ions adsorbed. The adsorption mechanism of Pb(II) on montmorillonite may be explained in two aspects: the chemical binding between Pb(II) ions and surface hydroxyl groups; and the electrostatic binding between Pb(II) ions and the permanent negatively charged sites of montmorillonite.