Synthesis of Polycarbonate-Layered Silicate Nanocomposites via Cyclic Oligomers

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.

Probing the Properties of Nanocomposites Synthesized from Aramid and Surface-Modified Clay

Nanocomposites were prepared by the inclusion of layered silicates into the aramid matrix via a solution intercalation technique. Polyamide was synthesized by reacting 4,4′-oxydianiline with isophthaloyl chloride and then end-capping with carbonyl chloride end groups using excess diacid chloride. The compatibility between the two phases was obtained through surface modification of montmorillonite with long-chain alkyl diamine. The nanocomposites were characterized with regard to structural, morphological, mechanical, thermal, and water absorption measurements. These investigations confirmed the formation of delaminated and disordered intercalated nanostructures at different clay loadings. Mechanical properties were significantly enhanced relative to pristine polyamide, even with the addition of only 2 wt-% of nanoclay. Thermal decomposition temperatures of the nanocomposites were in the range 300–450°C. Glass transition temperature data exhibited improvement (123°C) up to 16 wt-% addition of organoclay. Water absorption of the neat aramid was rather high (5.7%), but decreased with augmenting clay content.

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).

Surface modification of montmorillonite on surface Acid-base characteristics of clay and thermal stability of epoxy/clay nanocomposites

In this work, the effect of surface treatments on smectitic clay was investigated in surface energetics and thermal behaviors of epoxy/clay nanocomposites. The pH values, X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FT-IR) were used to analyze the effect of cation exchange on clay surface and the exfoliation phenomenon of clay interlayer. The surface energetics of clay and thermal properties of epoxy/clay nanocomposites were investigated in contact angles and thermogravimetric analysis (TGA), respectively. From the experimental results, the surface modification of clay by dodecylammonium chloride led to the increases in both distance between silicate layers of about 8 A and surface acid values, as well as in the electron acceptor component (gamma(+)(s)) of surface free energy, resulting in improved interfacial adhesion between basic (or electron donor) epoxy resins and acidic (electron acceptor) clay interlayers. Also, the thermal stability of nanocomposites was highly superior to pure epoxy resin due to the presence of the well-dispersed clay nanolayer, which has a barrier property in a composite system.