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The fire performance of polyamide 6 (PA6) blended with phenyl phosphonic acid functionalized halloysite nanotubes (PPA-HNTs) is evaluated in order to determine if there is any fire performance gains over the unmodified composite. In the continuing search for safe halogen-free fire retardants for polymers, and the desire to more fully capture the advantages of nano-materials, this research seeks to utilize any synergy which might result in improved fire performance of PA6, via the known advantages offered by nano particles and phosphorus-based compounds. HNTs offer the ability for functionalization by exchange at their hydroxyl sites, while PPA can readily attach at these sites because of its acidity. In this context, the nanotubes act as a carrier for the acid within the polyamide polymeric matrix because it is readily intercalated and functionalized with the acid. The intercalated nano particles are added to the polyamide via melt extrusion and then analyzed using thermal analysis and cone calorimetry. The key finding from this work is that functionalization of HNTs with PPA, followed by blending into PA6 results in a significant improvement in fire performance by altering the combustion dynamics of the polymer. This work proposes a new synergistic fire retardant system for polyamides utilising relatively safe and inexpensive components. More broadly, the concept of using a carrier such as HNTs, which is so easily functionalized, can be applied to other thermoplastic materials, and other additives, for improvements in material properties other than fire. Copyright © 2012 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Abstract: We describe here phase and morphological changes that are induced when polyethylene-containing dispersion of nanoclay is isothermally crystallized in the pressure range of 0.1–150MPa. To delineate and separate the effects of applied crystallization pressure from nanoparticle effects, a relative comparison is made between neat polyethylene and polyethylene containing dispersion of nanoclay under similar experimental conditions. X-ray diffraction studies support the evidence of monoclinic phase at high crystallization pressure in addition to commonly observed orthorhombic phase of polyethylene. The nucleation of monoclinic phase is encouraged by nanoclay even at low crystallization pressures. Furthermore, orientation effects were observed in the nanocomposite system. The equilibrium melting point is insignificantly influenced on the addition of nanoclay and weakly refines the structure, such that the crystallization pressure has no obvious effect. The weak thermodynamic interaction between nanoclay and polyethylene compared to polypropylene–nanoclay system is supported by the small shift in glass transition temperature and no changes in the modification of absorption bands of polyethylene in Fourier transform infrared spectrum. [Copyright &y& Elsevier]

Abstract: We report here for the first time the changes in spherulitic structure and phase formation that occur in polypropylene in the presence of nanoclay on crystallization at high pressures. To delineate the effects of pressure and nanoclay on the crystallization behavior, polypropylene with and without nanoclay were studied under identical experimental conditions. The two important findings are (i) the spherulite size and morphology of polypropylene in the absence and presence of nanoclay is a function of the crystallization pressure and (ii) at constant crystallization pressure, the presence of nanoclay reduced the spherulite size from 155μm to 19μm at 0.1MPa. Another important observation was the evidence of γ-phase in polypropylene with nanoclay at pressures between ∼0.1MPa and 59MPa. In neat polypropylene, increasing crystallization pressure changed the deformation process from vein-type crazing to fibrillation, while in polypropylene-containing 4wt.% clay, an increased tendency towards fibrillated fracture with increase in crystallization pressure was observed. At the present time, the observations imply the following possibilities for future considerations: (a) nanoclay changes the equilibrium state of the polymer chain or its conformation and (b) nanoclay provides a surface that is favorable for possible epitaxial growth of γ-phase because the lattice mismatch is <10%. The observed nanoparticle and pressure-induced effects, namely dramatic reduction in spherulite size and γ-phase appears to be beneficial for impact strength with consequent change in the micromechanism of plastic deformation. [Copyright &y& Elsevier]

The authors describe here the chemical processing methodology and physicochemical response of superparamagnetic nickel ferrite nanoparticles, which were encapsulated and functionalised with polyethylene glycol to form a core shell structure. The outer shell was subsequently conjugated with tumour recognition moiety, folic acid and loaded with doxorubicin drug to achieve tumour specific drug delivery. Fourier transform infrared spectroscopy confirmed the functionalisation and conjugation steps used in the synthesis of the nanocarrier. The drug release response was characterised by an initial rapid release followed by a controlled release. The study also indicated that it is important to optimise the thickness of the polyethylene glycol shell on the magnetic nickel ferrite core to avoid reduction in the ability of the nanocarrier to experience alternate compressive and tensile stresses caused by the external magnetic field because this leads to reduction in the percentage of drug release. [ABSTRACT FROM AUTHOR]

Abstract: We examine here the mechanical behavior and the micromechanism of fracture in impact tested neat and nanoclay-reinforced thermoplastic olefins, both of which have been processed under similar conditions. The reinforcement of thermoplastic olefins with nanoclay increases modulus and yields strength of the resulting nanocomposite and retains impact strength. The enhancement of modulus and yield strength is related to the reinforcement effect of nanoclay, while the retention of impact strength on reinforcement is attributed to the strong interaction between clay and polymer matrix. Both neat and clay-reinforced thermoplastic olefins are characterized by plastic deformation processes that involve ductile ploughing, fibrillation and voiding. [Copyright &y& Elsevier]

Abstract: The reinforcement of polyethylene and polypropylene with 4wt.% nanoclay exhibits a striking variation in impact toughness behavior in the temperature range of −40 to +70°C under identical processing conditions. The reinforcement of polypropylene with nanoclay increases the impact strength, while polyethylene experiences a decrease in the impact strength. To explain this dissimilar and contrasting behavior, we discuss here the possibility of clay–polymer interaction based on conclusions derived from differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), transmission electron microscopy (TEM), wide-angle X-ray diffraction (WAXD), and Fourier transform infrared spectroscopy (FTIR). The observations suggest the possibility of a strong polypropylene–clay interaction, whereas the polyethylene–clay interaction is weak. The strong interaction in polypropylene–clay system is responsible for significant change in physical and mechanical properties. [Copyright &y& Elsevier]

Abstract: The influence of two concentrations of clay nanoparticles on the nonisothermal crystallization behavior of the intercalated polypropylene–clay nanocomposites is investigated here. It is observed that the crystallization peak temperature (T p) of PP–clay nanocomposites is marginally higher than neat PP at various cooling rates. Furthermore, the half-time for crystallization (t 0.5) decreased with increase in clay content, implying the nucleating role of clay nanoparticles. The nonisothermal crystallization data is analyzed using Avrami, Ozawa and Mo and coworkers methods. The validity of kinetic models on the nonisothermal crystallization process of PP–clay nanocomposites is discussed. The approach developed by Mo and coworkers successfully describes the nonisothermal crystallization behavior of PP and PP–clay nanocomposites. The activation energy for nonisothermal crystallization of pure PP and PP–clay nanocomposites based on Kissinger method is evaluated. [Copyright &y& Elsevier]

Abstract: The micromechanism of plastic deformation during impact loading of polypropylene–clay nanocomposites is examined and compared with the unreinforced polypropylene under identical conditions of processing to underscore the determining role of clay. The addition of clay to polypropylene increases the impact strength in the temperature range of 0 to +70°C. Differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA) and transmission electron microscopy (TEM), wide-angle X-ray diffraction (WAXD) and scanning electron microscopy (SEM) techniques provided an understanding of the micromechanism of plastic deformation in terms of the response of the polymer matrix, nucleating capability of the reinforcement, crystal structure, percentage crystallinity, lamellae thickness, and particle–matrix interface. The enhancement of toughness on reinforcement of polypropylene with nanoclay is associated with change in the primary mechanism of plastic deformation from crazing and vein-type in neat polypropylene to microvoid-coalescence-fibrillation process in the nanocomposite. [Copyright &y& Elsevier]

Abstract: The mechanical response of clay–reinforced polyethylene nanocomposite is investigated and the behavior compared with the un-reinforced polyethylene under identical conditions of processing. The micromechanism of plastic deformation during impact loading of neat polyethylene and clay–reinforced polyethylene nanocomposite are studied with scanning electron microscopy (SEM). The impact strength of composites is linked to structural studies by differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA) and transmission electron microscopy (TEM) and SEM observations. The addition of clay to polyethylene retains adequately high-impact strength in the investigated temperature range of −40 to +70°C. The micromechanism of deformation is altered from a combination of craze and drawing of fibrils in neat polyethylene to microvoid coalescence-fibrillated process in the nanocomposite. The aspects related to micromechanism of deformation are discussed. [Copyright &y& Elsevier]

Abstract: The objective of the study described here is to investigate the determining influence of impact modifier on the microstructure and physico-chemical and mechanical properties of polypropylene crystallized at elevated pressures. The impact modified polypropylene referred as thermoplastic olefin (TPO) is characterized by a small spherulite size in the range of ∼1–8μm and the effect is retained when nanoclay is introduced into TPO. The impact strength of TPO and TPO–nanoclay system though similar, but is significantly higher than the polypropylene system, a behavior attributed to refinement of spherulite size. The study demonstrates that the nanoclay in TPO retains the impact strength of TPO and controls the dispersion of elastomer. [Copyright &y& Elsevier]