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Abstract: Phyllosilicates including mica offer one of the easiest methods to obtain atomically flat surface of macroscopic size by cleavage. Thus, thin films of polypropylene crystallized at different pressure and as a function of polypropylene concentration were investigated. The objective was to probe the nucleation and chain organization in thin films on basal plane surface from the view point of relating the nucleation and growth process to the intergallery space between the clay layers. The crystal morphology was altered from leaf-like structure at high undercooling to fully developed spherulites at low undercooling. Furthermore, the lamellae structure change from well-oriented to cross-hatched with increase in the crystallization pressure was indicative of epitaxial growth between polymer matrix and mica surface. The possible epitaxial mechanism is discussed here. The study provides a method to explore the macro- and microstructure of polymer and epitaxy between polymer matrix and inorganic particle surface. The good interfacial bonding favored by epitaxial crystallization is beneficial for toughness. [Copyright &y& Elsevier]

Abstract: We describe here phase evolution and structural changes that are induced when high density polyethylene (HDPE) containing dispersion of nano-calcium carbonate is isothermally crystallized in the pressure range of 0.1–100MPa. To delineate and separate the effects of applied crystallization pressure from nanoparticle effects, a relative comparison is made between neat HDPE and HDPE containing nano-calcium carbonate under similar experimental conditions. X-ray diffraction studies point toward the evolution of monoclinic phase at high crystallization pressure together with the commonly observed orthorhombic phase of HDPE. Furthermore, the nucleation of monoclinic phase is promoted by nanoparticles even at low crystallization pressure. The equilibrium melting point is insignificantly influenced on the addition of nanoparticle, such that the crystallization pressure has no obvious effect. The strong thermodynamic interaction between nano-calcium carbonate and HDPE is supported by the shift in glass transition temperature and changes in the modification of absorption bands of HDPE in Fourier transform infrared (FTIR) spectrum. Furthermore, the reinforcement of HDPE with nano-calcium carbonate increases impact strength and alters the micromechanism from crazing-tearing in polyethylene to fibrillated fracture in polymer nanocomposite, such that the fibrillation increases with crystallization pressure. [ABSTRACT FROM AUTHOR]

Abstract: Significant differences in the microstructure occur when the polypropylene matrix dispersed with 4wt.% and 8wt.% nanoclay. In neat polypropylene, α-crystals nucleate in the low to moderate crystallization pressure range of (∼0.1–60MPa), while γ-phase nucleates at crystallization pressure of ∼60–200MPa. In contrast to neat polypropylene, the presence of nanoclay in the polymer matrix, promotes the formation of γ-phase at ambient crystallization pressure of 0.1MPa. Nanoclay and pressure-induced crystallization governs phase evolution and microstructure of polypropylene and is associated with change in the thermodynamic and physical properties such as equilibrium melting point and glass transition temperature. This change in equilibrium melting point and glass transition temperature points toward thermodynamic interaction between polymer-nanoparticle and nanoparticle interface-driven microstructural evolution. The dependence of equilibrium melting point on crystallization pressure and spherulite size on undercooling delineates two distinct regimes which are ascribed to dominant α- and γ-phases of polypropylene. However, the effect of nanoparticles is less dramatic when nanoclay content is increased from 4wt.% to 8wt.% implying that the effect maximizes at ∼4wt.% nanoclay. [ABSTRACT FROM AUTHOR]

Abstract: We describe here the relationship between fracture resistance and microstructural changes that are induced when polymers containing dispersion of nanoparticles are isothermally crystallized at elevated pressures. To identify the effects of applied crystallization pressure from nanoparticle effects, a relative comparison is made between polyethylene and polyethylene containing dispersion of nanoclay under similar experimental conditions. At high crystallization pressure, besides commonly observed orthorhombic phase, monoclinic phase is also observed. The nucleation of monoclinic phase is promoted by nanoclay even at low crystallization pressure, implying that both pressure and nanoclay have an influence on phase evolution. The addition of nanoclay to polyethylene retains adequately high impact strength and the micromechanism of deformation is altered from a combination of craze and drawing of fibrils in polyethylene to microvoid coalescence–fibrillation in polyethylene with dispersion of nanoclay. The monoclinic phase has no obvious influence on fracture resistance. [Copyright &y& Elsevier]

Abstract: The objective of this study is to describe the evolution of structure and phases during pressure-induced crystallization of polymers containing dispersion of nanoparticles, in the pressure range of 0.1–200MPa. The model material for nanoparticles is nanoclay and the model polymer is polypropylene, which can potentially form several crystalline phases. While the phase selection in polypropylene is dictated by pressure and temperature, however, the introduction of nanoparticles alters the nucleation and growth of phases via nanoparticle interface driven evolution. To delineate and separate the effects of applied crystallization pressure from nanoparticle effects, a relative comparison is made between neat polypropylene and polypropylene containing dispersion of nanoclay under similar experimental conditions. The significant finding is that nanoclay interacts with the host polypropylene in a manner such that it alters the structural morphology of α- and γ-crystals of polypropylene. Furthermore, nanoclay promotes the formation of γ-phase at ambient pressure suggesting its role as structure and morphology director in the stabilization of the less accessible γ-phase, and with the possibility of epitaxial growth that enhances toughness. The equilibrium melting point measurements point to thermodynamic interaction between nanoclay and polypropylene, which is supported by the change in glass transition temperature. Thus, the two components, nanoclay and pressure, together provide a unique opportunity to tune hierarchical structures and phase evolution, which has significant implication on physico-chemical and mechanical properties. [Copyright &y& Elsevier]

Abstract: We describe an innovative concept of synthesizing a novel hybrid bimodal network elastomer with high strength–high ductility combination involving utilization of functionalized nanocrystalline titania as short-chain cross-links between neighboring elastomer chains. This subject is germane both fundamentally and from an application viewpoint. Silicone rubber is selected as the model elastomer. The short-chain cross-links are acrylic acid functionalized nanocrystalline titania that are an integral component of bimodal network structure of the elastomer. To delineate and separate the effects of functionalization from nanoparticle effects, a relative comparison is made between silicone rubber–titania nanocomposite (i.e. containing dispersion of titania as a reinforcement filler) and silicone rubber–titania hybrid network elastomer (i.e. titania as short chain cross-links). An important finding is that the effect of functionalized titania present as short chain cross-links is far more significant than non-functionalized titania present as reinforcement filler, on mechanical behavior. This is presently ascribed to the double bonds introduced to nanocrystalline titania via functionalization with acrylic acid that provide active sites for the cross-linking reaction resulting in inorganic bridging chains. The basic physical mechanisms that govern elastic recovery in hybrid bimodal network elastomer with short chain cross-links of functionalized nanocrystalline inorganic particles are discussed. The hypothesis of the study described here is that the hybrid bimodal network elastomer with short chain cross-links of functionalized nanocrystalline inorganic particles modifies the unimodal long chain network elastomer with consequent increase in modulus and high strength–ductility combination. [Copyright &y& Elsevier]

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]

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 mechanical response of calcium carbonate-reinforced high density polyethylene nanocomposite is investigated and the behavior compared with the unreinforced polyethylene processed under similar conditions. The reinforcement of high density polyethylene with nanocalcium carbonate retains adequately high strength in the temperature range of −40 to +20°C. The positive influence of reinforcement on the impact strength is reflected in the fracture characteristics and is attributed predominantly to the nucleating effect of calcium carbonate in decreasing the spherulite size. The achievement of high impact strength is accompanied by increase in modulus and no loss in yield strength. The reinforcement of neat high density polyethylene (HDPE) with nanocalcium carbonate alters the deformation micromechanism from crazing–tearing in HDPE to fibrillated fracture in polymer nanocomposite. [Copyright &y& Elsevier]

Abstract: The study describes the surface deformation behavior and susceptibility to surface damage in two clay-reinforced intercalated polymer nanocomposite systems that have significant differences in ductility. Neat polybutene (PB) experiences a severe and distinct ‘quasi-periodic psiloma-type’ deformation process that was absent on reinforcement with clay. In clay-PB nanocomposite system, ‘ironing,’ a less severe surface damage mechanism is dominant. While in the less ductile polymethylpentene (PMP) polymer system, ploughing–tearing and micro-voiding constitute the surface deformation mechanism. Both the clay-reinforced polymer nanocomposite systems experience significantly reduced stress whitening and is characterized by a lower change in gray level. The optical transparency of the polymeric systems is governed by the micromechanism of deformation and is greater for the ductile PB system. The difference in the susceptibility to surface deformation behavior is discussed in terms of mechanical properties and clay-induced structural changes. The reinforcement of polymers with nanoclay has a positive overriding positive influence on the modulus and yield strength that increases the resistance to surface deformation. [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]

Abstract: The near surface deformation during scratching of neat polypropylene (PP) and polymer nanocomposites (PP–clay) at loads of 0.2–6kgf is described in terms of characteristics of scratch morphology and scratch deformation parameters. In neat PP, the application of higher loads introduces severe ironing deformation, disrupting the periodic parabolic nature of scratch tracks such that the material plastically flows along the ironing zone. Under identical test conditions, the severity of surface deformation in PP–clay nanocomposites, which leads to stress whitening is significantly reduced. At lower loads, the periodic nature of tracks is retained together with ironing, while at higher loads, ploughing occurred. The resistance to scratch deformation is discussed in terms of modulus, elastic recovery, and scratch hardness. [Copyright &y& Elsevier]

Zr 50-x/2 Co 50-x/2 Al x (x = 0, 4, 7) alloys fabricated by water-cooled copper mold casting yields excellent mechanical properties like high strength and large plasticity. Al can reduce the stacking fault energy and simultaneously improve strength and yield strength of the alloys. With increasing Al content, the effect of grain refinement strengthening, solid solution strengthening and second phase precipitation strengthening are enhanced to a certain extent. The good plasticity of these alloys primarily originates from the dislocation entanglement at the end of dislocation pileup and the transformation-induced plasticity associated with B2-to-B33 deformation-induced martensitic transformation. Zr 46.5 Co 46.5 Al 7 alloy shows the highest ultimate compressive strength of 1787 MPa, and the largest ultimate failure strain of more than 25%. • Al element can effectively increase the strength of Zr 50- x /2 Co 50- x /2 Al x (x = 0, 4, 7) alloy. • The good plasticity mainly originates from dislocation entanglement and TRIP. • Comprehensive mechanical properties originate from the synergy of various strengthening mechanisms. [ABSTRACT FROM AUTHOR]