Influence of a particulate nucleating agent on the quiescent and flow-induced crystallization of isotactic polypropylene

Flow induced crystallization of commercial isotactic polypropylene (iPP) and its blends with sodium 2,2′-methylene bis-(4,6-di-tert-butylphenyl) phosphate (also known as NA11) is studied by means of in-situ time resolved small-angle X-ray scattering (SAXS). The isothermal crystallization at 145 °C (i.e. well below melting temperature of polymer) is performed after the application of steady shear to probe the anisotropic structure formation. In order to separate the influence of shear rate and shear time on polymer crystallization, four different shear conditions (60 s⁻¹ for 1 s, 30 s⁻¹ for 2 s, 15 s⁻¹ for 4 s and 6 s⁻¹ for 10 s) are applied while maintaining the same imposed strain in the polymer melt. Further the effect of different concentration of nucleating agent on the crystallization kinetics of iPP is examined both under quiescent and shear flow conditions. For instance, under quiescent condition, the crystallization half-time (τ_1/2) decreases with the increasing concentration of nucleating agent in the polymer. Under shear flow conditions, our observations are as follows: In the case of neat iPP, τ_1/2 decreases significantly at higher shear rates (≥30 s⁻¹). Compared to the neat iPP, for the same concentration of NA11 in the NA11/iPP blends differences in τ_1/2 with the increase in applied shear rates are significantly smaller. In other words, the crystallization kinetics is dominated by the amount of nucleating agent in the NA11/iPP blends as opposed to shear rates in the neat iPP. The present study shows that the critical value of shear rate required for chain orientation in the molten polymer is lower in the presence of the nucleating agent compared to neat iPP. The self-nucleation process investigated with the aid of differential scanning calorimetry (DSC), indicates that the nucleating efficiency of NA11 on iPP is around 60%.     

Compatibilization Mechanism of Nanoclay in Immiscible PS/PMMA Blend Using Unmodified Nanoclay

Organically modified nanoclays have been reported to play the role of a compatibilizer for immiscible polymer blends. However, the mechanism of compatibilization by nanoclay has been reported differently. In this work, we investigated the exact mechanism of compatibilization of nanoclay in immiscible polystyrene (PS)/poly(methyl methacrylate) (PMMA) blend in the presence of sodium-montmorillonite (Na-MMT) through selective dispersion of clay in the matrix phase. Through a detailed investigation of the morphology of PS/PMMA/Na-MMT blend nanocomposites, the plausible mechanism behind the compatibilization effect of clay in immiscible blends has been proposed.     

Yucca-derived synthesis of gold nanomaterial and their catalytic potential

AuNPs ranging in 20 to 300 nm size were synthesized at a room temperature using Yucca filamentosa leaf extract. Diverse nanomaterial morphologies were obtained by varying the extract concentration, reaction pH, and temperature. While low volumes of extract (0.25 and 0.5 mL) induced the formation of microscale Au sheets with edge length greater than 1 μm, high volumes yielded spherical particles ranging from 20 to 200 nm. Varying pH of the solution significantly influenced the particle shape with the production of largely spherical particles at pH 5 to 6 and truncated triangles at pH 2. Separation of multidimensional nanostructures was achieved using a novel method of sucrose density gradient centrifugation. The catalytic function of Yucca-derived AuNPs was demonstrated by degradation of a wastewater dye: methylene blue using spectrophotometric measurements over time. Treatment with Au nanosheets and spheres demonstrated methylene blue degradation approximately 100% greater than the activity in control at 60 min.     

Video frame rate up conversion under inconsistent camera motion

In this paper, we address the problem of video frame rate up-conversion (FRC) in the compressed domain. FRC is often recognized as video temporal interpolation. This problem is very challenging when targeted for video sequences with inconsistent camera and object motion, such as sports videos. A novel compressed domain motion compensation scheme is presented and applied in this paper, aiming at up-sampling frame rates in sports videos. MPEG-2 encoded motion vectors (MVs) are utilized as inputs in the proposed algorithm. The decoded MVs undergo a cumulative spatiotemporal interpolation. An iterative rejection scheme based on the dense motion vector field (MVF) and the generalized affine motion model is exploited to detect global camera motion. Subsequently, the foreground object separation is performed by additionally examining the temporal consistency of the output of iterative rejections. This consistency check process helps coalesce the resulting foreground blocks and weed out the unqualified blocks. Finally, different compensation strategies for the camera and object motions are applied to interpolate the new frames. Illustrative examples are provided to demonstrate the efficacy of the proposed approach. Experimental results are compared with the popular block and non-block based frame interpolation approaches.

Preparation of antimicrobial sutures by preirradiation grafting of acrylonitrile onto polypropylene monofilament. II. Mechanical,physical, and thermal characteristics

Polypropylene‐g‐polyacrylonitrile sutures were prepared by graft polymerization of acrylonitrile onto polypropylene monofilament by preirradiation method. Sutures with various graft levels were characterized by Fourier Transform Infrared Spectroscopy (FTIR), Density, Birefriengence, X‐ray Diffraction, Scanning Electron Microscopy (SEM), and Differential Scanning Calorimetry (DSC). Mechanical properties of the unmodified and grafted sutures were also evaluated. The physical characteristics of sutures were markedly affected by the graft levels. Density of the polypropylene sutures increased with an increased in the degree of grafting. The heat of fusion and heat of crystallization decreased with the increase in the degree of grafting. X‐ray diffraction also revealed decrease in crystallinity with the increase in the graft levels. Tenacity of the monofilament improved, whereas the elongation at break decreased in grafted samples. Scanning electron microscopy showed significant variation in surface morphology in the grafted samples. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 1224–1229, 2004     

Characterization of phosphate accumulation in Lolium multiflorum for remediation of phosphorus-enriched soils

Deterioration in water quality caused by the movement of excessive soil P has created a condition necessary for the development of a sustainable P remediation technology. In this investigation, the phytoremediation potential of Gulf and Marshall ryegrass (Lolium multiflorum) grown in a greenhouse was determined under varying conditions of soil P concentration, pH, and temperature. Both genotypes demonstrated P accumulations > or =1% shoot dry weight depending on soil P concentrations (0-10 g of P/kg of soil), with higher shoot P in Gulf than Marshall ryegrass. An increase in plant biomass was proportional to the increasing concentrations of P up to a level of 10 g of P/kg of soil. The effect of soil pH on plant uptake of P was noticeable with a significant rise in shoot P in acidic soil (pH 5.6) as compared to soil with pH 7.8. Significant differences were observed in the biomass productivity and shoot P accumulation at varying temperatures in both grass types. The patterns of acid phosphomonoesterase and phytase activities in plant roots were interesting, activities being 2-fold higher in alkaline soil than acidic soil in both genotypes. The effect of P supply on the enzyme activity was also distinct, as plants growing in a high P concentration showed higher activity (nearly 30%) than those growing under P deficiency conditions (with no addition of P). These results indicate that Gulf and Marshall ryegrass can accumulate high P under optimal conditions and thus reduce soil P concentrations in successive cropping.     

Mapping of optimum operating condition for LiBr–water refrigeration cycles

In this work, optimum operating condition maps are generated covering wide ranges of refrigeration and sink temperatures for single- and double-effect LiBr–water vapour absorption refrigeration cycle. These optimum condition maps will be useful to choose optimum operating conditions while designing LiBr–water cycle for desired applications. Methodology for generating such maps is discussed in detail, which can also be used for other absorption refrigeration cycles with various working fluids. Three configurations of LiBr–water absorption refrigeration cycles, single effect, double-effect series flow and double-effect parallel flow, are analysed with the most accurate thermodynamic property correlation available in the literature. Sensitivity of cycle performance to various operating variables such as generator, absorber and condenser temperatures is determined. Second law analysis shows that when a higher temperature heat source is available, double-effect cycles are more effective over single effect as they have higher coefficient of performance.