Rheological properties of bimodal polyethylenes produced with silica nanoparticle supported catalysts

The rheological properties of bimodal ultra-high-molecular-weight polyethylenes (UHMWPEs) are investigated with an emphasis on the influence of the catalyst support. Bimodal UHMWPEs were produced in a single reactor with double support (DS) and single support (SS) catalyst systems. Dynamic measurements showed that the SS samples have a higher storage modulus at low frequencies than the DS samples with the same weight average molecular weight. After extrusion, the storage modulus of the bimodal DS samples increased to an identical value. The results indicate that the SS sample has a higher homogeneity than the DS sample. The steady-shear viscosities were measured to determine zero shear viscosities (η₀) of the bimodal samples. The results show that the SS samples follow the relation η₀ = KM_w^α with α = 3.19 . However, the DS samples exhibit a substantial deviation from this relation especially in the intermediate M_w range around 1000 kg mol⁻¹. The reason for the deviation is attributed to the heterogeneity in DS samples. The results demonstrate that the DS systems do not produce bimodal PEs with an intimate degree of mixing of short and long polymer chains even if silica nanoparticles are used as the support. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47577.     

Tetraplegia after a tracheal resection procedure

We describe a 27-year-old patient who was admitted to our hospital for a tracheal stenosis caused by an adenocystic carcinoma. A tracheal resection procedure was performed and the head was fixed to the anterior chest wall by two sutures. Postoperatively he became tetraplegic, from which he completely recovered after the sutures were removed. We think that the decreased blood flow in the arterial spinal artery with flexion of the neck in combination with hypotension was the direct cause of this major complication.     

CPMD-mindful task assignment for NPS-F

The multiprocessor scheduling scheme NPS-F for sporadic tasks has a high utilisation bound and an overall number of preemptions bounded at design time. NPS-F binpacks tasks offline to as many servers as needed. At runtime, the scheduler ensures that each server is mapped to at most one of the m processors, at any instant. When scheduled, servers use EDF to select which of their tasks to run. Yet, unlike the overall number of preemptions, the migrations per se are not tightly bounded. Moreover, we cannot know a priori which task a server will be currently executing at the instant when it migrates. This uncertainty complicates the estimation of cache-related preemption and migration costs (CPMD), potentially resulting in their overestimation. Therefore, to simplify the CPMD estimation, we propose an amended bin-packing scheme for NPS-F allowing us (i) to identify at design time, which task migrates at which instant and (ii) bound a priori the number of migrating tasks, while preserving the utilisation bound of NPS-F.     

Monitoring environmental health using SPOT-VEGETATION-derived and field-measured spectral indices in Karabash,Russia

The objective of this study was to use satellite imagery combined with field-based spectral analysis to assess the impacts of mining-related activities on vegetation around the smelter town of Karabash, South Ural Mountains of Russia. Time series analysis of normalized difference vegetation index (NDVI) and fraction of absorbed photosynthetically active radiation (FAPAR) images derived from Système Pour l’Observation de la Terre (SPOT)-VEGETATION was combined with the analysis of vegetation stress indices calculated from 140 in situ spectral measurements. Correlation analyses have revealed that vegetation stress affects vegetation density and resilience, and that it impedes a gradual increase in photosynthetic activity in the most affected areas ranging up to 10 km from the smelter. The prolongation of the growing season of healthier vegetation at greater distances, showing higher vegetation density, lower variation, and a more positive trend over time, can possibly be related to climate change. Although land cover shows a concentric pattern around Karabash, the analysis revealed that both spectral and time series-derived indices are defined more by the distance to the Karabash smelter and vegetation stress, rather than by the land cover class.     

Thermoreversible cross-linking of maleated ethylene/propylene copolymers with diamines and amino-alcohols

Maleated ethylene/propylene copolymers (MAn-g-EPM) were thermoreversibly cross-linked using diamines and amino-alcohols. Covalent cross-links are formed via the equilibrium reaction of the grafted anhydride groups with di-functional cross-linkers containing combinations of primary (1°) and secondary (2°) amines and alcohols, while a shift of the equilibrium at elevated temperatures may result in their (partial) removal. Materials cross-linked with cross-linkers containing two 2° amine groups (2°-2°) and 2° amine and alcohol groups (2°-OH) are repeatedly processable via compression molding without chemical changes, which is an improvement in reversibility compared to the previously-studied cross-linking reactions with diols, for which irreversible side reactions limited the reversibility to some extent. The use of 1° amine groups results in materials that are not reprocessable via compression molding, due to irreversible imide formation. The 2°-2° and 2°-OH materials have higher levels of cross-linking after remolding than the diol-cross-linked MAn-g-EPM, which results in significant differences in rubber properties. Fourier transform infrared (FTIR) spectroscopy suggested that the reprocessability of these materials is caused by a continuous, dynamic exchange between cross-linked and free groups. Finally, the use of cross-linkers containing 3° amine groups results in the formation of ionic interactions. These materials are easily reprocessable at temperatures as low as 125 °C and have significantly different properties than the covalently cross-linked materials, due to the occurrence of ion hopping.     

Influence of synthesis parameters on morphology and phase composition of porous titania layers prepared via water based chemical solution deposition

In this work, thick nanocrystalline mesoporous titania layers are synthesized via chemical solution deposition using a water based citratoperoxo-Ti(IV)-precursor solution. The aqueous citratoperoxo-Ti(IV)-precursor solution is modified by the addition of polyvinyl alcohol (PVA), which acts as a thickener and pore forming agent. Layers are tape casted onto ITO-coated glass substrates and are thermally processed. The influence of process parameters like Ti(IV)-concentration, blade thickness, crystallization temperature and time on the film's phase composition, morphology and thickness are investigated by means of X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), variable angle spectroscopic ellipsometry (VASE), atomic force microscopy (AFM) and profilometry.

It is shown that the Ti(IV)-concentration and heat treatment influence the size and shape of the grains of which the films are composed, the film morphology (porosity, surface roughness) and the layer thickness, but no influence on the phase formation is observed. In all cases phase pure anatase layers are obtained.     

Tailoring the morphology and properties of poly(lactic acid)/poly(ethylene)‐co‐(vinyl acetate)/starch blends via reactive compatibilization

Poly(lactic acid)/poly(ethylene‐co‐vinyl acetate)/starch (PLA/EVA/starch) ternary blends were prepared by multi‐step melt processing (reactive extrusion) in the presence of maleic anhydride (MA), benzoyl peroxide and glycerol. The effects of MA and glycerol concentration on the morphology and properties of the PLA/EVA/starch blends were studied using scanning electron microscopy, transmission electron microscopy, atomic force microscopy, the Molau experiment, dynamic mechanical thermal analysis and differential scanning calorimetry etc. The plasticization and compatibilization provided a synergistic effect to these blends accompanied by a significant reduction in starch particle size and an increase in interfacial adhesion. Starch was finely dispersed in the ternary blends with a dimension of 0.5 ? 2 µm. Furthermore, EVA‐coated starch or a starch‐in‐EVA type of morphology was observed for the reactively compatibilized PLA/EVA/starch blends. The EVA with starch gradually changed into a co‐continuous phase with increasing MA concentration. Consequently, the toughness of the blends was improved. Since property stability of starch is an issue, the tensile properties of these blends were measured after different storage times and the blends showed good property stability. Copyright © 2012 Society of Chemical Industry     

Phase separation in poly(butylene terephthalate)-based materials prepared by solid-state modification

The morphology of a series of poly(butylene terephthalate) (PBT)/fatty acid dimer diol (FADD)-based copolyesters prepared by solid-state modification (SSM) was studied. It was shown that in copolyesters containing less than 10 wt% FADD two different phases, i.e. a PBT crystalline phase and a PBT-rich amorphous phase, are present. The FADD residues were more or less homogeneously distributed throughout the interlamellar regions. For copolymers containing more than 10 wt% of FADD, a three-phase morphological model has to be used due to phase separation of a FADD-rich amorphous phase from the PBT-rich matrix, as confirmed by solid-state nuclear magnetic resonance spectroscopy and transmission electron microscopy. The final morphology was dependent on the morphology of the PBT/FADD-based physical mixtures prior to SSM. In addition, it was shown that FADD diffusion during SSM influences the final morphology.