Novel use of mesoporous aluminas as supports for Cp2ZrCl2 and Cp*ZrMe3: Ethylene polymerization and formation of polyethylene nanofibers

Mesoporous aluminas with average pore sizes of 4.3–7.8 nm were prepared by anodization of an aluminum film (AAO), and by a sol–gel templating method (TPL). In addition to a commercial alumina and sulfated TPL, the aluminas were used as supports for cyclopentadienyl zirconocene dichloride (Cp₂ZrCl₂) and trimethyl(η5‐pentamethylcyclopentadienyl)zirconium (Cp*ZrMe₃) and tested in the polymerization of ethylene. The metallocenes supported on the alumina prepared with the templating method and its sulfated modification exhibited polymerization activities of 440 and 350 kg_PE/(mol_Zr × h × bar), respectively, comparable to that obtained with silica‐supported metallocenes (390 kg_PE/(mol_Zr × h × bar)). The acid site distribution of the aluminas was studied with FTIR and temperature programmed desorption (TPD) of pyridine, and also the amount of medium and strong acid sites was determined gravimetrically from the adsorption of pyridine. Relative to the surface area, AAO with the highest amount of acid sites (2.10 μmol_py/m) adsorbed Cp₂ZrCl₂ and Cp*ZrMe₃ the most. Study of the polymers' morphology with a scanning electron microscope revealed polyethylene nanofibers in all the polymer samples, also in those obtained from the reference polymerizations with homogeneous Cp₂ZrCl₂ and Cp*ZrMe₃. This finding suggests that a catalyst support with a tubular pore structure is not a prerequisite for the formation of polymer nanofibers. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4002–4012, 2007     

通过自动加速效应的调控反应挤出制备聚甲基丙烯酸甲酯

利用旋转流变仪、哈克转矩流变仪以及双螺杆挤出机,研究了剪切速率对自加速效应的影响,且通过反应挤出聚合制备了聚甲基丙烯酸甲酯(PMMA)。采用多检测凝胶渗透色谱(GPC)、动态力学分析(DMA)等方法,对聚合物结构和性能进行了表征。结果表明,在反应挤出聚合过程中,改变剪切速率可有效地调控自加速效应。通过新单体补加技术充分利用自加速效应,不仅可以提高聚合速率,而且可以获得高分子量、窄分子量分布的PMMA。制备的PMMA性能优于市售PMMA。     

Melt Extrusion Encapsulation of Flavors: A Review

Encapsulation of flavor and aroma compounds has been largely explored in order to meet appraisal demands from consumers by improving the impact of flavor during the consumption of food products. Even though several techniques have been used for encapsulating volatile compounds, i.e., spray drying, fluidized bed coating, coacervation, and melt extrusion, those most frequently used in the food industry are spray drying and melt extrusion. In this article, the different techniques of encapsulation of flavors and fragrances in polymer-based matrices by extrusion are reviewed and partly re-defined, emphasizing the differences between the various techniques reported so far and the role of matrix types, additives, and operative conditions. Also, the role of water as a key parameter for controlled release and shelf stability of the delivery system will be discussed.     

Effect of AlSiFe on the anodizing process of 6063 aluminum

AlSiFe phase can form microscopic galvanic couples that decrease corrosion resistance of 6063 aluminum which may influence the anodizing process. Two samples of 6063 aluminum were prepared. One sample was cut along the extrusion direction of the billet, and the other was cut perpendicular to the extrusion direction. Both samples exhibited the same characteristics, except for the distribution of the second phase AlSiFe. Both samples were subjected to anodizing treatments. Comparison between anodic oxide films was performed. The microstructure of Al substrates and anodic oxide films were examined using a scanning electron microscope, an optical microscope, and a glow discharge optical emission spectrometer. Results indicated that the thicknesses and elemental distributions of the anodic oxide films were almost the same. Moreover, the second phase AlSiFe influenced the anodic oxidation process, resulting in cavities in the anodic oxide film that affected its brightness. Copyright © 2016 John Wiley & Sons, Ltd.     

A Facile Method to Prepare Double‐Layer Isoporous Hollow Fiber Membrane by In Situ Hydrogen Bond Formation in the Spinning Line

A double‐layer hollow fiber is fabricated where an isoporous surface of polystyrene‐block‐poly(4‐vinylpyridine) is fixed on a support layer by co‐extrusion. Due to the sulfonation of the support layer material, delamination of the two layers is suppressed without increasing the number of subsequent processing steps for isoporous composite membrane formation. Electron microscope‐energy‐dispersive X‐ray spectroscopy images unveil the existence of a high sulfur concentration in the interfacial region by which in‐process H‐bond formation between the layers is evidenced. For the very first time, our study reports a facile method to fabricate a sturdy isoporous double‐layer hollow fiber.

     

IMPROVED PROPERTIES OF METALLOCENE-CATALYZED LINEAR LOW-DENSITY POLYETHYLENE/POLYPROPYLENE BLENDS DURING ULTRASONIC EXTRUSION

Metallocene-catalyzed linear low-density polyethylene/polypropylene （mLLDPE/PP） blends were prepared by ultrasonic extrusion in this work. Their extrusion processing behaviors were estimated by online measured data, such as the die pressure and flow rate. Crystallization and mechanical properties of the blends were also investigated. The results show that the addition of PP improves the processing behaviors of mLLDPE, but has little effect on its mechanical properties. On the other hand, the addition of mLLDPE improves the impact strength of PP, but has little effect on its processing behavior. The processing behaviors and mechanical properties of mLLDPE/PP blends get further improved due to the presence of ultrasonic oscillation during extrusion. Compared with PP-rich blends, the apparent viscosity drop of mLLDPE-rich blends is more sensitive to ultrasonic oscillation. The ultrasonic oscillation affects the crystal nucleation, while barely the other crystalline behaviors of the blends.     

往复挤压准晶增强快速凝固Mg92.5Zn6.4Y1.1合金

采用往复挤压工艺将快速凝固Mg92.5Zn6.4Y1.1合金薄带在330℃挤压2道次和4道次,然后正挤压制成Φ10 mm的棒材。用OM,TEM,XRD及DTA研究了往复挤压过程中准晶相I-Mg3YZn6弥散析出及对力学性能的影响。研究表明,往复挤压有利于快速凝固Mg92.5Zn6.4Y1.1合金薄带的焊合,获得组织致密、均匀、高强韧合金。往复挤压2道次,相组成为-αMg和准晶I-Mg3YZn6,脱溶析出纳米准晶相较少;4道次相组成为-αMg和准晶I-Mg3YZn6及MgZn相,脱溶弥散析出的纳米I-Mg3YZn6准晶相及MgZn相较多。往复挤压提高材料的拉伸性能,其主要原因是细晶强化和析出强化。     

Influence of thermal and thermo-mechanical treatment

Two lipids with similar melting ranges but of different composition were analyzed using differential scanning calorimetry and X-ray diffraction. The lipids were processed via extrusion or were tempered at different temperatures; they were analyzed directly after extrusion and after storage at 40°C. Precirol ATO 5® showed high sensitivity to storage time and varied temperature exposure. Extrusion showed only marginal influences on the solid state. Melting peaks were narrower and shifted to higher temperatures in comparison to the untreated powder. Dynasan 114® was more robust, changes in the solid state could only be shown for samples treated above the melting range. Thus, Dynasan 114® is more appropriate for solid lipid extrusion of pharmaceutical products.     

Correlation between chemical composition and radical scavenging activity of 10 commercial essential oils: Impact of microencapsulation on functional properties of essential oils

A comparative study was carried out on the essential oils of 10 aromatic plants that are extensively used in Egypt for their distinctive aroma and functional properties. Each essential oil (EO) was characterized by means of gas chromatography-mass spectrometry (GC–MS) analysis and evaluated for its radical scavenging activity by 2,2-diphenyl-1-picrylhydrazyl (DPPH) and 2,2-azinobis (2-ethyl-benzolhiaxoline-6-sulfonic acid)(ABTS) assays. The phenolic content of the 10 EOs was in the descending order: clove > thyme > majoram > basil > anise > chamomile > cinnamon > dill > ginger > rosemary. The radical scavenging activity of the EOs was correlated to the presence of phenolic compounds, such as eugenol, thymol, carvacrol and trans-anethol, or the synergism between the antioxidant activity of nonphenolic compounds such as terpinene-4-ol, α-terpinene, curcumene and chamazulene. Clove essential oil exhibited the highest oil content and radical scavenging activity so it was encapsulated, separately, in three coating materials. Sodium alginate showed the highest retention, encapsulation efficiency and loading capacity of clove EO. Microencapsulation in sodium alginate and chitosan improved the antioxidant activity and phenolic content of the encapsulated clove EO compared with carboxymethyl cellulose. The results support the possibility of using the encapsulated EOs as natural and easy handle antioxidants.     

Generation of ortho-quinone methides upon thermal extrusion of sulfur dioxide from benzosultones

3H-1,2-Benzoxathiole 2,2-dioxides (benzosultones) undergo thermal extrusion of sulfur dioxide to form ortho-quinone methides that enter Diels-Alder reaction with maleimides to form chroman 2,3-dicarboxylic acid derivatives.