Color inhibition of phenolic antioxidants in Ziegler‐Natta polyethylene. I. In‐situ polymer studies

Although the level of transition‐metal catalyst residues in polyethylene (PE) has been drastically reduced over the years, they can still give rise to discoloration, particularly when associated with other additives such as antioxidants. This first of this series of papers screens a variety of candidate color suppressants featuring a range of functional groups, including alcohols, amine/sulfur compounds, and acid‐containing species. These candidate color suppressants were melt‐blended into a Ziegler‐Natta linear low‐density PE in combination with 2,2′‐isobutylidenebis(4,6‐dimethylphenol) (a highly discoloring hindered bisphenol antioxidant) and zinc stearate antacid. Yellowness index measurements made after multiple extruder passes indicated that dipentaerythritol (DPE) and triisopropylamine (TIPA) gave good color inhibition and, in some cases, outperformed established phosphites. The DPE and TIPA were found (via melt flow rate measurement) not to affect melt stability, and hydroperoxide determination revealed that DPE had no peroxide decomposition activity. The latter results indicate that the color‐suppression mechanism of DPE and TIPA is different from that associated with phosphites. J. VINYL ADDIT. TECHNOL., 2009. © 2009 Society of Plastics Engineers     

A microvalve for lab-on-a-chip applications based on electrochemically actuated SU8 cantilevers

Increasing the complexity and functionality of Lab-on-a-Chip devices requires integrated valves for internal flow regulation. The device introduced in this work is an electrochemical SU8 microvalve, featuring a cantilevered structure that seals an adjacent channel under the action of a growing electrolysis bubble. The valve is based on previously reported movable microcantilevers embedded in microchannels. As opposed to membrane valves moving perpendicular to the substrate, the cantilever valve is patterned next to the channel and closes it by moving horizontally, dramatically reducing footprint. Its compact, monolithic and 2D construction reduces assembly problems and results in negligible increase in dead volume (14.5 nl). Besides, its location in the way of the channels avoids the need for auxiliary filling ports or separate working media for actuation. Effective sealing with negligible leakage at 20 kPa has been achieved. The valve also displays passive flow regulation induced by the pressure differential generated across the valve chamber under flow conditions (42-72% flow decrease).     

A comparison between optimization-based human motion prediction methods: data-based, knowledge-based and hybrid approaches

In this paper an optimization-based hybrid dynamic motion prediction method is presented. The method is hybrid as the prediction relies both on actually performed motions for reference (following a data-based approach) and on the definition of appropriate performance measures (following a knowledge-based approach). The prediction is carried out through the definition of a constrained non-linear optimization problem, in which the objective function is composed of a weighted combination of data-based and knowledge-based contributions. The weights of each contribution are varied in order to generate a battery of hybrid predictions, which range from purely data-based to purely knowledge-based. The results of the predictions are analyzed and compared against actually performed motions both qualitatively and quantitatively, using a measure of realism defined as the distance of the predicted motions from the mean of the actually performed motions. The method is applied to clutch pedal depression motions and the comparison between the different approaches favors the hybrid solution, which seems to combine the strengths of both data- and knowledge-based approaches, enhancing the realism of the predicted motion.     

屋顶与绿化——BTEK科技展览中心

两座连续的金字塔既是BTEK科技展览中心的屋顶,也是该建筑地面以上的所有部分。一个深蓝色的锐角与覆盖草皮的斜坡相映成趣,位于地下的展览中心也制造了与众不同的空间体验。在此案中,屋顶不仅具有独特的形态,也参与空间的塑造和实现绿化的功能。     

Enantioselective Flow Synthesis of a Tetrahydroquinoline SERM Enabled by Immobilized Chiral Phosphoric Acid Catalysis and Diboronic Acid Mediated Selective Nitro Reduction

An asymmetric enantioselective flow process is reported for the formal synthesis of a 1,2,3,4-tetrahydroquinoline selective estrogen receptor modulator. Starting from an easily available 2-nitrochalcone, the first part of the process comprised a telescoped nitro reduction/intramolecular cyclocondensation sequence using diboronic acid as a simple reductant. Subsequent enantioselective transfer hydrogenation in the presence of an immobilized phosphoric acid organocatalyst followed by telescoped N-alkylation furnished the targeted chiral intermediate. The approach ensures flexibility regarding the scale of the synthesis, whilst minimizing the need for intermediate purifications and ensuring environmentally benign metal-free conditions.     

Additive interactions in the stabilization of film grade high-density polyethylene. Part I: Stabilization and influence of zinc stearate during melt processing

The melt stabilization activity of some of the most commercially significant phenolic antioxidants and phosphites (alone and in combination), without and with zinc stearate, was studied in high-density polyethylene (HDPE) produced by Phillips catalyst technology. Multiple pass extrusion experiments were used to degrade the polymer melt progressively. The effect of stabilizers was assessed via melt flow rate (MFR) and yellowness index (YI) measurements conducted as a function of the number of passes. The level of the phenolic antioxidant remaining after each extrusion was determined by high-performance liquid chromatography (HPLC). Phenolic antioxidants and phosphites both improved the melt stability of the polymer in terms of elt viscosity retention; the influence of zinc stearate was found to be almost insignificant. However, phosphites and zinc stearate decreased the discoloration caused by the phenolic antioxidants. A correlation was found between the melt stabilization performance of phosphites and their hydroperoxide decomposition efficiency determind via a model hydroperoxide compound. Steric and electronic effects associated with the phosphorus atom influenced the reactivity towards hydroperoxides. Furthermore, high hydrolytic stability did not automatically result in lower efficiency. Besides phosphite molecular structure, stabilization activity was also influenced by the structure of the primary phenolic antioxidant and the presence of zinc stearate.     

Stem and bunch banana fibers from cultivation wastes: Effect of treatments on physico‐chemical behavior

Much research related to the use of natural fibers in polymeric matrix composites has been developed. The presence of ? OH groups in the chemical components of the natural fibers generates an important hydrophylic tendency that produces adhesion lacks with hydrophobic polymeric matrices. In this work natural fiber bundles mechanically extracted from both stem and bunch of cultivation banana wastes have been modified by both alkalization and silanization treatments. To evaluate the changes introduced by treatments on the chemical structure of fibers, Fourier‐transform infrared spectrophotometry has been employed. The evaluation of advancing dynamic contact angles along with the determination of total surface free energy by using the Owens–Wendt method indicate that the treatments allow reduction of their hydrophilic tendency by alterations on the physicochemical characteristics of the fibers. This behavior is confirmed by the reduction of moisture uptake, analyzed by thermogravimetric analysis. Small differences on noncellulosic components of stem and bunch fiber bundles have been found. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 1489–1495, 2004     

Robot guided bolt tensioning tool with adaptive process control for the automated assembly of wind turbine rotor blade bearings

The three rotor blade bearings of a wind turbine hub are mounted to the rotor by several hundred bolted joints. Within this assembly process, a specific preload force has to be applied to these bolts in order to achieve a defined clamping force between the bearing and the rotor. Despite high manual labour intensity and safety concerns (platforms need to be raised to reach bolted joint at a height of 4 m), workers use hydraulic bolt tensioning cylinders which need to be threaded on each bolt individually. In order to automate this recurring assembly process, a robot guided bolt tensioning tool has been developed, which is part of a self-adaptive assembly system. Hence, we are able to locate each bolted joint, mount the bolt tensioning tool and apply the preload to each bolt of the bearing sequentially. In order to be flexible for different product variants and compensate the tolerances of large product dimensions in the wind turbine assembly, an adaptive process has been created. Therefore, the relevant parameters describing the product and assembly process are identified which can be adapted depending on the rotor hub type. Furthermore, the tolerance chain is analysed and improved by integrating measurement techniques to the new tool and using these sensors in the adaptive process control.