Characterization of ramie yarn treated with sodium hydroxide and crosslinked by 1,2,3,4‐butanetetracarboxylic acid

Ramie yarns were treated with various concentrations of NaOH at room temperature and subsequently crosslinked with 1,2,3,4‐butanetetracarboxylic acid (BTCA). The microstructure and tensile properties of the treated yarns were characterized. X‐ray diffraction (XRD) and FTIR were used to study the crystalline structure of the resultant ramie yarns. The results showed that the maximum change in the structure of the alkali‐modified ramie took place at 16% NaOH, which would completely transform cellulose I to cellulose II. At the same time, the crystallinity index and fiber orientation decreased to the minimum value while the absorption properties were enhanced. The average degree of polymerization (DP ) of the treated ramie yarns slightly decreased after NaOH treatment. Tensile properties including tenacity, breaking elongation, and modulus of the treated yarns were also investigated. Scanning electron microscopy (SEM) was used to investigate the breakage of the treated yarns. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 1857–1864, 2004     

Horizontal reactive distillation for multicomponent chiral resolution

A novel horizontal reactive distillation apparatus and a new overall process scheme are proposed for continuous multicomponent chiral resolution via reversible enantioselective acylation of a chiral (racemic) substrate by a chiral (racemic) acyl donor. The process enables simultaneous production of up to four enantiomers with enhanced chiral purity. Kinetic studies, miniplant experiments, and process simulation results are described for a model lipase‐catalyzed reaction: (R)‐enantioselective transesterification of (R,S)‐1‐n‐butoxy‐2‐propanol with (R,S)‐1‐methoxy‐2‐acetoxypropane to produce (R)‐1‐n‐butoxy‐2‐acetoxypropane, (R)‐1‐methoxy‐2‐propanol, and the two unreacted (S)‐enantiomers of the (R,S)‐reagents. A horizontal, compartmentalized reactive distillation vessel is specified instead of a conventional reactive distillation column to provide longer liquid‐phase residence time needed for adequate conversion. Low vapor‐traffic pressure drop allows operation under vacuum at reduced temperatures for good enzyme stability and enantioselectivity. The general technology has potential as a means to producing a wide range of chiral synthons used in asymmetric syntheses of chiral pharmaceuticals and other biologically active products. © 2013 American Institute of Chemical Engineers AIChE J, 59: 2603–2620, 2013     

Chemical Modifications for a Next Generation of Nucleic Acid Aptamers

In the past three decades, in vitro systematic evolution of ligands by exponential enrichment (SELEX) has yielded many aptamers for translational applications in both research and clinical settings. Despite their promise as an alternative to antibodies, the low success rate of SELEX (∼30 %) has been a major bottleneck that hampers the further development of aptamers. One hurdle is the lack of chemical diversity in nucleic acids. To address this, the aptamer chemical repertoire has been extended by introducing exotic chemical groups, which provide novel binding functionalities. This review will focus on how modified aptamers can be selected and evolved, with illustration of some successful examples. In particular, unique chemistries are exemplified. Various strategies of incorporating modified building blocks into the standard SELEX protocol are highlighted, with a comparison of the differences between pre-SELEX and post-SELEX modifications. Nucleic acid aptamers with extended functionality evolved from non-natural chemistries will open up new vistas for function and application of nucleic acids.     

An efficient birdcage resonator at 2.5 MHz using a novel multilayer self-capacitance construction technique

The birdcage resonator, well appreciated for its high signal-to-noise ratio and its magnetic field uniformity characteristics, operates efficiently in mid- to high-field MRI systems but, unfortunately not for low-field (<0.4 T) applications. The inherently low inductance of the birdcage architecture is the main obstacle to achieving low-frequency resonance because of the need to use very high-value capacitors for the tuning. Small-case-size, high-value ceramic capacitors are known to have high dissipation factors which when used in the fabrication of RF coils could result in poor efficiency. To overcome this limitation, a novel technique known as multilayer self-capacitance (MLSC) construction has been developed and a prototype 2.5-MHz bird-cage resonator of length 25 cm and diameter 20 cm has been built. The technique involves the modification of the leg sections of the conductors constituting the bird cage into integrated capacitors using very low-loss materials as dielectrics. The observed unloaded Q-factor was 267 using the MLSC construction, and when loaded with a 16-cm-diameter bottle of 0.45% saline, its Q dropped to 246, The RF field uniformity plots have demonstrated that the MLSC technique has no adverse effects on the magnetic field homogeneity of the bird-cage resonator.     

Dendrimer-encapsulated metal nanoparticles: synthesis, characterization, and applications to catalysis

This Account reports the synthesis and characterization of dendrimer-encapsulated metal nanoparticles and their applications to catalysis. These materials are prepared by sequestering metal ions within dendrimers followed by chemical reduction to yield the corresponding zerovalent metal nanoparticle. The size of such particles depends on the number of metal ions initially loaded into the dendrimer. Intradendrimer hydrogenation and carbon-carbon coupling reactions in water, organic solvents, biphasic fluorous/organic solvents, and supercritical CO2 are also described.     

n- and p-Type modulation of ZnO nanomesh coated graphene field effect transistors

Periodic zinc oxide (ZnO) nanomeshes of different thicknesses were deposited on single-layer graphene to form back-gated field effect transistors (GFETs). The GFETs exhibit tunable electronic properties, featuring n- and p-type characteristics by merely controlling the thickness of the ZnO nanomesh layer. Furthermore, the effect of thermal strain on the GFETs from the substrate is suppressed by the ZnO nanomesh, which improves the thermal stability of the GFETs. This nanopatterning technique could modulate the electronic properties of the GFETs effectively.     

Effect of the reaction bath temperature in a fixed-bed reactor for oxidation of oxylene over V2O5/TiO2 catalysts

The effects of the reaction variables in the operation of a fixed-bed reactor for oxidation ofo-xylene over V₂O₅/TiO₂ catalysts were studied experimentally using a bench reactor. Reaction temperature, feed flow rate and feed concentration ofo-xylene were found to have significant effects on the product distribution and the temperature profile in the reactor. Drastic enhancements ofo-xylene oxidation reaction were observed at some conditions, which was ascribed to the effect of heat accumulated in the bed and indicated a possible way to increase the productivity in the industrial condition. This paper was presented at the 8th APCChE (Asia Pacific Confederation of Chemical Engineering) Congress held at Seoul between August 16 and 19, 1999.     

The influence of heat treatment on the properties of shape memory fibers. II. Tensile properties,dimensional stability,recovery force relaxation,and thermomechanical cyclic properties

Shape memory fibers (SMFs) were prepared via a melt spinning process. The fibers were subject to different heat treatments to eliminate internal stress and structure deficiency caused during the melt spinning process. The influences of heat treatments on the SMF thermal properties, molecular orientation, tensile properties, dimensional stability, recovery force relaxation, and thermomechanical cyclic properties were studied. It was found that the heat treatments increased soft segment crystallinity and phase separation while decreased molecular orientation. The low‐temperature heat treatment increased the breaking elongation, shape fixity ratios, and decreased boiling water shrinkage while shape recovery ratios were decreased. High‐temperature treatment increased both the shape recovery ratios, fixity ratios, recovery stress stability and at the same time decreasing the fiber mechanical strength. The results from differential scanning calorimetry, molecular orientation apparatus, and cyclic tensile testing were used to illustrate the mechanism governing the mechanical properties and shape memory effect. To obtain comprehensive outstanding properties, the SMF is expected to be treated at a high temperature because of the hard segment high glass transition temperature. Unfortunately, the heat treatment could not be conducted at a too high temperature because the SMF became too tacky and soft due to the melting of the soft segment phase. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Dynamic modelling of CO2 absorption for post combustion capture in coal-fired power plants

Power generation from fossil fuel-fired power plants is the largest single source of CO₂ emissions. Post combustion capture via chemical absorption is viewed as the most mature CO₂ capture technique. This paper presents a study of the post combustion CO₂ capture with monoethanolamine (MEA) based on dynamic modelling of the process. The aims of the project were to compare two different approaches (the equilibrium-based approach versus the rate-based approach) in modelling the absorber dynamically and to understand the dynamic behaviour of the absorber during part load operation and with disturbances from the stripper. A powerful modelling and simulation tool gPROMS was chosen to implement the proposed work. The study indicates that the rate-based model gives a better prediction of the chemical absorption process than the equilibrium-based model. The dynamic simulation of the absorber indicates normal absorber column operation could be maintained during part load operation by maintaining the ratio of the flow rates of the lean solvent and flue gas to the absorber. Disturbances in the CO₂ loading of the lean solvent to the absorber significantly affect absorber performance. Further work will extend the dynamic modelling to the stripper for whole plant analysis.