Twin‐screw extrusion of polypropylene‐clay nanocomposites: Influence of masterbatch processing,screw rotation mode,and sequence

This work seeks to optimize the twin‐screw compounding of polymer‐clay nanocomposites (PCNs). Proportional amounts (3:1) of maleic anhydride functionalized polypropylene compatibilizer (PP‐g‐MA) and organically modified montmorillonite clay at clay loadings of 1, 3, and 5 wt% were melt‐blended with a polypropylene (PP) homopolymer using a Leistritz Micro 27 twin‐screw extruder. Three melt‐blending approaches were pursued: (1) a masterbatch of PP‐g‐MA and organoclay were blended in one pass followed by dilution with the PP resin in a second pass; (2) all three components were processed in a single pass; and (3) uncompatibilized PP and organoclay were processed twice. Both corotation and counterrotation operation were utilized to investigate the effect of screw rotation mode and sequence on organoclay exfoliation and dispersion. X‐ray diffraction was employed to characterize basal spacing; however, since rheology is known to be highly sensitive to mesoscale organoclay structure, it is an ideal tool to examine the relationship between the various processing methods and exfoliation and dispersion. A holistic analysis of rheological data demonstrates the efficacy of the masterbatch approach, particularly when compatibilizer and organoclay are blended in counterrotating mode followed by dilution with matrix polymer in corotating mode. POLYM. ENG. SCI., 47:898–911, 2007. © 2007 Society of Plastics Engineers     

Trans Fatty Acid Intakes and Food Sources in the U.S. Population: NHANES 1999–2002

Because of efforts to decrease trans fatty acids (TFA) in the food supply, intake should be assessed in the population to establish a baseline TFA intake. The 1999?C2002 National Health and Nutrition Examination Survey (NHANES) was used to identify a benchmark for TFA intake. TFA was estimated by mean, median, and quintile of intake, TFA intake data were weighted using the NHANES 4-year sample weights. The main outcome measures included TFA intake in grams per day and percentage of energy in the top 25 food sources of TFA. Data are reported for 16,669 individuals ??3 years of age. Median TFA intake was 2.3?% of calories (5?g/day) with 0.9?C4.5?% of energy (1.5?C13.1?g/day) over different quintiles of intake. Mean TFA intake was 2.5?% of energy (6.1?g/day). The range of TFA intake in the fifth quintile was very large, i.e., 3.5?C12.5?% of energy or 8.8?C92.4?g/day. Increasing quintiles of TFA intake were associated with increases in total fat (26.7?C37.6?% of energy), saturated fat (7.6?C10.5?% of energy), and calories (for those >20?years of age: 2,416?C2,583 for men and 1,679?C1,886 for women). Major food sources of dietary TFA were cakes, cookies, pies, and pastries. Based on current dietary guidance to consume as little industrial TFA as possible, much progress is needed to attain this goal, including food industry efforts to remove TFA from the food supply and educating the public about making healthy food choices.     

The O<Subscript>2</Subscript> + NH<Subscript>3</Subscript> Reaction Over Rh(110): Steady State Kinetics and Oscillatory Behavior

Abstract  

The kinetics of ammonia oxidation with oxygen over a Rh(110) surface were studied in the pressure range 10⁻⁵–10⁻⁴ mbar. Nitrogen was found to be the preferred product at low partial pressures ratios \textp_{\texto 2} :\textp_{\textNH 3} {\text{p}}_{{{\text{o}}_{ 2} }} :{\text{p}}_{{{\text{NH}}_{ 3} }} , while the NO pathway was favored with oxygen rich gas mixtures and at high temperature. The reactive sticking coefficient of O₂ reaches up to 0.05 under steady state conditions. Pronounced hysteresis effects in the reaction rates were found in T-cycling experiments. Sustained oscillations in the reaction rates occurred under isothermal conditions at T = 620 K at a total pressure of 4 × 10⁻⁵ mbar.     

A high density of vertically-oriented graphenes for use in electric double layer capacitors

The growth, capacitance and frequency response of vertically-oriented graphenes grown by radio frequency plasma-enhanced chemical vapor deposition on nickel substrates and used as electrodes in electric double layer capacitors (EDLCs) are presented. The graphenes grown on the grain boundary of substrates show a faster growth rate, but less ordered structure than in the center of the nickel grain. At a few nanometers away from the grain boundaries the graphenes grow vertically at the rate of 70–80 nm per minute. The film height increased linearly with growth time from 700 nm (10 min sample) to 3.1 μm (40 min sample). Raman spectra show that the intensity ratio of the D band to G band gradually decreased with growth time to a value of 0.5, indicating that the crystalline order of the graphene increases with height. The specific capacitance of symmetric, parallel plate EDLC devices fabricated with these films was found to increase in a linear fashion with growth time up to values greater than 120 μF/cm² at 1 kHz. An impedance phase angle of ?45° was reached at 30 kHz. Specific capacitance normalized to growth height suggests that mechanisms other than double layer charge storage on planar surface area were operative.     

Glycerol citrate polyesters produced through heating without catalysis

The influence of various heating methods without catalysis to prepare polyesters from citric acid : glycerol blends were studied. In the presence of short-term microwave treatments, i.e., 60 s at 1200 W, blends of glycerol and citric acid invariably formed solid amorphous polyesters. Fourier transform infrared spectroscopy showed that citric acid and glycerol blends can form highly stable polymers composed of ester bonds. The glycerol citrate polyester polymers exhibited the least degradation in water, more in acid solutions (0.1–1.0M HCl), and the most deterioration in strong alkaline solutions (0.1–1.0M NaOH) after 72 h soakings. Polyesters of glycerol and citric acid were studied with differential scanning calorimetry and thermal gravimetric analysis. The polyesters were found to be thermally stable (up to 313°C). © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Tensile testing and fracture mechanism analysis of polyvinyl alcohol nanofibrous webs

A tensile properties testing study was conducted to understand the influence of thickness, cross-head speed (speed of testing), gauge length (GL; specimen test length), and sample shape on important tensile properties of polyvinyl alcohol (PVA) nanofiber webs. The effects of each testing parameter on load at break, extension at break, Young's modulus, and tensile stress–strain curve of PVA nanofiber webs are analyzed. The Welch two sample t-tests show the significant difference among tested data. Using interaction plots, two-way analysis of variance, and margin mean plots, the interaction effects among testing parameters have been analyzed. Of all the factors, cross-head speed, the interaction among GL, and sample thickness (GL: Thickness) and the interaction among GL, testing speed and sample thickness (GL: Speed: Thickness) have significant influence on the tensile properties of PVA nanofiber webs. Moreover, the hypothesized model of mechanism of tensile strain–stress curve of PVA nanofiber webs has been proposed. Based on the model, the tensile strain–stress curve can be split into three stages: linear elastic, partial break up, and complete breakage. This study will provide a better understanding of tensile testing parameters' effects and their interaction effects on the tensile properties of nanowebs.     

Selective Desulfurization Significantly Expands Sequence Variety of 3'-Peptidyl-tRNA Mimics Obtained by Native Chemical Ligation

Accessible: Functionally complex 3'-peptidyl-RNA conjugates can be efficiently desulfurized under free radical reaction conditions as demonstrated here. One-pot procedures for native chemical ligation (NCL) and desulfurization enable sequences for this class of bioconjugates that are inaccessible by other methods.     

H型气体水合物导热系数的分子动力学模拟

气体水合物^[1]是由水和小分子气体形成的非水学计量型笼型晶体。到目前为止,已经发现的气体水合物结构有3种,即Ⅰ型、Ⅱ型和H型,水合物的导热系数是一个很重要的物性参数,人们已对Ⅰ型和Ⅱ型水合物的导热系数进行了较多的实验和理论研究,包括分子模拟研究^[2],由于H型水合物发现较晚,其导热系数无论是实验值还是理论值均未见文献报道,因此本文对H型水合物的导热系数进行了分子动力学模拟。为了给H型气体水合物导热系数的模拟计算提供可靠的热能模型和模拟算法,本文首先对冰体系和空水合物的导热系数进行了分子动力学模拟。     

Synthetic Modular Antibody Construction by Using the SpyTag/SpyCatcher Protein-Ligase System

Efforts to engineer recombinant antibodies for specific diagnostic and therapy applications are time consuming and expensive, as each new recombinant antibody needs to be optimized for expression, stability, bio-distribution, and pharmacokinetics. We have developed a new way to construct recombinant antibody-like “devices” by using a bottom-up approach to build them from well-behaved discrete recombinant antibody domains or “parts”. Studies on antibody structure and function have identified antibody constant and variable domains with specific functions that can be expressed in isolation. We used the SpyTag/SpyCatcher protein ligase to join these parts together, thereby creating devices with desired properties based on summed properties of parts and in configurations that cannot be obtained by using genetic engineering. This strategy will create optimized recombinant antibody devices at reduced costs and with shortened development times.