Graft copolymerization onto starch. IV. Grafting of methyl methacrylate to granular native potato starch by manganic pyrophosphate initiation

A study has been made of graft copolymerization of methyl methacrylate onto native potato starch in aqueous slurry at 30°C. As Mn³⁺ concentration was increased from 0.15 X 10^-3M to 1.0 X 10^-3M, conversion of monomer to polymer and add-on of polymer to starch increased and frequency of grafts (anhydroglucose units per grafted chain) decreased sharply. The average molecular weights of the PMMA grafts also decreased in this range. At Mn³⁺ concentrations from 1.0 X 10^-3M to 3.0 X 10^-3M, only minor changes in grafting parameters were observed. When the amount of starch charged per batch was increased threefold, the add-on decreased sharply, the molecular weight increased slightly, and the conversion of MMA monomer to polymer remained almost constant. The increase in frequency of grafts (AGU/chain) was almost directly proportional to the increase in the amount of starch charged. In all cases the average molecular weights of grafts were of the order of 10⁶ and the grafting efficiencies high, normally greater than 85%. These results were compared with those previously obtained for grafting of acrylonitrile onto starch. They were interpreted in terms of initial (Mn³⁺)/(AGU) ratio, total number of radicals initiating grafting, and compatibility of methyl methacrylate monomer with poly(methyl methacrylate) chains.     

Kinetic Modelling in Automotive Catalysis

There are no general accepted models for CO and HC oxidation and NO _x reduction in automotive catalysis. Many factors affect the observed kinetics e.g. the catalyst preparation method and conditioning, the composition of the exhaust gases, mass and heat transfer, and all the reaction conditions that the catalyst has been exposed to prior to an experiment. However, most experiments are done under idealized conditions with a fresh catalyst and without water, SO₂, etc. Simple models will only describe the individual experiments and more complex models require determination of the parameters from independent measurements under realistic conditions. The kinetic models available in the literature are only reliable for the exact catalyst and reaction conditions for which they have been developed.     

The effects of plasticizers on the dynamic mechanical and thermal properties of poly(lactic acid)

Poly(lactic acid) (PLA) was blended with five plasticizers in a batchwise mixer and pressed into films. The films were analyzed by means of dynamic mechanical analysis and differential scanning calorimetry to investigate the properties of the blends. Triacetine and tributyl citrate proved to be effective as plasticizers when blended with PLA. The glass transition temperature of PLA decreased linearly as the plasticizer content was increased. Both plasticizers were miscible with PLA to an extent of ～ 25 wt %. At this point, the PLA seemed to be saturated with plasticizer and the blends tended to phase separate when more plasticizer was added. There were also signs of phase separation occurring in samples heated at 35, 50, and 80°C, most likely because of the material undergoing crystallization. The presence of the plasticizers induced an increased crystallinity by enhancing the molecular mobility. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 1227–1234, 2002     

Hydrogen storage in Pd nanodisks characterized with a novel nanoplasmonic sensing scheme

A novel nanoplasmonic sensing scheme is introduced based on remote real-time detection of induced electronic and shape/structural changes in a metal nanoparticle during the metal-hydride formation process. The localized surface plasmon resonance (LSPR) of the nanoparticle is utilized as signal transducer for optical readout. As a model system, hydrogen storage through metal-hydride formation is studied in Pd nanodisks. The experimentally obtained plasmonic response to hydrogen uptake yields pressure-LSPR-response isotherms. These isotherms are found to obey Sievert's law in the low-pressure range and exhibit a characteristic "plateau" at 18 Torr upon hydrogen charging and 7.5 Torr upon hydrogen discharging. An additional experiment also clearly shows the typical temperature dependence of the plateau pressure. Conversion of the LSPR signal to absolute hydrogen concentration, based on a proposed linear dependence of the LSPR response to hydrogen uptake, results in p-C isotherms in excellent agreement with those in the literature. This puts forward that the LSPR response is an extremely sensitive, remote, and real-time probe for "bulk" changes in a metal nanoparticle and can readily be used to study processes such as metal-hydride formation for hydrogen storage applications, alloying on the nanoscale, thermal reshaping, and so forth.     

Localization of intense electromagnetic waves in plasmas

We present theoretical and numerical studies of the interaction between relativistically intense laser light and a two-temperature plasma consisting of one relativistically hot and one cold component of electrons. Such plasmas are frequently encountered in intense laser-plasma experiments where collisionless heating via Raman instabilities leads to a high-energetic tail in the electron distribution function. The electromagnetic waves (EMWs) are governed by the Maxwell equations, and the plasma is governed by the relativistic Vlasov and hydrodynamic equations. Owing to the interaction between the laser light and the plasma, we can have trapping of electrons in the intense wakefield of the laser pulse and the formation of relativistic electron holes (REHs) in which laser light is trapped. Such electron holes are characterized by a non-Maxwellian distribution of electrons where we have trapped and free electron populations. We present a model for the interaction between laser light and REHs, and computer simulations that show the stability and dynamics of the coupled electron hole and EMW envelopes.     

Parametric study and multiple correlations on air-side heat transfer and friction characteristics of fin-and-tube heat exchangers with large number of large-diameter tube rows

In the present study, for industrial applications of large inter-coolers employed in multi-stage compressor systems the air-side laminar heat transfer and fluid flow characteristics of plain fin-and-tube heat exchangers with large number of tube rows and large diameter of the tubes are investigated numerically through three-dimensional simulations based on the SIMPLE algorithm in Cartesian coordinates. The effects of parameters such as Reynolds number, the number of tube rows, tube diameter, tube pitches and fin pitch are examined, and the variations of heat transfer due to variations of fin materials are also observed. It is found that the heat transfer and fluid flow approach fully developed conditions when the number of tube rows is greater than six, and the tube diameter as well as the fin pitch have much more significant effects than the tube pitch, and the heat transfer of high-conductivity material is larger than that of low-conductivity material especially in the high Reynolds number regime. Due to the fact that the existing correlations are not valid for large tube diameters and number of tube rows, the heat transfer and flow friction of the presented heat exchangers are correlated in the multiple forms. The correlation is so obtained that it can be used for further studies such as performance prediction or geometrical optimization.     

Performance predictions of laminar and turbulent heat transfer and fluid flow of heat exchangers having large tube-diameter and large tube-row by artificial neural networks

In this work an artificial neural network (ANN) is used to correlate experimentally determined and numerically computed Nusselt numbers and friction factors of three kinds of fin-and-tube heat exchangers having plain fins, slit fins and fins with longitudinal delta-winglet vortex generators with large tube-diameter and large the number of tube rows. First the experimental data for training the network was picked up from the database of nine samples with tube outside diameter of 18 mm, number of tube rows of six, nine, twelve, and Reynolds number between 4000 and 10,000. The artificial neural network configuration under consideration has twelve inputs of geometrical parameters and two outputs of heat transfer Nusselt number and fluid flow friction factor. The commonly-implemented feed-forward back propagation algorithm was used to train the neural network and modify weights. Different networks with various numbers of hidden neurons and layers were assessed to find the best architecture for predicting heat transfer and flow friction. The deviation between the predictions and experimental data was less than 4%. Compared to correlations for prediction, the performance of the ANN-based prediction exhibits ANN superiority. Then the ANN training database was expanded to include experimental data and numerical data of other similar geometries by computational fluid dynamics (CFD) for turbulent and laminar cases with the Reynolds number of 1000–10,000. This in turn indicated the prediction has a good agreement with the combined database. The satisfactory results suggest that the developed ANN model is generalized to predict the turbulent or/and laminar heat transfer and fluid flow of such three kinds of heat exchangers with large tube-diameter and large number of tube rows. Also in this paper the weights and biases corresponding to the neural network architecture are provided so that future research can be carried out. It is recommended that ANNs might be used to predict the performances of thermal systems in engineering applications, especially to model heat exchangers for heat transfer analysis.     

Water-based radiation-curable latexes

Film-forming polystyrene/poly(n-butyl acrylate-co-glycidyl methacrylate) [PS/P(BA-co-GMA)] core–shell latex particles were prepared via a two-stage emulsion polymerization procedure using a polystyrene latex seed. Delayed addition of GMA was used in order to locate functional epoxy groups close to the particle surfaces. It was found that a temperature of 25°C at the second-stage polymerization, in combination with a redox initiator system, was essential for the formation of a uniform shell of BA–GMA copolymer around the PS core. The latex particle morphology was investigated by transmission electron microscopy (TEM). Reactive double bonds were introduced into the particle shells in order to produce a film-forming latex system that could be cured by ultraviolet (UV)-radiation without any need to use reactive multifunctional monomers or oligomers as crosslinkers. The surface-bound epoxy groups were used as grafting sites for amine or carboxyl functional unsaturated monomers, respectively. The grafting was demonstrated by Fourier transform infrared (FTIR) spectroscopy. Films prepared from modified and unmodified latexes were exposed to UV radiation in the presence of a photoinitiator. Crosslinking was tested by thermal mechanical analysis (TMA) and by determination of swelling and gel content of exposed films. It was demonstrated that films from the modified latexes after irradiation had significantly higher stiffness and gel content and showed lower swelling than unmodified ones. © 1996 John Wiley & Sons, Inc.     

Viscoelastic properties and film morphology of heterogeneous styrene–butadiene latexes

Heterogeneous carboxylated styrene–butadiene (S/Bu) latexes were prepared by a twostage emulsion polymerization process, using three PS seeds with different molecular weights. The second-stage polymer was a copolymer with a fixed S/Bu ratio of 1 : 1 and a methacrylic acid (MAA) content of either 1 or 10 wt %. Morphological studies by transmission electron microscopy (TEM) as well as studies of the viscoelastic properties by mechanical spectroscopy have been performed on films prepared from the latexes. The studies showed that the glass transition temperature, T_g, of the second-stage polymer was considerably affected by copolymerization with MAA. An increase in the MAA content in the second-stage polymer increased the T_g of this phase significantly. Addition of DVB as a crosslinking agent in the preparation of the PS seed phase substantially increased the rubbery moduli of the films, whereas the glass transition temperature of the second-stage polymer was unaffected. On the other hand, the presence of a chain transfer agent reduced the glass transition of the second-stage copolymer containing 1 wt % MAA dramatically, whereas the rubbery modulus was unaffected. When the MAA content was increased to 10 wt % the influence of the MAA monomer had a dominating effect on T_g. Latexes containing 10 wt % MAA had T_g values close to each other, regardless of chain transfer agent present in the second-stage polymerization. It was found that the morphology of the latex particles influenced the rubbery modulus of the films. The presence of irregularly shaped seed particles in samples prepared from a crosslinked PS seed had a considerable reinforcing effect on the films, whereas spherical seed particles originating from core–shell particles had a less reinforcing effect. © 1996 John Wiley & Sons, Inc.     

Analysis of cyclodextrins using a calorimetric biosensor

A thermostable α-amylase catalyzed the exothermal hydrolysis of cyclodextrins. It was immobilized covalently via a spacer on controlled pore glass (CPG-10) or Silicagel. The temperature signal caused by the reaction heat of the cyclodextrin hydrolysis was determined in a one column calorimetric system (enzyme thermistor). It was correlated to the cyclodextrin concentration and depended on the type of enzyme carrier and kind of cyclodextrin hydrolyzed. The proposed technique offers a direct route to the determination of α-amylase activity, and the results are of importance for analysis of cyclodextrin concentration.