STUDY OF DEGRADATION KINETICS OF BLENDS OF EPOXY AND RESOLE: A STATISTICAL APPROACH

Blends of resole and epoxy were prepared by physical mixing, and cured with 30% polyamide based on blend resin and polyamide. Degradation of each sample was studied by dynamic thermogravimetric analysis in nitrogen atmosphere at a heating rate of 10°C min^-1. The degradation of blends of epoxy and resole having 30 wt % polyamide proceeded with 0.50th order. This result was found with the Coats-Redfern equation using best-fit analysis, and further confirmed by linear regression analysis. The validity of data was checked by t test analysis. From this value of reaction order, activation energy (E) and pre-exponential factor (Z) were calculated. The values of activation energy increased, whereas the values of pre-exponential factor decreased as the resole content in the blend decreased from 100 to 0 wt %.     

Viscosity studies of crown ether-containing polymers in solutions of alkali salts. Intra- versus intermolecular crown-cation complexes

The complexation of cations to poly(vinylbenzocrown ethers) strongly affects the viscosity of the polymers. In mixtures of THF-MeOH the reduced viscosities of the polymer-salt solutions at constant polymer concentration pass through a maximum, their values depending on the cation-to-crown ratio and the binding constant of the cations to the poly(crown ethers). Crosslinking and abnormally high viscosities are found when a cation can complex simultaneously with two crown ligands, e.g. in mixtures of potassium salts with styrene copolymers containing pendent benzo-15-crown-5 moieties. In such systems competition exists between the formation of inter- and intramolecular 2:1 crown-cation complexes, and their relative importance depends on the crown content of the copolymer. Spectrophotometric measurements in THF mixtures of styrene-vinylbenzo-15-crown-5 copolymers and potassium picrate reveal that at low crown concentration, intramolecular complexes can form when crown ligands are separated, on the average, by less than four styrene units. The data, in combination with calculations on the distribution of crown ligands along a chain as a function of crown content, can be used to rationalize the viscosity behaviour of these polymer solutions.     

Inference of optimal speed for sound centrifugal casting of Al-12Si alloys

True centrifugal casting is a standard casting technique for the manufacture of hollow, intricate and sound castings without the use of cores. The molten metal or alloy poured into the rotating mold forms a hollow casting as the centrifugal forces lift the liquid along the mold inner surface. When a mold is rotated at low and very high speeds defects are found in the final castings. Obtaining the critical speed for sound castings should not be a matter of guess or based on experience. The defects in the casting are mainly due to the behavior of the molten metal during the teeming and solidification process. Motion of molten metal at various speeds and its effect during casting are addressed in this paper. Eutectic Al-12Si alloy is taken as an experiment fluid and its performance during various rotational speeds is discussed.     

Dynamic analysis and split range control for maximization of operating range of continuous microbial fuel cell

Human development is inherently connected with availability of water and energy. Energy production requires water, whereas water treatment needs energy. On the other hand, microbial fuel cell has capability to produce energy and water simultaneously from waste water or organic matter. In this paper, first principle-based model of variable volume microbial fuel cell is simulated. Hydraulic retention time is selected as the manipulated variable using the study of steady state and dynamic responses. Classical PI and model predictive control strategies are developed for controlling the produced power from the cell, and its performance is tested for servo problem. Settling time for positive and negative set points is found to be 126 and 889 h in case of classical PI and 120 and 750 h in case of linear MPC, respectively along with large increase (three times order of magnitude) in working volume for negative set point. These control challenges are overcome by using split range controller with variable and constant volume microbial fuel cells. The settling time for negative set point is found to be 49 and 21 h for classical PI and linear MPC schemes, respectively, which is significantly lower than using only variable volume microbial fuel cell. Also, there is no increase in the working volume of the constant volume microbial fuel cell. Hence, operating range of the microbial fuel cell is enhanced using split range controller.     

Studies on the blends of modified epoxy resin and carboxyl-terminated polybutadiene (CTPB)—II: thermal and mechanical characteristics

Blend samples were prepared by physical mixing of resole–epoxy blend with carboxyl-terminated polybutadiene (CTPB) liquid rubber ranging between 0 and 25 wt% in the interval of 5 wt%. Resoles were synthesized with phenol and various alkyl phenols. The blends were cured with 40 wt% polyamide. The structural changes during the curing were investigated by infra-red spectroscopic analysis. The presence of CTPB in resole-epoxy blends did not affected the values of cure times and ΔH whereas the gel time decreased up to 15 wt% addition of CTPB in the blends. The blend systems containing p-cresolic resole, epoxy and CTPB showed minimum gel time amongst all other blend samples. A clear-cut two-step mass loss in thermogravimetric (TG) trace of unmodified and CTPB-modified systems was observed. The mechanical properties of the blend samples were found to be affected by the CTPB addition. The plane strain fracture toughness (K _IC) values of CTPB-modified matrix resins were greater that that for the unmodified resole/epoxy blends. This was further verified by scanning electron microscopic (SEM) analysis.     

Equilibrium solubility of CO<Subscript>2</Subscript> in aqueous binary mixture of 2-(diethylamine)ethanol and 1, 6-hexamethyldiamine

CO₂ solubility data are important for the efficient design and operation of the acid gas CO₂ capture process using aqueous amine mixture. 2-(Diethylamino)ethanol (DEEA) solvent can be manufactured from renewable sources like agricultural products/residue, and 1,6-hexamethyldiamine (HMDA) solvents have higher absorption capacity as well as reaction rate with CO₂ than conventional amine-based solvents. The equilibrium solubility of CO₂ into aqueous binary mixture of DEEA and HMDA was investigated in the temperature range of 303.13-333.13 K and inlet CO₂ partial pressure in the range of 10.133-20.265 kPa. Total concentration of aqueous amine mixtures in the range of 1.0-3.0 kmol/m³ and mole fraction of HMDA in total amine mixture in the range of 0.05-0.20 were taken in this work. CO₂ absorption experiment was performed using semi-batch operated laboratory scale bubble column to measure equilibrium solubility of CO₂ in amine mixture, and CO₂ absorbed amount in saturated carbonated amine mixture was analyzed by precipitation-titration method using BaCl₂. Maximum equilibrium CO₂ solubility in aqueous amine mixture was observed at 0.2 of HMDA mole fraction in total amine mixture with 1.0 kmol/m³ total amine concentration. New solubility data of CO₂ in DEEA+HMDA aqueous mixtures in the current study was compared with solubility data available in previous studies conducted by various researchers. The study shows that the new absorbent as a mixture of DEEA+HMDA is feasible for CO₂ removal from coal-fired power plant stack gas streams.     

Long-term Streamflow Forecasting Based on Ensemble Streamflow Prediction Technique: A Case Study in New Zealand

Streamflow forecasts are essential for optimal management of water resources for various demands, including irrigation, fisheries management, hydropower production and flood warning. Despite operational application of Ensemble Streamflow Prediction (ESP) for long-range streamflow forecasts in United States of America by the National Weather Service River Forecast System, no such approach has been explored in New Zealand. The objective of the present paper is to explore ESP-based forecasts in New Zealand catchments, highlighting its capability for seasonal flow forecasting. In this paper, a probabilistic forecast framework based on ESP technique is presented, with the basic assumption that future weather patterns will reflect those experienced historically. Hence, past forcing data (input to hydrological model) can be used with the current initial condition of a catchment to generate an ensemble of flow predictions. In the present study employs the ESP-based approach using the TopNet hydrological model with a range of past forcing data and current initial conditions. An ensemble stream flow predictions which provide probabilistic hydrological forecasts, reflecting the intrinsic uncertainty in climate, with lead time up to three months is presented for the Rangitata, Ahuriri, and Hooker and Jollie catchments in South Island, New Zealand. Verification of the forecast over the period 2000-2010 indicates a Ranked Probability Skill Score of 23 to 69 % (over climatology) across the four catchments. In general, improvement in ESP forecasting skill over climatology is greatest in summer for all catchments studied. The ESP based forecast exhibited higher skill for a greater percentage of the forecasting period than climatology. As a result, the ESP forecast can provide better over all information for integrated water resources management purpose. ESP-based forecasts using the TopNet hydrological model have potential as tools for water resource management in New Zealand catchments.     

Flame‐based synthesis and in situ functionalization of palladium alloy nanoparticles

Flame‐driven synthesis and functionalization of palladium‐containing nanoparticles is demonstrated using a high temperature reducing jet (HTRJ) process that decouples flame chemistry from particle formation chemistry and provides a reducing environment that enables synthesis of metal nanoparticles from low‐cost aqueous precursors. Nanoparticles with controlled palladium, copper, and silver content were synthesized and functionalized with amine‐containing ligands using both in situ and ex situ approaches. For in situ functionalization, octylamine was sprayed into the quench section of the HTRJ reactor to cap the nanoparticles in the gas phase. For the ex situ approach, the “bare” nanopowders were heated in various amines (hexylamine, octylamine, and oleylamine) to form stable dispersions. Use of oleylamine at high temperature allowed modification of the nanoparticle size and shape while maintaining the alloy composition. These in situ and ex situ functionalization methods provide flexibility to tailor particles for specific applications such as electrocatalysis or hydrogen purification. © 2018 American Institute of Chemical Engineers AIChE J, 64: 3826–3834, 2018     

A scheme to improve PCE of differential-drive CMOS rectifier for low RF input power

In this paper, a scheme to improve power conversion efficiency (PCE) of differential-drive CMOS rectifier for low RF input power is proposed. Auxiliary transistors are utilized to provide forward body biasing for the primary transistors of the rectifier. As a result, the threshold voltages of the primary transistors are reduced. Hence, higher PCE is achieved for lower RF input power. The circuits are designed in a standard 180 nm CMOS technology. Measurement results exhibit a considerable PCE improvement by the proposed design at the RF input frequency of 916 MHz in the three-stage configuration. For 50 K\(\mathrm{{\Omega }}\) resistive load, the proposed rectifier has a maximum 10.9 % PCE improvement and requires 2 dB less RF input power to achieve the comparable peak PCE.     

Error based criterion for on-line wavelet data compression

Wavelet based data compression methods have demonstrated superior performance over the conventional interpolative methods. However, the wavelet based methods need thresholding on the wavelet domain coefficients. Since wavelet coefficients are not commonly intuitive to engineers, significant a priori knowledge of either the wavelet coefficients or process thresholds is required. So unless thresholds are pre-specified, this requirement makes wavelets unsuitable for on-line implementations. Furthermore, as the relation between the wavelet domain coefficients and the measures of the quality of compression [root mean square error (RMSE) and local point error (LPE)] is not straightforward, it is difficult to achieve good control over the quality of compression by specifying thresholds on the wavelet coefficients. In this paper, an error based criterion is proposed for online wavelet data compression. It uses semantically straightforward measures of the quality of the result to be obtained to adaptively calculate the thresholds. Given a bound on time domain error limits like the RMSE and LPE, this technique adaptively computes the threshold values in wavelet domain. Experiments show that the resulting algorithm gives superior compression as compared to other wavelet based methods. Most importantly, it can be used on-line and provides an effective way of controlling LPE and RMSE. Finally, this method can easily be extended to other on-line wavelet applications such as data rectification and de-noising.