Blends of amorphous and crystalline polylactides with poly(methyl methacrylate) and poly(methyl acrylate): a miscibility study

Blends of amorphous and crystalline polylactides (PDLA and PLLA) with poly(methyl methacrylate) (PMMA) and poly(methyl acrylate) (PMA) have been prepared. Thermal behaviour and miscibility of these blends along the entire composition interval were studied by differential scanning calorimetry (d.s.c.). The results were compared with those obtained by dynamic mechanical analysis (DMTA). Only one T_g was found in PDLA/PMA and PDLA/PMMA blends, indicating a high degree of miscibility in both systems. Nevertheless, the PDLA/PMMA blend presented enlargements of the T_g width at high PMMA contents. In this case, additional evidence of complete miscibility was obtained by studying the evolution of the enthalpic recovery peaks which appear after different thermal annealing treatments. When the polylactide used was semicrystalline (PLLA), once the thermal history of the blends had been destroyed, crystallization of PLLA was disturbed in both blends PLLA/PMMA and PLLA/PMA, but in a rather different fashion: in the first case crystallization was almost prevented while in the second one it was favoured. This behaviour was explained in terms of the effect of the higher stiffness as indicated by the value of T_g for PMMA compared to that for PMA.     

CONTROL OF MOLECULAR WEIGHT IN A BATCH POLYMERIZATION REACTOR USING LONG-RANGE PREDICTIVE CONTROL METHODS

Recently two powerful control algorithms, namely, dynamic matrix control (DMC) and extended self-tuning regulator (ESTR), have been advocated for the design of robust industrial controllers. The present paper demonstrates the application of DMC and ESTR algorithms to a bulk methyl methacrylate batch polymerization reactor operating under strong diffusional limitations of termination and propagation reactions. A realistic mathematical model is employed to simulate the strong nonlinear, time-varying dynamics of the polymerization process. The general control objective is to maintain the monomer conversion and number-average molecular weight along some desired state trajectories despite the presence of process disturbances in the total initiator concentration. It is shown that both controllers can satisfactorily control the monomer conversion and number-average molecular weight by manipulating the polymerization temperature. The similarities and the main operating features of the two controllers are examined and their closed-loop performance is directly compared to the performance of a conventional linear quadratic controller (LQC). Finally the effects of DMC and ESTR tuning parameters on the calculated control action are investigated.     

优质中,高碳钢的冷轧长带生产

优质中、高碳钢的冷轧长带在生产过程中必须研究最合理的热处理工艺,以及最经济的热处理制度和轧程的安排,才能低耗高效地生产符合优质冷带技术标准的产品。     

Learning control of fermentation process with an improved DHP algorithm☆

Control of the fed-batch ethanol fermentation processes to produce maximum product ethanol is one of the key issues in the bioreactor system. However, ethanol fermentation processes exhibit complex behavior and nonlinear dynamics with respect to the cel mass, substrate, feed-rate, etc. An improved dual heuristic program-ming algorithm based on the least squares temporal difference with gradient correction (LSTDC) algorithm (LSTDC-DHP) is proposed to solve the learning control problem of a fed-batch ethanol fermentation process. As a new algorithm of adaptive critic designs, LSTDC-DHP is used to realize online learning control of chemical dynamical plants, where LSTDC is commonly employed to approximate the value functions. Application of the LSTDC-DHP algorithm to ethanol fermentation process can realize efficient online learning control in continuous spaces. Simulation results demonstrate the effectiveness of LSTDC-DHP, and show that LSTDC-DHP can obtain the near-optimal feed rate trajectory faster than other-based algorithms.     

Batch grinding kinetics in the presence of two active zones

It is shown that the presence of two active zones in a grinding mill leads to apparent non-first-order breakage of the top feed size in batch grinding. The equations to describe the kinetics of the breakage of the top size and of the total size distribution are obtained, and an analytical solution is given. Parametric analysis shows the influences of the relative magnitudes of the two active zones, the rates of breakage and the rate of mass transfer between the two active zones on the mill product. The concepts may be applicable to any type of mill where two active zones can exist.     

Intergranular corrosion behavior of the 7075-T6 aluminum alloy under different annealing conditions

The effect of annealing conditions producing various grain sizes on the intergranular corrosion behavior of high-strength aluminum alloy type 7075-T6 was investigated using electrochemical polarization techniques. Aluminum alloy specimens with large grain size exhibited lower breakdown potentials in deaerated 0.5 M NaCl solution. The breakdown potentials decreased with increasing grain size. Microscopic observations of the exposed surfaces during potentiostatic polarization testing showed that the coarse grain structure promotes intergranular crack growth.     

pH-dependant structural and morphology evolution of Ni(OH)2 nanostructures and their morphology retention upon thermal annealing to NiO

Nickel hydroxide nanosheets, nanobelts and nanorods were prepared by hydrothermal treatment of the precipitates obtained at different pH values. The morphology and crystal structure of the products could be controlled simply by adjusting the pH value at precipitation. Interconnected nanosheets of hexagonal β-Ni(OH)₂ with thickness around 10–20 nm were formed at pH ∼ 11, whereas nanobelts with typical widths around 40–80 nm, and nanorods with diameters around 50–60 nm of phase pure α-Ni(OH)₂ containing intercalated sulphate ions were obtained in the pH range ∼9.5–8.5. Thermal annealing of the hydroxides at 500 °C yielded cubic phase NiO with morphologies similar to their hydroxide precursors. X-ray powder diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), and energy dispersive X-ray (EDX) analysis were used to characterize the as-prepared products. The role of pH in controlling the phase and morphology of the products was discussed.     

Sorption of selenium oxyanions on TiO2 (rutile) studied by batch or column experiments and spectroscopic methods

Selenium is a known toxic element released in the environment by anthropogenic activities. The present study is devoted to the aqueous sorption behaviour of selenium oxyanions (selenate and selenite) on a reference oxide surface, namely rutile TiO(2). Batch sorption kinetics and isotherms have been studied using different physico-chemical conditions of the solution (changes of pH and ionic strength). The sorption was favoured for both anions in acidic conditions, in agreement with a surface complexation mechanism and CD-MUSIC predictions. Spectroscopic investigations of the sorbed rutile powder were also consistent with such a mechanism. EXAFS spectra confirmed that for selenite anions, an inner-sphere mechanism was the most probable process observed. Dynamic sorption experiments using a column filled with rutile powder also substantiated that a part of the surface complexes follows the inner-sphere mechanism, but also evidenced that an outer-sphere mechanism cannot be excluded, especially for selenate anions.