CONVECTIVE DRYING OF BANANA,GUAVA AND POTATO PIECES : EFFECT OF CYCLICAL VARIATIONS OF AIR TEMPERATURE ON DRYING KINETICS AND COLOR CHANGE

ABSTRACT

Pieces of banana, guava and potato were dried in a two-stage heat pump dryer capable of precise control of air humidity with predetermined cyclic variations of air temperature entering the drying chamber. The air temperature variations tested were : a cosine, a reversed cosine and three different square wave profiles with peak-to-valley variations from 20^°C to 40^°C. The cycle time was about 60 minutes with drying time of approximately 300 minutes. The drying samples were placed on trays in a thin layer. With appropriate choice of temperature-time variation, it is possible to reduce the overall color change while maintaining high drying rates.     

Ordering of block copolymer/nanoparticle composite thin films

The ordering behavior of polymer nanocomposites composed of gold nanoparticles confined in the polystyrene (PS) domains of PS based block copolymers was investigated. The results reveal that the self‐assembly of nanoparticles in the PS domains improved the ordering of microdomains. This is attributed to the presence of nanoparticles that reduced the degree of segregation of the system, causing slow phase separation. This facilitates the packing of the cylindrical microdomains, leading to a well‐ordered structure of the composite. When particles were incorporated into the major domains of cylindrically ordered block copolymer, the connectivity of the domains allowed particles to move to the top of the film to gain additional entropy of the system. In contrast, when particles were organized in parallel cylinders in the block copolymer, they were confined in the cylinders which prevented them from diffusing in the depth direction. The aggregation of nanoparticles was amplified when the composite was annealed in air. We believe that the results from this study will enable more understanding of the effects of nanoparticles on the ordering of block copolymer/nanoparticle composite thin films and will provide a tool in the fabrication of composite thin films. Copyright © 2012 Society of Chemical Industry     

Synthesis of poly(lactic acid)‐based polyurethanes

Poly(lactic acid) (PLA) is a biodegradable aliphatic polyester, but its brittleness makes it unsuitable for many packaging and appliance applications. The goal of the work reported was to create novel poly(ester urethane)s that incorporate biodegradable poly(lactic acid) diols (PLA‐OHs) and good mechanical properties of increased molecular weight via crosslinked network formation for engineering plastics applications. Three kinds of polyols (PLA‐OHs, PLA‐OHs/poly(tetramethylene ether) glycol or PLA‐OHs/poly(butylene adipate) glycol (PBA)) and two kinds of diisocyanates (4,4‐diphenylmethane diisocyanate (MDI) or toluene 2,4‐diisocyanate (TDI)) were chosen for the soft and hard segments to compare their mechanical properties. In addition, 1,4‐butanediol and trimethylolpropane were each used as chain extender agents. Results showed the PLA/PBA‐polyurethanes (PLA/PBA‐PUs) of the MDI series and the PLA/PBA‐PUs of the TDI series had improved thermal stability and enhanced mechanical properties. Degradation behavior showed the PLA‐based polyurethanes could be degraded in phosphate‐buffered saline solution and enzyme solution. © 2012 Society of Chemical Industry     

Effects of CaTiO3 addition on microstructures and electrical properties of Na0.52K0.48NbO3 lead-free piezoelectric ceramics

In this article, various amounts of CaTiO₃ (CT) were added into (Na_0.52K_0.48)NbO₃ (NKN) ceramics using conventional oxide-mixing method for improving NKN's properties. The experimental results show that the (1?x)(Na_0.52K_0.48)NbO₃–xCaTiO₃ (x=0～0.07) solid solution system can be successfully synthesized. Addition of CaTiO₃ not only effectively prevents materials from deliquescence, but also improves the density and the electrical properties of the ceramics. The dielectric constant–temperature (ε_r?T) curves exhibit that the temperatures of the Curie point (T_c) and the phase transition from tetragonal to orthorhombic (T_O?T) are decreasing monotonously as the amount of CT addition is increased. A morphotropic phase boundary (MPB) can be found in the (1?x)NKN?xCT solid solution system as the doping amount of x=0.03, and the 0.97NKN–0.03CT ceramics, with a high bulk density, 98% theoretical density, and an appropriate grain size of about 1～2 μm, present a superior domain switching ability and the optimum properties: d₃₃=117 pC/N, k_p=0.39, P_r=21 μC/cm², and T_c=333 °C.     

丁腈橡胶、腰果油改性酚醛树脂的研究

以丁腈橡胶粉和腰果油改性酚醛树脂为改性剂，通过对多种原料、橡胶助剂、摩擦性能调节剂的研究和配方筛选，制得高性能载重汽车刹车片内衬材料。该材料磨耗低、抗冲击强度高、硬度和摩擦系数适中、高温抗热衰退明显，生产过程中可省去投资大、能耗高的密炼工艺，具有重要的工业价值。     

Study on Reduction of MoO2 Powders with CO to Produce Mo2C

Molybdenum hemicarbide (Mo₂C), which is widely applied in steel and metal ceramics as well as catalysts, was successfully synthesized by using a simple method of reducing MoO₂ powders by CO. It was found that the final reduction product was all Mo₂C under both isothermal and nonisothermal conditions. However, the reduction mechanisms were significantly different at lower and higher temperatures: at lower temperatures (1070 to 1342 K), reduction of MoO₂ to Mo₂C followed a one‐step reaction (simultaneous reduction and carburization), while at higher temperatures (1423 to 1485 K), MoO₂ was first reduced to metallic Mo, and then Mo was carburized to Mo₂C. Mo₂C particles obtained at higher temperatures contained micrometer‐sized surface features which formed during the MoO₂ to Mo reduction step.     

Crack initiation and propagation in circular rubber bearings subjected to cyclic compression

The fatigue failure mechanism of rubber bearings under cyclic compression is important in evaluating their fatigue lives and thus is analyzed theoretically and numerically here. At first, the stress distributions in a bonded rubber cylinder derived from three different existing models were utilized to calculate the cracking energy densities within it. Next, the location of fatigue crack initiation and the direction of subsequent crack propagation in circular rubber bearings were consecutively determined. Furthermore, finite element numerical results were compared to those obtained theoretically from the three models to check their validity in predicting the fatigue crack initiation and propagation in circular rubber bearings. Based on the quasi‐statically theoretical and numerical results, it is found that the fatigue cracks initiate first at the outermost boundary between rubber and steel plates and propagate later inwards to the center of circular rubber bearings. The corresponding fatigue failure mechanism obtained theoretically and numerically is consistent with experimental findings reported previously. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Effects of the organometallic coupling agents on adhesion of the carbon fiber–BMI composites

In order to increase the chemical bonding force between fiber and resin, several kinds of organometallic coupling agent (such as titanate, zirconate, and zircoaluminate) were chosen and added in the BMI resin formulation, which possess the same solvent system with those coupling agents. The DSC analysis technique was used to find the best curing condition, and TGA was used to investigate the thermal stability property of the best curing condition. For the purpose of analyzing the bonding structure, ESCA surface element analysis techniques was applied in this study. Beside that, the mechanical properties of tensile, flexural, and short-beam shear strengths were measured for the effect of adding coupling agents, and the SEM of fracture surfaces were taken to study the fractural analysis. The results showed that composites with the application of organometallic coupling agents of [RO–Ti(OX–R′NH₂)₃] structure in the treatment of BMI resin were highly thermal stable. Also, it was shown that the mechanical strengths of composites fabricated by pretreatment of the carbon fibers with coupling agents were higher than those fabricated by adding coupling agents in resins, but there was no obvious improvement of mechanical properties with higher concentration of coupling agents. However, the SEM showed that the adhesion between fiber and resin can actually be improved by adding proper amount of coupling agents in the BMI resin formulation.