Porous eco-ceramics of low thermal conductivity and high EMI shielding effectiveness from sawdust and sucrose by paste molding

A facile method for making porous SiC ceramics from sawdust avoiding high-temperature liquid or vapor phase silicon infiltration has been outlined. Cylindrical bodies prepared by hand pressing of aqueous pastes produced from sawdust, silicon powder, sucrose, and sintering additives are subjected to freeze-drying followed by carbonization and ceramization heat-treatments to produce porous SiC. The carbon-silicon reaction is completed at a minimum temperature of 1550 °C as verified from TGA and XRD analysis. The SiC produced from sawdust particles is firmly held together by the sucrose-derived SiC. The pore channels inherited in the sawdust particle remain in the SiC ceramics. A large population of nanowires is observed throughout the sucrose-derived SiC as well as on the pore channel surfaces of SiC formed from sawdust particles. The porosity decreases from ~88 to 75 vol%, the compressive strength rises from 0.5 to 12.5 MPa, and thermal conductivity rises from 0.23 to 0.98 W/mK when the sucrose to sawdust weight ratio rises from 0.5 to 2.5. The reflection contribution (1.9–3 dB) to the total EMI shielding effectiveness (16 To 31 dB) of the porous SiC ceramics is very low compared to the absorption contribution (15–28 dB). The carbonized bodies are amenable to machinating enabling the production of near-net-shape before ceramization. The presence of large excess of silicon observed in biomorphic SiC made by molten liquid infiltration is avoided in this method.     

利用响应面分析法优化蔗糖-对甲酚树脂胶黏剂的合成

利用响应面分析法对蔗糖-对甲酚树脂胶黏剂的合成条件进行了优化。对催化剂用量、反应温度进行单因素实验,应用minitab软件选取4因素2水平全因子的响应面分析优化方法,找到了最佳工艺条件,即催化剂用量为8.39%,反应温度为75.33℃,反应时间为4h48min,物料比为3.94:1。通过验证试验,结果与模型预测值基本一致。     

In-situ reaction of the very early hydration of C3A-gypsum-sucrose system by Micro-Raman spectroscopy

This paper studied in situ, by Micro-Raman spectroscopy, the very early hydration of C₃A in the presence and absence of sulphates and with sucrose as an additive. For C₃A hydration in the absence of gypsum, when carbonation is not avoided, carbonate-AFm phases are formed, but in the presence of gypsum, hydroxi-AFm are the main phases. Ettringite is the AFm stable phase developed initially at 70 min of hydration with gypsum and no monosulphate is formed. In the presence of sucrose, this salt, instead of sulphate, is adsorbed over the surface of the C₃A, avoiding its reaction with sulphates until sucrose desorption. Three hours are necessary to lead to ettringite formation. A nucleation poisoning/adsorption surface mechanism is proposed for added sucrose systems.     

Encapsulation of citral in formulations containing sucrose or trehalose: Emulsions properties and stability

The performance of formulations for citral encapsulation by spray drying was assessed. Focus was put on the emulsions properties and stability. Formulations contained sucrose or trehalose with or without maltodextrin and a modified starch as emulsifier. Viscosity, molecular mobility, microstructure, droplet size distribution, and stability were analyzed before and after spray-drying. Instability processes operated in the emulsions bulk, being flocculation the main one. Droplet size and viscosity influenced the emulsions stability. An increase in viscosity attained by the addition of MD delayed the global destabilization processes. Emulsion properties and stability were similar between the formulations containing sucrose or trehalose. Also, there were no differences regarding aroma retention or sensorial perception of citral. The mixture of maltodextrin and trehalose presented higher T_g values allowing to maintain the glassy state of the powder in broader temperature and relative humidity conditions. Trehalose presented a promising performance as an ingredient in the carrier formulation to encapsulate citric flavors.     

Comparison of the use of sucrose and glucose as a substrate for hydrogen production in an upflow anaerobic fixed-bed reactor

This study evaluated the use of two types of substrates, glucose and sucrose, feeding an anaerobic fixed-bed bioreactor. The biogas produced was composed of H₂ and CO₂, without methane. Maximum hydrogen yields were 3.22 mol H₂ mol⁻¹ sucrose_converted and 1.51 mol H₂ mol⁻¹ glucose_converted. The main intermediates were acetic acid, butyric acid, and ethanol. The greatest difference, however, was in the stability of the process. The operation of the reactor with sucrose exhibited a drop in biogas production, whereas operation with glucose was stable after a slight decrease in biogas production. This decrease may have been caused by the differential growth of microbial populations in each reactor, namely, the growth of organisms that use the Wood–Ljungdahl metabolic pathway.     

Barrier and optical properties of edible hydroxypropyl methylcellulose coatings containing surfactants applied to fresh cut carrot slices

Coatings made from hydroxypropyl methylcellulose (HPMC) containing surfactant mixtures of sorbitan monostearate (SPAN 60) and sucrose palmitate (sucrose ester P-1570) in aqueous and hydroalcoholic media were developed to analyse the effect of the hydrocolloid/surfactant ratio (H/S), the hydrophilic–lipophilic balance (HLB) of the surfactant mixtures and the solvent type used as dispersing media on the water vapour barrier properties of the films and their optical effect when applied to carrot slices. The results showed that the solvent type, H/S ratio and HLB significantly affected viscosity, surface tension, and stability (particle size and flocculation rate) of the film-forming dispersions, which in turn had a great influence on the extensibility and final film structure of the coating on the carrot surface. All these aspects affected the water vapour barrier properties of the film. The best water vapour barrier properties were found in the coating made from hydroalcoholic dispersions with intermediate values of the surfactant's HLB. The colour of coated carrot slices was mainly affected by the solvent dispersion media, the induced changes being greater for aqueous dispersions.     

Effect of Operating Parameters on the Separation of Sugars by Nanofiltration

ABSTRACT

Due to the complexity of fermentation mixtures, separation of solutes and secondary substrates has a special importance. Membrane processes such as nanofiltration may offer good alternatives for the separation of fermentation products or recovery of substrates. For an efficient separation, the membrane type and operating parameters such as feed flow rate, operating pressure, and feed should be optimized. In this study the separation and recovery of sugars were targeted. It was found that with an increase of the feed flow rate, permeate flux increased since the effect of concentration polarization was minimized. As a result, experiments were carried out at the highest possible flow rate. The effect of pressure was studied at five pressures (10–50 bar). It was found that there is a linear relationship between the pressure and permeate flux up to 30 bars. Beyond 30 bars the effect of pressure became less significant. Thus, 30 bars was chosen as the operating pressure. To investigate the effect of concentration, 1 to 10 weight percentage sucrose and glucose solutions were utilized. It was observed that with an increase in concentration, permeate flux decreased and rejections increased, finally reaching a limiting value. Binary solutions of sucrose and glucose were also studied. It was seen that the separation factor slightly decreased, probably due to a glucose–sucrose interaction. Experimental data were used with a mathematical model to predict the permeate flux and rejection. Good agreement of the predicted results was obtained with the experimental data for a 500 MWCO membrane     

失水山梨醇单月桂酸酯的色谱分析

采用TLC对失水山梨醇单月桂酸酯 (Span 2 0 )组分进行分离 ,借助HPLC对其组分进行定性和定量分析。结果表明Span 2 0组成比较复杂。HPLC可用来测定Span 2 0中单酯、双酯、多酯的相对含量     

Impact of xanthan gum,sucrose and fructose on the viscoelastic properties of agarose hydrogels

Mixed carbohydrate systems are of special interest for the food and non-food industry as they offer a versatile range of unique and novel functional properties. However, intense research is required to understand the complex processes occurring in such systems on a molecular level and to be able to modify them aim-oriented. In food, characteristic properties are based on the physicochemical functions of the biopolymers added. Thus, small deformation tests and moisture analysis have been applied to study the impact of xanthan gum and two types of sugar on the viscoelastic properties, the sol–gel transition and the water holding capacity of 1% agarose hydrogels. Agarose gels are very elastic, turbid and prone to synaeresis, which impinges on their mouth feeling. Additions of xanthan gum revealed less elastic gels with an unaffected water holding capacity. Progressive addition of two different types of up to 40% of sugar yield an increase of the elasticity of agarose gels, whereby sugar concentrations of 60% partially result in a structural breakdown and thus a significant lower network structure but better water holding. In ternary systems, the effect of the sugar concentration and sugar type used is diminished by xanthan gum. The gelation mechanism of agarose gels with a distinct amount of co-solutes is presumably mainly affected by the water shortage evolved from the competition for it of all solutes present.     

Viscosity of Aqueous Carbohydrate Solutions at Different Temperatures and Concentrations

Experimental viscosity values of sucrose, glucose, and fructose aqueous solutions in a large range of temperatures (0 to 85°C) and concentrations (10 to 60% w/w) that might be encountered in food processes were obtained in order to contribute to extending the available database of food properties. The temperature dependence of viscosity could be adequately described by the Arrhenius model, and the activation energy was well represented by a unique function of the solute volume fraction, valid for sucrose, glucose, and fructose solutions.