正交试验优化纳米氧化锌前驱体乳液合成工艺

以醋酸锌和氨水为原料,结合并流沉淀和超声处理制备纳米氧化锌的前驱体乳液。再利用真空冷冻干燥方法得到前驱体,经过热处理得到纳米氧化锌(约15nm)。用正交试验方法分析了乳液制备工艺对其稳定性的影响,结果表明:分散剂加入量对前驱体乳液稳定性影响最大,合适的分散剂加入量为0.4%(体积分数)。     

Influence of intermolecular entanglements on crystallization behavior of ultra‐high molar mass polyethylene

Ultra high molar mass polyethylene (UHPE) was melted at 160°C for various times or at various temperatures for 5 min and then the crystallization of the UHPE was carried out on cooling. It was found that the crystallization temperature decreased as the heating time or heating temperature increased. During the melting process, thermal motion of the chains leads to a change of chain conformation from parallel‐extended chains to interpenetrated random coils, accompanied by the occurrence of entanglements. As a result, the crystallization temperature shifts to lower temperature. On the other hand, samples of UHPE with less entanglement were prepared from a dilute solution by a freeze‐drying procedure. It was observed that the crystallization temperature of the freeze‐dried samples from the melt depressed with dereasing solution concentration. UHPE would produce small crystals in the freezing process, thus leading to a reduction in melting point, and a sifting of crystallization temperature to lower temperature. Based on the melting point, the average volume of small crystals was estimated; it is even smaller than that of one single chain of the UHPE.     

Controlled freezing and freeze drying: a versatile route for porous and micro‐/nano‐structured materials

Freeze drying is a process whereby solutions are frozen in a cold bath and then the frozen solvents are removed via sublimation under vacuum, leading to formation of porous structures. Pore size, pore volume and pore morphology are dependent on variables such as freeze temperature, solution concentration, nature of solvent and solute, and the control of the freeze direction. Aqueous solutions, organic solutions, colloidal suspensions, and supercritical CO₂ solutions have been investigated to produce a wide range of porous and particulate structures. Emulsions have recently been employed in the freeze drying process, which can exert a systematic control on pore morphology and pore volume and can also lead to the preparation of organic micro‐ and nano‐particles. Spray freezing and directional freezing have been developed to form porous particles and aligned porous materials. This review describes the principles, latest progress and applications of materials prepared by controlled freezing and freeze drying. First of all the basics of freeze drying and the theory of freezing are discussed. Then the materials fabricated by controlled freezing and freeze drying are reviewed based on their morphologies: porous structures, microwires and nanowires, and microparticles and nanoparticles. The review concludes with new developments in this area and a brief look into the future. Copyright © 2010 Society of Chemical Industry     

红外辅助冷冻干燥装置摔制系统的研发

真空泠冻干燥产品质量优异,广受青睐,但其干燥速率慢、耗能较大,制约其在普通产品干燥的推广应用。本文基于红外辅助加热和搁板传导的结合,提高对物料加热的有效性。并研发了红外辅助冷冻干燥装置的控制系统,以实现对物料冻结和加热的可控性和用户友好操作。     

Some Aspects of Freeze Drying of Dairy Biomaterials

ABSTRACT

Different theoretical and experimental aspects of freeze drying of dairy biomaterials are reported. The following dairy biomaterials were chosen for investigations: three kefir bacterial cultures and one bacterial concentrate of a dairy vaccine. Experiments were performed both at one-region conductive or radiative heating and at combined two-region conductive-radiative heating. Emphasis was put on quality interactions between physical and biological properties of the material to be dried and freeze drying process parameters. Qualitative estimations of the following properties of biomaterials: a) colour, b)suppleness to caking and c) suppleness to scraping born the hot surface in dependence with the process parameters were performed using four-step subjective scales. On the basis of this estimations a synthetic quality criterion SQC was defined whose numerical value reflects general product quality. The results of mathematical modelling, numerical solution of the model and comparison with experimental data indicated that the process was heat transfer controlled and that the main factors resulting in good product quality and high SQC are low temperature of the conductive heated surface and vacuum chamber pressure affecting sublimation temperature. The influence of the sample freezing parameters on the elimination of the foaming or puffing and on the product quality was observed and examined. Furthermore, preliminary measurements of the dauy biomaterials viability after freeze drying were presented.     

Some Aspects of Freeze Drying of Dairy Biomaterials

Different theoretical and experimental aspects of freeze drying of dairy biomaterials are reported. The following dairy biomaterials were chosen for investigations: three kefir bacterial cultures and one bacterial concentrate of a dairy vaccine. Experiments were performed both at one-region conductive or radiative heating and at combined two-region conductive-radiative heating. Emphasis was put on quality interactions between physical and biological properties of the material to be dried and freeze drying process parameters. Qualitative estimations of the following properties of biomaterials: a) colour, b)suppleness to caking and c) suppleness to scraping born the hot surface in dependence with the process parameters were performed using four-step subjective scales. On the basis of this estimations a synthetic quality criterion SQC was defined whose numerical value reflects general product quality. The results of mathematical modelling, numerical solution of the model and comparison with experimental data indicated that the process was heat transfer controlled and that the main factors resulting in good product quality and high SQC are low temperature of the conductive heated surface and vacuum chamber pressure affecting sublimation temperature. The influence of the sample freezing parameters on the elimination of the foaming or puffing and on the product quality was observed and examined. Furthermore, preliminary measurements of the dauy biomaterials viability after freeze drying were presented.     

Preparation of a unique,multihollow‐core honeycomb structure via the unidirectional freezing of a binary solvent system

Unidirectional freezing is a simple and environmentally friendly method for preparing polymeric porous materials from polymer solutions for use in various applications. In this study, a unique, multihollow‐core honeycomb structure was prepared from diurethandimethacrylate (DUDM) in a 1,4‐dioxane (Dx) and tertiary butanol (TBA) binary solvent system via unidirectional freezing, subsequent photopolymerization and freeze‐drying. The multihollow‐core honeycomb consists of two different hollow tubular structures: one structure is noncircular with an atypical cross‐sectional area, and the other is circular and measures approximately 5–10 μm in diameter. Both structures are aligned parallel to the freezing direction. These hollow structures were formed by using the sequential growth of Dx and TBA crystals as a template. During the unidirectional freezing process, the Dx crystals grew in the solution along the freezing direction and expelled DUDM and TBA from its crystalline phase into the solution. When the freezing temperature was further decreased, small, needle‐shaped TBA crystals grew along the freezing direction and were confined by the Dx crystals. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

冷冻干燥法制备层状多孔羟基磷灰石支架过程中的溶剂升华行为

采用水基羟基磷灰石(hydroxyapatite,HA)浆料,经冷冻干燥和烧结工艺(1 250℃烧结3 h)制备了层状多孔HA支架.研究了冷冻温度、干燥压力和干燥温度对水基HA浆料中溶剂升华行为的影响.结果表明:随着冷冻温度的降低,多孔HA支架的层间距逐渐减小,支架的升华时间增加;由于样品的干燥过程同时受到传热和传质的...     

MICROWAVE FREEZE DRYING CHARACTERISTICS OF BEEF

Microwave freeze drying characteristics of unsaturated raw beef were studied experimentally for various levels of electric field strength, vacuum pressure, sample thickness and initial saturation. The results show that drying time is proportional to initial saturation and inversely proportional to the electric field strength and sample thickness. The effect of vacuum pressure on drying time is negligible. Some advantages of microwave freeze-drying over conventional freeze drying with radiant heating are pointed out     

Production of Tomato Powder by Refractance Window Drying

The aims of this work were to investigate the drying of tomato pulp by refractance window (RW) and the effects of process conditions on the drying rates and characteristics of the dry powder. Different heating water temperatures (65, 75, 85, and 95°C) and pulp thickness (2 and 3 mm) were studied for drying 4.8–5.2 °Brix pulps. The powder characteristics were assessed from its solubility, dispersion time, water sorption isotherm, and color. Shorter drying time (17 minutes) was observed to the lower pulp thickness and higher drying temperature. The solubility of tomato powders was approximately 80%, and the dispersion time was lower than one minute. The color change (ΔE) of rehydrated powder showed an increase with increasing process temperature. These results indicate that RW is an adequate procedure for the production of tomato powder.     

预冻在冻干过程中的作用简

预冻环节中降温速度、冻结温度、冻结时间都是重要的工艺参数,它们互相作用,影响着冻结体的结晶情况,最终会对冻干过程形成决定性的影响。本文通过实例,介绍了预冻过程中冻结速率对冻干结果的影响。说明适当的预冻参数可大大提高冻干效率和产品质量。     

介电材料辅助的微波冷冻干燥的实验研究

设计、加工和装配了一套实验室规模的微波冷冻干燥装置,旨在实验验证介电材料对微波冷冻干燥液体物料的强化作用。介电材料用烧结的碳化硅(SiC),石英玻璃作为介电材料的参照物;甘露醇,一种典型的药物赋形剂被选为待干溶液中的溶质。实验结果表明使用介电材料可以有效地强化微波冷冻干燥过程。与传统冷冻干燥相比干燥速率大大加快,在试验条件下干燥时间可以节省20%。微波加热逐渐生效并且主要体现在干燥过程的后半部分。当溶液中的固含量很低或者固体物质具有很小的介电损耗因子时,如果不用介电材料,微波加热的效果不明显。     

瓶装物料的冻干规律研究

以脱脂牛奶为物料,进行了瓶装物料的冷冻干燥试验,探索了加热温度,辐射温度与冻干室压强对冻干过程的影响规律,分析了所得冻干曲线的特征,并对冻干机理和物料温度的监测井行阐述,得到在加热温度与辐射温度相同时恒温恒压操作的最佳参数,并提出了一些强经冻干过程的措施。本研究对实验冻干生产有一定的指导作用,也为瓶装物料的二维理论模型研究提供了基础。     

MICROWAVE FREEZE DRYING CHARACTERISTICS OF BEEF

ABSTRACT

Microwave freeze drying characteristics of unsaturated raw beef were studied experimentally for various levels of electric field strength, vacuum pressure, sample thickness and initial saturation. The results show that drying time is proportional to initial saturation and inversely proportional to the electric field strength and sample thickness. The effect of vacuum pressure on drying time is negligible. Some advantages of microwave freeze-drying over conventional freeze drying with radiant heating are pointed out     

EFFECTS OF HEATING METHODS ON VACUUM FREEZE DRYING

The heat and mass transfer during freeze drying of raw beef by different heating methods is studied theoretically and experimentally. The difference between radiant heating and microwave heating in freeze drying process has been analyzed. The results obtained are important for the selection of the heating methods in practical freeze dryers.     

Comparison of freeze drying and spray drying to obtain porous nanostructured granules from nanosized suspensions

This work studies the spray drying and freeze drying of different nanosized ceramic materials and the physicochemical characteristics of the obtained granules. Colloidal suspensions of alumina, titania, and a 87/13 mixture were studied. The influence of temperature, pressure, nozzle diameter, and solids loading on the morphology and characteristics of dried granules were evaluated. It was demonstrated that these processing parameters have practically no influence, and the only parameter determining the granules characteristics is the solids content of the suspensions, in both processes. Spray drying leads to a monomodal distribution with higher granule size, while freeze drying produces more porous granules, with a bimodal intragranular distribution. The flowability of spray-dried powder is better than that of the freeze-dried powder and suit better the requirements of a feedstock targeted to obtain coatings by plasma thermal spraying whereas freeze drying can produce high porosity, softer granules.     

Photocatalytic Silver Recovery Using ZnO Nanopowders Synthesized by Modified Glycine-Nitrate Process

Zinc oxide (ZnO) powders were synthesized by the modified glycine-nitrate process (MGNP) with various oxidants and fuels. Single-phase ZnO powders were easily obtained regardless of oxidants and fuels. The particle size and shape of ZnO powders were dependent on the types of fuels. The ZnO powder synthesized using Zn(OH)₂ and glycine as an oxidant and a fuel, at a fuel/oxidant ratio of 0.8, showed the best powder characteristics, such as an average grain size of 30 nm and the specific surface area of 120 m²/g. The removal of silver ions from the waste-development solution was tried to confirm photocatalytic activities of the synthesized ZnO powder. The silver ions were completely removed within 15 min. This silver recovery rate is three times higher than that of commercial state-of-the-art TiO₂. The photoluminescence (PL) measurement also showed the PL intensity at ultraviolet (UV) of the synthesized ZnO powder is almost three times higher than that of commercial state-of-the-art TiO₂. The synthesized ZnO nanopowder absorbed more UV than any other powders, including commercial state-of-the-art TiO₂ and ZnO powders. This means the high UV absorption efficiency leads to the generation of more electrons that are involved in the reduction of silver ions.     

Microwave Freeze Drying of Sea Cucumber Coated with Nanoscale Silver

To develop an improved dehydration method for sea cucumber, microwave freeze drying was tested as a potential method. According to our experimental results, microwave freeze drying can reduce drying time to about half of the traditional vacuum freeze-drying process. To ensure a high degree of sterilization, a novel nanoscale silver coating technique was combined with microwave freeze drying. Microwave freeze drying combined with nanoscale silver coating treatment leads to a much lower microorganism number with no significant effect on drying efficiency and sensory quality.