The Brittle-Ductile Transition of an Amorphous Food System

As a dry amorphous food system absorbs moisture or increases in temperature, the brittle food becomes soft and deformable. The temperature at which this transition occurs in the food system for a given moisture content is called the brittle-ductile transition temperature (T_b). Three different methods of determining this transition were used. The method that was chosen to best describe the food system was the intersection of brittle strength and yield strength measured in flexure as a function of both temperature and moisture content. T_b decreased linearly with increasing moisture content with a strong linear relationship (r² = 0.98).     

Correlating Perceived Crispness Intensity to Physical Changes in an Amorphous Snack Food

A crispy amorphous food was equilibrated to different moisture contents. These samples were tested for the glass transition temperature (T_g) using mechanical methods. The brittle-ductile transition temperature (T_b) was determined using force-deformation methods. Finally, the temperature where the onset to the sharp decrease in crispness intensity occurred (T_ci) was determined by a 10-member sensory panel rating the crispness intensity. The relationships of the T_g, the T_b, and the T_ci were determined using three different statistical methods. The results of this research indicated that the T_g, the T_b, and the T_ci were related to one another as a function of moisture content.     

Correlating Perceived Crispness Intensity to Physical Changes in an Amorphous Snack Food

Abstract

A crispy amorphous food was equilibrated to different moisture contents. These samples were tested for the glass transition temperature (T_g) using mechanical methods. The brittle-ductile transition temperature (T_b) was determined using force-deformation methods. Finally, the temperature where the onset to the sharp decrease in crispness intensity occurred (T_ci) was determined by a 10-member sensory panel rating the crispness intensity. The relationships of the T_g, the T_b, and the T_ci were determined using three different statistical methods. The results of this research indicated that the T_g, the T_b, and the T_ci were related to one another as a function of moisture content.     

聚合物脆韧转变判据及影响因素研究进展

综述了聚合物脆韧转变的几种判据,其中着重介绍了Bucknall判据、临界基体层厚度判据、损伤竞争准数判据、分子链参数判据、临界黏结条件判据等。而且结合聚合物脆韧转变判据,分析了基体性质、分散相形态、界面黏结强度以及外界因素对聚合物脆韧性的影响,并指出了结合各因素的影响综合考虑聚合物脆韧转变判据的研究方向。     

淀粉可食餐具中的食品添加剂剂量的测定

随着社会发展,资源的合理利用和保护生态环境已经成为21世纪重要的课题,研究制备替代发泡塑料餐具的绿色环保可降解餐具具有重要意义。以淀粉为原料制备环保型可食用餐具具备一定的使用性能,但综合使用性能并不十分理想。通过添加一些食品级添加剂,能提高淀粉餐具的综合使用性能。用预实验确定影响餐具性能的添加食品添加剂的种类及其范围,(参考GB2760《食品添加剂使用卫生标准》),利用正交试验确定淀粉餐具综合使用性能最佳的添加剂配比。结果表明:当其甲基纤维素钠的添加量为0.75 g/100 g、明胶的添加量为0.9 g/100 g、琼脂的添加量为1.575 g/100 g、甘油的添加量为1.5 g/100 g时淀粉可食餐具具有最佳的使用性能。     

聚合物材料脆韧转变判据及影响因素分析

综述了聚合物共混增韧机理包括弹性体增韧、刚性粒子增韧、弹性体与刚性粒子协同增韧等研究进展；着重介绍了临界基体层厚度、损伤竞争准数、分子链参数、临界界面黏结条件、临界特征长度等几种源于单一粒子填充的脆韧转变判据，并分析其在复合粒子填充改性聚合物中的适用性。此外，还结合增韧机理和脆韧转变判据讨论了基体性能、分散相状态及相间界面黏结强度等因素对复合体系韧性的影响，提出寻找合适的复合分散相、适当调整复合粒子的结构比例、改善相间界面黏结以及设计最佳断裂路径仍将是今后努力的方向。     

纳米莫来石填充PP/EPDM共混物的脆韧转变

制备了含纳米莫来石的三元乙丙橡胶(EPDM)和马来酸酐接枝三元乙丙橡胶(EPDM-g-MAH)母料,研究了纳米莫来石对聚丙烯(PP)/EPDM和PP/EPDM-g-MAH共混物脆韧转变的影响。结果表明:纳米莫来石的加入使PP/EPDM和PP/EPDM-g-MAH共混物的脆韧转变提前,尤其在纳米莫来石用KH-550改性后,PP/EPDM共混物发生脆韧转变时EPDM的含量由15%降至10%;在橡胶相含量相同时,加入纳米莫来石后共混物的弹性模量和拉伸强度略有下降,而断裂伸长率显著下降。     

两类PE-HD/E-TMB共混物的脆韧转变及断面形态

用自制增韧母料(E-TMB)分别与2200J型高密度聚乙烯(PE-HD)(HE1)和2911型PE-HD(HE2)热机械共混制得HE1/E-TMB和HE2/E-TMB共混物,用力学性能测试法和扫描电子显微镜研究了两类共混物的脆韧转变和断面形态。结果表明,HE1/E-TMB共混物比HE2/E-TMB共混物在弹性体含量较低的情况下发生脆韧转变,二者的脆韧转变区分别是共混物弹性体质量分数的3%～10%和10%～14%;弹性体质量分数为8%时,HE1/E-TMB共混物的冲击断面为韧性断裂,HE2/E-TMB共混物的冲击断面为脆性断裂,二者属于不同的断裂机理。     

The Spray Drying of Food Flavors

Abstract

Spray drying is the most commonly used technique for the production of dry flavorings. In spray drying, an aqueous infeed material (water, carrier, and flavor) is atomized into a stream of hot air. The atomized articles dry very rapidly, trapping volatile flavor constituents inside the droplets. The powder is recovered via cyclone collectors. Flavor retention is quite satisfactory if dryer operating parameters are properly chosen. Flavor retention is maximized by using a high infeed solids level, high viscosity infeed, optimum inlet (160–210°C) and high exit (>100°C) air temperatures, and high molecular weight flavor molecules. The shelf life of oxidizable flavor compounds is strongly influenced by the flavor carrier.     

Moisture Adsorption Isotherms and Glass Transition Temperature of Xanthan Gum

The moisture adsorption isotherms of the xanthan gum were determined at 30-70°C over water activity ranging from 0.11 to 0.94. The moisture adsorption isotherms revealed that the equilibrium moisture content increased with water activity. Increased temperature, in general, resulted in decreased equilibrium moisture content. However, in some cases equilibrium moisture content values increased with temperature. Selected sorption models were tested to describe the adsorption isotherms. Parameters of each sorption model were determined by nonlinear regression analysis. The modified Oswin model gave the best fit for xanthan gum. The isosteric heat of sorption decreased with increase in moisture content and varied between 1.66 and 7.61 kJ/mol. The glass transition temperature decreased with increase in moisture content for xanthan gum.     

Moisture Adsorption Isotherms and Glass Transition Temperature of Xanthan Gum

The moisture adsorption isotherms of the xanthan gum were determined at 30–70°C over water activity ranging from 0.11 to 0.94. The moisture adsorption isotherms revealed that the equilibrium moisture content increased with water activity. Increased temperature, in general, resulted in decreased equilibrium moisture content. However, in some cases equilibrium moisture content values increased with temperature. Selected sorption models were tested to describe the adsorption isotherms. Parameters of each sorption model were determined by nonlinear regression analysis. The modified Oswin model gave the best fit for xanthan gum. The isosteric heat of sorption decreased with increase in moisture content and varied between 1.66 and 7.61 kJ/mol. The glass transition temperature decreased with increase in moisture content for xanthan gum.     

Effect of cavitations on brittle-ductile transition of particle toughened thermoplastics

In this study, we established a correlation between cavitations volume and the brittle-ductile transition (BDT) for particle toughened thermoplastics. The brittle-ductile transition temperature (T_BD) was calculated as a function of T^∗ and interparticle distance (ID), respectively, where T^∗ was a parameter related to the volume of cavitations. The results showed that the smaller the cavitations volume, the higher the brittle-ductile transition temperature. The calculations correlated well with the experimental data. With respect to rubber particle, the rigid particle was too hard to be voided during deformation, thereby the T_BD of the blend was much higher than that of rubber particle toughened thermoplastic. This was a main reason that rubber particle could toughen thermoplastics effectively, whereas rigid particle could not.     

Brittle-ductile transition of particle toughened polymers: influence of the matrix properties

It was theoretically pointed out that the product of the yield stress and yield strain of matrix polymer that determined the brittle-ductile transition (BDT) of particle toughened polymers. For given particle and test condition, the higher the product of the yield stress and the yield strain of the matrix polymer, the smaller the critical interparticle distance (ID_c) of the blends was. This was why the ID_c (0.15 μm) of the polypropylene (PP)/rubber blends was smaller than that (0.30 μm) of the nylon 66/rubber blends, and the ID_c of the nylon 66/rubber blends was smaller than that (0.60 μm) of the high density polyethylene (HDPE)/rubber blends.     

A Generalized Relationship for Determination of Tensile Strength of Fine-Grained Soils from Shrinkage Characteristics

Tensile strength of fine-grained soils has been extensively investigated by earlier researchers and several methodologies have been evolved for its determination. However, either most of these methods are not valid/applicable for a wide range of moisture contents or they involve tedious sample/specimen preparation. In this context, the methodology of determining tensile strength by employing thin films, which is available in the literature, has been found to be quite handy and useful. It has been observed that a unique relationship exists among the tensile strength, moisture content, and shrinkage characteristics of fine-grained soils. This methodology is appreciable due to its applicability to a wide range of moisture contents, comparable ease of sample preparation and testing, and the obtained results lack generalization. Exhaustive tests were conducted on fine-grained soils of entirely different characteristics and generalized relationships have been proposed between the percentage linear shrinkage, tensile strength, and moisture content (defined as liquid to solid ratio). Based on a critical analysis of the results available in the literature, the efficiency of such relationships for determination of tensile strength of fine-grained soils has been demonstrated. In the authors’ opinion, such relationships would be quite useful for determining tensile strength of fine-grained soils from their linear shrinkage, which can easily be measured in a conventional geotechnical engineering laboratory.     

Microwave Moisture Measurement System for Hardwood Lumber Drying

The goal of this project was to develop a prototype microwave-based moisture sensor system suitable for the kiln drying of hardwood lumber. The moisture sensors developed are battery powered and are capable of communicating with a host kiln control system via spread spectrum wireless communications. We have developed two designs of the sensors working at 4.5 to 6 GHz with linear response to moisture content (MC) over a range of 6–100%. These sensors allow us to make a swept frequency microwave transmission measurement through a small area of a board. Using the prototype electronics and sensors, we have obtained measurements of MC over the above MC range for red oak and yellow poplar with standard deviations of less than 1.5% MC. We have developed data for board thickness corrections and for temperature corrections for the MC measurement system.     

Applications of the Cyclone Stickiness Test for Characterization of Stickiness in Food Powders

The cyclone stickiness test (CST) technique was applied to measure the stickiness temperature and relative humidity of whey, honey, and apple juice powders. A moisture sorption isotherm study was conducted to analyze the surface moisture content of whey powder. The glass transition temperatures of the sample powder were analyzed using differential scanning calorimetry (DSC). The stickiness results of these products were found within 20°C above their surface glass transition temperatures, which is well within the normal temperature range for glass transition in general. The results obtained by the CST technique were found consistent with DSC values.     

Applications of the Cyclone Stickiness Test for Characterization of Stickiness in Food Powders

The cyclone stickiness test (CST) technique was applied to measure the stickiness temperature and relative humidity of whey, honey, and apple juice powders. A moisture sorption isotherm study was conducted to analyze the surface moisture content of whey powder. The glass transition temperatures of the sample powder were analyzed using differential scanning calorimetry (DSC). The stickiness results of these products were found within 20°C above their surface glass transition temperatures, which is well within the normal temperature range for glass transition in general. The results obtained by the CST technique were found consistent with DSC values.     

食品添加剂氢氧化钠中汞含量的测定

食品添加剂氢氧化钠中汞含量的测定方法——冷原子吸收分光光度法（NCG-1冷原子吸收测汞仪）进行了探讨。该法在1~5 ng/mL线性范围内,RSD为6.80%～7.79%,最大相对偏差为17.7%。本法具有操作简单,精密度高,重现性好等优点,适合大批样品的分析检测。     

Brittle-ductile transition of polymer blends

Based on the Ludwik-Davidenkov-Orowan theory, a new criterion of BDT for polymer blends is proposed. In this approach fracture stress (_b) and shear yielding stress (_y) governing the brittle-ductile transition (BDT) of polymer blends is combined into a dimensionless group as D_a = _b ²/_y ². The theory dictates that BDT occurs at a critical condition D_ac = 1, brittle fracture occurs when D_a < 1, and ductile fracture occurs when D_a > 1. It can be shown that D_a = F_g · L_ym/L_D, where L_ym measures the length of shear band of the matrix, L_D is a parameter determined by the morphology and interfacial adhesion of dispersed phase, and F_g is related to specimen geometry and other extrinsic parameters. It is suggested that the onset of BDT depends on the competition between the L_ym and L_D. With due consideration to blend morphology, interfacial adhesion and matrix properties, existing experimental evidence supports the applicability of the proposed criterion.The project supported by FORD and NSFC No. 09415312     

Dynamic properties of concrete in direct tension

An experimental study on the strain-rate dependent behavior of concrete in tension was carried out by means of a servo-hydraulic testing machine. The specimens were made in dumbbell shape and the tested strain rate ranged from 10^− 5/s to 10^− 0.3/s. Strain-rate effects on the tensile strength, the modulus of elasticity, the critical strain, the Poisson's ratio and the energy absorption capacity of concrete were studied. More emphasis was placed on the influence of temperature and moisture content on the strain-rate sensitivity. All test data were analyzed, discussed and compared with available reference materials. In addition, strain-rate effects on the damage pattern of specimens were studied. It was observed that the fractured surfaces of the specimens became more and more flattened and a number of coarse aggregates were broken along the failure surfaces. Based on this phenomenon an explanation to the physical mechanisms of strain-rate enhancement during rapid loading was proposed.