Effect of model heat treatment conditions on selected properties of milk fat

In this study, the effect of diverse thermal treatments on the physical characteristics of anhydrous milk fat was monitored with the use of scanning calorimetry, firmness analysis, electron microscopy and image analysis. The optimal properties of milk fat were achieved for the thermal treatment taking into account its composition as well as melting and solidification points of the main triacylglycerol fractions (temperatures: 6/20.5/14 °C). Unfavourable results were obtained for the one‐stage system (10 °C/13 h). These results may be helpful in optimising parameters of milk fat crystallisation in high‐fat products, and the fractal analysis has proven to be useful in the evaluation of fat crystallisation.     

热处理对竹浆纤维微观结构和力学性能的影响

以普通粘胶纤维为对比,采用松弛干热处理方法,研究热处理时间和温度对竹浆纤维结晶结构、白度以及力学性能的影响。结果表明：竹浆纤维经不同温度热处理后结晶度比原样有下降;当热处理温度为180℃时,随处理时间的延长,竹浆纤维的结晶度呈明显的下降趋势;热处理对竹浆纤维结晶结构的破坏较普通粘胶纤维的大;热处理后竹浆纤维的白度下降比粘胶纤维明显,断裂强度、断裂伸长率和断裂比功的下降幅度也大于普通粘胶纤维。说明竹浆纤维的耐热性不如普通粘胶纤维。     

热处理后超高分子量聚乙烯纤维结构及力学性能

超高分子量聚乙烯纤维是一种高强、高模量、高结晶及高取向的纤维,但由于其耐热性较低,在使用过程中难免会遇到热的作用,因此研究其受热后力学性能的变化具有一定的实际意义.通过DSC、广角X衍射及力学性能分析,探讨热处理对成型纤维力学性能的作用.通过DSC发现随着热处理温度的升高纤维的熔融温度范围变窄.从X衍射图谱上观察,纤维的结晶形式并没有发生变化,只是微晶尺寸有减小的趋势.通过研究不同温度处理超高分子量聚乙烯纤维力学性能的变化,表明不同温度处理后纤维的力学性能差异并不大,即熔融温度以下的短时间的热处理不会给纤维的力学性能带来损伤.     

热处理对玉米纤维力学性能的影响

对玉米纤维进行不同方式的热处理实验,得出了热处理温度和热处理时间对断裂强度、断裂伸长、初始模量、断裂功的影响规律。研究结果表明:随着热处理温度的提高,玉米纤维的断裂强度逐渐下降,断裂伸长率呈现逐渐上升的趋势;随着热处理温度和时间的增加,玉米纤维的初始模量逐渐下降;在温度不超过130℃时,温度对玉米纤维的力学性能影响不大,但在高温处理时力学性能显著变差,温度和时间对力学性均有影响,热处理时间超过20 min,力学性能显著变差。     

Changes in the properties of light-irradiated wood with heat treatment

This study investigated the changes in the color of wood with heat treatment after exposure to light at various conditions. The change with exposure is attributed to the decomposition of lignin, and the process follows a first-order reaction law. The degree of color change in softwood was greater than in hardwood, while there was no significant difference between the reaction rates for softwood and hardwood. This is attributed to differences in the lignin content. The change in the color of light-irradiated wood with heat treatment increased with light-irradiation time, heating temperature, while the changes in the color of wood irradiated for more than 30 to 40 h were similar. With the investigation of the effect of wavelength, the change in the lightness, L*, of all the woods tested decreased with wavelength. L* became positive for light-irradiated Japanese cypress and hackberry; however, this effect disappeared with heat treatment. The chroma coordinates a* and b* of all species were minimal when irradiated with wavelengths longer than 500 and 440 nm, respectively. However, this effect disappeared with heat treatment. In softwood, b* was negative when exposed to light longer than 440 nm, while in hardwood, it turned negative when exposed to 390, 440, and 500 nm. However, the minimum value observed with light-irradiation disappeared with heat treatment after light-irradiation. Therefore, it is thought that chemical changes involved in the color changes due to light-irradiation differ form those involved in the color changes due to heat treatment.

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Veränderung der Eigenschaften von Licht-bestrahltem Holz nach HitzebehandlungTeil 2: Einfluss von Bestrahlungszeit und Wellenlänge

Zusammenfassung Die Farbänderungen von Holz durch Hitzebehandlung nach Lichtbestrahlung unter verschiedenen Bedingungen wird untersucht. Die Farbänderung wird auf Ligninabbau zurückgeführt. Der Prozess folgt einer Reaktion 1. Ordnung. Das Ausmass der Farbänderung war bei Nadelholz größer als bei Laubholz, während die Reaktionsraten keine signifikanten Unterschiede aufwiesen. Dies wird auf Unterschiede im Ligningehalt zurückgeführt. Die Farbänderung der Licht-bestrahlten Proben nach Hitzebehandlung verstärkt sich mit der Bestrahlungszeit und der Temperatur der Hitzebehandlung; nach Behandlungszeiten von mehr als 30 bis 40 Stunden gleichen sich die Farbänderungen jedoch an. Auch der Einfluss der Wellenlänge wurde untersucht. Dabei erhöhte sich die Helligkeit, L*, bei allen Proben mit der Wellenlänge. L* wurde positiv für japanische Zypresse und Zürgelbaum; allerdings verschwand dieser Effekt nach Hitzebehandlung. Die Koordinaten a* and b* waren bei allen Proebn minimal, wenn mit Wellenlängen >500 bzw. >440 nm bestrahlt wurde. Auch dieser Effekt verschwand nach Hitzebehandlung. Bei Nabelholz war b* negativ nach Bestrahlungen mit Wellenlängen von 390, 440 und 500 nm. Die beobachteten Minima verschwanden allerdings nach der anschließenden Hitzebehandlung. Daraus ergibt sich, daß die chemischen Veränderungen aufgrund der Bestrahlung anderer Art sind als die durch Hitzebehandlung verursachten.

     

日本落叶松热处理材表面显微硬度变化研究

以过热蒸汽为传热介质和保护性气体,在热处理温度为165℃、180℃、195℃、210℃,热处理时间为10h的条件下对日本落叶松木材进行高温热处理,研究日本落叶松木材在不同热处理温度下的表面显微硬度变化。结果表明,随着热处理温度升高,热处理材表面显微硬度逐渐升高,当热处理温度低于195℃时,木材表面显微硬度变化趋势不明显,当热处理温度达到210℃时,热处理材的表面显微硬度显著提高,变化率高达44.12%。     

Effect of thermal treatment on some properties of lime wood

Thermal treatment of lime wood was performed in a drying oven at two temperature levels (180 and 200 °C) and for four durations (1, 2, 3 and 4 h). Mass loss, color change, swelling and hygroscopicity were investigated. The dimensional stabilization reached up to 66.4 % and the hygroscopicity reduction up to 33 %, both maximum values being attained at 200 °C/4 h, associated with a mass loss of 9.3 %. The results will be realized in the manufacturing of solid wood panels made of heat-treated lime wood lamellas for outdoor uses.     

Effect of water activity on the mechanical properties of selected legumes and nuts

Two legumes (kidney beans and chickpeas) and two nut kernels (almonds and hazelnuts) were compressed intact with a Universal testing machine at various a_w levels in the range of 0·11–0·85 at an ambient temperature of 22°C. Mechanical characterisation of the four was done through four parameters; the slope of the initial part of force–displacement curve, considered a measure of stiffness, the failure force, considered a measure of strength, the deformation at failure, considered a measure of brittleness or deformability and the area under the force–displacement curve corresponding to 20% compression, considered a measure of toughness. Among these parameters only the latter could be determined and used effectively in all four seeds and along the whole water activity range. The jaggedness of the force–displacement curve was also determined in terms of its apparent fractal dimension calculated with two different algorithms for verification. There was a noticeable difference between the mechanical behaviour of the two groups. The nut kernels, apparently because of their high oil content, had a much smoother force–displacement curve, and the effect of absorbed moisture on their texture was generally more moderate than on that of the legumes. But in all the four types of seeds tested, each mechanical property had its own specific moisture dependency, an observation consistent with previous reports on cereal-based products. ©1997 SCI     

木桁架齿板连接性能模拟的研究现状

从齿板连接构件材料及连接性质确定和连接性能模拟两方面介绍国内外木桁架齿板连接性能理论及模拟研究现状,并对三种常用的齿板连接性能研究的分析软件SAT、PPSAⅡ和ANSYS作了简单介绍。通过对文献资料的系统分析,认为齿板连接性能研究具有重要的科研和应用价值。     

热处理对PTFE牵伸性能的影响

为用膜裂法制备高强度的PTFE(polytetrafluoroethylene聚四氟乙烯)长丝,以单向拉伸膜经膜裂制成的PTFE基带为原料,在加以适当张力的条件下,经不同加热温度及加热时间等处理后,再经加捻、热牵伸和热定型制备了PTFE长丝。采用SEM观察表面形貌,DSC测试熔融温度和结晶度,单纤维强力仪测试力学性能。结果表明,热处理使得PTFE长丝的结晶度降低,导致PTFE长丝断裂伸长率大幅提高,可以在很大程度上提高PTFE长丝的牵伸倍数,因此,在膜裂法制备PTFE长丝的前期进行适当的热处理,有利于加工成高强度、低细度的PTFE缝纫线。     

Comparison of selected physical and mechanical properties of densified beech wood plasticized by ammonia and saturated steam

Gaseous ammonia treatment in combination with densification of wood has been known for several decades, but these days there is no industrial production of materials modified in this way; also, little has been published in this area of wood science. In this study, selected physical and mechanical properties, i.e. density profile, bending strength, hardness and moisture absorption were investigated for Lignamon (1), which was obtained from the Czech industrial production. Selected properties were also investigated using steam-densified beech (2) and native beech (3) and compared with each other. Densitometry of Lignamon showed a large variability in the density profile compared to that of only densified beech. It is affected by the degree of densification, temperature and moisture gradients, and their relationship to the glass transition of the wood cell wall. Modulus of elasticity, hardness, moisture exclusion and anti-swelling efficiency of Lignamon are enhanced compared to densified beech. The enhanced dimensional stability and lower hygroscopicity of Lignamon are probably caused by heat treatment during the process. Further investigation will be carried out with self-produced Lignamon samples.     

热处理对PTT纤维结构和力学性能的影响

通过SEM观察及对拉伸曲线和弹性回复率等性能的测定,研究了热处理温度和拉伸张力对PTT纤维结构和力学性能的影响。结果表明在120～140℃相对较低的温度进行拉伸处理时,PTT纤维结构容易受到损伤,并导致其抗变形能力和回弹性能下降;而在160℃左右进行适当的拉伸热处理,则有利于形成更完善的内部结构,提高其抗变形能力、强力及回弹性能;在160℃左右对PTT纤维织物进行热定型加工,能最大限度地维持并优化PTT纤维的高回弹性能。     

Influence of steaming on selected wood properties of four hardwood species

Influence of steaming on various mechanical and physical properties of two European (Robinia pseudoacacia L., Quercus robur L.) and two tropical (Intsia bijuga, Hymenolobium petraeum) hardwood species were investigated. Each of these wood species requires adequate adhesive systems for the use as dimension stock because of their highly reactive surface chemistry. In order to optimize the gluing behaviour of the timbers involved, steaming processes with five different sets of parameters (steaming time and temperature) were carried out. In addition to the adhesive test, bending strength, hardness, and colour of the modified timbers were examined. The result of steaming highly depends on the wood species. For black locust, steaming is a suitable method of colour homogenization and colourization. Short term, low temperature treatment improves the adhesion performance also, whereas the colour change value reaches its maximum in the case of long term, high temperature steaming. Hue shift of oak and sapupira was inconsiderable for any applied set of parameters, only a small L* decrease was observed at higher temperatures. The colour of merbau samples shifted slightly during the treatment. Bending strength and hardness of wood samples in all of the four wood species decreased during the treatment. However, steaming time is more important than temperature while aspect of colour change both time and temperature has the same significance. Adhesive properties of sapupira can be greatly improved by hydrothermal treatment.     

Effect of accelerated aging on selected physical and mechanical properties of Bambusa rigida bamboo

Bambusa rigida bamboos were subjected to accelerated aging test, and the main physical and mechanical properties before and after aging were comparatively investigated. The results revealed that the aged bamboos lost parts of their original physical and strength properties. Furthermore, mechanical strength properties and basic density of both control and aged specimens increased significantly with the height of the culms, while that for the volumetric shrinkage was reverse. The effect of accelerated aging on the properties of base portion specimens was much more significant than that of the middle and top portions.     

Influence of heat pressure steaming (HPS) on the mechanical and physical properties of common oak wood

Common oak (Quercus robur) was thermally treated applying a heat pressure steaming procedure. Physical and mechanical properties of treated and untreated samples were investigated extensively. Swelling, water absorption, water vapour resistance, porosity and thermal conductivity were tested and the mechanical properties of tensile, bending and compression strength and of Young’s modulus (static and dynamic) as well as Poisson’s ratio and shear modulus were determined. The tests were carried out in the standard climate 20 °C and 65 % relative humidity and also in all three anatomical main directions: longitudinal, radial and tangential. The equilibrium moisture content at 20 °C and 65 % relative humidity for HPS (heat pressure steamed) oak (determined in adsorption test) was 6.7 % and for untreated oak 9.1 %. Swelling in longitudinal direction was not affected: a reduction of 17 and 10 % could be observed in radial and tangential direction, respectively. The porosity of the treated samples was 53.9 % in comparison to the untreated samples with 51.0 %. The thermal conductivity depending on the modification procedure changed only slightly which was related to the different densities of the samples. The water vapour resistance of the modified samples increases compared to the untreated samples. The values are double (dry-cup) respectively three times (wet-cup) higher than those of the reference samples. The elastic properties were not influenced by heat pressure steaming. The MOE does not show a significant change depending on the treatment. Bending and tensile strength of HPS oak decrease. In longitudinal direction, the tensile strength drops by 26 % and the bending strength by 25 %.     

Effect of heat treatment duration on the thermal conductivity of spruce and poplar wood

Changes in the thermal conductivity and density of Pannónia poplar (Populus x euramericana cv. Pannónia) and spruce (Picea abies) caused by heat treatment were examined. The specimens were treated at 180?°C for 15, 25 and 35 h. Treatment duration had different impact on both the density and the thermal conductivity of poplar and spruce. The density of poplar decreased by 9.1, 12.1 and 13.4%, and the thermal conductivity decreased by 16.9, 24.0, 29.1% after 15, 25 and 35 h of treatment, respectively. In the case of spruce, the density decreased by 5.2, 7.6 and 8.7%, and the heat conductivity by 7.4, 14.1 and 22.0%, respectively.     

Effect of radiata pine juvenile wood on the physical and mechanical properties of oriented strandboard

This work analyzes the impact of radiata pine (Pinus radiata D. Don) juvenile wood on the physical and mechanical properties of oriented strandboards (OSB). Radiata pine logs were obtained from 10 trees of a 26-year old managed stand located in the 8th Region of Chile. The experimental design considered the proportion of juvenile wood and strand orientation as independent variables. OSB panels of 0.4 m×0.4 m×12 mm were produced and tested. The results show that the juvenile wood proportion has a significant impact on the physical and mechanical properties of OSB. Strands orientation had a significant impact on all the properties studied with the exception of the modulus of elasticity in bending. However, this impact was small in all cases and would not change panel grade with the exception of linear expansion. In this case, panels made from tangential strands showed a higher linear expansion. According to these results, radiata pine juvenile wood can be used for the manufacturing of OSB up to a proportion of 70% of the oven-dry wood weight without significant losses of the physical and mechanical properties if the juvenile wood strands are located in the surface layers.