剑麻纤维素微晶的制备与表征

通过对剑麻纤维进行预处理、碱处理、酸解等步骤制备剑麻纤维素微晶,采用红外光谱(FT-IR)、X射线衍射(XRD)、偏光显微镜(POM)、扫描电镜(SEM)、差示扫描量热(DSC)和热重分析(TGA)等方法对产物进行了表征。红外谱图分析表明,所制备的剑麻纤维素微晶的主要成分为纤维素;而XRD、POM和SEM结果表明,剑麻纤维素微晶以纤维素Ⅰ的形式存在,长度尺寸在50μm~150μm之间,直径10μm左右;DSC和TGA热分析结果表明,剑麻纤维素微晶在323.7℃处有一尖锐的结晶熔融吸热峰,其初始热分解温度达到337℃,比普通剑麻纤维的初始热分解温度提高60℃,并且其在700℃时的最后残留物仅为0.05%。     

碱处理对马尼拉麻纤维结构及纸质振膜电声性能的影响

纸质振膜的力学性能会影响扬声器的电声(频率响应)特性,通过对天然纤维改性处理能改善振膜的力学性能。讨论了碱液浓度和处理时间对马尼拉麻纤维结构及纸质振膜力学性能和电声性能的影响。采用SEM、XRD、FT-IR、TGA等表征方法对碱处理前后的马尼拉麻纤维表面形貌、结晶结构、化学组分等进行测试分析。结果表明,随着碱液浓度或处理时间的增加,纤维表面粗糙度增大、纤维的结晶度先增大后减小、纤维表面的木质素及半纤维素减少、纤维素热稳定性提高,木质素的热稳定性降低。碱液浓度过大或处理时间过长,均会导致纤维素的降解,影响振膜力学强度。碱液浓度为5%(质量分数)、室温处理3h时,纤维振膜的力学性能和电声性能达到最佳。     

甘蔗渣显微结构对聚乳酸/甘蔗渣复合材料结构与性能的影响

采用碱处理、硅烷偶联剂处理以及碱处理配合硅烷偶联剂处理等方式改性甘蔗渣(BF),采用傅里叶变换红外光谱(FTIR)、X射线衍射(XRD)、扫描电镜(SEM)、X射线光电子能谱(XPS)、热重分析(TGA)以及力学性能测试等研究改性后BF结构的变化。结果表明,不同改性方法均明显改变了BF的结构及改性剂的键合方式。碱处理能够去除BF中的半纤维素等小分子聚合物以及部分非晶区的纤维素,导致BF热稳定性降低,结晶度上升。碱液浓度偏高以及碱处理时间过长会导致BF的纤维表面原纤化,虽然能增加与偶联剂反应的面积,但BF的强度大大下降,不利于BF的增强作用。因此,硅烷偶联剂处理的BF/PLA复合材料的相容性及力学性能最佳,其次为碱处理配合硅烷偶联剂处理的BF/PLA复合材料,最后为碱处理的BF/PLA复合材料。     

纳米纤维素表面乙酰化改性及其表征

通过乙酸酐对纳米纤维素(NCC)表面进行化学改性,通过酸碱滴定和核磁氢谱得到改性纳米纤维素的取代度,利用FT-IR、~(13)C-NMR、XRD、TEM和TGA等对改性产物的极性、热性能等进行了表征。结果表明:改性后的纳米纤维素(mNCC)的取代度为1.6左右,形貌没有太大变化,内部结晶结构得到保持,疏水性得到明显提高,在有机溶剂中的分散性得到改善。     

生物质纤维填充聚合物复合材料的界面行为

将木粉和聚合物加入HAAKE流变仪中熔融共混制备了木粉/聚合物复合材料,对比不同木粉预处理方式(碱处理、酸处理)及相容剂改善木粉与聚合物界面相容性的效果。红外光谱(FT-IR)结果表明,碱处理木粉去除了木粉中的小分子物质,酸处理木粉使木粉表面被酯化。木粉碱处理提高了木粉/聚合物复合材料的力学性能,扫描电镜(SEM)照片表明预处理后木粉与聚合物间的相容性得到了改善。使用合适的相容剂也可以改善木粉与聚合物的相容性,提高复合材料的力学性能。同时相容剂和碱处理木粉及酸处理木粉存在协同效应。     

壳聚糖改性纤维素共混复合物的制备及性能

利于壳聚糖共混改性纤维素,介绍了共混改性复合物的制备方法,并利用红外光谱(FT-IR)、扫描电子显微(SEM)、x射线衍射(XRD)、热失重分析(TGA)、平衡水分含量及力学性能的测试对共混复合物的特征进行研究.结果表明,在共混复合物中纤维素和壳聚糖具有良好的相容性,没有相分离发生;共混壳聚糖后,随着壳聚糖含量的增加,...     

可循环混合溶剂分离水稻秸秆纤维素

粉碎的水稻秸秆经水煮和抽提预处理后,采用乙二醇(EG)和水的混合体系(体积比9∶1)为溶剂,在酸或碱催化作用下,分离得到纤维素,同时回收木质素和半纤维素;对所得样品的组分含量、晶体结构、微观形貌等进行了分析。结果表明:经水煮和抽提预处理后,秸秆纤维束状结构变得疏松;在0.1mol/L的硫酸催化下,经混合溶剂处理所得样品的综纤维素含量达到86.59%(其中纤维素含量为83.09%),酸不溶木质素含量为3.70%;相同条件下,以0.1mol/L氢氧化钠为催化剂,所得样品中酸不溶木质素含量为4.21%。研究还发现,混合溶剂可高效回收并循环使用。基于实验结果和结论分析,对催化剂可能的作用机理解释为:在适当浓度的酸或碱作用下,木质素的重聚合被有效抑制,从而促进了其在混合溶剂中溶解,并使其从秸秆组织中分离。     

棉秆皮纤维的提取及其结构、性能研究

为更有效地利用废弃农作物秸秆资源,研究了常温常压碱处理提取天然棉秆皮纤维的技术,讨论了氢氧化钠溶液质量浓度、温度和时间等碱提取工艺参数对棉秆皮失重率的影响,并采用FT-IR、SEM、XRD等方法对优化工艺提取的棉秆皮纤维的化学成分、表面形态、结晶结构、力学性能等进行了表征。结果表明,NaOH质量浓度为15g/L、液固比为30mL/g、处理温度为100℃、处理时间为120min时,棉秆皮失重率较大,木质素、半纤维素、果胶等杂质去除较多。天然棉秆皮纤维结晶度为53.72%,断裂强度约1.6cN.dtex-1,断裂伸长率为5.91%,性能接近天然纤维素纤维黄麻。     

蒸汽闪爆与碱处理结合法制备棉秆皮纤维

在当前绿色环保的大环境下,为了更环保、有效地利用废弃农作物秸秆资源,采用蒸汽闪爆和低浓度的碱处理相结合的方法制备棉秆皮纤维,并与仅采用碱处理制备的棉秆皮纤维进行比较。采用纤维成分分析,FT-IR、XRD、SEM及拉伸性能测试等方法研究了2种制备方法对棉杆皮纤维的成分、结晶结构、表面形态,断裂强度的影响。结果表明:蒸汽闪爆和碱处理结合制备的棉秆皮纤维的性能较好,棉秆皮纤维的纤维素含量增加,其长度为53.4mm,细度值为29dtex,断裂强度为2.56cN/dtex。     

DMSO/AmimCl体系应用于微晶纤维素的制备

利用二甲基亚砜/氯化1-烯丙基-3-甲基咪唑(DMSO/AmimCl)体系通过溶解纤维素无定型区及残缺的结晶区来制备微晶纤维素。利用FT-IR、XRD、TGA和SEM等技术对微晶纤维素的结晶度、得率、结构、热稳定性能以及形态特性进行分析。研究结果表明,在DMSO/AmimCl质量比为0.4的溶剂体系中,得到的微晶纤维素性能最好,并对此实验的再现性进行了论证。FT-IR和XRD结果表明,所得微晶纤维素的化学结构以及结晶结构与商品微晶纤维素基本一致,微晶纤维素的晶型为纤维素Ⅰ型,结晶度为69.23%。TGA和SEM表明微晶纤维素的热稳定性能优异,多数纤维形态呈棒状,通常表面具有长条形凹痕。     

Estimation of Parameters of Universal Distribution of Moments of Failure of Products

A method is proposed for estimating the parameters of a mixture of exponential and Weibull distributions for which the accuracy of preliminary estimates obtained by graphical analysis is refined in accordance with the criterion of maximum likelihood. The efficiency of the proposed method is supported by the results of statistical modeling.     

Assessment of intakes of mixtures of radionuclides

Australia has several uranium mines and a large number of mineral sand mines, with associated processing facilities. Exposures resulting from these mining and processing operations usually involve intakes of mixtures of radionuclides. This work describes the development of a suite of first order, linear compartment models, based on the ICRP Publication 66 respiratory tract model, and an analytical solution to the decay equations, for assessing the consequences of such intakes. The computer programs based on these models directly compute excretion, organ retention and organ and whole-body doses for intakes of either single radionuclides or any mixture of radionuclides belonging to the same radioactive decay chain. The intake can be via inhalation, ingestion or injection, and can be acute, chronic or of limited duration. The starting concentration and degree of secular (dis)equilibrium can be specified for each radionuclide. No assumptions need to be made about the relative magnitudes of the radioactive half-lives of the different nuclides.     

Evaluation of optical properties of highly scattering media by moments of distributions of times of flight of photons

A novel method for the determination of the optical properties of tissue from time-domain measurements is presented. The data analysis is based on the evaluation of the first moment and the second centralized moment, i.e., the mean time of flight and the variance of the measured distribution of times of flight (DTOF) of photons injected by short (picosecond) laser pulses. Analytical expressions are derived for calculation of absorption and of reduced scattering coefficients from these moments by application of diffusion theory for infinite and semi-infinite homogeneous media. The proposed method was tested on experimental data obtained with phantoms, and results for absorption and reduced scattering coefficients obtained by the proposed method are compared with those obtained by fitting of the same data with analytical solutions of the diffusion equation. Furthermore, the accuracy of the moment analysis was investigated for a range of integration limits of the DTOF. The moment analysis may serve as a comparatively fast method for evaluating optical properties with sufficient accuracy and can be used, e.g., for on-line monitoring of optical properties of biological tissue.     

Analysis of anisotropy of properties on the basis of studies of texture of coarse-grained ingots of thermoelectric materials

An analysis of anisotropy of the properties of a Bi₂Se_0.3Te_2.7 solid solution was carried out using construction of demonstrative surfaces for thermoelectric effectiveness and thermal expansion coefficients. It is shown that the texture is an important factor forming anisotropy of properties and technological fitness of ingots for manufacturing modules. Anisotropy of properties based on the studies of the ingot textures obtained using the float-zone method and Bridgman method (growing thermoelectric plates in a flat cavity) was studied.     

Numerical study of methods of linearization of the output characteristics of radio-frequency sensors of the level of dielectric media

Different constructions of the sensing elements of radio-frequency level sensors based on sections of long lines are numerically investigated by means of the Matlab program for the purpose of minimizing the measurement error caused by the nonlinearity of the output characteristic. It is shown that the nonlinearity is lowest for U-shaped designs. The nonlinearity factor KN may be regulated by varying the capacitance of a correcting capacitor connected to the input of the sensing element and (or) the length of one of the sections of the long line. In selecting an optimal capacitance of the correcting capacitor KN ≤ 0.15% for control media with dielectric permittivity in the range 2.2–30.     

Possibilities of Decreasing the Errors of Determination of the Height of the Pole of a Sessile Drop of Melt

We analyze the possibilities of decreasing the errors of measuring the height of the pole of a sessile drop of melt above its equator by determining the position of the equator according to the midpoints of vertical chords of the image of the drop. The optimal distance between these chords and the edge of the image of the drop is chosen within 10–20% of the radius of the equator. The proposed method guarantees the same level of errors of evaluation of the height of the pole and the radius of the equator, which enables one to substantially increase the accuracy of evaluation of the capillary constant and the surface energy of the melt according to the geometric parameters of the sessile drop.     

Analysis of the rate of propagation of the wave of change of boiling modes

An approximate analytical expression is derived for the velocity of the front of the wave of change of boiling modes on a rod and on a plate. The impact of the Thomson effect and of the heater orientation in the gravity field is included. Adequate agreement is demonstrated between the derived relations and experimental data.     

Estimation of potentialities of methods of summation of direct measurement errors

Conventional methods for summation of direct measurement errors are considered. Conditions under which these methods provide consistent results are stated. It is proposed to utilize for characteristic of the total error, its interval estimator or the half-sum of the value obtained by adding up its arithmetic and geometric random errors.Translated from Izmeritel'naya Tekhnika, No. 4, pp. 10–12, April, 1995.