芳纶标准回潮率测试方法的改进

针对现有GB/T 6503—2008测试纤维回潮率的缺陷,提出测试芳纶标准回潮率的改进方法:采用烘箱法先将纤维试样在烘箱中烘至恒重,然后将烘至恒重的试样在标准大气条件下调湿至平衡状态,最后将调湿平衡的试样在烘箱中烘至恒重,测试芳纶的标准回潮率。结果表明:该方法中起初的预烘干处理消除了芳纶表面的油剂等对测试有干扰的因素,测得的标准回潮率更准确,标准回潮率的相对标准偏差为0.64%,方法的重复性好。     

微波加热技术用于重量法测定SO4^2—

介绍利用玻璃坩埚过滤BaSO4沉淀,微波加热恒重,测定磷矿石、湿法磷酸及合成标样中的SO42-,利用提高酸度和一次性加入BaCl2溶液减少干扰离子的共沉淀现象.通过试验确定了微波恒重时间45min即可,并推荐磷矿试样采用酸溶分解法,好于熔融法.     

微波加热技术用于重量法测定SO_4~(2-)

介绍利用玻璃坩埚过滤ＢａＳＯ４沉淀,微波加热恒重,测定磷矿石、湿法磷酸及合成标样中的ＳＯ４２－,利用提高酸度和一次性加入 ＢａＣｌ２溶液减少干扰离子的共沉淀现象。通过试验确定了微波恒重时间 ４５ ｍｉｎ即可,并推荐磷矿试样采用酸溶分解法,好于熔融法。     

新重量法镀液分析示例

1 前言 在定量分析中,经典重量法因准确可靠而倍受重视,但是操作过程却非常麻烦又费时间.新重量法在准确可靠的基础上,操作更简便省时.所谓新重量法[1]就是不用坩埚及其反复高温灼烧或省去砂芯漏斗及其恒重,而是只用滤纸代替来实施重量法的测定,亦称滤纸烘重法.     

影响废水中悬浮物测定结果的因素

对重量法测量悬浮物浓度中的关键技术,包括样品采集、取样、过滤、烘干温度、烘干时间、恒重时间和过滤体积进行分析探讨.通过分析得出在重量法测量悬浮物浓度中合适的测量条件和采样条件.     

微波干燥法用于石油产品中机械杂质的测定

采用了微波干燥法测定石油产品中的机械杂质,确定了较佳的微波干燥条件：滤纸与称量瓶的恒重。在功率540W时,恒重时间3min;机械杂质在0．5g左右,功率540w时,恒重时间只需7min;机械杂质在0．1g左右,功率540W,恒重时间则只需5min。和传统的方法相比,本法具有快速、准确度高、操作方便、节约能耗、提高工作效率等优点,可用于各种石油产品中机械杂质测定,也可推广应用于其它重量分析法。     

醋酸乙烯溶液聚合过程中转化率的快速测定

醋酸乙烯在溶液聚合过程中转化率的测定,一般采用溴量法或烘干恒重法。溴量法有严重的缺点:(1)费时较长(因为粘稠的聚醋酸乙烯用甲醇溶解就需1小时左右。丙酮可迅速溶解,但对该法有所干扰),整个操作过程约需80分钟左右。(2)误差较大(因聚醋酸乙烯的甲醇溶液,加入溴水后即有大块粘稠物析出,对溴和醋酸乙烯均有包藏作用,对碘有吸附作用)。烘干恒重法,因样品不易处理,在生产上应用也不合适。作者根据达斯(Das)的乙烯基醋酸汞测定法和莫尔阔特(Marquardt)等的试验,采用丙酮将样     

微波炉在重量法测定磷矿中全磷的应用

<正>近年来采用微波炉加热重量法测定的报道不少,笔者利用玻璃砂芯坩埚过滤磷钼酸喹啉沉淀,微波炉加热恒重,重量法测定了磷矿样品中的全磷,结果准确、快速,与烘箱恒重结果无明显差     

热重-红外光谱联用法同时测定石膏中结晶水和二氧化碳含量

当前,石膏中结晶水含量是将试样置于230℃烘箱中烘至恒重,通过前后质量差来计算;二氧化碳含量的测定是采用碱石棉吸收重量法。两者操作繁琐耗时,人为误差也不易控制。本文依托科技部创新方法工作专项项目（2011IM030600）,提出采用热重-红外光谱联用法同时测定石膏中结晶水和二氧化碳含量。     

四苯硼钾微波重量法测定硫酸钾、氯化钾中氧化钾的研究

研究建立了在样品处理过程中不使用甲醛并用G4玻璃坩埚过滤四苯硼钾沉淀,微波加热恒重。测定硫酸钾、氯化钾中氧化钾含量的方法。确定了微波功率300W,加热干燥恒重时间6min。方法省时、简便、实用、无毒害、符合生产要求。     

简介磷钼酸喹啉沉淀所用玻璃砂心坩埚的处理方法

在酸性介质中,试样溶液中的正磷酸根与喹钼柠酮试剂反应生成黄色的磷钼酸喹啉沉淀,用磷钼酸喹啉重量法测定其含量。通常采用预先在180±2℃干燥箱内干燥至恒重的玻璃砂心坩埚进行过滤。而过滤后带有磷钼酸喹啉沉淀坩埚的处理,却一直是一个让工作人员很头痛的问题。     

Determination of water content of granulated detergents

A quick analytical procedure was described for the determination of water content of granulated detergents. A constant weight loss of sample was obtained within 5 min by microwave drying. The weight loss agrees with the water content by the modified distillation method. The coefficient of variation was 0.7%.     

Kinetic modeling of atom transfer radical copolymerization of methyl methacrylate and 2‐(trimethylsilyl) ethyl methacrylate in a train of continuous stirred‐tank reactors

A comprehensive model was developed using the method of moments to describe the atom transfer radical copolymerization (ATRcoP) of methyl methacrylate and 2‐(trimethylsilyl) ethyl methacrylate in a train of continuous stirred‐tank reactors (CSTRs). The use of a train of CSTRs effectively decreases the residence time distribution and molecular weight distribution. Two different constraint conditions (i.e., constant feeding flow rate and constant total average residence time) were simulated. At constant feeding flow rate, the monomer conversion and average molecular weight are significantly improved by increasing the number of CSTRs in the train. Moreover, a constant total average residence time increases the productivity of copolymers with the increase in the number of CSTRs in the series. Thus, a train of CSTRs can be used to produce copolymers continuously with consistent quality. This method is important in obtaining a balance between the quality and quantity of the copolymer production for ATRcoP. POLYM. ENG. SCI., 55:1030–1038, 2015. © 2014 Society of Plastics Engineers     

New use of size exclusion chromatography in kinetics of mechanical degradation of polymers in solution

A new method to investigate the mechanical degradation of polymers in solution is described that uses size exclusion chromatograms of the initial polymer and of the degraded sample. The incipient parts of these chromatograms are analyzed to obtain kinetic data about degradation at the level of infinitesimal fractions. The procedure is based on the fact that mechanical degradation of the polymers is a first-order reaction and macromolecules are cleaved mostly in their central region. The rate constant and the variation in the rate constant with molecular weight are determined in a single experiment, avoiding additional fractionation steps. Moreover, the slope of the size exclusion chromatographic calibration curve is derived, opening new ways to determine polydispersities or even to make rapid calibration for unknown polymers. To verify the method, the rate constant and the molecular weight dependence of the rate constant were determined for the sonic degradation of polystyrene in toluene. The rate constant is found to vary with the square of the molecular weight, and its value is in good agreement with results reported using much more laborious methods. © 1993 John Wiley & Sons, Inc.     

Concentration dependence of zero-shear viscosity for polymer solutions: A test of the lyons-tobolsky equation

The empirical equation proposed by Lyons and Tobolsky (1) to describe the concentration dependence of zero-shear viscosity in polymer solutions was tested on a variety of data taken from the literature, covering different polymer-solvent systems, molecular weight, temperature, and the whole concentration range. This equation was fitted to each set of experimental viscosity-concentration data by a least squares method. The validity of this equation is verified. The dependence of the optimal values obtained for the three parameters intrinsic viscosity, [η], Huggins constant, k, and new empirical constant, b, on molecular weight, temperature, and solvent is also discussed.     

Light scattering Rayleigh linewidth measurements upon solutions of globular proteins containing high molecular weight impurities

A theory is presented showing that the effect of a very small amount of high molecular weight impurity on a globular protein solution is to decrease the measured diffusion constant and increase the weight average molecular weight in equal proportions. This applies when the diffusion constant is determined by a light scattering Rayleigh linewidth measurement using the autocorrelation method. Experimental verification of this is provided by the results of measurements upon a solution of bovine plasma albumin containing a high molecular weight impurity. The effects of different amounts of impurity were simulated by making measurements at different angles of scatter. The limitations of the theory are discussed.     

High-resolution thermogravimetric analysis of polyurethane/poly(ethyl methacrylate) interpenetrating polymer networks

Thermal degradation of a series of polyurethane/poly(ethyl methacrylate) interpenetrating polymer networks and their constituent networks were studied by three modes of thermogravimetric analysis: the conventional method, the constant reaction rate method, and the dynamic rate technique. The best understanding of the degradation mechanism was achieved by the last method, which allows much better resolution of overlapping events. In addition, the weight losses correspond well with the results obtained from the constant reaction rate analysis, but are achieved in shorter times. © 1998 John Wiley & Sons, Inc. J. Appl. Polym. Sci. 70: 287–295, 1998     

Polymerization mechanisms and molecular weight distribution. II. AIBN-initiated polymerization of styrene at 60°C

An experimental study was carried out on the AIBN-initiated polymerization of styrene at 60°C. The kinetic rate constants were determined by the method of moments and the MWD method, which was proposed in a previous paper. The results compared favorably with the data in the literature and the MWD method was noted to yield more consistent results than the method of moments, which indicates the importance of considering the whole molecular weight distribution. The theoretical MWD was found to approximate the experimental MWD well. The chain-transfer constant to AIBN was found to be between 0.09 and 0.14.     

Heat capacity of polypropylene composite at high pressure and temperature

The heat capacities of isotactic polypropylene and its composite with glass fiber have been measured at high pressure, up to 7 MPa, in the melt state by high pressure differential scanning calorimetry (HPDSC). The values also have been calculated from the data of specific volume (V) measured by dilatometry and thermal conductivity (κ) and thermal diffusivity (α) measured by a compensating hot wire method. The values of the heat capacity measured from HPDSC are consistent with those from the calculation method. The heat capacities of molten polypropylene and its composite increase linearly with temperature at a constant pressure and decrease with pressure at a constant temperature. It was found that the heat capacity of polypropylene is insensitive to molecular weight. The heat capacities of molten polypropylene composites are found to be predicted by an additive rule from the weight fractions of heat capacities of polypropylene and glass fiber.     

Effect of molecular weight distribution on elongational viscosity of undiluted polymer fluids

A combination of the Bersted model, giving the relaxation spectrum in terms of the molecular weight distribution (MWD), and the rubberlike-liquid model of I odge is used to describe the elongational viscosity for constant extensional strain rates in terms of the MWD. Predictions of this hybrid model are in reasonable agreement with experimental results for polystyrene, if one assumes a strain rate dependent truncation of the relaxation spectrum. The predicted effects of varying molecular weight and breadth of the molecular weight distribution on the extensional viscosity are presented. At constant weight average molecular weight and constant strain, a narrower MWD is predicted to yield an extensional viscosity-strain rate curve that is essentially shifted to higher strain rates relative to a broader MWD. Furthermore, at constant weight, average molecular weight, constant strain, and high strain rates, a narrower MWD is predicted to yield a higher extensional viscosity.