Rheology of PVC Plastisol: Formation of Immobilized Layer in Pseudoplastic Flow

Hoffman in the early 1970s examined mechanism of dilatancy and fracture of plastisol under high-shear conditions. The samples were monodispersed spherical particles of PVC. He discovered formation of immobilized layer in the pseudoplastic flow preceding dilatancy and subsequent destruction of the layer at the fracture. However, his analysis was focused primarily on the mechanism of the fracture, and the mechanism of pseudoplastic flow remains unexplored. The present work begins with analyses of Hoffman's data to show that pseudoplastic flow, i.e., the decrease of viscosity with the increase of shear rate, is a result of the development of the immobilized layer and creation of a mobile layer of low-viscosity fluid. Hoffman took the mobile layer to consist of pure plasticizer. The present work shows that the mobile layer contains PVC particles. The thickness of mobile layer decreases (and the thickness of immobilized layer increases) with the increase of shear rate. The particle concentration and hence viscosity of the mobile layer decrease with the increase of shear rate. Similar analyses of our dynamic viscosity-frequency relationship show that (1) the pseudoplastic behavior is a result of formation of immobilized layer, which grows thicker with the increasing frequency, and (2) the mobile layer contains dispersed particles, the concentration of which decreases with increasing frequency. (3) A presence of coarse particles results in a tighter packing of the immobilized layer and lower viscosity of the mobile layer for a given volume fraction of particles. This explains why the presence and the amount of the coarse particles are important parameters in plastisol formulation. The elastic modulus-frequency relationship is also interpreted with the development of the immobilized layer, giving strain amplification. Copyright 2001 Academic Press.     

Effect of Particle Size Distribution on the Rheology of Dispersed Systems

The rheological properties of aqueous polystyrene latex dispersions from three synthetic batches, with nearly the same z-average particle sizes, 400 nm, but varying degrees of polydispersity, 0.085, 0.301, and 0.485, respectively, were systematically investigated using steady-state shear and oscillatory shear measurements. The particles were sized with photon correlation spectroscopy and transmission electron microscopy and were stabilized sterically with PEO–PPO–PEO triblock copolymer (Synperonic F127). Results from steady-state shear measurements show that the viscosities of the systems exhibit shear-thinning behavior at high solid fractions. However, the degree of shear thinning depends on the breadth of particle size distribution, with the narrowest distribution suspension exhibiting the highest degree of shear thinning. The Herschel–Bulkley relationship best describes the flow curves. The relative viscosities as a function of volume fraction data were compared, and it was found that the broadest distribution suspension had the lowest viscosity for a given volume fraction. In addition, the data were fitted to the Krieger–Dougherty equation for hard spheres. A reasonable agreement of theory with experiment is observed, particularly and surprisingly for the very broad distribution. However, when the contribution to the volume due to the adsorbed polymer layer is considered, the agreement between experiment and theory becomes closer for all the suspensions, although the agreement for the broad distribution suspension is now worse. Fitting the Dougherty–Krieger theory to the experimental data based on our experimental maximum packing fractions gives very good agreement for all the systems studied. From oscillatory shear measurements, the moduli were obtained as a function of frequency at various latex volume fractions. The results show general change of the dispersions from viscous (G" > G′) at low volume fractions (0.25–0.30) to moderately elastic (G′ > G") at moderately high volume fractions (0.41–0.45). The change at this concentration level is likely due to some compression and interpenetration of the stabilizing polymer chain at the periphery, indicating the dominance of the interparticle forces. Overall, the very broad distribution was found to have the lowest elastic modulus for a given volume fraction.     

分散剂类型对聚苯胺粒径分布和电化学特性的影响

采用化学氧化聚合法以苯胺为单体、过硫酸铵为氧化剂,在不同分散剂体系中合成聚苯胺,考察分散剂对聚苯胺性能的影响。通过激光粒度仪、傅里叶红外吸收光谱、四探针电阻仪和电化学工作站等测试手段研究聚苯胺的结构、导电性、粒径分布及电化学性能。结果表明：分散剂能降低聚苯胺的粒径分布,提高聚苯胺的导电性和电化学稳定性;当分散剂聚乙二醇占苯胺单体质量的20％时,聚苯胺的平均粒径为3．85μm,导电率为4．68S／cm,极化电位为0．73V。     

弛豫法研究预交联颗粒凝胶的界面扩张流变性质

采用界面张力弛豫方法研究了一种新型聚合物--预交联颗粒凝胶(PPG)的界面流变性质, 考察了电解质及传统直链聚丙烯酰胺与PPG的相互作用对体系界面性质的影响, 计算得到了各体系界面扩张弹性和黏性的全频谱, 并通过归一法计算得到了相应的Cole-Cole图. 结果表明, 随着体相浓度的增加, PPG在界面层中形成网络结构, 界面扩张弹性和黏性大幅增强. 电解质能够中和PPG结构中的电荷, 明显降低扩张弹性和黏性. 直链聚丙烯酰胺与PPG在界面上可能形成更为复杂的结构, 膜的黏弹性由PPG决定.     

超细碳酸钙填充聚氯乙烯糊触变性能研究

超细碳酸钙填充聚氯乙烯糊触变性能研究陈飞跃，许勇，胡黎明（华东理工大学技术化学物理研究所，上海，２００２３７）关键词超细碳酸钙，触变性，聚氯乙烯糊，表面改性，屈服应力触变性是一种重要的工艺参数和性能指标，例如，汽车底漆用聚氯乙烯糊就要求有良好的触变性...     

Viscoelastic and thermal characterization of crosslinked PVC

Soft PVC is employed for the manufacturing of a wide range of products with different properties and a relatively low cost. The utilization of soft PVC is restricted by the poor thermal, chemical and mechanical resistance properties. Also, plasticizer migration can modify the properties or can make useless the materials for some applications because of toxicity or a general loss of properties. PVC crosslinking is the most effective way to improve mechanical and transport properties of rigid or flexible PVC at high temperatures, but at the same time the thermal stability of PVC may be significantly reduced. In this work, the crosslinking reaction of plasticized poly(vinyl chloride) (PVC) through difunctional amines was studied. The mechanisms involved in the crosslinking reaction were explained by Fourier transform infrared (FTIR) analysis. The thermal activated crosslinking reaction was studied by cone and plate rheometry, analyzing the evolution of viscoelastic properties of the suspension as a function of time and temperature. The effect of the addition of crosslinking agents on the thermal stability of the polymer was studied by thermogravimetric analysis (TGA), which revealed that crosslinking reactions promote thermal degradation phenomena in the polymer matrix. This is attributed to the formation of HCl and other species promoting polymer degradation during crosslinking, thus leading to higher weight loss during thermal treatment with respect to unmodified PVC plastisols. This was also confirmed by an evident yellowing after crosslinking, especially at higher temperatures.     

快淬NdFeB磁粉颗粒度对聚合物粘结NdFeB磁体永磁性能的影响

研究了快淬ＮｄＦｅＢ永磁粉颗粒及其分布对聚合物粘结ＮｄＦｅＢ永磁材料性能的影响。快淬Ｎｄ－ＦｅＢ永磁粉颗凿大小及其分布显著地影响聚合物结ＮｄＦｅＢ永磁材料的磁性能。适当尺寸的快淬ＮｄＦｅＢ磁粉组合可获得高的结ＮｄＦｅＢ永磁帝主要是由于快淬ＮｄＦｅＢ磁粉硬度高,呈鳞片状,其尺雨越大越难获得高密度,但尺寸太小又将破坏磁粉的结构,导致磁性能恶化。     

Use of a Cross-Sectional Model for Determining Rheology in Settling Slurries: Effect of Solvent,Particle Size,and Density

Transport models for partially settling slurries need accurate rheology correlations, particularly describing viscosity relationship to the particle concentration. A method is needed to untangle the effects of settling on apparent viscosity and the real effects of particle concentration on viscosity during rheology measurements. Our approach is based on model inversion of a cross-section model for the vertical particle concentration gradient and the local rheologies in the gap of a Couette type rheometer, established by a balance between gravitational particle settling and shear induced migration of the particles. The Krieger-Dougherty rheology correlation with adjustable parameters has been applied, where the parameters are determined by minimizing the difference between the measured viscosity data and those calculated by the model. Fairly mono-disperse silver coated polystyrene particles with two sizes and densities were used in both the aqueous and oil phase. In the raw data an apparent shear thinning tendency is observed. Through the model inversion process, this is accounted for by the shear dependent settling and the steep increase of viscosity with particle concentration. Maximum packing fraction was obtained through settling experiments. The difference between this value and the maximum packing fraction from the model inversion was less than 3% for oil-based suspensions. The larger difference was found for smaller particle size in water which is attributed to the larger effect of interparticle forces.     

凝并和成核机理下颗粒尺度分布的Monte Carlo求解

颗粒的凝并和成核现象影响其尺度分布,现有的MonteCarlo方法描述颗粒尺度分布的时间演变过程存在若干困难.提出了一种新的多重MonteCarlo(MMC)算法,基于时间驱动,利用加权的虚拟颗粒的思想,在模拟过程中保持虚拟颗粒总数不变和计算区域体积不变.利用该算法对“常凝并核,一阶成核”的情况下颗粒尺度分布的时间演变过程进行了数值求解,所得结果与数值解相符,表明MMC算法具有高且稳定的计算精度.另外,MMC算法由于跟踪比实际颗粒数目少得多的虚拟颗粒而具有较低的计算代价.     

毛细管区带电泳测定纳米粒子粒度分布的研究

建立了一种用毛细管区带电泳测定纳米粒子平均粒径及粒径分布的新方法。该方法通过外标定量法对样品的原始电泳谱图进行定量校正,从而得到样品的粒径分布图及平均粒径。外标定量法包括迁移时间-粒径校正曲线的建立及不同粒径含量校正曲线的建立。该方法所需样品量少,且粒度分布结果具有统计代表性。     

Population Balance Model for Emulsion Polymerisation Under Pseudo-Bulk Conditions: Combined Particle Size Distribution and Molecular Weight Distribution

A comprehensive model for emulsion polymerisation is presented, accounting for particle size distribution (PSD) and molecular weight distribution (MWD). The PSD information is incorporated through a population balance framework. A mechanistic formulation is adopted in modelling the average number of radicals/particle under pseudo-bulk compartmentalisation conditions. The method of moments is adopted to simplify the MWD equations over each discrete size class. The impact of the pseudo-bulk assumption on the PSD and MWD results is assessed. An identification of potential manipulated variables for control of PSD and MWD is done through sensitivity analysis.     

粒度分析及粒度标准物质研究进展

综述了当前粒度分析测试方法的研究进展,并简单介绍了各种测试方法的基本原理以及包括美国、欧洲、中国在内的国家和地区在粒度标准物质方面的研究概况。     

细粒径石蜡微胶囊相变材料的制备与性能

采用阳离子和非离子复配乳化剂,通过原位聚合制备以丙烯酸酯为壁材,石蜡为芯材的细粒径微胶囊相变材料.采用傅里叶变换红外光谱(FTIR)、扫描电子显微镜(SEM)、差示扫描量热(DSC)、热重(TG)及激光粒度仪分析表征了微胶囊相变材料的化学结构、表面形貌和热性能.结果表明,乳化剂的种类和壁材单体的配比对微胶囊性能有重要的影响.当采用阳离子和非离子复配乳化剂,壁材中单体甲基丙烯酸甲酯(MMA)与丙烯酸(AA)的质量比为9∶1时,微胶囊相变材料呈球形且表面光滑紧凑,尺寸仅为0.2~0.35μm,具有良好的储热能力,相变潜热高达169 J/g;微胶囊中壁材对石蜡芯材的分解具有明显热阻滞作用,分解温度比纯石蜡提高了150℃.     

Particle Size Distribution Measurement and Assessment of Agglomeration of Commercial Nanosized Ceramic Particles

ABSTRACT

Commercially available powders with primary particle sizes of 10–100?nm (transition aluminas, Boehmites, and a commercially available silica dispersion) have been studied using three different instruments, a photocentrifuge (Horiba CAPA 700), photon correlation spectroscopy (PCS, Malvern Zetasizer 4), and an x-ray disc centrifuge (XDC, Brookhaven X-ray Disc Centrifuge BI-XDC). Particle size distributions for five powders were collected with each instrument and in conjunction with nitrogen adsorption measurements an agglomeration factor calculated. An example is given to show the importance of using a light scattering correction when measuring particle size distributions with a photocentrifuge for a gamma alumina powder where the uncorrected data can overestimate the D _V50 by up to a factor of 10 depending on the powder. The importance of the assessment of agglomeration and how different treatments such as milling modifies the agglomeration factor F _AG is illustrated for an “as received” and attrition milled gamma alumina. Results are discussed with respect to the assumptions and limitations of the different instruments. Results are presented after consideration of the hydrodynamic density in the sedimentation methods, and light scattering for the optical based methods. For narrow size distributions in the 15–25?nm range all three instruments show very a good correlation. When the size range approaches the 40–100?nm regime PCS is very sensitivity to small populations of agglomerates. The instrument giving the best resolution in the 10–100?nm range was found to be the XDC. The speed of measurement should also be born in mind and varies enormously from several minutes for the PCS to several hours for the sedimentation techniques. To assess the accuracy of the measured sizes a model spherical silica powder was analyzed on all the instruments as well as by image analysis. The results with the silica powder showed how the accuracy of the sedimentation methods depends strongly on a knowledge of the suspended particles hydrodynamic density. This can be effected greatly by particle or agglomerate porosity and the thickness of the electrical double layer in the aqueous dispersions investigated. The results with the silica suggest accuracy's on the size better than ±20% is difficult without an accurate hydrodynamic density whereas consistency between methods for narrow size distributions can be better than 5% for median volume diameters.     

Rheology of PVC Plastisol--V: storage modulus and network formed by particle contact

Our previous work with PVC plastisols showed that pseudo-plastic behavior under increasing frequency of dynamic measurement was a result of the development of an immobilized layer. Subsequently, the dynamic viscosity and the storage modulus of the mobile phase were evaluated. The samples consisted of fine and coarse particles, of which the fine/coarse ratio was varied. The present work relates the storage modulus at different frequencies to the fine/coarse ratio through a model network consisting of particle-particle contacts. The contacts are of three kinds, fine-fine (f-f), fine-coarse (f-c), and coarse-coarse (c-c). The average number of contact points per particle has been evaluated for the above kinds of contacts at different frequencies. Also, a number of particles participating in the network have been evaluated as a relative measure. At lower frequency relatively larger numbers of f-f contact points exist per particle but fewer numbers of particles participate in the network. Therefore, the network is rather loose. The f-c contact shows a similar trend but fewer contact points per particle at all frequency levels. The c-c contact is limited to a pair formation, i.e., only 0.5 contact point per particle on average. However, c-c contact contributes significantly to the magnitude of the modulus, because of the size of the particle. At the higher frequency there are fewer f-f contacts, but a larger number of particles are participating in the network. The trend with the f-c contact is very similar. The c-c contact increases significantly at the higher frequencies.     

同时测量纳米颗粒悬浊液粒度、密度及浓度的方法研究

提出了一种基于超声检测同时测量纳米颗粒悬浊液的粒度、密度和浓度的方法.设计了一套高频宽带脉冲超声波检测系统,以纳米掺锑氧化锡(ATO)悬浊液为研究对象,结合脉冲回波技术,获得了频率为17 ～ 26 MHz的声衰减谱.据此运用最优正则化方法求解粒度反演方程,得到纳米ATO颗粒的分布曲线,中位径为22.07 nm,该值与离...     

氯乙醇法制备氧化铝超微粒的形态及其粒径分布

本文报道用透射电子显微镜(TEM)进行氯乙醇法制备氧化铝超微粒形态与粒径分布的研究。从实验数据和分布曲线近似得出了理论分布曲线。并分析和讨论了实验曲线和理论曲线偏离的原因以及本试样的微粒形态和粒径分布的关系。     

超声衰减谱测量电池浆料的粒度分布

电池浆料中颗粒状活性物质的粒度大小和分散均匀性对电池的内阻、 电压、 局部表面电流和总极化程度等性能有直接影响, 实现对其的在线实时测量对电池的质量控制具有重要意义. 基于电池浆料的高固含量、 高黏度和低透光性的特点, 本文利用超声衰减谱的方式测量了其粒度分布(PSD). 应用于电池浆料的粒度分布测量的最大难点是其利用超声衰减谱法预测粒度分布的模型需要难以获得的分散相和连续相的物性参数. 本文采用主成分分析(PCA)结合误差反向传播(BP)神经网络建立预测模型解决了超声衰减谱法的难点, 并引入遗传算法(GA)优化BP神经网络的初始阈值和权值. 通过以LiCoO₂为活性物质的电池浆料进行了验证, 结果表明, PCA-GA-BP神经网络能够有效对不同固含量电池浆料的粒度分布进行预测, 预测值与真实值的峰形重合度高, 峰高偏差小, 两者的均方误差为0.1358, 拟合度(R²)为0.9816, 说明超声衰减谱法可作为测量电池浆料粒度分布的重要方式.     

N-Alkanes in an Equatorial Sedimentary Environment: Their Distribution as a Function of Particle Size

Abstract

In order to investigate the biogeochemistry of organic matter deposited in an equatorial deltaic environment, the Mahakam delta, Borneo, analysis of geochemical markers has been realised both on various sediments and on sediments separated as a function of particle size.

Sediments were selected from two levels (-150m and -500m) of a continuous core sampled in the Mahakam delta in 1981 (Misedor Programme) and represent various lithotypes of the deltaic environment and different diagenetic conditions. After separation into sand size (> 50 μm), silt size (50–5 4mUm) and clay size (< 5 μm) fractions, free lipids have been extracted and hydrocarbons isolated by micro-column chromatography, and analysed by capillary gas liquid chromatography. Concentrations and carbon number distributions of n-alkanes are discussed in terms of the relationship between the sedimentary environment and the importance of terrigenous inputs. The distribution patterns of n-alkanes of different sediment size fractions are characterized by the predominance of high molecular weight compounds in the range C23–C37, which are also encountered for the actual deltaic plain flora: mangrove and nipah-nipah. Carbon Preference Index (CPI) values are higher in the coarse and intermediate fractions reflecting their enrichment in continentally-derived vegetation debris.