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。     

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。     

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℃.     

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。     

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.     

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.     

Rheology of PVC plastisol--VI: criteria for yielding and fracture of an immobilized layer

PVC plastisol exhibits pseudo-plastic flow in steady shear; that is, viscosity decreases with the increasing shear rate. At higher shear rates viscosity reaches a minimum and then increases, i.e., dilatant behavior. Previously, pseudo-plastic behavior was explained by a mechanism in which the suspended particles partition into an immobilized layer and a mobile phase. The development of the immobilized layer with the increase in shear rate was shown to quantitatively account for pseudo-plastic behavior. In higher shear rates dilatation of the immobilized layer was shown to be the cause of dilatacy. At even higher shear rates the immobilized layer fractures. In this paper the viscosity minimum was interpreted as the yielding of the immobilized layer. Subsequently, data in the literature were analyzed to find criteria for the yielding and fracture of the immobilized layer. Yielding was found to obey Coulomb's criterion, from which the coefficient of friction and the cohesive strength of the immobilized layer were evaluated. These properties were controlled by the nature of particle assembly in the immobilized layer and the plasticizer type had only a minor effect. The value of the coefficient of friction was on the lower side and within the range of values found in the literature for other materials. There were two modes of fracture of the immobilized layer, one with low strength, low strain to break, and the other with high strength, high strain to break. The former is analogous to the brittle fracture of solids and the latter ductile failure. The strength of brittle fracture was somewhat higher than cohesive strength, which was evaluated from yielding data. This is akin to Griffith's criterion for brittle fracture of a solid. Ductile failure occurred when the shear stress exceeded normal stress.     

Latex Particle Size Distribution by Dynamic Light Scattering: Computer Evaluation of Two Alternative Calculation Paths

Two calculation paths for estimating the particle size distribution (PSD) of a polymer latex from single-angle dynamic light scattering (DLS) measurements are evaluated on the basis of a numerical example. In the more common "double-step method," two calculation steps are applied, with the intermediate estimation of the particle light intensity distribution (PLID). In the "single-step method," the calculation is performed in one operation. From the specification of several PSDs, a mathematical model is used to produce the synthetic measurements. An iterative procedure was applied for determining the diameter range and the number of PSD points. The inversion operations were carried out using a regularization technique. For narrow distributions with diameters in the range 100-1000 nm, the PSD and the PLID are similar in shape, and both calculation paths produce similar results. For broad PSDs in the range 100-1000 nm, and for arbitrary PSDs in the range 10-100 nm (i.e., in the Rayleigh region), the single-step method proved preferable. Copyright 2000 Academic Press.     

纳米ATO颗粒粒度分布的脉冲超声波测量研究

讨论了脉冲超声波测量纳米ATO颗粒粒度分布方法中的3个步骤,即超声波衰减谱测量、严格数学模型的选型以及颗粒粒度分布的反演计算.通过发射脉冲超声波并利用变声程方法测量25 ℃时2%(体积分数)的纳米ATO-H2O分散液的超声衰减谱;选取McClements理论模型叠加BLBL理论模型共同描述纳米ATO颗粒分散液中的超声衰减现象;采用最优正则优化反演算法反演得到纳米ATO颗粒的粒度分布以及平均粒径.脉冲超声法检测结果显示,纳米ATO颗粒的平均粒径为25.6 nm,粒度分布为11.4 ～47.1 nm,CPS离心沉降纳米粒度分析仪测定结果分别为22.1 nm和10.1 ～62.6 nm.脉冲超声法检测结果与透射电镜图像以及离心沉降纳米粒度分析仪检测结果吻合较好,证明了脉冲超声波测量纳米颗粒粒度分布以及平均粒径的可行性与可靠性.     

超细钛硅分子筛粒径的激光粒度分析

研究了试样浓度、超声波强度、分散时间及分散剂的加入对钛硅分子筛粒度测定结果的影响，结果表明，试样浓度低或高，粒度测定结果偏大；超声波强度的增大和超声波分散时间适当的延长有利于粒子的分散，也有利于粒度的准确测定；加入分散剂六偏磷酸钠后，测试结果重复性好。     

Properties of PVC. I. Properties of PVC films prepared by casting and by precipitation

This investigation compares the properties of PVC films prepared both by casting from tetrahydrofuran solution and from samples obtained by precipitation with properties of samples from the original PVC. The differences in properties are explained on the basis of solvent residues remaining in the samples even after tempering at higher temperatures and after extremely long times of drying. Attention was given to the difficulties caused by this fact, namely, in observing the influence of molecular weight and of distribution of molecular weights of fractions on PVC properties. Reasons were given for the retention of the tetrahydrofuran by PVC.     

Adsorption of SDBS and Its Effect on Rheology of Preformed Particle Gels

The adsorption of anionic surfactant sodium dodecylbenzenesulfonate (SDBS) onto preformed particle gels (PPGs) and the effect of SDBS on the swelling ratio and rheology of PPGs were investigated. SDBS molecules can adsorb onto PPGs because of the hydrophobic association with the chain of PPGs at low concentration and the association of the SDBS micelles with the chains of PPGs at high concentration. PPGs contract and the shear stress of PPGs decreases after adsorption of SDBS. In addition, the storage modulus decreases first and then increases with increasing SDBS concentration.     

Effects of Some Parameters on Particle Size Distribution of Chitosan Nanoparticles Prepared by Ionic Gelation Method

In this research, chitosan nanoparticles were prepared based on the ionic gelation of chitosan with tripolyphosphate anions. Effects of parameters such as chitosan concentration, tripolyphosphate concentration, and reaction time on the particle size distribution were investigated. In order to determine optimum conditions, tests were designed by Qualitek-4 software, using Taguchi method. The best conditions were determined based on three factors at three levels. Therefore, the main object was to investigate the effect of some parameters on particle size distribution and determine the optimum conditions for preparing chitosan nanoparticles by ionic gelation, followed by evaluation of the physicochemical and structural properties. The size distribution of original chitosan and chitosan nanoparticles were determined by Laser Diffraction and Dynamic Light Scattering, respectively. The physicochemical properties of the chitosan nanoparticles were studied using SEM, TEM, XRD pattern, FTIR, UV–vis, TGA, and NMR spectra. The optimum chitosan concentration, tripolyphosphate concentration, and reaction time were found to be 1.0 mg/ml, 1.0 mg/ml, and 60 min, respectively.