The use of a temperature programmable brabender mixing head for the evaluation of the processing characteristics of poly(vinyl chloride)

A technique is described for determining the temperature-torque profile of a PVC compound in a Brabender Plasticorder mixing chamber from room temperature to the temperature at which degradation occurs. Within this temperature range many PVC compounds show three characteristic peaks in the torque temperature trace. It is suggested that these three peaks are associated with the breakdown of the PVC powder particles (Stage III, 100 to 150 μm), micro-granules (Stage II, 0.5 to 2 μm), and primary particles (Stage I, 10 nm), respectively. The positions and shapes of these peaks are functions of the compound being investigated and as such can be used to characterize the processing behavior of the compound.

The greater part of the work has been carried out using suspension polymers but application of the technique to mass and emulsion polymers suggests that the conclusions are applicable to all polymers which possess a particulate substructure.     

Stress whitening and yielding mechanism of rubber-modified PVC

Structure-property relationships were investigated for blends of grafted rubbery polymers with PVC. Increasing grafting levels as well as higher blending temperatures improved the dispersion of the graft copolymers in PVC, lowered the impact strength, and reduced stress whitening. Presuming a mechanistic connection between impact strength and stress whitening, the causes of whitening due to mechanical deformations were studied by a variety of methods. Electron microscopy of stress-whitened zones revealed a large number of cavities formed by rupture of rubber particles, which correlated with the extent of whitening. Density measurements and quantitative evaluations of the volume increase due to the cavities in the stress-whitened zones were in agreement and proved that crazing did not significantly contribute to either volume dilation or stress-whitening. Light scattering studies indicated the existence of reflecting planes oriented at an angle of 55 to 64° to the direction of the applied stress, depending on the particle size of the modifier in the blends. The orientation of the scattered light could not be attributed to the cavities in the rubber particles because of their smallness (< 0.5 μm). An explanation was finally found by transmission light microscopy at various resolving powers. It was demonstrated that the ruptured rubber particles were accumulated in bands which corresponded to shear bands in the PVC matrix. Thus it was concluded that the rubber particles improved the impact strength of PVC by initiating shear bands and not by generating crazes.     

A Pulsed Field Gradient NMR Technique for the Determination of the Structure of Suspensions of Non-Brownian Particles with Application to Packings of Spheres

The internal structure of systems of particles in a liquid is studied with a novel NMR technique based on the measurement of the squared modulus of the magnetization in presence of a pulsed field gradient. The formalism is analogous to the one used in classical scattering techniques (light, X-rays, neutrons); it allows similar information to be obtained about the structure (in particular, the structure factorS(q)). The main improvement is that the range of particles sizes is 10 μm to 1 mm, as compared with the range of the scattering techniques (<5 μm). The NMR technique was validated by studying packings of spherical particles of mean diameter 240 μm created by sedimentation. The profile of the experimental squared modulus of the magnetization versus the wave vector provides results for the mean size of particles and the compacity. The main feature is that it depends on the pair distribution function, and the present results are in good agreement with a model based on the Percus–Yevick approximation. This technique is then particularly adapted to systems such as non-Brownian suspensions, fluidized beds, porous media, and sediments.     

Multiple scattering of light by water cloud droplets with external and internal mixing of black carbon aerosols

The mixture of water cloud droplets with black carbon impurities is modeled by external and internal mixing models.The internal mixing model is modeled with a two-layered sphere(water cloud droplets containing black carbon(BC) inclusions),and the single scattering and absorption characteristics are calculated at the visible wavelength of 0.55 μm by using the Lorenz-Mie theory.The external mixing model is developed assuming that the same amount of BC particles are mixed with the water droplets externally.The multiple scattering characteristics are computed by using the Monte Carlo method.The results show that when the size of the BC aerosol is small,the reflection intensity of the internal mixing model is bigger than that of the external mixing model.However,if the size of the BC aerosol is big,the absorption of the internal mixing model will be larger than that of the external mixing model.     

Influence of In-situ Grafting on the Dispersion of Carbon Black in Solvents and Natural Rubber

In-situ grafting of natural rubber (NR) onto the carbon black (CB) surface by a solid-state method was used to obtain grafted carbon black (GCB). The morphology of the original CB and GCB particles was observed by AFM and TEM. The original CB particles fused together and occurred as large dendritic agglomerates while the GCB particles occurred as small aggregates about 150 nm in diameter. The dispersion and dispersion stability of CB and GCB in toluene and cyclohexene were studied by zeta potential and a spectrophotometer. The results showed that the grafting procedure can improve both dispersion and dispersion stability of CB particles. The dispersion in NR was studied by DMA and observed by SEM. It was shown that GCB has better dispersion than CB in a NR matrix. As expected a weakened filler-filler interaction and enhanced filler-polymer interaction occurred after grafting modification.     

Aerosol Generation Method for Measuring Particles Suspended in Water – Detection of Particulate Impurities in Ultrapure Water and Sizing of Fine Powders –

The method described is based on the fact that the measurement of particles in the gaseous phase is generally easier than that in the liquid phase for fine particles smaller than 1 μm in diameter. The system consists of a liquid nebulizing unit, evaporator, condenser, mixing diluter and two different aerosol sizing instruments. It has been found that this method can continuously detect particulate impurities in ultrapure water in situ and can measure the size distribution of fine powders in the submicron particle size range down to about 0.05 μm.     

随机分布黑碳-硅酸盐混合凝聚粒子的消光特性研究

基于分形理论,采用蒙特卡罗方法对随机分布的混合凝聚粒子的空间结构进行了仿真模拟。利用Bruggeman有效介质理论得到了占有不同体积份额黑碳的内混合凝聚粒子的等效复折射率。采用离散偶极子近似方法对随机分布混合凝聚粒子在内外混合状态下的吸收、散射和消光效率因子等消光特性参量进行了数值计算,深入探讨了混合方式、容积含量、入射波长以及基本粒子粒径和数量对混合凝聚粒子消光特性的影响规律。通过将所得数值结果与T矩阵方法的数值结果进行比较发现,两种数值方法计算的结果非常相近。结果表明,随机分布混合凝聚粒子的散射效率因子对混合方式非常敏感,消光效率因子对混合方式较敏感,而吸收效率因子对混合方式不敏感。随着凝聚粒子尺度参数的增大,混合方式对散射和消光效率因子的影响逐渐显著。内外混合方式下,随着黑碳体积比的增大随机分布混合凝聚粒子的吸收、散射和消光效率因子均近似线性增大,并且增大的幅度随着粒子尺度参数的增大而增大。     

玻璃-橡胶混合颗粒体系的弹性行为研究

废旧橡胶制品颗粒与砂土颗粒混合物作为建筑填充材料具有环保、轻质、减震效果好等特点.软硬组分的混合比例可以调制体系力学性能从而实现兼顾材料柔韧性与强度的需求,但细观层面上材料性能改变的原因尚不明确.本文主要研究玻璃-橡胶混合颗粒体系的弹性行为及其微观机制.利用飞行时间法测量混合材料等效动弹性模量,发现随着橡胶颗粒增加,体系逐渐从类玻璃刚性行为转变为类橡胶柔性行为.离散元模拟结果与实验结果类似.此外,模拟显示低橡胶颗粒占比样品内主要由玻璃颗粒构成主力链结构,而橡胶颗粒基本不参与强力链的构成.当橡胶颗粒占比较大时,玻璃颗粒和橡胶颗粒共同构成主力链网络结构,但颗粒间法向接触力分布相对更为均匀,可视为玻璃颗粒悬浮于橡胶颗粒中.基于上述结果,提出了改进的等效介质理论,用于描述混合颗粒体系的弹性行为.研究认为:橡胶颗粒占比较小时内部颗粒的变形相对均匀,材料近似满足等应变假设,视为并联弹簧模型;橡胶颗粒占比较大时混合材料近似满足等应力假设,视为串联弹簧模型.两种模型得到的结果与模拟结果一致.上述结果有利于从微观角度揭示混合颗粒材料弹性行为的变化机制.     

随机取向烟尘团簇粒子的光学截面的数值计算

采用蒙特卡罗方法根据团簇—团簇凝聚（CCA）模型对由球形原始微粒凝聚而成的烟尘团簇粒子进行了模拟,利用离散偶极子近似（DDA）方法数值计算了不同原始微粒粒径和数目组成的随机取向的烟尘团簇粒子的总消光截面、吸收截面及散射截面等光学特性参数,研究了原始微粒粒径及数目对随机取向烟尘团簇粒子光学特性的影响。结果表明：当入射波长一定时,随机取向烟尘団簇粒子的光学特性主要取决于原始微粒的粒径和数目;烟尘团簇粒子对不同波段激光的吸收和散射存在差别,这种差别随原始微粒粒径及数目变化而变化。这一工作为研究电磁波在烟尘中的传输特性提供重要参考数据。     

Properties of blends of poly(vinyl chloride) and chlorinated polyethylene. I. Optical methods of characterization of PVC multiphase systems

Hitherto it has not been possible to produce a microscopic image with adequate resolution of the high-impact two-phase system poly(vinyl chloride) (PVC)/chlorinated polyethylene (CPE) due to inadequate phase contrast. With the aid of various chemical staining methods and through ion etching, a way has been found for studying the microstructure of the PVC/CPE system by light microscopy and electron microscopy. These independent visualization techniques and scanning electron micrographs of fracture surfaces show, as the morphology with optimal mechanical and rheological properties, networklike distribution of the rubber phase and, imbedded in this, a PVC phase consisting of primary particles.     

Light scattering by agglomerates: Interconnecting size and absorption effects (PROGRA2 experiment)

Linear polarization of the scattered light by clouds of dust particles and by very large agglomerates deposited on a surface are studied with the PROGRA² experiment. A first series of measurements use bare silica spheres and black-coated spheres to compare the phase curves obtained by different sizes of agglomerates with varying albedos. The refractive indices are evaluated by comparison with numerical simulations. Then, the maximum polarization, P_max, on the phase curves for irregular particles is studied as a function of the size of the grains (equivalent diameters from submicron-sized to hundreds of micrometres) and of the agglomerates (from micrometres to centimetres). A minimum value of P_max is obtained for silica (about 5% for lifted agglomerates and 3% for layers of particles with a grain size of about 50 μm) and amorphous carbon (about 40% for lifted agglomerates and layers with a grain size of about 0.2 μm). For smaller grain sizes, P_max increases when the grain size decreases. For larger grain sizes, P_max increases when the grain size increases. Differences between transparent and absorbing materials are underlined. Such studies may be used to interpret remote observations of light scattering by dust particles in cometary comae and Titan's atmosphere.     

Controlling cohesive particle mixing and segregation

We observe experimentally that particle systems that would otherwise mix can be made to segregate and vice versa simply by adding moisture. Using a newly developed theoretical approach, we generate phase diagrams that exhibit both mixed and segregated phases and show how the location of phase boundaries may be manipulated via modifying the mechanical and surface properties of the particles. These results have implications for industrial mixing/separation processes as well as novel particle production methods (e.g., engineered agglomerates with precisely prescribed compositions).     

随机分布烟尘簇团粒子缪勒矩阵的数值计算

利用蒙特卡罗方法根据团簇-团簇凝聚（CCA）模型对由球形原始粒子凝聚而成的烟尘簇团粒子进行了模拟,用离散偶极子近似（DDA）方法对随机分布的烟尘簇团粒子的缪勒矩阵元素进行了数值计算,给出了不同入射波长情况下随机分布烟尘簇团粒子的缪勒矩阵元素与组成簇团粒子的基本粒子的粒径和数目的数值关系,为进一步研究随机分布簇团粒子的形成机理、形态特性、散射特性提供了一种理论方法. 关键词： 烟尘簇团粒子 缪勒矩阵 离散偶极子近似方法     

Nanocomposites Prepared by Solution Blending: Microstructure and Mechanical Properties

Composites of poly(vinyl chloride) (PVC) filled with micron‐ and nanosized calcium carbonate (CaCO₃) particles were prepared by solution blending. The influences of particle size and CaCO₃ content on the microstructure and mechanical properties of the PVC composites were investigated by means of polarized optical microscopy and mechanical testing. The polarized optical microscope images revealed that nanosized CaCO₃ particles were more agglomerated than micron‐sized CaCO₃ particles and the amount of agglomerates increased with increasing particle content. PVC/CaCO₃‐0.22 composites (PVC nanocomposite filled with 220‐nm‐particle‐sized CaCO₃) 5 phr CaCO₃ content had the maximum tensile strength. The Young's modulus of all composites increased with increasing particle content. The energy at break of all composites showed a decreasing trend as a function of CaCO₃ content and varied with particle size.     

红外显微观测被俘获吸光性颗粒

光镊技术被广泛应用在俘获和操纵微纳米尺寸颗粒, 目前被研究学者普遍接受的俘获吸光性颗粒的机理为光泳力. 本文实现了对空气中被俘获的吸光性颗粒的红外显微观测. 当激光器功率为1.0 W时, 成功观测到被俘获墨粉颗粒(直径约7 μm)和甲苯胺蓝颗粒(直径约为1–20 μm)的温升约为14 K, 为光泳力理论提供了强有力的证据. 另外, 首次用可见光显微镜和红外显微镜同时观测到被俘获颗粒的周期振荡现象, 并分析了振荡现象的产生机理. 关键词： 光镊 光俘获 红外显微     

Light propagation in two-dimensional photonic crystals illuminated by a tightly focused laser beam

By using a tightly focused laser beam, we have studied light propagation in two-dimensional photonic crystals consisting of closed-packed hexagonal arrays of polystyrene particles with diameter of 1∼5 μm. The light propagation is found to depend strongly on the focal point positioning, the incident beam polarization and the interaction between particles and glass substrates.     

Mechanical Properties of Rubber Sheets Produced by Direct Molding of Ground Rubber Tire Powder

The so called “direct powder molding” is a compressions molding process which can be directly applied to ground rubber tire (GRT). This study shows that the GRT can be re-used to produce medium-size parts with good mechanical properties without any addition of virgin rubber. For rubber sheets prepared from the mechanically ground rubber tire (MGRT) and the cryogenically ground rubber tire (CGRT), the densities and crosslink densities of the rubber sheets increased with a decrease of the particle size of the waste tire powder. The tensile strength of the rubber sheets increased with the decreasing of the particle size for the two types of waste tire powder to 250 μm and 120 μm, respectively, and then became level. The moulding pressure had no effect on the densities, tensile strength or elongation at break of the rubber sheets. These results suggested that the effect of the particle size is important and is correlated with the mechanical properties of the rubber sheets produced by direct powder moulding technology. In general, the best mechanical properties were obtained with waste tire rubber with a size of about 250 μm for the rubber particles obtained from the mechanical grinding method of waste tire powdering.     

整体毛细管X光透镜在大气颗粒物单颗粒分析中的应用

对大气颗粒物进行单颗粒X射线荧光(XRF)分析,是一种识别大气颗粒物来源的有力手段.为了利用实验室X射线光源对大气颗粒物进行单颗粒XRF分析,建立了基于整体毛细管X光透镜和实验室X射线光源的微束X射线谱仪.透镜焦斑处的功率密度增益在103数量级,焦斑直径为30 μm左右.该微束X射线谱仪对Fe-Kα线的最小探测极限为0.7 Pg.在Mo靶光源电压和电流分别为30 kV和50 mA的条件下,利用该谱仪对直径为9 μm的大气颗粒物单颗粒进行XRF分析时,测谱时间在180 s左右.实验表明,基于毛细管X光透镜和实验室X射线光源的微束X射线分析技术在大气颗粒物单颗粒分析中有着潜在的应用价值.     

薄滚筒内二元湿颗粒体系混合行为的离散单元模拟研究

采用所建立的四方程线性弹性-阻尼离散单元模型,同时考虑了液桥力的作用,对填充量为40%、含液量为3%的水平薄滚筒内S型(不同直径颗粒)二元湿颗粒体系混合过程进行了数值模拟,并与同等操作条件下不含液的干颗粒体系的混合行为进行了比较,分析了液体对颗粒体系混合行为的影响. 同时还将计算结果与文献中的实验结果进行了比较. 结果表明,由于湿颗粒间液桥力的牵引作用使不同性质的颗粒不易分离,使部分颗粒聚结成团,减弱了离析作用的影响,使得滚筒内湿颗粒的混合程度高于相同条件下的干颗粒体系,且接触力的分布较干颗粒体系更加均匀. 通过对混合过程的模拟,直观地反映了混合过程中颗粒的微观运动特性和内部的力学结构,为研究湿颗粒体系混合过程机理提供了依据和参考. 关键词： 湿颗粒体系 混合 分离 离散单元法     

Tunable cw infrared radiation by noncollinear difference-frequency mixing

Tunable cw infrared radiation has been generated by non-collinear difference-frequency mixing in LiJO₃, using the intracavity radiation of a Nd:YAG laser and the output of a Rhodamine 6G dye laser. Infrared powers of ∽35 μW tunable from 1.28 μm to 1.62 μm have been obtained.