超临界反溶剂过程制备银杏叶提取物超细微粒

超临界反溶剂过程是近年来提出的一种制备纳微米粉体材料的新方法。应用超临界反溶剂过程实验装置制备银杏提取物(GBE)超细微粒,实验中以乙醇为溶剂,超临界CO2为反溶剂,制备出平均直径在1μm至2μm范围内的GBE超细微粒。同时研究了操作压力、操作温度及二氧化碳与溶液流率比等操作参数对制备的超细微粒粒径、形态及粒径分布的影响。实验结果表明：操作压力、温度对制备的GBE微粒影响较为显著。     

超临界CO2GAS沉析HMX制细过程的影响因素

研究了超临界CO2GAS沉析丙酮溶液中HMX的过程压力、温度、溶液初始浓度和溶液的膨胀速度及影响晶体粒度的因素。结果表明，压力增加，沉析颗粒的平均粒度减小；温度控制沉析晶体的晶型，对颗粒度的影响相对较小，温度增加，沉析平均粒度略有增加；溶液初始浓度对平均粒度的影响相对较大，膨胀速度亦是影响粒度及其分布的一个因素。快速膨胀溶液．并使过饱和度足够大，使过饱和度主要消耗在成核上，可得到颗粒小、分布窄的HMX颗粒。     

超临界流体技术在粉体粒子制备中的应用

超临界流体技术是制备和控制粉体材料的一种有效手段,利用该技术所获得微粒的平均粒径小,粒子尺寸分布可控。简述了超临界流体技术制备粉体粒子的基本原理、发展历史以及取得的一些研究成果,为超临界流体技术的应用拓展了领域。     

悬浮-乳液耦合聚合制备大粒径核-壳结构PS/PMMA复合粒子

采用在苯乙烯(St)悬浮聚合不同时期滴加甲基丙烯酸甲酯(MMA)乳液聚合组分的悬浮-乳液耦合聚合方法,制备大粒径核-壳结构复合粒子。研究发现：在St悬浮聚合初期和宏观成粒基本完成的聚合后期滴加MMA乳液聚合组分,分别得到由初级粒子凝并的非核-壳结构粒子和核-壳结构不完整的复合粒子,粒径分布较宽;在St悬浮聚合中期滴加MMA乳液聚合组分,MMA和PMMA乳胶粒子易于向PS粒子扩散或粘并,制备得到平均粒径大于100gm、粒径分布窄和核-壳结构良好的PS／PMMA复合粒子。     

Particle features of a poly(methyl methacrylate) resin prepared by a new emulsion polymerization process

A new emulsion polymerization process, in which water acted as the dispersed phase and a mixture of methyl methacrylate (MMA) and cyclohexane acted as the continuous phase, was applied to the preparation of a poly(methyl methacrylate) (PMMA) resin. The primary (latex) particles were formed in the early stage of polymerization and coagulated as the polymerization conversion increased. Scanning electron micrographs showed that the final PMMA particles were porous and composed of loosely aggregated primary particles. The porosity characterized by cold di(2‐ethylhexyl) phthalate absorption increased as the water/oil and cyclohexane/MMA mass ratios increased. The PMMA primary particles were smaller than the primary particles in the PMMA resin prepared by suspension polymerization in the presence of cyclohexane. Because of the phase composition of the reaction system, the solubility of PMMA in a mixture of cyclohexane and MMA, and the particle morphology of PMMA, a particle formation mechanism, including the formation, growth, and coagulation of primary particles in dispersed water droplets, was proposed. The primary particles formed mainly through a homogeneous nucleation mechanism and increased in size as MMA diffused from the oil phase to the water phase to the primary particles. The coagulation of the primary particles occurred because of the lower colloidal stability and the space limitations of the primary particles. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 1905–1911, 2004     

Effect of the phase ratio on the particle properties of poly(vinyl chloride) resins produced by suspension polymerization

The effects of the dispersed phase to continuous phase ratio (weight of VCM (gr)/weight of water (gr) (φ = g_VCM/g_water)) on the particle properties of a poly(vinyl chloride) (PVC) suspension were investigated experimentally. A series of experiments were performed with different φ values in a pilot‐scale reactor. The cold plasticizer absorption of the resin decreased with φ. Scanning electron micrographs showed that by the reduction of φ, many of the produced particles had a regular shape, a smooth surface, and greater porosity. An increase in φ caused a wider and multimodal particle size distribution of the produced PVC particles. The mean particle size and bulk density also increased with φ, whereas the molecular weight and polydispersity index did not change. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Preparation of magnetic poly(vinyl alcohol) (PVA) materials by in situ synthesis of magnetite in a PVA matrix

An easy method for manufacturing homogeneous inorganic–organic materials, especially composite fibers, was obtained by the in situ synthesis of inorganic particles within polymer matrices. In this article, nanosized magnetite particles were synthesized in situ within poly(vinyl alcohol) (PVA) solutions by precipitating Fe²⁺ ions or a mixture of Fe²⁺ and Fe³⁺ ions with NaOH solution. As a result, magnetite particles with an average diameter of 20 nm were obtained homogeneously within the solutions because of the tridimensional structure and chelating capacities of PVA. Transparent films were obtained by a casting method, and six kinds of magnetic PVA fibers were also prepared by a wet‐spinning method from the solutions containing magnetite nanoparticles. The mechanical properties and the saturation magnetization of the fibers were measured. These fibers, which contain iron ions with a maximum content of 17.63 wt %, can be successfully fabricated by the in situ synthesis and they exhibit excellent magnetization properties (i.e., the largest saturation magnetization is 13.38 emu/g). © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 1239–1247, 2003     

激光颗粒仪测定聚四氟乙烯细粒模压粉的平均粒径

运用激光粒度仪研究了聚四氟乙烯细粒模压粉的平均粒径和粒径分布的测定方法，通过试验确定了分散方法、分散剂用量、试样量、分散时间等影响因素，以建立稳定的测量体系。     

Particles from fires—a screening of common materials found in buildings

Small combustion generated particles are known to have a negative impact on human health and on the environment. In spite of the huge amount of particles generated locally in a fire accident, few investigations have been made on the particles from such fires. In this article, 24 different materials or products, typically found in buildings have been exposed to burning conditions in order to examine their particle generating capacity. In addition, a carbon fibre based composite material was tested in order to investigate if asbestos‐resembling particles could be generated in a fire situation. The majority of the experiments were performed in the small‐scale cone calorimeter, and some further data were collected in intermediate scale (SBI) and full scale (room‐corner) tests. Additional testing of the composite material was made in a small‐scale tubular reactor. The amount of particles and particle size distributions were measured by the use of a low‐pressure impactor and particle aerodynamic diameter sizes from 30 nm to 10 μm were measured. The results from the project show that the yield of particles generated varied significantly between materials but that the shape of mass and number size distributions were very similar for all the materials tested. The maximum amount of particles was obtained from materials that did not burn well (e.g. flame retarded materials). Well‐burning materials, e.g. wood materials, tend to oxidize all available substances and thereby minimize the amount of particles in the smoke gas. It was found that asbestos‐resembling particles could be produced from under‐ventilated combustion of the composite material tested. Copyright © 2003 John Wiley & Sons, Ltd.     

Preparation and characterization of monodisperse magnetic poly(styrene butyl acrylate methacrylic acid) microspheres in the presence of a polar solvent

Magnetic poly(styrene butyl acrylate methacrylic acid) [P(St–BA–MAA)] microspheres were prepared by emulsifier‐free emulsion polymerization in the presence of a polar solvent and a ferrofluid prepared by a coprecipitation method. The effects of some polymerization parameters, such as the medium polarity, reaction temperature, initiator content, and surfactant content in the ferrofluid, on the particle diameter and particle size distribution of magnetic P(St–BA–MAA) microspheres were examined in detail. The results showed that the electrostatic repulsion in the polymerization system significantly affected the monodispersity of the resulting magnetic polymer microspheres. The proper electrostatic repulsion, achieved through changes in the medium polarity and amount of surfactant in the polymerization system, improved the monodispersity, but a higher or lower repulsion led to a decrease in the monodispersity. Although the existence of surfactant and magnetite particles reduced the monodispersity more or less, the polymerization behavior of an emulsifier‐free emulsion polymerization in the presence of the ferrofluid was analogous to that of a conventional emulsifier‐free emulsion polymerization. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 87: 1733–1738, 2003     

水泥粒度分布的分维评价研究

对比分析了7种水泥样品的粒度分布实测值与Fuller曲线计算值，结果表明：所研究的水泥样品中较细颗粒的含量与较粗颗粒的含量均偏少，而中间段颗粒的含量偏多；测算了水泥样品实测粒度分布分维与Fuller曲线计算粒度分布分维，将两者分维的差值作为表征水泥粒度分布偏离最佳粒度分布程度的参数。研究发现：7种水泥样品的粒度分布均偏离了最佳粒度分布，随着分维差值的减小，样品空隙率降低。     

Narrow size‐distribution poly(methyl methacrylate) nanoparticles made by semicontinuous heterophase polymerization

The effect of surfactant (sodium dodecyl sulfate) concentration on particle size, molar masses, glass transition, and tacticity of poly(methyl methacrylate) (PMMA) nanoparticles synthesized by semicontinuous heterophase polymerization under monomer‐starved condition at constant monomer feeding rate is reported. Starved conditions are confirmed by the low amount of residual monomer throughout the reaction and by the fact that the instantaneous polymerization rate is similar to the feeding rate of monomer. Under these conditions, polymer particles in the nanometer range (20–30 nm) were obtained with narrow size distribution (1.07 < D_w/D_n < 1.18), depending of surfactant concentration. Final particle size diminishes as the surfactant concentration is increased. Glass transition temperatures and syndiotactic content (54%–59%) of the produced polymers are substantially higher than those reported for commercial and bulk‐made PMMA. Molar masses are much lower than those expected from termination by chain transfer to monomer, which is the typical termination mechanism in 0–1 emulsion and microemulsion polymerization of this monomer. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Effect of Polymethyl Methacrylate (PMMA) Powder to Liquid Monomer (P/L) Ratio and Powder Molecular Weight on the Properties of PMMA Cement

The present study investigated the effect of PMMA powder to liquid monomer (P/L) ratio and molecular weight of PMMA powder on the properties of PMMA cement. Two types of PMMA powder (Mw: 120,000 and 350,000) were prepared with different P/L ratios (based on wt/wt ratios); 0.75:1, 1:1, 1.25:1, and 1.5:1. Characterization of PMMA powders, handling characteristics and flexural properties of cured PMMA samples were investigated. In conclusion, low P/L ratio and high molecular weight of PMMA powders are desirable to produce PMMA cement with good handling properties and high flexural properties.     

Preparation of polystyrene/poly(methyl methacrylate) core‐shell composite particles by suspension‐emulsion combined polymerization

Suspension‐emulsion combined polymerization process, in which methyl methacrylate (MMA) emulsion polymerization constituents (EPC) were drop wise added to styrene (St) suspension polymerization system, was applied to prepare polystyrene/poly(methyl methacrylate) (PS/PMMA) composite particles. The influences of the feeding condition and the composition of EPC on the particle feature of the resulting composite polymer particles were investigated. It was found that PS/PMMA core‐shell composite particles with a narrow particle size distribution and a great size would be formed when the EPC was added at the viscous energy dominated particle formation stage of St suspension polymerization with a suitable feeding rate, whereas St‐MMA copolymer particles or PS/PMMA composite particles with imperfect core‐shell structure would be formed when the EPC was added at the earlier or later stage of St suspension polymerization, respectively. It was also showed that the EPC composition affected the composite particles formation process. The individual latex particles would exist in the final product when the concentrations of MMA monomer, sodium dodecyl sulfate emulsifier, and potassium persulfate initiator were great in the EPC. Considering the feature of St suspension polymerization and the morphology of PS/PMMA composite particles, the formation mechanism of PS/PMMA particles with core‐shell structure was proposed. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

A novel application of using a commercial Fraunhofer diffractometer to size particles dispersed in a solid matrix

After a proper modification of a commercial Coulter LS230 particle size analyzer that is based on Fraunhofer principle, we have developed its novel application in directly sizing particles dispersed inside a solid matrix. Using several particle standards, we have demonstrated its validity by comparing the particle size distributions, respectively, obtained in water and directly inside different solid matrixes. In comparison with other conventional sizing methods, such as transmission electron microscopy (TEM) and scanning electron microscopy (SEM), this novel application of Fraunhofer diffraction provides a fast, convenient, and direct way to characterize particles dispersed inside a transparent or translucent solid matrix. It can be envisioned that this application can be extended to directly size fillers inside a polymer materials, microdomains inside a polymer blends, and bubbles inside a foam. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 1165–1168, 2000     

Synthesis of nanosized poly(ethyl acrylate) particles via differential emulsion polymerization

Nanoparticles of poly(ethyl acrylate) were synthesized via a semibatch differential emulsion polymerization method with potassium persulfate as the initiator and sodium dodecyl sulfate as the surfactant. The effects of the reaction temperature, aging time, and surfactant/initiator/monomer ratios on the polymer particle sizes were investigated. Poly(ethyl acrylate) with particle sizes of less than 20 nm was synthesized under mild conditions. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 1609–1614, 2006     

Composite polymer particles with a gradated resin composition by suspension polymerization

We have conducted a study of composite polymer particles with a gradated resin composition by suspension polymerization, in which the resin composition gradually changes from the surface to the center of the particles. The binder resin of the polymer particles consists primarily of styrene, butyl acrylate, and methacrylic acid (MAA). Fourier transform infrared/photoacoustic spectroscopy analysis of the polymer particles by suspension polymerization has proved that MAA, having a higher polarity, concentrates near the surface of the particles, and this results in a formation similar to a core–shell structure. These composite polymer particles are excellent in blocking resistivity because the resin, containing a higher concentration of MAA, has a high glass‐transition temperature. Composite polymer particles with a gradated MAA concentration could be used for toner applications in low‐power hot‐roll fusing electrophotography systems because the melting property of the core resin is controlled and allows fusing at lower temperatures. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 682–690, 2005     

Fundamentals of Adhesion Failure for a Model Adhesive (PMMA/Glass) Joint in Humid Environments

The origins for the abrupt adhesion loss at a critical relative humidity (RH) for polymeric adhesives bonded to inorganic surfaces were explored using a poly(methyl methacrylate) (PMMA) film on silicon oxide as a model system. The interfacial and bulk water concentrations within the polymer film were quantified as a function of D₂O partial pressure using neutron reflectivity. The adhesive fracture energies of these PMMA/SiO₂ interfaces at the same conditions were determined using a shaft-loaded blister test. Discontinuities in the adhesive fracture energy, bulk moisture solubility, and the width of the interfacial moisture excess near the interface were observed at the critical RH. A mechanism based on the coupling of bulk swelling-induced stresses with the decreased cohesive strength due to moisture accumulation at the interface is proposed and is consistent with all experimental observations.     

Fundamentals of Adhesion Failure for a Model Adhesive (PMMA/Glass) Joint in Humid Environments

The origins for the abrupt adhesion loss at a critical relative humidity (RH) for polymeric adhesives bonded to inorganic surfaces were explored using a poly(methyl methacrylate) (PMMA) film on silicon oxide as a model system. The interfacial and bulk water concentrations within the polymer film were quantified as a function of D₂O partial pressure using neutron reflectivity. The adhesive fracture energies of these PMMA/SiO₂ interfaces at the same conditions were determined using a shaft-loaded blister test. Discontinuities in the adhesive fracture energy, bulk moisture solubility, and the width of the interfacial moisture excess near the interface were observed at the critical RH. A mechanism based on the coupling of bulk swelling-induced stresses with the decreased cohesive strength due to moisture accumulation at the interface is proposed and is consistent with all experimental observations.     

The Use of an Ionic Liquid in a Karr Reciprocating Plate Extraction Column: Drop Size Distribution

Ionic liquids (ILs) offer a new class of fluids for solvent extraction. This work presents drop size distribution data for the [bmim][PF₆]/water system and examines the basis of existing drop size prediction models developed for traditional organic/aqueous systems in a Karr reciprocating plate column and recommends how they may be used for these new class of materials.