Optimizing the balance between viscosity/modulus and impact in particulate composites

The objective of this study was to develop some new concepts of importance when trying to optimize the viscosity/modulus and impact relative to the particle‐size distribution in suspensions and particulate composites. The results of this study appear to indicate that, conceptually, it is possible to significantly improve the viscosity versus the impact balance for material formulations by optimizing the particle‐size distribution. For binary particle‐size distributions, the influence of the preferred particle‐size distribution, as determined using a square‐root distribution, did not yield the most desirable particle‐size distribution if the particle‐to‐particle component of the interaction coefficient was high. However, if three or more particles were utilized in the distribution, then the optimum particle‐size distribution utilized can apparently be characterized using the square‐root distribution even when the particle–particle component, σ_pc, of the interaction coefficient, σ, was found to be quite high. In addition, this same square‐root particle‐size distribution can also satisfactorily predict a probability of impact that can remain consistently high as long as the particles utilized are well chosen and not too close in size. Thus, this preferred particle‐size distribution can be utilized to predict at least one of the preferred distributions to optimize the balance of properties between impact and the viscosity/modulus. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 291–304, 2002     

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.     

TPO based nanocomposites. Part 1. Morphology and mechanical properties

The relationship between morphology and the mechanical properties of thermoplastic olefin (TPO) materials that are reinforced with organoclay fillers and prepared by melt processing is reported. Nanocomposites based on blends of polypropylene and elastomer and using an organoclay masterbatch were prepared in a twin-screw extruder. Transmission electron microscopy, atomic force microscopy and wide-angle X-ray scattering were employed to carry out a detailed particle analysis of the morphology of the dispersed clay and elastomer phases for these nanocomposites. The improvement in mechanical properties, e.g. stiffness enhancement as evaluated by stress-strain analysis and impact strength obtained from notched Izod impact tests, were successfully explained in terms of morphological changes induced by the presence of the clay and elastomer particles. Quantitative analyses of TEM micrographs and AFM images revealed a decrease in the aspect ratio of the clay particles and a reduction in the size of elastomer particles with increasing clay content. In addition, WAXD scans indicated a skin-core effect for the injection molded specimens in terms of both polypropylene crystal orientation and clay filler orientation. This information is essential for the understanding of the mechanism of mechanical property enhancement in nanocomposite materials.     

Monte Carlo modeling of fluidized bed coating and layering processes

A stochastic modeling approach based on a Monte Carlo method for fluidized bed layering and coating is presented. In this method, the process is described by droplet deposition on the particle surface, droplet drying and the formation of a solid layer due to drying. The model is able to provide information about the coating coverage (fraction of the particle surface covered with coating), the particle‐size distribution, and the layer thickness distribution of single particles. Analytical solutions for simplified test cases are used to validate the model theoretically. The simulation results are compared with experimental data on particle‐size distributions and layer thickness distributions of single particles coated in a lab‐scale fluidized bed. Good agreement between the simulation results and the measured data is observed. © 2016 American Institute of Chemical Engineers AIChE J, 62: 2670–2680, 2016     

锂离子电池异构建模及内部传质机理探究：粒径分布的影响

锂离子电池是目前应用较广的储能设备,具有能量密度高、使用寿命长等特点。随着锂离子电池正极材料实际能量密度接近理论值,电池组装工艺参数的优化成了提升其性能的重要途径,其中电极颗粒粒径及分布是十分重要的参数。因此,本文针对石墨-LiFePO₄体系锂离子电池,利用异构模型构建单粒径和双粒径电极的几何结构,再结合Newman模型模拟其放电过程,定量研究了正极材料粒径分布对锂离子电池性能的影响,探究了存在粒径分布的电极中不同粒径的颗粒在充放电过程的作用机制。模拟结果表明,粒径的减小可以减小固相扩散系数对电池性能的影响,但会增加液相扩散阻力;而粒径的分布可以促进锂离子在电解液中的扩散,提高小粒径颗粒的锂嵌入量,但会引起极化增大,导致大颗粒的锂嵌入量降低。粒径分布宽度越大,总体粒度越大,锂离子电池的能量密度越小。选择合适的粒径分布宽度,适当减小总体粒度的大小,能有效提升电极的能量密度。研究结果对于锂离子电池电极活性材料颗粒粒径分布的选择提供了有益的基础知识和指导。     

Droplet Size Distribution Obtained by Atomization with Two‐Fluid Nozzles in a Spray Dryer

The possibility of predicting the droplet size distribution from the particle size distribution was investigated. For that purpose, suspensions of different types of materials were dried in a laboratory‐scale spray drier. Drying of suspensions was performed with different sizes of two‐fluid nozzles. Droplet size distribution was evaluated from the data obtained for spray drying of bismuth molybdate suspension. The method was validated experimentally with other tested materials. Investigated systems involve processes of drying, crystallization, and coating. The proposed methodology can be applied when nonagglomerated particles, spherical particles, or spherical agglomerates were obtained by spray drying.     

In-situ characterization of ultrafine particles by laser-induced incandescence: sizing and particle structure determination

The laser-induced incandescence (LII) method is applied to the in situ size analysis of aerosol particles of different origin at room temperature. A detailed theoretical model of the particle heating and cooling for the different size fractions incorporating a solution of a Fredholm integral equation of the first kind is used to retrieve the particle size distribution from the time-dependent aerosol thermal emission detected after a ns laser pulse. The results are compared with TEM data of deposited aerosol particles along with online measurements employing a differential mobility analyzer (DMA). Besides the size distribution, the LII signal contains information on the internal structure of particle agglomerates, which can be obtained by analyzing the changes in the measured size distribution with the laser pulse energy. The objective of the paper is an evaluation of LII for its capability to measure the size distributions of various types of aerosols in the size range about 5–200 nm and to determine the primary particle sizes in the case of agglomerated particles.     

Charakterisierung von Suspensionen nanoskaliger Partikel mittels Ultraschallspektroskopie und elektroakustischer Methoden

Technical control over dispersions with particles in the nanometer size realm should bring about a boost in innovations for some parts of industry. Requirements for the development of these new products is the accurate characterization of the various materials systems. A characterization should always include a determination of the particle size distribution, since it is coupled to the specific effects of these systems. Ultrasound measurement techniques and electroacoustics are two if the available techniques that allow determination of the size distribution and zeta potential of particles with dimensions up to 10 nanometers. A further fundamental advantage of the method is the possibility of carrying out measurements in high‐concentration materials systems. This report describes ultrasound spectroscopy for the measurement of fine‐ and very‐fine‐dispersion particles, and the known theoretical concepts for the interpretation of spectra. In addition, experiences in the use of currently available measurement techniques are presented.     

Smoke Characterization and Feasibility of the Moment Method for Spacecraft Fire Detection

The Smoke Aerosol Measurement Experiment (SAME) has been conducted twice by the National Aeronautics and Space Administration and provided real-time aerosol data in a spacecraft micro-gravity environment. Flight experiment results have been recently analyzed with respect to comparable ground-based experiments. The ground tests included an electrical mobility analyzer as a reference instrument for measuring particle size distributions of the smoke produced from overheating five common spacecraft materials. Repeatable sample surface temperatures were obtained with the SAME ground-based hardware, and measurements were taken with the aerosol instruments returned from the International Space Station comprising two commercial smoke detectors, three aerosol instruments, which measure moments of the particle size distribution, and a thermal precipitator for collecting smoke particles for transmission electron microscopy (TEM). Moment averages from the particle number concentration (zeroth moment), the diameter concentration (first moment), and the mass concentration (third moment) allowed calculation of the count mean diameter and the diameter of average mass of smoke particles. Additional size distribution information, including geometric mean diameter and geometric standard deviations, can be calculated if the particle size distribution is assumed to be lognormal. Both unaged and aged smoke particle size distributions from ground experiments were analyzed to determine the validity of the lognormal assumption. Comparisons are made between flight experiment particle size distribution statistics generated by moment calculations and microscopy particle size distributions (using projected area equivalent diameter) from TEM grids, which have been returned to the Earth.

Copyright 2015 American Association for Aerosol Research     

Axial segregation in bubbling gas‐fluidized beds with Gaussian and lognormal distributions of Geldart Group B particles

Bubbling, gas‐fluidized bed experiments involving Geldart Group B particles with continuous‐size distributions have been carried out. Sand of various widths of Gaussian or lognormal distributions were completely fluidized, then axial concentration profiles were obtained from frozen‐bed sectioning. Similar to previous works on binary systems, results show that mean particle diameter decreases with increasing bed height, and that wider Gaussian distributions show increased segregation extents. Surprisingly, however, lognormal distributions exhibit a nonmonotonic segregation trend with respect to distribution widths. In addition, the shape of the local‐size distribution is largely preserved with respect to that of the overall distribution. These findings on the nature of local‐size distribution provide experimental confirmation of previous results for granular and gas‐solid simulations. Lastly, an interesting observation is that although monodisperse Geldart Group D particles cannot be completely fluidized, their presence in lognormal distributions investigated still results in complete fluidization of all particles. © 2010 American Institute of Chemical Engineers AIChE J, 2010     

Novel methods for synthesis of high‐impact polystyrene with bimodal distribution of rubber particle size

By using in situ prepolymerization and radiation curing, high‐impact polystyrene (HIPS) with a bimodal distribution of the size of the rubber particles (bimodal HIPS) was synthesized in the presence of ultrafine full‐vulcanized powdered styrene–butadiene rubber (UFPSBR) and polybutadiene rubber (BR). TEM photographs indicated that UFPSBR was dispersed uniformly as a single particle with a diameter of about 100 nm. On the other hand, bimodal HIPS with different rubber particle size distributions could also be obtained by blending HIPS and UFPSBR grafting styrene (UFPSBR‐g‐St) with different grafting yields. The bimodal HIPS with the smallest rubber particle size, at about 100 nm, could be prepared by blending the monomodal HIPS containing big rubber particles with polystyrene/UFPSBR. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Preparation and Properties of Submicrometer‐Sized LLM‐105 via Spray‐Crystallization Method

Submicrometer‐sized 2,6‐diamino‐3,5‐dinitropyrazine‐1‐oxide (LLM‐105) crystals were prepared by spray‐crystallization method with dimethyl sulfoxide (DMSO) and ultra‐pure water with surfactant as the solvent and anti solvent, respectively. Submicrometer‐sized LLM‐105 particles were characterized by scanning electron microscopy (SEM), X‐ray diffraction (XRD), and particle size analysis. The thermal stability and sensitivity properties of submicrometer‐sized LLM‐105 were also investigated. The results revealed that the submicrometer‐sized LLM‐105 particles are spherelike in morphology with a narrow particle size distribution at the range of 100–600 nm. The submicrometer‐sized LLM‐105 has a lower exothermic peak at about 343.7 °C compared with the synthesized material. Sensitivity tests showed that submicrometer‐sized LLM‐105 is more insensitive under impact stimulus with a drop height (H₅₀) of 102 cm. The submicrometer‐sized LLM‐105‐based PBX is more sensitive for short impulse shock wave that can be initiated at lower initiation current.     

纳米CaCO3/弹性体/PP杂化材料的性能及应用研究

采用母料共混法,制备了纳米CaCO3/弹性体/PP杂化材料,研究了力学性能和微观形态,以及在汽车保险杠中的应用。结果表明,纳米CaCO3/弹性体/PP杂化材料冲击强度较高,尤其是低温冲击强度。纳米CaCO3粒子具有使弹性体颗粒细化的作用。纳米CaCO3/弹性体/PP杂化材料应用于汽车保险杠料,可使低温冲击强度大幅度提高,弯曲弹性模量也同时提高。     

Synthesis and characterization of the properties of thermosensitive elastomers with thermoplastic and magnetic particles for application in soft robotics

In the currently rapidly developing field of soft robots, smart materials with controllable properties play the central role. Thermosensitive elastomers are soft, smart materials whose material properties can be controlled by changing their temperature. The aim of this work is to investigate the mechanical properties, to analyze the surface, the inner structure, and the heat transfer within the thermosensitive elastomer materials. This should provide a knowledge base for new combinations, such as a combination of thermosensitive and the well-known magneto sensitive elastomers, in order to realize new applications. Thermoplastic polycaprolactone particles were incorporated into a flexible polydimethylsiloxane matrix to produce thermosensitive elastomer samples. With a low melting point in the range of 58–60°C, polycaprolactone offers good application potential compared to other thermoplastic materials such as polymethamethylacrylate with a melting point above 160°C. Test samples of different material compositions and geometries were made to examine temperature-depending material properties. Two useful effects were identified: temperature-dependent change in stiffness and the shape memory effect. In certain examinations, carbonyl iron particles were also included to find out if the two particle systems are compatible with each other and can be combined in the polydimethylsiloxane matrix without disadvantages. Changes in shore hardness before and after the influence of temperature were investigated. Micro computed tomography images and scanning electron microscopy images of the respective samples were also obtained in order to detect the temperature influence on the material internally as well as on the surface of the thermosensitive elastomers in combination with carbonyl iron particles. In order to investigate the heat transfer within the samples, heating tests were carried out and the influence of different particle concentrations of the thermosensitive elastomers with and without carbonyl iron particles was determined. Further work will focus on comprehensive investigations of thermo-magneto-sensitive elastomers, as this will enable the functional integration in the material to be implemented with increased efficiency. By means of the different investigations, the authors see future applications for this class of materials in adaptive sensor and gripper elements in soft robotics.     

Analysis of polymer blend morphologies from transmission electron micrographs

Thermomechanical properties of polymer blends seem to depend on their morphology on microscales and in particular on the size of the dispersed phase particles and/or their distances (ligament thickness). Precise characterization of morphologies by few simple geometrical parameters is often a quite delicate task, in particular because of the strong polydispersity of these systems. We present here a simple method based on image analysis of transmission electron micrographs (TEM) to estimate both distributions in particle size and ligament thickness. We first reconstruct three-dimensional distributions in particle size from two-dimensional measurements and show in particular that corrections from section thickness become significant when thickness is comparable to particle size. Knowing the distribution in particle size, we extend the model initially proposed by Wu to estimate the distribution in ligament thickness. This method provides a more detailed relation between the distribution in particle size and the distribution in ligament thickness. Advantages and limitations of the method are illustrated by practical examples on polyamide-12 systems filled with various particle dispersions.     

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 and characterization of poly(butyl acrylate‐co‐ethylhexyl acrylate)/ poly(vinyl chloride)[P(BA‐EHA)/PVC] novel core‐shell modifier and its impact modification for a poly(vinyl chloride)‐based blend

Synthesis of poly(butyl acrylate‐co‐ethylhexyl acrylate)‐core/poly(vinyl chloride)‐shell [P(BA‐EHA)/PVC] used as a modifying agent of PVC via semicontinuous seeded emulsion copolymerization is reported here. Diameter distributions and morphology of the composite latex particles were characterized with the aid of particle size analyzer and transmission electron microscopy (TEM). The grafting efficiency (GE) and grafting ratio (GR) of vinyl chloride (VC) grafted onto the P(BA‐EHA) with varying content of crosslinking agent and core‐shell ratios were investigated. TEM studies indicated that the P(BA‐EHA)/PVC latex particles have core‐shell structure, and the P(BA‐EHA) rubbery particles in blending materials were uniformly dispersed in PVC matrix. Dynamic mechanical analysis (DMA) results revealed that the compatibility between the P(BA‐EHA) and the PVC matrix was significantly improved due to the presence of the P(BA‐EHA)‐grafted‐VC copolymer. The notched impact strength of the blending material with 3 wt% of rubber content was seven times that of the PVC. Linear regressions of mechanical properties as loading of the modifier were made. The resulting data of notched impact strength and elongation at break for the blending materials deviated significantly from regression lines within 3–4.5 wt% of the P(BA‐EHA) content. The PVC blends modified by the modifier exhibited good toughness and easy processability. POLYM. ENG. SCI., 2010. © 2009 Society of Plastics Engineers     

Particle size distributions in heterogeneous catalysts: What do they tell us about the sintering mechanism?

Supported metal catalysts were treated at temperatures up to 900 °C, and sintering times up to 4000 h and the particle size distributions were determined via transmission electron microscopy (TEM), SEM and scanning transmission electron microscope (STEM). Sintering conditions were chosen so that the mechanism of sintering would range from Ostwald ripening to particle migration and coalescence. Previous theoretical models have suggested that a size distribution skewed towards small particles can arise from Ostwald ripening, while a size distribution with a long tail towards large particles can only come from particle migration and coalescence. Some of our experimental measurements were performed under conditions that favor Ostwald ripening, while others were performed under conditions that favor particle migration and coalescence. In every instance, the experimental particle size distributions could be fitted to a log normal distribution, and were always skewed to the right, with a tail towards larger particle diameters. Hence, we conclude that no inference about sintering mechanism can be derived from the particle size distribution.     

Polyamide nanocomposites with improved toughness

Polymer nanocomposites containing several percent of exfoliated layered silicates are materials with a unique weight/performance ratio. The only parameter that is not enhanced, but even decreased, is toughness. This work focused on the toughness enhancement of these advanced systems with polyamide matrix prepared via melt‐mixing (i.e., by a conventional method of polymer processing having an advantage of easy simultaneous addition of other components). Analogously to ternary polyamide blends with improved mechanical behavior, containing finely and separately dispersed elastomer and rigid polymer, elastomer particles with an average size of 60 nm were incorporated in the nanocomposite. The very low particle size was achieved by in situ reactive compatibilization by using suitably functionalized elastomers. The simultaneously increasing viscosity of the system enhanced exfoliation of the silicate. Melt exfoliated nanocomposites containing 3 wt % of clay and 5 wt % of elastomer particles exhibit increased toughness without significant loss of other properties. Elastomer particles increase toughness by both acting as stress concentrators (by initiating energy absorbing microdeformations) and influencing the clay‐induced matrix crystalline structure. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 288–293, 2005     

Rubber toughening in polypropylene: A review

The recent advances in the studies of the toughening methods and theories of polypropylene (PP)–elastomer blends are reviewed in the present article. Inclusions are key to toughening PP; they can play the role of agent‐induced crazing, cause shear yielding of the matrix around them, and end the propagation of cracks. The major theories interpreting the toughening mechanisms of the blends are: multiple crazing, damage competition theory, shear‐yielding theory, microvoids, and cavitation theories. The factors affecting the toughening effect are relatively complicated. Therefore, these theories have been verified only in some cases when they have been applied in relevant conditions. To achieve the objective of better toughening, it is important to improve the uniform distribution of dispersed‐phase particle size and suitable filler size, as well as improving the dispersion of the inclusions formed in the matrix; in addition the matrix materials or fillers must be functional with suitable modifier in order to enhance the interfacial adhesion or to improve the interfacial morphological structure between the filler and matrix. However, the exact toughening mechanisms for PP–rubber blends have to be studied further because of complications resulting from the crystallinity of the matrix. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 409–417, 2000