Considerations on detailed analysis and particle growth in high impact polypropylene particles

Detailed analysis of the dispersion of ethylene and propylene copolymer components in high‐impact polypropylene particles was performed by the morphological observation, pore volume analysis, and microscopic Fourier transform infrared spectroscopy of SPring‐8. The results of the morphological observation and pore volume distribution suggest that copolymer components were formed in particles in such a manner as to fill the gaps of fine homopolypropylene particles. The results of the analysis by microscopic Fourier transform infrared spectroscopy were that the distribution of the amount of ethylene in the particles was homogeneous and indicated that copolymer components were dispersed uniformly within the particles. Moreover, spots with high amounts of ethylene were formed on the particle surface, and when voids existed within the particle, spots with high amounts of ethylene were also formed on the void surface. The structure of the copolymer components existing locally on the surface was practically similar to the structure of the copolymer components within the particles. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Effect of rigid particle size on the toughness of filled polypropylene

The role of rigid particle size in the deformation and fracture behavior of filled semicrystalline polymer was investigated with systems based on polypropylene (PP) and model rigid fillers [glass beads, Al(OH)₃]. The regularities of the influence of particle content and size on the microdeformation mechanisms and fracture toughness of the composites at low and high loading rates were found. The existence of the optimal particle size for fixed filler content promoting both maximum ultimate elongation of the composite at the tensile and maximum toughness at impact test was shown. The decrease of the toughening effect with both decreasing and increasing particle size regarding the optimal one was explained by dual role of particle size, correspondingly as either “adhesive” or “geometric” factors of fracture. The adhesive factor is due by the increase of debonding stress with the particle size decrease and the voiding difficulty resulting in the restriction of plastic flow. The geometric factor consists in the dramatic decrease of the composite strength at break if the void size exceeds the critical size of defect (for a given matrix) at which the crack initiation occurs. The analysis of the filled polymer toughness dependencies upon the particle size revealed that a capacity of rigid particles for the energy dissipation at the high loading rate depends on two factors: (i) ability of the dispersed particles to detach from matrix and to initiate the matrix local shear yielding at the vicinity of the voids and (ii) the size of the voids forming. Based on the findings it was concluded that the optimal minimal rigid particle size for the polymer toughening should answer the two main requirements: (i) to be smaller than the size of defect dangerous for polymer fracture and (ii) to have low debonding stress (essentially lower compared to the polymer matrix yield stress). © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 1917–1926, 2004     

Micro‐void toughening of thermosets and its mechanism

Void toughening is studied using epoxy resin. Voids were produced mechanically without any chemical agents so that it was possible to isolate the role of micro‐voids from other factors. Toughness of the epoxy resin owing to voids was improved over that of the control by an order of magnitude. The toughening mechanism was found to be strongly related to intervoid distance and, hence, to void‐to‐crack distance. Large deformation bands between the crack and voids were deduced to be the source of toughening. The intervoid distance was directly measured on scanning electron microscope photos. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 1290–1295, 2005     

Effect of maleated EVA on compatibility and toughness of PETG/EVA blend

Maleic anhydride (MAH) grafted onto ethylene vinyl acetate copolymer (EVA), mEVA (modified EVA) was blended with poly(ethylene glycol‐co‐cyclohexane‐1,4‐dimethanol terephthalate) (PETG) with various mEVA and EVA (unmodified) content in the internal mixer. The effect of reactive compatibilizer to decrease the dispersed particle diameter was observed. The brittle–ductile transition was found at about d_n: 0.37 µm and d_v: 0.55 µm of particle diameter, a critical particle diameter, regardless of EVA content, and the blend was also toughened at above the critical particle diameter regardless of dispersed EVA content and compatibility. The toughening mechanism and the effect of the particle diameter on the impact strength of the blend were investigated by morphological observation, and it was found that the toughening of the PETG/EVA blend system resulted from the shear deformation, induced by cavitation of dispersed EVA particles. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

An innovative unit operation of particle separation/classification by irradiating low‐frequency ultrasound into water

By irradiating kHz‐band ultrasound, submillimeter‐ or millimeter‐size particles that were dispersed in water with dissolved gases flocculated into a spherically flocculated particle swarm (SFPS). Acoustic cavitation‐oriented bubbles caused by the irradiation played essential roles in the formation of the SFPS. Unprecedented and promising phenomena were observed: the particles were separated based on their diameters through the precise control of the ultrasound irradiation, and the SFPS was easily manipulated using a motion‐controlled stick. The relationship between the sound‐pressure profiles and the manipulable range of the SFPS is discussed; that is, the effectively manipulable range was limited by the sound‐pressure profile. By means of manipulation control, we demonstrate the particle classification by particle diameters. On the basis of these findings, an example of a practical application of this technique is proposed. © 2017 American Institute of Chemical Engineers AIChE J, 64: 1564–1572, 2018     

On the Reversible Nature of Rubber Particle Cavitation in Toughened Thermoplastics

Toughening of brittle thermoplastics by addition of a separated rubber phase has been an important area of research in industrial material development. Several research groups have focused their efforts to understand the role of the dispersed rubber particles for toughening of plastics. As a result of the research work, the debonding of grafted rubber particles from the surrounding rigid matrix and as well the internal rupture of particles, i.e., cavitations, were considered as a possible dominating contribution of particles to toughening. Recently a method for the detection of rubber cavitation in rubber toughened thermoplastics, based on the observation of the rubber cavitation phenomena occurring during a cooling procedure and detected by means of thermal contraction measurements, has been developed by Dijkstra and co‐workers. During such experiments an S‐shaped deviation from linear thermal contraction has been observed. This behavior was attributed to the cavitation of rubber particles under thermally induced hydrostatic tensions during cooling. The present paper is aimed at showing that the observed S‐shaped deviation from linear thermal contraction during cooling reoccurs during subsequent cooling steps if an appropriate thermal loading of the samples takes place after the first cooling. This result provides an even stronger evidence that the S‐shaped deviation from linear thermal contraction during cooling is indeed caused by particle cavitation. It is also shown that the cavitation behavior of rubber particles in toughened thermoplastics depends strongly on thermal history, rubber phase volume of the sample under investigation and experimental conditions as well. Based on these results the method has to be used very carefully for a general quantitative comparison of different rubber modifiers in toughened plastics. However, such contraction tests can be considered as an additional tool to understand basic deformation behavior of rubber modified thermoplastics.     

Effects of Internal Stresses Due to a Dispersed Phase on the Fracture Toughness of Glass

The effects of thermal contraction mismatch on the toughening of glass by a dispersed phase were measured in a model system. Three toughening mechanisms were observed: prestressing of the dispersed phase, deflection of the crack by the stress field of the particle, and crack bowing between particles; deflection provided the greatest toughening. Toughening was increased by increasing particle size, decreasing particle spacing along the crack front, and increased particle spacing along the crack path.     

Estimate of confidence intervals for geometric mean diameter and geometric standard deviation of lognormal size distribution

Confidence of particle size distribution, which is the size distribution of sample particles selected from a large population with lognormal size distribution, has been studied theoretically. Theoretical equations were derived from the basic formulas commonly used in statistics to estimate confidence intervals for geometric mean diameter and geometric standard deviation. Computer simulation has provided size distribution of sample particles by random sampling in order to confirm the theoretical equations. For both geometric mean diameter and geometric standard deviation, the confidence intervals were calculated so that both values of population were placed approximately in the middle of the intervals. The tendencies for the intervals to decrease with an increase in sample particle number and/or significance level, and with a decrease in geometric standard deviation, were reasonable in statistics. The proposed theoretical equations should be useful for estimating confidence of lognormal size distribution.     

液固循环流化床中颗粒轴向速度的实验研究

利用超声多普勒测速仪实验测量了液固循环流化床中不同径向位置处颗粒瞬态轴向速度，研究了其概率密度分布特征。采用瞬态速度的标准偏差衡量瞬态速度的波动程度，考察了不同操作形式下的颗粒时均轴向速度的径向分布以及表观液速和颗粒循环速率等操作条件对速度波动程度和速度均衡径向分布的影响，利用相间作用力对两种分布的特点进行了机理分析，并对液固和气固循环流化床中颗粒的流动行为进行了比较。     

Fracture behavior of styrene‐ethylene‐propylene rubber‐toughened polypropylene

The morphology and fracture behavior of isotactic polypropylene toughened by styrene‐ethylene‐propylene (PP/SEP) were investigated. The SEP rubber, having an average particle size of 0.2 µm, is found to be well dispersed in the PP matrix. The fracture toughness of SEP‐modified PP is greatly improved. The toughening mechanism investigation shows that a widespread crazing zone is generated in the crack tip damage zone. An intense narrow damage band in the center of crazed zone is formed. Crazing and shear yielding are found to be the dominant toughening mechanisms in PP/SEP. The crazes are initiated only by large SEP particles in the blend. The small SEP particles (< 0.3 µm) can neither cavitate nor trigger crazing. As a result, large scale shear deformation is suppressed in this blend. These findings are consistent with the notion that the crack tip plane strain constraint has to be relieved in magnitude in order for the deviatoric stress to reach a critical value for widespread shear banding.     

Effect of packing on void morphology in resin transfer molded E‐glass/epoxy composites

Effects of applying a packing pressure on void content, void morphology, and void spatial distribution were investigated for resin transfer molding (RTM) E‐glass/epoxy composites. Packing pressures of zero and 570 kPa were respectively applied to center‐gated composites containing 17.5% randomly oriented, E‐glass fiber preform. Radial samples of these disk‐shaped composites were utilized to evaluate voidage via microscopic image analysis. Two adjacent surfaces were cut from each molded disk in order to evaluate void presence from both through‐the‐thickness and planar views. The packed composite was found to contain almost 92% less void content than the unpacked composite. While void fractions of 2.2 and 2.6% were measured, respectively, from the through‐the‐thickness and planar surfaces of the unpacked composite, only 0.2% void content was observed in the packed composite from both surfaces. Digital images obtained from through‐the‐thickness surface showed that average void size dropped from 59.3 μm in the unpacked composite to 31.7 μm in the packed composite. A similar reduction in average void size from 66.7 to 41.1 μm was observed from the planar surfaces. Circular voids were found to experience higher removal rates at 99%, followed by cylindrical and elliptical voids at 83 and 81%, respectively; while irregular voids show slightly lower void removal rates at 67%. Void proximity to fiber bundles was also observed to affect void reduction as voids located inside fiber tows experience lower void reduction rates. Along the radial direction of the molded disks, removal of voids with different proximities to fibers seems to depend on their arrangement at the end of the filling stage. These findings are believed to ascertain packing as an effective void removal method for RTM and similar liquid composite molding processes. POLYM. COMPOS., 26:614–627, 2005. © 2005 Society of Plastics Engineers     

Better Sintering through Green-State Deformation Processing

Aqueous colloidal suspensions of alumina were processed in the dispersed state and the flocculated state by controlling the double-layer interactions between the particles. Repulsive particle forces led to high packing densities but the green bodies were mechanically so weak that they were unable to retain their shape (the dispersed case). Attractive forces led to good green strength but the packing density was low and the particles were agglomerated (the flocculated case). The agglomerated structure of the flocced specimens could be fragmented by mechanical deformation of the green compact; the deformation was carried out under a superimposed hydrostatic pressure of less than 1 MPa. The flow stess of the flocculated structures depended on the deformation rate, and on the magnitude of the superimposed hydrostatic pressure. The flow stress was 2.5 kPa at a strain rate of 0.1 s⁻¹. Deformation processing of the flocced structures increased the green (relative) density from 0.51 to 0.62. The sintering behavior of underformed and deformation-processed flocced structures was studied. Deformation-processed green bodies sintered more rapidly and yielded a final grain size that was smaller and more uniform than that obtained from the undeformed specimens. The ability to homogenize and densify the packing of flocculated structures by deformation processing suggests new opportunities in green-state processing, for example (i) uniform mixing of more than one kind of particle or particles and fibers, and (ii) net shape forming by injection molding or extrusion, without the use of organic binders.     

Pressure Filtration Model of Ceramic Nanoparticles

The consolidation behavior of nanometer-sized particles at 20–800 nm was examined using a pressure filtration apparatus at a constant compressive rate. The relation of applied pressure (Δ P _t)–volume of dehydrated filtrate ( V _f) was compared with the established filtration theory for the well-dispersed suspension. The theory was effective in the early stage of the filtration but deviation between the experiment and the theory started when Δ P _t exceeded a critical pressure (Δ P _tc). It was found that this deviation is associated with the phase transition from a dispersed suspension to a flocculated suspension at Δ P _tc. The factors affecting Δ P _tc are the ζ potential, concentration, and size of the particles. Based on the colloidal phase transition, a new filtration theory was developed to explain the Δ P _t– h _t (height of suspension) relation for a flocculated suspension. Good agreement was shown between the developed theory and experimental results.     

Air‐void characterisation of foam concrete

The pore structure of cementitious material, predetermined by its porosity, permeability and pore size distribution, is a very important characteristic as it influence the properties of the material such as strength and durability. The pore parameter could therefore be a primary factor influencing the material properties of foam concrete and an in depth look into this aspect is required to establish relationships between this and material properties. In order to evaluate these relationships it was necessary to develop parameters to explain and quantify the air‐void structure of foam concrete. This paper discusses the investigations done to characterise the air‐void structure of foam concrete by identifying few parameters and influence of these parameters on density and strength. A camera connected to an optical microscope and computer with image analysis software were used to develop these parameters. It is found that out of the air‐void parameters investigated, volume, size and spacing of air voids have influence on strength and density. Mixes with a narrower air‐void size distribution showed higher strength. At higher foam volume merging of bubbles seems to produce larger voids, results in wide distribution of void sizes and lower strength. Air‐void shape has no influence on the properties of foam concrete.     

无机刚性粒子增韧增强PP研究进展

综述了近些年来无机刚性粒子增韧聚丙烯（PP）的结构设计、刚性粒子粒径及其分布、改性剂种类及用量对增韧增强效果的影响以及无机刚性粒子增韧PP的机理。大量的研究表明，在刚性粒子增韧PP中，弹性体包覆刚性粒子的壳一核结构设计具有优异的增韧效果。在定量分析PP增韧机理方面，介绍了脆韧转变分析中界面黏结判据和粒间距判据，以及有限元方法在此领域的应用，刚性粒子增韧机理主要为界面脱黏到空洞／银纹化损伤和空洞／剪切屈服损伤的转变。此外还介绍了目前刚性粒子与橡胶混杂增韧PP的研究进展。     

A numerical investigation of the void structure of fibrous materials

The void structure of particulate solids has been studied with the aid of a numerical packing algorithm based on the minimisation of an energy potential. This algorithm has been used to form densely packed assemblies of spherical and fibrous particles. The void space within these materials has been characterised using an algorithm that finds chains of voids that pass through the assemblies. The tortuosity (as defined by Carman [P.C. Carman, Fluid flow through granular beds, Trans. Instn. Chem. Engrs., v15 pp 150-166, 1937.]) and mean diameter of these chains have been determined and examined as important parameters that are relevant to the permeability of these materials. Tortuosity was approximately constant in the spherical particle assemblies, while the void size varied with the particle size. In general, the spherical particle assemblies showed much smaller void sizes (relative to the particle diameter) and lower tortuosity than the fibrous materials. The tortuosity of the fibrous materials was found to be a function of both the aspect ratio of the fibres, and the packing efficiency of the assembly.     

Thermal and mechanical characterization of epoxy resins toughened using preformed particles

Preformed, multilayer particles have been used to toughen an epoxy resin. The particles were formed by emulsion polymerization and consist of alternate glassy and rubbery layers, the outer layer having glycidyl groups to give the possibility of chemical bonding of the particles in the cured resin. Two variants of this type of particle were used, termed GM(47/15) and GM(47/37); both types have an overall diameter of 0.5 µm, but the former have a thicker rubbery layer. For comparison, acrylic toughening particles (ATP) with no surface functionality and a liquid carboxyl‐terminated butadiene–acrylonitrile (CTBN) rubber were used as toughening agents. The epoxy resin system consisted of a commercial diglycidyl ether of bisphenol A (Shell Epon 828) with diamino‐3,5‐diethyl toluene as hardener, two commercial sources of which were used, namely Ethacure‐100 (Albemarle SA) and DX6509 (Shell Chemicals). These hardeners contain a mixture of two isomers, namely 2,6‐diamino‐3,5‐diethyltoluene and 2,4‐diamino‐3,5‐diethyltoluene Thermogravimetry in nitrogen shows that the preformed toughening particles begin to degrade at 230 °C, whereas the cured resin begins to degrade rapidly at 350 °C. Thus, even though the particles are less thermally stable than the cured resin, their degradation temperature is well above the glass transition temperature of the resin, and their use does not affect the thermal stability of the toughened materials at normal use temperatures. The performance of the toughening agents was compared using Ethacure‐100 as the hardener. The GM(47/15) and GM(47/37) toughening particles gave rise to a greater toughening effect than the ATP and the CTBN. For example, the fracture energies were: 0.26 kJ m^?2 for the unmodified resin; 0.60 kJ m^?2 for the resin toughened with CTBN; and 0.69 kJ m^?2 for the resin toughened with the GM(47/15) particles. The ultimate tensile stress of the unmodified epoxy resin was 43 MPa, which increased to 55 MPa when 20 wt% of GM(47/15) toughening particles were added. The toughness of resins cured with the DX6509 hardener were superior to those obtained with the Ethacure‐100 hardener, most probably due to DX6509 producing a less‐highly‐crosslinked network. This highlights the sensitivity of the toughening process to the hardener used, even for hardeners of a similar nature. © 2001 Society of Chemical Industry     

用新的矩方法研究弯管中纳米颗粒的输运与凝结(英文)

Transport of nanoparticles and coagulation is simulated with the combination of CFD in a circular bend. The Taylor-expansion moment method (TEMOM) is employed to study dynamics of nanoparticles with Brownian motion, based on the flow field from numerical simulation. A fully developed flow pattern in the present simulation is compared with previous numerical results for validating the model and computational code. It is found that for the simulated particulate flow system, the particle mass concentration, number concentration, particle polydispersity, mean particle diameter and geometric standard deviation over cross-section increase with time. The distribution of particle mass concentration at different time is independent of the initial particle size. More particles are concentrated at outer edge of the bend. Coagulation plays more important role at initial stage than that in the subsequent period. The increase of Reynolds number and initial particle size leads to the increase of particle number concentration. The particle polydispersity, mean particle diameter and geometric standard deviation increase with decreasing Reynolds number and initial particle size.     

Modeling of Gravitational Wet Scrubbers with Electrostatic Enhancement

Conventional gravitational wet scrubbers, which generally perform removal of fine particles with low efficiency, cannot meet new standards for pollution emissions. One way of improving the collection efficiency of fine particles is to impose additional electrostatic forces upon particles by means of particle‐charging, or droplet‐charging, or even opposite‐charging of particles and droplets. A Monte Carlo method for population balance modeling is presented to describe the particle removal processes of gravitational wet scrubbers with electrostatic enhancement, in such a way that the grade collection efficiency and particle size distribution are calculated quantitatively. Numerical results show that, the grade collection efficiency of submicron particles is only ca. 5 % in conventional wet scrubbers. However, it reaches ca. 25 % in particle‐charging wet scrubbers, ca. 70 % in droplet‐charging wet scrubbers, and even above 99 % in opposite‐charging wet scrubbers. Furthermore, population balance modeling is used to optimize the operational parameters of the droplet‐charging wet scrubbers by means of the quantitative comparison of the grade collection efficiency. It is found that the operational parameters that are beneficial to the high‐efficiency removal of fine particles are faster gas velocity, slower droplet velocity, larger liquid‐to‐gas flow ratio, larger charge‐to‐mass ratio of droplets, smaller geometric mean diameter and smaller geometric standard deviation of droplets.     

Reactive melt blending of modified polyamide and polypropylene: Assessment of compatibilization by fractionated crystallization and blend morphology

The melting and crystallization behavior of nonreactive and reactive melt‐mixed blends of polypropylene and carboxylic‐modified polyamide (mPA) as the dispersed phase was investigated. It was found that the size of the mPA particles decreases and the crystallization behavior of the mPA particles changes in dependence on the mixing time of the blends with oxazoline‐modified PP (mPP). This indicates that an in situ reaction occurs between the oxazoline groups of mPP and the carboxylic acid groups of mPA, resulting in a compatibilizing effect. In blends with mPP, the crystallization of the dispersed mPA phase splits into two steps. Below a critical particle size, the mPA does not crystallize at temperatures typical for bulk crystallization. These finely dispersed mPA particles crystallize coincidently with the PP phase, and this part increases with increasing mixing time. Analysis of the crystallization heat of both steps in connection with the particle volume distribution permits the estimation of the critical particle size to be ≤4 μm. These investigations showed that the effect of fractionated crystallization can be used to follow the morphology development and to evaluate the efficiency of compatibilizing interfacial reactions during processing. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 3445–3453, 2002