The effect of filler particle size on the antibacterial properties of compounded polymer/silver fibers

Antibacterial activity has become a significant property of textiles used in applications such as medicine, clothing, and household products. In this study, we compounded polypropylene with either micro- or nano-sized silver powders. These polypropylene/silver compounds were prepared by direct melt-compounding using a conventional twin-screw mixer. We analyzed the characteristics of the compounds using wide-angle X-ray diffractometry (WAXS), differential scanning calorimetry (DSC), and scanning electron microscopy (SEM). The DSC and WAXS results indicated that the crystallinity of the polypropylene component decreased slightly when compared with that of the pure polymer. The SEM micrographs indicated that the silver particles had good dispersibility in the matrix. We measured the mechanical properties of these materials using a universal tensile tester and evaluated the antibacterial activities of these compounds by performing quantitative antibacterial tests using the AATCC-100 test method. From these evaluations of antibacterial activity, we conclude that the compounds incorporating the silver nanoparticles exhibited superior antibacterial activity relative to the samples containing micron-sized particles.     

The effect of filler particle size and orientation on the impact fracture toughness of a highly filled plasticized polymeric material

The effect of particle size and orientation on the inherent fracture toughness of a filled plasticized polymeric material has been determined by application of linear elastic fracture mechanics. Testing was caried out in a three-point bend mode under impact conditions. The material was a triple base gun propellant consisting of a matrix of nitrocellulose plasticized with nitroglycerine and filled with particles of nitroguanidine (NQ). The crystalline NQ was used in the “as-received” form of needles and in a “ground” state. The material containing as-received NQ consistently had a higher fracture toughness than the material with ground NQ, and the toughness was a maximum when the fillers were aligned perpendicularly to the fracture surface. The impact fracture toughness was found to be virtually independent of strain rate over the range from 3 to 90 sec⁻¹. Seven-perforated cylindrical grains of the material containing as-received and ground NQ crystals, and the grains were tested in a pneumatic gas gun and a Hopkinson bar apparatus. The grains containing the ground NQ have been shown to be generally less resistant to fracture than the grains containing as-received NQ.     

The effect of particle size distribution on barite reduction

The present study is a follow-up of investigation on barite reduction to barium sulfide as a function of starting particle size distribution and temperature of reaction. In this work we study the high temperature reduction process of barite from the view point of particle size distribution. Conversion-time data have been obtained using iodometry method in each isothermal condition. A modified kinetic model used to express the carbothermic reduction process. To obtain the values of activation energy and frequency factor, the same expression was selected for each sample at all temperatures. The rate of reaction is found to be related to the particle size distribution and the gasification reaction of coke which has influence on reduction process. The kinetic parameters calculated from standard analysis of isothermal kinetic data indicated that the particle size of barite controlled the reaction when it was coarser than 400 mesh both in presence and absence of catalyst.     

尘埃粒子计数器全粒径范围内计数效率的校准

为实现对尘埃粒子计数器全粒径范围内的计数效率校准,分别对尘埃粒子计数器(OPC)-凝结核粒子计数器(CPC)-气溶胶静电计(FCAE)的逐级溯源方法和光学显微镜计数方法进行技术研究,建立一套完整的校准方法和装置。结果表明:装置具有很好的溯源性,能保证国内关于尘埃粒子计数器计数效率的计量技术的准确性。     

The effect of particle size distribution on the rheology of an industrial suspension

The viscosity of a proprietary dental composite material, consisting of suspensions of crushed glass in a polymeric liquid of a 50/50 w/w urethane dimethacrylate and triethylene glycol dimethacrylate mixture has been measured using a tube viscometer. Narrow-sized fine (ultimate particle size of 0.2 m, which agglomerate to form particles with a mean diameter of 0.05 m), medium (d ₅₀= 1.7 m) and coarse (25.5 m) particle fractions were used as well as bimodal and trimodal mixtures. Total solids concentrations from 17% to 76(77)% by volume were covered. The results were analysed using extensions of the Farris theory for mixtures and reduced to the viscosity functions, h _i ( _i), for the three monomodal fractions. They were fitted to the Mooney, Krieger-Dougherty or the three-parameter Cheng equation. The effect of particle size distribution on the Krieger-Dougherty parameters is discussed. The viscosity functions summarize the experimental results and allow the viscosities of bimodal and trimodal mixtures not measured to be predicted. The use of the predictions for the formulation of the dental material is discussed. The methodology described can be used in the design of other suspension products.     

The effect of particle size and spacing on the retardation of recrystallization in two-phase copper crystals

The effect of stable dispersion of Al₂O₃ in copper crystals upon recrystallization kinetics has been studied in three alloys, termed L1, L2 and H2, and in pure copper. L1 and L2 contained particles of similar size (0.028m), but of differing interparticle spacing, and L1 and H2 contained particles of similar spacing (0.05m) but of differing size. After a cold-rolling reduction of 50%, alloys L1 and L2 showed retarded recrystallization at 700° C compared with pure copper, there being greater retardation in L2, which had the smaller inter-particle spacing. Extensive recovery prior to recrystallization was observed and this led to deviations from the Avrami equation in describing the recrystallization kinetics. Calculations show that the retardation cannot be due to grain-boundary or sub-boundary pinning by the dispersed phase, and it is concluded that the effect is due to the homogenization of dislocation distribution by the particles suppressing nucleation. Alloy H2 contained larger particles (0.041m), and exhibited accelerated recrystallization compared with pure copper. This indicates that a very delicate balance must exist between the factors tending to retard and those tending to accelerate recrystallization in these materials. It is suggested that the acceleration arises from an increased misorientation developing within the transition bands.     

The effect of particle humidity on separation efficiency for an axial cyclone separator

The objective of this study is to investigate the effects of particle humidity on the inlet particle size distribution, overall efficiency, grade efficiency and cut size diameter for an axial cyclone separator with inner diameter of 150?mm. The collection and grade efficiencies of the cyclone separator were measured by on-line method for inlet velocities, particle concentration and particle humidity in the ranges of 12–18?m/s, 30–500?mg/m³ and 8–30‰, respectively. By employing a set of fixed parameters for inlet velocity and particle concentration, the effect of particle humidity on separation efficiency was investigated. The experimental results show that the volume ratio of larger particle increases with the increasing of particle humidity due to particle agglomeration. When the inlet velocity and particle humidity remain constant, the collection and grade efficiencies improve greatly as the increasing of the particle concentration because of the particle aggregation. However, it was noticed that the grade efficiencies did not always increased with the increasing of particle humidity under the same conditions of inlet velocity and particle concentration. The trends of grade efficiency curves for different particle humidity change at the particle diameter of approximately 10?μm. The grade efficiency improves with the increasing of particle humidity when the particle diameter is larger than 10?μm, while a contrary tendency is observed when the particle diameter is smaller than 10?μm.     

Liquid-phase sintering in the glass-cordierite system: particle size effect

The effect of particle sizes of glass and ceramic filler on the densification kinetics of glassfilled ceramics has been studied using borosilicate glass-cordierite as the model system. Within the particle size range investigated, the densification is found to be significantly enhanced by increasing the cordierite size, reducing the glass size and increasing the green density. These results are attributed to both the increased driving force of densification by reducing the glass particle size and the decreased glass redistribution distance by either increasing the green density of compacts or increasing the particle size ratio between the cordierite and glass powders. In addition, a large cordierite-to-glass size ratio gives a dense, uniform microstructure of sintered body as a result of forming a homogeneous close packing of the low-melting glass phase around the refractory cordierite particles.     

The effect of particle size on the maximum permissible oxygen concentration to prevent dust explosions

The oxygen concentration in the gas phase at the boundary between an explosion and no explosion in a dust cloud, y_o^b, has been investigated for several particle sizes and for mixtures of coarse and fine dusts of the same material. The maximum permissible oxygen concentration, y_o^m, at which no explosion is obtained has also been determined. Measurements for several type of materials were made in the modified version of the standard small vertical tube apparatus. Nitrogen was used as the inert gas and a train of sparks as the source of ignition. The results obtained indicated that the oxygen concentration is dependent on the particle size, that is, values of y_o^m decrease with a decrease in the size of the particles. Below 100 μm, values of y_o^m become almost constant. Admixture of fine dust as low as 5% to coarse dusts is sufficient to reduce the y_o^m values severely.     

The effect of ash and filter media characteristics on particle filtration efficiency in fluidized bed

The phenomenon of filtering particles by a fluidized bed is complex and the parameters that affect the control efficiency of filtration have not yet been clarified. The major objective of the study focuses on the effect of characteristics of ash and filter media on filtration efficiency in a fluidized bed. The performance of the fluidized bed for removal of particles in flue gas at various fluidized operating conditions, and then the mechanisms of collecting particles were studied. The evaluated parameters included (1) various ashes (coal ash and incinerator ash); (2) bed material size; (3) operating gas velocity; and (4) bed temperature. The results indicate that the removal efficiency of coal ash increases initially with gas velocity, then decreases gradually as velocity exceeds some specific value. Furthermore, the removal of coal ash enhance with silica sand size decreasing. When the fluidized bed is operated at high temperature, diffusion is a more important mechanism than at room temperature especially for small particles. Although the inertial impaction is the main collection mechanism, the "bounce off" effect when the particles collide with the bed material could reduce the removal efficiency significantly. Because of layer inversion in fluidized bed, the removal efficiency of incinerator ash is decreased with increasing of gas velocity.     

Studies on the effect of particle size on some properties of dental stone

Most indirect dental restorations of gold or porcelain are constructed on stone working models or dies. If these models or dies are damaged during the construction of these restorations in the laboratory, then the clinical success of the restoration will be jeopardized. This study is related to particle size, surface area, hardness and scratch resistance of twelve gypsum model or die materials. No correlation was found between particle size and hardness or scratch resistance. There was very little difference in hardness and scratch resistance between most of the materials tested.     

The effect of HPMC particle size on the drug release rate and the percolation threshold in extended-release mini-tablets

The particle size of HPMC is a critical factor that can influence drug release rate from hydrophilic matrix systems. Percolation theory is a statistical tool which is used to study the disorder of particles in a lattice of a sample. The percolation threshold is the point at which a component is dominant in a cluster resulting in significant changes in drug release rates. Mini-tablets are compact dosage forms of 1.5–4?mm diameter, which have potential benefits in the delivery of drug to some patient groups such as pediatrics. In this study, the effect of HPMC particle size on hydrocortisone release and its associated percolation threshold for mini-tablets and tablets was assessed. For both mini-tablets and tablets, large polymer particles reduced tensile strength, but increased the drug release rate and the percolation threshold. Upon hydration, compacts with 45–125?μm HPMC particles formed a strong gel layer with low porosity, reducing hydrocortisone release rates. In comparison, faster drug release rates were obtained when 125–355?µm HPMC particles were used, due to the greater pore sizes that resulted in the formation of a weaker gel. Using 125–355?µm HPMC particles increased the percolation threshold for tablets and to a greater extent for mini-tablets. This work has demonstrated the importance of HPMC particle size in ER matrices, the effects of which are even more obvious for mini-tablets.     

The effect of particle content and matrix grain size on the recrystallisation of two-phase aluminium-iron alloys

The recrystallisation of aluminium alloys in the composition range 0.002 to 1.08 wt% iron has been followed metallographically and by hardness measurements. The recrystallisation of solid-solution alloys was retarded as the iron content increased, whereas that of the two-phase alloys was accelerated. This latter effect was associated with a marked increase in nucleation rate, with no significant change of growth rate, as the Al₃Fe particle spacing decreased from 15 to 4m. Decreasing the grain size of the two-phase alloys, at constant composition, also caused an acceleration of recrystallisation, the magnitude of which decreased as the Al₃Fe content increased. These effects have been shown to be independent of the size of the Al₃Fe particles, within the range studied (diameters 0.6 to 2.2m). The results are discussed in terms of a model (which is based on metallographic observations) of nucleation at matrix grain boundaries and at particle/ matrix interfaces. It is suggested that the retardation of nucleation, observed by other workers, in more closely spaced dispersions, occurs because nucleation at particle/ matrix interfaces becomes difficult when the inter-particle spacing becomes of the same order as the diameter of the sub-structure of the deformed matrix.     

A study of the mechanoelectrical effect in strained electrically conducting solids

The relation between mechanical and electromagnetic phenomena in deformed electrically conducting non-ferromagnetic solids was studied. Basic equations were derived for the charge, electric field intensity, and electric potential of a solid acted on by external forces. For the case of plane deformation the problem was reduced to a corresponding boundary problem for the functions of the electric field potential and intensity, ponderomotive forces being taken into account in the derivation of appropriate equations. A detailed analysis was carried out of the case of an infinite body with a cylindrical cavity under tensile loads.     

The effect of particle size and electrical charge on macrophage-osteoclast differentiation and bone resorption

In aseptic loosening, there is commonly periprosthetic bone loss and a heavy macrophage infiltrate in response to biomaterial wear particles generated from the implant materials. Macrophages which have phagocytosed wear particles are known to be capable of differentiation into bone resorbing osteoclasts. In this investigation we determine the role of particle size and particle charge on this process. Mouse monocytes and macrophages were co-cultured with osteoblast-like UMR106 cells and 1,25 dihydroxyvitamin D3 in the presence or the absence of (i) various sizes of latex beads (0.1, 1, 10 and 100 m) and (ii) uncharged, positively- or negatively-charged sephadex beads of uniform shape and composition. The extent of osteoclast differentiation by monocytes or foreign body macrophages was determined by the expression of the osteoclast-associated enzyme tartrate-resistant acid phosphatase and lacunar bone resorption. No significant difference in the extent of osteoclast formation and bone resorption was noted in response to particle size. Osteoclast formation was also not significantly different in the presence of positively/negatively charged and uncharged particles. These findings indicate that osteoclast formation is not significantly influenced by particle characteristics, such as particle size. They also add support to the hypothesis that macrophage involvement in periprosthetic osteolysis is not dependent on particle phagocytosis and that it may be induced by particle contact.     

The effect of particle size upon the annealing behaviour of plastically deformed two-phase crystals

Two-phase crystals of copper containing dispersed SiO₂ particles and of aluminium containing plates of CuAl₂ (-phase) have been prepared and plastically deformed at room temperature. The changes in dislocation distribution upon isothermal annealing have been followed by electron microscopy.It is shown that misoriented subgrains associated with the dispersed phase form on annealing only if the dislocation interactions during prior straining lead to the development of local lattice curvature in the matrix at these regions. When the dispersed particle size is small (i.e. < 3000 å in diameter) no such recrystallisation embryos are observed, and a microstructure which should provide optimum resistance to recrystallisation is suggested.