Polymer Particle Size Research Articles

An innovative microwave cavity sensor for non-destructive characterisation of polymers

This paper investigates the feasibility of using an innovative microwave sensing technology to characterise and study various properties of polymer material such as difference between various polymer types, particle size and particle size distribution, contamination and pigmentation. A microwave sensor designed previously has been utilised to carry out this initial study to analyse the capability of microwave techniques to carry out the analysis. The curves obtained from material response to microwaves are distinguishable showing the shift to the lower frequency end with the insertion of polymer material. S11 measurements have shown distinctive peaks for each size and type of the sample tested. The results are quantifiable in terms of various polymer properties under consideration. In terms of S21 measurements, microwave sensor clearly distinguishes between coarse and fine polymer samples in terms of particle size. The effect of air voids in the sample and the particle size distribution has also been studied. The results are promising and justifies a thorough design and development of a dedicated microwave sensor unit for the characterisation of polymers. The sensor will have a significant industrial benefit in terms of costs associated with the industrial analysis, increase in the efficiency of manufacturing and production operation as well as material quality, control and validation.

Electrical four-point probing of spherical metallic thin films coated onto micron sized polymer particles

Micron-sized metal-coated polymer spheres are frequently used as filler particles in conductive composites for electronic interconnects. However, the intrinsic electrical resistivity of the spherical thin films has not been attainable due to deficiency in methods that eliminate the effect of contact resistance. In this work, a four-point probing method using vacuum compatible piezo-actuated micro robots was developed to directly investigate the electric properties of individual silver-coated spheres under real-time observation in a scanning electron microscope. Poly(methyl methacrylate) spheres with a diameter of 30 μm and four different film thicknesses (270 nm, 150 nm, 100 nm, and 60 nm) were investigated. By multiplying the experimental results with geometrical correction factors obtained using finite element models, the resistivities of the thin films were estimated for the four thicknesses. These were higher than the resistivity of bulk silver.

Nanoheterogeneous ruthenium-containing catalysts based on dendrimers in the hydrogenation of aromatic compounds under two-phase conditions

Nanoheterogeneous catalysts based on ruthenium nanoparticles dispersed in crosslinked dendrimer matrixes with a size of polymer particles of 100–500 nm show high activity in the hydrogenation of aromatic compounds under two-phase conditions. The addition of water to the reaction medium exerts a strong promoting effect on the activity of the catalysts: The turnover frequency increases by a factor of 3–90 depending on the substrate. When bimetallic (PdRu) nanoparticles are incorporated into the catalyst composition, the rate of benzene hydrogenation increases while the rate of transformation of substituted benzenes decreases.

Polymer content and particle size effects on polymer-bonded Terfenol-D/PZT magnetoelectric composites

Polymer-bonded cylindrical Terfenol-D/PZT magnetoelectric (ME) composites have been prepared with varying polymer contents and Terfenol-D particle sizes. The axial ME voltage coefficient, αE,A, was investigated for studying the effects of polymer content and particle size on the composite ME performance. The Terfenol-D particles with four different size ranges (<75µm, 75–100µm, 100–150µm and 150–180µm) were used. Additionally, the epoxy content of the composites was studied with five different weight ratios of 9wt%, 12wt%, 14wt%, 16wt% and 19wt%. The composite with an epoxy content of 0.14wt% and 100–150µm particle range exhibited better overall ME performance. This investigation promotes selecting the appropriate polymer content and particle size to optimize fabrication of the polymer-bonded ME composites for high ME performance to meet practical applications.

Influence of concentration of redox couple on freeze–thaw stability of styrene-acrylic copolymer latex

Styrene-acrylic copolymer latexes were synthesized by emulsion polymerization process using sodium formaldehyde sulphoxylate (SFS) and tert-butyl hydroperoxide (TBHP) as redox initiators. Approximately 100% conversion was achieved successfully at 50°C. The redox polymerization was carried out at varied dosages of redox concentration; the lowest dosage of 0.3% was sufficient to achieve ~100% conversion. The molecular weight of the polymer was decreased with an increase in redox concentration as expected. The properties such as viscosity, specific conductivity, particle size, molecular weight, and Tg (by differential scanning calorimetric and dynamic mechanical analysis) of the redox polymers are reported. The other important property of the latexes is their freeze–thaw (F–T) stability. Even though ~100% conversion was achieved at 0.3% redox initiator couple, it failed in F–T stability test. Latexes prepared above 0.5% redox initiator couple successfully pass the five F–T cycles. The effect of sulfate from SFS, and tertiary butyl from TBHP species on the stability of the latexes is discussed. The F–T stability of the emulsions is very crucial in the coatings industry, and this article brings some insight into the effect of concentration of redox species on the stability of emulsions. Moreover, low-temperature processes are always appreciated in terms of safety and energy savings.

Quantitative understanding of the self-sharpening of growing polymer particle size distributions in soap-free emulsion polymerization

Soap-free emulsion polymerization is an environmentally desirable process that can produce highly monodisperse polymer particles with high purity. In the polymerization, knowledge on the mechanism of particle growth is important for size control of the polymer particles. Experimental and theoretical study is performed on the self-sharpening of particle size distributions appearing with particle growth in soap-free emulsion polymerization. The dependence of particle growth rate on particle size was determined with two experimental methods of the seeded growth and non-seeded polymerizations of styrene. In the seeded growth polymerization, polymer particles with two different sizes were used to measure relative growth rate of the particles in the same reaction field. In the non-seeded polymerization, the relative growth rates were measured from time-variation of a particle size distribution during the particle growth. Two initiators, potassium persulfate and 2,2′-azobis[N-(2-carboxyethyl)-2-methylpropionamidine] hydrate at various pH, were employed to conduct the experiments in a wide range of particle sizes 0.1–2 μm. Both the experiments showed the same tendency of the size-dependence, which indicated that the self-sharpening becomes weak with an increase in particle size. This tendency is quantitatively explained by the particle growth mechanism that considers the gel effect of radical polymerization and the interfacial energy of monomer-swollen polymer particles.

Tribo-electrification and Powder Adhesion Studies in the Development of Polymeric Hydrophilic Drug Matrices.

The generation of tribo-electric charge during pharmaceutical powder processing can cause a range of complications, including segregation of components leading to content uniformity and particle surface adhesion. This phenomenon becomes problematical when excipients are introduced to a powder mixture alongside the highly charging active pharmaceutical ingredient(s) (APIs). The aim of this study was to investigate the tribo-electric charging and adhesion properties of a model drug, theophylline. Moreover, binary powder mixtures of theophylline with methylcellulose (MC) and hydroxypropyl methylcellulose (HPMC), having different polymer to drug ratios, were formed in order to study the impact of polymer concentration, particle size, substitution ratio and molecular size on the tribo-electric charging and surface adhesion properties of the drug. Furthermore, the relationship between tribo-electric charging and surface adhesion was also studied. The diversity in physicochemical properties of MC/HPMC has shown a significant impact on the tribo-electric charging and adhesion behaviour of theophylline. It was found that the magnitude of electrostatic charge and the level of surface adhesion of the API were significantly reduced with an increase in MC and HPMC concentration, substitution ratios and molecular size. In addition, the tribo-electric charge showed a linear relationship with particle surface adhesion, but the involvement of other forces cannot be neglected.

An Investigation on the Effect of Polyethylene Oxide Concentration and Particle Size in Modulating Theophylline Release from Tablet Matrices.

Polyethylene oxide has been researched extensively as an alternative polymer to hydroxypropyl methylcellulose (HPMC) in controlled drug delivery due to its desirable swelling properties and its availability in a number of different viscosity grades. Previous studies on HPMC have pointed out the importance of particle size on drug release, but as of yet, no studies have investigated the effect of particle size of polyethylene oxide (polyox) on drug release. The present study explored the relationship between polymer level and particle size to sustain the drug release. Tablets produced contained theophylline as their active ingredient and consisted of different polyethylene oxide particle size fractions (20-45, 45-90, 90-180 and 180-425 μm). It was shown that matrices containing smaller particle sizes of polyox produced harder tablets than when larger polyox particles were used. The release studies showed that matrices consisting of large polyox particles showed a faster release rate than matrices made from smaller particles. Molecular weight (MW) of the polymer was a key determining step in attaining sustained release, with the high MW of polyox resulting in a delayed release profile. The results showed that the effect of particle size on drug release was more detrimental when a low concentration of polyox was used. This indicates that care must be taken when low levels of polyox with different particle size fractions are used. More robust formulations could be obtained when the concentration of polyox is high. Differential scanning calorimetry (DSC) traces showed that particle size had no major effect on the thermal behaviour of polyox particles.

CFD prediction of scale-up effect on the hydrodynamic behaviors of a pilot-plant fluidized bed reactor and preliminary exploration of its application for non-pelletizing polyethylene process

This work aims to explore the scale-up effect on the hydrodynamic natures in a pilot-plant gas phase ethylene polymerization fluidized bed reactor (FBR) based on two-dimensional (2D) transient Eulerian model integrating the kinetic theory of granular flow (KTGF). Unlike lab scale FBR, significant differences in the core–annulus structures caused by the scale-up effect are revealed. The core region in pilot-plant scale FBR is much broader, and the distribution is nearly flat for two phases. The annulus structure is thin, and exhibits a very small particle velocity fluctuation. The bed expanding section could reduce the solid velocity and improve the flow patterns of gas and polymer particles. Simulations are also performed to assess the effects of polymer particle size and gas velocity on the hydrodynamics for the non-pelletizing polyethylene process. With the increase of polymer particle diameter (446μm to 1338μm), the superficial gas velocity should be increased from 0.60m/s to 0.90m/s to achieve better steady fluidized state. The results are helpful for understanding how the local mean two phases' velocities and volume fractions vary in pilot-plant reactor for PE production caused by scale-up effect.

Microspheres Embedded In Microbeads: A Novel Approach to Improve Various Controlled Release Characteristics of Highly Water Soluble Drug through Ionic Gelation Method

Abstract: The major hindrance behind the preparation of gellan microbeads by simple ionic gelation technique with aqueous soluble drugs is their low entrapment efficiency and sometimes its faster dissolution characteristics. This limits the employment of such a simple method for the preparation of microbeads of water-soluble drugs like stavudine. In the present study a novel attempt has been undertaken by embedding stavudine loaded Eudragit RSPO microspheres into gellan microbeads by ionotropic gelation method with an aim to improve its controlled drug delivery characteristics. The prepared microbeads were characterized by scanning electron microscopy, Fourier transform infrared spectroscopy, and optical microscopy for surface topography, drug polymer interaction and particle size analysis respectively. Other studies like drug content, encapsulation efficiency and drug release studies were also carried out. The resulting microspheres embedded in microbeads were free flowing in nature with mean particle size ranging from 544.2-564.2 μm. SEM photomicrographs distinctly shows the microspheres embedded within the microbeads effectively with a smooth surface topography and the gellan microbeads containing D4T only are spherical in nature with rough surface. The FTIR study ascertained the compatibility of the drug within the formulation. The microspheres embedded in microbeads had enhanced percentage of drug content, drug entrapment efficiency and controlled release characteristics as compared to beads containing stavudine only. The mechanism of drug release from the formulations were found to follow non Fickian type diffusion with “n” value between 0.5 to 1but in case of stavudine loaded Eudragit RSPO microspheresit was found to be Fickian type. Key words: Gellan gum, Stavudine, Microbeads, Microsphere embedded in Microbeads, Entrapment efficiency, and Controlled release.

Modulation of particle size and molecular interactions by sonoprecipitation method for enhancing dissolution rate of poorly water-soluble drug

Aim of present work was to originally elucidate the roles of ultrasonication method for modulating the size and molecular interactions in controlling release of poorly water-soluble drug. Curcumin was chosen as a model drug. Three types of polymers were investigated as carriers for preparation of polymeric nanoparticles under various ultrasonication conditions and polymer–drug ratios. Changes in drug crystallinity, particle size, and molecular interactions which would be factors enhancing drug dissolution rate were evaluated. Amorphous form of curcumin, size reduction of nanoparticles and interaction between drug and polymer in formulations were attributed to improved drug dissolution rate. Particle size was strongly affected by polymer type, polymer–drug ratio and ultrasonication conditions. Interestingly, control of those factors caused differences in molecular interactions of the hydroxyl groups and then, highly affected particle size of the nanoparticles. It was obvious that there was a reciprocal influence between the drug–polymer interactions and particle size of the nanoparticles. This relation could be modulated by polymers and ultrasonication processes for enhancing drug dissolution rate.

Acrylamide inverse miniemulsion polymerization: in situ, real-time monitoring using nir spectroscopy

In this work, the ability of on-line NIR spectroscopy for the prediction of the evolution of monomer concentration, conversion and average particle diameter in acrylamide inverse miniemulsion polymerization was evaluated. The spectral ranges were chosen as those representing the decrease in concentration of monomer. An increase in the baseline shift indicated that the NIR spectra were affected by particle size. Multivariate partial least squares calibration models were developed to relate NIR spectra collected by the immersion probe with off-line conversion and polymer particle size data. The results showed good agreement between off-line data and values predicted by the NIR calibration models and these latter were also able to detect different types of operational disturbances. These results indicate that it is possible to monitor variables of interest during acrylamide inverse miniemulsion polymerizations.

The first report of polymerization and characterization of aniline bearing chiral alkyl group on ring via covalent bond; poly[(±)-2-(sec-butyl)aniline

A chiral alkyl substituted of polyaniline derivative, poly[(±)-2-(sec-butyl)aniline] was successfully synthesized by interfacial and conventional oxidative chemical polymerization. Both distilled and dark monomers (undistilled) were used in polymerization. The polymers were characterized in details by several techniques, proton nuclear magnetic resonance (1H NMR), carbon nuclear magnetic resonance (13C NMR), high resolution mass spectroscopy (HRMS), Fourier transform infrared (FT-IR), ultraviolet–visible (UV–vis) spectroscopy, elemental analysis (CHNS) and X-ray diffraction (XRD) as well as gel-permeation chromatography (GPC) and scanning electron microscopy (SEM) images. Conductivity of polymers was also measured. Spectroscopic studies have proved the formation of polymer and confirm the pernigraniline form of polyaniline. Mass spectra of polymers synthesized were studied exactly and prove the presence of both amine and iminium nitrogen as well as counter ions of Cl−, HSO4− and SO42−. Size of polymer particles is considerably smaller by interfacial polymerization. Polymers show semi-crystalline structure in XRD analysis. More crystalline structure and conductivity gained from interfacial polymerization. Molecular weights of polymers were lower in comparison with polyaniline according to GPC results. The effect of neutral salt (LiCl) was studied on molecular weight.

Online monitoring of emulsion polymerization using electrical impedance spectroscopy

A frequency-dependent electrical monitoring technique was developed for characterizing emulsion polymerization online. High resolution electrical impedance spectroscopy (EIS) was conducted to study emulsion polymerization of styrene in terms of the key process parameters. Relationships between EIS data and process and product attributes such as monomer conversion and particle size were investigated. Electrical impedance values were measured at frequencies ranging from 1 Hz to 100 kHz. EIS parameters revealed changes in emulsion properties with time for both aqueous and organic phases during polymerization. At relatively higher frequencies (≥1 kHz) EIS data were found to be dominated by events in the continuous phase showing transitions in polymerization rates and intervals, while changes in monomer droplet and polymer particle sizes were dominant at lower frequencies (1 Hz). The EIS data were found to correlate well with polymerization rate, monomer conversion and particle size profiles at the appropriate frequencies in real time. © 2014 Society of Chemical Industry

Kinetic studies of semibatch emulsion copolymerization of methyl methacrylate and styrene in the presence of high intensity ultrasound and initiator

The present work deals with kinetic studies of copolymerization of methyl methacrylate and styrene using ultrasound assisted semibatch emulsion copolymerization in the presence of sodium dodecyl sulfate (emulsifier) and potassium persulfate (external initiator). The effect of temperature, acoustic intensity, initiator loading, surfactant concentration and monomer concentration on the extent of conversion has been investigated. The extent of polymerization was observed to increase with an increase in the temperature, and concentrations of initiator, monomer and surfactant. Further, the initial polymerization rate increased with an increase in the acoustic intensity from 11.2 to 23.1Wcm−2 and then it was found to decrease with a further increase to 33.80Wcm−2. The novelty of this work lies in the fact that there have been only limited kinetic studies for the approach of ultrasound assisted emulsion copolymerization. It has been also established in the present work that the formation of fine and stable monomer droplets, due to the cavitational activity at/near the interface of immiscible monomer phase and subsequent disruption by micro jets, leads to the smaller final polymer particle size and under optimized conditions, it was found to be about 40nm.

A Study of a Powder Coating Gun Near Field: Particle Flow in an Isothermal Staggered Concentric Air Jet

An experimental study of inert particle dispersion in an isothermal concentric air jet near field was conducted for cases of standard non-staggered and alternative staggered jet nozzles, each taken from a polymer powder flame deposition gun. The experimental work consisted of analysis of high speed digital images of the inert two phase isothermal jet flow, illuminated by a laser light sheet along and across the jet axis. The analysis of particle spread in the jet, represented by families of particle density distributions, clearly showed that the staggered nozzles resulted in a better-focused flow, with narrower distributions in the near field, and in the elimination of the recirculation zone that disrupted the particle flow in a non-staggered nozzle arrangement. In all cases, histograms of the cross-sectional particle area density were found to be approximately Gaussian. It was also found that there was a wide variation in the size and shape of the ground polymer particles used and these two characteristics caused a wide variation in the radial and axial velocities of the particles. Despite the differences between single-phase numerical simulations and experimental results, reported in Payne et al. [1], the introduction of particles into a numerical model produced satisfactory agreement with the particle velocities found experimentally.

Shape-controllable formation of poly-imidazolium salts for stable palladium N-heterocyclic carbene polymers.

The imidazolium-based main-chain organic polymers are one of promising platforms in heterogeneous catalysis, the size and outer morphology of polymer particles are known to have important effects on their physical properties and catalytic applications, but main-chain ionic polymers usually generate amorphous or spherical particles. Herein, we presented a versatile and facile synthetic route for size- and shape-controllable synthesis of main-chain poly-imidazolium particles. The wire-shaped, spherical and ribbon-shaped morphologies of poly-imidazolium particles were readily synthesized through quaternization of bis-(imidazol-1-yl)methane and 2,4,6-tris(4-(bromomethyl)phenyl)-1,3,5-triazine, and the modification of their size and morphology were realized through adjusting solvent polarity, solubility, concentration and temperatures. The direct complexation of the particles with Pd(OAc)2 produced ionic polymers containing palladium N-heterocyclic carbene units (NHCs) with intactness of original morphologies. The particle morphologies have a significant effect on catalytic performances. Wire-shaped palladium-NHC polymer shows excellent catalytic activity and recyclabilty in heterogeneous Suzuki-Miyaura cross-coupling reaction.

Evaluation of conductive polymers as an adsorbent for eradication of As (III) from aqueous solution using inductively coupled plasma optical emission spectroscopy (ICP-OES)

1024x768 The main focused of this research work is the preparation of conductive polymers like polypyrrole, polyaniline and polythiophene and their application as adsorbent materials for the removal of hyper toxic metal As (III) from aqueous solution. The metal ions get attached on the π-electrons at the back bone of polymer that illustrate excellent affinity for metal ions. The adsorption of As (II) ions was carried out on polythiophene due to its redox properties and the stronger interaction between sulfur atoms with arsenic atoms. To attain large surface area and for maximum interaction of As (III) ions with polymers, the particle size of polymers was ranged in nano scale. As the surface area increases with decrease in particle size, the active sites for metal ions also increases. These polymers were characterized by FIIR spectroscopy and SEM analysis. Adsorption isothermal data was examined by two parameters (Langmuir, Freundlich, and Dubinin-Radushkevich) and three parameters Redlich-Petrson, Sips and Toth models. Experimental results showed that based on standard deviation (SD) and Chi square test (χ 2 ) the experimental data was best explained by Freundlich and Toth isotherm. Thermodynamics parameters such as free energy change (Δ G 0 ), enthalpy change (Δ H 0 ) and entropy change (Δ S 0 ) have been calculated respectively, which revealed the spontaneous, endothermic and feasible nature of adsorption process. Normal 0 false false false EN-US X-NONE X-NONE

Thermoplastic polyurethane/hydroxyapatite electrospun scaffolds for bone tissue engineering: Effects of polymer properties and particle size

Thermoplastic polyurethane (TPU)/hydroxyapatite (HA) scaffolds were fabricated via electrospinning. The effects of TPU properties and HA particle size on scaffold physical properties and osteoblast-like cell performance were investigated. It was found that the addition of micro-HA (mHA), which was inlayed in the fiber, decreased the electrospun fiber diameter. On the contrary, nano-HA (nHA), which was either embedded or existed inside of the fiber, increased the fiber diameter for both soft and hard TPUs. The soft TPU had a much lower Young's modulus and higher strain-at-break than the hard TPU. The addition of both mHA and nHA decreased the tensile properties; this decrease was more significant with mHA. The cells on the hard scaffolds actively proliferated and migrated compared to those on the soft scaffolds. On the other hand, cells on the soft scaffolds more effectively induced osteogenesis of human mesenchymal stem cells (hMSCs) than those on the hard scaffolds. In addition, our data suggest that the soft scaffolds with supplementation of nHA further enhanced osteogenesis of hMSCs compared to those without nHA. The soft TPU scaffolds containing nano-HA have the potential to be used in bone tissue engineering applications.

Impact of impeller type on methyl methacrylate emulsion polymerization in a batch reactor

AbstractThe emulsion polymerization of methyl methacrylate (MMA) was carried out in a lab‐scale reactor, which was equipped with a top‐entry agitator, four wall baffles, a U‐shaped cooling coil, and a temperature controller. Potassium per sulfate and sodium dodecyl sulfate as were used as the initiator and the surfactant, respectively. The experimental investigation demonstrated the impact of the impeller type (45° six pitched‐blade turbine and Rushton impeller), number of impellers (single and double impellers), and impeller speed (100–350 rpm) on the monomer conversion, polymer particles size, molecular weight, and glass transition temperature. The results revealed that the effect of the impeller speed on the characteristics of the polymer attained using the pitched‐blade turbine was more prominent than that for the Rushton turbine. It was also found that the impact of the impeller speed on the polymer characteristics was much more pronounced for the double pitched‐blade turbines rather than for the double Rushton turbines. However, more uniform size distribution was achieved with the Rushton turbine. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40496.