Bead Content Research Articles

Effects of EPS bead inclusions on stress–strain behaviour of sand

ABSTRACT: Lightweight fill solutions have been used in many civil engineering projects throughout the world. At locations with poor soil conditions, alternative lightweight construction fill materials such as expanded polystyrene (EPS) geofoam, wood chips, and tyre wastes may be used instead of conventional fill materials. These materials are used as an additive for the soil. It is known that the type, aspect ratio and content of the admixtures have an important role in the mechanical properties of the mixtures. The main objective of this study was to assess the feasibility of the potential use of EPS beads in geotechnical applications. The effect of EPS bead gradation on the stress–strain behaviour of lightweight composite materials composed of EPS bead–sand mixtures (EPS–sand) was investigated through a series of triaxial compression tests under three different confining pressures. Three different types of spherical EPS beads with different unit weights (EPS-1, EPS-2, and EPS-3) were mixed with sand with varying EPS bead content. This study has shown that the deviatoric stress of a EPS–sand mixture is not only a function of volumetric EPS bead content but it also depends on EPS bead grain size distribution (EPS bead type). Whereas volumetric EPS bead content increases when all other variables are constant (EPS bead type in EPS–sand), the initial modulus of elasticity decreases linearly. Consequently, EPS bead inclusion did not enhance the maximum deviatoric stress of EPS–sand when compared with that of the sand-only specimen. However, bead addition provides a lightweight aspect to the mixture which can be attractive to use in many geotechnical engineering projects. EPS bead content, confining pressure and EPS bead type-dependent multiple linear regression (MLR) equations were proposed to estimate the initial undrained elastic modulus of EPS–sand to reduce the cost and time involved in conventional laboratory testing of EPS–sand mixtures. Based on the stress–strain behaviour of EPS–sand, these mixtures may be utilised in geotechnical applications as a lightweight fill material.

Preparation and Study on the Properties of Expanded Perlite / Fly Ash Floating Beads Insulation Material

In this paper, expanded perlite / fly ash floating beads insulation material was made of expanded perlite, fly ash floating beads, cement, fly ash and VAE emulsion by adding decent additives, like waterproof agent, in the pressure forming process. The effects of molding pressure, VAE emulsion content, fly ash floating beads content and waterproofing agent content on the properties of thermal insulation material were studied, and the internal microscopic morphology of thermal insulation material was observed by SEM. Besides, the related action mechanism was explored. The test results show that the optimum ratio as follows: molding pressure of 0.46 MPa, VAE emulsion content of 20%, fly ash floating beads content of 20%, waterproof agent content of 7%.

An approach to reduce the percolation threshold of MWCNT in ABS/MWCNT nanocomposites through selective distribution of CNT in ABS matrix

In this article, we demonstrate a facile route to prepare ABS/MWCNT nanocomposites with high electrical conductivity at a significantly low percolation threshold of the CNT. The strategy involves in situ co-polymerization of styrene and acrylonitrile monomers in the presence of multi-wall carbon nanotubes (MWCNT) and commercially available acrylonitrile butadiene styrene (ABS) beads. A dramatic improvement in the electrical conductivity in the nanocomposites was evident with increasing content of ABS beads at a constant CNT loading, which might be explained in terms of the formation of a continuous network structure of CNTs throughout the in situ polymerized ABS matrix. Such selective dispersion of MWCNTs results in an electrical conductivity (3.01 × 10−7 S cm−1) in the nanocomposites at 30 vol% loading of ABS beads and 0.24 vol% loading of MWCNTs. An increase in electrical conductivity to 4.50 × 10−5 S cm−1 was evident when the ABS bead content was increased to 60 vol% at the same loading of MWCNTs. The morphological analysis of the nanocomposites indicates selective distribution of the MWCNTs in the in situ co-polymerized ABS phase of the nanocomposites leaving the externally added ABS beads free from CNT dispersion. This leads to an increase in effective concentration of the CNTs in the in situ co-polymerized ABS phase of the nanocomposites, which in turn creates a path of MWCNTs throughout the matrix, resulting in a decrease in the percolation threshold of the nanocomposites to a lower value (0.2 vol% MWCNT).

Influence of selective dispersion of MWCNT on electrical percolation of in-situ polymerized high-impact polystyrene/MWCNT nanocomposites

This work demonstrates a simple method to develop highly conducting high impact polystyrene (HIPS)/multi- wall carbon nanotube (MWCNT) nanocomposites through selective dispersion of MWCNT in HIPS matrix. The method involves in-situ polymerization of polybutadiene containing styrene monomer in the presence of HIPS beads and MWCNT. A significantly lower percolation threshold value than ever reported for HIPS/MWCNT systems was obtained using unmodified unaligned MWCNTs. With the increase in HIPS bead content (at a particular MWCNT loading) in the HIPS/MWCNT nanocomposites, the conductivity value was increased, suggesting that the presence of HIPS beads acted as excluded volume that decreased the percolation threshold. An increase in electrical conductivity from 1.91·10 -7 to 1.15·10 -5 S/cm was evident, when the HIPS bead content was increased from 30 to 60 wt% at a constant loading of MWCNT (i.e. 0.6 wt%). The morphological investigation of the HIPS/MWCNT nanocomposites revealed that, the MWC- NTs were selectively dispersed in the in-situ polymerized HIPS region, outside the HIPS beads, which resulted in the low- ering of the percolation threshold to a lower value of 0.54 wt%. The morphology and electrical properties of the nanocomposites have been discussed in detail in the manuscript.

Phase and size separations occurring during the injection of model pastes composed of β-tricalcium phosphate powder, glass beads and aqueous solutions

Glass beads a few hundred micrometers in size were added to aqueous β-tricalcium phosphate pastes to simulate the effect of porogens and drug-loaded microspheres on the injectability of calcium phosphate cements and putties. The composition of the pastes was monitored during the injection process to assess the effect of glass bead content, glass bead size and paste composition on the paste injectability. The results revealed that the injection process led to both liquid and glass bead segregations: the liquid flowed faster than the glass beads, which themselves flowed faster than the β-tricalcium phosphate microparticles. In fact, even the particle size distribution of the glass beads was modified during injection. These results reveal that a good design of multiphasic injectable pastes is essential to prevent phase separation.

Novel composite biopolymers of sodium alginate/natural rubber/coconut waste for adsorption of Pb(II) ions

A novel composite adsorbent in the form of beads for removal of Pb2+ from wastewater was prepared by blending a sodium alginate (NaAlg) solution, natural rubber (NR) latex, and coconut waste (cofiber). After being crosslinked by calcium chloride, the beads were highly stable, flexible, and easily used in the environment. The optimum composition of the beads with an average size of 1.1–1.2 mm was 4% NaAlg:NR latex (60% dry rubber content):cofiber at 50:1:0.72 and a 2%w/w CaCl2 solution used for cross linking. The physico‐chemical properties of the beads were examined by the swelling ratio measurement, ATR‐FTIR, and SEM. The effects of the amount of cofiber, NR, and initial Pb2+ ions, the pH of the medium, the bead content, and the contact time, on the adsorption of Pb2+ were investigated. NR improved the water resistance and, hence, the stability of the beads. The cofiber increased the porosity and contact area and, hence, the efficiency of the composite beads to adsorb the Pb2+ up to 99.6%. The prepared beads are promising material to use for the effective and economical removal of Pb2+ from water. POLYM. COMPOS., 35:1013–1021, 2014. © 2013 Society of Plastics Engineers

Slow delivery of a nitrification inhibitor (dicyandiamide) to soil using a biodegradable hydrogel of chitosan

Using chemical inhibitors to reduce soil nitrification decreases emissions of environmental damaging nitrate and nitrous oxide and improves nitrogen use efficiency in agricultural systems. The efficacy of nitrification inhibitors such as dicyandiamide (DCD) is limited in soil due to biodegradation. This study investigated if the persistence of DCD could be sustained in soil by slow release from a chitosan hydrogel. DCD was encapsulated in glyoxal-crosslinked chitosan beads where excess glyoxal was (i) partly removed (C beads) or (ii) allowed to dry (CG beads). The beads were tested in water and in soil. The beads contained two fractions of DCD: one which was quickly released in water, and one which was not. A large DCD fraction within C beads was readily available: 84% of total DCD bead content was released after 9h immersion in water, while between 74% and 98% was released after 7d in soil under low to high moisture conditions. A lower percentage of encapsulated DCD was readily released from CG beads: 19% after 9h in water, and 33% after 7d in soil under high rainfall conditions. Kinetic analysis indicated that the release in water occurred by quasi-Fickian diffusion. The results also suggest that DCD release was controlled by bead erosion and the leaching of glyoxal derivatives, predominantly a glyoxal-DCD adduct whose release was positively correlated with that of DCD (R2=0.99, p⩽0.0001). Therefore, novel chitosan/glyoxal composite beads show a promising slow-release potential in soil for agrochemicals like DCD.

Research on the Effect of Beads on Properties and Microstructure of Cementing Materials

The paper studied the effects of different contents of beads on powder pressure entity dense packing density, mechanical performance of composite cement paste. The microstructure of the composite paste is researched by SEM analysis and nitrogen adsorption method. The results show that when the beads content is low, the compacting voidage decreases with the increased bead contents. When the beads content is 30%, composite cementing material achieves the densest packing density. The compacting voidage of composite cement powder has strong correlation with the pore structure and strength of hardened cement paste. When the compacting voidage value reaches minimum, the average pore radius and maximum pore radius of hardened cement paste reach the minimum values. In addition, the 28d strength of composite cement paste is higher than ordinary cement paste.

Experimental Study on Expansion Characteristics, Frost Heaving Characteristics of EPS Beads Improved Expansive Soils

Proposed EPS beads for the improvement of expansive soil in cold regions. Based on laboratory soil test study the feasibility and mechanism of the EPS beads improving expansive soils. Through four sets of comparative test with different contents of the EPS beads, the result indicates: The expansion rate of the soil, frost heave amount decreases with the increase in EPS beads content, EPS beads can effectively inhibit the expansion of expansive soil and frost heaving, proposed the optimal dosage.

Development of a porous poly(DL‐lactic acid‐co‐glycolic acid)‐based scaffold for mastoid air‐cell regeneration

To develop a porous, biodegradable scaffold for mastoid air-cell regeneration. In vitro development of a temperature-sensitive poly(DL-lactic acid-co-glycolic acid)/poly(ethylene glycol) (PLGA/PEG) scaffold tailored for this application. Human mastoid bone microstructure and porosity were investigated using micro-computed tomography. PLGA/PEG-alginate scaffolds were developed, and scaffold porosity was assessed. Human bone marrow mesenchymal stem cells (hBM-MSCs) were cultured on the scaffolds in vitro. Scaffolds were loaded with ciprofloxacin, and release of ciprofloxacin over time in vitro was assessed. Porosity of human mastoid bone was measured at 83% with an average pore size of 1.3 mm. PLGA/PEG-alginate scaffold porosity ranged from 43% to 78% depending on the alginate bead content. The hBM-MSCs proliferate on the scaffolds in vitro, and release of ciprofloxacin from the scaffolds was demonstrated over 7 to 10 weeks. The PLGA/PEG-alginate scaffolds developed in this study demonstrate similar structural features to human mastoid bone, support cell growth, and display sustained antibiotic release. These scaffolds may be of potential clinical use in mastoid air-cell regeneration. Further in vivo studies to assess the suitability of PLGA/PEG-alginate scaffolds for this application are required.

Ultralow Electrical Percolation Threshold in Poly(styrene-co-acrylonitrile)/Carbon Nanotube Nanocomposites

Here, we demonstrate a new method that involves in situ copolymerization of styrene and acrylonitrile monomers in the presence of multiwall carbon nanotubes (MWCNTs) and commercial poly(styrene-co-acrylonitrile) (SAN) beads, for the preparation of electrically conducting SAN/MWCNT nanocomposites with a significantly low percolation threshold of the CNTs. At a constant CNT loading, the conductivity of the nanocomposites was increased with increasing content (weight percent) of the SAN beads, indicating the formation of a more continuous network structure of the CNTs in SAN matrix. Thus, the electrical conductivity (1.38 × 10–6 S·cm–1) of the nanocomposites with 40 wt % SAN beads increased to 8.07 × 10–5 S·cm–1 when the SAN bead content was increased to 70 wt % at constant CNT loading (i.e., 0.1 wt %). The morphology study revealed the dispersion and distribution of the MWCNTs selectively in the in situ polymerized SAN phase of the nanocomposites, leading to an increase in effective concentration of the CNTs in the in situ polymerized SAN phase of the nanocomposites. Thus, the percolation threshold of the nanocomposites was reduced to a lower value (0.032 wt % MWCNT), which was not reported elsewhere for SAN/MWCNT nanocomposites with unmodified, commercial MWCNTs of similar qualities. This report discusses detailed methodology of the process as well as other characteristics of the SAN/MWCNT nanocomposites.

Effects of the glass bead content and the surface treatment on the mechanical properties of polypropylene composites

AbstractPolypropylene composites filled with glass beads (GBs) were prepared by means of a twin‐screw extruder. The tensile properties and impact‐fracture strength of the composites were measured at room temperature to identify the effects of the GB content and surface treatment on the mechanical properties. The results show that the relative elastic modulus increased nonlinearly, whereas the tensile strength decreased with increasing GB volume fraction (ϕf). The notched impact strength increased with increasing ϕf when ϕf was less than 11%, and then, it decreased; this might have been related to the GB aggregation in the case of higher concentration. The mechanical properties of the composite systems in which the GB surface was treated with silane coupling agent were better than those of the composite systems filled with the untreated GBs under the same conditions. Furthermore, the impact‐fractured surfaces were observed with a scanning electron microscope to understand the interfacial morphology between the inclusion and the matrix and to examine the toughening mechanisms. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

NIR Spectroscopy Applications in the Development of a Compacted Multiparticulate System for Modified Release

The purpose of this study was to utilize near-infrared spectroscopy and chemical imaging to characterize extrusion-spheronized drug beads, lipid-based placebo beads, and modified release tablets prepared from blends of these beads. The tablet drug load (10.5-19.5 mg) of theophylline (2.25 mg increments) and cimetidine (3 mg increments) could easily be differentiated using univariate analyses. To evaluate other tablet attributes (i.e., compression force, crushing force, content uniformity), multivariate analyses were used. Partial least squares (PLS) models were used for prediction and principal component analysis (PCA) was used for classification. The PLS prediction models (R (2) >0.98) for content uniformity of uncoated compacted theophylline and cimetidine beads produced the most robust models. Content uniformity data for tablets with drug content ranging between 10.5 and 19.5 mg showed standard error of calibration (SEC), standard error of cross-validation, and standard error of prediction (SEP) values as 0.31, 0.43, and 0.37 mg, and 0.47, 0.59, and 0.49 mg, for theophylline and cimetidine, respectively, with SEP/SEC ratios less than 1.3. PCA could detect blend segregation during tableting for preparations using different ratios of uncoated cimetidine beads to placebo beads (20:80, 50:50, and 80:20). Using NIR chemical imaging, the 80:20 formulations showed the most pronounced blend segregation during the tableting process. Furthermore, imaging was capable of quantitating the cimetidine bead content among the different blend ratios. Segregation testing (ASTM D6940-04 method) indicated that blends of coated cimetidine beads and placebo beads (50:50 ratio) also tended to segregate.

Measuring and Modeling Proportion-Dependent Stress-Strain Behavior of EPS-SandMixture

A geofoam was produced by blending expanded polystyrene (EPS) beads and sands in proportions. The formed mixtures, known as EPS-sands, were 26–63% lighter than general earth fills (e.g., sand). Consolidated-drained (CD) triaxial compression tests were conducted on EPS-sand mixture specimens to observe their stress-strain characteristics, specifically, the stress-strain responses in relation to the EPS contents (0.5, 1.5, and 2.5% by weight) used in the mixtures and confining pressures (100, 200, 300 to 400 kPa) loaded on the specimens. The EPS content and confining pressure were found to influence the stress-strain and volumetric strain behavior of the mixtures. Increasing EPS content led to decreased shear strength and increased volumetric strain. Increasing confining pressures enhanced the strength of the mixture. EPS-sand mixtures underwent a shear contraction throughout the CD tests. The optimum EPS bead content (i.e., the one reasonably balancing the unit weight, strength, and deformation) was in the order of 0.5% by weight. EPS content dependent strain increment equations were derived by compromising Cam-clay and modified Cam-clay, and used to model the stress-strain characteristics of EPS-sand mixtures. The established equations were verified being able to depict the stress-strain observations of EPS-sand specimens, at least for the ranges of EPS contents and confinements considered in this study.

Fabrication of three-dimensional porous cell-laden hydrogel for tissue engineering

For tissue engineering applications, scaffolds should be porous to enable rapid nutrient and oxygen transfer while providing a three-dimensional (3D) microenvironment for the encapsulated cells. This dual characteristic can be achieved by fabrication of porous hydrogels that contain encapsulated cells. In this work, we developed a simple method that allows cell encapsulation and pore generation inside alginate hydrogels simultaneously. Gelatin beads of 150–300 µm diameter were used as a sacrificial porogen for generating pores within cell-laden hydrogels. Gelation of gelatin at low temperature (4 °C) was used to form beads without chemical crosslinking and their subsequent dissolution after cell encapsulation led to generation of pores within cell-laden hydrogels. The pore size and porosity of the scaffolds were controlled by the gelatin bead size and their volume ratio, respectively. Fabricated hydrogels were characterized for their internal microarchitecture, mechanical properties and permeability. Hydrogels exhibited a high degree of porosity with increasing gelatin bead content in contrast to nonporous alginate hydrogel. Furthermore, permeability increased by two to three orders while compressive modulus decreased with increasing porosity of the scaffolds. Application of these scaffolds for tissue engineering was tested by encapsulation of hepatocarcinoma cell line (HepG2). All the scaffolds showed similar cell viability; however, cell proliferation was enhanced under porous conditions. Furthermore, porous alginate hydrogels resulted in formation of larger spheroids and higher albumin secretion compared to nonporous conditions. These data suggest that porous alginate hydrogels may have provided a better environment for cell proliferation and albumin production. This may be due to the enhanced mass transfer of nutrients, oxygen and waste removal, which is potentially beneficial for tissue engineering and regenerative medicine applications.

Effect of glass bead content and diameter on shrinkage and warpage of injection‐molded PA6

AbstractA simple technique has been introduced to evaluate the shrinkage and warpage behavior of injection molded products. Using the shrinkage values measured on specific locations of the specimen, three deformation factors have been defined to characterize the warpage behavior of the materials examined. Experiments were carried out to determine these properties of injection molded polyamide 6 (PA6) composites with solid glass bead (GB) contents of 10, 20, 30, 40 wt% and diameters of 11, 85, 156, 203 μm. It was concluded that the flow directional shrinkages can principally be described by the change in the bead content and diameter; it was proven that the increase in bead content and in bead diameter induces a reduction in flow directional shrinkage. The rising bead content and diameter increased the deformation factor, defined by the shrinkage differences caused by the pressure drop. It was pointed out that the ideal bead content can be determined in the function of bead diameter. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers

Viscoelastic properties and characterization of inorganic particulate‐filled polymer composites

AbstractTo identify effects of glass bead (GB) content on the dynamic mechanical properties of filled low‐density‐polyethylene (LDPE) composites, the storage modulus, loss modulus, glass transition temperature, and mechanical damping of these composites were measured using a Du Pont dynamical mechanical analysis instrument in temperature range from −150 to 100°C. It was found that the storage modulus increased nonlinearly with an increase of the GB volume fraction. On the basis of Eshelby's method and Mori's work, an equation describing the relationship between the relative storage modulus (E′R) and filler volume fraction for polymeric composites was proposed, and the E′R of LDPE/GB composites were estimated by means of this equation at temperatures of −25, 0, and 25°C, and the calculations were compared with the experimental data, good agreement was showed between the predictions and the measured data. Furthermore, this equation was verified by the experimental from Al(OH)3 filled EPDM composites at glassy state reported in a reference. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

Permeability of compacted granule–clay mixtures

Achieving a sufficiently low permeability for the aggregate-clay mixtures, whether used as the core of embankment dam or soil liner, is essential. The study illustrates the role of granule (bead or aggregate) content and size, confining stress and fabric anisotropy on the permeability of ceramic bead–lean clay and aggregate-fat clay mixtures. It is shown that depending on the plasticity of the clay, the permeability may decrease or increase with bead/aggregate content. The permeability also decreases when either granule size or confining stress increases. It is found that the permeability is affected by fabric anisotropy in such a manner that its value in the horizontal direction ( k h ) is more than that in the vertical direction ( k v ), however, k h / k v decreases towards 1 for bead contents equal to or below 40%. In high bead content mixtures (i.e., 60% beads) k h / k v reaches as high as 3 with an increase in the confining stress. The concept of the development of heterogeneous field of density in the clay is also used to demonstrate the impact of granule size and fabric anisotropy on the permeability.

System Development for Generating Homogeneous Cell Suspensions and Transporting them in Microfluidic Components

AbstractMiniaturized biological test assays require an even distribution of the utilized cells in every single segment. For the cell dispension, two devices with a volume of about 2 milliliter were developed enabling simultaneous mixing and processing of suspensions into capillaries. These items will be used to generate homogeneous suspensions for a duration of up to one hour and distributing them with special microfluidic chips. Both devices could be easily sterilized by autoclaving and contain an agitator which is contactlessly driven with variable speed. Precise transportation of the mixed fluid in the lower microliter per minute range was realized by the use of syringe pumps. Suspensions with yeast, mammalian cells and beads were applied to investigate the efficiency of mixing and transportation as well as the effect on viability. At certain time intervals, samples were taken from the outlet, and the cell and bead content with the related viability was determined using an automated particle analyzer and counting chamber under the microscope. Yeast suspensions were handled up to two hours and hybridoma cells up to one hour without remarkable loss of viability whereby the degree of mixing was sufficient for these time periods. The results show that these modules are feasible tools for homogeneous mixing of cell suspensions, and transport through microfluidic devices allows dispensation of them into fluid segments on a microliter or nanoliter scale.

Rheological hybrid effect in nylon 6/liquid crystalline polymer blends caused by added glass beads

The “Rheological hybrid” effect, a phenomenon in which the melt viscosity of a ternary polymer blend decreases with increasing filler loading, due to the influence of the minor polymer phase in the blend, was investigated for Nylon 6/liquid crystalline polymer (LCP) blends after the addition of glass beads (GB). The apparent viscosity of the blended melts was measured by means of capillary rheometry. The viscosity of ternary Nylon 6/GB/LCP hybrid blends was the lowest among all the melts, i.e. lower than that of neat Nylon 6, LCP, binary Nylon 6/LCP and Nylon 6/GB blends. The viscosity of ternary Nylon 6/GB/LCP hybrid blends decreased with increasing glass bead content. Correspondingly, the morphology of the LCP droplets changed from spherical to fibrous with increasing glass bead content as well. For ternary hybrid blends with the same glass bead content and different bead sizes, the blend containing the smallest beads (1.2 μm in the diameter) had the lowest viscosity and strongest tendency to LCP fibrillation. A mechanism was proposed for correlating the rheological hybrid effect with LCP fibrillation in these ternary hybrid blends.