Open Porous Materials Research Articles

Dynamic Analysis of 2D FG Porous Thick Cylindrical Shells Under Thermal Shock

In this research, a thick hollow cylindrical shell made of bidirectional functionally graded open cell porous materials under internal thermal shock according to the classical theory of linear thermo-elasticity is examined for the first time. The cylinder is made of a porous cellular material and its porosity varies along both radial and axial directions continuously. The governing motion equations are obtained by using 2D-axisymmetric theory of linear thermo-elasticity rather than shell theories. This theory represents thickness stretching and gives more precise results. Graded finite element method is employed to model the problem. Applying this method rather than conventional FEM leads to more accurate results, especially for dynamic analyses. The cubic higher order element is used for dividing the solution domain. To obtain transient temperatures, Crank–Nicolson algorithm is used and then the Newmark procedure is used to derive time responses of displacement and stress components. The time history of displacements and stress components for different radial and axial power law exponents, porosity coefficient, boundary conditions, length-to-thickness ratio and two different porosity patterns are investigated in detail. The obtained results show that thermal-induced vibration is generally caused by hoop stress, and frequency and amplitude of vibrations and velocity of stress waves are considerably influenced by the porosity distribution, porosity coefficient and power law exponents in both directions.

Sound Absorption Properties of Porous Concrete Layers for Noise Barrier

The porous concrete layer is an open pore material placed on the noise incident face of a sound barrier structure on the road. Pore characteristics such as diameter, area and distribution are the main characteristics of porous concrete different from conventional concrete and play a dominant role in sound absorption properties. Factors affecting the pore structure of typical porous concrete have been discussed. The effects of macroscopic properties on sound absorption properties such as maximum sound absorption coefficient (SAC max), noise reduction and noise average were reviewed. The porous concrete containing other types of aggregate such as recycle, waste material, and lightweight in porous concrete innovation were discussed. Consequently, the effect of thickness, two layers and multiple layers of porous concrete to improve sound absorption at low frequencies. Finally, the guidances were proposed for the mixture composition for producing porous layer for good sound absorbing properties.

Single-step concentration of whey proteins using the pressurized gas eXpanded (PGX) liquid technology: Effect on physicochemical properties and scale-up

Pressurized Gas eXpanded (PGX) Liquid Technology precipitates and dries biopolymers using CO2-expanded organic solvents, producing open-porous materials with micro- and nanostructures. This study investigated the concentration of whey proteins from sweet whey liquid using PGX Technology as a single-step process at different scales and mass flow rate ratios (θPGX) of PGX fluid (CO2+Ethanol) to sweet whey liquid. The PGX process efficiently removed >50% dwb lactose and lipids from the feedstock, forming a whey protein concentrate (PGX-W, ≥45% protein dwb) consisting mainly of β-lactoglobulin, α-lactalbumin, and bovine serum albumin. At low θPGX, PGX-W had high protein concentrations (50% dwb), with reduced solvent effects on protein secondary structure. At high θPGX, PGX-W contained 14% dwb lactose, higher than the <5% dwb obtained at lower flow rates and had finer morphologies (tens of nm) with increased specific surface area (13–29 m2/g). Resulting PGX-W powders were free-flowing with low bulk density (35–74 g/L) and high-water solubility (≥80%).

Application of Lévêque Analogy to Open Cellular Porous Materials

Open-porous materials are used for thermal management applications, catalyst support, heat exchangers, and others owing to their enhanced heat transfer. Designing porous material for a specific heat transfer application requires quantifying effective thermal conductivity, pressure drop, and heat transfer as computed data or experimental correlations. This work extends the Lévêque analogy proposed for calculating heat transfer performance from pressure drop data for tube bundles and cross-rod matrices to porous materials. The current work shows the applicability of this analogy for periodic open-cellular porous materials. Seven unit cell geometries representing periodic cellular structures with 75% - 95% porosity are considered. Periodic flow and heat transfer simulation is performed in ANSYS Fluent for Reynolds numbers between 1 and 100 to provide pressure drop and heat transfer results. Permeability and inertial coefficient are estimated, and permeability is correlated successfully with the porosity and fiber diameter of the unit cell geometries. This correlation is validated using experimental data available in the literature, which allows for predicting pressure drops directly from the geometry. Lévêque’s analogy in the original form is explored using the pressure drop coefficient and Nusselt number, which provides a 44% frictional contribution to the total pressure drop. The correlation for the current geometries is further improved using a modified version of the Lévêque analogy, where the exponent is estimated using best fit instead of fixing at 1/3. The modified correlation is validated using experimental data from the literature, and a guideline to predict pressure drop and heat transfer from geometry is provided for periodic open-cellular porous materials.

Influence of pore‐structure characteristics on the mechanical properties of open‐porous cellular materials

AbstractThe influence of the pore structure characteristics on the macroscopic mechanical properties of open‐porous cellular materials has been computationally investigated in this contribution. While the effects of the pore‐size distribution on the macroscopic mechanical response of open‐porous cellular materials have been studied previously, the investigations regarding the effects of the pore structure characteristics are relatively scarce. The pore walls of open porous cellular materials are often modelled as beams and the pore wall structure is assumed to have a constant cross section. Although this assumption is valid for a large class of materials, insights into the influence of this assumption on the calculations of the properties of those materials that exhibit a rather pearl‐necklace‐like pore wall morphology are described in this paper. On comparing the simulation results for a corrugated pore‐wall with that having a constant cross‐section, it is observed that the maximal stresses in the pore wall may differ significantly.

A new surface treatment method for simplifying and enhancing the segmentation of open space pore object

This paper aims to present a new method for surface treatment of open pore materials and specimens to aid and fasten the segmentation process. The study is divided into two parts. In the first part of the investigation, three materials were tested on a plastic surface under laboratory conditions: X-ray contrast dental adhesive, wax, and zinc spray. After careful observation of the results, the zinc spray was selected for the purposes of the study. In the second part, the experiment was repeated with zinc contrast layers on a single-rooted tooth in two and three layers, zinc spray on sintered glass and a multirooted tooth in three layers. Region growing method was selected for the segmentation. The selected specimens were covered with a contrast layer, scanned, and images were reconstructed and analysed. After both the scanning and reconstruction stages, success was achieved in the samples with three layers. As a next step, the volumes of the root canal and the sintered glass were calculated successfully. In conclusion, using zinc spray as an X-ray contrast coating may be a successful approach in micro-computed tomography.

The Effect of Particle Necks on the Mechanical Properties of Aerogels.

Mechanical properties of open-porous materials are often described by constructing a cellular network with beams of constant cross sections as the struts of the cells. Such models have been applied to describe, for example, thermal and mechanical properties of aerogels. However, in many aerogels, the pore walls or the skeletal network is better described as a pearl-necklace, in which the particles making up the network appear as a string of pearls. In this paper, we investigate the effect of neck sizes on the mechanical properties of such pore walls. We present an analytical and a numerical solution by modeling these walls as corrugated beams and study the subsequent deviations from the classical scaling theory. Additionally, a full numerical model of such pearl-necklace-like walls with concave necks of varying sizes are simulated. The results of the numerical model are shown to be in good agreement with those resulting from the computational one.

Impact of pearl-necklace-like skeleton on pore sizes and mechanical properties of porous materials: A theoretical view

The structural and mechanical properties of open-porous cellular materials are often described in terms of simple beam-based models. A common assumption in these models is that the pore walls have a constant cross section, which may be in agreement for a vast majority of such materials. However, for many of those materials that are characterized by a pearl-necklace-like network, this assumption seems too idealized. Aerogels are perfect examples of such materials. In this paper, we investigate the effect of such pore walls having a string of pearls-like morphology on the properties of such open-porous materials. First, the pore size is mathematically modeled. Three scenarios are described, where the pore sizes are calculated for cells in 2D, 3D, and 3D with overlapping particles. The dependency of the skeletal features on the resulting pore size is investigated. In the second part, pore walls with 3D overlapping spheres are modeled and subjected to axial stretching, bending, and buckling. The effect of the particle sizes and the amount of overlap between the particles on the mechanical features is simulated and illustrated. The results are also compared with models that assume a constant cross section of pore-walls. It can be observed that neglecting the corrugations arising from the pearl-necklace-like morphology in open-porous cellular materials can result in serious miscalculations of their mechanical behavior. The goal of this paper is not to quantify the bulk mechanical properties of the materials by accounting for the pearl-necklace-like morphology but rather to demonstrate the significant deviations that may arise when not accounted for.

A sustainable acoustic customization of open porous materials using recycled plastics

Foams are commonly used as sound absorbers and thermal insulators for many industrial and construction applications. The insulating materials market is currently dominated by inorganic fibres like glass and mineral wool, as well as plastic foams. However, worldwide plastics consumption produces huge amounts of waste, generating concerns about soil, air and especially seawater pollution. Hence, new methods for recycling marine microplastic litter according to cleaner production criteria are being sought. This paper presents a novel, sustainable and eco-friendly foamy material made of microplastic waste, namely polyethylene terephthalate (PET) and polystyrene (PS), incorporated into a bio-based matrix. Samples with different compositions were prepared and then characterized for sound absorption properties. Evidence is presented of very good acoustic performances and of how the acoustic characteristics of the end product can be customized using different microplastic content and type. This allows envisioning many industrial and civil applications for this novel open-cell material.

Acoustic properties of commercially available thermal insulators − An experimental study

Thermal insulators are used structural applications, such as walls, floors, doors, roofs, duct wrappings, machine and wall linings, and vehicle envelopes. There is very little scientific comparative research about the acoustic performance of thermal insulator materials. The purpose of our study was to compare various acoustic properties of insulator materials to improve comprehensive understanding. Thirteen commercially available insulator types produced by several manufacturers were studied for thicknesses 50, 100, and 200 mm. The materials were stone wool, glass wool, cellulose, wood fiber, expanded polystyrene, polyisocyanurate, phenol foam, and cellular glass. Six acoustic quantities were measured: sound reduction index of bare insulator, sound reduction index of encapsulated insulator (insulator between two boards), sound absorption coefficient, airflow resistivity, dynamic stiffness, and reduction of impact sound pressure level in a floating floor. The acoustic performance differed significantly between insulator types for each quantity. The value range for the abovementioned six quantities for 100-mm thick insulator was extremely large: 10–27 dB, 33–52 dB, 0.20–0.78, 3.0–2700 kPa s/m2, 1.5–730 MN/m3, and 15–36 dB, respectively. Closed-pore materials usually carried worse acoustic properties than open-pore materials. Unexpectedly, lower thermal conductivity was associated with worse acoustic performance of two acoustic quantities. The study is the broadest acoustic investigation of thermal insulators because of the large number of studied acoustic quantities and insulator types. The study provides strong evidence that the choice of thermal insulator material plays an important role in the acoustic properties of the structural application. Manufacturers should consider declaring all six acoustic quantities to facilitate design.

Drying of sodium alginate using Pressurized Gas eXpanded (PGX) liquid technology

Pressurized Gas eXpanded (PGX) liquid technology is a scalable platform technology that simultaneously purifies, micronizes and dries aqueous solutions of biopolymers into fine structured open porous materials with unique morphologies using carbon dioxide (CO2) and ethanol at mild temperatures. The objective of this study was to investigate the effect of several PGX processing parameters on the physicochemical properties of sodium alginate (SA), a water-soluble polysaccharide from brown algae. PGX-processed SA (PGX-SA) had an open porous structure with a delicate network of fibrils, compared to the irregular shaped crystal-like non-porous particles of the raw SA dried using a conventional process. Upon PGX processing, the specific surface area was increased by more than 90 times compared to the raw SA. The use of low concentration (1.0% w/w) of the SA aqueous solution as the feed material and low ethanol flow rate (15 g/min), together with the mass flow rate ratio of 1:3.75:1.25 of aqueous solution:ethanol:CO2 resulted in a specific surface area of 164.5 m2/g of the PGX-SA. The PGX process shows great potential for simultaneously purifying and drying high molecular weight biopolymers into porous morphologies with large specific surface area for bioactive delivery systems in food, cosmetic and pharmaceutical applications.

Polymer-Nickel Composite Filaments for 3D Printing of Open Porous Materials.

Catalysis has been a key way of improving the efficiency-to-cost ratio of chemical and electrochemical processes. There have been recent developments in catalyst materials that enable the development of novel and more sophisticated devices that, for example, can be used in applications, such as membranes, batteries or fuel cells. Since catalytic reactions occur on the surface, most catalyst materials are based on open porous structures, which facilitates the transport of fluids (gas or liquid) and chemical (or electrochemical) specific surface activity, thus determining the overall efficiency of the device. Noble metals are typically used for low temperature catalysis, whereas lower cost materials, such as nickel, are used for catalysis at elevated temperatures. 3D printing has the potential to produce a more sophisticated fit for purpose catalyst material. This article presents the development, fabrication and performance comparison of three thermoplastic composites where PLA (polylactic acid), PVB (polyvinyl butyral) or ABS (acrylonitrile butadiene styrene) were used as the matrix, and nickel particles were used as filler with various volume fractions, from 5 to 25 vol%. The polymer–metal composites were extruded in the form of filaments and then used for 3D FDM (Fused Deposition Modeling) printing. The 3D printed composites were heat treated to remove the polymer and sinter the nickel particles. 3D printed composites were also prepared using nickel foam as a substrate to increase the final porosity and mechanical strength of the material. The result of the study demonstrates the ability of the optimized filament materials to be used in the fabrication of high open porosity (over 60%) structures that could be used in high-temperature catalysis and/or electrocatalysis.

Effect of 3D-Printed PLA Structure on Sound Reflection Properties.

3D printing technique is currently one of the promising emerging technologies. It is used in many areas of human activity, including acoustic applications. This paper focuses on studying the sound reflection behavior of four different types of 3D-printed open-porous polylactic acid (PLA) material structures, namely cartesian, octagonal, rhomboid and starlit structures. Sound reflection properties were evaluated by means of the normal incidence sound reflection coefficient based on the transfer function method using an acoustic impedance tube. In this study, various factors affecting the sound reflection performance of the investigated PLA samples were evaluated. It can be concluded that the sound reflection behavior of the tested PLA specimens was strongly affected by different factors. It was influenced, not only by the type of 3D-printed open-porous material structure, but also by the excitation frequency, the total volume porosity, the specimen thickness, and the air gap size behind the tested specimen inside the acoustic impedance tube.

Preparation and Characterization of Nanocellulose/Chitosan Aerogel Scaffolds Using Chemical-Free Approach.

Biopolymer-based aerogels are open three-dimensional porous materials that are characterized by outstanding properties, such as a low density, high porosity and high surface area, in addition to their biocompatibility and non-cytotoxicity. Here we fabricated pure and binary blended aerogels from cellulose nanofibers (CNFs) and chitosan (CS), using a chemical-free approach that consists of high-pressure homogenization and freeze-drying. The prepared aerogels showed a different porosity and density, depending on the material and mixing ratio. The porosity and density of the aerogels ranged from 99.1 to 90.8% and from 0.0081 to 0.141 g/cm3, respectively. Pure CNFs aerogel had the highest porosity and lightest density, but it showed poor mechanical properties and a high water absorption capacity. Mixing CS with CNFs significantly enhance the mechanical properties and reduce its water uptake. The two investigated ratios of aerogel blends had superior mechanical and thermal properties over the single-material aerogels, in addition to reduced water uptake and 2-log antibacterial activity. This green fabrication and chemical-free approach could have great potential in the preparation of biopolymeric scaffolds for different biomedical applications, such as tissue-engineering scaffolds.

Image segmentation and analysis for densification mapping of nanoporous gold after nanoindentation

Segmentation of scanning electron microscopy (SEM) images of focused ion beam (FIB) cross-sections through indented regions in nanoporous gold (np-Au) is carried out. A key challenge for image analysis of open porous materials is the appropriate binarization of the pore and gold ligament regions while excluding material lying below the cross-sectional plane. Here, a manual approach to thresholding is compared to global and local approaches. The global thresholding resulted in excessive deviations from the nominal solid fraction, due to a strong gray-scale gradient caused by the tilt angle during imaging and material shadowing. In contrast, the local thresholding approach delivered local solid fractions that were free of global gradients, and delivered a quality comparable to the manual segmentation. The extracted densification profiles vertically below the indenter as well as parallel to the surface showed an exponential-type decay from the indenter tip towards the nominal value of 1 far from the indenter.Graphic abstract

Study on preparing of ultrahigh‐molecular weight polyethylene microporous materials by novel non‐dense injection molding method

AbstractIn this article, a novel method called non‐dense injection molding with higher efficiency was proposed to prepare ultrahigh‐molecular weight polyethylene (UHMWPE) microcellular open porous materials. The characteristics and the basic principle of the molding process were described, and the effects of shot size, injection pressure, and injection speed on microstructure, average pore size, porosity, and pore size distribution were further studied. The results showed that under the parameters of the shot size, injection pressure and injection speed set as 60%, 63.9 MPa, and 100%, the microporous UHMWPE materials were obtained with the average pore size 38.9 μm and porosity 38.3 vol% respectively, which were close to the microporous structure and properties of the commercial filter products prepared by traditional powder sintering method.

Impact of entry–exit loss on the measurement of flow resistivity of porous materials

This study experimentally investigates the impact of low pore density and thickness on the flow resistivity, hence permeability, of periodic open porous materials. An experimental setup is developed to measure the flow resistivity of porous samples adhering to the guidelines provided by the International Standards Organization 9053 and American Society for Testing and Materials C522 standards. The flow resistivity of three different porous microlattices is considered. Two of the three lattices are obtained from a monospherical void subtraction method, while the third is the octet-truss lattice. The monospherical void geometries are body-centered-cubic and A15 lattices. The pore density, measured in terms of pores-per-inch (PPI), was varied from 1 PPI to 12 PPI for all three microlattices considered. At low PPIs, the pore sizes are on the order of macroscale thickness. Hence, the volume-averaging or homogenized equivalent fluid model may not be valid. The thickness variation for a fixed PPI is also considered over limits where traditional volume-averaging methods break down. It is shown that at extremely low PPIs and thicknesses, entrance and exit losses become dominant, and the flow resistivity measured as per standards ceases to be a constant with PPI or thickness. Furthermore, existing two-dimensional modeling approaches for losses due to flow in pipes are adopted to predict the entry and exit pressure loss coefficients for the considered microlattices with appropriate modifications.

Study of the Sound Absorption Properties of 3D-Printed Open-Porous ABS Material Structures.

Noise pollution is a negative factor that affects our environment. It is, therefore, necessary to take appropriate measures to minimize it. This article deals with the sound absorption properties of open-porous Acrylonitrile Butadiene Styrene (ABS) material structures that were produced using 3D printing technology. The material’s ability to damp sound was evaluated based on the normal incidence sound absorption coefficient and the noise reduction coefficient, which were experimentally measured by the transfer function method using an acoustic impedance tube. The different factors that affect the sound absorption behavior of the studied ABS specimens are presented in this work. In this study, it was discovered that the sound absorption properties of the tested ABS samples are significantly influenced by many factors, namely by the type of 3D-printed, open-porous material structure, the excitation frequency, the sample thickness, and the air gap size behind the sound-absorbing materials inside the acoustic impedance tube.

Extrusion of Porous Protein-Based Polymers and Their Liquid Absorption Characteristics.

The production of porous wheat gluten (WG) absorbent materials by means of extrusion processing is presented for the future development of sustainable superabsorbent polymers (SAPs). Different temperatures, formulations, and WG compositions were used to determine a useful protocol that provides the best combination of porosity and water swelling properties. The most optimal formulation was based on 50 wt.% WG in water that was processed at 80 °C as a mixture, which provided a porous core structure with a denser outer shell. As a green foaming agent, food-grade sodium bicarbonate was added during the processing, which allowed the formation of a more open porous material. This extruded WG material was able to swell 280% in water and, due to the open-cell structure, 28% with non-polar limonene. The results are paving the way towards production of porous bio macromolecular structures with high polar/non-polar liquid uptake, using extrusion as a solvent free and energy efficient production technique without toxic reagents.

Validation study for Large-Eddy Simulation of Forest Flow

The publication presents Large-Eddy Simulation (LES) of flow over a reduced-scale wind tunnel model of a forest canopy. The final aim of the study is to determine factors responsible for damage in forests by strong winds. The wind tunnel forest was represented by an open-porous foam material for the crown layer and wooden dowels for the trunk layer. The forest model was installed in the open test section of a Goettingen-type wind tunnel and Particle Image Velocimetry (PIV) measurements were made for the acquisition of the flow field data. The numerical simulations were performed with OpenFOAM®. The forest was modelled by an additional sink term in the momentum transport equations based on the leaf area density and a characteristic drag coefficient for the underlying tree specimen. Large-eddy simulations with different subgrid-scale (SGS) turbulence models were carried out and compared to wind tunnel data. The Smagorinsky SGS model outperformed the dynamic Lagrangian SGS model in the windward edge region (within a distance of approximately 2 tree heights from the leading edge) whereas the dynamic Lagrangian SGS model showed a better performance for regions farther downstream.