Foam Morphology Research Articles

Rheology of oil-based nitrogen foam at shallow reservoir conditions: Experiment and evaluation

Exhibiting as a combination of viscous, elastic, and plastic behavior, rheology is a branch of physics and is majorly concerned with continuum mechanics for flow characterizations, particularly non-Newtonian flow like foam. However, most existing studies of foam rheology are primarily focused on water-based foam, while oil-based foam rheology lacks adequate understanding, plus few comprehensive experimental analyses have been done. This study, for the first time, investigates the rheological behavior of oil-based nitrogen foam with full foam quality and shallow reservoir conditions through a newly-designed visualized capillary rheometer. Basically, the effects of foam quality and shear rate on foam morphology and apparent viscosity were elucidated, and the foam rheology at different temperatures and pressures was evaluated. More specifically, with increasing shear rate, the apparent viscosity of nitrogen foam decreases in a concave-down parabola pattern. With the foam quality of 86 %, the apparent viscosity of the foam flow is found to reach its maximum value, 58.4 mPa·s, at the flow rate of 4 mL/min, temperature of 25 °C and pressure of 5 MPa. The foam flow gradually becomes uniform and dense and the apparent viscosity elevates with increasing foam quality up to 86 %. After that, the foam flow tends to be slug flow and its stability becomes worse with linearly-decreasing apparent viscosity. With increasing pressure, the apparent viscosity and consistency coefficient increase, which result in the increase of rheological index and decrease of non-Newtonian property. The temperature effects on the foam flow are absolutely opposite but stronger in comparison to pressure effects as aforementioned. In addition, the rheological equations of nitrogen foam are determined by fitting the consistency coefficient and rheological index with foam quality. Overall, thorough investigations of the rheology of oil-based nitrogen foam would be of great importance for foam theory and practice.

Preparation of lightweight and high‐strength polypropylene‐based ternary conductive polymer foams by in situ microfiber reinforcement

AbstractConductive polymer composites (CPCs) have demonstrated significant potential in the aerospace, electronics, and communications industries. In this study, polypropylene (PP)/multiwalled carbon nanotubes (MWCNTs) binary composites and in situ fiber reinforced multicomposites made from PP/MWCNTs were fabricated by microcellular injection molding. In addition to crystallization behavior, foam morphology, mechanical properties, dielectric properties, and electromagnetic shielding properties of the composites were analyzed. According to the results, microporous structures can facilitate the distribution of conductive fillers, thereby enhancing the electromagnetic shielding performance and mechanical properties of the composite. In situ microfiber networks display a heterogeneous nucleation effect, resulting in an increase in foam density, which improves composite performance. In situ fiber‐reinforced microporous multicomposites are capable of exhibiting higher elongation at break and electromagnetic shielding properties than binary systems, and the multicomposites can achieve greater electromagnetic shielding effectiveness (SE) with fewer conductive fillers. Ultimately, fiber‐reinforced microporous composites with an elongation at break of 194.40%, an electromagnetic shielding effect of >20 dB, and an absorption mechanism are produced. A feasible method is presented in this study for preparing CPCs that produce light weight, excellent mechanical properties, and high electromagnetic SE at low filler levels.

Study on Properties of Regenerated Fluorinated Polyurethane Rigid Foam Prepared by Degrading Waste Polyurethane

Polyurethane (PU) has become one of the most widely used materials in the industrial field due to its excellent performance and wide range of applications. The increasing consumption of polyurethane materials has resulted in significant polyurethane waste. We can recycle waste polyurethane to obtain recycled polyurethane, but to make the recycled polyurethane meet different performance requirements in terms of utility and cost and enable the recycled polyether polyol to be further applied to high-end applications, it is necessary to improve the use value of recycled polyether polyol. In this paper, self-made Fluorodiol was added to the degradation process of waste polyurethane to obtain fluorinated regenerated polyether polyol. Recycled fluorinated polyurethane with excellent performance was prepared using fluorine-containing recycled polyether polyol. The regenerated fluorinated polyether polyols were characterized by infrared spectroscopy, viscosity, hydroxyl value, and GPC molecular weight distribution. The density, apparent morphology, water absorption, mechanical strength, thermal conductivity, and thermal stability of RFPU rigid foams with different fluorine contents were studied by scanning electron microscopy. The results show that when the addition of Fluorodiol was 8% of the mass of waste polyurethane, the density was 41.2 kg/m3, the immersion loss rate was 2.125%, the compressive strength was 0.315 Mpa, and the thermal conductivity was 0.0227 W/m·K. The RFPU prepared by Fluorodiol has low surface energy, good compressive strength, hydrolysis resistance, and is expected to be widely used in special insulation materials. Thus, the sustainable recycling of polyurethane is achieved.

Rational Design of a Polyurethane Foam.

Polyurethane (PU) foams are exceptionally versatile due to the nature of PU bond formation and the large variety of polymeric backbones and formulation components such as catalysts and surfactants. This versatility introduces a challenge, namely a near unlimited number of variables for formulating foams. In addition to this, PU foam development requires expert knowledge, not only in polyurethane chemistry but also in the art of evaluating the resulting foams. In this work, we demonstrate that a rational experimental design framework in conjunction with a design of experiments (DoE) approach reduces both the number of experiments required to understand the formulation space and reduces the need for tacit knowledge from a PU expert. We focus on an in-depth example where a catalyst and two surfactants of a known formulation are set as factors and foam physical properties are set as responses. An iterative DoE approach is used to generate a set of foams with substantially different cell morphology and hydrodynamic behaviour. We demonstrate that with 23 screening formulations and 16 final formulations, foam physical properties can be modelled from catalyst and surfactant loadings. This approach also allows for the exploration of relationships between the cell morphology of PU foam and its hydrodynamic behaviour.

Highly porous FeNi 3D foams produced by one-step electrodeposition: Electrochemical stability and mechanical properties

Highly porous iron‑nickel foams, including the first-ever reported pure iron foam, were prepared by the dynamic hydrogen bubble template electrodeposition method and studied regarding their electrochemical stability and mechanical properties. Changes on the morphology, microstructure, and electrochemical resistance of the foams were investigated as a function of the Fe:Ni ratio by scanning electron microscopy (SEM), d.c. polarization and electrochemical impedance spectroscopy (EIS). Tensile and bending tests were carried out to evaluate the mechanical behavior of the prepared foams. Both crystalline structure and morphology are affected by the increase of Ni content, evolving from a highly porous foam with a body-centered cubic (bcc) structure to a denser material with open pores and face-centered cubic (fcc) structure. Polarization curves reveal an ennoblement of the corrosion potential as the nickel content increases. The impedance response revealed a dependence on the foam porosity. An increased number of pores was found more detrimental to the mechanical properties of the foams, as fractures seem to propagate, preferentially by cracks due to connecting pores. As result, foams with higher Ni contents displayed better mechanical performance for both tensile and bending assays. Results show that this innovative and powerfull technique enables to design iron foams with the adequate properties required for industrial applications. • Fe and FeNi nanofoams are prepared by Dynamic Hydrogen Bubble Template Electrodeposition. • Pure iron foam is obtained for the first time. • Foams morphology change for higher Ni contents. • Faradaic resistance depends on both %Fe and the pore availability. • Improved mechanical resistance is observed for the less porous foams.

Preparation of Polyols and Polyurethane Foams from Olein By-Product of Tanning Industry

Olein produced from the solid residues of the tanning industry is already employed as raw material to obtain greasing oil for leather. However, new applications for this product may be advantageous regarding environmental impact and sustainability of this industry. In this work, flexible polyurethane foams (FPUFs) were prepared from polyols obtained from olein. A polyol from olein was prepared through alkaline glycerolysis. The glycerolysis conditions of temperature, glycerol/olein molar ratio, amount of catalyst and reaction time were optimized using a 24 factorial design, resulting in an olein polyol containing around 75% of monoacylglycerols, hydroxyl value (388.68±0.40 mg KOH.g-1), and hydroxyl functionality of 2.89. FPUFs were prepared at NCO/OH ratios of 1.2:1 and 1.3:1, using an aliphatic hexamethylene diisocyanate trimer and water as foaming agent. The foams were characterized through FTIR, thermogravimetry, morphology, extractable materials, and mechanical properties. Characteristics urethane/urea groups formation were verified by FTIR as well as typical mass loss steps in the thermal decomposition curves. The foams morphology showed a structure composed mainly for polygon-type closed-cells. The obtained FPUFs presented a content of extractable materials lower than 3%. The mechanical properties of the foams were dependent on the NCO/OH ratio, and the foam prepared at the ratio of 1.2:1 stood out as a potential material to be used in the production of mattresses. This study demonstrated the feasibility of transforming olein, a solid residue of the tanning industry, as a precursor to prepare PU foams, which may be a promising material for mattress applications, considering the observed features.

Utilization of supercritical CO2 for controlling the crystal phase transition and cell morphology of isotactic polybutene-1 foams

Isotactic polybutene-1 (iPB-1) is a semi-crystalline polymer with multiple crystal forms. In this work, we found a novel method to obtain and adjust the expansion ratio and bimodal cellular structures of iPB-1 foams with annealing and foaming using supercritical CO2. The form I′ can be obtained via the supercritical CO2 annealing, and the ratio of form I and I′ can be adjusted by controlling simply the annealing time. The effects of crystal form ratio on the thermal behavior, rheological behavior and cell morphology of foams were analyzed. Energy storage modulus (G′) and complex viscosity (|η*|) decrease with the increased content of form I. Crystal form I′ has a lower foaming temperature window and bubble growth resistance than form I, resulting in larger cell diameter and expansion ratio. The bimodal cell structure can be observed in the samples with 1:1 form I′/form I, where the average large and small cell size are 122 and 40 µm at 109 °C and 10 MPa CO2, respectively. To regulate the cell distribution, various ratios of mixed crystal phases were applied to investigate their effect on the foaming behavior and bimodal cells structure at different temperatures. Even with a similar expansion ratio, significantly different cell distributions of bimodal cell structure can be easily prepared by simply adjusting the content of form I′, which can broaden the application range of iPB-1 foams.

Modelling the effect of morphology on thermal aging of low-density closed-cell PU foams

Low-density closed-cell polyurethane (PU) foams are widely used in thermal insulation in diverse applications, therefore predicting their thermal aging has a distinct practical importance. Several approaches have been developed allowing forecasting the long-term changes of gas composition in foams, which manifest as the thermal aging. The accelerated aging test methods of foams need to be applied to each foam morphology of interest, while diffusion modelling-based methods, employing characterisation of the gas transport properties of PU polymer or monitoring the evolution of gas composition in foam cells, are relatively complicated. In this study, the experimentally determined evolution of PU foam conductivity is used for estimating the effective diffusivities of gases, based on which permeability of the PU polymer is subsequently evaluated by a structural model assuming Kelvin cell geometry of foam cells. The proposed approach enables prediction of aging dynamics of foams developed from the same PU polymer but possessing a markedly different morphology.

Zn-doped titania nanoparticles as building blocks for solid foam filters of water and air via photocatalytic oxidation

Photocatalytic oxidation (PCO) could provide energy-efficient purification of water and air. Its efficacy is constrained mainly by limited photocatalytic activity and active surface. To address both, solid foams with hierarchic porous structures spanning multiple length-scales, stabilized by photocatalytic Zn-doped titania nanoparticles (NP) were synthesized and tested. The NP were characterized by SEM, EDS, DLS, XRD, Raman and UV–Vis spectroscopies. Solid foams were stabilized by NP complexes with cationic surfactants. The foam morphology was characterized and photocatalytic activity was demonstrated in water. The present work paves the way for the development of efficient systems for air and water purification in demanding technological sectors, such as aerospace.

Morphological Features of PUR-Wood Particle Composite Foams.

The aim of this study was to apply waste wood particles (WP) with different sizes from primary wood processing as a filler for open-cell PUR foams. For this purpose, various wood particle sizes were added as a filler for polyurethane foams (PUR). The effects of the addition of of 0.05–<0.125 mm, 0.125–<0.315 mm, 0.315–1.25 mm, and >1.25–2.0 of WP to the polyurethane matrix on the density, the kinetics of PUR foaming, the cell structure, and the morphology were investigated. Scanning electron microscope (SEM) and X-ray computer tomography were used. Based on the results, it was found that the addition of WP in the amount of 10% leads to an increase in density with an increase in particle size. The research shows that the morphology of the PUR-WP foam is influenced by its particle size. The difference in the number and size of cells in PUR-WP composites depends on the wood particle size. The addition of dust causes the formation of cells of much smaller sizes; confirmed by SEM images. Moreover, computer tomography clearly demonstrates that the WP are well-dispersed within the foams’ structures.

Anisotropic Enhancement in Thermal Conductivity of Graphene Foam/Polymer Composites Based on Uniaxial Compression

AbstractHigh‐performance thermal interface materials are in increasing demand because of the problems of dissipating heat from high‐power computing devices. To solve this problem, this study proposes a method of microstructural design through uniaxial compression of graphene foam along the out‐of‐plane direction. The thermal conductivity of the composites with graphene foam shows an anisotropic growth along the direction of the compressive strain. The in‐plane thermal conductivity increases significantly from 0.189 to 1.669 W m−1 K−1 at an extremely low filler content of 2.24 vol%, whereas the out‐of‐plane thermal conductivity increases slightly to 0.303 W m−1 K−1. Moreover, the samples exhibit outstanding in‐plane thermal conductivity enhanced efficiency, which reaches 415.19% at a 1.29 vol% graphene content. The mechanism of anisotropic thermal conductivity enhancement is revealed by constructing a theoretical model based on a geometrical unit cell simplified from the morphology of graphene foam. This uniaxial compression method of a 3 structure provides a novel direction for improving the thermal conductivity of polymeric matrix composites more controllably.

Revealing the Combined Nanoconfinement Effect by Soft and Stiff Inclusions in PMMA/Silica CO2 Blown Foams

AbstractThis study shows the importance of nanoparticle (NP) spatial arrangement on the nucleation, morphology, and properties of nanocomposite foams. It probes CO2 blown PMMA with three types of nanosilica structures with exactly the same chemical composition: aggregates, chain bound clusters, and individually dispersed NPs. A systematic but nontrivial scaling of morphology, glass transition temperature, static and impact mechanical properties, and thermal conductivity is discussed with special regard to the combined nanoconfinement by soft and stiff inclusions. The presented results suggest a limited potential of simultaneous toughening by nanoreinforcement and shear banding, which can draw significant implications for both the fundamental science and industrial practice dealing with nanoreinforced cellular materials.

Effect of bio-based polyols and chain extender on the microphase separation structure, mechanical properties and morphology of rigid polyurethane foams

The preparation of polyurethane foams from bio-based polyols was a preferable alternative to save fossil resources, and the investigation of the microphase separation structure of foams can effectively guide their application. In this work, rigid polyurethane (PU) foams from three bio-based polyols and different content of chain extender of 1,4-butanediol were prepared. Microphase separation behavior and thermodynamic properties of the foams were analyzed by ATR-FTIR, SEM, TG, DSC and DMA. The hydrogen bond content increases and the microphase separation tendency is suppressed with the addition of bio-based polyols. The TG analysis reveals that the thermal loss of bio-based foams is earlier than that of petroleum-based foams at the initial stage. The hydrogen bond content of bio-based rigid PU foam derived from corn stalks increases by 6.03 % relative to petroleum-based foam, and the compression strength reaches 160.18 KPa. Furthermore, with the addition of 1,4-butanediol (5 wt%), the compression strength of bio-based rigid PU foam derived from corn stalks rises to 325.05 KPa, while the proportion of ordered hydrogen bonds is considerably higher than that of the original foam, demonstrating the increase in the degree of microphase separation.

Creating 3 dimensional foam morphology of lead dioxide on the polyaniline film for improving the performance of lead flow batteries

In the present study, we investigate the effect of polyaniline as a conductive surface modifier on the morphology of the lead dioxide, PbO2, as a positive active material of lead-acid redox flow batteries. We used cyclic voltammetry to electrodeposit PbO2 on the surface of the bare and polyaniline-modified graphite substrates. We characterized the morphology and crystal structure of the electrodeposited PbO2 film using X-ray diffraction and scanning electron microscopy. In addition, we used electrochemical polarization and electrochemical impedance spectroscopy techniques to investigate the kinetics of the lead dioxide charge transfer in the presence and absence of polyaniline. To analyze the effect of the polymer film on the battery performance, we discharged the cells at different rates, and studied the cycle life of the cells. The results show that lead dioxide adopts an interconnected 3D fiber-like morphology on the surface of the polyaniline-modified graphite, resulting in a higher surface area, a better cycle life, and a higher coulombic efficiency, along with a retarded short-circuit problem. Besides, polyaniline modification increased the electron transfer rate of lead dioxide, reduced the internal resistance, enhanced the discharge plateau with less oscillation in the voltage range from 1.4 to 1.6 V, and increased the average specific power up to 367 mWg−1, resulted in a generally boosted battery performance.

Citric Acid-Crosslinked Highly Porous Cellulose Nanofiber Foam Prepared by an Environment-Friendly and Simple Process.

In this study, cellulose nanofiber (CNF) foams are prepared by an environment-friendly, time-saving, and simple process using bio-based citric acid (CA) as a green crosslinking agent. Scanning electron microscope and Fourier transform infrared spectroscopy examine the foam morphology and confirm the crosslinking. The prepared foam shows a very high porosity (>98%) with a low density (24.02mg cm-3) with more than 200% improvement in mechanical strength and modulus compared to the neat CNF foam. In addition, the inclusion of CA into CNF improves thermal stability, antioxidant activity, and hydrophobicity. Furthermore, the prepared foam demonstrates a good sound absorption behavior, suitable for environment-friendly and lightweight sound-absorbing foam.

Prediction of spectral radiative property based on the microscopic ligament morphology and pore-level structure of open-cell alumina foam

In this work, based on the complete structure model consisting of microscopic ligament morphology and pore-level structure, a trans-scale analysis method is presented for accurately predicting the spectral radiative properties of open-cell ceramic foams. The characteristic models of microscopic ligament morphologies are obtained by the SEM technique, while the network structure of ligaments is reconstructed by the μ-CT technique. According to the SEM data, the microscopic statistical models are developed for the rough surfaces and the internal porous media of ligaments. Additionally, based on the statistical models, the FDTD method is employed to analyze the spectral radiative transfer behaviors on the surfaces and inside the ligament media. The spectral directional-hemispherical reflectivity and specularity parameter for the ligament surface, as well as the extinction coefficient, the scattering albedo and the scattering phase function for the ligament medium are extracted from the FDTD simulations. The above parameters are used as the input data for the pore-level simulations of spectral radiative transfer inside the ligament network, where the Monte Carlo method is conducted. The apparent spectral absorptivity and reflectivity, as well as the equivalent volumetric spectral radiative properties of alumina foam sheets are predicted by the presented trans-scale analysis method. The trans-scale predicting method is verified and compared with the single pore-level simulations of radiative transfer inside alumina foams. The spectral radiative characteristics of alumina foams are analyzed for various wavelengths and incident angles. From the analysis, only when the specularity parameter is properly chosen, the pore-level simulation is also reliable for predicting the spectral radiative properties of ceramic foams.

Robust polymer foams from 2-hydroxyethyl cellulose: Fabrication, stability, and chemical functionalization

We describe the fabrication of polymer foams from aqueous solutions of 2-hydroxyethyl cellulose (HEC), using freezing-induced phase-separation and solvent removal methods. Freezing aqueous solutions of HEC produced 3D polymer networks by a mechanism involving polymer exclusion from ice crystals and concentration at grain boundaries. This phase-separation is viewed as a kinetically controlled process, with properties of the resultant foams reliant on the processing temperatures and other conditions employed. Specifically, HEC foams were obtained by removal of the ice phase either by lyophilization or solvent exchange techniques. The morphology and pore characteristics of the resultant foams were visualized by scanning electron microscopy (SEM), which showed fibrillar and flake-like polymer material embedded in an open-cell porous structure. Foam density and stiffness increased as a function of the initial HEC concentration employed, while the mechanical integrity of the resultant foams was improved by crosslinking with poly(acrylic acid) (PAA) or maleic anhydride (MA). Such crosslinking successfully enabled liquid water sorption into the foams without loss of structural integrity, thus providing opportunities for further incorporation of chemical moieties. Dynamic vapor sorption (DVS) was employed to assess water uptake into the HEC foams, which was generally greater for foams produced by lyophilization, and in all cases exceeded that achieved by conventional, commercially available cellulose foams.

Tailored design of a novel composite foam of sodium alginate used for fluoride ion removal.

Fluoride is an essential micronutrient for humans. Nonetheless, when the amount of fluoride ion is greater than required, it will cause skeletal fluorosis and dental fluorosis to threaten human health. In this paper, a series of sodium alginate (SA)-based foam materials are prepared by freeze-drying technique and anchored with the nano-activated alumina (nAl2O3) in the SA to obtain a novel adsorbent of SA-nAl2O3 foam used for fluoride ions removal. The SA-nAl2O3 foam morphology was further explored and confirmed that nAl2O3 existed stably in the SA. The adsorption results showed that the maximal fluoride ion adsorption capacity was 5.09 mg/g with 20 mg/L fluorine solutions at a pH of 3. The adsorption isotherm fitted adequately to the Langmuir isotherm model, which demonstrated that the adsorption process is closer to monolayer adsorption. The adsorption kinetics behavior of SA-nAl2O3 foam was described by a pseudo-second-order model, and the adsorption process occurred by chemisorption. Adsorption thermodynamics analysis emphasized that the adsorption process was spontaneous and endothermic. The main mechanism of the foam is ion exchange. The SA-nAl2O3 foam exhibited excellent regeneration performance and stability after three cycles.

Enhanced properties of starch based foams with modified starch/polyester blend as masterbatch

AbstractStarch/PBAT blends were reactively extruded as masterbatch with the addition of tartaric acid (TA) and epoxide chain extender ADR4468 (ADR). The effects of tartaric acid and chain extender on the mechanical properties and structure of starch/PBAT blends were evaluated. The tensile strength of starch/PBAT blends with TA and TA/ADR increased by 31.4% and 85.6%, respectively. Further, starch, plasticizer, and blowing agent were melt extruded with this blend masterbatch, and the effects of masterbatch on the foamability, morphology, and properties of starch foams were investigated. When the masterbatch content was 10 phr, the obtained foam had the lowest apparent density (445.1 kg m−3), and the compressive strength, recovery, and water resistance of the foam were also improved significantly.

Research on the feasibility of polyethylene terephthalate foam used in wind turbine blades

AbstractThe sandwich foam materials of wind turbine blades are mainly polyvinyl chloride (PVC) and styrene–acrylonitrile (SAN) foams due to their good mechanical properties. However, PVC foam is unrecyclable and not resistant to high‐temperature conditions, while SAN foam is more expensive than PVC foam. Polyethylene terephthalate (PET) has irreplaceable advantages than both PVC and SAN foams because of its better mechanical performance, fantastic heat‐resistant, low cost, and environmental friendliness (100% recyclability). In this article, the mechanical properties, thermal stability, resin uptake, and cellular morphology of PET T92, PVC H60, and SAN T400 foams were discussed. The results showed that the mechanical properties of T92 were equivalent to the existing H60 and T400, and even exceed their properties. It was found that the thermal stability of T92 was better than H60 and T400 under the same high temperature. Moreover, the pore of T92 was more uniform and regular than H60 and T400. Furthermore, the overall cost of T92 was lower than H60 and T400. The findings suggest that PET foam with a density of 100 kg/m3 can completely replace PVC 60 kg/m3 and SAN 71 kg/m3 foams from the perspective of mechanical performance, cost, thermal stability, and environmental protection.