Foam Structure Research Articles

Effect of pH shifting and temperature on the functional properties of a commercial pea protein isolate

AbstractBackground and ObjectivesIn the present study, the effect of a pH‐shifting method in combination with heat was investigated for its effects on the resulting surface and functional properties of a commercial pea protein isolate. The pH shifting process was performed at both acidic (pH 2) and alkaline (pH 10) pH and then adjusted back to neutrality. The heat‐treated samples were further subjected to heating and later neutralized at pH 7.FindingsThe results of these treatments indicated that an alkaline pH shifting, as well as its combination with heat, resulted in a significant increase in the solubility of the proteins, whereas an acidic pH shifting, and in combination with heat, reduced the stability of the proteins in solution. Additionally, some functional properties were enhanced by pH shifting, such as foaming capacity or emulsion stability, while other properties showed no alteration or were negatively impacted, such as foaming stability. Furthermore, analysis of the bubble structure of foams using a dynamic foam analyzer revealed that bubble sizes for samples shifted at pH 2 in combination with heat presented the biggest increase in bubble growth over time, creating a less stable foam.ConclusionsThe application of pH shifting and the use of heat can aid in the improvement of pea protein functionality and allow tailoring of these proteins for specific applications.Significance and NoveltyThis study utilized a simple method to achieve modifications in the protein structures, providing insights into the application of pea proteins into food products as emulsifying and foaming agents.

Effects of liquid fraction and contact angle on structure and coarsening in two-dimensional foams

Aqueous foams coarsen with time due to gas diffusion through the liquid between the bubbles. The mean bubble size grows, and small bubbles vanish. However, coarsening is little understood for foams with an intermediate liquid content, particularly in the presence of surfactant-induced attractive forces between the bubbles, measured by the interface contact angle where thin films meet the bulk liquid. Rigorous bubble growth laws have yet to be developed, and the evolution of bulk foam properties is unclear. We present a quasistatic numerical model for coarsening in two-dimensional wet foams, focusing on growth laws and related bubble properties. The deformation of bubble interfaces is modelled using a finite-element approach, and the gas flow through both films and Plateau borders is approximated. We give results for disordered two-dimensional wet foams with $256$ to $1024$ bubbles, at liquid fractions from $2\,\%$ to $25\,\%$ , beyond the zero-contact-angle unjamming transition, and with contact angles up to $10^\circ$ . Simple analytical models for the bubble pressures, film lengths and coarsening growth rates are developed to aid interpretation. If the contact angle is non-zero, we find that a prediction of the coarsening rate approaches a non-zero value as the liquid fraction is increased. We also find that an individual bubble's effective number of neighbours determines whether it grows or shrinks to a good approximation.

Effect of sonication time on physical and foaming properties of pasteurized milk

This study investigates the impact of ultrasonication duration on the properties of milk foam. Milk samples were subjected to ultrasonication for varying durations (1, 3, 5, 7, and 10 min), resulting in different sizes of native fat globules (249.5, 221.5, 222.6, 207.5, and 244.8 nm, respectively). The results indicate that viscosity increases as fat globule size decreases, with slight effect on zeta potential. NanoFoamer was identified as the optimal method providing the highest between foamability and stability (p < 0.05). Notably, foaming performance decreases after 7 min of sonication, highlighting the importance of selecting an appropriate frothing method to achieve the desired foam characteristics. Comparisons with non-ultrasonicated milk suggest that ultrasonication duration not only influences foamability by reducing fat globule size but also enhances foam stability through alterations in the fat globule sizes. Analysis of the foam structure revealed that smaller fat globules initially produce smaller, more numerous air bubbles with polyhedral shapes and well-defined lamellae. However, excessive reduction in fat globule size destabilizes the foam due to competitive protein adsorption and altered membrane composition, resulting in larger, less stable bubbles over time. Exploring ultrasonication times to enhances quality of milk and foam properties, offering significant benefits for dairy processing, product innovation and customer satisfaction.

Investigations into the foaming behavior of ABS by means of granule extrusion using expandable microspheres

The following investigations address the production of syntactic polymer foams using thermally expanding microspheres (TEM) in the extrusion process. A process model for the foaming behavior of acrylnitrile butadiene styrene (ABS) with thermally expanding microspheres as masterbatch is derived by varying the two basic process parameters extruder rotational speed and extruder temperature in a test matrix with five stages each. The investigations include the production of unfoamed and foamed strands and the measurement of process relevant properties and parameters such as extrusion mass flow, relative density of the structures, die-swelling and the characterization of the generated foam structures. The achievable density reduction is within the order of 50%. The process model resulting from the investigations allows the production of homogeneously foamed strands. These results are intended to serve as the basis for a transfer to the Large Scale Additive Manufacturing (LSAM) process.

One-step green synthesis of multi-morphological carbon nanotube forests for superior microwave absorption and electrocatalysis

Porous carbon materials with multiscale distinctive morphologies hold significant promise in electromagnetic wave stealth/protection and catalysis; however, formidable challenges are highly verbose and resource/time-consuming fabrication processes. Here, we report a one-step solvent/template-free self-expanding carbonization strategy for rapidly fabricating porous carbon foams (Ni/CNT) with zero-dimensional (0D) nanoparticles, one-dimensional (1D) nanotube forests, and three-dimensional (3D) hollow microvesicles. Owing to the multi-morphological structure and low-density feature, the resulting porous carbon foam Ni/CNT-800 achieves a minimum reflection loss of −56.48 dB and an effective bandwidth of 5.44 GHz at a low filler loading of only 9 wt%. Moreover, altering the electronic structure and surface chemistry of carbon foam by phosphorus doping enables a highly reduced durable overpotential (η) of 275 mV for oxygen evolution reaction. This work emphasizes a straightforward strategy for the facile design and efficient fabrication of carbon-based materials with unique multiscale porous morphologies, customizable functions, and various applications.

Enhancement of an intumescent fire shield paint from the nanotube rutile mineral for the fire performance of steel structures

Building and construction fire safety is an important issue for the protection of people and property. Research investigates nano-rutile minerals' synergistic role in intumescent fire shield paint (IFSP). A synergistic ingredient was introduced to intumescent fire shield paint to evaluate its impact on char morphology, fire protection test, fire propagation test, and compare it with current market products. A hydrothermal process was used to create a rutile mineral, with various techniques used to describe its structure, size, and composition. Intumescent char was found in a furnace using FESEM and X-ray fluorescence. The results showed that rutile minerals contain a rutile phase and a nanotube structure. The surface of the sample IFSP A's char showed layer and foam structures with homogenous voids during a fire test, indicating a high porosity structure. Large holes and recurring gaps were observed in the char of the IFSP B, C, and D. Sample IFSP A took more time at the structural critical temperature (about 550 o C) than other intumescent fire shield paint samples, making it a barrier layer that effectively shields the metal substrate from heat. The intumescent char residue had the highest C/O ratio of 0.57, indicating the best char yield degree and anti-oxidation abilities. The IFSP A had a phosphorous content of 36.2%, which could combine with phosphorus and TiO2 to form a ceramic barrier. The increased TiO2 in IFSP A suggests that char layers with TiO2 may still contain strong ceramic structures and function as effective thermal protection layers.

Supercritical N2 induced sandwich type lightweight and strong PP/CF foams with excellent electromagnetic shielding properties

The tremendous advances in communication technology and the explosion of electronic products led to an intensification of electromagnetic pollution, yet the efficient development of lightweight, high-strength fiber composite foams with excellent electromagnetic shielding properties was still a great challenge. Herein, this study, inspired by the sandwich structure, proposes a green foaming method with supercritical N2 to prepare a multilayered structure of carbon fiber reinforced polypropylene (PP/CF) foams, with a dense cellular structure in the core layer and a solid layer in the surface layer. The incorporation of CF improves the crystallization and rheological behavior of PP/CF, which guarantees a fine, dense and uniform cellular structure. This inner fine cellular structure and the solid layer on the surface contribute to the excellent mechanical properties. PP/30 %CF foam with a 1 mm mold opening distance displays an enhancement of 189.9 % in tensile strength and 196.3 % in flexural strength compared to pure PP. This also indicates more lightweight, high-strength and high-rigidity microcellular parts was obtained with less raw materials. Moreover, the formation of CF conductive network and internal foam structure contribute to excellent electromagnetic interference (EMI) shielding performance. The PP/CF composite foams maintain a level of EMI shielding performance greater than 30 dB despite the higher mold opening distance. Specifically, the PP/30 %CF foams at opening distance of 5 mm was enhanced to 58.3 dB·cm3/g with an improvement of 76.7 %. This implies that lightweight microcellular parts with both excellent strength and EMI shielding properties can be prepared, which enables PP/CF foams to possess a wide range of applications in various fields.

Current commercial reactive and polymeric flame retardants in polyurethane foams

Polyurethane foams encompass a wide range of materials which, depending on the foam structure, chemical composition, and presence of flame retardants, can be very combustible or fire resistant. The first commercial flame retardants for polyurethane foams were developed 60 years ago with a focus on fire retardant efficiency. These legacy flame retardants are relatively small volatile molecules that can migrate from the foam to the environment. Now the flame retardant industry has been changing with a focus on reactive or polymeric flame retardants. This article gives a short overview of these new commercial flame retardants.

Porosity gradient control of 3D-printed hybrid foam structures

Porosity gradient control of 3D-printed hybrid foam structures

Shape Memory Polymer Foam Based on Nanofibrillar Composites of Polylactide/Polyamide.

This paper presents the novel development of a shape memory polymer foam based on polymer-polymer nanocomposites. Herein, polylactide (PLA)/biosourced polyamide (PA) foams are fabricated by in situ fibrillation of polymer blends and a subsequent supercritical CO2 foaming technique. In this system, PLA serves as a shape memory polymer to endow this foam with a shape memory effect (SME), and in situ generated PA nanofibers are employed to reinforce the PLA cell walls and provide an additional permanent phase. A concentration of PA, 5 wt.%, was chosen to form an entangled nanofibrillar network. Foams of PLA/PA nanoblends with the same content of constituents were fabricated to reveal the effect of minor phase morphology on the cell structure and shape memory behavior of polymer foams. Profiting from the reinforcing effect of PA nanofibers, the PLA/PA nanocomposite foam exhibits smaller foam cells, a narrower cell size distribution and a comparable cell concentration than the PLA/PA nanoblend foam. In addition, PA nanofibers, unlike PA nanodroplets, favor the shape fixation ratio and recovery ratio and shorten the shape recovery time.

Preparation of antishrinkage and high strength poly(butylene adipate-co-terephthalate) microcellular foam via in situ fibrillation of polylactide

High-expansion-ratio microcellular poly (butylene adipate-co-terephthalate) (PBAT) foams exhibit severe shrinkage, which hinders their industrial applications. This study provides a facile method to prepare low-shrinkage, high-compressive-strength and high-resilience PBAT foam. CEPBAT/PLA blends (CE = chain extender, PLA = polylactide) were prepared via in situ fibrillation to obtain CEPBAT/PLA-S (CEPBAT/PLA containing PLA spherical phase) foam containing PLA spheres and CEPBAT/PLA-F (CEPBAT/PLA containing PLA fiber phase) foam with PLA nanofibers. The effects of the PLA nanofibers and spheres on the antishrinkage and compression strength of the PBAT foams were studied. The PLA nanofibers exhibited a higher specific surface area than the PLA spheres and a supporting network structure for the PBAT foam, thereby improving its melt strength. As a result, the antishrinkage performance and compression strength of CEPBAT/PLA-F improved by 100 % and 180 %, respectively, compared with the neat PBAT foam after aging for 144 h. However, the permanent deformation of CEPBAT/PLA-F increased only slightly after ten compression cycles. CEPBAT/PLA-F showed better antishrinkage performance, compression strength, and resilience than CEPBAT/PLA-S owing to the interface effect of the PLA nanofibers, whose nanolinear network structure provides enhancement and a larger deformation range under pressure to reduce plastic deformation.

Process Intensification via Structured Catalysts: Production of Sugar Alcohols

AbstractWith the aid of structured catalysts and reactors, such as monoliths, solid foams, and 3D printed structures, the limitations of conventional slurry and packed‐bed reactors can be surmounted. Multiphase mathematical models were presented for solid foam structures and the models were verified for the hydrogenation of arabinose, galactose, and xylose to the corresponding sugar alcohols. High product selectivities were obtained in batch and continuous experiments. Three kinetic models were considered: a competitive adsorption model, a semi‐competitive adsorption model as well as a non‐competitive adsorption model for sugar monomers and hydrogen. The models gave a good reproduction of the data, but the semi‐competitive adsorption model was the most plausible one because of the size difference between adsorbed sugar and hydrogen molecules.

Study on foaming behavior of block copolymer/inorganic particles co‐construction of toughened epoxy resin foams

AbstractLow toughness and brittleness limit its application range of thermosetting epoxy resin (EP) based foams. In current research, inorganic particles are commonly utilized as heterogeneous nucleating agents to enhance foaming quality and EP toughness. However, the increasing inorganic particle content usually leads to particle agglomeration, which negatively impacts foaming quality and reduces EP performance. Block copolymers, which appear as liquid to effectively mitigate agglomeration, are employed as toughening materials for EP. In this study, a small number of modified calcium silicate particles (MCS) were used as anchor points to induce the distribution of block copolymers (P‐F68) to improve EP toughness and effectively enhance cell nucleation, thus, EP/MCS/P‐F68 foams performance was improved. The research results showed that EP foams obtained excellent cell structure and very small foam density (0.256 g/cm3) at the P‐F68 content of 10 wt%. The continuous increase of P‐F68 content would lead to the thickening of cell wall and the increase of cell size. Simultaneously, the core‐shell structure formed by P‐F68 in EP effectively enhanced the toughness of EP foams and mitigated its brittleness, offering crucial theoretical guidance for toughening and regulating the cell structure of EP foams.

CO2 foam structure and displacement dynamics in a Hele–Shaw cell

The substitution of CO2 gas with CO2 foam for improved mobility control has recently attracted research attentions in enhanced oil recovery (EOR) as well as aquifer and soil remediation. However, the interplay between CO2 foam properties and oil displacement remains less investigated. In this work, using clear visualizations, we systematically investigate the dynamic advection-dominated foam morphology, its corresponding viscosity, and the efficiency and dynamics of oil displacement process by CO2 foam in a Hele–Shaw cell under the effects of gas ratio (Rg), fluid injection rates (Qt), and surfactant type. Clear visualization enables particle image velocimetry to calculate actual, rather than nominal, foam velocity that significantly affects the estimated foam viscosity. Our results demonstrate that at elevated gas ratios under constant total injection rate, larger and more uniform bubbles with less number density and greater interfacial area are obtained. Increasing the injection rates leads to finer foam texture at a constant gas ratio. Different foam structures have an impact on the foam viscosity, with a general increasing trend of viscosity for larger bubbles as Rg increases from 0.5 to 0.85. The higher the foam viscosity, the more stable displacement interfaces with less viscous fingers are observed, leading to improved sweeping rates. The green surfactants (saponin + Cellulose NanoFibers) provide foams with higher viscosity and, thus, more stable displacement interfaces. These findings highlight the important effect of Rg–dependent foam structure on its viscosity, which in turn is crucial for controlling the mobility of CO2 foam to maximize oil recovery rate during EOR processes.

Utilization of thermoplastic resin as foamed asphalt modifier in cold recycled mixtures

The utilization of foamed virgin asphalt in cold recycled mixtures results in insufficient bonding strength between aggregates, leading to rapid deterioration to the recycled asphalt pavement. This ultimately causes inefficient clean production and increased carbon emissions. The foaming performance of thermoplastic resin modified asphalt (TRA) under different foaming conditions was analyzed. Micro-scale chemical and physical tests were utilized to discover the foaming mechanism of TRA. The road performance of cold recycled mixtures with foamed TRA was evaluated through splitting, rutting and fatigue tests. The results showed that the increase in the TRA polar functional group index led to an increase in its surface tension, thus limiting its expansion capacity. However, the increase in the specific heat capacity of TRA indicated that it preserves a low viscosity level essential for its foaming efficacy post-ejection from the foaming machine, thereby enhancing its half-life. Furthermore, the dynamic viscosity of the TRA with an 8% thermoplastic resin dosage exceeded 40000 Pa s at 60 °C, meeting the specification requirements for high viscosity asphalt, while exhibiting a notably lower viscosity of only 120 mPa s at the foaming temperature of 170 °C. The observed low viscosity of the asphalt is anticipated to favorably enhance the formation of a stable foam structure. The mechanical properties and overall road performance of the cold recycled mixture with foamed TRA were significantly enhanced, especially in terms of moisture damage resistance and low-temperature crack resistance. The purpose of this paper is to serve as a valuable reference for investigating the mechanism of modified asphalt foaming and to enhance the efficiency of cold recycled pavement regeneration processes.

Density gradient structure foams prepared by novel two-step foaming strategy: Performance, simulation and optimization

Functional gradient foam materials play a crucial role in meeting the diverse performance and functionality requirements of modern engineering. Density gradients enable the distribution of mechanical, dielectric, and optical properties within materials, exhibiting a gradient representation. However, creating density gradients within foams poses a significant challenge, especially for semi-crystalline polymers. The paper proposed a novel two-step foaming method for preparing polypropylene (PP) foams with density gradient structure (DGS). Initially, a pre-foaming process was conducted to prepare PP pre-foams with uniform structure (US) at low temperatures, followed by a secondary foaming process on partially saturated PP pre-foams to fabricate PP DGS foams. By adjusting the duration of partial saturation time, PP foams with various DGS can be achieved. Compared with the commonly used one-step foaming method and uniform foaming method in the literature, the DGS foams prepared by the two-step foaming method exhibit not only a significant enhancement in mechanical property but also achieve the lowest thermal conductivity, while maintaining comparable and outstanding sound insulation performance. Finally, a comprehensive evaluation model using COMSOL Multiphysics was developed for the DGS foams, providing insights for optimizing foam performance through process enhancements.

Effect of Zn on the Structure and Mechanical Properties of Mg-Ca Foams

Effect of Zn on the Structure and Mechanical Properties of Mg-Ca Foams

Advanced CuO-Ag2WO4-Ni nanophotocatalyst in the synthesis of some chromeno[4,3-b]chromenes as effective lung cancer drugs

A novel heterogeneous nanocomposite CuO-Ag2WO4-Ni embedded within a foam matrix has been biosynthesized from Cressa Cretica leaves extract and comprehensively characterized using various techniques, including FT-IR, XRD, EDX, FE-SEM, DRS, TEM, and BET. This innovative nanocomposite demonstrates exceptional photocatalytic efficiency in the synthesis of some chromeno[4,3-b]chromenes, which have shown promise as effective medications in lung cancer treatment. The photocatalytic reactions are facilitated under a green laser light using ethanol as solvent. Compared to individual components of CuO-Ag2WO4-Ni, the nanocomposite exhibited superior performance in terms of light absorption, surface tunability, charge carrier generation, and stability. Noteworthy advantages of this nanocomposite include high reusability and ease of separation from the reaction mixture, thereby ensuring strong reproducibility. The foam structure plays a pivotal role in enhancing photocatalytic activity due to its high surface area and distinctive morphology. Mechanistic studies indicate that the generated holes and electrons effectively drive selective oxidation and reduction reactions, providing a reliable method for synthesizing a range of chromenes. The CuO-Ag2WO4-Ni exhibited remarkable stability across multiple catalytic cycles, with minimal morphological degradation and low leaching of the catalytic species, ensuring long-term effectiveness and cost efficiency for industrial applications. At the final part of this study, the MTT experiment was planned to investigate cytotoxicity of CuO-Ag2WO4-Ni on A549 lung cancer cells. This study affirmed that the performed nanomaterial has effective toxicity agaings the selected cell line.

Achieving high impact toughness in injection-molded SMMA foams via the synergistic effects of cell size and SBS

Optimizing the cellular structure of polymeric foams has long been considered one of the most economical and effective methods for enhancing their impact properties. However, the relationship between cell size and impact strength has rarely been systematically studied. In this study, styrene-butadiene-styrene (SBS) was used as a toughening agent to improve the toughness of Poly(styrene-co-methyl methacrylate) (SMMA). The expansion ratio of pure SMMA foams and their blended counterparts were controlled by fixing the mold-opening distance, while the cell size was adjusted by changing the blowing agent content and packing time. Notably, the impact strength of the optimized SMMA/SBS blend foam reached 15.5 kJ/m2, representing a significant increase of 1400 % compared to that of the pure SMMA foam. In addition, the impact strength of pure SMMA foams did not change significantly as the cell size increased from 29.7 μm to 278.9 μm. However, for SMMA/SBS blend foams, an optimal cell range (100−150 μm) was identified, where the impact strength was approximately twice that of foams with smaller cell sizes (1−25 μm). Then, examination of the impact-fractured surfaces at different cell sizes revealed that the synergistic effects of an appropriate cell size (100−150 μm) and the presence of SBS particles promoted craze initiation and expanded the plastic deformation area during crack initiation, leading toenhanced impact toughness in the blended foam. This work not only systematically elucidates the relationship between cell size and impact strength but also provides new insights into the synergistic effects of rubber particle and cell size on the mechanical properties of polymeric foams.

Green synthesis of nano silver-modified date syrup 3D graphene for adsorptive removal of heavy metals from wastewater and its antibacterial efficiency

Abstract Many researchers are focusing on the eco-friendly and cost-effective green synthesis of materials for removing heavy metals from wastewater using materials made from natural sources. In this research, date syrup was used as a rich carbon source while potassium chloride particles were used as a substrate. Green synthesized silver nanoparticles modified the graphene foam to enhance its heavy metal removal and antibacterial efficiency. The morphology and structure of the graphene foam were examined using scanning electron microscopy and Raman spectroscopy. The Brunauer-Emmett-Teller method examines textural features such as surface area, pore volume and diameter. The study focused on evaluating the efficiency of removing heavy metals including cadmium, lead, zinc, and chromium from water. The results indicated that the date syrup graphene foam has high heavy metal removal efficiency despite the short contact time, especially for Cd2+ and Pb2+, with removal efficiencies of 68% and 39%, respectively. It shows a relatively lower efficacy for Zn2+ and Cr2+, with removal efficiencies of 10% and 27%, respectively. The addition of silver nanoparticles greatly improved the removal efficiency of Cd2+ (75%), Zn+2 (22%), and Cr2+ (33%). Moreover, the antibacterial efficacy test showed significant improvement after the nanosilver modification to reach a 100% bacterial-killing rate.