Foaming Process Research Articles

Preparation and characterisation of novel foamed porous glass-ceramics on the basis of bioglass 45S5

This study determines the possibilities of synthesis of porous glass-ceramic materials based on Bioglass 45S5 using different methods obtained porous materials. In this work used foaming with sintering method for the set: bioglass 45S5 + glass cullet (CRT) + glass water (WG) and method sintering with forming-pore agents for the: bioglass + glass water (WG) + dried banana peels. The sets were melting and the next step sintering process. The resulting foams were examined and analysed for structural, microstructural, and physical properties. The research allowed for a quantitative and qualitative assessment of the foaming process generated by the presence of WG with the addition of CRT cullet and WG together with dried banana peel. It was found that WG with the addition of CRT cullet was a solution that offered the possibility of obtaining a large number of evenly distributed pores and higher total porosity compared the second set (WG + banana peel). Moreover, the use of CRT cullet and banana peel allowed the introduction of biogenic elements such as strontium, barium and potassium into the obtained materials, which have a positive effect on the stimulation of osteogenesis.

Impact of foam-mat drying conditions of “Gấc” aril on drying rate and bioactive compounds: Optimization by novel statistical approaches

This study was conducted to optimize the foam-mat drying conditions to maximize quality [β-carotene and total polyphenol content (TPC)] and drying rate of “Gấc” aril powder by using two novel statistical techniques as Response Surface Methodology (RSM) and Artificial Neural Network (ANN) couple with Genetic Algorithm (GA). During production process, level of egg albumin (EA) used for foaming process and drying temperature mainly influenced the drying rate and content of antioxidant compounds in powder. ANN model of 3–10-3 showed more accuracy and faster prediction capacity than RSM model did. ANN-GA model predicted the optimal conditions to be 13.31 % EA, 0.26 % xanthan gum and drying temperature of 73.1 °C, with the drying rate of 1.89 g-water/g-dry matter/min, β-carotene content of 395.88 μg/g, TPC of 1.68 mgGAE/g. These results confirmed the suitability and promising of foam-mat drying for “Gấc” aril powder production, to be producing food ingredient containing highly bioactive compounds.

Facile preparation of solid gelatin foams by a water-lean batch foaming process.

Existing polystyrenic and polyolefinic packaging foams are non-biodegradable, and persist in the environment for hundreds of years. Gelatin foams are an interesting alternative, given their biodegradability, biocompatibility, solution-based processability, low cost, and non-toxicity. However, current methods for preparing gelatin foams, such as freeze-drying, microfluidic foaming, and batch foaming, are not suitable for high-volume production. In this context, we report the preparation of solid gelatin foams by a water-lean batch foaming process that involves simply mixing bloomed gelatin with a blowing agent, selected from inorganic bicarbonates and cyclic organic carbonates, and heating the resulting mixture in an open mold. The foaming was primarily attributed to CO2 produced by blowing agents, while the transformation from discrete gelatin granules to a continuous foam was facilitated by the melting, flowing, and fusion of the bloomed gelatin granules into a homogeneous mass upon heating. This process is simple, inexpensive, sustainable, and versatile, making it highly suitable for high-volume production of biodegradable foams, particularly for use in loose-fill packaging applications.

Foamed calcium sulfoaluminate cement with controlled porous network for daily or seasonal heat storage in ettringite

Calcium sulfoaluminate (CSA) cement-based materials have high ettringite content enables heat storage, enhancing the thermal inertia of buildings. This study aims to optimize the porous network of foamed CSA material in terms of porosity, permeability and mechanical strength so that they can be effective in building applications as supporting structures with heat storage capacity. To achieve these goals, a foaming process method using hydrogen peroxide (H2O2) and surfactant was used to control the porous network. The H2O2 and surfactant contents varied from 0.5% to 1.2% and 0.01% to 0.05%, respectively, and generated a wide range of material densities from 589 to 1184 kg/m3 - and hence a wide range of properties in terms of porosity (43 - 70%), permeability (2.6 10-13 - 7.1 10-12 m2) and compressive strength (0.8 -9.4 MPa). Then, an abacus correlating material properties, found by surface fitting, linking porosity, gas permeability and compressive strength, allowed the material to be optimized in accordance with the needs of each building application. The CSA paste consisting of 1% H2O2 and 0.03% surfactant, with 66% porosity, 4.1 10-12 m2 permeability, and 1.8 MPa compressive strength, was the optimal mix-design for solar storage box applications (for short-term storage). The CSA paste consisting of 0.5% H2O2 and 0.01% surfactant, with 43% porosity, 5.6 10-13 m2 permeability, 9.4 MPa compressive strength, appeared to be optimal for self-supporting wall storing solar heat (long-term storage).

Hierarchically structured composite with 3D interlocking architecture for multi-band defense

The development of high-performance electromagnetic wave absorbing (EMWA) materials for radar stealth applications poses a persistent challenge, particularly when addressing the demanding requirements of diverse frequency bands in increasingly complex and dynamic environments. Precisely tailoring the microstructure of these materials presents a powerful strategy for achieving multifunctional integration and unlocking new possibilities for practical applications. In this work, we present a novel hierarchically structured composite foam with 3D interlocking architecture, fabricated through a straightforward foaming and calcination process. It features a unique dual three-dimensional continuous phase structure that facilitates the formation of an efficient conductive network, promoting free electron mobility and enhancing polarization loss. The composite demonstrates exceptional EMWA performance, exhibiting a wide effective absorption bandwidth (EAB) of 6.1 GHz and a remarkable absorption intensity of -63.2 dB along with RCS reduction value up to 28.7 dB m2. Furthermore, the composite illustrated strong infrared stealth properties and efficient photothermal conversion abilities. When heated to 56°C, its surface temperature only increased by 4°C in 10 minutes. Under direct sunlight, its surface temperature rose from 21°C to 71°C in just 6 minutes. Lightweight, flexible, and adaptable to diverse environmental conditions, the HCC composite holds significant promise as a multi-spectrum defense material. Its versatility makes it an ideal candidate for integration into a wide range of equipment, clothing, and wearable technologies, offering advanced capabilities for radar, infrared, and visible light signature reduction.

Aliphatic-acid coating and nano chitosan nucleator synergistically regulate the performance of PMMA “bone-Locking” foam dressing used for emergency fixation of clavicle fracture

Clavicle emergency fixation can prevent fractured end from piercing heart and lung organs, which is crucial for wounded life. Clavicle with complex structure, great individual differences, and adjacent to important organs, which places high-requirements on performance of fixation materials. Developing advanced clavicle fixation material is a prominent hot-topic in the field of emergency-engineering. We prepared a Polymethyl-methacrylate (PMMA) “bone-Locking” foam dressing via novel polymer foaming process. Innovatively used aliphatic-acid and bio-polar macromolecule nanoparticles to adjust structure in non-traditional self-curing polymer melts to achieve high-performance. Stearic acid coating was prepared on the surface of foaming agent can delay nucleation period, increasing the initial Polymer-Bubble interface viscosity and effectively retard nuclei growth and escape. Nano-chitosan was compounded synchronously to induce in-situ nucleation and construct polar hydrogen bonds between chains, improve the crystallinity of PMMA matrix, reduce the relaxation ability of PMMA molecular chains and increase the interface viscosity again to inhibit nuclei growth and escape, realizing spontaneous coordination between viscosity and the bubble holes formation process. Obtained high-performance foam with uniform and regular bubble holes structure eventually. More, Dynamic Dual-Variable Field Bubble-Growth Dynamics was proposed, revealing the Bubble-Growth behavior synergistic driven by Viscosity and Temperature theoretically, providing reference for improving theory in polymer foaming field. Prepared foam dressing can be directly and softly coated on clavicle and spontaneously conform to the contour of clavicle with remarkable precision, then quickly (3.5 min) curing into a lightweight (0.57 g/cm3), high-strength (40.5 MPa), breathable (224.73 mm/s) “Armor”, showing great application value in wound emergency engineering. The developed foaming method and theory provide technical and theoretical value for polymer foaming system. The foam dressing provides a promising new scheme for fixing various wound sites and ensuring the life safety of the wounded at the emergency scene.

Biopolymer foams composed of hydroxypropyl cellulose: Fabrication, aqueous stability, and mechanical integrity

We describe the fabrication of biopolymer foams formed from aqueous solutions of hydroxypropyl cellulose, whereby freezing-induced phase-separation and solvent removal yields robust foam structures that are elastic in air and when wet, and that are stable to repeated compression when fully saturated with water. Through mechanisms of phase-separation, pore formation, and covalent crosslinking, we discovered effective methods to prepare microporous HPC foams that resist gelation even when exposed to water for long time frames (at least months). Employing multifunctional carboxylic acid crosslinkers allowed the foams to maintain their integrity when dry or wet, while the presence of α-cellulose as an additive further augmented their mechanical integrity and provided a means to adjust elasticity. The amount of crosslinker employed in the foaming process significantly impacted foam stability and water uptake, while polymeric crosslinkers enabled insertion of sulfobetaine zwitterionic moieties into the foams. Notably, the thermal transition characteristic of HPC solutions and gels proved operative in foam form, as seen in release of water from a saturated HPC foam using a combination of compressive and thermal mechanisms.

Viscoelastic Polyurethane Foam Biocomposites with Enhanced Flame Retardancy.

The growing demand for viscoelastic polyurethane foams creates a need for new sustainable raw materials that support cost-effective production while maintaining the desired material performance and fire safety standards. In this regard, our study aimed to develop viscoelastic polyurethane foam composites with reduced flammability and a high proportion of renewable raw materials. To achieve this, blackcurrant pomace, expandable graphite and a third-generation blowing agent were introduced to a viscoelastic polyurethane foam composition containing a reactive flame retardant in the formulation. The effects of the incorporated additives on the foaming process, flammability, chemical structure, cellular structure, thermal properties and physico-mechanical properties of the composites were determined. The results showed that the viscoelastic foam composite containing 30 php of blackcurrant pomace and 15 php of expandable graphite had a pHRRmax 52% lower than that of the reference material. The additional use of a blowing agent enhanced the flame-retardant effect of the materials, resulting in a 67% reduction in pHRRmax of the composite compared to the reference material. Moreover, the developed biocomposites exhibited promising limiting oxygen index values of 26-28%, compared to the 21% shown for the reference sample. Consequently, the best-performing biocomposites achieved the V-0 flammability rating according to the UL-94 standard. This study's results indicate the composites' high application potential due to their reduced flammability and the materials' desirable physical and mechanical properties.

Advancements in Bamboo-Based Cushioning Material Manufacturing

The study focuses on producing cushioning packaging material from bamboo fibers. The effects of varying the surface treatment duration and the proportions of foaming agents, adhesives, plasticizers, cross-linking agents, and other components were analyzed in terms of foam density, foaming rate, elasticity, and bubble size. The optimal reagents and the ideal ratios for the different components were identified. The parameters for the foaming process were determined based on a high-efficiency, eco-friendly foaming mechanism. Impact testing was conducted to obtain curves for maximum acceleration versus static stress, dynamic stress versus strain, and dynamic buffering factor versus stress. The study examined the dynamic buffering performance as a function of drop height and compared it to other cushioning materials. The findings indicate that at a height of 450 mm, the bamboo pulp product exhibited a lower peak acceleration value than EPE and EPS in the stress range of 2.8-5.4 kPa, indicating superior cushioning performance under these conditions.

Preparation and performance study of microporous magnetorheological elastomer polishing pad

Chemical mechanical polishing (CMP) based on magnetorheological elastomer (MRE) polishing pad can achieve flexible mechanical removal by regulating the magneto-mechanical properties of the MRE polishing pad. In this study, a microporous MRE polishing pad was prepared using a solid-state microcellular foaming process, and the effects of foaming temperature, curing magnetic field strength, and thermal expansion microspheres (TEM) addition content on the properties of the microporous MRE were investigated. The results indicate that a foaming temperature of 115°C produces better foaming effects, an increase in curing magnetic field strength significantly enlarges the size of micropores in the MRE, and with an increase in microsphere content, the porosity of the MRE increases. Polishing single crystal SiC with MRE polishing pads containing different TEM contents revealed that a TEM content of 1 phr had the highest material removal rate (MRR) of 1252 nm/h and the lowest surface roughness of Ra 1.28 nm.

Visualization Experiments of Nanoparticle-Surfactant-Stabilized Foam Flooding in Cores with Different Permeabilities by NMR.

Nanoparticle-stabilized foams can overcome the problem that conventional foams are easy to defoam in complex reservoirs, thereby losing foam function and seriously affecting foam profile control and flooding effect. However, the oil displacement characteristics and effects of the nanoparticle-stabilized foam in cores with different permeabilities directly determine its application prospects. The nuclear magnetic resonance (NMR) visualization technology was combined with the traditional foam displacement method in this paper, with the nanoparticle-stabilized foam system and oil as the displacement medium and the displaced medium, respectively, and the core as the carrier to physically simulate the process of the nanoparticle-stabilized foam flooding oil. The oil displacement characteristics of the foam are visually observed by the NMR images, and the average size change of the pores where the fluid is located and the quality change of the fluid in the core are reflected by the T 2 spectrum to further study the visual profile control and displacement characteristics of the nanoparticle-stabilized foam in the core with different permeabilities.

Numerical simulation of bubble rising behavior in a tannin-based foaming precursor resin

A two-dimensional volume of fluid (VOF) model was developed to simulate the deformation of the bubble, the end speed of bubble rise, the distance of bubble rise and the movement trajectory in different initial conditions of tannin-based foaming precursor resin. In this study, bubble rising and coalescence characteristics are connected with parameters of the resin, especially viscosity, surface tension, the initial radius and location of the bubble also matter. The result shows that rising velocity of the bubble decreased as the viscosity increased, and at the same time, the flow rate of the bubble was lower. In addition, with the increase in surface tension, the ability of the bubble to change shape was impeded, whereas when the bubble radius increased, the rising velocity of the bubble was faster. The floating behavior of parallel double bubbles and coaxial double bubbles in resin was simulated. It was found that the distance had important effects on their coalescence behavior. For parallel doubles, the motion process is symmetric, because of their vortices, the bubbles will move away from each other, and their motion properties depend on the relative position of the bubbles which is crucial for the bubble merger. For coaxial double bubbles, the closer the distance between the two bubbles is, the faster the fusion speed will be. When the distance is fixed, the larger the radius is, the shorter the fusion time will be, which proves that there are differences in the growth rate of bubbles during the foaming process.

Effects of BET Surface Area and Silica Hydrophobicity on Natural Rubber Latex Foam Using the Dunlop Process.

To reinforce natural rubber latex foam, fumed silica and precipitated silica are introduced into latex foam prepared using the Dunlop process as fillers. Four types of silica, including Aerosil 200 (hydrophilic fumed silica), Reolosil DM30, Aerosil R972 (hydrophobic fumed silica), and Sipernat 22S (precipitated silica), are investigated. The latex foam with added silica presents better mechanical and physical properties compared with the non-silica foam. The hydrophobic nature of the fumed silica has better dispersion in natural rubber compared to hydrophilic silica. The specific surface area of silica particles (BET) also significantly influences the properties of the latex foam, with larger specific surface areas resulting in better dispersity in the rubber matrix. It was observed that exceeding 2 phr led to difficulties in the foaming process (bulking). Furthermore, higher loading of silica also affected the rubber foam, resulting in an increased shrinkage percentage, hardness, compression set, and crosslink density. The crosslink density increased from 11.0 ± 0.2 mol/cm3 for non-silica rubber to 11.6 ± 0.6 mol/cm3 for Reolosil DM30. Reolosil DM30 also had the highest hardness, with a hardness value of 52.0 ± 2.1 IRHD, compared to 45.0 ± 1.3 IRHD for non-silica foam rubber and 48 ± 2.4 IRHD for hydrophilic fumed silica Aerosil 200. Hydrophobic fumed silica also had the highest ability to return to its original shape, with a recovery percentage of 88.0% ± 3.5% compared to the other fumed silica. Overall, hydrophobic fumed silica had better results than hydrophilic silica in both fumed and precipitated silica.

Evaluation of critical process parameter on the production of sustainable bead foams based on polylactic acid

A commercial grade of polylactic acid (PLA) was foamed without using modifiers to obtain expanded polylactic acid bead foams (EPLA). Typically, the foaming process is influenced by both melt properties and crystallization behavior. While factors like water temperature, die structure, and die temperature are known to have effects on bead foam processing, these aspects have not been thoroughly explored in the context of PLA bead foam production. To address this gap, a comprehensive investigation was undertaken, varying water temperature, die structure, and die temperature to discern their impact on PLA processing behavior. Results revealed that water temperature significantly influenced foaming behavior, particularly at elevated temperatures near the glass transition of PLA. Additionally, the study demonstrated that die size wielded a notable influence on all foam properties, dictating process limits. With the selection of an appropriate die size, the die temperature could be manipulated within the range of 190°C to 160°C, revealing a substantial impact on the overall process. Remarkably, the lowest densities achieved were 63 kg/m3 with an average cell size of 36 µm and a cell density of 1.1*107 cells per cm3.

Optimizing Ammonium Polyphosphate-Acrylic Intumescent Coatings with Sustainable Fillers for Naval Fire Safety.

This study explores the potential of natural and recycled materials to enhance the fire behavior of eco-friendly intumescent coatings, compared to a traditional ammonium polyphosphate (APP)-based one. To achieve this, cork, halloysite clay, and recycled glass were evaluated as natural fillers and sustainable components within the coating formulation. The aim was to reduce the reliance on synthetic materials and minimize the environmental impact while maintaining fire performance. Fire exposure tests were conducted to assess the in situ char formation and its relationship to the heat source and char foaming process. The results highlighted that all functionalized coatings exhibited suitable intumescent behavior. The best results were evidenced by cork-filled coating that evidenced an intumescent capacity about 40% higher than the traditional ammonium polyphosphate (APP)-based one. This provided valuable insights into the coating's real-time response to fire, determining its suitability for various fire-resistant applications.

Effect of occupational exposure to ADCA on the incidence of allergic respiratory reactions - a literature review

1,1'-azodi(formamide) (ADCA) is widely used as a blowing agent, a chemical substance designed to induce foaming processes. In Poland, ADCA is manufactured by a company specializing in the production of polyethylene foam bags and laminates used in various industries including home appliances, electronics, construction, furniture, automotive, and sports and leisure. The mechanism of action of ADCA involves thermal decomposition, resulting in nitrogen, carbon monoxide, as well as ammonia and carbon dioxide as the main gaseous decomposition products. These penetrate the polymer matrix, contributing to expansion and foaming properties. Most studies evaluating the relationship between occupational exposure and the development of allergic respiratory diseases focus on workers involved in ADCA production or its use as a blowing agent in plastics. The objective is to assess the respiratory sensitizing effects of ADCA in humans due to occupational exposure, based on literature data. The presented data confirm that long-term occupational exposure to ADCA can lead to persistent bronchial hyperreactivity symptoms in workers. 1,1'-azodi(formamide) can induce occupational asthma, with initial symptoms including nasal congestion, conjunctivitis, wheezing, and cough. Subsequently, symptoms such as chest tightness, dyspnea, and nocturnal cough attacks may appear, with a latency period of several years observed before symptom onset. In some cases, symptom progression was noted with continued ADCA exposure, while in others, exposure was discontinued after initial symptoms, preventing observation of symptom exacerbation. Prior exposure to allergens, such as working in bakeries, appears to accelerate symptom onset. Improvement in allergy symptoms has been noted during weekend breaks from work. There is no safe concentration identified for ADCA that would not result in adverse health effects for workers. A concentration of 0.036 mg/m3 is considered the lowest observed adverse effect concentration, causing critical reduction in lung spirometric parameters. Med Pr Work Health Saf. 2024;75(5).

Ameliorating the comprehensive performance of rigid polyurethane foam insulating materials by green cork for building energy conservation

Biomass-modified polyurethane (PU) foam materials are vital to promote the sustainable development, but the balance between their mechanical strength and thermal insulating ability remains a challenge compared to the petrochemical-based PU foams. Herein, an appropriate amount of cork is introduced to fabricate PU composite foams with good thermal insulating performance and mechanical strength. The added cork could act as a nucleating agent during the foaming process, further tailor the foam structure and enhance their comprehensive performance. The optimal composite foams containing the peak cork usage of 24 % also belong to the high-efficiency insulating materials, with a thermal conductivity of 0.043 W m−1 K−1, a tensile strength of 0.17 MPa, a bending strength of 0.16 MPa, and good impact resistance. This research provides valuable insights for developing the comprehensive PU insulating materials by utilizing eco-friendly cork as substitutes, and offers a reference for highly efficient utilization of biomass resources.

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.

Facilely prepared extreme environments tolerable PIF /c-CNTx composites for piezoresistive sensor based on powder foaming strategy

Polyimide foams (PIF) are widely used in piezoresistive sensors due to their light weight and weather resistance to weathering at extreme temperatures. Nevertheless, the mechanical strength of PIF prepared by freeze-drying method is poor, with only tens to hundreds of kPa ranging from 50 % to 80 % compression. Herein, a polyimide composite reinforced with –COOH functionalized multi-walled carbon nanotubes (PIF/c-CNTx) was produced via a thermal foaming process using a powder-based method. The PIF/c-CNTx composites exhibit ultra-low density (0.165 g/cm3), excellent mechanical properties (compressive strength of up to 2.5 MPa at 60 % compressive strain, tens to hundreds of times higher than similar materials) as well as stable compressive properties and recoverability in liquid nitrogen and at high temperatures up to 200 ℃. The PIF/c-CNTx piezoresistive sensor achieves excellent sensing capability over a wide strain range, high sensitivity (GF = 12.9) and exhibit good stability over 5000 s of cyclic compression at a compression rate of 10 mm/min. The stability and reproducibility of the strong piezoresistive signal at extreme temperatures shows the great potential of PIF/c-CNTx composites as structural components under extreme conditions for applications in aerospace and polar exploration.

Achieving metallurgical bonding in steel faceplate/aluminum foam sandwich via hot pressing and foaming processes: interfacial microstructure evolution and tensile behavior

This study introduces an innovative approach to fabricating aluminum foam sandwich with aluminized steel faceplates through metallurgical bonding. The process involves the use of foamable precursor, prepared via melt stirring, and subsequent hot pressing and foaming, offering a cost-effective and industrially feasible method for producing lightweight structural materials and connection of steel/aluminum dissimilar metals. This study focuses on exploring the changes in the microstructure of the bonding interface before and after foaming, and revealing the impact of these changes on the tensile results. Foaming experiment shows that foamable sandwiches have superior foaming ability, and the core layer density after foaming is between 0.283 and 0.591 g/cm ³. Microstructural characterization results demonstrate that, during the hot pressing process, fine equiaxed grains are observed on the iron side of the interface, indicating dynamic recrystallization occurred. The formation of a small amount of η-Al5Fe2 at the interface is a primary factor causing the deflection of the fracture path. Subsequently, during the foaming process, intermetallic compounds (IMCs) θ-Al13Fe4, τ5-Al7Fe2Si, and β-Al4.5FeSi formed sequentially, mainly determined by the diffusion reaction of silicon elements. The formation of these IMCs led to an increase in microhardness at the interface and a decrease in shear strength. Digital image correlation was utilized to examine strain distribution under tensile loading. The result indicates that the damage accumulation is characterized by the formation and expansion of strain bands, with failure manifested as the interconnection of these strain bands.