Foaming Method Research Articles

Bio-based non-flammable foams with a circular end-of-life based on the self-foaming process

For conventional polymeric foams, over-utilization of harmful precursors and the problem with waste management are driving scientists to develop sustainable foaming methods and make polymeric foams from renewable precursors. This study developed a self-foaming system to create a lignin carbonate foam (LCF) from two non-toxic carbon storage precursors: lignin and ethylene carbonate (EC). Specifically, kraft lignin, in its isolated salt form, referred to as lignophenolate, is copolymerized with EC via the anionic ring-opening polymerization. Under the optimal condition, the gelation and solidification of the copolymers could coincide with trapping in-situ generated CO2 blowing gas from the copolymers to make the foams. Its unique composition endows the materials with comparable performances with those benchmark plastic foams (for example polyurethane foam, expanded polystyrene) considering the mechanical performances, thermal stability, shape fidelity, and non-flammability. Moreover, the carbonate linkages in LCFs render them to be reshaped or depolymerized with valuable precursors for end-of-life recycling. This study opens new avenues to fabricate polymeric foams from carbon storage precursors through a self-foaming process for applications in the construction industry.

Comparison of Conventional and Microcellular Injection Using New Chemical Agents

ABSTRACT This study is mainly focused to obtain stable dimensions for plastic products used in manufacturing industries. A technique of microcellular foaming injection method was chosen with added chemical blowing agents to decrease the mass, clamping force, and cycle time. Mold flow analysis was run to compare the conventional plastic injection (KP) method with chemical foaming injection molding method using added TecoCell H1 (TH) and CS (TCS). The primary process conditions are considered as temperature of the mold, velocity of injection, pressure and time of holding, and cooling time. The experiments were carried under polymer material as (polypropylene) Moplen EP548P. The new chemical blowing agents TH and TCS, having different reactive material ratios (50% and 25% endothermic) and gas concentration ratios, were utilized at a rate of 1% by weight claiming to be a novel method for producing the parts with high efficiency. The results of both the flow analysis and the injection molding experiments demonstrate that, plastic samples produced by conventional plastic injection could be made approximately 7.5% lesser weight, with 33% lesser force of clamping, and a gain of cycle time nearly 15% by adding chemical blowing agents to the process. Topsis technique is carried for determining the best fabrication method. It was observed that, the injection molding method with Tecocell H1 (TH) chemical foaming agent exhibited better results in terms of less clamping force, reduced cycle time, and weight of the product. The experimental results are validated using the Topsis method and the results are satisfied. Hence, the chemical blowing agent Tecocell H1 (TH) can be applied as a foaming agent for manufacturing the plastic products and increase the efficiency of the production.

Room-temperature prepared MXene foam via chemical foaming methods for high-capacity supercapacitors

Room-temperature prepared MXene foam via chemical foaming methods for high-capacity supercapacitors

Thermal properties of mullite based porous ceramics derived from high silica tailings obtained after extracting alumina from high alumina coal ash

In this study, to solve the problem of reducing the quantity and increasing the utilization of waste as resource for high silica tailings (HSTs) after extracting alumina from high alumina coal ash, lightweight thermal insulation materials for building were prepared by using the melt foaming method. The effects of the calcination temperature and holding time on the melting characteristics of ingredients with different melt indexes were investigated. The effects of the amount of foaming agent on the bulk density, total porosity, and thermal conductivity of porous ceramics were determined, and the thermal conductivity model structure was further elucidated by comparing the experimental data with the values predicted by a theoretical model. The results showed that porous ceramics with optimal performance were prepared by calcination at 1200 °C for 30–60 min with a melt index of 8 k, and the amount of added SiC foaming agent was 0.52 wt%. The bulk density, total porosity and thermal conductivity were determined for the prepared porous ceramics as 0.196 g cm−3, 93.8%, and 0.086 W m−1 K−1, respectively, where the added amount of HSTs reached 60 wt%. Comparison and verification of the thermal conductivity model confirmed that the prepared mullite based porous ceramics should be classified as materials with internal porosity, where the pores were dispersed in the mullite continuous phase to form isolated closed pores. The results obtained in this study are of economic significance for the reuse of HSTs at large dosages and with high added value.

Effects of wood fiber loading, silane modification and crosslinking on the thermomechanical properties and thermal conductivity of EPDM biocomposite foams

Ethylene propylene diene monomer (EPDM) rubber based bio-composites filled with silane-modified wood fiber (SiWF) were foamed by using chemical foaming method. The SiWF and the incorporation of dicumyl peroxide (DCP) generated crosslinking in the developed EPDM bio-composite foams, which showed much lower water absorption and improved thermomechanical properties. With SiWF and in situ cross-linking, the tensile strength and modulus of EPDM bio-composite foams exhibited up to 90% and 600% enhancement compared to the unfilled foam, respectively. The compressive strength and modulus individually showed up to 170% and 600% increase. The developed bio-composite foams also displayed lower apparent thermal conductivity than the unfilled EPDM foam over the heating temperature range, showing possible applications as insulation materials.

Foaming processes and properties of geopolymer foam concrete: Effect of the activator

In this paper, an ambient-cured geopolymer foam concrete (GFC) was produced based on the chemical foaming method, in which the mixed fly ash (FA) and ground granulated blast furnace slag (GGBS) were used as the precursor, water glass was used as the alkaline activator and aluminum powder was used as the foaming agent. The different properties of the alkali solution, including Na2O contents (i.e., from 4% to 7%) and modulus ratios (i.e., from 1.1 to 1.5), were adopted in the mixture design and the resultant properties were compared for investigating their effects. The density, compressive strength, and thermal conductivity of the GFC ranged within 280.8 ∼ 865.8 kg/m3, 1.10 ∼ 8.13 MPa, and 0.088 ∼ 0.20 W/(m × K), respectively. In addition, more attention was paid to the properties of GFC during the foaming process, including the gas generation rates and rheological properties of the geopolymer slurry, which were determinants of the pore characteristics (e.g., porosity, pore size distribution and roundness) and the macroscopic properties of the GFC (e.g., density, compressive strength, and thermal conductivity). The test results indicated that the higher gas generation rate and lower viscosity of the slurry, which were obtained at higher Na2O content and lower modulus ratio, resulted in higher porosity, lower compressive strength, and lower thermal conductivity.

Environment-adaptive, anti-fatigue thermal interface graphene foam

The rapid development of high-power and high-frequency devices in electronics leads to the urgent demands for advanced thermal interface materials (TIMs) with both superior thermal conductivity and excellent structural stability. Many attempts have exploited the silicone-based TIMs with higher thermal conductive fillers, however, their structural stability remains challenging in some extreme conditions. Here we fabricate the carbon-based graphene foam roll (GFR) as flexible TIM by hydroplastic foaming (HPF) and interface strengthening methods. The enhanced interface bonding within GFR by impregnation of graphene oxide (GO) enables its superior structural integrity. It can keep mechanical stability after 10,000 cycles at a compressive strain of 60% and sustain high temperature up to 500 °C, which has never been realized in previous reports. We demonstrate the GFR-TIM not only achieves very high structural stability but also exhibits higher thermal conductivity (∼17.42 W/mK) than most commercial TIMs (5–10 W/mK). The GFR-TIM can serve as an efficient heat-dissipation component for the CPU and shows superior cooling efficiency compared to commercial TIMs. Our work provides an advanced graphene-based TIM with excellent environment-adaptive and anti-fatigue properties, broadening their application in extreme environments, such as hypersonic vehicles, high-throughput satellites and high-power radar systems.

Lithium Foam for Deep Cycling Lithium Metal Batteries.

Li metal anode has been recognized as the most promising anode for its high theoretical capacity and low reduction potential. But its large-scale commercialization is hampered because of the infinite volume expansion, severe side reactions, and uncontrollable dendrite formation. Herein, the self-supporting porous lithium foam anode is obtained by a melt foaming method. The adjustable interpenetrating pore structure and dense Li3 N protective layer coating on the inner surface enable the lithium foam anode with great tolerance to electrode volume variation, parasitic reaction, and dendritic growth during cycling. Full cell using high areal capacity (4.0 mAh cm-2 ) LiNi0.8Co0.1Mn0.1 (NCM811)cathode with the N/P ratio of 2 and E/C ratio of 3g Ah-1 can stably operate for 200 times with 80% capacity retention. The corresponding pouch cell has <3% pressure fluctuation per cycle and almost zero pressure accumulation.

High-Expansion Open-Cell Polylactide Foams Prepared by Microcellular Foaming Based on Stereocomplexation Mechanism with Outstanding Oil-Water Separation.

Biodegradable polylactic acid (PLA) foams with open-cell structures are good candidates for oil-water separation. However, the foaming of PLA with high-expansion and uniform cell morphology by the traditional supercritical carbon dioxide microcellular foaming method remains a big challenge due to its low melting strength. Herein, a green facile strategy for the fabrication of open-cell fully biodegradable PLA-based foams is proposed by introducing the unique stereocomplexation mechanism between PLLA and synthesized star-shaped PDLA for the first time. A series of star-shaped PDLA with eight arms (8-s-PDLA) was synthesized with different molecular weights and added into the PLLA as modifiers. PLLA/8-s-PDLA foams with open-cells structure and high expansion ratios were fabricated by microcellular foaming with green supercritical carbon dioxide. In detail, the influences of induced 8-s-PDLA on the crystallization behavior, rheological properties, cell morphology and consequential oil-water separation performance of PLA-based foam were investigated systemically. The addition of 8-s-PDLA induced the formation of SC-PLA, enhancing crystallization by acting as nucleation sites and improving the melting strength through acting as physical cross-linking points. The further microcellular foaming of PLLA/8-s-PDLA resulted in open-cell foams of high porosity and high expansion ratios. With an optimized foaming condition, the PLLA/8-s-PDLA-13K foam exhibited an average cell size of about 61.7 μm and expansion ratio of 24. Furthermore, due to the high porosity of the interconnected open cells, the high-absorption performance of the carbon tetrachloride was up to 37 g/g. This work provides a facile green fabrication strategy for the development of environmentally friendly PLA foams with stable open-cell structures and high expansion ratios for oil-water separation.

Multifunctional Open-Cell Copper Foam with Sphere Pores by a Modified Sintering–Dissolution Process

In this study, open-cell copper foam with completely interconnected sphere pores was prepared by a modified sintering–dissolution process using a preformed calcium chloride template skeleton as space holder. Compared with the traditional foaming process method, the open-cell copper foam prepared by this method has fewer impurities and better surface morphology. In addition, the pore distribution can be controlled by adjusting the distribution of calcium chloride particles in the skeleton. The compression performance, airflow resistance, and filtration performance of the prepared open-cell copper foam were studied. The results show that with the increase in porosity, the bearing capacity of open-cell copper foam decreases, but the width of the stress platform increases. The prepared open-cell copper foam exhibits excellent energy absorption efficiency, reaching nearly 90% at a porosity of 85%. When the porosity is 85%, the static airflow resistance of the structure is as high as 9 KPa·s·m−2. Moreover, the structure has a filtration efficiency of more than 90% as the filtration thickness exceeds 20 mm, which demonstrates the excellent filtration ability. Such open-cell copper foam shows multi-functional potential as an impact damper, sound absorber, and impurity filter.

Physical and Chemical Foam Injection Moulding of Natural-Fibre-Reinforced Polypropylene—Assessment of Weight-Reduction Potential and Mechanical Properties

Reducing weight not only consumes fewer resources for manufacturing but also requires less energy for transportation, thus preserving resources and reducing CO2 emissions. The latter part is of utmost importance in mobility applications. For example, in the automotive industry, the large-scale production of lightweight structural parts is becoming a main issue. An effective method to meet these requirements is foam injection moulding. In this study, physical (MuCell technology) and chemical foam injection moulding was used to produce plates made from wood-fibre- and cellulose-fibre-reinforced polypropylene, respectively. For both technologies, the used core-back method enabled precise mould opening during injection and thus allowed for variation in the plate thickness and density. The simpler short-shot technology, used only for the chemical foaming trials with differing shot volumes, provided plates with constant thicknesses. The foam structure and finally the mechanical properties of the plates depended on the filler type, the foaming method and the density. The latter was directly linked to either the plate thickness or the shot volume. Physical foaming appeared to be slightly more effective regarding the achievable density reduction (up to 37% reduction), but the physically foamed parts had worse mechanical properties at equal density than their chemically foamed counterparts. Besides the comparison of different foaming methods, this study provides the tensile, flexural and impact properties of natural-fibre-reinforced polypropylene composites over a wide density range, thus offering a good basis for evaluating weight-saving potential for various applications.

An Inexpensive, Reproducible Method to Quantify Activated Sludge Foaming Potential: Validation through Lab-Scale Studies and Year-Long Full-Scale Sampling Campaign.

Activated sludge is a conventional treatment process for biochemical oxygen demand (BOD) and total suspended solids (TSS) removal at water resource recovery facilities (WRRFs). Foaming events are a common operational issue in activated sludge and can lead to decreased treatment efficiency, maintenance issues, and potential environmental health risks. Stable foaming events are caused by biological and chemical drivers (i.e., microbes and surfactants) during the aeration process. However, foaming events are difficult to predict and quantify. We present an inexpensive and easy-to-use method that can be applied at WRRFs to quantify foaming potential. Subsequently, the method was applied over a year long full-scale study while data on microbial community composition and functional parameters associated with foaming potential were collected from activated sludge samples at South Shore Water Reclamation Facility (WRF) (Oak Creek, WI). Results from the development of the foaming potential method using linear alkylbenzene sulfonate (LAS) showed that the method was reproducible (relative standard deviation < 20%) and able to capture changes in foam inducing constituents. Using full-scale activated sludge samples, higher relative abundance values for the following genera were associated with foaming events: Zoogloea, Flavobacterium, Variovorx, and Bdellovibrio. This is the first report that Variovorx and Bdellovibrio relative abundance was correlated with foaming events in activated sludge. Furthermore, the foaming potential positively correlated (p ≤ 0.05) with soluble total nitrogen. Characterizing foaming events through frequent sampling, and monitoring of specific genera and functional parameters may allow for predictions and preemptive mitigation efforts to avoid negative consequences in the future.

Microstructural characteristics and mechanical properties of 7075 aluminum alloy foam sandwich panels fabricated via integrated forming and foaming

A new integrated forming and foaming method based on friction stir welding (FSW) was proposed for foam sandwich panels. The microstructure characteristics of the precursors and foams with different welding parameters were analyzed using optical microscopy and scanning electron microscope (SEM/EDS). The temperature field and flow field of foam precursor joint in FSW were simulated by Fluent CFD software. The microstructural characteristics of foam precursor after hot forming were analyzed using electron backscattered diffraction (EBSD) and transmission electron microscopy (TEM). The effect of foam precursor deformation on foam evolution was also investigated. The results show that the formability of foam precursor is the same as that of rolled plate. Aluminum foam sandwich panel with homogenous pore structure is prepared at 680 °C for 225 s. After hot forming, the equiaxed recrystallized grain is obtained, and the dislocation and the second phase provide reinforcement. In addition, Rgoss{110}〈110〉 texture component strength increases. When the tensile strain is 0.15, smaller and more uniform pores are produced. Numerical simulations show that the peak temperature gradually decreases with the increase of the distance of the stirring head center. In addition, the temperature on the advancing side (AS) is higher than that on the retreating side (RS). When the tool travel speed is 50 mm/min and rotational speed is 2000 r/min, the maximum material flow velocity at the joint section is 184.2 mm/s and the highest concentration of powder tracing particles is 0.0123 kg/m3. It is proved that the integrated forming and foaming method can solve the problem in manufacturing of complex curved AFS components.

Research on the foaming mechanism of microbial foaming agent and its application in foam concrete

This paper firstly investigates the effect of stirring and foaming of culture medium solution and microbial solution under the same incubation conditions as well as the factors affecting microbial foaming through settling distance, water secretion rate, foaming times, functional groups, and surface tension, to clarify the foaming mechanism and optimal proportion of microbial foaming agent; then the mechanical properties of foam concrete prepared by different preparation processes (direct mixing method and prefabricated foam method) are investigated using the microbial foaming agent. The results show that the foaming nature of microbial foaming agents is the result of the synergistic effect of microorganisms, nutrients in the culture medium solution, and microbial metabolites. Excellent performance foams were produced when the microbial inoculum was 10%, the incubation time was 48 h, the pH was 7, the stirring time was 30 min and the gelatin admixture was 0.4%. At the same time, the performance of the foam concrete prepared by the prefabricated foam method is better than that of the direct mixing method, with a dry density of 967 kg/m3 and a 28th-day compressive strength of 4.7 MPa, which meets the requirements of the industry standard A10 density class and has a uniform pore size distribution.

Study on Preparation and Performance of CO2 Foamed Concrete for Heat Insulation and Carbon Storage.

Environmental problems caused by large amounts of CO2 generated by coal-electricity integration bases have raised concerns. To solve these problems, this study develops a CO2 foam concrete (CFC) material with both heat insulation and carbon fixation characteristics to realize CO2 in situ storage and utilization. In this study, a Portland-cement-based CO2 foam concrete (PC-CFC) with good thermal insulation performance and carbon fixation ability is prepared using carbonation pretreatment cement and a physical foaming method. The effects of CO2 on the compressive strength, thermal insulation, and carbon fixation properties of PC-CFC are studied. The internal relationship between the compressive strength, thermal insulation, and carbon fixation performance of PC-CFC is analyzed, and the feasibility of PC-CFC as a filling material to realize the in situ mineralization and storage of CO2 in the coal-electricity integration base is discussed. The experimental results show that the compressive strength of PC-CFC is significantly improved by CO2 curing. However, CO2 in the PC-CFC pores may weaken the strength of the pore structure, and the compressive strength decreases by 3.62% for each 1% increase in PC-CFC porosity. Using CO2 as a foaming gas and the physical foaming method to prepare CFC can achieve improved thermal insulation performance. The thermal conductivity of PC-CFC is 0.0512-0.0905 W/(m·K). In addition, the compressive strength of PC-CFC increases by 19.08% when the thermal conductivity of PC-CFC increases by 1%. On the premise of meeting the thermal insulation requirements, PC-CFC can achieve improved compressive strength. The carbon sequestration rate of the PC-CFC skeleton is 6.1-8.57%, and the carbon storage capacity of PC-CFC pores is 1.36-2.60 kg/ton, which has obvious carbon sequestration potential; however, the preparation process and parameters of PC-CFC still require further improvement. The research results show that PC-CFC has great potential for engineering applications and is of great significance for realizing carbon reduction at the coal-electricity integration base.

Study on the thermal stability and combustion performance of polyurethane foams modified with manganese phytate

Abstract A new environmental friendly flame retardant manganese phytate (MnPa) was prepared by a direct precipitation method and the polyurethane foam (PUF) modified with MnPa was obtained by a one-step all-water foaming method. The thermal stability and combustion performance of the MnPa-modified PUF (MnPUF) were investigated by using thermogravimetric (TG), thermal decomposition kinetics, smoke density characterization, limiting oxygen index (LOI) and UL-94 horizontal combustion test. The results indicated that the addition of MnPa significantly improved the thermal stability and combustion performance of the modified PUF. On the basis of the thermogravimetric analysis, Flynn-Wall-Ozawa method, Kissinger method and Coats Redfern method, it could be concluded that PUF with 7.5 wt% MnPa (MnPUF3) had the highest activation energy and the best thermal stability. Smoke density analysis, LOI and horizontal combustion analysis also showed that the addition of MnPa was positively correlated with smoke suppression, LOI value and burning time. The current research results can provide a reference for the subsequent flame retardant modification of PUF.

Preparation of Thermoplastic Polyurethane/Multi-Walled Carbon Nanotubes Composite Foam with High Resilience Performance via Fused Filament Fabrication and CO2 Foaming Technique.

Wearable flexible sensors with high sensitivity and wide detection range are applied in motion detection, medical diagnostic result and other fields, but poor resilience and hysteresis remain a challenge. In this study, a high-resilience foam sensor was prepared through a combination of additive manufacturing and green physical foaming method. The conductive filaments were prepared by using MWCNTs-modified TPU by the physical method of melt blending. Samples were prefabricated using the FFF printer and then saturated with CO2 in an autoclave before being removed and heated to foam. The composite foam effectively reduced residual strain, demonstrating the high resilience of the 3D-printed composite materials with a foam porous structure. The residual strain of the sample before foaming was >6% after a single cycle, and then gradually increased. The residual strain of the foamed samples is less than 5%. In addition, composite foam has high sensitivity and can monitor subtle pressure changes (0~40 kPa). The sensing performance of the composite foam was evaluated, and the current signal remained stable under different loading rates and small compression strains (2~5%). By using this highly resilient conductive composite material, a hierarchical shoe insole was designed that successfully detected human walking and running movements.

Flexible pressure sensor based on polystyrene foam with superelasticity and ultra-wide range

The use of flexible pressure sensors has significantly advanced and improved human life. However, several issues are hindering their applicability such as the difficulty to achieve high sensitivity over a wide pressure measurement range. Herein, a one-step foaming method and hydrothermal approach were used to fabricate a three-dimensional conductive porous foam comprising polyurethane, carbon nanotube, and polyaniline. The sensor exhibits excellent electrical conductivity due to its cellular foam structure, while its high durability enables a large response output across an extremely broad range (0–30 000 kPa). The sensor also exhibits exceptional stability over 1000 loading/unloading cycles, a fast response time of 80 ms, and high sensitivity of 0.019 53 kPa−1 (0–200 kPa), 0.126 48 kPa−1 (200–5000 kPa), and 0.038 85 kPa−1 (5000–30 000 kPa). Furthermore, rational material selection and structural design allows the sensor to monitor low- to high-signal stimuli, thereby providing a reference for the design of other large-scale sensors.

High strength and light weight polyamide 6/carbon fiber composite foams for electromagnetic interference shielding

AbstractIn this study, high strength and light weight polyamide 6/carbon fiber (PA6/CF) composite foams were prepared by chemical injection foaming method. The foaming performance, electromagnetic interference (EMI) shielding efficiency total(SET), and mechanical properties of PA6/CF composite foams with different CF contents were investigated. The results show that the shear viscosity and strain hardening behavior obvious increased with the augment of CF content, which helped to PA6/CF composite foams to take the cell structure with smaller size, greater density, and more regular morphology. PA6/CF composite foam with cell size of 56.8 μm, and cell density of 1.81 × 106 cells/cm3 was achieved at 22 wt% CF. Meanwhile, PA6/CF composite foam had good EMI SET, at 22 wt% CF addition. The specific EMI SET of PA6/CF composite foam is 36.6 dB, 27.6% higher than that of solid 26.5 dB, the excellent cell structure helps to improve the EMI SET. In addition, PA6/CF composite foams also had excellent mechanical properties. Therefore, PA6/CF composite foams had broad application prospect in EMI shielding materials field, combining the advantages of simple preparation process, light weight and EMI shielding.

Preparation and characterization of foamed ceramics from coal bottom ash for construction insulation materials

Foamed ceramic is a novel lightweight wall material combining high strength, low density, and excellent thermal insulation. This study used coal bottom ash (CBA) to fabricate microporous foamed ceramics by the high-temperature foaming method. The CBA content and heating rate effects on the bulk density, compressive strength, pore structure, and phase components of foamed ceramics were systematically investigated. The results demonstrate that using CBA in foamed ceramics can effectively improve the green body foaming capacity. With the increased CBA content, the bulk density of foamed ceramics dropped, while the average pore size and shape factor increased, jointly reducing the compressive strength. Meanwhile, the quartz phase content decreased, and the mullite phase appeared gradually. The transition of the main crystalline phase from MgAl2O4 to Mg0.7Fe0.23Al1.97O4 with the increased CBA content gave rise to a change in the color of the foamed ceramic. The elevation in the heating rate can improve the foaming ability of the green body, contributing to increased porosity. However, the rapid heating rate of 10 °C/min results in an uneven pore size distribution in the foamed ceramics containing more than 70 wt % CBA. It increases the temperature difference in the sample, promoting a stratified distribution of pore size in samples with a CBA content of less than 30 wt %.