Foam Pressure Research Articles

Characterizing and modeling the wide strain rate range behavior of air-filled open-cell polymeric foam

Air-filled open-cell polymeric foams are widely used for absorbing impact energy under various strain rates. Modeling their compression behavior under large deformation across a wide strain rate range remains a challenge, as the air pressure is dominated by viscous effect or inertial effect at different strain rates. In this study, the compression response of air-filled open-cell polyurethane (PU) foam is characterized across a wide strain rate range from 0.0001 s−1 to 5000 s−1. The plateau stress and energy absorption properties of the foam exhibit a power-law dependency on strain rate, showing lower rate sensitivity at quasi-static rates and increased sensitivity at high strain rates. To describe the observed rate sensitivity variation, the effect of airflow resistance is quantitatively modeled and a visco-hyperelastic constitutive model considering air pressure is developed. It shows that at high strain rates, the air pressure can constitute up to 30 % of the energy absorption contribution while it is relatively negligible at quasi-static strain rates, which significantly amplifies the difference in rate sensitivity between quasi-static and high strain rates. Furthermore, a simplified semi-empirical formula is proposed to rapidly estimate the air pressure in open-cell foams at high strain rates. This formula demonstrates the mechanical response transition from open-cell to closed-cell foams with increasing strain rates. This study is meaningful for understanding the dynamic response and the energy absorption capabilities of air or fluid filled open-cell foam.

Process Optimization of Pressure-induced Autoclave Foaming of Polylactide by Supercritical CO<sub>2</sub> Using Central Composite Design of Response Surface Methodology

A pressure-induced autoclave foaming assisted by supercritical CO2 of degradable polylactide (PLA) has been developed. A central composite design (CCD) of response surface methodology (RSM) is used to optimize three distinct process conditions: foaming temperature, pressure, and time. The mathematical model built for examining the effect of process conditions on the foam density and volume expansion ratio was verified and determined to be acceptable with an R-square value derived from the regression model of 0.930 and 0.934, respectively. The experimental and statistical results showed that of the three factors examined, the foaming pressure had the greatest impact on the density and volume expansion ratio of the PLA foams. The foaming temperature and time also had significant interaction impacts on both responses. It was observed that the following conditions are optimal for foaming of PLA, with a maximum VER of 10.107 and a minimum foam density of 0.123 g/cc: foaming temperature of 165.86 °C and foaming pressure of 152.4 bar for 2.38 h of foaming time.

Greener lightweight foam concrete using seaweed industrial by-product to replace natural sand with inorganic salt as a stabilizer

In recent years, the seaweed industry has expanded, resulting in higher volumes of seaweed industrial by-products (SWB). People commonly dispose SWB on land, which raises environmental concerns due to its hazardous chemical content. The use of waste materials as alternatives to natural sand has gained attention due to its potential to reduce environmental impact. Therefore, this study aimed to develop a greener lightweight foam concrete (LFC) by incorporating 0–30 % SWB as a replacement for natural sand in fine aggregates and evaluate its performance. Furthermore, the study investigated the inclusion of inorganic salt concentrations ranging from 0 to 15 % into the concrete mixture to improve performance. The production, sampling, and testing procedures followed the SNI 8640:2018 standards. Properties like density, water absorption, drying shrinkage, and compressive strength were analyzed for SWB percentage (0–30 %), salt concentration (0–15 %), foaming pressure (0.20, 0.39, and 0.59 MPa), and curing duration (7, 14, and 28 days). Viable specimens were further examined for microstructure, energy intensity, CO2 emission, and production cost. Specimen FS5 met standards with a density of 707.1 kg/m3, compressive strength of 2.12 MPa, water absorption of 25.45 % (v/v), and drying shrinkage of 0.13 %. The energy intensity, CO2 emission, and total cost of greener LFC were calculated to be 159.88 MJ/m3, 188.98 kg of CO2/m3, and IDR 682,130/m3, respectively. Ultimately, this work greatly contributes to the field of green manufacturing and environmental sustainability by successfully decreasing energy intensity, CO2 emissions, and environmental harm in LFC production processes.

Optimizing thermal performance in tube-in-tube heat exchangers with metal foam inserts: experimental and RSM analysis

ABSTRACT This study investigates tube-in-tube heat exchanger performance under steady-state conditions, examining co-current and counter-current flows. It explores various configurations, including metal foam enhancements, to optimize heat transfer efficiency and minimize pressure drop. Driven by the potential of metal foam to enhance heat transfer, the study aims to demonstrate significant improvements in thermal performance compared to conventional designs. Experimental methods involve testing four configurations with Nickel foam (10 PPI, 0.90 porosity) inserts, evaluating temperatures and pressure drops across flow rates of 25 to 50 LPH. Hot water at 65°C flows in the annulus, while normal water at 31°C flows in the outer annulus. Results show metal foam’s substantial enhancement in heat transfer, with counter-current metal foam configurations achieving up to 3.71 times greater efficiency than parallel flow setups. Moreover, comprehensive performance evaluation reveals that the counter-flow heat exchanger with metal foam is 2.03 times more efficient than the conventional co-current flow without metal foam. Conclusions highlight metal foam’s effectiveness in improving heat transfer performance and optimizing thermal systems through systematic parameter optimization using response surface methodology.

Experimental investigation on thermal performance of phase change materials–metal foam composites in ocean thermal engine

Because battery-powered underwater vehicles have limited long-term mission capacity, the development of ocean thermal engines that can harvest ocean thermal energy (OTE) is a potential solution to this “energy limitation” issue. Ocean thermal engines using solid-liquid phase change materials (PCM) for thermal–mechanical energy conversion. This study examined the effects of combining PCMs with metal foams (MF) on OTE harvesting. Two phase change materials and three MFs were considered. Experiments were conducted to measure the temperature change inside the PCM, phase change duration, and volume change to evaluate the thermal and energy-harvesting performances under different temperature and pressure conditions. Results show that(1) Mixed PCM composed of 95 % n-hexadecane and 5 % n-octane melting point decreased by 0.9–1.6 °C and volume change rate reduced by 16–40 % compared to pure n-hexadecane. (2) The mixed PCM has by 14–18 % higher output power than pure n-hexadecane. (3) Within the test range, to maximize the power density, the optimal porosity of copper foam and back pressure during melting were 94 % and 20 MPa, respectively. This study provides useful insights into the design and optimization of ocean thermal engines.

Preparation and properties of phenolic foam modified with boric acid and organosiloxane by supercritical CO2 technology

AbstractIn this study, a silica boron modified phenolic resin foam (SiBPF) is prepared in a reactor under specific pressure and temperature and using supercritical CO2 (scCO2) as a physical foaming agent, to improve phenolic foam (PF) brittle and friable properties and avoid environmental pollution caused by conventional physical foaming. To determine the partially curing degree for foaming, the influence of partially curing time at partially curing degrees between 39.88% and 53.17% was studied. Further, through an orthogonal experimental method, the optimized foaming process parameters—partially curing time of 6 h, adsorption time of 9 h, foaming pressure of 1 MPa, and foaming temperature of 130°C—were determined. The SiBPF, thus prepared under the optimized conditions, exhibited a density of 0.2356 g/cm3, an average cell size of 86.66 μm, and a cell density of 7.10 × 106 cells/cm3. Its compressive strength was found to be 7.28 MPa, with a specific compressive strength of 30.90 MPa/g·cm−3. At 800°C, the carbon residue rate, thermal decomposition temperature T5%, and Tmax reached 77.61%, 355.21, and 702.70°C, respectively. The thermal conductivity of SiBPF was measured to be 0.0644 W/mK, with the rear temperature stabilizing at 60°C on a hot platform of 100°C.

A flexible superhydrophobic thermoplastic polyurethane porous surface with good self-cleaning function prepared by supercritical CO2 foaming

Porous surfaces show great potential for superhydrophobic applications. Supercritical CO2 foaming is a green technology for preparing porous materials, but it is rarely used to prepare porous surfaces due to the non-porous skin caused by the escape of gas. In this study, a porous thermoplastic polyurethane (TPU) surface with dense cell and small cell spacing is prepared by employing bilayer TPU sheet to restrict the escape of gas from surfaces. The influence of the foaming pressure and temperature on the cells of the TPU surface is researched. Furthermore, bimodal cells are obtained by regulating the foaming process and the effect of cell structure on wettability is investigated. Subsequently, a flexible superhydrophobic material with low water-adhesion, mechanical stability, and self-cleaning properties is successfully prepared by modifying fluorinated silica particles on porous TPU surfaces.

Foamed waste oil-activated rubberized asphalt binder: A sustainable recycling approach for improving foaming effect and performance

This study prepared foamed waste oil-activated rubberized asphalt (ORA) by activating crumb rubber (CR) with waste vegetable oil (WVO) to address the issue of undesirable foaming effect. Optimal foaming parameters for different rubberized asphalt were determined based on foaming characteristic experiments. Furthermore, rheological properties, fatigue resistance, and adhesion performance of various unfoamed or foamed rubberized asphalt were evaluated through dynamic shear rheometer, bending beam rheometer, pull-out tests. Finally, the analytic hierarchy process was utilized to select the optimum foamed rubberized asphalt. The results show that foaming pressure has a great influence on rubberized asphalt foaming effect, and is recommended at 300 kPa. Compared to conventional rubberized asphalt whether foamed or not, with the increase of activation degree, low-temperature performance, and fatigue resistance of ORA are significantly ameliorated, and the adhesion property of ORA first increases and then decreases, but detrimental to high-temperature performance. The foaming process and foaming agent addition are conducive to low-temperature performance but unfavorable to fatigue resistance and high-temperature property, and have little effect on adhesion performance. ORA (mass ratio of WVO to CR is 1:5) with foaming agent is determined as the optimum selection.

Epoxy resin reinforced high-performance conductive composite foam with ultra-wide pressure sensing range

Flexible piezoresistive sensors based on conductive polymer composites (CPCs) have shown great potential and application in smart wearable devices, sports and health monitoring. Nevertheless, the practical use of many CPCs pressure sensors is often limited by their narrow monitoring range and low sensitivity. Here, a thermoplastic urethane/ epoxy resin/ carbon nanotubes/ polydopamine/ Ti3C2TX MXene (TPU/EP/CNT/PDA/MXene) composite foam was prepared using the commonly used freeze-drying and impregnation methods. Due to the high strength of the EP/TPU foam matrix and CNT@MXene's internal and external synergistic conductive network, the TECPMF has outstanding mechanical and conductive properties. As a result, the foam pressure sensor has an extremely wide monitoring range (0∼300 kPa) and a sensitivity of 2.42 kPa−1 (0∼5 kPa). Furthermore, the superior performance of the foam provides fast response (100 ms) and outstanding durability of more than 8000 cycles. The piezoresistive TECPMF sensor can be used for real-time monitoring of human movement, as well as the magnitude and position of various pressures and air pressures. These promise to enable a wide range of smart wearable and engineering applications. This work opens up a new avenue for the design of more advanced piezoresistive sensors.

Foam Pressure Mapping with Optimized Electrodes

Nano-composite piezo-responsive foam (NCPF) is an inexpensive foam that can be used to measure a static load while still providing a comfortable interface. The purpose of this study was to create a modularized foam-based pressure measurement system. A measurement system was developed that uses an interdigitated electrode applied to the NCPF. Applied pressure changes the impedance of the NCPF, which, in turn, is converted into a voltage using a voltage divider. A modular measurement system is described that uses an ATtiny 1627 microcontroller to measure the pressure at nine electrodes. The nine electrode modules are controlled by an ESP32 microcontroller that aggregates the data and wirelessly transmits the data to a tablet. The modular system was demonstrated with 1008 individual electrodes. The characterization of the electrode combined with the NCPF is presented, along with optimization of the electrode geometry.

Estimation method of earthwork excavation using shield tunneling data -- a case study of Chengdu Metro

The occurrence of over-excavation or under-excavation in tunnel construction poses significant safety risks. Moreover, there is currently no automatic estimation method available for real-time estimation of earthwork excavation, particularly in the case of shield tunnels. In this study, we tracked the excavation process of Chengdu Metro Line 19, acquired tunneling parameters and earthwork excavation data using various sensors, and subsequently proposed an automatic estimation method that combines Bayesian optimization (BO) and gradient boosting regression tree (GBRT) algorithm. The results of our case study indicate that the BO-GBRT model improves the performance of earthwork excavation estimation, reducing the residual after each calculation with a root mean square error (RMSE) of 1.712 and mean absolute error (MAE) of 1.331. Furthermore, compared to other machine learning methods, the proposed BO-GBRT model demonstrates superior estimation performance. Additionally, the importance distribution of input parameters reveals that propulsion pressure, foam pressure, and rotation speed are the most critical factors affecting earthwork excavation. Overall, the proposed automatic estimation method shows great promise as a tool for efficiently estimating earthwork excavation in shield tunnel construction.

Preparation of Open-Cell Long-Chain Branched Polypropylene Foams for Oil Absorption.

This study aimed to prepare open-cell foams using a blend of long-chain branched polypropylene and polyolefin elastomer (LCBPP/POE) for the production of reusable oil absorbents. The supercritical CO2 foaming process was conducted using a two-step batch rapid depressurization method. This unique two-step foaming approach significantly expanded the temperature and pressure windows, resulting in more uniform cells with smaller sizes, ultimately leading to higher expansion ratios and an increased open cell content. The foaming process was optimized by adjusting parameters, such as the LCBPP/POE ratio, foaming temperature, and foaming pressure, reaching a maximum open cell content of 97.6% and a maximum expansion ratio of 48. The influence of polypropylene (PP) crystallization was investigated with the aid of scanning electron microscopy and differential scanning calorimetry. Furthermore, the hydrophobic and lipophilic characteristics of the LCBPP/POE open-cell foam were determined via contact angle measurements and oil/water separation tests. Oil absorption tests revealed that the blended LCBPP/POE foam has a higher oil absorption capacity than that of the pure LCBPP foam. The cyclic oil absorption tests demonstrated the outstanding ductility and recoverability of the LCBPP/POE open-cell foam in comparison to those of the pure LCBPP foam. Over 10 cycles, the LCBPP/POE foam maintained a substantial adsorption capacity, retaining 99.3% of its initial oil absorption capacity. With its notable features, including a high open cell content, excellent hydrophobic and lipophilic characteristics, superior oil absorption capacity, impressive cyclic oil absorption performance, and robust reusability, LCBPP/POE open-cell foams exhibit significant promise as potential oil adsorbents for use in oil spill cleanup applications.

Synthesis and fabrication of lightweight microcellular thermoplastic polyimide foams using supercritical CO2 foaming

Polyimide foams (PIFs) are usually synthesized by solution polymerization, followed by chemical foaming to prepare thermosetting foam. In this research, lightweight microcellular thermoplastic polyimide foams (TPIFs) were fabricated via a novel two-step foaming approach using supercritical carbon dioxide (scCO2) as a blowing agent. The poly(amic acid) (PAA) and polyester ammonium salt (PEAS) precursor solutions were synthesized with pyromellitic dianhydride (PMDA) as dianhydride reagents and polyether amine Jeffamine D230 as aliphatic diamine reagent via blending and solution polymerization, respectively. The solution polymerization process demonstrated a higher molecular weight and superior formability than the blending process. The optimum thermal imidization temperature of 200 °C was optimized via the thermal and rheological property analysis. The cell morphology and mechanical properties of the TPIFs could be turned by varying the saturation time, foaming pressure, and imidization temperature. At a thermal imidization temperature of 200 °C, the TPIFs exhibited a branched structure with a small mean cell diameter (123.78 μm), and a high compressive strength (0.4 MPa) under 10 % strain at high temperature and pressure, which was more than ten times that of the TPIFs with thermal imidization temperature of 130 °C. This research provides a feasible method for producing high volume expansion ratio TPIFs with adjustable microcellular structures and outstanding mechanical properties.

Effect of sintering on processability vis‐a‐vis microcellular foaming of ultrahigh molecular weight polyethylene

AbstractProcessing of ultrahigh molecular weight polyethylene (UHMWPE) involves sintering due to its high melt strength and no flowability above melting temperature. Variations in compression molding pressure during sintering lead to chain rearrangement at the sintered interphase and the boundary, affecting foamability. UHMWPE particles are sintered using compression molding; samples are prepared at two different pressures: UHPE‐HP (80 bar) and UHPE‐LP (40 bar) at 180°C. The sintering phenomenon of UHMWPE particles is observed through an optical microscope, and their effect on foaming was observed. UHPE‐HP foams are systematically studied to obtain the foaming window. Increasing foaming pressure (80–120 bar) made UHPE‐HP foams softer (0.350–0.219 g/cm3) with varying average cell size (26.37–46.1 μm) and foam cell density (3.98 × 107–1.06 × 108 cells/cm3), and compression modulus decreased from 9 to 5.4 MPa. DMA results showed a strong dependence of stiffness on crystallinity, and foamed samples exhibit higher stiffness than their unfoamed counterpart. The storage modulus for foamed samples decreases with increase in the gas content. The UHPE‐LP foam is relatively softer, with a lower foam density (0.233 g/cm3), a higher expansion ratio, bigger average foam cells (35.13 μm), and lower foam cell density (9.33 × 107 cells/cm3). This is due to constrained crystallinity at the interphase and pre‐existing cavities, favoring the foaming.

Clinical Evaluation of Medical Ozone Use in Domestic Feline Cutaneous Wounds-A Short Case Series.

Support and management of second-intention wound healing involves frequent dressing changes having different properties. Dressings can range from simple ones, such as nonadherent dressings, to more complex options, such as foam, hydrocolloid, alginate or negative pressure dressings. Seven cats were enrolled in the study with a total of nine wounds of various sizes with different etiology sizes and localizations. Three methods of local ozone administration were used to cover more of the ozone properties in the treatment of wounds: bagging, perilesional subcutaneous infiltrations and lavages with ozonated saline. Evaluation of the healing process was performed by clinical observation and wound area measurements every seven days until the complete recovery of the patients. The results of this study should encourage clinicians to consider medical ozone as a new therapeutic approach with regenerative properties in the second-intention healing of cats presenting cutaneous wounds.

Effect of inorganic salts in coal seams on the sand-carrying capacity of hydroxypropyl guar foam-fracturing fluid: An experimental study

Coal seam water typically contains inorganic salts, which could affect the sand-carrying capacity of foam-fracturing fluid. This study selected the standard cationic surfactant cetyltrimethylammonium bromide as the foaming agent, used the high molecular polymer hydroxypropyl guar gum as the foam stabilizer to prepare foam-fracturing fluid, and selected silica particles as the proppant. The effects of different CaCl2, NaHCO3, MgSO4, and KCl concentrations on sand-carrying sedimentation of foam-fracturing fluid were evaluated. The effects of inorganic salts on foam morphology and foam morphology on proppant sedimentation were obtained through microscope observation, and the mechanism of inorganic salts on proppant sedimentation in foam-fracturing fluids was explored. The results show that 1% CaCl2 and 0.1% NaHCO3 inhibited the sand-carrying capacity of the foam-fracturing fluid, whereas two concentrations of MgSO4 and KCl promote the sand-carrying capacity of the foam-fracturing fluid. The effect of inorganic salts on the sand-carrying properties of cationic surfactant foam-fracturing fluids is divided into two main stages. During the settling phase, inorganic salts affect settling by changing the viscosity of the foam-fracturing fluid and the repulsive force of the double electric layer on the proppant. During the suspension phase, the proppant improves the probability of collision between the proppant and the foam by promoting the foam particle size and improves the hindering effect of foam pressure and structural forces on the proppant. The results have a guiding significance for developing foam-fracturing technology.

Key factors for regulation of cell morphology in supercritical CO2 direct rapid depressurization foaming silicone rubber process

Silicone rubber foam was prepared by direct rapid depressurization foaming process using supercritical CO2 as foaming agent. It was found that under high temperature and pressure, the dissolution of CO2 and the vulcanization reaction occurred simultaneously. The vulcanization degree range with good cell morphology was between 19.8% and 48.2%. When the saturation pressure exceeded 16 MPa, the cell morphology did not depend on foaming pressure. When the temperature was increased from 110 °C to 140 °C, the degree of vulcanization increased from 1.8% to 60.5%, and the cell size ranged from 13.9 µm to 646.4 µm, with an order of magnitude variation in cell density. This study identified the key control factors for supercritical CO2 relief foaming of silicone rubber and provided a fast and efficient preparation method, as well as theoretical guidance, for obtaining lightweight microporous silicone rubber foams.

Effect of crystalline transformation on supercritical CO2 foaming and cell morphology of isotactic polybutene-1

As a polycrystalline polymer, isotactic polybutene-1 (iPB-1) will form different crystalline structures when it crystallizes under different conditions. In this work, we found a simple method to manipulate the cell structure of iPB-1 foams by controlling the annealing time of crystalline form II at room temperature and employing supercritical CO2 foaming. As the content of crystalline form II increases, the storage modulus (G′) and complex viscosity (|η * |) increase, and the solubility of CO2 in iPB-1 increases. Crystalline form II has a wider foaming temperature window compared to crystalline form I and exhibits a more uniform cell structure at temperatures between 95 °C and 125 °C. The average cell diameters of crystalline form II and I are 33.9 µm and 11.2 µm at 115 °C and 15 MPa CO2, respectively. A small amount of crystalline form I acts as a heterogeneous nucleation agent during the foaming process, resulting in the formation of a “petal-like” cell structure. During the foaming saturation process, the melted portion of iPB-1 with unstable crystalline form II transforms into crystalline form I′ under high-pressure CO2, while the unmelted portion transforms into crystalline form I. As the pressure increases, the cell structure of iPB-1 undergoes a transition from “petal-like” to bimodal cell structure, ultimately achieving a more uniform structure. Moreover, increasing foaming pressure can also change the cell structure of the foamed material from closed-cell to open-cell. The occurrence of bimodal melting peaks in the foamed samples is beneficial for the adhesion of beads during the molding process.

Structure-tunable poly(butylene adipate-co-terephthalate) foams with enhanced mechanical performance derived by microcellular foaming with carbon dioxide as blowing agents

Poly(butylene adipate-co-terephthalate) (PBAT) is an advanced environment-friendly polymer that exhibits excellent biodegradability and outstanding mechanical properties. Microcellular foaming can endow PBAT with many admirable properties, which is significant for broadening its applications. Nevertheless, it is still challenging to prepare high-performance PBAT foams with tailored structures due to poor foaming ability. Moreover, the unclear relationships between foaming process, cellular structure, and mechanical properties significantly limit its development and application. In this study, microcellular foaming with carbon dioxide as blowing agents was developed to prepare structure-tunable PBAT foams with enhanced mechanical performance. Firstly, microcellular foaming experiments were conducted under various foaming pressures and temperatures to investigate the dependence of cellular morphology on foaming conditions. Under the investigated foaming conditions, the cell diameter and expansion ratio of PBAT foams can be manipulated in the ranges of 10–100 µm and 1–20, respectively. Furtherly, the dependence of tensile properties and compressive properties on cellular morphology was clarified. Compared with cell diameter, expansion ratio exhibited a much more significant effect on both the tensile and compressive properties of foams. In particular, PBAT foams with a tensile property of 5 MPa and a compressive property of 0.5 MPa were prepared, which possessed a lower density of 0.15 g/cm3. The prepared structure-tunable PBAT foams showed much lower density but obviously enhanced mechanical properties than the PBAT foams reported in literature.

Morphological, Mechanical and Thermal Properties of Rubber Foams: A Review Based on Recent Investigations.

During recent decades, rubber foams have found their way into several areas of the modern world because these materials have interesting properties such as high flexibility, elasticity, deformability (especially at low temperature), resistance to abrasion and energy absorption (damping properties). Therefore, they are widely used in automobiles, aeronautics, packaging, medicine, construction, etc. In general, the mechanical, physical and thermal properties are related to the foam's structural features, including porosity, cell size, cell shape and cell density. To control these morphological properties, several parameters related to the formulation and processing conditions are important, including foaming agents, matrix, nanofillers, temperature and pressure. In this review, the morphological, physical and mechanical properties of rubber foams are discussed and compared based on recent studies to present a basic overview of these materials depending on their final application. Openings for future developments are also presented.