Foam Expansion Ratio Research Articles

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.

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.

Kinetics and dynamics of Gas-liquid separation and bubble generation in surfactant solutions: Role of bulk/interfacial properties and hydrodynamic conditions

Understanding the kinetics and dynamics of gas–liquid separation and bubble generation in surfactant solutions is important for many industrial applications. To explore the potential mechanisms affecting the physical properties (expansion ratio, bubble size, and foam stability) of foams and bubbles, the surface tension of the solution, including the equilibrium and dynamic properties, was investigated. Then, the morphology of the surfactant aggregates was explored by cryo-transmission electron microscopy (cryo-TEM). Based on these experimental results, the effects of various physical and chemical factors (including the relative concentration of surfactant, dynamic surface tension, surface coverage, surface elasticity, surface mobility, aggregate morphology, etc.) on the expansion ratio and bubble size were analysed to identify which “universal” parameters can explain the phenomenon for all aqueous solutions in the gas–liquid separation process. Research has shown that the morphology of aggregates in a solution largely determines the surface properties of the solution at 1.5 ms (surface tension, surface coverage, surface elasticity, and so on). These surface properties significantly affect the expansion ratio. However, no good correlation was found between bubble size and these surface properties because surfactant vesicles can directly affect bubble size. In addition, the liquid flow rate and gas–liquid ratio have a significant impact on the expansion ratio and bubble size. Ultimately, we found that the foam stability, bubble size, and expansion ration can be described by a simple linear relationship. Our research provides new opinions for further understanding the effects of bulk/interfacial properties and hydrodynamic conditions on the physical properties of bubbles in the gas–liquid separation process.

Influence of modified additives on the properties of compressed air foam

The object of this study is the properties of compressed air foam with the use of modified additives: its drainage time and expansion ratio. The main properties of compressed air foam that affect the effectiveness of fire extinguishing are its drainage time and expansion ratio. At the same time, a number of authors have confirmed that the introduction of chemically modified additives into the composition of water fire extinguishing substances makes it possible to increase the effectiveness of fire extinguishing. The problem to be solved was to determine the influence of five modified additives (NH4)2HPO4, NH4H2PO4, (NH4)2СO3, K2CO3 and KCl in the concentration range of 1–5 % by mass on the expansion ratio and drainage time of the compressed air foam. The results showed that the content of additives (NH4)2HPO4, NH4H2PO4 and (NH4)2СO3 in the aqueous solution of the foaming agent does not affect its expansion ratio within the given limits. On the other hand, with K2CO3 and KCl additives, it was not possible to obtain compressed air foam with a expansion ratio of 5–20, that is, their inefficiency in compressed air foam was noted. The characteristic dependence of the effect of (NH4)2HPO4, NH4H2PO4 and (NH4)2СO3 additives on drainage time has been determined. The greatest drainage time is characteristic of the K≈20 generation mode. The highest recorded drainage time index was established for NH4H2PO4, namely 5.45 min; for (NH4)2HPO4 the drainage time was lower by 8 %; for (NH4)2СO3 the drainage time was lower by 20 %. At the same time, with the use of (NH4)2HPO4, NH4H2PO4 and (NH4)2СO3, it is characteristic to obtain a foam with lower drainage time compared to foam of a conventional composition. Thus, for foam with a expansion ratio of K≈20, the drainage time of foam with NH4H2PO4 is lower by 17 %, with (NH4)2HPO4 by 23 %, and with (NH4)2СO3 by 33 %. The effect of reducing the drainage time of the foam can have a decisive role in reducing its effectiveness when used for extinguishing flammable liquids due to the extinguishing mechanism but is not decisive for extinguishing solid substances. Therefore, the fire-extinguishing effectiveness of compressed air foam with modified additives during the extinguishing of solid combustible materials in comparison with the conventional CAF composition requires further study

Active learning-based research of foaming agent for EPB shield soil conditioning in gravel stratum

Injecting soil conditioner into the soil during EPB shield construction is crucial for soil enhancement. Foam agent consumption is common but developing their composition and qualities is time-consuming. Hence, there is an urgent need for a novel approach to material design. This study presents the development of an active learning-based model for foam agents to enhance soil conditioning in gravel strata during EPB shield operations. Foaming volume and half-lift time were forecasted using six machine learning algorithms. The Extra Tree Regression (ETR) model was the most effective for volume prediction, while CatBoost Integration (CB) model performed best for time prediction. The new foam has a half-life of 945 s and the Foam Expansion Ratio (FER) of 21, suitable for EPB shield soil conditioning. The results of slump value and shear strength experiments show a positive correlation between soil slump value, shear strength, and an increase in Foam Inject Ratio (FIR).

Facile fabrication of lightweight and high expanded TPU/PBS bead blend foam with segregated microcellular network for reduced shrinkage and enhanced interface bonding

The emergence of expanded thermoplastic polyurethane foam beads (ETPU) has expanded the application range of polymer foam materials. However, most of the prepared bead foam products suffer from high shrinkage rate, high density, and poor interfacial bonding, severely affecting the mechanical stability and lightweighting of the products. Herein, this study constructed thermoplastic polyurethane/polybutylene succinate (TPU/PBS) bead blend foams with a segregated microcellular network structure (SMNS) for the first time, where the TPU/PBS continuous phase formed the SMNS and the bead phase was consisted of TPU foam beads. The results showed good interfacial bonding between the continuous and bead phases. By adding PBS to the continuous phase, the shrinkage percentage of TPU/PBS bead blend foam decreased from 79.19 % to 67.31 %, reduced by 15.0 %. In addition, the foam expansion ratio gradually decreased with increasing PBS content, dropping from 12.07 to 9.03. Moreover, TPU/PBS bead blend foams exhibited good energy absorption and mechanical stability without sacrificing thermal insulation performance. This work effectively reduced the shrinkage of TPU based foam materials, offering a simple and economical solution for the preparation of dimensionally stable, well-interfaced, and lightweight polymer foams.

Systematically varying zwitterionic-siloxane surfactant structure to affect interfacial properties, foam stability, and fire suppression

Zwitterionic siloxane-sulfobetaine (siloxaneSB) surfactants are developed to replace per- and poly-fluoroalkyl substances (PFAS) used currently in aqueous firefighting foams because PFAS pose significant threats to environment and human health. SiloxaneSB surfactant's head and tail structures are varied gradually, one step at a time, to vary hydrophilicity of the head and hydrophobicity, and oleophobicity of the tail. Identical methods and conditions are used across all the surfactants to correlate surfactant structure to interfacial and foam properties, and fire suppression. The results suggest that the amphiphilic balance of the siloxane surfactant have dramatic effects on CMC, interfacial tension, foam expansion ratio, foam degradation, heptane vapor permeation through a foam layer, and fire suppression but little effect on bubble size, coarsening, and liquid drainage. They show synergism between siloxaneSB and alkylpolyglycoside in gasoline fire suppression while trisiloxane-polyoxyethylene exhibited synergism in heptane fire suppression. A 28 ft2 gasoline pool-fire suppression results were consistent with the bench-scale findings for tetrasiloxaneSB and trisiloxane-polyoxyethylene formulations. Small changes to surfactant molecular structure can dramatically improve its amphiphilic balance, synergisms, fuel-foam interactions resulting in improved effectiveness of fluorine-free foams but depend very much on the fuel, unlike the fluorocarbon surfactants.

Foaming of thermoplastic polyurethane using supercritical CO2 AND N2: Antishrinking strategy

The transformation of thermoplastic polyurethanes into polymeric foams is attracting great interest nowadays. However, this technology has some challenges that it is necessary to resolve, being one of the most important the shrinkage suffered by the polymeric foams over time. For that reason, this work explores several alternatives to mitigate this phenomenon. These alternatives are divided into two groups: on the one hand, the refoaming of the shrunken foams using supercritical CO2 and N2 was explored; on the other hand, the foaming using mixtures of supercritical CO2 and N2 as foaming agents was carried out. After experiments, it was seen that, the refoaming with N2 of shrunken foams obtained by supercritical CO2 technology can increase and keep constant the initial expansion ratio of the shrunken foams. Moreover, it was also observed that ratios of CO2/N2 between 80/20 and 60/40 can avoid the shrinking issues suffered by the polymeric foams after foaming using supercritical technology.

Development of an environmentally friendly gel foam and assessment of its thermal stability and fire suppression properties in liquid pool fires

Large-scale tank fires are one of the most challenging firefighting scenarios and pose significant threats to the safety of personnel and the integrity of equipment. The development of effective extinguishing agents is thus of both fundamental and practical importance in the controlling, mitigation, and suppression of tank fires. In this study, a novel environmentally friendly fire suppression foam based on gel-glycoside was developed using alpha-olefin sulfonate (AOS) and alkyl ethoxy polyglycosides (AEG) as the foaming agents, and sodium silicate, and sodium bicarbonate as the gelling and cross-linking agents respectively. The optimal ratios of the foaming agents were determined firstly by examining the foam expansion ratio and foam comprehensive value. Subsequently, the foamability, thermal stability, cross-linking time, and spreadability of the optimized formulations were analyzed. Finally, the fire extinguishing effects and performance in suppressing burnback of these formulations were examined and compared with those of a traditional film-forming fluoroprotein foam (FFFP). The experimental results indicated that the gel-glycoside foam, consisting of a composite foaming agent (AOS:AEG = 1:9), sodium silicate, and sodium bicarbonate at concentrations of 0.6, 2.4 and 3.7 wt%, respectively, exhibited the best spreadability and thermal stability. This formulation also showed excellent performance in cooling and suppressing burnback in the fire extinguishing tests, with a 90 % burnback time of 485 s, 45 % higher than that of FFFP. The present results clearly demonstrated that gel-glycoside foams can effectively control and suppress liquid pool fires and hence reduce the risk in potential re-ignition. These findings are also important for the further development of gel foams for extinguishing large-scale oil storage tank fires.

Green preparation of poly (butylene succinate-co-butylene terephthalate) foam with tunable degradability and mechanical properties by supercritical CO2

Poly (butylene succinate-butylene terephthalate) (PBST) with different chain segments was synthesized by in-situ polycondensation, and foams were prepared by supercritical CO2 foaming. The crystallinity and tensile modulus of PBST increases with the aromatic content, slowing down the diffusion of CO2 and enhancing the dimensional stability of PBST foam. The rheological analysis reveals that a higher temperature of PBST modulus platform is correlated with a higher aromatic content, which is more conducive to the cell stability. The foaming temperature window is 60 - 80 °C at 30% aromatic content, which moves to 160 - 175 °C at 70% aromatic content, and the maximum expansion ratio of PBST foam decreases from 40.7 to 9.8. With the increase of aromatic content from 30% to 70%, there is an obvious improvement in the compressive modulus of PBST foam, from 0.92 MPa to 6.65 MPa, accompanied by a reduction in the weight loss rate of degradation decreased from 10.78% to 3.04% in 10 days. Hence, there is a careful balance between degradability and foamability of PBST foams. Introducing a suitable aromatic content obtained higher strength to improve the cell stability on the premise that the strong degradability can be maintained, which provides an effective strategy to prepare PBST foams with good degradability and favorable mechanical properties.

Rheological characterization of the conditioned sandy soil under gas-loading pressure for earth pressure balance shield tunnelling

Soil conditioning technology is usually required to modify the excavated soil to a fluid plastic state during the construction with earth pressure balance (EPB) shield. The steady pressure distribution in the excavation face is linked to soil fluidity. Compared with the slump test, the rheological behavior of the conditioned soil can better reflect the dynamic flow characteristics. A gas-loading rotational rheometer is developed to test the rheological properties of the conditioning agents and the conditioned sandy soil, which can overcome the disadvantage of uneven mechanical loading and create gas-loading conditions. The rheological properties of sandy soil conditioned by different agents under atmospheric and gas-loading pressure conditions were studied, and the influences of foam injection ratio (FIR), bentonite slurry injection ratio (SIR), and polymer injection ratio (PIR) on soil viscosity were analyzed. The test results show that the ambient air pressure only greatly influences the experimental group with foam. Under the same gas-loading pressure, the foam’s apparent viscosity decreases with the foam expansion ratio (FER) increasing. The rheological behavior of the conditioned sandy soil conforms to the Bingham model under atmospheric pressure and conforms to the Power Law model when PIR ≤ 5 % under gas-loading pressure of 3 bar. The Weissenberg effect accounts for the differences. When PIR > 10 %, the rheological curve of three agents conditioned sand conforms to the Herschel Bulkley model. The higher content polymer reacts with bentonite to increase the soil viscosity, and blocks the foam seepage channel, making it difficult for the foam to re-enter the soil under gas-loading pressure. Investigating the rheological behavior of different conditioned sandy soil provides optimization strategies for EPB performance.

Construction of a three-dimensional network in branched PETG to prepare PETG composite microcellular foam with outstanding mechanical properties at low temperatures

In response to the escalating demands in cold chain logistics, in this study, we developed a high-compression strength foam resistant to low temperatures using a proficient and accessible approach. The microcellular foam was prepared through chain modification and in situ-fibrillated technology of polytetrafluoroethylene (PTFE). An epoxy chain extender, ADR4468, was incorporated to enhance the foamability of poly(ethylene glycol-co-cyclohexane-1,4-dimethanol terephthalate) (PETG). In addition, chain-extended PETG (CEPETG)–PTFE nanocomposites were formulated by integrating a PTFE three-dimensional (3D) nanofiber network. The PTFE nanofiber serves as an effective nucleation agent owing to its large specific surface area and undergoes a crystal-shaped transformation to further augment its strength. By leveraging the synergistic influence of these two principles, we employed the scCO2 foaming technology to obtain CEPETG–PTFE nanocomposite microcellular foam, which exhibited high-compression strength at low temperatures. The introduction of the chain extender improved the foaming characteristics of PETG. Consequently, the expansion ratio of the PETG foam increased from 5.18 to 36.01. Moreover, the formation of the PTFE 3D nanofiber network decreased the cell size from 16.16 to 2.38 μm. Furthermore, the low-temperature compression of the foam increased by 266 %, with an improvement in its toughness.

Development of Eco-Friendly and High-Strength Foam Sensors Based on Segregated Elastomer Composites with a Large Work Range and High Sensitivity.

Achieving a high-strength piezoresistive foam with high sensitivity and a large workable range remains a major challenge. To realize these goals, we developed a facile, novel, and eco-friendly strategy for constructing segregated microcellular structures fabricated using coating, heat compression molding, and supercritical CO2 (ScCO2) foaming. The segregated poly(ether block amide) (PEBA)/carbon nanostructure (CNS) composites were fabricated via compression molding. This effectively improved the foamability and cell morphology of PEBA/CNS composites. Moreover, compared with the randomly distributed structure, the segregated structure also endowed the foams with better conductivity and sensing capability. Subsequently, the ScCO2 foaming was employed to fabricate segregated PEBA/CNS composite foams. The foaming gave composites a large compressibility and reduced their percolation threshold. Under 1 wt % CNS loading, via tuning the expansion ratio of foam from ∼2.1 to 4.1, the compression stress at 50% compression strain of foam varied from ∼3.3 to 0.5 MPa, and the conductivity changed from 4.89 × 10-3 to 1.93 × 10-6 s/m, implying a tunable conductivity. Additionally, the adjustable conductivity enabled the sensitivity of segregated composite foams to be regulated. The segregated PEBA/CNS foam (FCNS1-4.1) exhibited a good combination of high sensitivity (GF = 3.5), large work range (80% strain), and high compression strength (∼0.5 MPa at 50% strain) as well as a stable, reproducible, and durable sensing response under a low CNS content (∼0.11 vol %). Furthermore, the ΔI/I0 of FCNS1-4.1 (75.6% porosity) reached a high value of ∼810 and exhibited an ultrahigh sensitivity of ∼3706 () from 60 to 80% strain. Moreover, the foam sensor could be used as a sensing function sole for monitoring diverse human motions. Therefore, the segregated PEBA/CNS composite foams with outstanding piezoresistive performances show promising potential applications in monitoring human motions as wearable electronics and provides a new design strategy for a new generation of foam sensors with high performance.

Effect of soil conditioning on the permeability of coarse-grained soil in mechanized tunnelling

In coarse-grained soils, the reduction of soil permeability via conditioning can effectively prevent groundwater from entering the chamber, thus providing better tunnel face control and ultimately preventing excessive settlements of the surface. In this study, several mixtures of coarse-grained and soil-foam mixtures were utilized in experiments. In which, effects of the foam expansion ratio, foam injection ratio, soil water content, pressure, and grain size distribution on the soil permeability were investigated. In these experiments, two soil types of poorly graded sand (SP) and poorly graded sand with silt and gravel (SP-SM), with different grain sizes were utilized. Based on the experimental results, it has been observed that the soil permeability increases with increasing foam expansion ratio, water pressure, and the coarse-grained portion of the soil. Meanwhile, soil permeability decreases with increasing foam injection ratio and soil water content. Based on the observations, it can be inferred that optimal soil permeability for soil moisture of 15 %, the pressure of 1 bar with a certain grain size occurs at a foam expansion ratio of 7.5 and a foam injection ratio of 52 %.

Foaming behaviors and mechanical properties investigation of high‐strength polyethylene terephthalate/polycarbonate bead foam

AbstractDue to the low melt strength, PET foam cells easily grow, and due to the low CO2 concentration in PET, generating more nucleation sites during the foaming process is difficult. As a result, PET foam produced using the supercritical CO2 foaming method possesses a large cell size and a low expansion ratio, which leads to poor mechanical performance. In addition, there has not been much research on how to improve CO2 concentration in PET. In this work, the PC with higher melt strength and CO2 absorption capacity was incorporated into the PET matrix to improve the foaming behaviors of the blend. The results showed that the melt strength and CO2 concentration of PET/PC blends are much higher than that of pure PET. For instance, the melt strength and CO2 concentration of the PET/PC10 blend would be more than twice that of pure PET when the PC content is only 10%wt. By studying the foaming behavior, it was found that high melt strength inhibited the cell overgrowth and collapse of PET/PC foam, resulting in the foam with good cell structure was obtained. In addition, the high CO2 concentration in PET/PC blend is conducive to cell nucleation, thereby increasing the foam expansion ratio during the CO2 foaming process. Finally, the PET/PC blend foam with excellent mechanical properties was obtained. To be specific, the expansion ratio of the PET/PC blend foam was about 9.61, and the average cell size was only 40.38 μm. And the PET/PC blend foam possessed an excellent compressive strength of 7.41 MPa due to the strong interfacial bead cohesion, which showed the application prospect in the field of construction engineering.

Study of the microstructure, foaming property and cyclic compression performance of poly(ether-block-amide) foams fabricated by supercritical CO2 foaming

This paper systematically explored the effects of molecular structure on the foaming behavior of poly(ether-block-amide) (PEBA) and its influence on foam cyclic compression properties. It was demonstrated that increasing the hard segment (HS) content of PEBA not only improved crystallization and melting strength, but also narrowed the melting peak and shifted it to higher temperatures. In contrast to other thermoplastic elastomers such as TPU, PEBA with a higher HS content showed a lager foam expansion ratio but a narrower foaming window. Increasing HS content improved compression strength but deteriorated resilience of PEBA foams. As the expansion ratio increased to 5-fold, there was no significant reinforcing effect of HS on strength and modulus of PEBA foams, while the resilience of the foams increased constantly with decreasing HS content and increasing expansion ratio.

Effect of conditioning schemes on mechanical properties of EPB shield soil

Shearing conditioned sands under different pressure conditions requires understanding their mechanical properties with various conditioning schemes to ensure feasible conditioning during earth pressure balance (EPB) shield tunnelling in sandy strata. This paper investigates the effect of bentonite slurry and foam, conditioned with sodium carboxymethyl cellulose (Na-CMC), on the workability of sand with varying water content, to obtain preliminary conditioning schemes. The conditioned sands with suitable workability are tested using a pressurized vane shear apparatus to obtain their mechanical properties, including compressibility, resilience, and shear strength before and after resiling. Results indicate that Na-CMC can reduce filtration loss of bentonite slurry and foam expansion ratio (FER) of foam, whereas enhance the stability of them. The foam injection ratio (FIR) of foam-conditioned sands and the maximum slurry addition of slurry-foam-conditioned sands decrease linearly with increasing the initial water content of sand, provided the conditioned sands have suitable workability. Increasing the FIR can remarkably increase the void ratio of conditioned sands, which maintains high compressibility and resilience, and low shear strength before and after resiling. The addition of bentonite improves the workability of sand. The conditioning schemes are feasible when the total stress is lower than a specific critical value. The critical total stress can be increased by increasing FIR and reducing the water content of sand or slurry-conditioned sands. This paper provides critical guidance for the design of conditioning schemes.

Fire Damage Characteristics of Fire-Resistant Coating Materials in Petrochemical Plant Facilities

As industrial facilities, petrochemical plants require prompt investigation, diagnosis, and recovery in the event of fire damage associated with disasters and accidents. Due to the characteristics of petrochemical plants, which are mostly composed of steel structures with fire-resistant coating materials, the coating materials are the first to be damaged. Accordingly, in this study, the fire damage characteristics of fire-resistant coating materials were analyzed experimentally, verifying the possibility of estimating the heating temperatures based on such characteristics. The results show a correlation between the foam expansion ratio and the heating temperature of intumescent fire-resistant coating materials with foam properties. A significant correlation was found between the density and adhesion strength ratio and the heating temperature of spray-applied fire-resistant coatings. The results suggest the possibility of estimating the heating temperatures based solely on the fire damage characteristics of the coating materials, which could provide a platform for simplifying existing methods for investigating and diagnosing fire damage.

Aerosol formation during foam application of non-volatile biocidal substances.

The application of biocidal products by foam is considered an alternative to droplet spraying when disinfecting surfaces or fighting infestations. Inhalation exposure to aerosols containing the biocidal substances cannot be ruled out during foaming. In contrast to droplet spraying, very little is known about aerosol source strength during foaming. In this study, the formation of inhalable aerosols was quantified according to the aerosol release fractions of the active substance. The aerosol release fraction is defined as the mass of active substance transferred into inhalable airborne particles during foaming, normalised to the total amount of active substance released through the foam nozzle. Aerosol release fractions were measured in control chamber experiments where common foaming technologies were operated according to their typical conditions of use. These investigations include foams generated mechanically by actively mixing air with a foaming liquid as well as systems that use a blowing agent for foam formation. The values of the aerosol release fraction ranged from 3.4 × 10-6 to 5.7 × 10-3 (average values). For foaming processes based on mixing air and the foaming liquid, the release fractions could be correlated to the process and foam parameters such as foam exit velocity, nozzle dimensions, and foam expansion ratio.

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.