Microcellular Foaming Process Research Articles

Development of Dynamic Four-Dimensional Printing Technology for Patterned Structures by Applying Microcellular Foaming Process.

Four-dimensional (4D) printing adds the dimension of time to 3D-printed specimens, causing movement when external stimuli are applied. This movement enables applications across various fields, including the soft robotics, aerospace, apparel, and automotive industries. Traditionally, 4D printing has utilized special materials such as shape-memory polymers (SMPs) or shape-memory alloys (SMAs) to achieve this movement. This study explores a novel approach to 4D printing by applying microcellular foaming processes (MCPs) to 3D printing. This study primarily aims to design and fabricate patterned specimens using common materials, such as PLA, through 3D printing and to analyze their dynamic behavior under various foaming conditions. To demonstrate the potential applications of this technology, the degree of bending was measured by controlling the patterning and foaming conditions. The 3D-printed specimens with microcellular foaming exhibited predictable deformations owing to the asymmetric expansion caused by differential gas saturation. The results confirm that 4D printing can be realized using conventional materials without the need for smart materials and can introduce foaming processes as a new external stimulus. This study highlights the potential of combining 3D printing with microcellular foaming for advanced 4D printing applications.

Development of a biocompatible radiotherapy spacer using 3D printing and microcellular foaming process for enhanced prostate cancer treatment

In this study, a new active spacer was developed using three-dimensional (3D) printing technology and microcellular foaming process to overcome the limitations of current spacers used in prostate cancer treatment. In prostate cancer treatment, a spacer is inserted between the prostate and rectum to increase the distance between the two organs so as to reduce the radiation dose to the rectum. Radiotherapy spacer is widely used in particle therapy, such as proton and carbon beams, and X-ray radiation therapies, including intensity-modulated radiotherapy and stereotactic body radiation therapy. However, existing spacers have been reported to cause significant side effects. Therefore, this study introduces a 3D printing technique using polycaprolactone to develop a spacer that provides customized treatment and minimizes side effects. This technique utilizes the volume expansion that occurs when a 3D spacer printed to fit a patient’s organs undergoes foaming through a supercritical carbon dioxide (scCO2)-assisted microcellular foaming process. Additionally, the use of scCO2 allows simultaneous gas absorption and sterilization, thereby reducing the number of process steps. This study confirms the potential of the newly developed spacer to provide effective and safe radiotherapy for prostate cancer, reduce patient discomfort, and minimize rectal side effects during radiation treatment.

Incorporation of canola meal as a sustainable natural filler in PLA foams

The canola oil industry generates significant waste as canola meal (CM) which has limited scope and applications. This study demonstrates the possibility of valorization of CM as a sustainable natural filler in a biodegradable polymer composite of Poly(lactic acid) (PLA). Generally, interfacial bonding between natural fibers and the polymer matrix in the composite is weak and non-uniform. One possible solution is to derivatize natural fibre to introduce interfacial bond strength and compatibility with the PLA polymer matrix. Here, CM was succinylated in a reactive extrusion process using succinic anhydride at 30 wt% to get 14% derivatization with 0.02 g of -COOH density per g of CM. The CM or succinylated CM at 5 and 15 wt% was co-extruded with amorphous PLA to get composite fibers. CM-PLA and succinylated CM-PLA biocomposites were foamed using a mild and green microcellular foaming process, with CO2 as an impregnating agent without any addition of organic solvents. The properties of the foams were analyzed using differential scanning calorimetry (DSC), Dynamic mechanical thermal analysis (DMTA), shrinkage, and imaging. The addition of CM or succinylated CM as a natural filler did not significantly change the glass transition temperature, melting point, percent crystallization, stiffness, and thermal stability of PLA foams. This suggests succinylation (modification) of CM is not a mandatory step for improving interphase compatibility with the amorphous PLA. The new PLA-CM foams can be a good alternative in the packaging industry replacing the existing petroleum-based polymer foams.Graphical

Development of smart materials with versatile bending capabilities using microcellular foaming process: influence of foaming and desorption time

Abstract Herein, a smart material with versatile bending capability is developed using a microcellular foaming process (MCPs). In contrast to previous hydrogel-based approaches, the bi-layered smart material is fabricated using typical thermoplastics, polyethylene terephthalate glycol (PETG) and polymethyl methacrylate (PMMA), to achieve shape deformation in response to thermal stimuli. Further, the theoretical model for bi-layered smart materials based on the modified Timoshenko’s model is employed to predict and comprehend this thermal response phenomenon. Due to the distinct foaming characteristics of the two polymers, a reversal in the bending direction is achieved by manipulating the foaming and desorption time. The length variation after foaming differs depending on the desorption time for each polymer. PMMA decreases in length after foaming, measuring 56.25 mm at a desorption time of 40 min and 53.16 mm at 80 min. On the other hand, PETG shows an increase in length after foaming, measuring 53.33 mm at 40 min and 58.25 mm at 80 min. Consequently, when the two polymers are bonded and foamed, bending occurs depending on the desorption time, and a reversal in the bending direction is observed at the critical desorption time of around 60 min. Based on this result, the folding direction of a five-leafed flower-shaped object is successfully altered under thermal stimuli. This innovative approach extends the category of smart materials beyond the hydrogels and showcases the potential of the MCPs for the creation of smart materials for various applications that require versatile shape changes in response to temperature.

An efficient pre-foamed method to fabricate low density poly(ether-block-amide) foams

Poly (ether-block-amide) PEBA foams have been widely used in many industrial fields. However, compared with amorphous polymers, the microcellular foaming process of PEBA is more complicated due to their complex phase morphology evolution behavior. Moreover, the productivity was limited owing to the long saturation time for thick samples. In this study, we proposed an efficient pre-foamed method to fabricate low density poly(ether-block-amide) foams. PEBA foams with controlled rather high density were firstly prepared by microcellular foaming under relatively low foaming temperatures. Afterwards, the pre-foamed PEBA sample with a high density were further foamed into much lower density by using secondary microcellular foaming under relatively high foaming temperature. The microphase separation phenomenon in PEBA was clearly studied by scanning transmission electron microscopy and atomic force microscopy-based infrared spectroscopy technique. Thanks to pre-foaming process, the diffusion rate of CO2 in PEBA matrix was greatly increased, resulting in shorter saturation time in microcellular foaming process. Most interestingly, pre-foaming process can also help PEBA achieve a higher expansion ratio compared with traditional microcellular foaming process with the same foaming parameters. Pre-foaming driven foaming process was a practical way of achieving low-density PEBA foams efficiently without adding new equipment, especially for thick parts.

Friction and Wear Characteristics of Bacterial Cellulose Modified by Microcellular Foaming Process

Bacterial cellulose (BC) is a biodegradable, non-toxic, natural substance that can be obtained by culturing bacteria. It can be approached in various ways from physical, chemical, and biological points. BC nanoparticles have been applied as lubricating additives to improve the load capacity, anti-wear, and friction. The microcellular foaming process was created using a technology based on the saturation of the polymer by supercritical CO2 and rapid decompression. An increase in saturation pressure leads to an increase in the molecular potential energy of CO2, which can be more easily compressed into the cellulose matrix. Moreover, the high crystallinity and water content combination contribute to thermal stability. Specimen membranes produced by Komagataeibacter xylinus prepared with a thickness of 2 mm were saturated in supercritical condition, 10 MPa of CO2 for 4 h, and foamed at a temperature of 120 °C in a hot press. After the foaming process, we used dry ice to cool the BC. Before foaming, the friction coefficient continuously increased with the increase in cycles, and after foaming, a stable friction coefficient of 0.3 or less was secured despite the increase in the cycle. The microcellular foaming process significantly reduced and made BC’s coefficient of friction stable.

Developing sustainable and recyclable high-efficiency electromagnetic interference shielding nanocomposite foams from the upcycling of recycled poly(ethylene terephthalate)

The demand for high-performance electromagnetic interference (EMI) shielding composite foams with satisfactory environmental friendliness and high sustainability has increased considerably. However, considerable obstacles are frequently encountered in the practical development of incorporating upcycling of plastic wastes and environmentally friendly foaming technologies into the manufacture of such EMI shielding systems. In this research, we developed a lightweight sustainable nanocomposite foam system with outstanding EMI shielding performance from the integration of chemical upcycling of recycled poly(ethylene terephthalate) (PET) and supercritical carbon dioxide (sc-CO2) microcellular foaming. First, a green thermoplastic polyamide elastomer (TPAE) system was synthesized using a renewable bis(6-aminohexyl)terephthalamide (BAHT) monomer derived through the aminolysis of recycled PET, followed by adding single-walled carbon nanotubes (SWCNTs) into the TPAE system for the manufacture of TPAE/SWCNT nanocomposites. The π–π stacking of BAHT efficiently enhanced the melt strength of the material system, which was conducive for microcellular foaming process. After sc-CO2 foaming, a series of highly expanded nanocomposite foams with uniform microporous structure that could enable multiple reflections of electromagnetic waves were fabricated. Upon adding only 2 wt% SWCNTs, the foam system achieved a favorable conductivity of 0.15 S/cm and an extremely high specific shielding effectiveness (SSE) of 213.26 (dB cm3/g). Furthermore, the green nanocomposite foam possessed excellent durability. After being bent or twisted 1000 times, the foam maintained EMI shielding effectiveness of > 90% of the original value. Moreover, the foam could be easily recycled, reprocessed, and refoamed. For developing sustainable EMI shielding products, we believe that this study provides a promising direction with benefits of alleviating waste accumulation and reducing the use of virgin plastics in manufacture of foams, showing potential for advanced sustainable electronic applications.

Solid-State Surface Patterning on Polymer Using the Microcellular Foaming Process

This study proposes a novel process that integrates the molding and patterning of solid-state polymers with the force generated from the volume expansion of the microcellular-foaming process (MCP) and the softening of solid-state polymers due to gas adsorption. The batch-foaming process, which is one of the MCPs, is a useful process that can cause thermal, acoustic, and electrical characteristic changes in polymer materials. However, its development is limited due to low productivity. A pattern was imprinted on the surface using a polymer gas mixture with a 3D-printed polymer mold. The process was controlled with changing weight gain by controlling saturation time. A scanning electron microscope (SEM) and confocal laser scanning microscopy were used to obtain the results. The maximum depth could be formed in the same manner as the mold geometry (sample depth: 208.7 μm; mold depth: 200 μm). Furthermore, the same pattern could be imprinted as a layer thickness of 3D printing (sample pattern gap and mold layer gap: 0.4 mm), and surface roughness was increased according to increase in the foaming ratio. This process can be used as a novel method to expand the limited applications of the batch-foaming process considering that MCPs can impart various high-value-added characteristics to polymers.

Processing Effects on the Through-Plane Electrical Conductivities and Tensile Strengths of Microcellular-Injection-Molded Polypropylene Composites with Carbon Fibers.

Polymers reinforced with conducting fibers to achieve electrical conductivity have attracted remarkable attention in several engineering applications, and injection molding provides a cost-effective way for mass production. However, the electrical performance usually varies with the molding conditions. Moreover, high added content of conducting fibers usually results in molding difficulties. In this study, we propose using microcellular (MuCell) injection molding for polypropylene (PP)/carbon fiber (CF, 20, and 30 wt%) composites and hope that the MuCell injection molding process can improve both electrical and mechanical performance as compared with conventional injection molded (CIM) parts under the same CF content. Both molding techniques were also employed with and without gas counter pressure (GCP), and the overall fiber orientation, through-plane electrical conductivity (TPEC), and tensile strength (TS) of the composites were characterized. Based on the various processing technologies, the results can be described in four aspects: (1) Compared with CIM, microcellular foaming significantly influenced the fiber orientation, and the TPECs of the samples with 20 and 30 wt% CF were 18–78 and 5–8 times higher than those of the corresponding samples molded by CIM, respectively; (2) when GCP was employed in the CIM process, the TPEC of the samples with 20 and 30 wt% CF increased by 3 and 2 times, respectively. Similar results were obtained in the case of microcellular injection molding—the TPEC of the 20 and 30 wt% composites increased by 7–74 and 18–32 times, respectively; (3) although microcellular injection molding alone (i.e., without GCP) showed the greatest influence on the randomness of the fiber orientation and the TPEC, the TS of the samples was the lowest due to the uncontrollable foaming cell size and cell size uniformity; (4) in contrast, when GCP was employed in the microcellular foaming process, high TS was obtained, and the TPEC was significantly enhanced. The high foaming quality owing to the GCP implementation improved the randomness of fiber orientation, as well as the electrical and mechanical properties of the composites. Generally speaking, microcellular injection combined with gas counter pressure does provide a promising way to achieve high electrical and mechanical performance for carbon-fiber-added polypropylene composites.

Structure-gradient thermoplastic polyurethane foams with enhanced resilience derived by microcellular foaming

Polymer foams with gradient cellular structure show superior mechanical and physical properties, while developing polymer foams with tailored gradient-structures is still challenging. Herein, an environmentally-friendly foaming process with CO2 as blowing agents was developed for fabricating structure-gradient thermoplastic polyurethane (TPU) foams. In the unique microcellular foaming process, a two-step sorption procedure with a low CO2 pressure at the first stage and a high CO2 pressure at the second stage was used to generate gradient CO2 concentration in the solid TPU samples, which results in gradient cellular morphology in TPU foams. By varying the second sorption time, TPU foams with various gradient cellular morphology were prepared. Interestingly, the gradient cellular morphology helped to increase compression strength by 71.4% and modulus by 113.8%, to enhance resilience with a 24.7% reduction in energy loss coefficient and a rebound coefficient of 61.4%, and also to benefit shape-recovery after long compression deformation.

Acoustic Characteristics of Microcellular Foamed Ceramic Urethane.

Noise pollution critically degrades the quality of human life, and its effects are becoming more severe due to rapid population growth and the development of industry and transportation. Acoustic wave aggregation in the 30–8000 Hz band can have a negative impact on human health, especially following continuous exposure to low-frequency noise. This study investigates the acoustic performance of microcellular foams made of a mixture of brittle and soft materials and their potential use as absorption materials. It is common to use porous materials to improve acoustic properties. Specimens prepared by mixing ceramic and urethane were made into microcellular foamed ceramic urethane by a batch process using carbon dioxide. The specimens were expected to exhibit characteristics of porous sound-absorbing materials. After measuring the acoustic characteristics using an impedance tube, a significant sound-absorption coefficient at a specific frequency was noted, a characteristic of a resonance-type sound-absorbing material. However, the sound-absorption properties were generally worse than those before foaming. Differences based on the size, shape, and structure of the pores were also noted. It will be necessary to check the effects of cellular morphological differences on the absorption properties by controlling the variables of the microcellular foaming process in a future study.

3D‐Printed Polyurethane Tissue‐Engineering Scaffold with Hierarchical Microcellular Foam Structure and Antibacterial Properties

This work proposes a facile fabrication strategy of polyurethane (TPU) tissue‐engineering scaffold with hierarchical structure, designed by combination of the fused deposition modeling (FDM) 3D printing and supercritical microcellular foaming by carbon dioxide (CO2). Further surface modification of TPU scaffold with graphene oxide (GO) was carried out by in situ polymerization of polydopamine (PDA) to ensure stable loading of GO with antibacterial properties. The influence of 3D‐printing temperature and speed on the microcellular cell morphology of TPU scaffold was investigated and optimized. The microcellular foaming and expansion process was indicated to compensate mechanical loss because of the gaps of stacking layers by FDM printing, and the reported tensile strength of 28 MPa matched well with that of natural cartilage tissue constructs. More interesting, the formation of interconnected open pores on the surface of foamed TPU scaffold shows much more enhanced cell adhesion because of the bigger specific surface area of microcellular structure. Similarly, the foamed TPU scaffold exhibits good absorption of GO nanosheets by the synthesized PDA on the surface and antibacterial properties, compared with the unfoamed TPU scaffold. This work offers a strategy for designing and manufacturing polymer tissue‐engineering scaffold with hierarchical structure and good antibacterial property.

Vibration and Sound Response of Glass-Fiber-Reinforced Polyamide 6 Using Microcellular-Foaming-Process-Applied Injection Molding Process.

In this study, the vibration and sound response characteristics of composites produced via injection molding applied with a microcellular foaming process (MCPs) were improved. The study was conducted using PA6 and glass fiber composites, which are representative thermoplastic engineering plastics. Two types of specimens were used: a plate specimen to confirm the basic sound and vibration characteristics, and a large roof-rack specimen from an actual vehicle with a complex shape. The frequency response function curve was calculated by conducting an impact test, and natural frequency and damping ratio were measured based on the curve. The results confirmed that, in the case of a specimen manufactured through the injection molding process to which MCPs were applied, the natural frequency was lowered, and the damping ratio decreased. The degree of change in the natural frequency and damping ratio was confirmed. To determine the cause of the change in the natural frequency and damping ratio, the mode shape at the natural frequency of each specimen was measured and the relationship was confirmed by measuring the density and the elastic modulus of the composite. In addition, the usability of the specimens to which MCPs were applied was verified by conducting impact strength and tensile strength tests.

Enhanced Foaming Behavior of Ultrahigh Molecular Weight Polyethylene by Blending Silicone Powder in Microcellular Foaming

Microcellular foaming with CO2 as the blowing agent is developed to prepare low‐density ultrahigh molecular weight polyethylene (UHMWPE) foams. To improve the foaming behavior of UHMWPE, silicone powder is used to modify UHMWPE by twin‐screw compounding. The silicone powder contents, foaming temperatures, and foaming pressures are varied to investigate their effect on the foaming behavior of UHMWPE in a one‐step microcellular foaming process. The results show that the addition of silicone powder leads to significantly improved foaming behavior of UHMWPE by simultaneously increasing the expansion ratio and refining cellular morphology. With the presence of silicone powder, UHMWPE with an expansion ratio up to 34‐fold is prepared, while the maximum expansion ratio of pure UHMWPE foam that can be achieved is only 15‐fold. Moreover, for the foams with the same expansion ratio, the presence of silicone powder leads to significantly refined cellular morphology. The improved melt flowability and accelerated crystallization by adding silicone powder are responsible for the significantly enhanced foaming ability of UHMWPE. The heterogeneous nucleation effect of silicone powder plays a critical role in refining the cellular morphology by promoting cell nucleation and reducing cell collapse.

Exfoliation and distribution behavior of graphene nanoplatelets in polystyrene-based foams fabricated by supercritical CO2 assisted microcellular foaming

The effects of supercritical CO2 (scCO2) on polymer chains’ mobility and graphene nanoplatelets (GNPs) exfoliation and distribution in a microcellular foaming process are investigated by the molecular dynamics (MD) simulations and experiments. The results of MD simulations and visualization analysis confirm that the synergistic effect of scCO2 molecules and polystyrene (PS) chains is beneficial for them to penetrate into the interlayer of GNPs during the scCO2 treatment at high saturation pressure. The scanning electron microscope images show that some cells exist in the interlayer of GNPs in the foam fabricated in the highest saturation pressure and shortest depressurization time. With foaming in different depressurization time, the growing cells facilitate the movement of GNPs after their exfoliation, leading to alignment around the cells. As compared to large diameter GNPs, the GNPs with small diameter rearrange easily and distribute more homogeneously due to lower resistance of GNPs’ movement.

Biodegradable highly porous interconnected poly(ε‐caprolactone)/poly(L‐lactide‐co‐ε‐caprolactone) scaffolds by supercritical foaming for small‐diameter vascular tissue engineering

AbstractBiodegradable ϕ4 mm tubular porous poly(ε‐caprolactone)/poly(L‐lactide‐co‐ε‐caprolactone) (PCL/PLCL) scaffolds are fabricated successfully via one‐step microcellular supercritical carbon dioxide foaming process. The effect of blending ratio on the rheology, pore structures, mechanical property, wettability, and biocompatibility of PCL/PLCL blends tubular scaffold are reported. Rheological results show that PCL matrix and PLCL dispersed phase has good compatibility. The melt strength of PCL can be enhanced obviously by adding PLCL. With an increase of PLCL content from 10 to 30 wt%, the pore size increases from 7.6 to 24.9 μm due to the homogeneous nucleation effect. The maximum open‐cell content can reach 77% for PCL/PLCL foamed sample. Cyclical tensile and compliance tests show that few content of dispersed PLCL (10–20 wt%) improves the flexibility and recoverability. Cell viability results demonstrate that human umbilical vein endothelial cells (HUVECs) cultured on all PCL/PLCL porous scaffolds exhibit a typical spindle‐like cell morphology. Moreover, HUVECs have a higher density and spreading areas on surface of 10% PLCL scaffold. The results gathered in this paper may open a new perspective for the fabrication of small‐diameter vascular tissue engineering scaffold.

Nanocellular TPU composite foams achieved by stretch-assisted microcellular foaming with low-pressure gaseous CO2 as blowing agent

Microcellular foaming is an advanced eco-friendly foaming technology with carbon dioxide as blowing agent. Generally, high-pressure supercritical blowing agents is needed to achieve microcellular structure with cell size less than 10 μm, which places high requirements on the foaming equipment and brings safety issues, thereby resulting in high production and maintenance costs. Herein, the stretch-assisted microcellular foaming technology was developed to prepare TPU, TPU/nanographite, and TPU/PMMA foams with significantly refined cellular structure. The results demonstrate that stretch can dramatically promote cell nucleation. For the neat TPU, the cell density can be increased by more than 8 orders of magnitude by applying a linear strain of 50 % in microcellular foaming. Increasing the amount of stretching can continue to refine the cell morphology. Compared with the neat TPU foam, the TPU/nanographite composite foam and the TPU/PMMA composite foam show further refined cellular morphology under the same foaming condition. Surprisingly, with low-pressure (300 psi) gaseous carbon dioxide as blowing agents, microcellular TPU and TPU/nanographite foams, and nanocellular TPU/PMMA foam were achieved by the stretch-assisted microcellular foaming. Furthermore, the modified classical cell nucleation theory by considering the role of elastic distortion energy in cell nucleation was proposed to clarify the cell nucleation behavior in the stretch-assisted microcellular foaming process. According to the theory, the synergistic effect of stretch-induced cell nucleation and heterogeneous phase-induced cell nucleation is the underlying mechanism of the significantly refined cellular morphology.

Energy Harvesting of Ionic Polymer-Metal Composites Based on Microcellular Foamed Nafion in Aqueous Environment

The purpose of this study was to determine how to improve the energy-harvesting properties of polymer electrolyte membranes by varying their porosity. We achieved this by applying microcellular foaming process (MCP) to Nafion-based ionic polymer–metal composites (IPMCs). We manufactured an IPMC by forming a Pt electrode through an electroless plating method on the Nafion film, to which porosity was imparted by varying the foaming ratio and inducing deformation by vibrating the specimen using a prototype device that we developed ourselves. We attempted to harvest energy via fluid flow that occurred owing to displacement movement. When the Nafion film was foamed at a temperature of 140 °C or higher, it was observed that cells with size of approximately 1 µm or more were formed, and when the saturation temperature was lowered, a denser and larger number of cells were formed. Moreover, the cells formed on the electrolyte membrane allowed the retention of more water. Water retention generated charges contributed to the operational stability of IPMC. This was attributed to the difference in the amount of charge generated by changing only the internal morphology of the electrolyte membrane, without changing the substrate or the electrode material.

Shape-Memory-Recovery Characteristics of Microcellular Foamed Thermoplastic Polyurethane.

We investigated the shape-recovery characteristics of thermoplastic polyurethane (TPU) with a microcellular foaming process (MCP). Additionally, we investigated the correlation between changes in the microstructure and the shape-recovery characteristics of the polymers. TPU was selected as the base material, and the shape-recovery characteristics were confirmed using a universal testing machine, by manufacturing dog-bone-type injection-molded specimens. TPUs are reticular polymers with both soft and hard segments. In this study, we investigated the shape-memory mechanism of foamed polymers by maximizing the shape-memory properties of these polymers through a physical foaming process. Toward this end, TPU specimens were prepared by varying the gas pressure, foaming temperature, and type of foaming gas in the batch MCP. The effects of internal structural changes were investigated. These experimental variables affected the microstructure and shape-recovery characteristics of the foamed polymer. The generated cell density changed, which affected the shape-recovery characteristics. In general, a higher cell density corresponded to a higher shape-recovery ratio.

Depressurization induced morphology control in solid-state microcellular batch foaming process

This research article describes the impact of the depressurization rate change on the morphology of microcellular polycarbonate foams (PCMFs) using batch-wise foaming with carbon dioxide as a physical blowing agent. It was expected that the depressurization rate will affect the foaming behavior of microcellular foamed polycarbonate (PCMFs). While keeping other variables constant and changing depressurization rate, the depressurization rate affects the cell size, cell density, cell size distribution, and expansion ratio. The result showed cell diameter 5 ± 0.5, 7 ± 0.8, 9 ± 1.2, and 9.5 ± 1.5 µm and expansion ratio 5.2, 5.5, 6.0, and 6.3 at depressurization rate of 0.5 (D1), 0.05 (D2), 0.01 (D3), and 0.005 (D4) MPa/Sec, respectively. The cell area distribution showed that a higher depressurization rate leads to the more regular distribution of cells. The cell densities were observed as 2.6 × 1010, 4.6 × 109, 2 × 109, and 8.2 × 108 cells/cm3 at D1, D2, D3, and D4. It is investigated that as compare to depressurization rate other variables such as saturation pressure, foaming temperature and foaming time has more impact on properties of PCMFs.