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Thermoplastic polyamide elastomer (TPAE)/calcium silicate (CaSiO3) open‐cell foam with low shrinkage and high expansion ratio was prepared by using supercritical CO2 as a blowing agent. Adding CaSiO3 led to increased melt viscoelasticity and reduced crystallinity of TPAE. The primary mechanism of CaSiO3 promoting TPAE foam to form the open‐cell structure was discussed. The interaction between CaSiO3 and TPAE is fragile, making CaSiO3 easy to fall off the cell wall and form the open‐cell structure during foaming process. The increasing CaSiO3 content leads to increased cell density and thinned cell walls, thus increasing the tensile stress on cell wall. On the other hand, the agglomeration of CaSiO3 increases particle size, making it easier to fall off from the adhesion of TPAE matrix. The two aspects work together to improve the open‐cell content of TPAE foam up to 93.28%. The open‐cell structure is conducive to increasing the gas exchange rate and significantly decreasing foam shrinkage ratio. Finally, TPAE foam with a shrinkage ratio of only 2.68% and an expansion ratio of 18.77 times was obtained. In addition, open‐cell structure improves the adsorption performance of TPAE/CaSiO3 foam by 500%. [ABSTRACT FROM AUTHOR]

Research on nanocellular foams is motivated in part by the promise of physical properties, in particular mechanical properties, that can go beyond the classical mechanical framework. However, due to the difficulty in obtaining foams of a given density but different cell sizes, determining the effect of cell size on the mechanical properties of polymer foams remains a challenge. To overcome this difficulty, studies on the mechanical behaviour of mesocellular, microcellular and nanocellular polymer foams have been compiled in this review article. After describing the different cellular structures between meso-, micro- and nanocellular foams, the mechanical properties are examined as a function of relative density and cell size. It is shown that for small strains and at low strain rates, nanocellular foams exhibit mechanical behaviour predicted by the Gibson and Ashby model. Relative density remains the first important factor to be taken into account when studying the Young's modulus and buckling stress of nanocellular foams. The focus then shifts to fracture properties, as microcellular foams have already been shown to be far superior to more conventional foams. As studies are still scarce and different methodologies have been used, no general conclusions can be drawn. However, the fracture and impact properties could be greatly improved by this change in scale. The local confinement of molecular chains in polymeric nanocellular foams or the relaxation of the triaxial stress state in front of the crack tip could explain these observations. [ABSTRACT FROM AUTHOR]

Hot air, water, and glycerol were studied as foaming mediums for the production of ETPU to evaluate their influence on the behavior of the foam and compare the optimal particles for each of the foaming temperatures selected. The results showed that the times of water foaming and glycerol foaming were shorter by about 2/3 than with hot-air foaming. The best foaming temperatures for hot-air foaming, glycerol foaming, and water foaming are 110–115 °C, 75 °C, and 90 °C, respectively. The particles of glycerol foam have a matte appearance and their gloss is not very good. However, the particles in hot-air foaming are light, and the gloss is very satisfactory. The gloss of the surface of water-foaming particles is dim. At the same time, there is a faint matte appearance. Particles made with glycerol foaming and water foaming are more even than those made with hot-air foaming. The density of foaming materials from glycerol foaming, hot-air foaming, and water foaming are raised accordingly, while the hardness of foaming materials from glycerol foaming, water foaming, and hot-air foaming are successively increased. [ABSTRACT FROM AUTHOR]

Thermoplastic polyurethane (TPU) elastomer is a commonly used material for foam preparation. However, its application is hindered by significant shrinkage behavior. To reduce the foam shrinkage, polylactic acid (PLA) and calcium stearate‐modified montmorillonite (MMT‐St) are incorporated into the polyurethane matrix. The TPU/PLA/MMT‐St composite foams are formed using an intermittent supercritical carbon‐dioxide‐foaming process. The addition of PLA inhibits the relaxation of TPU chain segments, while the introduction of calcium stearate (GaSt2) improves the dispersion of MMT within the matrix, increases the nucleation sites of cell growth, and improves cell structure. The cell diameter decreases from 10 to 4 μm, while the cell density increased from 4.1 × 1012 to 15.8 × 1012 cell cm−3. In addition, the cell distribution range narrows from 4–19 to 2–6 μm. Incorporating MMT‐St increases the crystallinity and thermal stability of TPU/PLA, mitigates chain relaxation at room temperature, and enhances foam dimensional stability. As a result, this leads to a decrease in shrinkage rate from 27.5% to 5%. As both matrices of the material are thermoplastic, this composite foam possesses recyclability with enhanced material utilization. [ABSTRACT FROM AUTHOR]

The elevated rates of electromagnetic radiation pollution, resulting from the growing need for wireless communication systems and electronic gadgets, have sparked interest in creating shielding materials that are lightweight, flexible, non‐corrosive, simply processable, and affordable. In this study, a collection of microcellular nanocomposites based on ethylene octane copolymer (EOC) were created utilizing Vulcan XC 72 conductive carbon black (VCB) by a dual mixing process involving both melt and solution mixing. A chemical blowing agent was utilized to induce the cellular architecture in the composite, resulting in its lightweight nature (maximum density of 0.65 g/cc). The composite foam, when loaded with 30 parts per hundred of volume (phr) of VCB, displays a conductive network and also achieves an electromagnetic interference (EMI) shielding efficiency of 23.2 decibels (dB), satisfying commercial requirements. Furthermore, the findings indicated that the composite's cellular structure significantly influences the absorption‐dominated EMI shielding mechanism with an absorption rate of 89%–94% and a specific shielding effectiveness of 194 dBcm2/g within the frequency range of 8.2–12.4 GHz (X band). The foam composite also demonstrated as a thermal management system, with a maximum thermal conductivity of 0.3 W/mK. As a result, this lightweight, easily processable, electrical conductive EOC/VCB polymer composite foams are projected to be used as EMI shielding materials in electronics, cars, and packaging. Highlights: Fabrication of lightweight microcellular Carbon black‐loaded EOC compositeRheological, mechanical, and thermal properties of foam compositesThe cell density filled composites reduces by the cellular foam structuresCarbon black pronouncedly enhanced the electrical conductivity of foam compositeAn absorption‐dominated shielding effectiveness with ultra‐low reflection. [ABSTRACT FROM AUTHOR]

Processing 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. [ABSTRACT FROM AUTHOR]

Challenges remain in large-scale and successive preparation of porous polymer composite component, which limits its practical applications for high-performance electromagnetic interference (EMI) shielding. Herein, a scalable and efficient method based on mold-opening foam injection molding was developed to fabricate carbon fiber (CF) reinforced polymer composite foams for EMI shielding applications. Thanks to the novel foaming process and heterogeneous nucleation effect of CF, real microcellular poly(ether-block-amide) (PEBA)/CF composite foams with an average cell size of 6.6 μm and a cell density of up to 109 cells/cm3 were achieved. Due to the significantly refined cellular morphology, the PEBA/CF composite foams exhibit superior EMI shielding performance over the unfoamed composites which was characterized by absorption-dominated shielding characteristics and significantly enhanced EMI shielding effectiveness. Furthermore, compared with the unfoamed case, the foamed PEBA/CF composites with refined cellular morphology shows greatly improved cold toughness and duality, and the tensile strain at break and specific tensile toughness are increased by 88.6% and 109.1%, respectively. Moreover, real-microcellular PEBA/CF composite foams have remarkably enhanced surface quality than those fabricated by regular foam injection molding process, and the surface roughness can be maximumly increased by 91.6%. Thus, this study provides a promising strategy for producing lightweight and strong components for high-performance EMI shielding applications.

Copyright of China Plastics / Zhongguo Suliao is the property of Journal Office of CHINA PLASTICS and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Lightweight porous materials have garnered increasing attention in application domains of intelligent construction and flexible thermal insulation, owing to their customizable 3D porous structures and outstanding performances. Nonetheless, the severe environmental pollution resulting from the accumulation of non-degradable plastic waste in the ecosystem has sparked significant interest in developing bio-degradable thermal insulation foams. The preparation of biodegradable foam, however, typically requires operating specialized equipment for long periods under extreme conditions, which diminishes its environmental friendliness as claimed. Herein, we present a pioneering "Reinforcing-Foaming-Recovering" strategy to achieve ultralight and recyclable green foams with excellent thermal insulation properties. This innovative strategy, involving materials reinforcing and low-pressure foaming complemented by nitrogen-assisted gas recovering enables the preparation of low-density (0.08 g/cm3) biodegradable foams with restricted shrinkage ratio (<5%). Thanks to the easy-to-control foaming method, combined with the improved 3D network cellular structures caused by nitrogen-assisted gas exchange, the achieved green foams exhibit favorable thermal insulation (39.8 mW/m·K) and superior biodegradation efficiency (11.5%/2 months). The approach of energy-efficient nitrogen-assisted low-pressure foaming of degradable polymers offers a promising and practical solution for producing eco-friendly and multifunctional porous materials with economic advantages. [ABSTRACT FROM AUTHOR]

In the present work, a series of polyurethane ayered double hydroxide (PU‐LDH) nanocomposite molded foams were developed using Mg/Al LDH as the chemical blowing agent. Morphological, physicochemical, thermal and mechanical characterizations were performed to elucidate the mechanistic insight of the chemical blowing effect of the LDH and subsequently its enhanced blowing (foam formation) property. The characterization of standard urethane peaks by Fourier transform infrared spectroscopy attenuated total reflectance (FTIR‐ATR) studies confirmed PU foam formation. The DSC thermogram of all the PU‐LDH nanocomposite foams shows a low temperature glass transition for the soft segment (Tg) and a high temperature peak related to the hard segment. The TGA and DSC studies also reveal an improved phase separation behavior of the nanocomposite foam with increase in LDH content. The volume of the foam generated is increased with increase in LDH. The developed PU‐LDH nanocomposite foams are flexible and light weight. The results demonstrate that LDH can be an alternative cost effective and environmentally friendly blowing agent, whilst supporting other thermal, mechanical and chemical properties through synergistic optimization for the intended/specific application. © 2022 Society of Industrial Chemistry. [ABSTRACT FROM AUTHOR]

Polypropylene (PP)/Carbon-Nanotube (CNT) nanocomposites and PP/CNT/Glass fiber (GF) hybrids were foamed using supercritical carbon dioxide (CO2) through a batch foaming process. Uniform nanofiller dispersion was assessed by field emission scanning electron microscopy (FE-SEM). By incorporating CNTs in the matrix, the average cell size was reduced to less than one-second that of neat foam (from 49 to 22.5 µm), and cell density increased. As a matter of fact, high electrical conductivity is crucial to achieving a great electromagnetic interference (EMI) shielding performance. Hence, CNTs were loaded up to 3 wt%. By incorporation of CNTs, electrical conductivity increased from ~10-16 to ~10-4 and ~10-5 S/cm for unfoamed and foamed PP/CNT3 samples, respectively, and EMI shielding effectiveness increased to 11 dB and 9.5 dB for unfoamed and foamed PP/CNT3 samples, respectively. After evaluating the microstructural and electrical properties of the nanocomposites and their foams, as well as elucidating the foaming process's role in the EMI shielding performance of the hybrids and foams, there was a great need to investigate the mechanical properties of hybrid systems and the effect of fiber concentration. Tensile properties revealed that by increasing the fiber content, young modulus and tensile strength increased for unfoamed samples and decreased for foams. The compression test of hybrid foams showed that by loading nanotubes and glass fibers, compressive mechanical properties increased. Also, by adding CNTs and glass fibers, impact properties increased and decreased, respectively, for solid and foamed hybrids. Moreover, by loading both additives impact properties enhanced. [ABSTRACT FROM AUTHOR]

Abstract In this work, polystyrene was filled with carbon black (CB) at 1, 3, and 5 wt% and were foamed via microwave‐assisted (MA) foaming. The composite morphology was tracked by scanning electron microscopy, transmission electron microscopy, and rheology. CB played the dominant role as the selective microwave absorbers to provide the required heat for the cell nucleation and growth. MA foaming is a controllable technique to reach proper foam density and cell size by controlling microwave energy. MA foams microstructurally were compared with the foams created via the conventional foaming procedures, including oil bath heating and fast pressure drop. One advantage of the MA method is increasing the temperature of the bulk and surface of the thick specimen simultaneously. As a result, cell nucleation and growth are uniform throughout the thick composite. Samples with a thickness of 1 cm were foamed via the MA method.

Blends from the thermoplastic elastomer (TPE) of Propylene/1-butene copolymers (PPB) and Ethylene–propylene–diene monomer (EPDM) were successfully prepared by melt-mixed in an internal mixer and crosslinking through highenergy electron beam irradiation technology. The foaming process was achieved with the assistance of eco-friendly supercritical carbon dioxide (sc-CO2). The effect of EPDM content on foaming, morphology, thermal, and mechanical properties of EPDM/PPB blends with varied irradiation dose were investigated. Microstructural analysis revealed a perfect compatibility of PPB and EPDM in TPE. The increased EPDM content caused a decrease in the mechanical properties (hardness and tensile strength) of TPE; however, it has been improved with the increased irradiation dose. The thermal analysis indicated that the addition of EPDM and high-energy electron beam crosslinking resulted in a new melting peak near 150 °C in TPE, and a new crystalline phase appears during the crystallization process. Repeated processing performance tests showed that the incorporation of higher PPB content reduces the loss of mechanical properties of the prepared blend. The micro-morphology of the cell structure in foamed TPE material was investigated, and it was found that the size of cell structure gradually decreased with the increased EPDM content; however, the cell size has a tendency to increase first and then decrease with the increase of irradiation dose. At 40 kGy irradiation dose, the cell structure size is the largest among all EPDM/PPB foams. The cyclic compression test of the TPE foamed material showed that the material’s resistance to repeated compression got promoted with the increased EPDM content.

In this article, the effects of different foam production times and temperatures on the mechanical, physical, and structural properties of polypropylene (PP) foam has been investigated. The microcellular PP foams were carried out using supercritical carbon dioxide (sc-CO2) as a physical foaming agent in a batch process. The samples were placed in a pressure vessel and were saturated with sc-CO2 at room temperature (23 - 25 °C) and saturation pressure of 40 MPa for 35 hours. Then, samples were removed from the vessel after releasing the pressure and were immersed in a glycerin bath for different times of 90, 180, and 270 seconds and different temperatures of 155 °C, 165 °C, and 175 °C. The mechanical responses of samples, e.g., flexural, Izod impact, and dynamic mechanical thermal properties, and physical characterization containing water absorption and relative density, were studied. Scanning Electron Microscopy (SEM) was applied to investigate the surface morphology. The cell size, cell density, and cell structure of PP foams were investigated by morphological parameters. X-ray diffractometer was utilized to evaluate the interaction effect on the samples. Results showed that in the semi-crystalline polymers such as polypropylene, the foaming temperature must be higher than the melting temperature of PP. A simultaneous examination of mechanical, physical, and morphological test results as well as cell structure properties indicate that the best temperature and time conditions for producing PP foams are the temperature of 175 °C and time of 270 seconds, respectively. These optimum conditions could be used in the industrial production of PP foams.

Copyright of China Plastics / Zhongguo Suliao is the property of Journal Office of CHINA PLASTICS and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Blends from the thermoplastic elastomer (TPE) of Propylene/1-butene copolymers (PPB) and Ethylene-propylene- diene monomer (EPDM) were successfully prepared by melt-mixed in an internal mixer and crosslinking through highenergy electron beam irradiation technology. The foaming process was achieved with the assistance of eco-friendly supercritical carbon dioxide (sc-CO2). The effect of EPDM content on foaming, morphology, thermal, and mechanical properties of EPDM/PPB blends with varied irradiation dose were investigated. Microstructural analysis revealed a perfect compatibility of PPB and EPDM in TPE. The increased EPDM content caused a decrease in the mechanical properties (hardness and tensile strength) of TPE; however, it has been improved with the increased irradiation dose. The thermal analysis indicated that the addition of EPDM and high-energy electron beam crosslinking resulted in a new melting peak near 150 °C in TPE, and a new crystalline phase appears during the crystallization process. Repeated processing performance tests showed that the incorporation of higher PPB content reduces the loss of mechanical properties of the prepared blend. The micro-morphology of the cell structure in foamed TPE material was investigated, and it was found that the size of cell structure gradually decreased with the increased EPDM content; however, the cell size has a tendency to increase first and then decrease with the increase of irradiation dose. At 40 kGy irradiation dose, the cell structure size is the largest among all EPDM/PPB foams. The cyclic compression test of the TPE foamed material showed that the material's resistance to repeated compression got promoted with the increased EPDM content. [ABSTRACT FROM AUTHOR]

Currently, the fabrication of microcell and bimodal cell structures (BCS) in polymer foams by using supercritical fluids has become a hot as well as a challenging research area worldwide. In this work, an environmentally friendly, effective, facile, and CO2‐based foaming technique was presented to fabricate microcellular polypropylene (PP) foams with BCS via blending with thermoplastic polyurethane (TPU). The toughness, thermal properties, rheological properties, and foamability of PP were systematically investigated with gradual incorporation of TPU. Representative sea‐island structure was observed in the scanning electron microscopy (SEM) images for the fracture surface of various PP/TPU samples. Rheological measurement results demonstrated that the viscoelasticity of various PP/TPU samples was improved remarkably compared with that of pure PP and pure TPU. The impact strength of various PP/TPU samples possessed the highest value as 12.4 kJ/m2 with the TPU content of 15 wt%. After the addition of TPU, an ameliorative cellular morphology was observed in the SEM micrographs of various PP/TPU samples and their volume expansion ratio was enhanced significantly thanks to their improved melt elasticity. Moreover, it is worth noting that BCS appeared in various PP/TPU foams when the TPU content exceeded 5 wt%. [ABSTRACT FROM AUTHOR]

The cross-section of an injection-molded plate of foamed long glass fiber reinforced polypropylene was analyzed using scanning electron microscopy. The distribution of the glass fiber orientations and the microcellular structure in the thickness direction were also studied. A multilayer representative volume element was constructed based on the fiber orientation tensors and the cell distribution. Nested and two-step homogenization methods based on the Mori–Tanaka and Voigt models were used to homogenize each layer of the representative volume element. Finally, classic laminate theory was used to obtain the effective elastic modulus of the material. The computed elastic moduli of the single-layer and multilayer representative volume element models with different loading directions predicted by the homogenization and finite element methods were compared with the experimental results. We found that the constructed multilayer representative volume element model can predict the elastic moduli of the foamed glass fiber reinforced polypropylene effectively and that the predicted results were accurate and stable. [ABSTRACT FROM AUTHOR]

The microcellular foaming of chain-extended polyethylene terephthalate (CPET) by crystallization induction method was reported in this article. The crystallization behaviors of various polyethylene terephthalate (PET) samples which were affected by the combined effect of pyromellitic dianhydride, Surlyn, and CO2 were investigated. After Surlyn was added to CPET, the crystal nucleation of various CPET samples was improved, and numerous but small spherulites were generated. Two kinds of CPET samples with the content of 0 phr and 1 phr Surlyn were foamed at various temperature by batch foaming method. Changing the saturation temperature could adjust the appearance of high-temperature melting crystals which would affect the final cellular structures in various CPET foams. With the decrease of saturation temperature, the cell size decreased while cell density increased. At the saturation temperature of 265°C and 250°C, the cell density of CPET foam with Surlyn was one magnitude larger than CPET foam without Surlyn. At the saturation temperature of 247°C, the microcellular PET foams with the cell density of 109 cells cm−3 and the cell size less than 10 µm had been developed successfully. [ABSTRACT FROM AUTHOR]

Thermoplastic elastomer from ethylene vinyl acetate (EVA) was blended with a biodegradable polymer, poly(lactic acid) (PLA), to develop ecofriendly EVA/PLA foams. The thermal and mechanical properties and the morphologies of the blends with various PLA contents between 0 and 40% were investigated. The rheological properties during gel formation were monitored via in-situ through the evolution of torque with curing time. The EVA/PLA blends showed a two-phase morphology made of a continuous EVA matrix and micron or submicron nodules, and also increased the tensile strength and modulus, as well as hardness, with the increase of the added PLA content. This should be attributed to the micronic dispersion of the rigid PLA in the elastic EVA matrix. The foam samples containing below 30% of PLA exhibited a similar cell structure and foaming ratio to the pure EVA; however, the cell size and foaming ratio gradually reduced with the increase of the added PLA content. [ABSTRACT FROM AUTHOR]

Isotactic polypropylene–polyethylene copolymer microcellular foams of various relative densities were prepared using nitrogen (N2) in supercritical solid state. Also, series of copolymers with different polyethylene weight percentages were prepared. Mechanical properties (compression and impact conditions) dependence on relative density, PE content, and strain rate was studied. Results showed that yield stress gradually decreased with lower density. The yield stress of PP copolymer foams decreased with the relative densities, and was always smaller than that of the solid PP copolymer. Nevertheless, the sensitivity to strain rate effect decreases at impact velocities. Analytical models were developed including the effects of both relative density and strain rate. [ABSTRACT FROM AUTHOR]

In this work, the foaming process was employed to achieve lightweight thermoplastic polyurethane materials, and then the hysteresis and residual strain of corresponding materials in the tensile process were quantitatively calculated. In order to study the deformed mechanism, the influences of cell type and skin-core structure on the tensile elasticity of thermoplastic polyurethane foam were investigated. The open-cell thermoplastic polyurethane foam exhibited much lower hysteresis and residual strain compared to thermoplastic polyurethane film without cell structure, which demonstrated that the open-cell structure benefited to the tensile elasticity. In the case of closed-cell thermoplastic polyurethane foam, it had lower hysteresis and residual strain than thermoplastic polyurethane film; however, higher value than the thermoplastic polyurethane film can be observed beyond 100% strain, resulting from the stress concentration in the skin-core structure. Consequently, the hysteresis phenomenon can be improved by adjusting the ratio of skin-core structure. Moreover, the influence of density on the elasticity of the open-cell thermoplastic polyurethane foam was also discussed in this study. [ABSTRACT FROM AUTHOR]

Microcellular thermoplastic polyurethane foams are examined as absorbing materials in the X-band (8.2-12.4 GHz) frequency range by means of experiment. In this work, we aim to establish relationships between foam morphology including cell size and air volume fraction and electromagnetic properties including absorption, transmission and reflection quality. Nanocomposites based on thermoplastic polyurethane containing carbon black were prepared by coagulation method. In this procedure 15 wt% carbon black-containing nanocomposite was converted to microcellular foams using batch foaming process and supercritical carbon dioxide as physical foaming agent. The morphology of the foams was evaluated by scanning electron microscopy. S-parameters of the samples were measured by a vector network analyzer (VNA) and the effect of morphological parameters such as cell size and air volume fraction on the absorbing properties was investigated. We also established structure/properties relationships which were essential for further optimizations of the materials used in the construction of radar absorbing composites. Foaming reduced the percolation threshold of the nanocomposites due to the reduction in the average distance between nanoparticles. Foaming and dielectric constant reduction dropped the reflection percentage significantly. The increase in air volume fraction in the foam increased absorption per its weight, because of multiple scattering in composite media. The sensitivity of electromagnetic wave toward the variation of cell size is strongly weaker than that toward the variation of air volume fraction. Electromagnetic properties of the microcellular foams deviated a little from effective medium theories (EMTs). Air volume fraction of the cells was a function of cell size and smaller cells showed higher absorption.

A mold foaming process for preparing thermoplastic polyurethane foam sheets was proposed and realized in pilot scale hot-press machine based on the mechanism of solid-state polymer foaming. Thermoplastic polyurethane microcellular sheets with volume expansion ratios of 2.2–7.0 were prepared by adjusting foaming temperature of 95–120°C at the fixed CO2 pressure of 12 MPa with natural post-curing. The good foam dimensional stability and the uniform cell morphology of these thermoplastic polyurethane foams suggested that the mold foaming of thermoplastic polyurethane sheet was feasible. Regardless of volume expansion ratio, a linear shrinkage of 17–19% occurred to all thermoplastic polyurethane foams after post-curing. The flexible properties of these post-cured thermoplastic polyurethane foams, such as hardness, rebound resilience, compression set, and dynamic shock absorption, were investigated. The test results indicated that these thermoplastic polyurethane foams were excellent flexible materials. [ABSTRACT FROM AUTHOR]

A mold foaming process for preparing thermoplastic polyurethane foam sheets was proposed and realized in pilot scale hot-press machine based on the mechanism of solid-state polymer foaming. Thermoplastic polyurethane microcellular sheets with volume expansion ratios of 2.2–7.0 were prepared by adjusting foaming temperature of 95–120°C at the fixed CO2 pressure of 12 MPa with natural post-curing. The good foam dimensional stability and the uniform cell morphology of these thermoplastic polyurethane foams suggested that the mold foaming of thermoplastic polyurethane sheet was feasible. Regardless of volume expansion ratio, a linear shrinkage of 17–19% occurred to all thermoplastic polyurethane foams after post-curing. The flexible properties of these post-cured thermoplastic polyurethane foams, such as hardness, rebound resilience, compression set, and dynamic shock absorption, were investigated. The test results indicated that these thermoplastic polyurethane foams were excellent flexible materials. [ABSTRACT FROM AUTHOR]

• Microcellular TPU foams were fabricated by H-foaming and C-foaming. • C-foaming TPU foams show superior resilience than H-foaming TPU foams. • C-foaming TPU foams show higher strength and modulus than H-foaming TPU foams. • Larger cells lead to improved mechanical properties of TPU foam. Towards fabricating structurally tunable TPU foams with improved mechanical properties, the foaming behavior of TPU in two foaming routes including H-foaming and C-foaming were investigated. In H-foaming, foaming took place as raising temperature from low to high levels. In C-foaming, foaming took place as reducing temperature from high to low levels. Foaming temperatures and CO 2 pressures were regulated to tailor foam structure. Low density microcellular TPU foams with tunable structures were fabricated. Furthermore, with these structurally tunable TPU foams, the influences of foaming methods and cellular structures on foam's compressive mechanical properties were investigated. TPU foams fabricated by C-foaming showed superior resilience and strength than those fabricated by H-foaming. TPU foams with larger cells exhibited better resilience and strength than those with smaller cells. This study is of great significance in enriching the understanding of both the foaming behavior of TPU and the structure-property relationships of TPU foams. [ABSTRACT FROM AUTHOR]

A series of microcellular multiwall carbon nanotube (MWCNT)/silicone rubber foams were produced by supercritical foaming method. The effects of MWCNT on the rheological behavior, cellular structure• thermal and dielectric properties of microcellular silicone rubber foams were investigated. The results showed that MWCNT could improve the cellular morphology of microcellular silicone rubber foams. Tn addition, the onset thermal decomposition temperature of the microcellular MWCNT/silicone rubber foams increased from 441 to 467 °C when the MWCNT content increased from 0 to 6,0 wt%. The percolation threshold of the foam materials was nearly 2.0wt%, and the corresponding dielectric constant and dielectric loss of the foams could reach to 8,44 and 0.02 at 100 Hz, respectively. [ABSTRACT FROM AUTHOR]

In order to study the conductive and microwave absorption performance of multi-dimensional multiphase filler conductive foam composites, carbon nanotubes (CNTs)/carbon black (CB)/polymethyl methacrylate (PMMA) nanocomposites with different porosity were fabricated via supercritical carbon dioxide (ScCO _2 ) one-step physical constraint foaming technology. The effects of filler component and porosity on the conductivity and absorbing properties of CNTs/PMMA/CB composite foam were studied. The Monte-Carlo method was used to study the percolation of composites and the effect of introduced microcells on the conductive network of multi-dimensional fillers. The results revealed that the volume conductivity of CNTs(3 vol%)/PMMA composites increased from 0.88 S m ^−1 to 3.31 S m ^−1 after the addition of 1 vol% CB. CNTs and CB had obvious synergistic effect on improving the conductivity of the composites, and the microwave absorption efficiency rose from 12.6 dB to 17.2 dB. With the increase of porosity, the electromagnetic wave absorption peak of CNTs/CB/PMMA composite foam moved to low frequency, while the conductivity showed a first rise and then a decline. The simulated percolation probability obtained by representative volume element (RVE) with different porosity also showed a similar trend, which turned out that with the increase of porosity, the effect of microcells on the convertion of conductive network construction from promoting to inhibiting.

• A novel fiber, basalt fiber (BF), is firstly proposed to improve the crystallization and rheological behavior of PP. • Fine and dense cellular structure is prepared using mold-opening foaming injection molding process. • Even with a weight reduction ratio as high as 66.7%, excellent bending modulus and impact strength can still be maintained. • Lightweight and ductile PP/BF composite foams were successfully fabricated. Basalt fiber (BF), as an emerging natural and environmental-friendly material, possesses a broad application prospect. Herein, lightweight and strong BF reinforced polypropylene (BF/PP) composite foams were successfully prepared using mold opening foam injection molding (MOFIM) technology. It was revealed that the combination of increased crystallinity and enhanced rheological behavior in turn contributes to the improved foaming behavior of 20%BF/PP, which reduces the cell size of PP to 36.38 μm and boosts the cell density by a factor of 2 under an expansion ratio of 1.2. The improvement effect of BF on cell structure is more obvious at higher expansion ratio. This fine and dense cell structure further augments the impact performance and flexural modulus of BF/PP composite foams. Compared to pure PP, 20%BF/PP composite foams experienced an increasement of impact performance, which is increased by 68.8% to 2.7 kJ/m2, and its flexural modulus also elevated significantly by 224.8% to 2440.25 GPa. Due to its excellent weight reduction effect, the specific impact strength and specific flexural modulus remain at much higher levels than those of PP foam. This indicates that BF and MOFIM technique successfully prepared a ductile material with excellent impact resistance, modulus and thermal insulation properties. [ABSTRACT FROM AUTHOR]

Nanocomposites containing poly(methyl methacrylate) (PMMA) and surface functionalized Multi-Walled Carbon Nanotubes (MWNTs) were synthesized. The dispersion of MWNTs in PMMA was characterized using Transmission Electron Microscopy (TEM).The synthesized nanocomposites were successfully foamed using a simple method based on the in-situ generation of supercritical carbon dioxide (CO2). This method in contrast with conventional methods exempted from high-pressure pump and separated CO2 tank. The effect of MWNTs concentration, saturation temperature and saturation pressure on cellular morphology of the prepared microcellular foams were studied by Scanning Electron Microscopy (SEM), and average cell size and cell density of the prepared foams were studied by image analysis. An increase in cell density, as well as a reduction of cell size, was observed with an increase in the concentration of carbon nanotubes. It was also observed that an elevation of saturation temperature from 90 °C to 100 °C, at constant saturation pressure, leads to a higher cell density and a lower average cell size. Furthermore, an increase in saturation pressure results in a decrease in average cell diameter as well as an increase in cell density. However, the effects of MWNTs concentration on both of average cell size and cell density were proved to be more striking than those of saturation pressure.

Natural fiber reinforced biocomposites have recently attracted many researchers because of their biodegradability, cost effectiveness and ecofriendliness. The present study investigates the properties of willow-fiber reinforced poly(lactic acid) based composites and their foam processability. Microcellular foams of the composites were prepared by foam injection moulding using nitrogen gas as the blowing agent. The effects of willow-fiber addition on the morphology, mechanical properties, thermal stability, crystallization, and heat deflection temperature (HDT) were studied. At 30 weight percent [wt%] willow-fiber content, unfoamed composites showed good improvement in specific tensile and flexural moduli. Addition of willow-fiber increased crystallinity and the rate of crystallization and yielded narrow crystallite size distribution as observed by differential scanning calorimetry (DSC). Scanning electron microscopy (SEM) results of the foamed composites revealed that increase in willow-fiber content caused smaller average cell size and higher cell density. Specific notch impact strength of foamed composites at both 20 and 30 wt% willow-fiber content showed increasing trend compared to that of their unfoamed counterparts.

Based on the industrialized reduced graphene oxide (RGO) product, polyetherimide (PEI)/RGO composite foam was prepared by a water‐vapor‐induced phase separation process by incorporation of polysiloxane (SI) as a compatibilizer. It was found that PEI/SI molecules were intercalated into the RGO layers through strong interfacial interaction and RGO with increased layer thickness was uniformly distributed in the PEI matrix. The composite foam possessed a homogeneous spherical‐like cell structure with narrow cell size distribution and low apparent density. In the range of 0–1 wt% RGO‐SI content, the area under the stress–strain curves increased dramatically, indicating the significantly increased toughness of the composite foam, while the tensile strength reached a maximum of 14.5 MPa at 1 wt% RGO‐SI as a result of the reinforcing effect of RGO‐SI on the foam. The addition of RGO‐SI led to a remarkable increase in Tg. Compared with neat PEI foam, the thermal degradation temperature and char yield of the composite foam clearly increased, while in the range of 0.5–3 wt% RGO‐SI a high storage modulus was maintained at high temperature, reaching about 300 MPa at 200 °C, indicating a remarkable improvement of the thermal mechanical stability of the foam. © 2018 Society of Chemical Industry Polyetherimide (PEI)/reduced graphene oxide (RGO) polysiloxane (SI) composite foam was fabricated via a water‐vapor‐induced phase separation process. RGO‐SI with a uniform dispersion in the matrix presented a thermal stabilizing and reinforcing effect on PEI. [ABSTRACT FROM AUTHOR]

Microcellular polystyrene (PS)/carbon‐based nanoparticle (CbN) composites were prepared by a pressure release process using supercritical CO2 as the foaming agent. Nanocomposite foams with different shapes or dimensions but with CbNs with a similar surface structure showed a quite different cell nucleation. The underlying nucleation mechanism was semi‐quantitatively analyzed by classical nucleation theory, which indicated that the energy barrier for heterogeneous nucleation was related to the shapes of the fillers. Below 80 °C and 20 MPa, the nucleation density of the composites with different fillers showed marked differences, among which the nucleation density of PS/fullerene (FE) was the highest, followed by PS/carbon nanotubes (CNTs) and PS/thermally reduced graphene (TRG). However, the difference in nucleation density of PS/CbNs decreased with increase in filler content to 0.3 wt%. With increase in foaming temperature, the PS/TRG composite foams showed the highest cell density and no cellular merging and collapsing at 100 and 120 °C. The results obtained from DSC, rheology and positron annihilation lifetime spectroscopy measurements showed that FE nanoparticles exhibited the strongest plasticization effects on the matrix followed by CNTs and TRG nanoparticles. The distinctive plasticization suggested that the shapes of CbNs have a strong influence on the interaction between the PS matrix and the nanoparticles, which could affect the energy barrier for heterogeneous nucleation. The influence of CO2 on the rheology and thermal properties of the composites was investigated using high pressure DSC and high pressure rheology measurements. The results revealed that at high temperature high viscosity became the key factor to determining the cell morphology of nanocomposite foams by preventing bubble coalescence and collapse. © 2018 Society of Chemical Industry Polystyrene composite foams with differently shaped carbon‐based nanoparticles show a distinctive nucleation density. They were investigated by classical nucleation theory, indicating that the energy barrier of heterogeneous nucleation is also related to the shapes of the nanofillers. [ABSTRACT FROM AUTHOR]

Nowadays, polymer-based foams have gained much attention for absorption of electromagnetic wave due to their desirable properties such as wide absorption band, low reflection and also light weight. However, the impact of the foam morphology including shape, cell size and its structure as open and close cell, on the electromagnetic wave has been rarely investigated. In this study, the operational conditions for manufacturing various structured foams based on poly(methyl methacrylate)/graphene nanoparticle sheets have been optimized for investigating the effect of cellular structure on the characteristics of electromagnetic wave as well as electrical properties. Hence, a foaming system with great controllability and repeatability has been employed. It should be noted that this system is capable of stabilizing the cellular structure with millisecond accuracy during and after the pressure drop. The close cell structured foam showed a decrement in the electrical and electromagnetic properties with increasing the cell size and shifting from spherical to polygonal shape. Moreover, the results related to the prepared open cell structured foams with similar cell size and density to close cell ones, have demonstrated higher absorption characteristics for microcellular open cell foams while shielding was better in close cell counterparts. [ABSTRACT FROM AUTHOR]

Mixed matrix membranes made from silica nanoparticles and microcellular polymers were prepared from Matrimid® 5218 combined with tetramethoxysilane, tetraethoxysilane, and tetrapropoxysilane via the sol–gel method. The nanoparticles were prepared in situ during membrane casting yielding a homogeneous distribution inside a foamed polyimide structure. Mixed matrix membranes with SiO2 contents up to 16% wt. were treated at 60℃, 100℃, 150℃, and 200℃. Thermal gravimetric analysis and Fourier transform infrared spectroscopy analyses were performed providing information on chemical composition and thermal stability, while the porous structure (average cell diameter and cell density) was studied by scanning electron micrograph. Also, dynamic mechanical analysis was used to determine the glass transition temperature (Tg) and elastic modulus. Finally, the gas transport properties were studied in terms of treatment temperature, feed pressure, SiO2 loading, and testing temperature. CO2 permeability was found to increase by a factor of 3–4 at 3% SiO2 content using tetraethoxysilane in Matrimid, while ideal selectivity for CO2/CH4 separation was constant. Finally, the plasticization effect was practically eliminated by the introduction of SiO2 nanoparticles. [ABSTRACT FROM AUTHOR]

Microcellular polystyrene foam sheets prepared by extrusion foaming with CO2 as the blowing agent were found to exhibit a significant anisotropy in mechanical behavior which could not be explained solely by the shape anisotropy of the cells and/or the preferential orientation of polystyrene molecules in the machine direction. Surprisingly, samples allowed to fully relax were still found to maintain part of their mechanical anisotropy, which was attributed to the weakness of the cell walls perpendicular to machine direction. [ABSTRACT FROM AUTHOR]

Microcellular silicone rubber/nanographite foam with the smallest cell diameter and the largest cell density compared to the previous studies was prepared using supercritical carbon dioxide as an environmentally benign foaming agent in this study. Both the cell microstructure and properties of porous composite were investigated in detail. In silicone rubber/nanographite system, the incorporation of nanographite into silicone rubber significantly induced heterogeneous bubble nucleation and enhanced the matrix strength, which resulted in the decreased average cell diameter from 4.97 to 1.12 μm and the increased cell density from 8.87 × 10 8 cells/cm 3 to 1.25 × 10 10 cells/cm 3 . The microcellular rubber foam with decreased cell size, increased cell density and narrow cell distribution was corresponded to the excellent compressive strength and higher hardness, which reduced the content of silica. Furthermore, the thermal decomposition temperature of the obtained foam increased from 380 °C to 413 °C due to the introduction of nanographite. The silicone rubber/nanographite foam with improved performance possessed potential in wide applications. [ABSTRACT FROM AUTHOR]

Success in the typical extrusion foaming process is always achieved by adding inorganic/organic fillers, which inevitably sacrifice poly(lactic acid) (PLA)’s green nature. Herein, we successfully fabricated well-defined cell structures of fully bio-based PLA foams using a series of asymmetric biodegradable poly( l -lactide) (PLLA) and poly( d -lactide) (PDLA) blends with small amounts of PDLA. We obtained large-scale PLLA/PDLA blends using a continuous melt compounding technique. The crystallization kinetics in the presence of dissolved carbon dioxide (CO 2 ) under high pressures was investigated by using regular and high-pressure DSC. The PLA’s crystallization rates were notably accelerated due to the significant synergy of the dissolved CO 2 and the reserved SC crystallites. The continuous extrusion process, which could be easily scaled-up to industry, was used to fabricate the PLLA/PDLA blended foams. Using the neat PLLA foam, we successfully demonstrated how to make fully bio-based PLA foams with three orders of magnitude increased cell density, an enhanced expansion ratio over ten-fold, and increased crystallinity by 15%. Such a high cell density, a high expansion ratio and a high crystallinity are unprecedented in the continuous processing of fully green PLA foams. They possess great potential for use as a sustainable product in thermoformed food packaging applications. [ABSTRACT FROM AUTHOR]

Polymer foams play an increasingly significant role in the field of thermal insulation due to their low thermal conductivities. As thermal insulation materials, their performances are primarily determined by the cellular structure. However, the correlation between the foam’s properties and its cellular structure is still not fully understood. This greatly limits the development of high-performance polymer foams with optimal cellular structures. Hereby, we report the fabrication of poly (methyl methacrylate) (PMMA) foams with widely tunable cellular structures by using CO 2 as the blowing agent. In particular, the microcellular PMMA foam with a void fraction of 0.956 and with an average cell size of 4.7 μm was obtained, which, to the best of knowledge, is by far the largest void fraction of polymer foam with a cell size of less than 5 μm. The PMMA foam presents an excellent thermal-insulation behaviour with a thermal conductivity of as low as 29.9 mW/m K. Meanwhile, the PMMA foam exhibits excellent mechanical properties due to its extremely small cell sizes. Moreover, the dependences of thermal and mechanical properties on cellular structure are obtained by independently analyzing the effects of cell size and void fraction. All these results demonstrate a promising method to fabricate environmentally friendly and economical thermal insulation materials with improved thermal-insulation and compressive mechanical properties. [ABSTRACT FROM AUTHOR]

ABSTRACT A series of microcellular high temperature vulcanized (HTV) silicone rubber foams were prepared using CO2 as a physical blowing agent. Rheological properties, gas diffusive behavior, and foaming parameters of silicone rubber were investigated. The results show that saturation pressure has a significant effect on the diffusivity of CO2 in HTV silicone rubber matrix. The gas concentration and diffusivity increase from 2.45 wt % to 3.24 wt %, and from 1.62 × 10−5 cm2/s to 7.83 × 10−5 cm2/s as the saturation pressure increases from 2 MPa to 5 MPa, respectively. The value of the gas diffusivity in HTV silicone rubber is almost 1000 times higher than that of the gas diffusivity in polyetherimide (PEI) matrix. Additionally, microcellular HTV silicone rubber foams with the smallest cell diameter of 9.8 μm and cell density exceeding 108 cells/cm3 are achieved. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 44807. [ABSTRACT FROM AUTHOR]

ABSTRACT In this study, polypropylene (PP) foams were prepared with cucurbit[6]uril (Q[6]) used as a novel nucleating agent through a microcellular injection molding foaming process. The effect of Q[6] content (0.5-2.0 wt %) on the foaming behavior, as well as thermal, rheological and mechanical characterizations of the PP/Q[6] (PQ) samples were performed. According to scanning electron microscopy (SEM) images, the microstructure of foams exhibited a smaller cell size, higher cell density, and more homogeneous distribution of cells at a higher Q[6] content. It was found that the peak temperature of crystallization, the crystallinity and the crystallization rate of PP can be obviously improved by adding a low content of Q[6] (0.25-1.0 wt %), whereas further increasing the content of Q[6] (2.0 wt %) would disfavor the effect. With increasing the Q[6] concentration, the PQ composites had higher complex viscosities at low frequencies and higher modulus than that of PP except the content of 2.0 wt %. Furthermore, the introduction of Q[6] into PP can produce a mild increase in tensile strength, flexural strength and impact strength of PQ foams. This can be due to the well dispersion of Q[6], good compatibility between PP and Q[6], as well as the improvement of the cell morphology. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 44538. [ABSTRACT FROM AUTHOR]

Thermoplastic polyurethane possesses many special characteristics. Its flexibility, rigidity, and elasticity can be adjusted by controlling the ratio of soft segments to hard segments. Due to its versatile physical properties, thermoplastic polyurethane is commonly used in transportation, construction, and biomaterials. However, methods for thermoplastic polyurethane foam production using CO2 are still under investigation. We have previously prepared nanoporous thermoplastic polyurethane foam using commercially available thermoplastic polyurethane; however, in this study, thermoplastic polyurethane was synthesized using 4,40-methylenebis(phenyl isocyanate), poly(propylene glycol) and 1,4-butanediol, without solvents, using a pre-polymer method. The properties of the synthesized thermoplastic polyurethane were characterized by Fourier transform infrared spectroscopy, thermal analysis, and their mechanical properties were measured. The synthesized thermoplastic polyurethane was foamed by batch foaming using supercritical CO2 as the blowing agent. The effect of saturation temperature and saturation time on the cell morphology of the thermoplastic polyurethane foam was examined. [ABSTRACT FROM AUTHOR]

In spite of great concern on the wide application of silicone rubber foams, few works have been reported about easy-operating foaming method. In this study, the effects of silica content and foaming process on the porous structure of high-temperature-vulcanized silicon rubber foams are evaluated, which are prepared by supercritical CO2 at different conditions, with fumed silica used for reinforcement. Silicone rubber foams with cell size in 8-120 μm, cell density in 105-108 cm−3, and density between 0.45 and 0.9 g cm−3 are prepared under different saturation conditions. The results show that increasing silica content can decrease cell size. It is also found that cell density improves exponentially with increasing saturation pressure and decreasing saturation temperature. Besides, it demands less than 1 h for specimens to reach equilibrium on thickness around 3 mm. All the results indicate that the porous structures of silicone foams can be tailored by foaming process parameters facilely and are predictable with fitted equation. [ABSTRACT FROM AUTHOR]

In spite of great concern on the wide application of silicone rubber foams, few works have been reported about easy-operating foaming method. In this study, the effects of silica content and foaming process on the porous structure of high-temperature-vulcanized silicon rubber foams are evaluated, which are prepared by supercritical CO2 at different conditions, with fumed silica used for reinforcement. Silicone rubber foams with cell size in 8-120 μm, cell density in 105-108 cm−3, and density between 0.45 and 0.9 g cm−3 are prepared under different saturation conditions. The results show that increasing silica content can decrease cell size. It is also found that cell density improves exponentially with increasing saturation pressure and decreasing saturation temperature. Besides, it demands less than 1 h for specimens to reach equilibrium on thickness around 3 mm. All the results indicate that the porous structures of silicone foams can be tailored by foaming process parameters facilely and are predictable with fitted equation. [ABSTRACT FROM AUTHOR]

In this study, flame-retardant poly(lactic acid) foams with satisfactory cell structures were prepared by microcellular foaming technology using phosphorus-containing flame retardant and graphene as the charring agent. The introduction of 5–30 wt% flame retardant increased the limited oxygen index value of poly(lactic acid) from 19.0 to 26.5–37.8% and simultaneously increased the foam expansion of poly(lactic acid) foams from 4.4 to 5.8–17.5. In addition, all the prepared poly(lactic acid)/flame-retardant composites passed the UL-94 V-0 rating. The addition of 0.5 wt% graphene increased the limited oxygen index value of poly(lactic acid)/flame-retardant composite with flame-retardant content of 15 wt% from 27.9 to 29.2%, and more graphene additions improved the antidripping behavior of poly(lactic acid) composites. The possible mechanisms of the effects of the resultant cellular structure on the flame-retardant properties of poly(lactic acid) composites were also discussed. [ABSTRACT FROM AUTHOR]

Open-celled foams are capable to allow the passage of fluids through their structure, because of interconnections between the open cells or bubbles and therefore these structures can be used as a membrane and filter. In thiswork, we have studied the production of polystyrene open-celled microcellular foam by using CO2 as blowing agent. To achieve such structures, it is necessary to control the stages of growth in such a way that the cells would connect to each other through the pores without any coalescence. The required processing condition to achieve open-celled structures is predictable by a model theory of opened-cell. This model suggests that at least a 130 bar saturation pressure and foaming time between 9 and 58 s are required for this system. The temperature range has been selected for to be both higher than polymer glass transition temperature and facilitating the foaming process. Experimental results in the batch foaming process has verified the model quite well. The SEM and mercury porousimetry tests show the presence of pores between the cells with open-celled structure. Experimental results show that by increasing the saturation pressure and the foaming temperature, there is a drop in the time required for open-celled structure formation. A 130 bar saturation pressure, 150o C foaming temperature and 60 s foaming time, suggest the attainment of open-celled microcellular foam based on polystyrene/CO2 system in the batch process.