Supercritical Carbon Dioxide Foaming Research Articles

Asymmetric electrical-magnetic composite foams with oriented cells fabricated by supercritical CO2 foaming and thermal stretching for efficient absorption dominated electromagnetic interference shielding

Asymmetric composite foams (TCFAs) based on thermoplastic polyurethane (TPU) containing carbon nanotubes (CNTs) and Fe3O4-decorated reduced graphene oxide (Fe3O4@rGO) electrical-magnetic dual networks with oriented cell structures and a silver layer were fabricated through supercritical carbon dioxide foaming, thermal stretching and a knife coating process. The oriented cells prolonged the electromagnetic (EM) wave transmission path and induced more multiple reflections, and the asymmetric silver layer enabled a special “absorption-reflection-reabsorption” mechanism, which contributed to a high electromagnetic interference (EMI) shielding effectiveness (SE) of 89.5 dB with an A value of 0.748 at a relatively low total filler content of 1.784 vol%. By regulating the oriented cell structure and the incorporation of asymmetric design, the TCFA-1 achieved 10 times improvement in EMI SET with a low EMI SER of 1.27 dB. This work offers new insights into the design and fabrication strategies for high performance absorption-dominated EMI shielding foams.

Preparation of a High-Expansion-Ratio Blend Foam with Low Thermal Conductivity Using Poly(vinyl alcohol)-Polycaprolactone Mixture Solution via Supercritical Carbon Dioxide Foaming Technology

Preparation of a High-Expansion-Ratio Blend Foam with Low Thermal Conductivity Using Poly(vinyl alcohol)-Polycaprolactone Mixture Solution via Supercritical Carbon Dioxide Foaming Technology

Effects of Three Different Kinds of Foaming Medium on the Properties of Expanded Thermal Plastic Polyurethane Prepared via Supercritical Carbon Dioxide Foaming.

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.

Multistage microcellular waterborne polyurethane composite with optionally low-reflection behavior for ultra-efficient electromagnetic interference shielding

Electromagnetic interference (EMI) shielding materials with superior shielding efficiency and low-reflection properties hold promising potential for utilization across electronic components, precision instruments, and fifth-generation communication equipment. In this study, multistage microcellular waterborne polyurethane (WPU) composites were constructed via gradient induction, layer-by-layer casting, and supercritical carbon dioxide foaming. The gradient-structured WPU/iron-cobalt loaded reduced graphene oxide (FeCo@rGO) foam serves as an impedance-matched absorption layer, while the highly conductive WPU/silver loaded glass microspheres (Ag@GM) layer is employed as a reflection layer. Thanks to the incorporation of an asymmetric structure, as well as the introduction of gradient and porous configurations, the composite foam demonstrates excellent conductivity, outstanding EMI SE (74.9 dB), and minimal reflection characteristics (35.28 %) in 8.2–12.4 GHz, implying that more than 99.99999 % of electromagnetic (EM) waves were blocked and only 35.28 % were reflected to the external environment. Interestingly, the reflectivity of the composite foam is reduced to 0.41 % at 10.88 GHz due to the resonance for incident and reflected EM waves. Beyond that, the composite foam is characterized by low density (0.47 g/cm3) and great stability of EMI shielding properties. This work offers a viable approach for crafting lightweight, highly shielding, and minimally reflective EMI shielding composites.

Preparation of hollow TiO2 nanospheres with highly porous surface for effective nucleating agents in supercritical carbon dioxide foaming of thermoplastic polyurethanes

Preparation of hollow TiO2 nanospheres with highly porous surface for effective nucleating agents in supercritical carbon dioxide foaming of thermoplastic polyurethanes

Development of Anti-Shrinkage and High-Elastic Thermoplastic Poly(Ether-Ester) Elastomer Foams Via Supercritical Carbon Dioxide Foaming

Development of Anti-Shrinkage and High-Elastic Thermoplastic Poly(Ether-Ester) Elastomer Foams Via Supercritical Carbon Dioxide Foaming

Super thermal-insulation PS/PMMA/CNTs composite foams with shape recovery property formed by the synergy of ultrasound and H2O in scCO2 foaming

For polymer foams, a high expansion rate is often required to obtain a low thermal conductivity. However, polymer foams with high expansion ratio faces a difficulty of shape recovery. In this work, polystyrene (PS)/polymethyl methacrylate (PMMA)/carbon nanotubes (CNTs) composite foams were prepared by the synergy of ultrasound and H2O in supercritical carbon dioxide (scCO2) foaming. The introduction of ultrasound and H2O is beneficial to improving expansion ratio. CNTs can enhance the melt strength of PS/PMMA, which also absorb part of the thermal radiation. Therefore, the PS/PMMA/CNTs foams with 0.5 wt% CNTs exhibits the high expansion ratio (80.7 times), low thermal conductivity (25.98 mW/mK) and 100% compression recovery in water at 85 °C after one compression. In addition, with the increasing of filler contents, the reusability of the foam is further improved. After ten compressions, the PS/PMMA/CNTs foams with 2 wt% CNTs still achieve the 99% recovery. This work provides a new way to prepare polymer foams with super-insulation and reusability.

Fabrication of Sustainable Composite Foam from Ethylene Vinyl Acetate-Based Sole Waste via Solid-State Shear Milling and Supercritical Carbon Dioxide Foaming Technologies

Fabrication of Sustainable Composite Foam from Ethylene Vinyl Acetate-Based Sole Waste via Solid-State Shear Milling and Supercritical Carbon Dioxide Foaming Technologies

Triple-electrode integrated self-supporting triboelectric nanogenerators with high output and durability based on dynamic supercritical carbon dioxide foaming

Durable and sustainable energy harvesting in harsh environments using triboelectric nanogenerators (TENGs) is a grand challenge. Herein, highly compacted and integrated TENGs are developed using dynamic supercritical carbon dioxide (scCO2) foaming technique. The self-assembled internal-electrode TENG (SAI-TENG) which is consisted of a polydimethylsiloxane (PDMS) coated internal metal electrode covered by a corrugated wrinkled foam (CWF) is readily obtained by the foaming process. The CWF can support itself and maintains air gaps to facilitate contact electrification and the biomimetic wrinkles that are induced by the scCO2 flow field, greatly enhance the triboelectric output performance. By sandwiching the SAI-TENG using two internal-electrode PDMS films, a triple-electrode integrated self-supporting TENG (TIS-TENG), which has eight-friction layers in a single device, is developed. The TIS-TENG realized maximum utilization of the wrinkled CWF surface, which is equivalent to three parallel connected TENGs. Moreover, the output was further boosted by adding tea powders and patterning micro domes on the PDMS films, which resulted in a high Voc of 106.3 V and a power density of 32.5 mW/m2. Attributing to the embedded electrode and high elasticity of CWF, the TIS-TENG has remarkable stability and tolerance to harsh conditions and can be used as self-powered sensors for monitoring vehicle parking and working conditions of workers. This work provides new insights into the green fabrication and development of highly integrated self-supporting TENGs with high performance and durability.

Facile fabrication of flexible TPU‐based microcellular nanocomposite piezoresistive sensors with tunable piezoresistivity via modulating cell structure

AbstractThermoplastic polyurethane/multi‐wall carbon nanotubes/graphene nanoplates (TPU/MWCNTs/GNPs) microcellular nanocomposites used for assembling flexible piezoresistive sensors are prepared via melt mixing and then supercritical carbon dioxide foaming. The adjustable piezoresistivity and higher resilience of the sensors are achieved by creating tunable closed‐cell structure in the nanocomposites through foaming. The sensor assembled with the microcellular nanocomposite having a relatively uniform cell structure and moderately thicker cell walls exhibits a wider linear response range (0%–45% strain) and relatively higher sensitivity (gauge factor of 1.84). It shows repeatable piezoresistive response and good durability, and can be used to detect typical medium‐high pressure human motions. The sensor assembled with the microcellular nanocomposite having moderately larger cell diameter and thinner cell walls displays a higher sensitivity (gauge factor of 4.17) and obviously lower detection limit (0.8 kPa), but a narrower linear response range (0%–13% strain). It can accurately detect weak human physiological signals. Moreover, the enhanced performances of the sensors are also attributed to the hybrid conductive nanofillers (1D MWCNTs and 2D GNPs) distributing in the cell walls. The strategy for preparing the microcellular nanocomposites in this work gives a guidance for the development of flexible sensors in wide‐range of pressure sensing applications.

Ultrasound and H2O assisted scCO2 foaming technology for preparation of PS/PMMA composite foams with ultra-lightweight and super thermal-insulation

Porous polymer with lower density is more favorable for practical thermal insulation. In this work, a judicious combination of mechanical mixing and supercritical carbon dioxide foaming was applied to prepare ultra-lightweight polymer microcellular foam. The polymer foaming behavior is improved by adding water and ultrasound as an external energy source. The presence of water greatly increases the efficiency of ultrasound propagation, resulting in an almost two-fold increase in expansion ratio of foams. With the assistance of water and ultrasonic irradiation, the prepared foams have a 79-fold foaming expansion ratio and an average thermal conductivity as low as 26.79 mW/mK. The ultrasound also affects the process of foaming in both the saturation and release stage, but is more effective in the release stage than in the saturation stage. Consequently, this study provides a novel, facile, versatile, green approach for the preparation of microcellular polymers with ultra-lightweight and super thermal insulation.

Asymmetric magnetic-electric dual-functional composite foams for ultra-efficient electromagnetic interference shielding with unprecedented low reflection

• Magnetic-electric dual-functional network is constructed in TPU by Fe 3 O 4 @rGO and CNT via scCO 2 foaming. • TPU/CNT/Fe 3 O 4 @rGO composite foam exhibits high EM wave absorption property with an RL min of -46.8 dB. • EMI shielding and EM wave absorption are further improved by introducing an Ag reflection layer. • Asymmetric TPU/CNT/Fe 3 O 4 @rGO/Ag composites possess a high EMI SE of 89.2 dB and the lowest reflection of 0.001. Asymmetric composite foams comprised of iron oxide decorated reduced graphene oxide (Fe 3 O 4 @rGO)/carbon nanotube (CNT)/thermoplastic polyurethane (TPU) foams and a silver layer were developed by vacuum-assisted hot-pressing and supercritical carbon dioxide (scCO 2 ) foaming. The magnetic-electric dual-functional network constructed by Fe 3 O 4 @rGO and CNT nanofillers rendered the foam excellent impedance matching and wave attenuation capability, achieving -46.8 dB reflection loss at ∼2 mm sample thickness. With the reflective silver layer, the asymmetric composite foam realized a unique “low reflection-absorption-reflection-reabsorption” EM wave depletion mechanism and reached preeminent total shielding effectiveness (SE T ) of 89.2-103.5 dB with a reflection shielding effectiveness (SE R ) of 0.24-0.83 dB. The optimized composite foam achieved a low reflectivity (R) of 0.05 (Average value) and a minimum value of 0.001, which holds the lowest record among EMI shielding materials with comparable SE. This work provides new insights into the design of high-efficiency shielding materials with ultra-low reflection features for cutting-edge EMI shielding applications.

A comparative study of the effect of multidimensional carbon fillers on polystyrene using supercritical carbon dioxide foaming

Due to its low thermal conductivity on average (~0.039 W/(m·K)), supercritical expanded polystyrene (PS) foam could be used as an insulation material in buildings to save energy and minimize the maintenance costs. However, the specific solubilizing and fast diffusing behavior of CO 2 in PS limited the formation of micropores and the further increase of macropores, which resulted in on limited decrease in thermal conductivity. In this study, one-dimensional carbon nanotubes, two-dimensional graphene, and three-dimensional activated carbon were loaded on PS using supercritical CO 2 foaming. The results demonstrated that all these three carbon nanomaterials doped on PS could generate more micropores and macropores during foaming. Moreover, the composite PS foams presented much lower specific thermal conductivity (0.360 cm 3 ·W/(g·m·K)), higher cell density (up to 3.23 × 10 14 cell/cm 3 ), and compressive modulus (up to 1.66 MPa), overwhelming those of pure PS. Particularly, the continuous infrared thermography measurements found that two-dimensional graphene thermally outperformed the others, meaning comparatively better heat insulation effect after foaming. Therefore, multidimensional carbon nanomaterials were promising to minimize the negative environmental impact of PS foaming while comprehensively reinforcing it. • The reinforcements of multidimensional carbon fillers on polystyrene were varied. • Graphene thermally/physically outperformed carbon nanotubes and activated carbon. • Improved coupling of its plasmon with phonon-polariton thermally enhanced graphene. • Carbon nanomaterials are comprehensively better fillers for polystyrene.

Progress in the Foaming of Polymer-based Electromagnetic Interference Shielding Composites by Supercritical CO2.

As a critical action plan formulated for peaking carbon dioxide emissions, polymeric electromagnetic interference (EMI) shielding materials based on CO2 foaming technology have recently been attracting widespread attention in both research and industry, attributable to their efficient use of CO2 , high specific strength, corrosion resistance and low-cost characteristics. In the past decade, the emergence of novel design concepts and preparation techniques for CO2 foaming technology has led to the development of new high-performance EMI shielding materials in this field. This review summarizes the research progress made to date on the fabrication of EMI shielding composite foams by supercritical carbon dioxide (scCO2 ) foaming. We also explore the structure-activity relationships between the component/distribution and EMI shielding properties. Additionally, the application prospects and development challenges of new EMI shielding composite foams are described.

Microwave-assisted foaming and sintering high-strength and antistatic polypropylene bead foams by constructing conductive 3D skeleton structure

Polypropylene (PP) bead foam parts, one of the most widely used automotive interiors, are traditionally welded by high-pressure steam, while their large inter-bead gaps result in the poor mechanical properties. Herein, syndiotactic polypropylene (sPP) powders, with low melting point, coated with carbon nanotubes (CNTs) were adopted as the microwave absorbing medium to weld the surface of expanded isotactic polypropylene (EiPP) beads, which were initially prepared by supercritical carbon dioxide (scCO2) foaming. Then, the modified EiPP (EiPP coated with CNTs@sPP powders, denoted as mEiPP) composite foams were successfully fabricated by microwave-assisted foaming and sintering. The obtained foam part consisted of porous iPP bead structure (body) and interconnected CNTs@sPP pathway (3D skeleton), which showed superior mechanical properties with tensile strength of 4.07 MPa and compressive strength of 4.64 MPa (10 % strain). Due to the conductive 3D skeleton, the requirements of antistatic PP bead foams could be sufficed with the lower CNTs loading.

The distribution of electrospun polylactic acid in polycaprolactone matrix controlled by traction rate and its effect on the foamed porous tissue engineering scaffolds

AbstractPolycaprolactone (PCL) matrix scaffolds have been extensively studied for tissue engineering applications, which were limited by poor cell adhesion and mechanical strength. Fiber reinforcement modification could be used to improve material properties and optimize material structure. In this study, polylactic acid (PLA) electrospun nanofibers were dispersed in PCL powder, and then the composites were extruded and blended at different traction speed. During the blending and extrusion process, the nanofibrous phase was uniformly dispersed in the matrix, and a kind of tissue engineering scaffold with high connectivity and network structure was prepared using supercritical carbon dioxide foaming. The effect of nanofibers on the foaming behavior of PCL matrix composites prepared at different traction rates was investigated, and the addition of nanofibers promoted the connectivity of the scaffold. Human umbilical vein endothelial cells (HUVECs) culture results showed that the high‐connectivity scaffold was biocompatible and could significantly promote the adhesion and growth of HUVECs. Therefore, fiber‐reinforced porous scaffolds have great application potential in the field of tissue engineering scaffolds.

Fabrication of lightweight flexible thermoplastic polyurethane/multiwalled carbon nanotubes composite foams for adjustable frequency-selective electromagnetic interference shielding by supercritical carbon dioxide

In this study, the thermoplastic polyurethane (TPU)/multiwalled carbon nanotubes (MWCNTs) lightweight flexible foam with sandwich structure was achieved by supercritical carbon dioxide (scCO2) foaming. This work studied the relationship between foaming behavior and electromagnetic interference (EMI) shielding performance. The results showed that the formation of cell structure could not only achieve the purpose of lightweight, but also control the position of electromagnetic interference shielding efficiency (EMI SE) peak by adjusting foaming temperatures. The EMI SE peak could shift to high frequencies as the foaming temperature increases, and the adjustable frequency ranged from 9.76 GHz to 14.72 GHz. The maximum EMI SE of TPU/MWCNTs composite foams increased to 44.86 dB under 2.5 wt% filler content with a density of 0.61 g/cm3. This work provided a feasible idea for the preparation of lightweight and adjustable frequency-selective EMI shielding composite materials by supercritical fluid foaming.

Fabrication of super-hydrophilic and highly open-porous poly (lactic acid) scaffolds using supercritical carbon dioxide foaming.

Porous poly (lactic acid) (PLA)-based scaffolds have been widely used as a promising product in tissue engineering. However, it is still a challenge to prepare the PLA-based scaffolds with high expansion ratio, good hydrophilicity, and excellent cytocompatibility by a green and cost-effective fabrication approach. Herein, we prepared porous PLA-based scaffolds using carbon dioxide (CO2) as the physical foaming agent. To improve the hydrophilicity and foaming behavior of PLA, poly (ethylene glycol) (PEG) was selected as a good additive to blend with PLA. It revealed that the introduction of PEG could improve the foaming behavior of PLA and promote the formation of opening cells via reducing the matrix strength of PLA. The obtained 3D PLA/PEG scaffolds exhibited high expansion ratio (9.1), high open-cell content (95.2%), and super-hydrophilicity (water contact angle 0°). Additionally, the mouse fibroblast NIH/3T3 cells with live/dead cell fluorescence staining assay was utilized to examine the biocompatibility of PLA/PEG scaffolds. The result demonstrated that the proliferation ratio of NIH/3T3 cells on the surface of PLA/PEG scaffolds was higher than that of PLA scaffolds, indicating that the highly interconnected cell structure was conducive to cell adhesion and attachment. Consequently, such hydrophilic open-cell structure obtained by adding PEG into PLA possesses great potential for use in tissue engineering.

Fabrication of skinless cellular poly (vinylidene fluoride) films by surface-constrained supercritical CO2 foaming using elastic gas barrier layers

Removing the solid skin of polymer foams is a challenging approach for supercritical carbon dioxide (scCO2) foaming. Herein, a surface-constrained foaming method was used to fabricate skinless cellular poly (vinylidene fluoride) (PVDF) films. The use of organosilicone and nature latex as gas barrier layers resulted in low CO2 diffusion rates of 2.16 × 10−11 m2/s and 4.73 × 10−13 m2/s, and trigger heterogeneous nucleation of cells on the PVDF/barrier layer interface. The skin layer and the cell size gradient in the region close to the surface were successfully eliminated, and the surface cell density and cell size could be controlled in the range of 7.2 × 106 cells/cm3, and 13–41 µm, respectively. Moreover, the fabricated skinless cellular PVDF films exhibited an enhanced melting temperature and crystallinity due to the plasticizing effect of scCO2. The present study provides new thoughts for the fabrication of skinless polymer films using surface-constrained scCO2 foaming.

Ultrahigh and Tunable Electromagnetic Interference Shielding Performance of PVDF Composite Induced by Nano-Micro Cellular Structure.

Lightweight and efficient electromagnetic interference (EMI) shielding materials play a vital role in protecting high-precision electronic devices and human health. Porous PVDF/CNTs/urchin-like Ni composites with different cell sizes from nanoscale to microscale were fabricated through one-step supercritical carbon dioxide (CO2) foaming. The electrical conductivity and electromagnetic interference (EMI) shielding performance of the composites with different cell sizes were examined in detail. The results indicated that the nanoscale cell structure diminishes the EMI shielding performance of the composite, whereas the microscale cell structure with an appropriate size is beneficial for improving the EMI shielding performance. A maximum EMI shielding effectiveness (SE) of 43.4 dB was achieved by the composite foams which is about twice that of the solid composite. Furthermore, as the supercritical CO2 foaming process reduces the density of the composite by 25–50%, the EMI SSE (specific shielding effectiveness)/t(thickness) of the composite reaches 402 dB/(g/cm2), which is the highest value of polymer foam obtained to the best of the authors’ knowledge. Finally, compression tests were performed to show that the composites still maintained excellent mechanical properties after the supercritical CO2 foaming process.