Preparation of Thermoplastic Polyurethane (TPU) Perforated Membrane via CO2 Foaming and Its Particle Separation Performance

Skinless Polyphenylene Sulfide Foam with Enhanced Thermal Insulation Properties Fabricated by Constructing Aligned Gas Barrier Layers for Surface-Constrained sc-CO2 Foaming

A solid skin layer inevitably forms on the foam surface for supercritical carbon dioxide (sc-CO₂) foaming technology, leading to deterioration of some inherent properties of polymeric foams. In this work, skinless polyphenylene sulfide (PPS) foam was fabricated with a surface-constrained sc-CO₂ foaming method by innovatively constructing aligned epoxy resin/ferromagnetic graphene oxide composites (EP/GO@Fe₃O₄) as a CO₂ barrier layer under a magnetic field. Introduction of GO@Fe₃O₄ and its ordered alignment led to an obvious decrease in the CO₂ permeability coefficient of the barrier layer, a significant increase of the CO₂ concentration in the PPS matrix, and a decrease of desorption diffusivity in the depressurization stage, suggesting that the composite layers effectively inhibited the escape of CO₂ dissolved in the matrix. Meanwhile, the strong interfacial interaction between the composite layer and the PPS matrix remarkably enhanced the heterogeneous nucleation of cells at the interface, resulting in elimination of the solid skin layer and formation of an obvious cellular structure on the foam surface. Moreover, by the alignment of GO@Fe₃O₄ in EP, the CO₂ permeability coefficient of the barrier layer became much lower, and the cell density on the foam surface further increased with decreasing cell size, which was even higher than that of the cross section of foam, attributed to stronger heterogeneous nucleation at the interface than the homogeneous nucleation in the core region of the sample. As a result, the thermal conductivity of the skinless PPS foam reached as low as 0.0365 W/m·k, decreasing by 49.5% compared with that of regular PPS foam, showing a remarkable improvement in the thermal insulation properties of PPS foam. This work provided a novel and effective method for fabricating skinless PPS foam with enhanced thermal insulation properties.

Green and effective fabrication of porous surfaces with adjustable cell structure by foaming at incomplete healed polymer-polymer interface

Porous surfaces of materials have shown huge potentialities for endowing materials with multifarious functions. Despite introducing gas-confined-barriers in supercritical CO₂ foaming technology is effective to weaken the gas escape effect and facilitate the preparation of porous surfaces, the differences in intrinsic properties between barriers and polymers result in bottlenecks like cell structure adjustment limitation and incompletely eliminated solid skin layers. This study undertakes a preparation approach for porous surfaces by foaming at incompletely healed polystyrene/polystyrene interfaces. In contrast with employing gas-confined-barriers reported before, the porous surfaces foamed at incompletely healed polymer/polymer interfaces show a monolayer, full-open cell morphology, and wide adjustable range in cell structures including cell size (120 nm∼15.68 μm), cell density (3.40 × 10⁵ cells/cm²∼3.47 × 10⁹ cells/cm²), and surface roughness (0.50 μm∼7.22 μm). Furthermore, the wettability of obtained porous surfaces depending on the cell structures is systematically discussed. Finally, a super-hydrophobic surface with hierarchical micro-nanoscale roughness, low water adhesion, and high water-impact resistance is built by depositing nanoparticles on a porous surface. Consequently, this study offers a clean and simple method to prepare porous surfaces with adjustable cell structures, which is expected to open a door to developing a new fabrication technique for micro/nano-porous surfaces.

Passive Daytime Radiative Cooling by Thermoplastic Polyurethane Wrapping Films with Controlled Hierarchical Porous Structures

Current research has focused on effective solutions to mitigate global warming and the accelerating greenhouse gas emissions. Compared to most cooling methods requiring energy and resources, passive daytime radiative cooling (PDRC) technology offers excellent energy savings as it requires no energy consumption. However, existing PDRC materials encounter unprecedented problems such as complex structures, low flexibility, and performance degradation after stretching. Thus, this study reports a porous structured thermoplastic polyurethane (TPU) film with bimodal pores to produce high-efficiency PDRC with efficient solar scattering using a simple process. The TPU film exhibited an adequately high solar reflectivity of 0.93 and an emissivity of 0.90 in the atmospheric window to achieve an ambient cooling of 5.6 °C at midday under a solar intensity of 800 W m^-2 . Thus, the highly elastic and flexible TPU film was extremely suitable for application on objects with complex shapes. The radiative cooling performance of 3D-printed models covered with these TPU films demonstrated their superior indoor cooling efficiency compared to commercial white paint (8.76 °C). Thus, the proposed design of high-efficiency PDRC materials is applicable in various urban infrastructural objects such as buildings and vehicles.

A green fabrication method of poly (lactic acid) perforated membrane via tuned crystallization and gas diffusion process

Poly (lactic acid) (PLA) perforated membrane is typically obtained through the solvent-volatilization-induced or non-solvent-induced phase separation (NIPS) method. However, the residual organic solvents would unavoidably limit the application of PLA perforated membrane in biomedical and high-end water purification fields. Herein, an innovative solution-free method was proposed for preparing the PLA perforated membrane via a simple and environmentally friendly way. We have successfully fabricated the PLA perforated membrane using a physical foaming technique with CO₂ as the blowing agent. By tuning the primary film thickness, saturation pressure, and foaming temperature, PLA perforated membrane's cell morphology could be accordingly adjusted. The PLA perforated membrane with a highly-ordered straight pore channel and high open cell content (OCC) approximately 72% was obtained under a mild condition. The formation mechanism of the PLA perforated membrane was discussed via the interaction of crystallization behavior and gas diffusion process. This green and solvent-free PLA perforated membrane possesses great potential for use in areas like the tissue engineering and high-end water purification.

The polydopamine-enhanced superadhesion and fracture strength of honeycomb polyurethane porous membranes

The superhydrophobic properties of biological surfaces in nature have attracted extensive attention in scientific and industrial circles. Relative to the rolling superhydrophobic state of lotus leaves, the adhesive superhydrophobic state of geckos and Parthenocissus tricuspidata is also significant in many fields. In this work, polydopamine (PDA) with its excellent biological compatibility and strong adhesion was selected as a substance to simulate the secretion of the suckers of P. tricuspidata and it was precipitated at the surface of honeycomb polyurethane porous membranes (PUPM). The results demonstrated that the honeycomb PUPM, as prepared, displayed special super-adhesion properties similar to those of geckos and P. tricuspidata. PDA formed via self-polymerization in aqueous solution was equivalent to a double-sided adhesive, acquiring a micro-nano structure of PDA and PUPM and displaying increased surface hydrophobicity and improved adhesion properties. Even when the surface precipitation of PDA and modification with n-dodecyl mercaptan made the contact angle increase to more than 160°, the surface adhesion to water was rather strong and remained stable. The addition of the PDA adhesive can effectively change the microporous structure of PUPM, enhancing the viscosity, and facilitating an enhancement in the fracture strength.