Thermoplastic polyester elastomer (TPEE) is valued for its flexibility but suffers from low melt strength and high flowability, which impair its printability in fused filament fabrication (FFF). Inspired by the fiber-controlled ink flow in Chinese calligraphy, this study introduces aramid fiber (AF) powder to modulate TPEE's rheology. The anisotropic AF powder significantly enhances the stress transfer capability while reducing the melt flowability of TPEE. Extensional tests showed AF increased melt fracture strain from 50% to 80%, reducing nozzle residue. Simultaneously, small-amplitude oscillatory shear (SAOS) tests confirmed a substantial boost in low-frequency storage modulus, curbing melt overflow. This synergy eliminated surface stringing and significantly improved printing surface quality. Leveraging this high-quality printing, we fabricated a multiscale biomimetic structure with a solid-foam gradient modulus using a double-nozzle printer and in-situ foaming technology. This bionic structure of AF-reinforced TPEE efficiently dissipated an impact force from 55.0 kN to 1.7 kN, achieving a 97 % energy absorption efficiency. This work provides a novel strategy for designing and manufacturing next-generation impact-resistant thermoplastic elastomers.

Flexible filaments used in fused filament fabrication (FFF) suffer from low printing speed, surface stringing, and poor interfacial bonding, which severely restrict their industrial application. Herein, we report an effective strategy to significantly improve the printability of thermoplastic polyester elastomer (TPEE) filaments without sacrificing product flexibility by utilizing the self-nucleation (SN) effect during extrusion. The SN treatment induces a more ordered crystalline structure with higher melting point, increasing the filament's Young's modulus by 38% and melt tensile stress by over one order of magnitude. Consequently, the printing speed is boosted by 110% (from 70 to 150 mm/s), and surface stringing is fully eliminated. More importantly, the interfacial bond strength of SN-printed samples approaches that of the bulk material, showing low anisotropy. In contrast, annealing and heterogeneous nucleation show limited improvements or even weaken interlayer adhesion. This work reveals the fundamental mechanism of self-nucleation on FFF printability of flexible polymers and offers a scalable extrusion-based thermal history control route toward industrial flexible 3D printing.

Elucidating the decisive role of the crystalline state in the narrow foaming window of polypropylene (PP) is critical for fabricating high-performance foams. Here, we systematically investigate the foaming behaviors of a highly crystalline isotactic polypropylene homopolymer (PPH) and a polypropylene copolymer (PPB) with lower crystallinity via CO2 batch foaming. The influence of foaming temperature, particularly around the Vicat softening temperature (VST), on the evolution of crystalline structure and final foam morphology is investigated. Results established the VST as a critical threshold separating two distinct foaming mechanisms. Below the VST, foaming proceeded via "solid-state tearing" mode, whereas above it, the mechanism transitioned to "high-elastic expansion". Owing to its highly stable crystals, PPH exhibited an extremely narrow foaming window of merely 3 degrees C (155-158 degrees C). In stark contrast, the lower crystalline stability of PPB enabled the high-elastic expansion regime to commence at a significantly lower temperature, yielding a broad foaming window (126-137 degrees C) and an ultrahigh expansion ratio exceeding 80. This work demonstrates the initial crystalline state as the primary factor dictating the foaming window and morphology of PP foams, establishing a crystal-state-governed framework for the rational design of advanced PP foams.

Fiber-reinforced elastomers can significantly enhance mechanical strength while retaining material softness, thereby expanding the application scope of elastomeric materials in scenarios requiring both high flexibility and high strength. Compared with thermoplastic polymers and ceramic materials, elastomers exhibit low modulus and high fracture strain, which result in more complex fiber-matrix interfacial behaviors. This review systematically elucidates the intrinsic relationships between microscopic stress transfer mechanisms and macroscopic mechanical properties in fiber-reinforced elastomers, summarizes research progress in this field over the past two decades, and highlights the effects of various reinforcement strategies on performance optimization, providing a theoretical basis for the design and development of next-generation high-performance fiber-reinforced elastomers.

ABSTRACT With frequent extreme heat events, cooling demand is no longer confined to traditional low‐latitude hot regions. Passive radiative cooling is usually designed to achieve the high reflectivity and emissivity under fixed conditions, whereas actual cooling demand changes with latitude‐dependent thermal boundaries. Inspired by the structural‐spectral distribution rule formed by butterfly‐wings in response to their habitats, this work proposes an environment‐guided gradient porous radiative cooling film design strategy. In the TPU/PMMA/ZrO 2 system, thickness‐direction gradient pore regulates photon transmission, PMMA dispersed‐phase introduces secondary scattering on pore‐walls, and ZrO 2 nanoparticles enhance local optical contrast. The optimized G‐TPU/PMMA/ZrO 2 film achieves 96.4% solar reflectance and 98.5% infrared emissivity, exhibiting the lowest outdoor temperature and highest net cooling power. By adjusting the supercritical CO 2 foaming process parameters, the same material system can form large‐pore‐rich, balanced‐gradient, and dense‐small‐pore‐rich architectures to adapt to different thermal environments. Climate‐chamber tests further verified that the optimal pore structure changes with the external environment. EnergyPlus simulations show that radiative cooling cannot be treated as a universal year‐round cooling surface, while an appropriate cooling method should be selected based on climatic characteristics. This work advances porous radiative cooling from single‐condition performance maximization to structural adaptation for different thermal boundaries within one material platform.

Physical foaming of ethylene-vinyl acetate (EVA) elastomers for high expansion ratio remains challenging due to the narrow processing window and low matrix modulus. This work systematically investigates the topological influence of chemical crosslinking on the viscoelasticity and subsequent foaming behavior of EVA. Crosslinking transforms the EVA melt into a robust elastic network, significantly extending stress relaxation times and inhibiting viscous flow. An optimal sparse network containing 0.2-0.6 phr crosslinker effectively balances melt strength against chain mobility, facilitating stable cell growth. Notably, by leveraging the synergistic effect of a CO2/N2 mixture, an ultrahigh expansion ratio of 30-fold (density: 0.031 g/cm3) with uniform cell morphology was achieved in the lightly crosslinked sample. In contrast, excessive crosslinking induces brittle fracture due to the restricted chain extensibility under high expansion force. The foaming mechanism is governed by the competition between the gas expansion force and the confinement of the crosslinked network. This work provides a strategic framework for designing high-performance elastomeric foams through the precise modulation of network architecture and blowing agent composition.

With the rapid development of infrared detection methods and military surveillance technologies, flexible and wearable infrared stealth materials (ISM) have attracted increasing attention. Inspired by the layered structure of penguins' fat-feather-oil, this study prepared a three-layer MXene/waterborne polyurethane (WPU)-foam rubber-phase change microcapsule (PCM)/WPU composite material (M-F-P) via the solution blending and doctor-blading method. The outermost layer of the M-F-P composite is an MXene/WPU conductive film, which features a low infrared emissivity and Joule heating performance to adapt to suddenly cold environments. The porous foam rubber in the middle layer provides excellent thermal insulation performance, which effectively inhibits heat conduction and enhances infrared stealth efficiency. Meanwhile, as a four-directional elastic material, it exhibits deformation recovery capability in both the warp and weft directions as well as the 45° direction. The bottom layer of the PCM/WPU film has a phase change enthalpy of 154.3 J/g and possesses efficient thermal management capability. It achieves dynamic thermal regulation through the cycle of heat absorption at high temperatures and heat release at low temperatures.

Amidst the nationwide fitness craze, people are increasingly concerned about comfort during exercise. Although existing textiles can achieve functions such as moisture management and cooling, it remains challenging to integrate radiation cooling, directional water transport, lightweight design, and sufficient mechanical strength into a single shoe upper. Herein, we proposed a large-scale preparation strategy for a supercritical reinforced foamed fiber with an enhanced structure and formed a tridimensional textile (RFTT) using tridimensional knitting technology. Based on experimental and simulation results, we reveal the influence of pore morphology, distribution, and interface effects on scattering phenomena, explaining the role of anisotropic scattering mechanisms in radiative cooling capacity. By using multiple nucleation foaming methods to form a hierarchical porous structure that enhances scattering, RFTT achieves a reflectivity of up to 99.4% and a mid-infrared emissivity of 98.9%. Additionally, RFTT exhibits a net radiative cooling power of 153.2 W m- 2 during daylight hours and 174.5 W m- 2 at night, with an average cooling temperature 7.6°C lower than cotton textiles and 6.3°C lower than PET textiles. Together with its moisture-transport, cushioning, and durability-related performance, RFTT provides an upper-relevant textile architecture for combining radiative cooling and hygrothermal management under dynamic use conditions.

Emerging solar desalination technology shows great potential in response to the growing global water crisis owing to its convenience and low environmental impact. Boosting the exposure height of solar evaporators helps enhance evaporation efficiency. However, the elevated 3D solar evaporator confronts the crucial challenges of poor salt tolerance and insufficient fluid transport height. Herein, inspired by natural rattan, a salt‐tolerant elevated 3D solar evaporator with multi‐scale long‐range aligned fluid channels is fabricated by a continuous bubble freeze casting technique. The capillary‐driven vertical transport in aligned fluid channels endows the evaporator with an elevated exposure height, which helps increase environmental energy utilization, breaking the energy conversion efficiency limitation of conventional 2D evaporators. Moreover, the aligned fluid channel helps to quickly replenish the interfacial water loss and reduce the tortuousness of salt return paths to promote salt circulation, overcoming the long‐standing challenge of salt accumulation in traditional elevated 3D solar evaporators. With rattan‐like structures employed, apparent solar‐to‐steam efficiency of 209.3%, and water evaporation rate of 3.51 ± 0.1 kg m −2 h −1 are gained for seawater desalination under 1 sun radiation without salt accumulation. The creation of rattan‐inspired solar evaporators offers important insights into the structure design of efficient and salt‐tolerant elevated 3D solar evaporators.

Polyether block amide (PEBA) foams have attracted considerable attention in advanced footwear technology, owing to their low density and exceptional resilience. However, existing research predominantly focuses on block-type PEBA foams, with relatively limited investigation into bead foam molding techniques. Herein, we introduce an in-mold foaming and molding (IMFM) strategy, where low-melting-point ethylene-vinyl acetate (EVA) was blended with PEBA to overcome the challenge of poor inter-bead bonding in pure PEBA bead foam parts. The molten EVA acts as an effective interfacial adhesive during the IMFM process. This is demonstrated by a fundamental shift in the fracture mode: from inter-bead failure in pure PEBA parts to intra-bead fracture in the PEBA/EVA blends. Consequently, the optimal formulation with 5 wt% EVA achieved a low density of 0.107 g/ cm3 and a high rebound resilience of 73.8 %, coupled with a 15 % increase in tensile strength (to 0.63 +/- 0.04 MPa) and an 84 % increase in elongation at break (to 137 +/- 6.6 %). Furthermore, the confined nature of the IMFM process generates sufficient internal pressure to stabilize the cellular structure, preventing cell collapse. This straightforward strategy offers a scalable and feasible approach for the mass production of highperformance PEBA bead foam products.

Porous materials are widely used in various scenarios due to their advantages such as good thermal insulation, flexibility, and ultra-lightness. Foaming technology has given porous materials more application areas by introducing uniformly distributed cellular structures into the polymer collective. In the past decade, we have conducted systematic studies around the preparation of multi-component polymer microporous materials and functional applications of porous materials. In this work, we propose the preparation of foamed TPU fibers and foamed fabrics (FT-fabric) with anisotropic cell structure using TPU as substrate by micro-extrusion foaming techniques. Thanks to the multistage cell distribution of the FT-fabric and the vibrational absorption of the polymer in the MIR band, the prepared FT-fabric has a near-infrared reflectance of >97

Cross-linked ethylene-vinyl acetate copolymer (EVA) possesses excellent mechanical properties that are widely used in sports and the photovoltaic industry, but it cannot be recycled through melt reprocessing. The emergence of dynamic chemistry provides a viable approach to achieve both high mechanical performance and recyclability in cross-linked EVA. Herein, this study fabricated a dual cross-linked EVA containing covalently cross-linked sites and dynamically cross-linked sites, which improved the mechanical properties and endowed it with reprocessability. The optimal cross-linking network structure was determined, and the bond exchange was clarified through chemical, rheological, and mechanical analysis. The dual cross-linked EVA could be well foamed through supercritical fluid and the foaming temperature was broadened to 180 degrees C. Low-density and uniform cell structure was obtained for the dual cross-linked EVA foam that exhibited excellent cushioning performance, the peak impact force was reduced from 8081 N to 1281 N, and achieved a superior energy absorption efficiency of 84.1 %. Meanwhile, the dual cross-linked EVA foam could be recycled through a re-foaming strategy. This study demonstrates that incorporating dynamic bonds into the covalent network is beneficial for balancing mechanical properties and recyclability, which provides a valuable insight for designing recyclable and cushioning EVA foam.

High-hardness thermoplastic polyurethane (HD-TPU) are utilized in advanced engineering applications due to their superior strength, flexibility, and abrasion resistance. However, the high content of hard segments reduced the gas solubility, making it difficult to generate uniform microcellular foams. In this study, the metal-organic framework (MOF) zeolitic imidazolate framework-8 (ZIF-8) was employed as both a heterogeneous nucleating agent and a gas enrichment "nano-reservoir" to enhance HD-TPU foamability. Dopamine modification was applied to greatly improve ZIF-8 dispersion in HD-TPU. ZIF-8 significantly enhanced the CO2 solubility in the TPU/MOF composites. The dual effects of MOF facilitate the preparation of microcellular HD-TPU/ZIF-8 foams with uniform cell size distribution after low-pressure saturation (3-5 MPa). Cell density and expansion ratio were increased by 50 and 1.5 times, respectively. The cyclic compression performance of HD-TPU/ZIF-8 foams was significantly enhanced. This study presents a novel method for preparing high-performance HD-TPU microcellular foams by introducing porous nanoparticles.

Poly (butylene adipate-co-terephthalate) (PBAT) foam sheets prepared by foaming supercritical fluids are characterized by high resilience, homogeneous cellular structure, and well-defined biodegradability. However, the inert chemical structure and the rigid hard segments restrict the diffusion of CO2 within the PBAT matrix, resulting in extremely long gas saturation times as long as 9 h at a thickness of 12 mm. In this study, microporous structures were pre-introduced into the PBAT matrix to provide a fast gas diffusion pathway during the saturation process. After 2 h of saturation, PBAT foam sheets with expansion ratio of 10 to 13.8 times were prepared. The interaction of CO2 with PBAT was systematically investigated, and the CO2 sorption process was evaluated kinetically and thermodynamically using the Fickian diffusion theory. The solubility and diffusion rate of CO2 in pretreated PBAT sheets with different microporous sizes and densities were investigated, and the effects of pretreatment strategies on the foaming behavior and cell structure of PBAT foam sheets were discussed. The introduction of a microporous structure not only reduces saturation time but also enhances solubility, enabling the successful preparation of soft foams with high expansion ratios and resilience. After undergoing foaming treatment, the PBAT pretreated sheets with a 10 μm microporous structure and a density of 0.45 g/cm3 demonstrated improved mechanical properties: their hardness decreased to 35 C while resilience increased to 58%, reflecting enhanced elastic recovery capabilities. The pretreatment method, which increases the diffusion rate of CO2 in PBAT sheets, offers a straightforward approach that provides valuable insights into achieving rapid and efficient foaming of thick PBAT sheets in industrial applications.

Thermoplastic elastomer foams, such as ethylene−vinyl acetate (EVA) foams, have received extensive attention for their soft touching, low‐density, and excellent mechanical properties and have been emerging in lightweight footwear. However, the EVA foam suffers from its inadequate rebound resilience properties and poor thermal stability due to the low melting point. Herein, olefin block copolymer (OBC) with excellent rebound properties and high melting peak temperature of 120 °C is introduced into the EVA matrix to improve its foaming behavior and foam properties. A series of lightweight EVA/OBC composite foams with adjustable cellular structures are prepared by supercritical mixed N 2 /CO 2 . It is worth noting that the foaming temperature windows are greatly improved under the action of OBC, and an extremely low‐density as low as 0.06 g cm −3 is achieved. In addition, the as‐prepared EVA/OBC foams exhibit the improved foam shrinkage resistance, resulting from the rapid crystallization ability of OBC phase. Furthermore, the residual strain and hysteresis loss ratio of as‐prepared elastomer foams are as low as 1.56 and 12.95%, respectively. These distinct advantages together with the green foaming process make the EVA/OBC elastomer foams very promising toward high‐performance flexible cellular polymeric materials.

The cell structure uniformity of microcellular polymers significantly impacts material performance, especially for low-porosity microcellular TPU used in chip polishing. The distribution of the cell structure of polishing pads directly affects the removal rate and process repeatability. Despite its importance, no quantitative method for evaluating cell structure uniformity has been reported in the literature. In this study, a digital image processing method that involves morphological operations of scanning electron microscopy (SEM) images, binarization, and cell localization, and the statistical evaluation of cell structure parameters was established to evaluate cell structure uniformity. A quantitative metric, the cell structure uniformity index (CUI), was calculated based on cell structure indices, incorporating the cell size index (Ud), the cell number index (Un), and the cell local spacing index (Ur). By establishing an ideal model and analyzing representative SEM images, the effectiveness and efficiency of the method for evaluating cell structure uniformity of microcellular TPU were successfully validated. The results demonstrated that low-porosity TPU foams exhibited relatively low cell structure uniformity compared to the ideal model. The heterogeneous nucleation process in TPU caused non-uniform cell structures due to the temporal and spatial non-homogeneities during the early cell nucleation process. As the cells grew, they merged and reduced the distance between them, resulting in improved cell structure uniformity.

The soft PBAT foam shows good flexibility, high elasticity, degradable nature, and it can be used as an environmental-friendly candidate for EVA and PU foams. Unfortunately, there are few reports on the application of PBAT as a soft foam. In this study, PBAT foam was fabricated by a pressure quenching method using CO2 as the blowing agent. A significant volume shrinkage of about 81% occurred, where the initial PBAT foam had an extremely high expansion ratio, of about 31 times. A 5–10 wt% PBS with high crystallinity was blended, and N2 with low gas solubility and diffusivity was mixed, with the aim of resisting foam shrinkage and preparing PBAT with a high final expansion ratio of 14.7 times. The possible mechanism behind this phenomenon was established, and the increased matrix modulus and decreased pressure difference within and outside the cell structure were the main reasons for the shrinkage resistance. The properties of PBAT and PBAT/PBS foams with a density of 0.1 g/cm3 were measured, based on the requirements for shoe applications. The 5–10 wt% PBS loading presented advantages in reducing thermal shrinkage at 75 °C/40 min, without compromising the hardness, elasticity, and the compression set, which ensures that PBAT/PBS foams have good prospects for use as soft foams.

Bead foams, lightweight materials produced from expandable or expanded beads, are widely used in industries, including automotive, consumer goods, and packaging. Traditional molding methods, which separate foaming from molding, increase both the production complexity and cycle time. This study demonstrates a simple one-step in-mold foaming and molding (IMFM) method, effectively achieving strong in situ bonding of polymer beads due to elevated foaming temperatures and compressive forces during constrained bead expansion. Constrained expansion resulted in increased cell wall thickness and greater tortuosity of the gas diffusion pathway in the bead foams, ensuring structural stability at high temperatures. High hardness thermoplastic polyurethane molded parts were obtained using IMFM and the molded parts with a density of 0.184 g/cm(3) exhibited a tensile strength of 1.51 MPa and an elongation at break of 181.1%. The IMFM shows significant promise for producing bead foam parts from high-performance polymers, owing to its straightforward bead fusion process and freedom from molding temperature restrictions.

Maintaining the stability of human body temperature is the basis of ensuring the normal life activities of witness, and the emergence of various functional clothing is committed to assisting the human body temperature in thermal comfort range in the changeable environment. However, achieve dual-mode thermal regulation for cooling and insulation on an integrated material without energy input and addition of functional particles has thus far been a huge challenge. Herein, a biomimetic camel-fur designed micro-extruded physically foamed porous elastic fiber (MEPF) using thermoplastic polyurethane (TPU) elastomer as raw material is reported, and its dual-layered fabric (MEPFT-d) for effective personal thermal comfortable management at extreme temperature differences. Benefit from its micro-nano-pores structure, MEPFT-d represents radiate cooling capacity by high solar reflectance and emissivity, behaves low thermal conductivity delaying heat scattering, and promotes evaporative cooling by unidirectional water transport. These excellent properties ensure that MEPFT-d reduces heat loss in cold weather (7.2 °C higher than cotton) and blocks outside heat in hot weather (10.2 °C lower than cotton), which is suitable for various complex outdoor scenes. The cost-effectiveness and superior wearing comfort of this work provide innovative pathways for sustainable energy, smart textiles, and personal thermal comfort applications.

Clarifying the relationship between crystal evolution and the physical foaming behavior of high-hardness thermoplastic polyurethane (HD-TPU) is essential for preparing HD-TPU foams with controllable cellular morphology. In this study, two thermal treatment methods, isothermal annealing and isothermal crystallization, were utilized to control the crystal structure of HD-TPU. The effect of crystals on the physical foaming behavior of HD-TPU foams was examined. The annealing process produced mainly lamellae and Form Ⅰ structure, while isothermal crystallization primarily led to Form Ⅱ spherulites. Foams based on original and pre-treated HD-TPU were prepared by pressure quench foaming. The evolution of foam density and cell morphology was discussed. At low foaming temperatures, crystals induced the heterogeneous nucleation. Realizing a uniform cell structure at high foaming temperatures could be challenging when the spherulite size was large. When the size of the spherulite was small but loosely distributed, larger cells with thinner cell walls could be obtained. However, if the spherulite distribution was dense, the spherulites hindered cell growth, resulting in unevenly distributed and deformed cells.