Ceramic Meta-Aerogel with Thermal Superinsulation up to 1700 °C Constructed by Self-Crosslinked Nanofibrous Network via Reaction Electrospinning.

Thermal insulation under extreme conditions requires the materials to be capable of withstanding complex thermo-mechanical stress, significant gradient temperature transition, and high-frequency thermal shock. The excellent structural and functional properties of ceramic aerogels make them attractive for thermal insulation. However, in extremely high-temperature environments (above 1500 °C), they typically exhibit limited insulation capacity and thermo-mechanical stability, which may lead to catastrophic accidents, and this problem is never effectively addressed. Here, a novel ceramic meta-aerogel constructed from a crosslinked nanofiber network using a reaction electrospinning strategy, which ensures excellent thermo-mechanical stability and superinsulation under extreme conditions, is designed. The ceramic meta-aerogel has an ultralow thermal conductivity of 0.027 W m-1 k-1, and the cold surface temperature is only 303 °C in a 1700 °C high-temperature environment. After undergoing a significant gradient temperature transition from liquid nitrogen to 1700 °C flame burning, the ceramic meta-aerogel can still withstand thousands of shears, flexures, compressions, and other complex forms of mechanical action without structural collapse. This work provides a new insight for developing ceramic aerogels that can be used for a long period in extremely high-temperature environments.

Effect of rheological behaviors of polyacrylonitrile grafted sericin solution on film structure and mechanical properties.

Sericin protein possesses excellent biocompatibility, antioxidation, and processability. Nevertheless, manufacturing large quantities of strong and tough pure regenerated sericin materials remains a significant challenge. Herein, we design a lightweight structural sericin film with high ductility by combining radical chain polymerization reaction and liquid-solid phase inversion method. The resulting polyacrylonitrile grafted sericin films exhibit the ability to switch between high strength and high toughness effortlessly, the maximum tensile strength and Young's modulus values are 21.92 ± 1.51 MPa and 8.14 ± 0.09 MPa, respectively, while the elongation at break and toughness reaches up to 344.10 ± 35.40 % and 10.84 ± 1.02 MJ·m-3, respectively. Our findings suggest that incorporating sericin into regenerated films contributes to the transformation of their mechanical properties through influencing the entanglement of molecular chains within polymerized solutions. Structural analyses conducted using infrared spectroscopy and X-ray diffraction confirm that sericin modulates the mechanical properties by affecting the transition of condensed matter conformation. This work presents a convenient yet effective strategy for simultaneously addressing the recycling of sericin as well as producing regenerated protein-based films that hold potential applications in biomedical, wearable, or food packaging.

Biomimetic Bouligand chiral fibers array enables strong and superelastic ceramic aerogels.

Ceramic aerogels are often used when thermal insulation materials are desired; however, they are still plagued by poor mechanical stability under thermal shock. Here, inspired by the dactyl clubs of mantis shrimp found in nature, which form by directed assembly into hierarchical, chiral and Bouligand (twisted plywood) structure exhibiting superior mechanical properties, we present a compositional and structural engineering strategy to develop strong, superelastic and fatigue resistance ceramic aerogels with chiral fibers array resembling Bouligand architecture. Benefiting from the stress dissipation, crack torsion and mechanical reinforcement of micro-/nano-scale Bouligand array, the tensile strength of these aerogels (170.38 MPa) is between one and two orders of magnitude greater than that of state-of-the-art nanofibrous aerogels. In addition, the developed aerogels feature low density and thermal conductivity, good compressive properties with rapid recovery from 80 % strain, and thermal stability up to 1200 °C, making them ideal for thermal insulation applications.

Inhibited Grain Growth Through Phase Transition Modulation Enables Excellent Mechanical Properties in Oxide Ceramic Nanofibers up to 1700 °C.

Oxide ceramics are widely used as thermal protection materials due to their excellent structural properties and earth abundance. However, in extremely high-temperature environments (above 1500 °C), the explosive growth of grain size causes irreversible damage to the microstructure of oxide ceramics, thus exhibiting poor thermomechanical stability. This problem, which may lead to catastrophic accidents, remains a great challenge for oxide ceramic materials. Here, a novel strategy of phase transition modulation is proposed to control the grain growth at high temperatures in oxide ceramic nanofibers, realizing effective regulation of the crystalline forms as well as the size uniformity of primary grains, and thus suppressing the malignant growth of the grains. The resulting oxide ceramic nanofibers have excellent mechanical strength and flexibility, delivering an average tensile strength as high as 1.02 GPa after being exposed to 1700 °C for 30 min, and can withstand thousands of flexural cycles without obvious damage. This work may provide new insight into the development of advanced oxide ceramic materials that can serve in extremely high-temperature environments with long-term durability.

Effect of Weaving Structures on the Water Wicking-Evaporating Behavior of Woven Fabrics.

Water transfer through porous textiles consists of two sequential processes: synchronous wicking-evaporating and evaporating alone. In this work we set out to identify the main structural parameters affecting the water transfer process of cotton fabrics. Eight woven fabrics with different floats were produced. The fabrics were evaluated on a specially designed instrument capable of measuring the water loss through a vertical wicking process. Each test took 120 min, and two phases were defined: Phase I for the first 10 min and Phase II for the last 110 min according to wicking behavior transition. Principal components and multivariate statistical methods were utilized to analyze the data collected. The results showed that Phase I dominated the whole wicking-evaporating process, and the moisture transfer speed in this phase varied with fabric structure, whereas the moisture transfer speeds in Phase II were similar and constant regardless of fabric structure. In addition, fabric with more floats has high water transfer speed in Phase I due to its loosened structure with more macropores.

Study on the Moisture Absorption and Thermal Properties of Hygroscopic Exothermic Fibers and Related Interactions with Water Molecules.

The aim of this paper is to study the hygroscopic behavior of hygroscopic exothermic fiber-based materials and to obtain a better understanding of the thermal performance of these fibers during the moisture absorption process. The temperature distribution of different kinds of hygroscopic exothermic fibers in the process of moisture absorption, observed by infrared camera, demonstrated two types of heating performance of these fibers, which might be related to its hygroscopic behavior. Based on the sorption isotherms, a Guggenheim-Anderson-de Boer (GAB) multi-layer adsorption model was selected as the optimal moisture absorption fitting model to describe the moisture absorption process of these fibers, which illustrated that water sorption capacity and the water-fiber/water-water interaction had a significant influence on its heating performance. The net isosteric heats of sorption decreased with an increase of moisture content, which further explained the main factor affecting the heat dissipation of fibers under different moisture contents. The state of adsorbed water and water vapor interaction on the fiber surface were studied by simultaneous thermal analysis (TGA-DSC) measurement. The percentage of bound and unbound water formation at low and high humidity had a profound effect on the thermal performance of fibers. It can therefore be concluded that the content of tightly bound water a strong water-fiber interaction was the main factor affecting the heating performance of fibers at low moisture content, and the content of loosely bound water reflected that water sorption capacity was the main factor affecting the heating performance of fibers at high moisture content. This was further proven by the heat of desorption.

A Numerical and Experimental Study on a Pre-Twisted Ring Spinning System.

The ring spinning process is the most widely used method in the spinning industry. Nowadays, the labor cost become more and more expensive, and it is essential to improve productivity. For increasing the productivity, a modification of adding a pre-twister and holding roller on the traditional ring spinning system have been discussed in this paper. The computational fluid dynamics (CFD) are introduced to study the effects of pre-twister and spinning tests are implemented for verification. The numerical simulations show that the cavity conical degree and nozzle numbers of the pre-twister are the key parameters which affect the airflow fluctuation in the cavity, and have obvious effects on the resultant yarn twist. By contrast, the axial angle and tangential angle of the nozzle have less effect on the resultant yarn twist. When the fiber bundles pass by the front nip, they are affected by the vortex and result in a partially strengthened and wrapped structure which could be subsequently twisted less by the traveler and ring, so the productivity could be potentially increased. According to the spinning tests, an evident productivity increase by nearly 30% for medium cotton yarns can be achieved, and the yarns have an acceptable reduction in nearly all properties.