Enhanced mechanical and dielectric properties of lignocellulosic composite papers with biomimetic multilayered structure and multiple hydrogen-bonding interactions.

Lignocellulosic papers (LCP) are favored for electrical insulating applications due to their environmental friendliness, ease of processing, and cost-effectiveness. However, the loose structure and numerous pores inside LCP result in the poor mechanical and electrical insulating properties, posing challenges in meeting the requirements for the rapid upgrading of high-voltage electrical equipment. Herein, a 3D interconnective structure composed of 3D aramid nanofibers (ANF) and 2D carbonylated basalt nanosheets (CBSNs) is introduced to enhance the structure and the chemical bonding interactions of LCP. This is achieved by impregnating LCP into an ANF-CBSNs suspension, where the 3D interconnective ANF framework hosts numerous CBSNs. The resultant LCP/ANF-CBSNs (LCP/A-C) composite papers exhibit multilayered structure and multiple hydrogen-bonding interactions, demonstrating excellent mechanical and electrical insulating properties. Notably, the optimized LCP/A-C5 composite papers exhibit remarkable tensile strength (23.15 MPa) and dielectric breakdown strength (20.14 kV·mm-1), respectively, representing 229 % and 145 % increase compared to those of the control LCP. These impressive properties are integrated with excellent bending ability, outstanding high temperature resistance, exceptional volume resistivity, and low dielectric constant and loss, demonstrating their potential as highly promising electrical insulating papers for advanced high-power electrical equipment.

Nacre-Inspired Aramid Nanofibers/Basalt Fibers Composite Paper with Excellent Flame Retardance and Thermal Stability by Constructing an Organic-Inorganic Fiber Alternating Layered Structure.

The flame-retardant paper has gradually evolved into a necessary material in various industries as a result of the rising importance of fire safety, energy efficiency, and environmental preservation. Traditional cellulose paper requires the addition of a large amount of flame retardants to achieve flame retardancy, which poses a serious threat to mechanical quality and the environment. Therefore, there is an urgent need to develop inorganic fiber flame-retardant paper with good flexibility, high thermal stability, and inherent flame retardancy. Herein, inspired by the "brick-and-mortar" layered structure of nature nacre, we developed a layered composite paper with a unique alternating arrangement of organic-inorganic fibers by synergistically integrating environmentally sustainable basalt fiber (BF) and high-performance aramid nanofibers (ANFs) through a vacuum-assisted filtration process. The as-prepared ANFs/BF composite paper exhibited low thermal conductivity (0.024 W m-1 K-1), high tensile strength (54.22 MPa), and excellent flexibility. Thanks to its excellent thermal stability, the mechanical strength remains at a high level (92%) after heat treatment at 300 °C for 60 min. Furthermore, the peak heat release rate and smoke generation of ANFs/BF composite paper decreased by 44.6 and 95.3%, respectively. Therefore, the composite paper is promising for applications as a protective layer in flexible electronic devices, cables, and fire-retardant and high-temperature fields.

Nacre-inspired composite paper of PVA crosslinked basalt scale and nanocellulose with enhanced mechanical, electrical insulating and ultraviolet-resistant aging performance.

Silicate scales are commonly incorporated into cellulose nanofiber (CNF) as functional fillers to enhance electrical insulation and UV-shielding properties. Nevertheless, the addition of substantial quantities of silicate scales in the quest for enhanced functional properties results in reduced interface bonding capability and compromised mechanical properties, thereby restricting their application. Here, inspired from nacre, layered composite paper with excellent mechanical strength, electrical insulation and UV-resistance properties was fabricated through vacuum assisted self-assembly using CNF, PVA and basalt scales (BS). Unlike the conventional blending strategy, the pre-mixed PVA and BS suspension facilitates the formation of Al-O-C bond, thereby enhancing the interfacial bonding between BS and CNF. Consequently, the composite paper (BS@PVA/PVA/CNF) containing 60 wt% BS demonstrates higher mechanical strength-approximately 140 % higher than that of BS/CNF composite paper, achieving a strength of 33.5 MPa. Additionally, it demonstrates enhanced dielectric properties, surpassing those of CNF paper by up to 107 %. Moreover, it exhibits robust ultraviolet-resistant aging performance, retaining ~87 % of its tensile strength after undergoing a simulated two-year aging period. As a result, this work presents a simple and innovative design strategy for enhancing interfacial bonding and optimizing layer structure, providing essential guidelines for large-scale production of high-performance insulation and aging-resistant composite paper.

Flexible Basalt Fiber/Aramid Nanofiber/Carbon Nanotube Electromagnetic Shielding Paper with Outstanding Environmental Stability and Joule Heating Performance.

In the field of electromagnetic shielding, it has become an important trend to manufacture thinner and better-performing electromagnetic interference (EMI) shielding materials. However, EMI shielding materials that are recyclable and resistant to extreme environments are of great significance for sustainable development and expanding their application areas. In this study, a composite paper with a "rebar-concrete" layered structure through the vacuum-assisted filtration approach by utilizing basalt fibers (BF) and aramid nanofibers (ANFs) with excellent temperature resistance and multiwalled carbon nanotubes with high electrical conductivity was prepared. The composite paper not only delivers a high electrical conductivity of 15.9 S cm-1 and a high electromagnetic interference shielding efficiency (EMI SE) of 24.6 dB but also exhibits a high specific shielding efficiency (SSE/t) of 12,504 dB cm2 g-1 at a thickness of 48 µm. Thanks to the excellent thermal stability of basalt fibers and aramid nanofibers, the composite paper exhibits long-term stable EMI shielding performance and structural integrity in various extreme environments, including fire, high/low temperature (-196 to 300 °C), and acid-base corrosion. Furthermore, the BF/ANF/CNT composite paper also shows excellent Joule heating performance, rapid electrothermal response, and good temperature controllability. Based on these excellent properties, the BF/ANF/CNT composite paper shows tremendous potential for practical applications to meet the requirements of various extreme environments.

Novel Fabrication of Basalt Nanosheets with Ultrahigh Aspect Ratios Toward Enhanced Mechanical and Dielectric Properties of Aramid Nanofiber-Based Composite Nanopapers.

The rapid development of modern electrical equipment has led to urgent demands for electrical insulating materials with mechanical reliability and excellent dielectric properties. Herein, basalt nanosheets (BSNs) with high aspect ratios (≈780.1) are first exfoliated from basalt scales (BS) through a reliable chemical/mechanical approach. Meanwhile, inspired by the layered architecture of natural nacre, nacre-mimetic composite nanopapers are reported containing a 3D aramid nanofibers (ANF) framework as a matrix and BSNs as ideal building blocks through vacuum-assisted filtration. The as-prepared ANF-BSNs composite nanopapers exhibit considerably enhanced mechanical properties with ultralow BSNs content. These superiorities are wonderfully integrated with exceptional dielectric breakdown strength, prominent volume resistivity, and extremely low dielectric constant and loss, which are far superior to conventional nacre-mimetic composite nanopapers. Notably, the tensile strength and breakdown strength of ANF-BSNs composite nanopapers with a mere 1.0 wt% BSNs reach 269.40 MPa and 77.91 kV mm-1 , respectively, representing an 87% and 133% increase compared to those of the control ANF nanopaper. Their properties are superior to those of previously reported nacre-mimetic composite nanopapers and commercial insulating micropapers, indicating that ANF-BSNs composite nanopapers are a highly promising electrical insulating material for miniaturized high-power electrical equipment.