Next-generation all-organic composites: A sustainable successor to organic-inorganic hybrid materials

This Review presents an overview of all-organic nanocomposites, a sustainable alternative to organic-inorganic hybrids. All-organic nanocomposites contain nanocellulose, nanochitin, and aramid nanofibers as highly rigid reinforcing fillers. They offer superior mechanical properties and lightweight characteristics suitable for diverse applications. The Review discusses various methods for preparing the organic nanofillers, including top-down and bottom-up approaches. It highlights in situ polymerization as the preferred method for incorporating these nanomaterials into polymer matrices to achieve homogeneous filler dispersion, a crucial factor for realizing desired performance. Furthermore, the Review explores several applications of all-organic nanocomposites in diverse fields including food packaging, performance-advantaged plastics, and electronic materials. Future research directions-developing sustainable production methods, expanding biomedical applications, and enhancing resistance against heat, chemicals, and radiation of all-organic nanocomposites to permit their use in extreme environments-are explored. This Review offers insights into the potential of all-organic nanocomposites to drive sustainable growth while meeting the demand for high-performance materials across various industries.

Aqueous Dispersion of Aramid Nanofibers Achieved by Using Tannic Acid for Ultrahigh Strength Films

Polymer nanofibers have established a robust foundation and possess immense potential in various emerging fields such as sensors and biotechnology. In this study, aqueous dispersions of aramid nanofibers (ANFs) were successfully prepared by using tannic acid (TA). Morphological analysis revealed that TA effectively prevented self-aggregation of ANFs, and preserved the nanofiber structure during TA-assisted solvent exchange. Subsequently, the ANF and TA/ANF films were fabricated using casting and vacuum-assisted filtration techniques. Notably, the tensile strength of the casting TA/ANF film reached 393.8 MPa, exhibiting a remarkable improvement of 41.3% compared to that of the pure ANF film. These exceptional mechanical properties can be attributed to the well-dispersed nanostructures, hydrogen-bonding interactions, zigzag structures, and fiber-bridging effects. Furthermore, the TA/ANF film demonstrated superior ultraviolet (UV) shielding capabilities, visible transparency properties, and excellent resistance to chemical reagents. The above-mentioned interesting findings demonstrate its potential as a nanofiber-reinforced material for poly(vinyl alcohol) (PVA) composites.

Visible Microfluidic Deprotonation for Aramid Nanofibers as Building Blocks of Cascade-Microfluidic-Processed Colloidal Aerogels

 Microfluidic deprotonation approach is proposed to realize continuous, scalable, efficient, and uniform production of aramid nanofibers (ANFs) by virtue of large specific surface area, high mixing efficiency, strong heat transfer capacity, narrow residence time distribution, mild laminar-flow process, and amplification-free effect of the microchannel reactor. By means of monitoring capabilities endowed by the high transparency of the microchannel, the kinetic exfoliation process of original aramid particles is in situ observed and the corresponding exfoliation mechanism is established quantificationally. The deprotonated time can be reduced from the traditional several days to 7 min for the final colloidal dispersion due to the synergistic effect between enhanced local shearing/mixing and the rotational motion of aramid particles in microchannel revealed by numerical simulations. Furthermore, the cascade microfluidic processing approach is used to make various ANF colloidal aerogels including aerogel fibers, aerogel films, and 3D-printed aerogel articles. Comprehensive characterizations show that these cascade-microfluidic-processed colloidal aerogels have identical features as those prepared in batch-style mode, revealing the versatile use value of these ANFs. This work achieves significant progress toward continuous and efficient production of ANFs, bringing about appreciable prospects for the practical application of ANF-based materials and providing inspiration for exfoliating any other nano-building blocks.

Self-Reinforced Doping Strategy in the Multiscale PMIA Paper for High Mechanical Properties and Insulating Performance

The poly(m-phenylene isophthalamide) (PMIA) paper has attracted extensive interests due to its ultrahigh mechanical properties as an ideal protective material for anti-impact damage applications. In the pursuit of additional properties, composites based on the PMIA matrix and various fillers are widely explored. However, additional improvements are frequently obtained at the expense of mechanical properties because of the serious interfacial compatibility brought by different components. In this study, a self-reinforced doping strategy is proposed by combining microscale PMIA fibers as the fillers and nanoscale PMIA fibers as the matrix to form a micronano paper. Without the limitation of the interfacial compatibility issues, the nanofibers are tightly aligned and adhered to the microfibers, enabling the in situ generation of hydrogen bonds at the interfaces. A compact interfacial structure is thus constructed with reduced porosity on the surface. It indicates that the microfibers have a positive impact on the improvement of mechanical properties. In our optimized sample with 5 wt % microfibers, the elastic modulus, tensile strength, and elongation are 1530 MPa, 24.8 MPa, and 5.3%, respectively, which are 142, 49.4, and 65% higher than those of the pristine nano-PMIA paper. In addition, the insulating performance is also improved, facilitating its further application extended to broad fields.

Accelerated Design of Ultra-High-Performance Aramid Copolymers via a High-Throughput Screening Approach

Developing advanced materials, such as functional polymers, poses a significant challenge as a result of the vastness of the material space that needs to be explored, which could potentially be infinite in principle. We propose a data-driven high-throughput screening approach coupled with molecular dynamics (MD) simulations to address this issue in the design of high-performance co-polymerized aramid fibers. We aimed to identify diamine monomers that could replace 3,4'-oxydianiline in Technora from a large-scale set (1 920 304) of possible monomers that were prepared from the PubChem database. We initially screened these monomers using a cheminformatics-based approach, considering four criteria: complexity, neutrality, linearity, and gyration radius of the molecule. Then, we performed subsequent screening based on MD simulations to estimate interchain interaction energies under both stretched and melted conditions and tensile strength simulations. Our screening approach successfully identified 31 promising and novel diamine monomers for aramid copolymers. This demonstrates the potential and effectiveness of our approach as a promising protocol for exploring targeted chemical spaces in designing novel monomers for high-performance aramid fibers and possibly other advanced polymers.

Recent Advances in Self-Assembly and Application of Para-Aramids

Poly(p-phenylene terephthalamide) (PPTA) is one kind of lyotropic liquid crystal polymer. Kevlar fibers performed from PPTA are widely used in many fields due to their superior mechanical properties resulting from their highly oriented macromolecular structure. However, the “infusible and insoluble” characteristic of PPTA gives rise to its poor processability, which limits its scope of application. The strong interactions and orientation characteristic of aromatic amide segments make PPTA attractive in the field of self-assembly. Chemical derivation has proved an effective way to modify the molecular structure of PPTA to improve its solubility and amphiphilicity, which resulted in different liquid crystal behaviors or supramolecular aggregates, but the modification of PPTA is usually complex and difficult. Alternatively, higher-order all-PPTA structures have also been realized through the controllable hierarchical self-assembly of PPTA from the polymerization process to the formation of macroscopic products. This review briefly summarizes the self-assembly methods of PPTA-based materials in recent years, and focuses on the polymerization-induced PPTA nanofibers which can be further fabricated into different macroscopic architectures when other self-assembly methods are combined. This monomer-started hierarchical self-assembly strategy evokes the feasible processing of PPTA, and enriches the diversity of product, which is expected to be expanded to other liquid crystal polymers.

Ultrafast formation of ANFs with kinetic advantage and new insight into the mechanism

Aramid nanofibers (ANFs) have important applications in many fields, including electrical insulation and battery separators. However, a few limitations seriously restrict the application of ANFs currently, such as low preparation efficiency and the unclear preparation mechanism. To overcome these limitations, the present work proposes a new view-point from the perspective of reaction kinetics. The preparation efficiency was proven to essentially rely on the effective c(OH^-). With a simple pre-treatment, a kinetic advantage was created and the preparation time of ANFs was reduced from multiple hours to 10 minutes, which was a considerable step towards practical applications. Moreover, the resultant ANF membranes still exhibited excellent properties in terms of mechanical strength (tensile strength > 160 MPa), thermal stability, light transmittance, and electrical insulation (above 90 kV mm^-1). This work not only presents an ultrafast method to produce ANFs but also provides new insights into the mechanism that will benefit the subsequent development of ANF-based materials.

Aramid-Zirconia Nanocomposite Coating With Excellent Corrosion Protection of Stainless Steel in Saline Media

Resistance to stainless steel corrosion in marine-based industries requires more research into materials with an improved surface and enhanced protection by utilizing surface coatings. Herein, a thermally stable aramid–zirconia nanocomposite has been successfully prepared using the sol–gel method to produce a zirconia network-structure bonded to the polymer chain. Using thermal gravimetric analysis (TGA), the residue mass of zirconia retained after the thermal degradation of aramid-zirconia film was determined and found to be 10% by mass. The investigated nanocomposite (using 10% zirconia) was coated on the stainless-steel surface through a facile and effective spin coating method and its protection was examined in saline solution (3.5% NaCl). The aramid–zirconia nanocomposite coating (Ar-Zr10) was found to provide an outstanding corrosion resistance to steel surfaces which led to protecting it against the corrosive marine environment. The electrochemical impedance (EIS) measurements were carried out to evaluate steel resistance against dissolution in chloride solution in the absence and presence of the investigated coatings showed a corrosion protection efficiency of 99.3% using Ar-Zr10 compared to 92.1% using pure aramid. Moreover, the potentiodynamic polarization (PDP) plots showed a pronounced decrease in the corrosion current values which confirmed the formation of a passive layer which mitigated the corrosion reaction and ions diffusion. The water contact angle of stainless-steel coated with pure aramid and the aramid–zirconia was found to be 84.2° and 125°, respectively, confirming the hydrophobic nature of the hybrid coating Ar-Zr10. On the other hand, the results achieved through the electrochemical and surface techniques were used to clarify the protection mechanism. The aramid–zirconia nanocomposite coating showed a remarkable protection performance by controlling the charge transfer at the interface between the steel alloy and the electrolyte which prevented the alloy dissolution.

Aramid Nanomaterials of Various Morphologies: Preparation and Mechanical Property Enhancement

Aramid nanofibers (ANFs) are a novel type of promising nanoscale building blocks for high-performance nanocomposites. Conventionally, ANFs are used to composite with polymers containing polar groups such as –OH and –NH₂ since those polymers can interact with the amide groups in ANFs through polar-polar interaction such as hydrogen bonding. In this study, ANFs were derivatized with non-polar alkyl groups including ethyl, octyl and dodecyl groups and used as a performance-enhancing additive to polyvinyl chloride (PVC) with weak polarity. Interestingly, it was observed that the morphologies of the resulting alkyl-derivatized aramid nanomaterials (R-ANMs) varied significantly including nanofibers, nanobranches, nanosheets, and nanospheres, all of which depended on the degree of substitution (DS) and the chain length of the alkyl group. As an additive, R-ANMs improved the Young's modulus, toughness and yield strength of the PVC films. This study proves the concept that ANFs can be used to composite weakly polar or non-polar polymers.

Ultrathin MXene/aramid nanofiber composite paper with excellent mechanical properties for efficient electromagnetic interference shielding

MXenes, new two-dimensional compounds with hydrophilic surfaces and high metallic conductivity, have attracted significant interest in the electromagnetic interference shielding field in recent years. Nevertheless, poor mechanical properties and brittle nature are bottlenecks for their commercial application. Herein, one-dimensional ANFs were designed as the intermolecular cross-linker between d-Ti₃C₂T_x flakes and MXene (d-Ti₃C₂T_x)/aramid nanofiber (ANF) composite paper with a multi-layered structure was fabricated via the vacuum-assisted filtration approach. Further investigation revealed that the ANFs and MXene displayed good combination by hydrogen bonding, and MXene/ANF composite papers exhibited excellent mechanical properties and superior electrical conductivity. The MXene/ANF composite paper possessed a favorable shielding effectiveness (SE) which reached ∼28 dB in 8.2-12.4 GHz (X band) with an ultra-thin thickness ∼17 μm and showed potential application prospects as an advanced composite in sensitive electronic products.

Surface modification of an aramid fiber via grafting epichlorohydrin assisted by supercritical CO2

In order to improve the interface combination property between an aramid fiber (AF) and an epoxy resin matrix, the surface modification of AF with epichlorohydrin (ECH) assisted by supercritical CO2 (ScCO2) was investigated. The fiber surface was characterized by X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and dynamic contact angle (DCA) analysis. At the same time, we utilized interfacial shear strength (IFSS) and interlaminar shear strength (ILSS) to characterize the bond strength between the fiber and epoxy resin. An ideal modification effect of the fiber surface was acquired when the fiber treated with ECH in ScCO2 compared with the fiber treated in pure ScCO2. The results showed that ECH could be successfully grafted onto the fiber surface under an anhydrous aluminum chloride (AlCl3) catalyst in ScCO2, and the relative content of oxygen on the fiber surface increased after modification; simultaneously, the morphology of the fiber surface became rougher and the fiber's wettability was upgraded. Finally, the IFSS property of the fiber with the epoxy resin increased, and the ILSS property of the AF-reinforced resin composites was also improved compared with those of the untreated materials.

Timesaving, High-Efficiency Approaches To Fabricate Aramid Nanofibers

Aramid nanofibers (ANFs) have become promising nanoscale building blocks due to their extraordinary performance. However, there are numerous challenges related to the preparation of ANFs, such as the lengthy preparation cycle (7-10 days), low preparation concentration (0.2 wt %), and high difficulty in quantitatively judging the end point of the deprotonation reaction. Herein, we report three time-saving and high-efficiency strategies (fibrillation, ultrasonication, and proton donor-assisted deprotonation) to prepare ANFs with excellent performance. The fiber micromorphology during the deprotonation and protonation recovery processes was first investigated. Then the end point of the deprotonation reaction was detected by Raman spectra and the cationic demand of the ANF/DMSO system. Finally, the size, preparation cycle, and performance of the corresponding ANFs and ANF films fabricated by different approaches were investigated in detail. The results showed that proton donor-assisted deprotonation significantly shortened the traditional preparation cycle from 7 days to 4 h, and is the most efficient method reported thus far. It is noteworthy that a high concentration of ANFs (4.0 wt %) could also be achieved within 12 h. Interestingly, the fabricated ANFs exhibit rigid morphology and a small diameter with a narrow size distribution (10.7 ± 1.0 nm). The resultant ANF film displays desired characteristics of high strength and toughness. The work offers a timesaving, feasible and effective strategy to realize the large-scale production for ANFs, which will facilitate the application of ANFs in the production of advanced nanomaterials.

A new approach to the preparation of poly(p-phenylene terephthalamide) nanofibers

Poly(p-phenylene terephthalamide) nanofibers were prepared via a polymerization induced self-assembly process with the assistance of methoxy polyethylene glycol (mPEG).

Preparation of polybenzoxazole nanofibers by a downsizing process

Poly(p-phenylene benzobisoxazole) (PBO) nanofibers were prepared from commercially available PBO fiber by a simple downsizing process for the first time.