Sustainable lignocellulose aerogel for air purifier with thermal insulation, flame retardancy, mechanical strength, and its life cycle assessment

In-situ polymerized tourmaline/polypyrrole/lignocellulose aerogel for flame-resistant and intelligent fire alarm sensor

Fires in buildings made of woody materials pose threats to human lives and property. Therefore, an intelligent, efficient sensors made of lignocellulosic materials for early fire warnings that can detect fires quickly and exhibit satisfactory flame retardancy is urgently needed. In this study, a flame-retardant lignocellulose aerogel (TPLA) with a thermosensitive alarm sensor response is prepared by the vacuum impregnation of tourmaline particles (TPs) and in-situ polymerization of pyrrole in lignocellulose aerogel specimens. A β-FeOOH scaffold produced via thermal hydrolysis provided ample space for the growth of polypyrrole (PPy), and PPy along with TPs improved the flame retardancy and thermoelectric performance of the aerogel. A comparison with pristine wood showed that the heat release rate and total heat release of TPLA were 69.43 % and 72.60 % lower, respectively. The limiting oxygen index of TPLA was substantially higher by 20.48 %, and the UL-94 flame retardant rating was upgraded to V-0. The Seebeck coefficient of the TPLA reached 23.88 μV·K-1 at 298 K, and this generated a potential difference of >100 mV upon encountering fires, showing that the material has good fire alarm properties. Thus, TPLA is promising for the development of smart fire alarm systems with satisfactory fire retardancy.

Dual chemical crosslinking strategy to fabricate lightweight, flame-retardant, high-modulus and hydrophobic cellulose cryogel

Cellulose cryogel shows great application potential as a thermal insulation material because of its eco-friendliness, lightweight, high porosity and highly-efficient thermal insulation property. However, the high flammability and hydrophilicity have become bottlenecks to restrict its application in the thermal insulation field. Herein, we synthesized an amylose derivative with ammonium phosphate groups (AM), and reported a dual chemical crosslinking strategy to fabricate lightweight, flame-retardant, high-modulus and hydrophobic cellulose cryogel with AM and methyltrimethoxysilane (MTMS) via baking-crosslinking and chemical vapor deposition techniques. The dual crosslinking structure endowed the composite cryogel (AM30Si) with a high specific modulus of 47.0 MPa/(g/cm3), which enabled it to sustain 12,500 times its own weight. The thermal conductivity of AM30Si was only 28.7 mW/(m·K), which benefited from its anfractuous three-dimensional porous network structure. The P/N/Si synergy enhanced the flame retardancy of AM30Si, and its UL-94 rating and LOI value reached V-0 and 39.2%, respectively. Moreover, AM30Si possessed satisfactory hydrophobicity, oil absorption and continuous oil-water separation ability. This study provides not only an insight into the syntheses of reactive polysaccharide derivatives with high flame-retardant activity, but also an innovative solution to simultaneously address the inflammability, hydrophilicity and inadequate strength of cellulose cryogel while largely maintaining its lightweight feature.

Synergic Cellulose Nanofiber/Tourmaline Nanoparticle-Assembled Layered Piezoelectric Cryogels for High-Performance Airborne Particulate Filtration

Here, hybrid stimuli-responsive (exhibiting pyroelectricity and piezoelectricity) porous cryogels are engineered by embedding tourmaline nanoparticles (TNs) in a cellulose nanofiber (CNF) skeleton to generate high-performance CNF-TN-based airborne particulate matter (PM) filters. First, single-layer hybrid cryogels with varying TN contents (0-5% w v-1) are assembled, and the design principles for multilayered filters are established based on a novel sequential pre-freezing and freeze-drying technique. As observed, the embedded TNs transformed the CNF network into a more homogeneous, isotropic, and firm structure, thus improving the structural integrity and thermal stability of the assembled cryogels while maintaining their ultrahigh porosity and low density. The TN induced piezoelectric voltage in the cryogels during filtration significantly enhanced the filtration performance. Furthermore, the patterned surface texture of the cryogels notably improved quality factor (Qf) and the reusability of the layered filters overall. The explored hybrid cryogels, particularly those exhibiting multilayered configurations, can be deployed for high-performance airborne particulates filtration owing to the synergistic effect of their mechanical robustness, stability, and high filtration efficiency. As far as it is known that, the Qf values (>0.04) obtained by the three-layered cryogels are similar to or even higher than those of the reported best aerosol filters.

Strong and Fireproof Regenerated Wood via a Combined Phosphorylation-Surface Nanofibrillation and Ionic Cross-Linking Strategy

To reduce the environmental impact of plastics, an increasing number of high-performance sustainable materials have emerged. Among them, wood-based high-performance structural materials have gained growing attention due to their outstanding mechanical and thermal properties. Here, we introduce phosphate groups onto the wood veneers for surface nanofibrillation, effectively altering both the molecular structure and surface morphology of wood, which enhances the interactions between wood veneers and endows the wood with excellent fire resistance properties. With these phosphorylated wood-based building blocks, "chemical welding" structural materials (CWSMs) obtained through chemical cross-linking exhibit excellent mechanical properties. The flexural strength of CWSM reaches 225 MPa, and the modulus reaches 16 GPa, surpassing those of various types of natural wood. At the same time, phosphorylation has endowed CWSM with excellent fire resistance, with a limiting oxygen index reaching 49%, making it completely noncombustible. More importantly, as a biomass-based structural material, CWSM exhibits mechanical, thermal, and fire resistance properties and degradability far superior to those of traditional petroleum-based plastics, making it an ideal candidate for plastic replacement.

Recent Advancements of Bio-Derived Flame Retardants for Polymeric Materials

The sustainable flame retardancy of polymeric materials is a key focus for the direction of the next generation in the field of fire safety. Bio-derived flame retardants are gaining attention as environmentally friendly additives due to their low ecological impact and decreasing costs. These compounds can enhance char formation in polymeric materials by swelling upon heating, attributed to their functional groups. This review explores various biomolecules used as flame retardants, including phytic acid, chitosan, lignin, tannic acid, and bio-derived phosphorus and nitrogen compounds, emphasizing their flame-retardant properties and compatibility with different polymer matrices. The primary focus is on the structural characteristics, modifications, and flame-retardant behaviors of these bio-derived additives, particularly regarding their mechanisms of action within polymeric materials. Finally, the review explores the opportunities, current challenges, and future directions for the practical application of bio-derived flame retardants in polymer materials.

Develop a novel and multifunctional soy protein adhesive constructed by rosin acid emulsion and TiO2 organic-inorganic hybrid structure

Soy protein adhesives (SPI) exhibit broad prospects in substituting aldehyde-based resin due to the economic and environmental-friendly characteristics, but still face a challenge because of the dissatisfied bonding strength and terrible water resistance. Herein, prompted by organic-inorganic hierarchy, a multifunctional and novel soy protein adhesive (SPI-RAE-TiO2) consisting of rosin acid emulsion (RAE) and TiO2 nanoparticles (TiO2) were proposed. In comparison with original SPI, the dry and wet shear strengths of modified adhesive reached 2.01 and 1.21 MPa, respectively, which were increased by 130 % and 200 %. Furthermore, SPI-6RAE-0.5TiO2 was selected as the best proportion via the method of response surface methodology (RSM). What's more, SPI-6RAE-0.5TiO2 adhesive demonstrated prominent coating performance in both dry and wet surface conditions. Meanwhile, SPI-6RAE-0.5TiO2 adhesive possessed excellent mildew resistance and antibacterial ability with Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus), reflecting the antibacterial rates 97.71 % and 98.16 %, respectively. In addition, SPI-6RAE-0.5TiO2 adhesive also exhibited the outstanding green features such as the reduction of formaldehyde pollution and greenhouse effect through Life Cycle Assessment (LCA). Thus, this work provided a novel and functional approach to design multifunctional, superior-property and low-carbon footprint soy protein adhesive.

Harnessing the Flexibility of Lightweight Cellulose Nanofiber Composite Aerogels for Superior Thermal Insulation and Fire Protection

Thermally insulating materials from renewable and readily available resources are in high demand for ecologically beneficial applications. Cellulose aerogels made from lignocellulosic waste have various advantages. However, they are fragile and breakable when bent or compressed. In addition, cellulose aerogels are flammable and weather-sensitive. Hence, to overcome these problems, this work included the preparation of polyurethane (PU)-based cellulose nanofiber (CNF) aerogels that had flexibility, flame retardancy, and thermal insulation. Methyl trimethoxysilane (MTMS) and water-soluble ammonium polyphosphate (APP) were added to improve the cross-linking, hydrophobicity, and flame-retardant properties of aerogels. The flexibility of chemically cross-linked CNF aerogels is enhanced through the incorporation of polyurethane via the wet coagulating process. The aerogels obtained during this study have exhibited low weight (density: 35.3-91.96 kg/m3) together with enhanced hydrophobic properties, flame retardancy, and decreased thermal conductivity (26.7-36.7 mW/m K at 25 °C). Additionally, the flame-retardant properties were comprehensively examined and the underlying mechanism was deduced. The aerogels prepared in this study are considered unique in the nanocellulose aerogel category due to their integrated structural and performance benefits. The invention is considered to substantially contribute to the large-scale manufacture and use of insulation in construction, automobiles, and aerospace.

Construction of Nanofibrillar Networked Wood Aerogels Derived from Typical Softwood and Hardwood: A Comparative Study on the In Situ Formation Mechanism of Nanofibrillar Networks

The construction of networks within natural wood (NW) lumens to produce porous wood aerogels (WAs) with fascinating characteristics of being lightweight, flexible, and porous is significant for the high value-added utilization of wood. Nonetheless, how wood species affect the structure and properties of WAs has not been comprehensively investigated. Herein, typical softwood of fir and hardwoods of poplar and balsa are employed to fabricate WAs with abundant nanofibrillar networks using the method of lignin removal and nanofibril's in situ regeneration. Benefiting from the avoidance of xylem ray restriction and the exposure of the cellulose framework, hardwood has a stronger tendency to form nanofibrillar networks compared to softwood. Specifically, a larger and more evenly distributed network structure is displayed in the lumens of balsa WAs (WA-3) with a low density (59 kg m-3), a high porosity (96%), and high compressive properties (strain = 40%; maximum stress = 0.42 MPa; height retention = 100%) because of the unique structure and properties of WA-3. Comparatively, the specific surface area (SSA) exhibits 25-, 27-, and 34-fold increments in the cases of fir WAs (WA-1), poplar WAs (WA-2), and WA-3. The formation of nanofibrillar networks depends on the low-density and thin cell walls of hardwood. This work offers a foundation for investigating the formation mechanisms of nanonetworks and for expanding the potential applications of WAs.