Advances in the Study of Flame-Retardant Cellulose and Its Application in Polymers: A Review

Cellulose, as a green and renewable polymer material, has attracted the attention of a wide range of scholars for its excellent mechanical strength, easy chemical modification and degradability. However, its flammability limits its application in automotive, aerospace, construction, textile and electronic fields. This review recapitulates the modification methods of flame-retardant cellulose and their applications in polymers in recent years. This paper discusses the fabrication of flame-retardant cellulose from various aspects such as boron, nitrogen, phosphorus, sulphur, inorganic and heterogeneous synergistic modification, respectively, and evaluates the flame retardancy of flame-retardant cellulose by means of thermogravimetry, cone calorimetry, limiting oxygen index, the vertical combustion of UL94, etc. Finally, it discusses the application of flame-retardant cellulose in actual composites, which fully reflects the extraordinary potential of flame-retardant cellulose for applications in polymers. Currently, flame-retardant cellulose has significantly improved its flame-retardant properties through multi-faceted modification strategies and has shown a broad application prospect in composite materials. However, interfacial compatibility, environmental protection and process optimisation are still the key directions for future research, and efficient, low-toxic and industrialised flame-retardant cellulose materials need to be realised through innovative design.

Revealing the flame retardancy of cotton fabrics treated with ammonium ethylenediamine tetramethylenephosphonate and trimethylol melamine

Phosphorus-nitrogen containing polymers have been attracting considerable interest as potential flame retardants (FR) for cotton fabrics. In this work, we report an experimental-theoretical joint study on flame retardancy of cotton fibres treated with ammonium ethylenediamine tetramethylenephosphonate (AEDTMP) as FR and trimethylol melamine (TMM) as binder. Through material characterization and FR test, we find that the cotton fabric samples treated with 5% AEDTMP and 5% TMM solutions exhibit better flame retardancy and durability than those with 25% AEDTMP solution by forming multilayer coatings on the fabrics. Our calculations within the density functional theory framework reveal that the P-O-C and C-O-C bonds are newly formed by reactions between the AEDTMP FR and TMM binder, and the multilayer coating enhances such binding reactions. Our work highlights that the multilayer coating with AEDTMP of lower density is superior for flame retardancy and durability of treated cotton.

Design of New Bis(1,2,3-triazol-1-yl)methane-Based Nitrogen Ligands: Synthesis and Coordination Chemistry

The reaction between bis(1,2,3-triazol-1-yl)methane derivatives and nBuLi and various aldehydes, yielded novel neutral ligand precursors incorporating alcohol functional groups. The resulting compounds exhibited distinct characteristics depending on the steric hindrance of the aldehyde employed. In instances where aromatic aldehydes were utilized, functionalization occurred at the methine group bridging both triazole rings. Conversely, the use of pivalic aldehyde prompted functionalization at the C5 position of the triazole ring. These compounds were subsequently employed as ligand precursors in the synthesis of organometallic aluminum and zinc complexes, yielding dinuclear complexes with high efficiency. The structural elucidation of all compounds was accomplished through spectroscopic methods and validated by X-ray crystallography. Preliminary catalytic investigations into the coupling reaction of cyclohexene oxide and CO2 revealed that aluminum and zinc complexes catalyzed the selective formation of polyether and polycarbonate materials, respectively.

Phosphamide-Based Washing-Durable Flame Retardant for Cotton Fabrics

A formaldehyde-free reactive flame retardant, an ammonium salt of triethylenetetramine phosphoryl dimethyl ester phosphamide phosphoric acid (ATPEPDPA), was synthesized and characterized using nuclear magnetic resonance (NMR). Fourier transform infrared spectroscopy test (FT-IR), durability test and scanning electron microscopy (SEM) results suggested that ATPEPDPA was successfully grafted on cotton fabrics through a -N-P(=O)-O-C covalent bond. Moreover, the limiting oxygen index (LOI) value of 20 wt% ATPEPDPA-treated cotton was 44.6%, which met stringent washing standard after 50 laundering cycles (LCs). The high washing resistance of the ATPEPDPA-treated cotton was due to the p-π conjugation between the N atom and the P(=O) group in the flame-retardant molecule, which strengthened the stability of the -N-P(=O)-O-C bonds between ATPEPDPA and cellulose, and the -N-P(=O)-(O-CH3)2 groups in the ATPEPDPA. The cone calorimetric test showed that the treated cotton had excellent flame retardance. In addition, the TG and TG-IR tests suggested that ATPEPDPA performed a condensed flame retardance mechanism. Furthermore, the physical properties and hand feel of the treated cotton were well maintained. These results suggested that introducing -N-P(=O)-(O-CH3)2 and -N-P(=O)-(ONH4)2 groups into ATPEPDPA could significantly increase the fire resistance and durability of cotton fabrics.

Synthesis and evaluation of an eco-friendly and durable flame-retardant cotton fabrics based on a high-phosphorous-content

Cotton fabrics are extremely flammable. Therefore, ammonium salt of dipentaerythritol hexaphosphoric acid (ADPHPA), a novel reactive phosphorus flame retardant without halogen and formaldehyde, was synthesized by solvent-free synthesis method. Surface chemical graft modification was chosen to introduce flame retardant, imparting its flame retardancy and washability. SEM indicated that ADPHPA entered the interior of cotton fiber, which was grafted with OH of control cotton fabrics (CCF) by forming POC covalent bonds to obtain treated cotton fabrics (TCF). There were no apparent differences in the fiber morphology and crystal structure after treatment according to SEM and XRD analysis. TG analysis demonstrated that the decomposition process of TCF was changed compared with CCF, while lower heat release rate and total heat release of TCF indicated its combustion efficiency was also reduced based on cone calorimetry test. Meanwhile, in the durability test, TCF had undergone 50 laundering cycles (LCs) in accordance with AATCC-61-2013 3A standard and had a short vertical combustion charcoal length, which were able to be regard as durable flame-retardant fabrics. The mechanical properties of TCF decreased to a degree, but did not affect the actual use of cotton fabrics. Taken as a whole, ADPHPA has research significance and development potential as a durable phosphorus-based flame retardant.

Highly efficient and durable antibacterial cotton fabrics finished with zwitterionic polysulfobetaine by one-step eco-friendly strategy

In this work, a novel formulation of polysulfobetaine, poly (sulfobetaine-acrylamide-allyl glycidyl ether) (PSPB-AM-AGE), was synthesized and grafted onto cotton. The synthesis of PSPB-AM-AGE and its grafting on the cotton fabrics were confirmed by FTIR, XPS and SEM. The PSPB-AM-AGE treated cotton fabrics exhibited a high level of antibacterial rate against both Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus), which are 95.18% and 98.74%, separately, as well as a good laundry durability. The mechanical tests showed that the essential cotton properties can be largely preserved in the treatment process. Moreover, the hydrophilicity, air and water permeability of the cotton were improved after treated with PSPB-AM-AGE, indicating a better wearing comfort performance. The whiteness of the cotton fabrics did not decrease significantly. The safety evaluation demonstrated that PSPB-AM-AGE had no cytotoxicity. The developed antibacterial finishing introduced a new method to apply polysulfobetaine interfaced on cellulose, providing great potential for biomedical fabric application.

Flame-Retardant Textile-Based Triboelectric Nanogenerators for Fire Protection Applications

Textile-based triboelectric nanogenerators (T-TENGs), combining the functions of energy harvesting and self-powered sensing with advantages of breathability and flexibility, have received intensive attention, which is vital to the rapid advancements in smart textiles. However, there exists few reports of T-TENGs applied to fires under the intelligent era of high requirements for devices with versatility and multiscenario practicability. Here, in combination with flame-retardant conductive cotton fabric, polytetrafluoroethylene-coated cotton fabric, and a divider, a low-cost and environmentally friendly flame-retardant textile-based triboelectric nanogenerator (FT-TENG) is developed, which is endowed with excellent fire resistance and outstanding energy harvesting capabilities. The cotton fabrics treated with a layer-by-layer self-assembly method show great self-extinguishing performance. Besides, the maximum peak power density of the FT-TENG can reach 343.19 mW/m² under the tapping frequency of 3 Hz. Furthermore, the FT-TENG still keeps 49.2% of the initial electrical output even after being burned at 17 different positions; 34.48% of the electrical output is also retained when the FT-TENG is exposed to 220 °C. Moreover, the FT-TENGs are successfully applied as energy harvesters for firefighters and self-powered sensors for forest self-rescue and fire alarm systems. This work may provide a promising potential for multifunctional smart textiles in energy harvesting, self-powered sensing, and life or property security.

2D Hexagonal Boron Nitride-Coated Cotton Fabric with Self-Extinguishing Property

Here, we report on the fabrication of flame retardant hydrophobic cotton fabrics based on the coating with two-dimensional hexagonal boron nitride (2D hBN) nanosheets. A simple one-step solution dipping process was used to coat the fabrics by taking advantage of the strong bonding between diethylenetriamine and hBN on the cotton surface. Exposure to direct flame confirmed the improvement of the flame retardant properties of the coated cotton fabrics. In turn, removal of the flame source revealed self-extinguishing properties. Molecular dynamics simulations indicate that hBN hinders combustion by reducing the rate at which oxygen molecules reach the cotton surface. This time-saving and one-step approach for the fabrication of flame-retardant cotton fabrics offers significant advantages over other, less efficient production methods.

Development and Evaluation of a Water-Based Flame Retardant Spray Coating for Cotton Fabrics

In this Research Article, we report on the development of water-based flame retardant coating based on phospho-nitrogen combination for cotton fabrics. A one-step spray-on process was employed to coat the fabrics by taking advantage of the spontaneous reaction between para-phenylenediamine (PDA) and tetrakis(hydroxymethyl)phosphonium chloride (THPC) resulting in an instantaneous precipitation of poly[1,4-diaminophenylene-tris(dimethyl hydroxymethyl)phosphine] (PApP) on the fabric surface. The effectiveness of PApP in improving the flame retardant properties like ignition resistance and lateral flame spread were evaluated in accordance with ASTM D6413 and BS EN ISO 15025 flammability tests. Despite the early (thermal) decomposition onset for coated fabrics under both oxidative and pyrolytic conditions, remarkably, self-extinguishing behavior (<3 s) without any lateral flame spread was observed. Possible reaction scheme was also proposed to correlate flame retardant mechanism of the coated fabrics with the observations. Additional analysis via pyrolysis combustion flow calorimetry and vertical flame testing before and after washing showed that flame retardant efficiency did decrease with washing, but the overall performance was still promising.