Superior radical scavenging and catalytic carbonization capacities of bioderived assembly modified ammonium polyphosphate as a mono-component intumescent flame retardant for epoxy resin

The improvement of flame retardancy and compatibility of PBAT/PLLA via a hybrid polyurethane

Poly (butylene adipate-co-terephthalate)/poly (L-lactic acid) (PBAT/PLLA) is one of the most important biodegradable polymer combinations; however, they are flammable with heavy melt dripping and incompatible. To achieve the objective of flame retardation and compatibility, a hybrid polyurethane (PU) with multiple flame retardation elements is synthesized via a new ring-opening polymerization (ROP) method and integrated into PBAT/PLLA film. The PU not only dissolves in different organic solvents at mild temperature but also improves the compatibility of PBAT/PLLA. As PU with respect to PBAT/PLLA is 20 wt%, the limiting oxygen index (LOI) and UL-94 reach 25.5 % and V-0 rating, respectively. In cone calorimeter test, the peak heat release rate (pHRR) of PU/PBAT/PLLA is ahead of PBAT/PLLA, and the total heat release (THR) decreases to 25.85 MJ/m2. The fire safety is achieved successfully. The initial pyrolysis of PU promotes the formation of a seed carbon layer; it continuously breaks down into a series of phosphorus‑oxygen radicals and generates different inert gases, while the pyrolytic solid products accelerate the carbonization to form the carbon/silicon composite layer. Then the polymeric combustion is braked completely. Besides, the PU can also tune the mechanical properties of PBAT/PLLA film and enhance its hydrophobicity. This work opens a new window for developing multifunctional flame retardant and paves the way for the richening engineering application of PBAT/PLLA.

Nonflammable Polyfluorides-Anchored Quasi-Solid Electrolytes for Ultra-Safe Anode-Free Lithium Pouch Cells without Thermal Runaway

The safe operation of rechargeable batteries is crucial because of numerous instances of fire and explosion mishaps. However, battery chemistry involving metallic lithium (Li) as the anode is prone to thermal runaway in flammable organic electrolytes under abusive conditions. Herein, an in situ encapsulation strategy is proposed to construct nonflammable quasi-solid electrolytes through the radical polymerization of a hexafluorobutyl acrylate (HFBA) monomer and a pentaerythritol tetraacrylate (PETEA) crosslinker. The quasi-solid system eliminates the inherent flammability of ether electrolytes with zero self-extinguishing time owing to the gas-phase radical capturing ability of HFBA. Additionally, the graphitized carbon layer generated during the decomposition of PETEA at high temperatures obstructs the heat and oxygen required for combustion. When coupled with Au-modified reduced graphene oxide anodic current collectors and lithium sulfide cathodes, the assembled anode-free Li-metal cell based on the quasi-solid electrolyte exhibits no signs of cell expansion or gas generation during cycling, and thermal runaway is eliminated under multiple mechanical, electrical, and thermal abuse scenarios and even rigorous strikes. This nonflammable quasi-solid configuration with gas- and condensed-phase flame-retardant mechanisms can drive a technological leap in anode-free Li-metal pouch cells and secure the practical applications necessary to power this society in a safe manner.

Construction of hierarchical SiO2 microcapsule towards flame retardation, low toxicity and mechanical enhancement of epoxy resins

A novel approach for improving the flame retardancy, smoke suppression and mechanical properties of epoxy resins (EPs) has been proposed by incorporating functionalized hollow mesoporous silica microcapsules (SHP) loaded with phosphorous silane flame retardants (SCA) and coated with polydopamine (PDA) and transition metals. The proposed approach involves a multi-level structure that combines several mechanisms to enhance the flame-retardant properties of EP. The physical barrier provided by silica serves to impede heat and mass transfer during combustion, while the catalytic carbonization effect of phosphorus and transition metals promotes the formation of a protective char layer, which acts as a barrier to further flame propagation. Incorporating a low loading amount of 3 wt% SHP into the epoxy matrix resulted in EP/SHP-3 composites with significantly improved flame retardancy, as evidenced by a limiting oxygen index of 31.5% and a V-1 rating, in contrast to the values obtained for unmodified EP, which were 23.8% and no rating, respectively. In addition, cone calorimeter test (CCT) results indicated that the total heat release, peak heat release rate and total smoke production of EP/SHP-3 decreased by 18.2%, 25.2% and 18.4%, respectively. Moreover, the improved interfacial compatibility facilitated by polydopamine assists in the dispersion and compatibility of the SHP with the epoxy matrix, leading to better mechanical properties. Herein, the addition of 1 wt% SHP to EP significantly improved its mechanical performance, with a 16.7% increase in tensile strength and a 19.2% increase in impact strength. The design of the multi-level structural approach has the potential to provide new ideas for the simultaneous improvement of fire safety as well as mechanical properties of polymers.

Effects of Processing Conditions on the Properties of Monoammonium Phosphate Microcapsules with Melamine-Formaldehyde Resin Shell

To develop monoammonium phosphate (MAP) as a novel acid source for durable intumescent fire retardants (IFR), MAP microcapsules (MCMAPs) containing MAP as the internal core and melamine-formaldehyde (MF) as the external shell were prepared by in situ polymerization in this study. The influences of synthesis conditions (including reaction temperature, polymerization time, and reaction pH value) on the properties of obtained MCMAPs (MAP content, yield, morphologies, and thermal properties) were then investigated systematically. The morphologies, chemical structures, and thermal properties were characterized by optical microscopy, scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), Fourier transform infrared (FTIR) spectroscopy, and thermogravimetry analyzer (TGA). The results show that MAP was well encapsulated by MF resin. No microcapsules are obtained at <55 °C or with polymerization times <1 h. Optimal preparation conditions of reaction temperature, polymerization time, and reaction pH value are 75 °C, 3 h, and 5.5, respectively. Those results provide process reference and theoretical basis for preparing MCMAPs and could promote the application of MAP microcapsules in wood flame-retardant materials.

Research and Application of Biomass-Based Wood Flame Retardants: A Review

Wood is widely used as a construction material due to its many advantages, such as good mechanical properties, low production costs, and renewability. However, its flammability limits its use in construction. To solve the problem of wood flammability, the most common method to improve the fire safety of wood is to modify the wood by deep impregnation or surface coating with flame retardants. Therefore, many researchers have found that environmentally friendly and low-cost biomass materials can be used as a source of green flame retardants. Two aspects of biomass-based intumescent flame retardants are summarized in this paper. On the one hand, biomass is used as one of the three sources or as a flame-retardant synergist in combination with other flame retardants, which are called composite biomass intumescent flame retardants. On the other hand, biomass is used alone as a feedstock to produce all-biomass intumescent flame retardants. In addition, the potential of biomass-based materials as an environmentally friendly and low-cost FR source to produce high-performance biomass-based flame retardants with improved technology was also discussed in detail. The development of biomass-based intumescent flame retardants represents a viable and promising approach for the efficient and environmentally friendly production of biomass-based flame retardants.

Improved flame retardancy and smoke suppression properties of phenolic resin by incorporating MoO3 particles

Phenolic resin (PF) is widely used in aerospace, composite materials, and other fields. However, large amount of heat and smoke are produced during its combustion process, which is an important factor limiting its usage. To solve this problem, additive flame retardant MoO3 has been incorporated into PF for improving its flame retardancy and smoke suppression properties. Thermogravimetric analyses results show that the T5% of PF composites was gradually decreased from 264°C to 184°C and the char yield of PF-10% MoO3 is 57 wt.%, higher than that of neat PF (50 wt.%). The PF composites with 10 wt.% MoO3 passed UL-94 V-0 rating with a limiting oxygen index value of 29.8%. Meanwhile, the total heat release and total smoke production of PF-10% MoO3 are 37.60 MJ/m2 and 5.79 m2 respectively, which are reduced by 30.5% and 24.8% compared with neat PF. Only 10 wt.% MoO3 provide a 56.5% reduction (from 255 to 111) in maximal smoke density, meaning the good smoke suppression properties of MoO3. The pyrolysis products components are determined by thermogravimetric analysis combined with Fourier transform infrared spectroscopy. Furthermore, the micromorphology and chemical structure of char residue are also investigated by scanning electron microscopy, x-ray diffraction and Raman spectroscopy techniques. The promoting carbonization effect of MoO3 significantly reduces the heat release and toxic smoke production of PF composites.

Bio-based arginine surface-modified ammonium polyphosphate: an efficient intumescent flame retardant for epoxy resin

In this work, ammonium polyphosphate (APP) was surface-modified by bio-based arginine (Arg) for the first time to enhance its flame retardance for fire-safety epoxy resin (EP). The structure of Arg modified APP (Arg-APP) was characterized by Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), ¹H nuclear magnetic resonance (¹H-NMR), and scanning electron microscopy (SEM). The results illustrated that Arg was attached on the surface of APP through a cation exchange reaction. With Arg acting as the efficient carbon source, the char-forming ability of Arg-APP was significantly improved as illustrated by thermogravimetric analysis (TGA). The flame retardance of EP/APP and EP/Arg-APP composites was evaluated using the limit oxygen index (LOI), vertical burning tests (UL-94), and cone calorimeter tests (CCT). The results showed that at the same weight loading (15 wt%), Arg-APP had better flame retardance and smoke suppression performance compared with pristine APP, which can be attributed to Arg-APP constituting an integrated intumescent flame retardant (IFR) and facilitating formation of char residues with significantly expanded structures and higher carbonization degrees. When the weight loading of Arg-APP reached 25 wt%, the EP/Arg-APP composite could achieve an LOI value as high as 34.7%, pass V-0 requirements in UL-94 tests, and decrease the peak heat release rate and total smoke production by 83.5% and 61.1% compared with neat EP in CCT, respectively, indicating the superior flame retardance performance of Arg-APP. Finally, the effects of the flame retardant additives on the mechanical properties of EP were evaluated by the differential scanning calorimetry (DSC) tests and tensile-strain tests. At the same additive weight loading (15 wt%), the EP/Arg-APP composite showed higher glass-transition temperature and better tensile-strain properties compared with EP/APP composite, which can be attributed to the Arg shell structure improving the compatibility between APP and the organic substrate. In conclusion, this work presents a convenient and environmentally friendly method to improve the practical performance of APP.

Arginine modified ammonium polyphosphate was prepared through the cation-exchange reaction and applied as an intumescent flame retardant for epoxy resin.

A flame retardant containing biomass-based polydopamine for high-performance rigid polyurethane foam

An inorganic/polymer flame retardant system constructed from biomass can improve the comprehensive properties of rigid polyurethane foam.

Fabrication of Diaminodiphenylmethane Modified Ammonium Polyphosphate to Remarkably Reduce the Fire Hazard of Epoxy Resins

A novel diaminodiphenylmethane (DDM) modified ammonium polyphosphate (APP) flame retardant, DDP, was successfully synthesized via ion-exchange reaction. DDP was introduced into epoxy resins (EPs) to reduce flammability. A comparable level of DDP exerts better flame-retardant and smoke suppression efficiencies in EP than APP. An EP blend containing 15 wt% DDP displays a limiting oxygen index (LOI) value of 37.1% and a UL 94 V-0 rating, and further exhibits a 32.3% reduction in total heat release and a 48.0% reduction in total smoke production compared with pure EP. The presence of DDP greatly facilitates char formation during combustion, and the char mass from thermal decomposition of an EP blend is 37.8% smaller than that of an EP blend containing 15 wt% DDP at 800 °C. The incorporation of DDP into EP blends has a smaller impact on the glass transition temperature and tensile strength than those of a comparable level of APP. This reflects the better compatibility of DDP with the EP matrix compared with that for APP.

Synergistic Flame Retardant Effect of Barium Phytate and Intumescent Flame Retardant for Epoxy Resin

Recently, widespread concern has been aroused on environmentally friendly materials. In this article, barium phytate (Pa-Ba) was prepared by the reaction of phytic acid with barium carbonate in deionized water, which was used to blend with intumescent flame retardant (IFR) as a flame retardant and was added to epoxy resin (EP). Afterward, the chemical structure and thermal stability of Pa-Ba were characterized by Fourier transform infrared (FTIR) spectroscopy and thermogravimetric analysis (TGA), respectively. On this basis, the flammability and flame retardancy of EP composites were researched. It is shown that EP/14IFR/2Ba composite has the highest limiting oxygen index (LOI) value of 30.7%. Moreover, the peak heat release rate (PHRR) of EP/14IFR/2Ba decreases by 69.13% compared with pure EP. SEM and Raman spectra reveal the carbonization quality of EP/14IFR/2Ba is better than that of other composites. The results prove that Pa-Ba can cooperate with IFR to improve the flame retardancy of EP, reducing the addition amount of IFR in EP, thus expanding the application range of EP. In conclusion, adding Pa-Ba to IFR is a more environmentally friendly and efficient method compared with others.

A Study on Circular Economy Material Using Fish Scales as a Natural Flame Retardant and the Properties of Its Composite Materials

Fish scales (FSs) are fishery wastes that can cause environmental pollution. This study aimed to solve this environmental problem. FSs were used as a flame retardant for polymer materials, making them valuable. Fish scales were combined with a commercial flame retardant, ammonium polyphosphate (APP), through synergistic effects to reduce the amount of commercial flame retardant. The use of FSs conforms to the concept of a circular economy and lowers costs by reducing the consumption of APP. Thermogravimetric analysis (TGA), integral procedural decomposition temperature (IPDT), pyrolysis kinetics, limiting oxygen index (LOI), the Underwriters Laboratories 94 (UL94) flammability test, scanning election microscopy, Raman spectroscopy, and energy-dispersive X-ray spectroscopy were used to determine the thermal properties, flame retardant properties, flame retardant mechanism, char morphology, and composition of the composites. The TGA results indicated that the addition of 40% flame retardant raised the char residue from 16.45 wt.% (pure EP) to 36.07 wt.%; IPDT from 685.6 °C (pure EP) to 1143.1°C; LOI from 21% (pure EP) to 30%; and UL94 classification from fail (pure EP) to V-0. These results suggest an increase in char residue, which indicates better protection of the polymer matrix material. The improvements in IPDT, LOI, and UL94 classification, which indicate greater thermal stability, lower flammability (from flammable to fireproof), and higher flammability rating (from fail to V-0), respectively, suggest that the composite material has favorable thermal properties and is less inflammable.