Flame Retardancy Of Rigid Polyurethane Foam Research Articles

Optimization Design of Flame-Retardant Rigid Polyurethane Foam Modified by Piperazine pyrophosphate/ Zinc Tailings/ Sodium Ligninsulfonate based on Orthogonal experiment

The flammability of rigid polyurethane foams (RPUF) is a significant concern for application. This study introduces a novel flame-retardant RPUF modified by piperazine pyrophosphate (PAPP), zinc tailings (ZTs), and sodium lignosulfonate (LS). The result of cone calorimeter test reveals that the peak heat release rate (p-HRR) and total heat release (THR) of the RPUF doped with 18wt.% PAPP, 10wt.% ZTs and 2.5wt.% LS decreases by 49.4% and 58.3% respectively. The Fire Resistance Index (FRI) achieved a value of 10.17, and vertical combustion tests indicated V-0 rating, signifying improved flame retardancy. Furthermore, the TG/DTG analysis shows that the decomposition activation energy (Eα) increased from 132.85kJ·mol-1 to 222.12kJ·mol-1 in the main stage of decomposition (249~342 ℃), representing enhanced thermal stability. Subsequently, the orthogonal experiments and regression analysis reveal that LS has the most significant impact on p-HRR, followed by ZTs. The combination of ZTs and LS exerts the most significant synergistic influence on p-HRR, whereas the combination of PAPP and LS has the most insignificant impact. The introduction of LS provides carbon and gas source, and improve the dispersion of PAPP and ZTs in the whole system. The optimal experimental ratio of modified RPUF is obtained through regression optimization. Consequently, the flame-retardant RPUF represents a sustainable bio-based composite material that effectively utilizes industrial and biowaste resources.

A reactive melamine-DOPO based flame retardant for superior thermal stability and flame retardancy in rigid polyurethane foam

The flame-retardant effect of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) and its derivatives in reducing the flammability of polymeric materials are well known. In this study, flame-retardant rigid polyurethane foams (FR-RPUF) were synthesized using a melamine-DOPO-based flame-retardant (MDFR). Additionally, MDFR was also used for preparation of a flame-retardant elastomeric polyurethane (FR-PUE). The chemical structure and thermal properties of the FR-RPUF and FR-PUE samples were studied with Fourier transform infrared (FTIR), field emission-scanning electron microscopy (FE-SEM), and thermogravimetric analysis (TGA). TGA results revealed that the incorporation of MDFR into the PU matrix significantly increased the char residue. The char residue of FR-RPUF with 0.5 wt% MDFR increased from 4.75% to 44.36%, as compared to the pure RPUF. Results from the microscale combustion calorimeter (MCC) test illustrated that the peak of heat release rate (pHRR), total heat release (THR), and heat release capacity (HRC) of the FR-RPUF and FR-PUE samples were reduced, as compared to the pure PU samples. The pHRR value of FR-RPUF with 3 wt% of MDFR decreased 12%, as compared to the pure RPUF, while the pHRR was obtained 34% lower than of the pure PUE. Furthermore, FR-RPUFs successfully passed the UL94 testing, achieving a V-0 grade.

Rigid polyurethane foam with durable hydrophobicity and flame retardancy endowed by novel functional surfactants

Traditional rigid polyurethane foam (RPUF) with flame retardancy might be easily damaged in some moist condition due to its hydrophobicity, which would lead to unsafety. Therefore, novel surfactants with both hydrophobic fluorinated group and flame-retardant phosphorus group were synthesized. With lower surface tension and more hydrogen bonds formed in polyurethane, the mixed surfactants, which were used in the preparation of RPUF, have not only obviously improved the size uniformity and integrity of cells but also enhanced its hydrophobicity, compressive strength and thermal insulating performance. Besides, effective ‘protection’ could be constructed on the surface of RPUF by prepared surfactants, when ammonium polyphosphate (APP) and expandable graphite (EG) were introduced to provide good flame retardancy. As a result, with just 2.8 wt% content of those functional surfactants, hydrophobic and flame-retardant RPUF with water contact angle of 126 °, limiting oxygen index of 25 %, compressive strength of 1.3 MPa and thermal conductivity of 27 mW/mK, were finally obtained, which is ahead of other flame-retardant RPUF reported before. It’s worth noting that, this hydrophobic and flame-retardant RPUF exhibits more stable and durable properties when soaking in HCl solution (2 mol/L), NaOH solution (2 mol/L), NaCl saturated solution and various solvents (THF and EtOH), or under strong fiction for 100 times and high and low temperature cycling test for 20 times. This would provide a novel and effective strategy to endow RPUF with enhanced and durable flame retardancy, hydrophobicity, compressive strength and thermal insulating performance even under extreme conditions.

Highly efficient flame retardancy and fire spread behavior of rigid polyurethane foams with extremely low content of flame retardant

In recent years, flame-retardant rigid polyurethane foam (RPUF) has once again captured the scholars’ attention due to the growing the growing demands in the field of building energy efficiency. However, the inherent flammability of RPUF is high and the complexities of its flame-retardant mechanisms remain inadequately understood. In this study, a modified biomass material, amino starch phosphate ester was successfully synthesized which was then combined with expandable graphite (EG) and incorporated into RPUF. The research delved into the optimal ratio and minimal flame-retardant additive required to achieve the stringent UL-94 V-0 rating, while also thoroughly investigating the flame retardancy and thermal properties of the composite system. The findings revealed that with just 6 wt.% of flame retardants, the RPUF achieved the UL-94 V-0 rating, with a 41.1 % reduction in peak heat release rate (pHRR) and a 23.7 % decrease in total heat release (THR). Additionally, it diminishes the flame's size and width, leading to quicker extinction, while also lowering the internal combustion temperature of the polyurethane, thereby delaying both preheating and combustion times. The synergistic interaction between amino starch phosphate ester and EG during combustion results in the formation of a dense, continuous char layer, effectively inhibiting the pyrolysis and combustion of RPUF. This study provides a theoretical foundation for the development of efficient flame-retardant systems for RPUF.

Flame retardant rigid polyurethane foam composites based on hexaphenoxycyclotriphosphonitrile: flame retardancy, combustion properties and pyrolysis kinetics

Flame retardant rigid polyurethane foam composites based on hexaphenoxycyclotriphosphonitrile: flame retardancy, combustion properties and pyrolysis kinetics

Flame Retardant Rigid Polyurethane Foam Derived from Biobased Polyols and Water as Co-Blowing Agent: Synergistic Effect of Expanded Graphite and Boron Nitride

Using a bio-based polyol system one-shot free-rising method, bio-based flame-retardant rigid polyurethane foam (FR-RPUF) was prepared. Environmentally friendly blowing agent (Cyclopentane) and co-blowing agent water along with expanded graphite (EG) and boron nitride (BN) were used as admixtures to develop a synergistic flame-retardant composite at a variable ratio of EG and BN respectively. The flame retardancy of the composite was evaluated using various techniques like burning tests, UL 94, and cone calorimetry. At the same time, the morphological aspects and functional groups were analyzed by scanning electron microscopy (SEM) and Fourier Transform Infrared spectroscopy (FTIR) respectively. The FR-RPUF synthesized using EG and BN at a ratio of 1:1 has impressive flame-retardancy and smoke-suppressing properties, with a "V-1" rating in the UL-94 vertical burning testing. Additionally, EG/BN- FR-RPUF has a compressive modulus of 4.92MPa, making it suitable for discontinuous panel applications.

Green flame-retardant rigid polyurethane foam with cobalt hydroxystannate to improve the thermal stability, flame retardancy and smoke suppression properties

The ecological benefits and concerns surrounding fossil fuels had led to increased interest in bio-based rigid polyurethane foam (RPUF). Nonetheless, due to its flammability, it had limited application in various fields. To solve this problem, a green bio-flame retardant, cobalt hydroxystannate (CoSn(OH)6), was prepared and compounded with montmorillonite (MMT) and chick feather protein (CF), and applied to RPUF, which not only realized the regeneration of resources, but also provided RPUF with better thermal stability, flame retardancy and smoke suppression properties. The experimental results showed that when 3 wt% CoSn(OH)6 was added, the RPUF (CF1/MMT3/Co3) had the greatest activation energy. In addition, the peak heat release rate (PHRR) and total heat release (THR) of CF1/MMT3/Co3 decreased by 12.73%, and 11.16% respectively, compared with no CoSn(OH)6. In addition, its Ds decreased by 28.9% and the light transmittance increased by 17.6% compared with the RPUF without CoSn(OH)6. At the same time, its peak smoke production rate (PSPR) and the total smoke release (TSR) decreased by 25% and 18%. And CF1/MMT3/Co3 also had the lowest fire risk evaluation index. This study presented possibilities for practical utilization of the RPUF substances founded on bio-based flame inhibitors.

Research Progress in Halogen-Free Flame Retardant Rigid Polyurethane Foam

The article reviews the research advances on halogen-free flame retardant rigid polyurethane foam (HFR-RPUF), mainly covering three categories of flame retardants: additive, reactive and coating. The additive category includes different types such as organic, inorganic, bio-based, microencapsulated, expandable graphite. The reactive category introduces some flame retardants that can react with isocyanate or hydroxyl groups. The coating category presents examples of some organic, inorganic and carbon nanomaterial flame retardants. The article analyzes the effects and factors of various flame retardants, and contrasts their strengths and weaknesses. Lastly, the article summarizes the characteristics and development directions of HFR-RPUF, and offers future perspectives and recommendations. The review aims to provide references for researchers in the field of flame retardant rigid polyurethane foam.

Enhanced Fire Safety of Energy-Saving Foam by Self-Cleavage CO2 Pre-Combustion and Phosphorus Release Post-Combustion.

Rigid polyurethane foam (RPUF) is widely utilized in construction and rail transportation due to its lightweight properties and low thermal conductivity, contributing to energy conservation and emission reduction. However, the inherent flammability of RPUF presents significant challenges. Delaying the time to ignition and preventing flame spread post-combustion is crucial for ensuring sufficient evacuation time in the event of a fire. Based on this principle, this study explores the efficacy of using potassium salts as a catalyst to promote the self-cleavage of RPUF, generating substantial amounts of CO2, thereby reducing the local oxygen concentration and delaying ignition. Additionally, the inclusion of a reactive flame retardant (DFD) facilitates the release of phosphorus-oxygen free radicals during combustion, disrupting the combustion chain reaction and thus mitigating flame propagation. Moreover, potassium salt-induced catalytic carbonization and phosphorus derivative cross-linking enhance the condensed phase flame retardancy. Consequently, the combined application of potassium salts and DFD increases the limiting oxygen index (LOI) and reduces both peak heat release rate (PHRR) and total heat release (THR). Importantly, the incorporation of these additives does not compromise the compressive strength or thermal insulation performance of RPUF. This integrated approach offers a new and effective strategy for the development of flame retardant RPUF.

Thermal and Combustion Properties of Biomass-Based Flame-Retardant Polyurethane Foams Containing P and N.

Biomass has been widely used due to its environmental friendliness, sustainability, and low toxicity. In this study, aminophosphorylated cellulose (PNC), a biomass flame retardant containing phosphorus and nitrogen, was synthesized by esterification from cellulose and introduced into polyurethane to prepare flame-retardant rigid polyurethane foam. The combustion properties of the PU and PU/PNC composites were studied using the limiting oxygen index (LOI), UL-94, and cone calorimeter (CCT) methods. The thermal degradation behavior of the PU and PU/PNC composites was analyzed by thermogravimetric analysis (TGA) and thermogravimetric infrared spectroscopy (TG-IR). The char layer after combustion was characterized using SEM, Raman, and XPS. The experimental results showed that the introduction of PNC significantly improved the flame-retardant effect and safety of PU/PNC composites. Adding 15 wt% PNC to PU resulted in a vertical burning grade of V-0 and a limiting oxygen index of 23.5%. Compared to the pure sample, the residual char content of PU/PNC15 in a nitrogen atmosphere increased by 181%, and the total heat release (THR) decreased by 56.3%. A Raman analysis of the char layer after CCT combustion revealed that the ID/IG ratio of PU/PNC15 decreased from 4.11 to 3.61, indicating that the flame retardant could increase the stability of the char layer. The TG-IR results showed that PNC diluted the concentration of O2 and combustible gases by releasing inert gases such as CO2. These findings suggest that the developed PU/PNC composites have significant potential for real-world applications, particularly in industries requiring enhanced fire safety, such as construction, transportation, and electronics. The use of PNC provides an eco-friendly alternative to traditional flame retardants. This research paves the way for the development of safer, more sustainable, and environmentally friendly fire-resistant materials for a wide range of applications.

Tri-phase flame retardant system towards advanced energy-saving building materials with highly efficient fire and smoke toxicity reductions

The extensive usage of rigid polyurethane foam (RPUF) as an energy-saving building materials in construction has raised concerns about fire risks and toxic hazards. To address these challenges, a melamine-derived polyol (MADP) was synthesized using the Mannich reaction, resulting in inherently flame-retardant RPUF materials with the introduction of flame-retardant functional groups. Furthermore, a novel MoS2-Cu2O nanohybrid was prepared and employed to enhance flame retardancy and suppress smoke toxicity in RPUF through a cooperative effect with expandable graphite (EG). The resulting M-RPUF/EG/MoS2-Cu2O nanocomposite exhibited remarkable fire safety, as evidenced by significant reductions in peak heat release rate (PHRR), total heat release (THR), total smoke production (TSP), and peak carbon monoxide (CO) release, amounting to 76.9 %, 64 %, 82 %, and 99 % respectively, compared to pristine RPUF. Furthermore, the nanocomposite effectively addressed interfacial defects and significantly enhanced the mechanical property and thermal stability. The significant improvement in fire safety is mainly ascribed to the catalytic charring effect of MADP and EG, as well as the catalytic oxidation of MoS2-Cu2O nanohybrids, resulting in the formation of a thermally stable protective layer in the condensed phase. Based on these results, the integration of the tri-phase flame retardant system holds great potential for advancing the development of fire-safe polyurethane materials.

Epoxy lignin-modified tetraethylenepentamethylene-CO2 halogen-free blown rigid polyurethane foam

A new halogen-free blowing agent for rigid polyurethane foam, E-Lig-TEPA-CO2, was synthesized by absorbing CO2 onto tetraethylenepentamine modified with epoxy lignin. The blowing agent was modified with lignin, which introduced hydrophobic groups such as benzene rings, carbon chains, and aromatic ethers. This modification enhanced its oil affinity and compatibility in the polyol mixture. Surface tension testing showed that the surface tension of the lignin-modified blowing agent decreased from 36 to 24 mN/m. Observations through Olympus microscopy revealed that the lignin-modified blowing agent was better dispersed in the polyol mixture, with fewer air bubbles and improved compatibility. Additionally, the main raw material used for this blowing agent was low molecular weight tetraethylenepentamine, resulting in a liquid-state blowing agent. This liquid-state blowing agent inherently possessed advantages in terms of dispersibility and compatibility compared to solid-state blowing agents. Finally, self-made lignin phosphate (P-Lig), expandable graphite (EG), and dimethyl methyl phosphonate (DMMP) were added as halogen-free flame retardants. Lignin-bio-based polyol was used as partial polyol. A new type of bio-based and halogen-free blown flame-retardant rigid polyurethane foam was prepared. The resulting foam demonstrated small and evenly distributed cell structures, as well as good compression strength (224 kPa) and thermal conductivity (0.029 W/(m·k)). The limiting oxygen index of foam increased to 30.6%, reached the V-0 level during the vertical burning process, the peak heat release rate decreased to 196 Kw/m2, and high-temperature thermal stability in thermogravimetric was enhanced.

Efficient and economical synthesis of flame retardant rigid polyurethane nanocomposite foam through phosphorus-based compounds and in-situ exfoliated microcrystal muscovite

ABSTRACT A flame retardant rigid polyurethane foam (FR-RPUF) boasting good mechanical properties is developed by integrating phosphorus-based compounds (DBHP/DMMP) and organically modified microcrystal muscovite (OM-MCM). During foaming, OM-MCM undergoes in-situ exfoliation, yielding RPUF nanocomposites with heightened mechanical strength. The combined deployment of OM-MCM and DBHP/DMMP enables FR-RPUF to achieve an excellent flame retardancy (such as UL94 V-0 rating). This flame retardant effect stems from a bi-phase mechanism: trapping effect of phosphorus-containing radicals in the gas phase and enhanced charring of nanominerals in the condensed phase. Overall, this accessible method enhances flame resistance in RPUF using conventional processes and available materials.

Conversion of waste PET into triazines-incorporated polyols and flame-retardant polyurethane foams

Preparation of flame retardant rigid polyurethane foams (RPUFs) from sustainable material sources like recycled polyethylene terephthalate (rPET) remains a challenge due to the difficulty in controlling the synthesis of polyols with flame retardant functionalities. Here, we propose a method for converting rPET into a polyester-amide-ether oligools incorporated flame retardant triazine-ring through the partial codepolymerization of rPET by 1,3,5-tris(hydroxymethyl isocyanurate (THMI), ethanolamine, and diethylene glycol, followed by linking oligools into polyols with phthalic anhydride. THMI was synthesized through nucleophilic additions of formaldehyde with isocyanuric acid. The codepolymerization and linking were carried out using a one-pot method. Single-factor experiments were implemented to optimize the process parameters such as reacting temperature and time. The L9 (43) orthogonal experiments were employed to systematically investigate the influence of the dosages of four raw materials on the performance of the synthesized polyols. Based on the range analysis of acid value, hydroxyl value, and viscosity of the synthesized polyols, the optimized polyol was synthesized as a candidate for preparing flame retardant RPUFs. Results demonstrated that the obtained RPUF derived from the optimized polyol could achieve a limiting oxygen index (LOI) value of 30.3% when mixed with phosphorous-containing flame-retardant DCPP, meeting the national standard of combustible stage B1.The high flame retardancy RPUF obtained from an rPET-based polyol with a triazine ring represents a novel and practical method of preparation, providing new insights into the optimization of synthesis parameters across multiple factors and levels.

Optimal design of energy-saving foam with multifunctional characteristics: Superb flame retardancy, outstanding hydrophobic, excellent thermal insulation and robust mechanical performances

The adoption of rigid polyurethane foam (RPUF) in construction and rail transit offers energy conservation and emissions reduction benefits, but its inherent flammability presents challenges. Traditional fireproofing methods often disrupt foaming balance, ultimately compromising flame retardancy and mechanical properties. While flame retardant coatings preserve the bulk physical properties of materials, it tends to be sensitive to moisture. In this study, we propose to address the issues by employing a combined approach of nano-reinforcement and surface treatment. The results demonstrate that the addition of 3 wt.% bio-based Phosphorus-Nitrogen-containing nanosheet (HACP-PA) to RPUF increases its yield strength and compressive strength (at 60% strain) by 63% and 86%, respectively. Subsequently, the surface coating comprising of polydopamine-encased ammonium polyphosphate (APP@PDA), polyethyleneimine (PEI) and 1-octadecanethiol-wrapped polydopamine (PDA@ODT) imparts the RPUF nanocomposite with remarkable properties, including an LOI as high as 42.5%, a satisfactory V-0 rating in the UL94 test, 44% reduction in PHRR, 30% reduction in THR, 507% increase in residues, and a water contact angle of 137° More importantly, this method does not affect the excellent thermal insulation properties of the RPUF. In summary, this advancement tackles the challenges associated with RPUF's flammability and provides a bio-based, low-cost, and eco-friendly approach for developing multifunctional flame retardant RPUF with superior comprehensive properties.

Combining hyperbranched polyol containing three flame retardant elements, P, N and Si, with expanded graphite to improve the flame retardancy of bio-based rigid polyurethane foam

The preparation of rigid polyurethane foam (RPUF) from vegetable oil and the improvement of its flame retardant properties are of great importance to broaden the application field of RPUF, which can satisfy the green environment and reduce the fire accidents caused by its flammability. In this paper, a reactive hyperbranched flame retardant polyol (DOPO-MASi) containing three flame retardant elements of P, N and Si was prepared by reacting 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO), a phosphorus-containing compound, with maleic anhydride, diethanolamine and Triethoxy(3-glycidyloxypropyl)silane (KH-561), respectively, and mixed with expandable graphite (EG) to obtain a vegetable oil-based flame retardant RPUF with the multi-flame retardant system. This foam has excellent flame retardant properties and smoke-suppressing effect, with a limiting oxygen index (LOI) of 30% and a “V-0″ level in the UL-94 vertical burning test, as well as its pHRR, THR, and TSP were reduced by 47.5%, 57.9% and 62.8%, respectively. More importantly, 5% EG/20% FR-RPUF also has good mechanical properties. The above properties provide a reference for the practical application of RPUF in environmental protection and flame retardant.

Surface coating of biomass-modified black phosphorus enhances flame retardancy of rigid polyurethane foam and its synergistic mechanism

A novel surface coating based on chitosan (CS) modified black phosphorus (BP) is obtained through layer-by-layer self-assembly and applied to flame-retardant rigid polyurethane foam (PUF). The CS-BP coating tightly adheres to the PUF surface through hydrogen bonding and electrostatic interaction, improving the PUF's thermal stability, photothermal conversion performance and fire safety performance without compromising its mechanical properties. The 9L-CS-BP/PUF exhibits reduced the peak of CO2 release, PHRR, and THR by 36.7%, 39.5%, and 28.8%, respectively, while increasing its residual carbon content by 35.2%. Moreover, a systematic comparison is made between the residual carbon inside and on the surface before and after combustion, and the results indicate that a large number of P-O-C structures and phosphoric acid derivatives are generated on the surface. The surface carbon layer formed by CS-BP effectively inhibited the thermo-oxidative degradation process of inner PUF. In the gas phase, modification of CS increases both the temperature range for the release of phosphorus-containing compounds during BP pyrolysis and the release of non-combustible gases during combustion, synergistically enhancing the gas-phase flame retardancy of CS-BP coating. This study provides a new approach to enhance the flame retardancy efficiency and broaden the application of BP-based flame retardants.

Effect of Microencapsulated Long‐Chain Chlorinated Paraffin on Flame Retardant of Rigid Polyurethane Foam

AbstractTo overcome the fire risk of rigid polyurethane foam (RPUF) and the poor thermal stability of long‐chain chlorinated paraffin (LCCP), the microcapsules of long‐chain chlorinated paraffin (MCP) were prepared by in‐situ polymerization with melamine formaldehyde resin (MF) as shell material, and the flame retardant rigid polyurethane foam (MCP/ RPUF) was obtained through introducing MCP as the flame retardant. Meanwhile, the core‐shell composition, surface morphology, chemical composition, particle size distribution, and thermal stability of flame retardant microcapsules were evaluated by Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), X‐ray photoelectron spectroscopy (XPS) and thermogravimetric analysis (TG). The characterization data indicated that the flame retardant microcapsules were successfully synthesized and had excellent particle size distribution. In addition, microcalorimeter (MCC), limiting oxygen index (LOI), UL‐94 vertical burning tests, scanning electron microscope (SEM), Raman spectroscopy, and other methods were used to analyse the flame retardancy and carbon residue of rigid polyurethane foam. The results show that the 20% MCP/RPUF composite can pass the V‐0 grade of UL‐94 and reach the material flame retardant grade. Compared with pure RPUF, the peak heat release rate and total heat release of the MCP/RPUF composite are greatly reduced. Therefore, the addition of flame retardant microcapsule improves the graphitization degree and compactness of rigid polyurethane foam carbon slag, increasing the fire safety of the composite.

Emerging trends in flame retardancy of rigid polyurethane foam and its composites: A review

Owing to the superior thermal insulating attributes of rigid polyurethane foam (RPUF) compared to other insulating materials (expanded and extruded polystyrene, mineral wool), it remains the most dominant insulating material and most studied polymer foam. Like other polyurethane foam, RPUF is highly flammable, necessitating the incorporation of flame retardants (FR) during production to lower combustibility, promoting its continuous use as insulation material in construction, transportation, and others. The popular approaches for correcting the high flammability of RPUF are copolymerization and blending (with FR). The second method has proven to be most effective as there are limited trade-offs in RPUF properties. Meanwhile, the high flammability of RPUF is still a significant hindrance in emerging applications (sensors, space travel, and others), and this has continuously inspired research in the flame retardancy of RPUF. In this study, properties, and preparation methods of RPUF are described, factors responsible for the high flammability of PUF are discussed, and flame retardancy of RPUF is thoroughly reviewed. Notably, most FR for RPUF are inorganic nanoparticles, lignin, intumescent FR systems of expandable graphite (EG), ammonium polyphosphate (APP), and hybridized APP or EG with other FR. These could be due to their ease of processing, low cost, and being environmentally benign. Elaborate discussion on RPUF FR mechanisms were also highlighted. Lastly, a summary and future perspectives in fireproofing RPUF are provided, which could inspire the design of new FR for RPUF.

Enhanced Flame Retardancy of Rigid Polyurethane Foams by Polyacrylamide/MXene Hydrogel Nanocomposite Coating.

Rigid polyurethane foam (RPUF) has been widely used in many fields, but its high flammability and frequent release of large amounts of toxic smoke during combustion limit its application. Hydrogel coatings, as a kind of environmentally friendly material, contain large amounts of water, which is beneficial to flame retardance of RPUF. MXene, as a two-dimensional inorganic nanomaterial, possesses a large specific surface area and good thermal stability, performing well in smoke suppression and as a physical barrier for flammable gas products and heat. Herein, to address the fire hazards of RPUF, MXene nanosheets were first grafted with double bonds, and then introduced into a polyacrylamide hydrogel system by radical polymerization to prepare MXene-based hydrogel coating (PAAm-MXene). The flame-retardant RPUF (coated RPUF) was prepared by painting the PAAm-MXene coating onto RPUF surface. The dispersion of modified MXene nanosheets (m-MXene) in hydrogels is improved compared with pristine MXene, and the addition of m-MXene contributes to the thermal stability enhancement of PAAm-MXene. Cone calorimetry, water retention test, and open flame combustion test were used to study the flame retardancy, smoke suppression, and water retention of flame-retardant RPUF. The coated RPUF exhibited significant flame retardancy, including reduced peak heat release rate (pHRR) at a maximum by 25.8%, and total heat release rate (THR) at a maximum by 24.6%, and total smoke production at a maximum by 38.9%. The results show that both MXene and m-MXene can improve the flame retardancy, smoke suppression, and water retention of hydrogels, but m-MXene has a better smoke suppression effect than MXene. That can be ascribed to the better dispersion of m-MXene than pristine MXene. The detailed performance improvement mechanisms are proposed. This work will not only improve the flame retardancy of RPUF, but also promotes the exploration of new flame-retardant strategies for RPUF.