Flame Retardancy Of Rigid Polyurethane Foam Research Articles

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.

Enhanced flame retardant performance of rigid polyurethane foam by using the modified OMMT layers with large surface area and ammonium polyphosphate

A phosphorus-containing organosilicon compound (PCOC) was synthesized and used to modify organic-montmorillonite named M-OMMT. The results showed that the interlayer spacing of the intercalated M-OMMT layers became larger and the exfoliated M-OMMT layers were connected by PCOC after the modification. Then, M-OMMT was combined with ammonium polyphosphate (APP) to improve the flame retardancy of rigid polyurethane foam (RPUF) composites. The thermal stability and flame retardancy of RPUF with M-OMMT and APP was lucubrated using thermogravimetric analysis (TGA), limited oxygen index (LOI) and cone calorimeter test. After the addition of modified OMMT layers, the Td,5%, Tmax1 and Tmax2 of RPFU/APP/M-OMMT (234 °C,304 °C and 462 °C) were all higher in contrast to RPUF/APP/OMMT (223 °C, 298 °C and 454 °C). Compared with RPUF/APP/OMMT, the peak heat release rate and total smoke release of RPUF/APP/M-OMMT were apparently reduced from 292 kW/m2 and 552 m2/ m2 to 156 kW/m2 and 350 m2/ m2, and the residual char yield increased by 37%. The SEM results showed that the addition of M-OMMT promoted the formation of a more compact and intumescent char layer. After the modification of PCOC, the layers of M-OMMT overlapped each other to form a larger surface area, which can exert a better physical barrier and protective effect together with APP on RPUF, fabricating the RPUF/APP/M-OMMT composite with the good flame-retardant property.

A Systematic Review and Bibliometric Analysis of Flame-Retardant Rigid Polyurethane Foam from 1963 to 2021.

Flame-retardant science and technology are sciences developed to prevent the occurrence of fire, meet the needs of social safety production, and protect people’s lives and property. Rigid polyurethane (PU) is a polymer formed by the additional polymerization reaction of a molecule with two or more isocyanate functional groups with a polyol containing two or more reactive hydroxyl groups under a suitable catalyst and in an appropriate ratio. Rigid polyurethane foam (RPUF) is a foam-like material with a large contact area with oxygen when burning, resulting in rapid combustion. At the same time, RPUF produces a lot of toxic gases when burning and endangers human health. Improving the flame-retardant properties of RPUF is an important theme in flame-retardant science and technology. This review discusses the development of flame-retardant RPUF through the lens of bibliometrics. A total of 194 articles are analyzed, spanning from 1963 to 2021. We describe the development and focus of this theme at different stages. The various directions of this theme are discussed through keyword co-occurrence and clustering analysis. Finally, we provide reasonable perspectives about the future research direction of this theme based on the bibliometric results.

Recent advances in fire-retardant rigid polyurethane foam

• This review reports the state-of-the-art design of flame-retardant RPUF. • The reactive, additive and coating type flame retardants for RPUF are discussed. • The flame-retardant and thermal conductive properties of RPUF are compared. • Key challenges and opportunities for future flame-retardant RPUF are described. Driven by global environmental concerns, many efforts have been made to develop halogen-free flame retardants for rigid polyurethane foam (RPUF). These environmentally benign flame retardants are mainly divided into (i) reactive, (ii) additive, and (iii) coating types. The last decade has witnessed great progress of these three strategies, which enhance the fire safety of RPUF and maintain even improve the thermal insulation properties. This comprehensive review focuses on the up-to-date design of the reactive, additive, and coating flame retardants, and their effects on flame retardancy and thermal conductivity of RPUF. Moreover, the practical applications of the as-prepared flame-retardant RPUFs are highlighted. Finally, key challenges associated with these three kinds of flame retardants are discussed and future research opportunities are also proposed.

Rigid polyurethane foam composites based on bivalent metal phytate: thermal stability, flame retardancy, and fire toxicity

ABSTRACT As the main form of phosphorus in plant seeds, phytic acid has potential value in flame retardant field. In this study, a series of bivalent metal phytate (PA-M) flame retardants were prepared using phytic acid and divalent metal salts as raw materials. FTIR, SEM-EDS, XRD, and TG tests confirmed that copper phytate (PA-Cu), zinc phytate (PA-Zn), cobalt phytate (PA-Co) and nickel phytate (PA-Ni) were successfully synthesized. Furthermore, flame retardant rigid polyurethane foam (RPUF/PA-M) composites were prepared by one-step water-blown technology using PA-M as flame retardant. TG test results showed that RPUF/PA-Cu30 had the highest char residue at 700 C, which was 26.2 wt%, significantly higher than 12.4 wt% of RPUF. Cone calorimetry, smoke density test, and TG-FTIR analysis confirmed that RPUF/PA-Co30 composite exhibited excellent smoke suppression and toxicity reduction performance when 30 phr PA-Co was added. Compared with RPUF, the THR, TSR, and SDR of RPUF/PA-Co30 were decreased by 13.9%, 27.3% and 43.9%, respectively, and the release of toxic gases (isocyanate compounds, aromatic compounds, CO and HCN) and combustible gases (hydrocarbons and esters) were significantly reduced. The analysis of char residues of RPUF/PA-M composites suggested that PA-M could promote the formation of dense carbon layer with high graphitization degree and improved the fire resistance of composites. This work provided a new way for fabricating fire safety RPUF composites.

Synthesis of reactive DOPO-based flame retardant and its application in rigid polyisocyanurate-polyurethane foam

In this study, a reactive flame-retardant diol (BEOPMS) was synthesized by the esterification reaction of 9,10-dihydro-10-[2,3-di(hydroxycarbonyl)propyl]-10- phospha-phenanthrene-10-oxide with diethylene glycol. The flame-retardant effect of it combined with polyaryl polymethylene isocyanate (PMDI) were tested for rigid polyisocyanurate-polyurethane foams (PIRs) fabricated via a one-step process. The higher limiting oxygen index (LOI) and char residue yield value of flame-retardant rigid polyurethane foam (FRPUF) (21.0 vol% and 21.9 wt%, respectively) at 3.5 wt% phosphorus content compared to those of the pure rigid polyurethane foam (RPUF) (17.0 vol% and 16.3 wt%, respectively), illustrating the great effect of BEOPMS on improving the flame retardancy of the foams. At a 3.5 molar ratio of NCO/OH and 3.5 wt% content of phosphorus, an even higher LOI value of PIR (28.0 vol%) with a highest char residue yield (44.7 wt%) was obtained. The flame-retardant mechanism was discussed according to the scanning electron microscope (SEM), energy dispersive spectrometer (EDS), cone calorimeter (CC) and thermal gravimetric analysis-Fourier-transform infrared analyses (TG-IR). It is recognized that the isocyanurate ring groups can improve the thermostability of resultant PIRs, and increase the char residue yield in combination with the higher content of PMDI. Meanwhile, the thermal degradation of BEOPMS produces phosphate in condensed phase and released PO and PO₂ free radicals, which inhibits the free radical chain reactions in the gas phase and thus enables a superior flame retardancy effect for polyurethane foams.

Synthesis of phosphorus/nitrogen containing intumescent flame retardants from p-hydroxybenzaldehyde, vanillin and syringaldehyde for rigid polyurethane foams

Intumescent flame retardants (IFR) with phosphorus (P)/nitrogen (N)-containing diphenols (DH, DV and DS) were synthesized from p-hydroxybenzaldehyde (H), vanillin (V) and syringaldehyde (S) with different methoxyl groups on its aromatic ring. The FTIR, 1H NMR, 13C NMR, XPS methods were used to characterize the structures of IFR, and LOI, CCT, SEM, TG methods were used to investigate the flame retardancy and thermal stability of rigid polyurethane (RPU) foams when the three IFR were incorporated into RPU foams.Compared with H, V and S, the DH, DV and DS FTIR spectra showed absorption peaks at 3450 cm−1, 1160 cm−1, and 1222 cm−1, 1050 cm−1 and 740 cm−1, respectively, which attributed to NH, CN, and P = O, P-O, P-C groups. The 1H NMR spectra of DH, DV and DS showed proton signals at 4.8 and 6.0 ppm, which were corresponding to H1 and H2 of CN groups, and corresponding C1 signal appeared around 62.3 ppm in the 13C NMR spectra. The XPS spectra of DH, DV, DS showed peaks at 285, 398 eV and 133.5, 532 eV, which may be due to corresponding C1s, N1s of CN groups and P2p and O1s of P-O-C groups, respectively. These results indicated that the target compounds P/N-containing diphenols DH, DV and DS were synthesized successfully. Flame retardancy index (FRI) values of RPU-DH, RPU-DV, and RPU-DS were 2.33, 2.30 and 2.43, respectively, suggesting that DH, DV, and DS were good flame retardant additives. The THR and HRR values of RPU-DH, RPU-DV, RPU-DS foams were much lower than that of RPU foam. The fire growth rate (FIGRA) of RPU-DH, RPU-DV, and RPU-DS was 29.4%, 30.3%, and 24.4% lower comparing to RPU foam. The LOI value of RPU foam was 19%, while LOI values of RPU-DH, RPU-DV and RPU-DS foams increased to around 26%. These results suggested that the flame retardancy of RPU foams were improved by incorporating DH, DV, and DS. Compared with RPU foam, the CY600 of RPU-DH, RPU-DV and RPU-DS foams increased by 215.2%, 152.2% and 195.6%, respectively, and the char residue after CCT were much compact and homogeneous, which could reduce heat and mass transfer, protecting underlying materials from further combustion in a fire.In conclusion, the P/N-containing diphenols DH, DV and DS were synthesized successfully, and they were good flame retardant additives. The char residue of RPU-DH, RPU-DV and RPU-DS foams increased remarkably, and formed compact and homogeneous char layer. The flame retardancy and thermal stability of RPU-DH, RPU-DV, RPU-DS foams were improved by incorporating DH, DV, and DS.

Flame retardant rigid polyurethane foam composites based on iron tailings and aluminum phosphate: A novel strategy for utilizing industrial solid wastes

AbstractTo widen the application field of iron tailings (ITs) and explore ITs potential use‐value, ITs and aluminum phosphate (AHP) were introduced to prepare flame‐retardant rigid polyurethane foam (FR‐RPUF) composites. The chemical composition and mineral composition of ITs were investigated by X‐ray diffraction, X‐ray fluorescence. The flame retardancy, thermal stability, combustion performance and gas‐phase products of FR‐RPUF composites were investigated by limiting oxygen index, underwriters laboratories vertical burning test (UL‐94), thermogravimetry (TG), cone calorimetry and thermogravimetric‐infrared spectrometry (TG‐FTIR). TG confirmed that ITs could effectively improve the thermal stability of FR‐RPUF composites at high temperature. Cone calorimetry implied that ITs could significantly reduce heat release and toxic smoke release and thus improve the fire safety of the composites. TG‐FTIR indicated that ITs effectively reduced the release intensity of hydrocarbons, aromatic compounds, CO, isocyanates and esters. Scanning electron microscope and Raman spectra showed ITs could improve the compactness and graphitization degree of the char residues for FR‐RPUF composites.

Phosphorus-containing soybean oil-derived polyols for flame-retardant and smoke-suppressant rigid polyurethane foams

To overcome the fire risk of rigid polyurethane foams (RPUFs) and comply with the sustainable development, this work aimed to develop a bio-based flame-retardant polyol (PESO) for rigid polyurethane foams (RPUFs) without deteriorating other physical properties. The effect of the PESO content on the morphology, thermal stability and flammability of the resulting flame-retardant RPUFs was investigated by SEM, TGA and cone calorimeter. The addition of the PESO slightly affected the thermal conductivity and the initial thermal stability. The char yield at the high temperature region was increased with the increment of the PESO content. As expected, the incorporation of the PESO significantly improved the flame-retardant property of the resulting RPUFs. Specifically, the peak heat release rate, total heat release, and total smoke production of the flame-retardant RPUF sample containing 12.3 wt% PESO were declined by 40%, 35%, and 49%, respectively, compared to those of the unmodified RPUF. The enhanced flame-retardant property of the resulting RPUFs could be attributed to the PESO promoted the charring ability of the polymer matrix and thus formed a protective barrier layer to suppress the heat release and the smoke emission during the combustion.

Rigid Polyurethane Foams Containing Modified Ammonium Polyphosphate Having Outstanding Charring Ability and Increased Flame Retardancy

Ammonium polyphosphate (APP) with different polymerization degrees were modified by a novel phosphorus-containing organosilicon compound (PCOC), and the products obtained were coded as MAPP-30 and MAPP-1000. Then they were applied to prepare flame-retardant rigid polyurethane foam (RPUF) separately. The impact of modified APP (MAPP) on the flame-retardant properties of RPUF was investigated by the limited oxygen index (LOI) test, horizontal burning test, and cone calorimeter test. The morphologies of the char residues were observed by SEM. Furthermore, the mechanical properties of RPUF composites were measured by the compressive strength test. The results showed that whether the degree of polymerization of MAPP is 30 or 1000, they both had greater charring ability and better flame-retardant properties than unmodified APP. The residual char yield of RPUF/MAPP-30 (37.3%) and RPUF/MAPP-1000 (36.5%) were both significantly higher than RPUF/APP-30 (22.8%) and RPUF/APP-1000 (24.9%). The peak heat release rate value of RPUF/MAPP-30 was 29.9% lower than that of RPUF/APP-30, and the drop of RPUF/MAPP-1000 was 50.9% compared to RPUF/APP-1000. Moreover, the total heat release of RPUF/MAPP-1000 (9.7 MJ/m2) was much lower than that of RPUF/MAPP-30 (11.3 MJ/m2). In summary, MAPP-1000 has the best flame-retardant properties among all RPUF composites. In addition, the results also showed that flame-retardant performance and the mechanical properties dramatically decreased with the increase in the addition of MAPP-1000, and the RPUF composite had the best comprehensive performance with 20% content of MAPP-1000.