Improved Flame Retardancy Research Articles

Improved Flame Retardancy and Tensile Property of Aramid Fiber‐Reinforced Aluminum Hydroxide/Zinc Borate/Low‐Density Polyethylene Composites

ABSTRACTLow‐density polyethylene (LDPE) is a preferred material for engineering applications due to its flexibility and erosion resistance. However, LDPE demonstrates inherent flammability with limiting oxygen index (LOI) being around 17.5%. This work aims to enhance flame retardancy and tensile property of LDPE by incorporating aluminum hydroxide (ATH), zinc borate (ZB), and aramid fibers (AF). The reinforced LDPE containing 1.5 wt% AFs exhibits optimal flame retardancy among the samples as tested. Compared to the composites without AFs, the melt flow index of the composites is reduced by 95.5%, the LOI increased by 4.48% and a UL‐94 V‐0 rating is achieved. The thermogravimetric analysis test shows that the final residual mass reaches 44.2%. The cone calorimeter tests reveal the heat release rate is 110.0 kW/m2 and the smoke production rate is 0.016 m2/s, which are declined by 3.7% and 14.3%, respectively. Fourier‐transform infrared spectroscopy and scanning electron microscopy prove that the tensile action of AFs plays an active role in the formation of stable char which is beneficial for flame‐retardant performances. Apart from enhanced flame retardancy, the tensile strength of the reinforced composites reaches an increase of over 50% while meeting flame‐retardant requirements.

Flame Retardancy and Heat Shielding in Green Polypropylene Composites Using Biohybrid Fibers and Agro-Waste Fillers.

The current work presents the flame-retardant performance of hybrid polypropylene composites, reinforced with specific short woven flax fabrics (SWFs), short basalt fibers (BFs), and rice husk powder (RHP), using polypropylene grafted maleic anhydride (MAPP) as the coupling agent. Horizontal burning test (HBT), microcalorimeter test (MCT), and cone calorimeter test (CCT) were conducted on these composites. The formulations used were 25% SWF/PP, 25% SWF/20% BF/PP, and 25% SWF/20% BF/PP with 6% RHP and 25% SWF/20% BF/PP with varying RHP contents (6, 12, and 18%) in combination with 6% MAPP. A peak heat release rate (pHRR) reduction of 14.42% was recorded in microcalorimeter test results. However, cone calorimeter test results indicated a reduction of 80.95% in pHRR and 23.84% in total heat release rate (THR). Furthermore, the emissions of CO and CO2 were reduced by 68 and 67%, respectively, in the 25SWF/20BF/PP.6MAPP-18RHP composite compared to pure PP, indicating an overall improvement in combustion efficiency. Fire performance index (FPI) also improved remarkably: FPI increased by 130% and fire growth index (FGI) improved by 81.34%. Moreover, the horizontal burning test showed an improved performance, with the burning rate further reduced by 11.10% compared to that of the 25% SWF/PP composite. These results highlight the synergy among natural fibers, agro-waste fillers, and MAPP in improving flame retardancy of polypropylene composites, and hence their potential application in automobiles and construction, where the demand for fire safety is very high.

Multi-functional bio-based DOPO derivative for enhanced flame retardancy and mechanical strength in epoxy resin

Sustainable flame retardants are crucial to address environmental concerns and meet the demands of high-performance materials. A novel bio-based flame retardant (ANDD) with multiple reactive groups was synthesized using a one-pot method. ANDD served as a co-curing agent for 4,4′-diaminodiphenylmethane (DDM) in the cross-linking of EP. Differential scanning calorimetry (DSC) revealed that ANDD accelerates the curing process of bisphenol A diglycidyl ether (DGEBA). Thermogravimetric analysis indicated that incorporating ANDD lowered the T5% and Tmax values of the EP/ANDD composites, while enhancing residual char at high temperatures due to its carbon-forming capability. The EP/ANDD composites exhibited improved flame retardancy, with a limiting oxygen index (LOI) of 33.6 % at a 5 wt% ANDD loading (P content of 0.372 %), achieving a V-0 rating in UL-94. Cone calorimetry showed that, compared to pure EP, EP/ANDD-5 reduced the peak heat release rate (pHRR) by 41.7 % and total smoke production (TSP) by 24.4 %, outperforming EP/DOPO with equivalent phosphorus content. This enhanced flame retardancy is attributed to the char layer’s protective role in the condensed phase and radical quenching in the gas phase. Additionally, EP/ANDD-3 demonstrated a 13.8 % increase in tensile strength and a 20.8 % increase in tensile modulus compared to pure EP. This study indicates that ANDD, as a bio-based flame retardant with multiple reactive groups, presents a promising pathway for the development of high-performance functional thermoset materials.

Addition of ammonium polyphosphate for simultaneous enhancement of flame retardancy, mechanical, and viscoelastic properties of PALF‐reinforced bio‐HDPE composite

AbstractThis work is focused on reducing the flammability of 25 wt.% pineapple leaf fiber (PALF)‐reinforced bio‐based high‐density polyethylene (bio‐HDPE) composites. Varying contents of ammonium polyphosphate (APP) up to 10 wt.%, have been incorporated as a flame retardant while its effects on mechanical and viscoelastic properties are also evaluated. The linear burning rate is reduced by up to 26% for 10% APP content in the horizontal burn test. The incorporation of APP also proved beneficial in arresting the dripping of the polymer matrix during the vertical burn test. Thermal analysis showed that the interaction between APP and natural fibers enhanced the residual char content by up to 9%. Furthermore, dynamic mechanical analysis revealed an increase in the damping factor (loss tangent) with APP addition. The findings recommend incorporating up to 5% APP in PALF/Bio‐HDPE composites as optimum. PALF‐reinforced Bio‐HDPE composite with improved flame retardancy, mechanical, and damping properties is achieved, offering an alternative to conventional composites used in automobile and construction industries.Highlights Flame‐retardant composites made from 25% PALF and 10% APP. 10% APP base composite showed a 26% reduced UL 94 horizontal burning rate. APP incorporation increases residual char content and prevents dripping also. APP enhances both the mechanical properties and damping factor of composites.

Functionalized Attapulgite With Phosphaphenanthrene and Triazine‐Trione Groups for Improving Flame Retardancy of PBT Composites

ABSTRACTIn this study, silane‐based phosphorus flame retardants (DOPO‐KH560) and silane‐based nitrogen flame retardants (TGIC‐KH550) were first synthesized via a ring‐opening addition reaction, and the DOPO‐KH560 and TGIC‐KH550 were further grafted onto the surface of ATP to obtain ATPD and ATPT flame retardants, respectively. The resulting flame retardants, ATPD and ATPT, with different phosphorus/nitrogen (P/N) ratios, were then incorporated into poly(butylene terephthalate) (PBT) at a loading of 10 wt% to improve the flame retardancy and mechanical integrity of the PBT composites. Specifically, PBT composite containing 8 wt.% ATPD and 2 wt.% ATPT achieved a V‐0 rating and an oxygen index (LOI) of 28.3%, and the peak heat release rate (pHRR) and total heat release rate (THR) decreased by 29.4% and 7.7% compared to the PBT. Due to good interfacial adhesion between ATPT and PBT matrix, the PBT/6ATPD/4ATPT composite exhibited a tensile strength of 58.7 MPa, exceeding the strength of PBT and the PBT/ATP composite by 9.7% and 8.1%, respectively. As a result, the integration of ATPD and ATPT as flame retardants not only improved fire resistance but also optimized the mechanical properties of PBT composites.

High Gas Barrier Elastomer/Boehmite Composites with Mechanical Robustness and Improved Flame Retardance Enabled by Segregated Structure with Interfacial Dynamic Cross-Links

High Gas Barrier Elastomer/Boehmite Composites with Mechanical Robustness and Improved Flame Retardance Enabled by Segregated Structure with Interfacial Dynamic Cross-Links

Improved Flame Retardancy of Bacterial Cellulose Fabrics Treated Using the Plant-Based Materials Banana Peel, Beet, and Spinach

ABSTRACT This study identified plant-based materials for use as flame retardants in combination with bacterial cellulose (BC) and enhanced the flame retardancy of BC fabrics. Eight plant-based materials were screened via thermogravimetric analysis, and banana peel, beet, and spinach were selected as plant-based flame retardants. The chemical and physical structure analyses of BC samples treated with banana peel, beet, and spinach, respectively, revealed that the plant-based flame retardants were entrapped within the BC matrices without changing the structure of BC. The flame retardancy of the plant-based flame retardant-treated BC samples was compared to that of BC treated with the sodium metasilicate nonahydrate, which is a commercial flame retardant. Vertical flammability and char morphology studies confirmed that the plant-based flame retardant-treated BC samples formed honeycomb chars during combustion. The limiting oxygen indices of the plant-based flame retardant-treated BC samples were 40–47%, which exceeded that of sodium metasilicate nonahydrate-treated BC of 36%. In thermogravimetric analysis, the residual masses of the plant-based flame retardant-treated BC samples were similar to that of sodium metasilicate nonahydrate-treated BC. Therefore, BC fabrics with improved flame retardancy were developed using plant-based flame retardants.

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.

Bio-inspired construction of hydrophobic Mg(OH)2/Co-MOF/DOPO hybrids for simultaneously improving flame retardancy and mechanical properties of poly(L-lactic acid) composites

Bio-inspired construction of hydrophobic Mg(OH)2/Co-MOF/DOPO hybrids for simultaneously improving flame retardancy and mechanical properties of poly(L-lactic acid) composites

Polymer-based phosphoramidite flame retardant for TPU: Enhanced fire resistance with preserved transparency and mechanical properties

In this work, a polymeric flame retardant (POP) containing a phosphoramidite bond was synthesized from piperazine and phenyl dichlorophosphate. The chemical structure of POP was confirmed using FTIR, TGA, DSC, 1H NMR, 31P NMR, 13C NMR and PY-GC–MS. Adding POP to TPU significantly improved its flame retardancy while maintaining its mechanical properties and transparency. Only 3 wt% of POP reduced the peak heat release rate (PHRR) of the TPU composite by 50.1 %. With increasing POP content, the PHRR and total heat release (THR) of the TPU composites decreased further, and the char residue increased. At 15 % POP, the THR and PHRR of TPU decreased by 40.7 % and 60.2 %, with char residue reaching 21.6 %. Moreover, when the amount of POP was 30 %, the TPU composite reached a LOI value of 29.2 %, passing UL 94 V-0 level. The improved flame retardancy resulted from the prior concentrated emission of CO2 in the gaseous phase and the creation of denser, more graphitized char residue within the condensed phase. Additionally, the excellent compatibility between POP and TPU ensured minimal impact on the mechanical properties and transparency. The tensile strength, elongation at break, and transmittance of TPU/15 % POP were 40.2 MPa, 525 %, and 81.5 %, nearly matching the performance of pure TPU.

A fully bio-based intumescent flame retardant for enhancing the flame retardancy and smoke suppression properties of wood flour polypropylene composites

In this study, a fully bio-based intumescent flame retardant, phytic acid vanillin arginine salt (VR-PA), was designed and synthesized by l-arginine (AR) and vanillin (VA) via a Schiff base reaction, followed by the introduction of phytic acid (PA) using electrostatic ionic interactions. The intumescent flame retardant, VR-PA, was incorporated into wood flour polypropylene composites (WFPP) to enhance their flame retardant and smoke suppression properties. Compared to pure WF, the limiting oxygen index (LOI) of WFPP with 20 wt% VR-PA increased to 28.2 %, while the peak heat release rate and total heat release were reduced by 35.4 % and 20.6 %, respectively. Additionally, the WF with 15 wt% VR-PA exhibited the greatest reduction in total smoke production, with a significant decrease of 42.1 %. The improved flame retardant and smoke suppression performance of the WF is attributed to the free radical trapping effect of VR-PA in the gas phase during the combustion process, as well as the formation of an expanded and continuous carbon layer during in the condensed phase. This study provides a green method to enhance the flame retardancy and smoke suppression of WFPP composites.

Biobased Hyperbranched Flame Retardant for Epoxy Resin Modification: Simultaneously Improved Flame Retardancy, Toughness, and Smoke Toxicity Suppression

Biobased Hyperbranched Flame Retardant for Epoxy Resin Modification: Simultaneously Improved Flame Retardancy, Toughness, and Smoke Toxicity Suppression

All-In-One Epoxy/MXene Nanocomposites with Bead-Type Polymeric Imidazole Latent Curing Agent for Enhancing Storage Stability and Flame Retardancy.

Developing a single-component epoxy system is challenging but crucial for advanced thermoset applications. Unfortunately, conventional latent curing agents using chemical or physical passivation do not provide satisfactory storage stability and the necessary property requirements. Here, it is demonstrated that all-in-one epoxy/MXene nanocomposite system, comprising epoxy resin, polymeric imidazole latent curing agent beads (PILCAB), and Ti3C2Tx MXene, exhibits excellent storage stability, improved flame retardancy, and enhanced mechanical strength. PILCABs, prepared through a Diels-Alder (DA) crosslinking reaction between furan groups of poly(imidazolyl methacrylate)-random poly (furfuryl methacrylate) (PIm-r-PFu) copolymer and bismaleimide (BMI), exhibit excellent storage stability, as stable as under 60 °C storage due to the imidazole reactivity being suppressed synergistically by both physical and chemical passivation mechanisms. Ti3C2Tx MXene flakes, surface-functionalized with alkylated 3,4-dihydroxyl-L-phenylalanine, exhibit excellent compatibility with the epoxy matrix. Consequently, the enhanced storage stability, flame retardancy, and mechanical strength of the all-in-one epoxy/MXene nanocomposite are attributed to the strong DA bond formation in latent curing agent, efficient charring capability of MXene and BMI, and the catalytic effect of the MXene. This study opens new avenues for designing and developing single-component epoxy systems that satisfy demanding requirements, including storage stability, mechanical strength, and flame retardancy, which are essential for practical applications.

Physicochemical Mechanism of Flame‐Retardant Enhancement for Elastomeric Polyurea: A Mini‐Review

ABSTRACTPolyurea coatings are widely used in various industries due to their excellent mechanical properties, such as high tensile strength, abrasion resistance, and chemical resistance. However, their lack of inherent flame retardancy limits their use in applications where fire safety is critical. Therefore, reinforcing the fire‐retardant properties of traditional polyurea through various means can effectively protect the product while reducing the risk of fire. This paper provides a summary of several advanced methods for improving flame retardancy. It systematically analyzes the advantages and disadvantages of these methods and proposes improvement measures to enhance efficiency. Additionally, the paper proposes new methods to increase the fire resistance of polyurea. These include the addition of new flame‐retardant additives and the substitution of the backbone of polyurea, making it suitable for more industrial applications. This mini‐review can also serve as a valuable reference for future research on improving the flame retardancy of elastomeric polyurea materials.

Preparation of Montmorillonite–Melamine Cyanurate and Inhibition of the Emission of Phosphine from PA6/Aluminum Hypophosphate

In order to mitigate the release of toxic phosphine from aluminum hypophosphite in twin-screw processing, montmorillonite–melamine cyanurate was prepared by three methods: (1) mechanical intercalation, (2) water intercalation and (3) in situ intercalation. The sheet spacing of montmorillonite was increased from 1.140 nm to 1.141 nm, 1.208 nm and 1.217 nm for these three methods, respectively, and scanning electron microscope (SEM) and transmission electron microscopy (TEM) proved that melamine cyanurate was successfully inserted into the montmorillonite sheets. The montmorillonite–melamine cyanurate from in situ intercalation can best inhibit the release of PH3 from aluminum hypophosphite, and the peaks of phosphine, mean values of phosphine and integral of phosphine were reduced by 81.9%, 72.1% and 72.2%, respectively. The mode of action of montmorillonite–melamine cyanuric inhibition of the emission of phosphine from aluminum hypophosphite can be attributed to the physical absorption of montmorillonite and the chemical bonding of melamine cyanurate. In addition, in situ intercalation can slightly improve flame retardancy, attributed to incomplete exfoliation of montmorillonite sheets.

Multifunctional aluminum 12-hydroxystearate/lignin polyurethane foam for selective gelation and efficient separation of oil and organic solvents

During frequent transportation, the marine environment is continuously exposed to significant threats from crude oil and organic solvent leakage. Non-covalent self-assembly of organogelator on the adsorbent matrix to fix non-polar solvents is an efficient and sustainable remediation method. This contribution proposes an organogelator-adsorbent composite by blending aluminum 12-hydroxystearate (Al HSA) and expanded graphite (EG) during lignin-based polyurethane foaming. Al HSA molecule synergizes with EG to modulate the shape (hexagonal), oil retention, mechanical property, and hydrophobicity (water contact angle = 151.3°) of the lignin-based polyurethane foam (LPUF) skeleton. Al HSA-LPUF (OTS-LPUF/EAH) superhydrophobic foam exhibits sorption capacity up to 13.2–53.0 g g−1 in various oils and organic solvents. From the microscopic morphology, the Al HSA on the skeleton self-assembles into spherical nanoclusters driven by hydrogen bonding, realizing the capturing of oils and organic solvents. Even after 20 cycles, the foam still has a high oil/water separation capacity and mechanical performance. OTS-LPUF/EAH also shows improved flame retardancy and a 61 % reduction in total smoke release (TSR) compared to pristine LPUF.

Fabrication of a 2D/2D g-C3N4@ZnTDA nanosheets catalyst for highly efficient degradation of 2,4-dibromophenol and improved flame retardancy of polyurethane foam

High charge separation and transfer efficiency are considered as key factors of photocatalysts in wastewater treatment applications. In this work, a high performance photocatalyst g-C3N4@ZnTDA was designed and applied through a facile solvothermal strategy. The microstructural, morphological, physicochemical, and photoelectrochemical properties of g-C3N4@ZnTDA were fully characterized. The photocatalytic activity of g-C3N4@ZnTDA nanoparticles under visible light source in degrading the 2,4-dibromophenol(2,4-dB) contaminants was also successfully studied. Additionally, the g-C3N4@ZnTDA composite demonstrates easy operation and good regeneration ability, making it highly promising for the efficient removal of phenolic pollutants from wastewater. Besides, a novel reutilization method for used catalyst as flame retardant and for PU foams was successfully testified. The MCN-3 as a fire-safety coating could reduce the heat release and improve flame retardancy of PU composites. This work opens a new window for valuable inspiration and structural design of reutilized MOF composites.

Improving flame retardancy of microfiber synthetic leather by decorating with phosphorus/boron hybrid polysiloxanes

Microfiber synthetic leather (MSL) as a fiber reinforced composite has famous application. However, its highly flammability as well as melt-dripping need to be solved. Currently, enhancing the flame retardancy of MSL is still challenging. In this study, we developed a phosphorus/boron hybrid polysiloxane coating on MSL by co-depositing phosphorus-based polysiloxane (PDPTES) and boric acid (BA), creating a multi-element synergistic flame-retardant system. By decorating with phosphorus/boron hybrid polysiloxanes, the modified MSLs with PDPTES and PDPTES-BA achieved a limited oxygen index (LOI) of 27.0 % and 28.8 %, achieving self-extinguishing ability with short damage length and no melt-dripping in vertical flammability test (VFT). Both PDPTES and PDPTES-BA well-maintained the good thermal stability of MSL and char residues at high temperature was obviously increased. The incorporation of BA could enhance the char-forming ability of PDPTES modified MSL. The peak heat release rate (PHRR) and total heat release (THR) of MSL-PDPTES-BA was 20 % and 25 %, respectively. This multi-elemental flame retardant system owned both condensed and gaseous phase action by strengthening the carbonization effects, reducing the release of combustible volatiles and releasing silicon/phosphorus/boron-containing fragments. Additionally, the modification of PDPTES and PDPTES-BA has little effect on the air permeability of MSL. Thus, this work provides a suitable strategy for developing microfiber synthetic leather with good flame-retardant performance.

Effects of Anchovy, Mussel, and Shrimp Powders on the Flame Retardancy of Bacterial Cellulose

ABSTRACT This study aims to fabricate bacterial cellulose with improved flame retardancy by applying anchovy, mussel, and shrimp powders. The elemental analysis confirmed that raw marine powders contained nitrogen and sulfur elements which could play important roles in enhancing the flame retardancy of bacterial cellulose. Thermogravimetric analysis revealed the improved thermal stability of bacterial cellulose following entrapping and crosslinking of the marine powders. The fabricated bacterial celluloses with marine powders had similar levels of flame retardancy as that of bacterial cellulose treated with a commercial flame-retardant, sodium metasilicate nonahydrate, which was confirmed by the vertical flammability test and limiting oxygen index. The char morphology analysis revealed intumescent char on the surface of the samples, confirming the effect of marine powders on the flame retardancy of bacterial cellulose. Moreover, the marine powders were entrapped and crosslinked with bacterial cellulose nanostructures, and the chemical and crystalline structures of bacterial cellulose were retained. This study proposes an efficient method to improve the flame retardancy of bacterial cellulose by introducing marine powders via the combined entrapment and crosslinking method.

Study on Innovative Laminated Flooring with Resin-Impregnated Paper

A new type of laminated flooring decorated by resin impregnated paper (LWFWRIP) was designed, with the advantages of low formaldehyde emission, improved flame retardant, and high wear resistance. The structure of this new type of wood flooring is based on the ordinary laminated flooring, followed by a decorative layer of thin wood pieces, and then the transparent improved flame retardant, wear-resistant paper is added to the top. It is found that the hot-pressing temperature is the most significant factor affecting the adhesion of resin impregnated paper. The optimal hot-pressing parameters are selected as the hot-pressing pressure of 3.5 MPa, hot-pressing temperature of 180 °C, and hot-pressing time of 40 s. The new laminated flooring was improved with high flame retardant, high wear-resistant, combined with the conventional advantages of both solid wood composite flooring and reinforced wood flooring. The new laminated flooring decorated by resin impregnated paper has broad application prospects.