Enhanced Flame Retardancy Research Articles

Vanillin-derived co-curing agent for enhanced flame retardancy and mechanical properties in epoxy resin

Herein, we present the synthesis and characterization of a novel phosphorus-containing epoxy co-curing agent, ANVD, fabricated via a one-pot method utilizing vanillin, 1,5-diaminonaphthalene, and DOPO as raw materials. Structural analysis conducted through FTIR and NMR spectroscopy confirmed the composition of ANVD. Differential scanning calorimetry (DSC) results indicated ANVD has significant contribution to the curing crosslinking of DGEBA, resulting in a slightly decreased Tg value for EP/ANVD compared to EP/DOPO, albeit still notably higher. Thermogravimetric analysis (TGA) revealed a reduction in the T5% and Tmax values of EP/ANVD, yet ANVD’s superior char-forming ability increased char residue mass at elevated temperatures. Combustion tests showcased the outstanding flame retardancy of EP/ANVD, with EP/ANVD-5 exhibiting a limiting oxygen index (LOI) value of 33.2 % and achieving a V-0 rating in the UL-94 test. Furthermore, EP/ANVD-5 displayed a notable decrease of 38.6 % and 32.1 % in pHRR and av-HRR, respectively, compared to pure EP, surpassing EP/DOPO with equivalent phosphorus content. Analysis of decomposition products in both condensed and gas phases revealed ANVD’s role in forming dense and continuous expanded char layers during combustion, releasing phosphorus radicals and non-combustible gases, thus exhibiting dual-phase flame retardant effects. Additionally, EP/ANVD-3 exhibited enhanced mechanical properties, with tensile strength and modulus increasing from 68.5 MPa and 0.75 GPa to 76.5 MPa and 0.86 GPa, respectively, compared to pure EP. Overall, the introduction of the bio-based flame retardant ANVD presents promising opportunities for the utilization of bio-based materials in flame retardancy applications.

A system with efficient flame retardant and antibacterial properties for the development of exceptional durable functional cotton fabrics

Phosphorus-based flame retardants are widely employed in the study of flame retardancy for cotton fabrics due to their halogen-free nature and high efficiency. The addition of nitrogen and other elements can further enhance flame retardant properties through synergistic effects. However, the synthesis of flame-retardant multifunctional additives based on phosphoramidic ammonium salts has been scarcely reported. In this study, a halogen-free and formaldehyde-free phosphoramidite ammonium salt was synthesized as a synergistic flame retardant multifunctional additive. This compound, with phosphorus as the primary flame retardant element and a nitrogen-containing guanidine group, was used to modify cotton fabrics. The treated fabrics exhibited enhanced flame retardant and antibacterial properties. Notably, cotton fabrics treated with a 17.9 % weight gain showed a damaged length of 4 cm in the vertical flame test, and the LOI value increased to 41.5 %, remaining at 27.3 % even after 50 washing cycles. The results of the cone calorimeter test (CCT) revealed that the peak heat release rate (PHRR) and total heat release (THR) of treated cotton were 30.35 kW/m2 and 5.46 MJ/m2, respectively, representing reductions of 87.04 % and 36.07 % compared to untreated cotton. Physical performance tests indicated only a slight decrease in the strength and whiteness of the cotton fabrics, while softness increased after treatment. Moreover, the treated cotton fabric exhibited excellent antibacterial properties, with antibacterial rates of 99.26 % against E. coli and 98.54 % against S. aureus.

Enhancing flame retardancy and heat insulation performances of polyamide 66 composite film by adding CNC/Al2O3 nanohybrids

Polyamide 66 (PA66) has garnered significant attention due to its exceptional properties; unfortunately, its flammability is challenging. Adding flame retardants (FRs) is a primary approach to enhance PA66 flame retardancy. This study developed a highly flame-retardant PA66 composite film by adding corn-like functional nanohybrids (CNC/Al2O3). Interestingly, CNC/Al2O3 nanohybrids not only formed hydrogen bond interactions with PA66 but also improved crystallization properties as heterogeneous nucleating agents, resulting in the excellent mechanical properties of PA66 composite film. Remarkably, the incorporation of 3 wt% CNC/Al2O3 nanohybrids into PA66 matrix contributed to increasing the LOI to 28.5 %. The pHRR, THR, and TSR were reduced obviously by 55.7 %, 15.3 %, and 65.2 %, respectively. The excellent flame retardancy of PA66 composite film was attributed to the forming of a compact carbon layer catalyzed by the CNC/Al2O3 nanohybrids. Besides, the homogeneous distribution of CNC/Al2O3 nanohybrids endowed the composite film with excellent heat insulation, and the heat insulation rate was up to 31.9 %. Thus, such PA66 composite films with excellent flame retardancy, heat insulation, and mechanical properties could meet the broader application requirements.

Organic-inorganic hybrid-modified polyester/cotton fabric: Strategy for enhanced flame retardancy, chemical stability and amphiphobicity

As surface treatments for the application of functional components to substrates have gained increasing attention, there is a growing interest in endowing fabrics with multiple functionalities in addition to flame retardancy. This study describes the successful formation of a fluorination treatment of Al2O3 cross-linked onto the surface of a self-assembled PEI/PA coating for polyester/cotton (PC) fabrics. This coating approach aims to improve the flame retardancy, amphiphobicity, chemical stability, and self-cleaning properties of PC fabrics. The treated fabrics demonstrated exceptional fire resistance, with a significant reduction of 55.4 % in the peak heat release rate (pHRR) during combustion. Correspondingly, there was a decrease of 53.8 % in the peak release rate of CO2, while the limiting oxygen index increased from 17.9 % to 30.4 %. Additionally, the contact angles of water, glycol, and peanut oil droplets before and after treatment increased from 20.4°, 65.1°, and 34.6° to 146.0°, 143.1°, and 97.9°, respectively. The coating exhibits durable self-cleaning performance in both ambient and hot water and remains stable across a pH range of 1–14. This research offers a viable pathway for achieving flame retardancy on fabrics while enhancing their multifunctionality.

Enhanced flame-retardant phase change materials with good shape stability for thermal management

Phase change materials (PCMs) have become pivotal components in many fields such as energy storage, thermal management, and photothermal conversion. However, challenges including leakage, flammability, and low thermal conductivity have impeded their broad application. In this work, a cross-linked solid-solid PCM (SPEG) using polyethylene glycol (PEG) and styrene-maleic anhydride copolymer (SMA) was synthesized. To enhance flame retardancy and thermal conductivity, black phosphorus (BP) and expandable graphite (EG) were introduced into the PCM matrix, yielding the target product (SPEG-BP/EG PCM) with enhanced properties. The analysis demonstrated that the SPEG-BP/EG sample with the ratio BP/EG of 1:1 (SPEG-BP/EG-1) exhibited a notable decrease in peak heat release rate and total heat release by 55.2 % and 13.2 %, respectively, compared to the SPEG sample. Moreover, thermal conductivity was improved from 0.18 W m−1 K−1 (SPEG) to 0.59 W m−1 K−1 for SPEG-BP/EG-1. The inclusion of SMA in crosslinking facilitated the transition of PEG's phase change behavior from solid-liquid to solid-solid, maintaining an enthalpy efficiency of 64.0 %. SPEG-BP/EG-1 exhibited excellent dimensional stability and cycling performance in open heating/cooling cycle tests, remaining chemically stable even after 60 heating/cooling cycles, as confirmed by DSC analysis. Furthermore, thermal management performance was evaluated using an LED light bulb, revealing a notable reduction of 9.4 °C in the maximal working temperature facilitated by SPEG-BP/EG PCM. This work presented a comprehensive strategy to mitigate the challenges of flammability, low thermal conductivity, and leakage associated with conventional PCM (PEG), thereby having great potential in practical applications in thermal management.

Enhancing Thermal Insulating and Flame Retardancy of Electromagnetic Shielding Polyester-Based Nonwoven Fabric

Enhancing Thermal Insulating and Flame Retardancy of Electromagnetic Shielding Polyester-Based Nonwoven Fabric

Enhancing Flame Retardancy and Smoke Suppression in EPDM Rubber Using Sepiolite-Based Systems.

The burning of Ethylene-Propylene-Diene Monomer (EPDM) rubber generates substantial smoke, posing a severe threat to the environment and personal safety. Considering the growing emphasis on safety and environmental protection, conventional non-smoke-suppressing flame retardants no longer satisfy the present application requirements. Consequently, there is an urgent need to develop a novel flame retardant capable of suppressing smoke formation while providing flame retardancy. Sepiolite (SEP), a porous silicate clay mineral abundant in silica and magnesium, exhibits notable advantages in the realm of flame retardancy and smoke suppression. This research focuses on the synthesis of two highly efficient flame-retardant smoke suppression systems, namely AEGS and PEGS, using Enteromorpha (EN), graphene (GE), sepiolite (SEP), ammonium polyphosphate (APP), and/or piperazine pyrophosphate (PPAP). The studied flame-retardant systems were then applied to EPDM rubber and the flame-retardant and smoke suppression abilities of EPDM/AEGS and EPDM/PEGS composites were compared. The findings indicate that the porous structure of sepiolite plays a significant role in reducing smoke emissions for EPDM composites during combustion.

Preparation of P/N/Si‐containing covalent organic framework‐based flame retardants and their application in epoxy resins

AbstractBalancing the enhancement of flame retardancy of epoxy resin while maintaining its mechanical capacities intact poses a significant challenge in the realm of flame‐retardant epoxy resins. To reach the above objectives, a COF‐based synergistic flame retardant with phosphorus, nitrogen, and silicon (PA‐COF@MT) was synthesized using phytic acid (PA), montmorillonite (MT), and covalent organic framework (COF). When PA‐COF@MT was added at 4 wt%, EP/PA‐COF@MT exhibited a reduction of 42.1% in peak heat release rate (PHRR), 45.84% in total heat release (THR), and 59.8% in total smoke production (TSP) compared with the pure EP. LOI increased by 30.5% and UL‐94 tested to V‐0 grade. flame‐retardant index (FRI) value of 3.03, achieving a “good” rating. Fire growth indices and mean effective combustion heat were increased while mechanical properties also improved. These findings suggest that the flame retarding mechanism of PA‐COF@MT is mainly through vapor phase and condensed phase actions. The combined effects of phosphorus, nitrogen, and silicon make the surface of carbon residue solid and dense, resulting in excellent heat insulation and smoke suppression effects. In simple terms, this study provides new insights into COF‐based flame retardants. Combining low‐cost and simple preparation methods, PA‐COF@MT has broad application prospects in flame‐retardant epoxy resin systems.

Enhancement of flame retardancy in ceramic polymer composite materials with ammonium polyphosphate/melamine cyanurate

AbstractTo enhance the flame‐retardant characteristics of ceramifiable polyethylene (PE) composites, a composite flame retardant comprising ammonium polyphosphate (APP) and melamine cyanurate (MCA) was integrated. This addition markedly bolstered their flame‐retardant attributes. A meticulous exploration was conducted to ascertain the impacts of APP and MCA on the ceramifiable PE composites' visible morphology, mechanical robustness, and dimensional constancy, and to study the phase transition and microstructure deformation during sintering. Findings underscored that the amalgamation of APP/MCA markedly enhanced the flame resistance of these ceramifiable composites, registering a limiting oxygen index of 25.6% and achieving the vertical burning test (UL‐94) rating of V‐0. The collaborative flame‐retardant action of APP/MCA significantly enhanced the flame resistance of the PE composites while effectively mitigating the composite's propensity to drip. Upon detailed phase analysis, a eutectic reaction was observed between APP and wollastonite fiber, culminating in the genesis of a novel crystalline phase, calcium pyrophosphate (Ca2P2O7). When subjected to elevated temperatures, glass–ceramics manifest with both crystalline and vitreous phases. The proportion of the vitreous phase plays a pivotal role in influencing the ceramic's overall performance.

Enhancing flame retardancy and multi-functionalization of environmentally friendly cotton fabrics with a polydimethylsiloxane-based polyurethane

Phosphorus-containing flame retardants are prone to result in the buildup of biotoxins, while halogen flame retardants easily lead to hazardous gases. Therefore, it is crucial to develop a multifunctional flame-retardant cotton fabric without phosphorus and halogen. Herein, single-ended hydroxy-terminated polydimethylsiloxane (PDMS-ID) was synthesized through single-ended hydrosilicone oil and 1,4-butanediol, followed by the preparation of a waterborne polyurethane (RWPU) containing side chain polydimethylsiloxane through the reaction of PDMS-ID with isocyanate prepolymer. Characterization data shows that its particle size distribution is relatively dispersed while maintaining good emulsification performance. Based on this, a halogen-free and phosphorus-free multifunctional flame retardant cotton fabric (COF-BBN@RWPU) was successfully prepared through treatment with boric acid/borax/3-aminopropyltriethoxysilane solution and subsequent RWPU encapsulation. In vertical flammability test (VFT), COF-BBN@RWPU has a char length of 57 mm and a limiting oxygen index (LOI) of 42.3 % with a 11 % weight gain while pure cotton was burned through with a LOI of 18.0 %. In addition, the total heat release and total smoke release of COF-BBN@RWPU decreased by 80.0 % and 47.2 %, compared with pure cotton. Additionally, COF-BBN@RWPU can achieve a maximum contact angle of 140.1° with an oil-water separation rate of 98.4 %. This study presents an eco-friendly approach to achieving the multifunctionality of cellulose fabrics.

Flame retardant and mechanically enhanced polyacrylonitrile fibers prepared by amination and phosphorylation

To improve the flame retardancy of polyacrylonitrile (PAN) fibers, PAN fibers were firstly modified through amination with diethylenetriamine (DETA) to obtain ammoniated PAN fibers (A-PAN). Then, A-PAN underwent phosphorylation modification via phosphorus-containing flame retardant, i.e., tetrakis (hydroxymethyl) phosphonium sulfate (THPS) to fabricate flame retardant PAN fibers (THPS-A-PAN). XPS and FTIR confirmed the covalent bonding of DETA and THPS with PAN fibers. TGA showed improved thermal stability, particularly in increased char residue at high temperatures. The modified PAN fibers exhibited enhanced flame retardancy in vertical burning tests and MCC analysis, with LOI values increasing from 17% to 32.5% and maintaining at 26.5% after 30 laundering cycles (LCs). Fire safety parameters such as heat release capacity (HRC), total heat release (THR), and the fire growth index (FGI) decreased by 51.5%, 46.9%, and 41.9%, respectively. In addition, the tensile strength and elongation at break of THPS-A-PAN increased from 2.69 cN/dtex and 28.6% to 3.08 cN/dtex and 30.1% respectively, indicating enhanced mechanical properties. This work develops a feasible strategy to improve the flame retardancy of PAN fibers while endowing them with reinforced mechanical properties, which provides a possible research direction for the practical application of flame retardant PAN fibers.

Mullite-Fibers-Reinforced Bagasse Cellulose Aerogels with Excellent Mechanical, Flame Retardant, and Thermal Insulation Properties.

Cellulose aerogels are considered as ideal thermal insulation materials owing to their excellent properties such as a low density, high porosity, and low thermal conductivity. However, they still suffer from poor mechanical properties and low flame retardancy. In this study, mullite-fibers-reinforced bagasse cellulose (Mubce) aerogels are designed using bagasse cellulose as the raw material, mullite fibers as the reinforcing agent, glutaraldehyde as the cross-linking agent, and chitosan as the additive. The resulted Mubce aerogels exhibit a low density of 0.085 g/cm3, a high porosity of 93.2%, a low thermal conductivity of 0.0276 W/(m∙K), superior mechanical performances, and an enhanced flame retardancy. The present work offers a novel and straightforward strategy for creating high-performance aerogels, aiming to broaden the application of cellulose aerogels in thermal insulation.

Syringaldehyde‐DOPO derivative for enhancing flame retardancy and mechanical properties of epoxy resin

AbstractWith the wide application of epoxy resins in adhesives, electronic packaging materials, and aerospace fields, it is necessary to prepare high‐performance flame‐retardant epoxy resins to reduce the fire risk caused by their flammability. In this study, the rigid structure intermediate Schiff base (DMDA‐SH) was synthesized by condensation reaction of syringaldehyde (SH) with O‐Tolidine (DMDA). Then, DMDA‐SH‐DOPO, a novel P/N‐structured biobased flame‐retardant curing agent, was synthesized by addition reaction with 9,10‐dihydro‐9‐oxaza‐10‐phosphame‐10‐oxide (DOPO) and was applied to the preparation of intrinsic flame‐retardant epoxy resin. As expected, DMDA‐SH‐DOPO has good flame‐retardant properties due to the synergistic action of N/P elements. Epoxy resin with only 2.5% DMDA‐SH‐DOPO (P = 0.16%) can pass the UL‐94 V‐0 test. Compared with DGEBA/DDM, DMDA‐SH‐DOPO‐7.5's (P = 0.49%) peak heat release rate was reduced by 48.4% and the limiting oxygen index (LOI) reached 27%, making it a flame‐retardant material. From the point of view of carbonaceous residue performance, the expansion height of carbon residue after DMDA‐SH‐DOPO‐7.5 combustion is significantly increased, and the amount of carbon residue at 800°C is increased by 36.4%. In addition, appropriate DMDA‐SH‐DOPO can effectively improve the bending property of epoxy resin. This study provides a new idea for preparing renewable high‐performance intrinsic flame‐retardant epoxy resin.

Quick self-grown ternary supramolecules embedded in sodium alginate to fabricate ultralight sponge exhibiting superior flame retardancy

To mitigate environmental and health risks associated with the use of halogenated flame retardants, effective halogen-free solutions have been extensively explored. In this study, melamine/boric acid/phosphoric acid (MBP)‑sodium alginate (SA) sponge was synthesized by treating MBP ternary supramolecules with microwave irradiation via one-pot, facile, and speedy synthesis, obtaining an MBP-SA sponge, a polysaccharide biopolymer. Crosslinking of SA with Ca2+ ion formed an intact network, and this was confirmed using scanning electron microscopy (SEM). Thereafter, the flame retardancy of the as-synthesized SA/MBP sponge was investigated by exposing it to a spirit lamp and a Bunsen burner; the sponge remained intact for up to 540 s and 370 s, respectively, demonstrating the enhanced flame retardancy of MBP supramolecules in the SA/MBP sponge. The limiting oxygen index of the SA/MBP sponge was up to 62 %, demonstrating the self-extinguishing and thermal insulation properties of the as-synthesized sponge. The findings of this study provide insights for developing a new strategy to use SA/MBP sponges for fire protection.

Polydopamine-primed FeCo-LDH endowed epoxy resin with enhanced flame retardancy and mechanical properties

The integration of layered double metal hydroxides (LDH) into epoxy resin (EP) for flame retardancy is in line with the principles of environmentally friendly and sustainable development. In this study, polydopamine (PDA)-primed intercalated LDH containing iron and cobalt ions (LDH-DBS@PDA) was prepared, and its chemical composition, structure and morphology were thoroughly characterized. Due to the synergistic flame-retardant properties exhibited by LDH and PDA, as well as the catalytic charring properties of iron and cobalt ions in both condensed and gaseous phases, EP composite with 5 wt% LDH-DBS@PDA achieved a UL-94 V-0 rating with a limiting oxygen index of 30.7 %. Moreover, EP/LDH-DBS@PDA exhibited a significant decrease in total heat release by 48 % and smoke release by 52 %, demonstrating remarkable fire safety performance. Additionally, the existence of LDH-DBS@PDA improved impact strength, tensile strength, and glass transition temperature due to strong interactions between PDA and EP matrix. This work presents a promising strategy for developing highly efficiency flame retardants with excellent compatibility for polymeric materials.

Preparation and properties of toughened/flame‐retardant PA6/glass‐fiber composites reinforced by linear polyphosphazene elastomers

AbstractIn this study, the challenges of brittleness and flammability in Polyamide 6/glass fiber (PA6/GF) composites, which are crucial for heat‐resistant and stress‐bearing structural parts, are addressed. Polyphosphazene (PZ) elastomers, known for their exceptional flame‐retardant properties, are introduced to enhance the robustness and safety of these composites. Specifically, poly(diaryloxy)phosphazene (PDAP) and poly(difluoroalkoxy)phosphazene (PDFP) are utilized, both contributing to the improved toughness and flame resistance of the PA6/GF composites. Experimental results show that PDAP mainly played the role of solid‐phase flame retardant, while PDFP mainly acted the role of gas‐phase flame retardant. For PA/PZs composites without adding GF, PDFP plays a more efficient flame retardant effect than PDAP. By introducing 15 Vol% of PDFP, the limiting oxygen index (LOI) of the composite reached 26.1%, while the notched impact strength increased by 297%. For PA/PZs/GF composites, PDAP plays a better flame retardant role than PDFP. Under the action of 30 vol% GF and 15 vol% PDAP, the LOI of PA6/PDAP/GF composite reached 26.8%, and the notch impact strength improved to 18.7 kJ/m2, which is 165% higher than that of PA6/GF, and the UL‐94 test reaches V‐0 level. The findings of the study highlight the potential of PDAP and PDFP to act as dual‐function modifiers. These modifiers can considerably ameliorate both the impact resistance and flame retardancy of PA6 and PA6/GF composites. Such dual enhancement surpasses the typical trade‐offs seen in conventional composites, indicating a constructive direction for future material innovation.Highlights Polyphosphazenes simultaneously enhance PA6's toughness & flame resistance. Distinct flame retardant mechanisms found in PDAP and PDFP. GF presence alters PDAP and PDFP's flame retardant efficacy. PDAP shows superior flame resistance in GF‐reinforced PA6 composites. Without GF, PDFP outperforms PDAP in enhancing flame retardancy.

Dynamic Schwarz Meta-Foams: Customizable Solutions for Environmental Noise Reduction.

In an era marked by increasing environmental challenges affecting human well-being, traditional acoustic materials struggle to effectively handle the diverse and multi-frequency nature of harmful environmental noises. This has spurred a demand for innovative acoustic metamaterial solutions by utilizing sustainable design strategies. This research introduces tunable Schwarz metamaterial capable of transforming into a soft meta-foam to solve the complex problems of varying environmental noises. This study primarily focuses on adjusting single to multiple sound-blocking bandgaps mechanism using a multi-layered approach, incorporating the Schwarz P-type triply periodic minimal surface (TPMS) and its elective soft foam counterpart, known as tunable Schwarz meta-foams (TSMF-x). The tunable design parameters of the unit cell, multi-layered TPMS, and soft programmable TSMF-lichen version are comprehensively explored including a fire-safety test. The results demonstrate these enhanced flame retardant meta-foam families have the potential to be used for mid-to-high-frequency environmental noises in industrial equipment and smart homes for sustainable architecture and environmental health applications.

Highly Efficient Phosphazene-Derivative-Based Flame Retardant with Comprehensive and Enhanced Fire Safety and Mechanical Performance for Polycarbonate.

Polycarbonate (PC) as a widely used engineering plastic that shows disadvantages of flammability and large smoke production during combustion. Although many flame-retardant PCs have been developed, most of them show enhanced flame retardancy but poor smoke suppression or worsened mechanical performance. In this work, a novel nitrogen-phosphorus-sulfur synergistic flame retardant (Pc-FR) was synthesized and incorporated into PC with polytetrafluoroethylene (PTFE). The extremely low content of PC-FR (0.1-0.5 wt%) contributes significantly to the flame retardancy, smoke suppression and mechanical performance of PC. PC/0.3 wt% Pc-FR/0.3 wt% PTFE (PC-P0.3) shows the UL-94 V-0 and LOI of 33.5%. The PHRR, THR, PSPR, PCO and TCO of PC-P0.3 decreased by 39.44%, 14.38%, 17.45%, 54.75% and 30.61%, respectively. The impact strength and storage modulus of PC-P0.1 increased by 7.7 kJ/m2 and 26 MPa, respectively. The pyrolysis mechanism of PC-P0.3 is also revealed. The pyrolysis mechanism of PC-P0.3 is stochastic nucleation and subsequent growth and satisfies the Aevrami-Erofeev equation. The reaction order of PC-P0.3 is 1/2. The activation energy of PC-P0.3 is larger than PC-0, which proves that the Pc-FR can suppress the pyrolysis of the PC. This work offers a direction on how to design high-performance PC.

Facile and rapid synthesis of core-shell structured MXene@Ag@PA hybrids for enhanced fire safety and radiation cross-linking in EVA/MH composites

In this study, MXene@Ag@PA hybrids were synthesized using radiation methods and chelation, aiming to enhance the key properties of EVA/MH composites, particularly their flame retardancy. The test results demonstrated that the addition of MXene@Ag@PA hybrids effectively reduced the amount of heat and smoke released during the combustion process of EVA composites. When 2 parts of MXene@Ag@PA hybrids were added, the peak heat release rate (pHRR) of the EVA/MH/2.0MXene@Ag@PA composite was reduced to 233 kW/m², representing a decrease of 78.5% and 63.3% compared to pure EVA and EVA/MH composites, respectively. Additionally, the time to reach the peak heat release rate was delayed to 300–400 s. Moreover, the MXene@Ag@PA hybrids further reduced the total smoke production (TSP) of the EVA composites to 3 m², which is 50% and 38.7% lower than that of pure EVA and EVA/MH composites, respectively. Besides providing significant flame-retardant enhancement to EVA/MH composites, the MXene@Ag@PA hybrids also acted as a radiation sensitizer. At an irradiation dose of 100 kGy, the addition of MXene@Ag@PA hybrids enhanced the cross-linking effect of EVA composites, thereby strengthening their mechanical properties.

Macromolecular piperazine/aluminum phosphate hybrid and its efficient intumescent flame retardant/thermal conductive polypropylene

Achieving a delicate balance between fire resistance and thermal conductivity in intumescent flame-retarded polypropylene (PP) poses a formidable challenge, primarily due to the susceptibility of intumescent barrier layers to functional fillers. To address this concern, a novel hybrid macromolecule (Al-PAP) was synthesized via polycondensation reaction, showcasing promising potential in constructing flame-retardant and thermally conductive PP. Remarkably, the inclusion of mere 14 wt% of the Al-PAP/melamine polyphosphate (Al-IFR) system raised the limiting oxygen index (LOI) of PP to 28.3 %, equivalent to that of PP containing 20 wt% of the conventional system, emphasizing the superior efficacy of the hybrid Al-PAP. Further, the PP with 20 wt% Al-IFR performed a 32.2 % of LOI, 850 °C of glow wire ignition temperature, >960 °C of glow wire flammable index and UL 94 V-0 ratings (3.2 mm & 1.6 mm), indicating the high flame retardancy. Subsequently, three thermal conductive fillers – aluminum oxide, boron nitride, and multi-walled carbon nanotubes – were evaluated based on a 20 wt% dosage of Al-IFR. Alumina emerged as the optimal candidate, enhancing flame retardancy and smoke suppression while imparting thermal conductivity to PP. Conversely, the other two fillers compromised fire-safety performance. Notably, the composite 5Al2O3/20Al-IFR/PP exhibited a 90.8 % lower peak heat release rate and an 88.2 % lower peak smoke production rate compared to PP. Additionally, its thermal diffusivity and thermal conductivity were 27.0 % and 48.9 % higher than those of PP, respectively. In short, this work combined molecular design and comprehensive screening to build the thermally conductive PP with high flame retardant efficiency, and relevant mechanisms were also investigated.