Vertical Burning Research Articles

Effect of microencapsulation flame retardant on flame retardancy and mechanical properties of rigid polyurethane foams

AbstractA microencapsulated flame retardant PMDOPO was synthesized by solution blending method using EGDMA as initiator and AIBN as cross‐linking agent. Rigid polyurethane foams were prepared in a one‐step process. PMDOPO was incorporated into the foams by blending with polycarbonate diols (PCDL) and foaming additives. The results of Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM) showed that PMDOPO was well formed and uniformly dispersed in the foam. The pore size and density of the foams first increased and then decreased with the addition of PMDOPO. X‐ray photoelectron spectroscopy (XPS), vertical combustion test, and thermogravimetric analysis (TGA) showed that the PMDOPO content was directly proportional to the flame retardancy and the thermal stability. The major weight loss shifted to higher temperature intervals. The amount of residual char of RPUF/PMDOPO‐25 was enhanced 50 times to 10.63% compared to pure RPUF. In addition, SEM and Raman analyses of the combustion residual char revealed that a phosphorus‐containing char layer was formed during thermal degradation. The dense charcoal layer helps to insulate heat and suppress combustion. The universal testing machine showed that RPUF with 15 wt% content had the best compression resistance, with an enhancement of 1.8 MPa over pure RPUF.

A novel sustainable phosphorus-containing heteroatom-based coating for polyamide 6.6 textiles: Enhanced flame retardancy and hydrophilicity

The demand for "green" materials increases due to concerns about the effects of flame-retardant textiles. Using natural plant-base compounds such as phytic acid (PA) and the most abundant green amino polysaccharide chitosan (CS) as effective and durable flame retardants for textiles is essential for creating sustainable and ecological textile products. This study aims to develop a novel, eco-friendly, phosphorus- and nitrogen-containing flame retardant known as ammonium phytate (AP), intending to improve the flame retardant properties of polyamide 6.6 (PA6.6) textiles. UV-induced grafting with 2-acrylamide-2-methylpropane sulfonic acid (AMPS) increases the surface functional groups of PA6.6 fabrics. Later, the surface-modified fabrics were coated with phosphorus-containing heteroatom-based components, namely, sulfur, nitrogen, silicon, and boron, onto a single flame retardant system via layer-by-layer (LBL) deposition of positively charged chitosan/boron drop (3-aminopropyl) triethoxysilane/silicon dioxide (CS/BAPTES/SiO2) sole solution and negatively charged AP solution to enhance superior hydrophilic and durable flame retardant performance. According to the data, a weight pick-up of 56.5% is attributable to only 4 BLs. However, all the flame-retardant-coated fabrics can completely stop the melting-dripping tendency and achieve B-3 to B-2 ratings after the UL-94 vertical burning test. In addition, the LOI values of treated fabrics increase from 18.5% to 23.5% compared to a pure sample. The AMPS grafted with a 4BL-deposited fabric sample exhibits a maximum decrease in peak heat release rate (PHRR) of more than 54%. Moreover, the thermogravimetric analysis (TGA) test reveals a significant increase in thermal stability and char yield. Additionally, the as-prepared phosphorus-containing heteroatom-based coatings impart a water contact angle value of approximately 0⁰ within 2 s, demonstrating that the treated fabrics exhibit superior hydrophilic performance. Moreover, using AMPS-grafted and only 2-BL-deposited treatments improves coating stability in washing and imparts durable flame retardancy that can resist up to 20 washing cycles. It is proposed that the sustainable phosphorus-containing heteroatom-based coating may be a potentially effective replacement for existing durable flame retardants routinely used in textile finishing operations.

The potential use of natural expanded perlite as a flame retardant additive for acrylonitrile‐butadiene‐styrene based composites

AbstractThis study aimed to reveal the effect of expanded perlite (EP) additive as a flame retardant for acrylonitrile‐butadiene‐styrene (ABS) copolymer based composites. Before composite preparation, fine powdered EP was characterized by Fourier transform infrared spectroscopy, x‐ray diffraction, thermogravimetric analysis, and scanning electron microscopic analyses. Also, maleic anhydride grafted ABS (MAH‐g‐ABS) with a grafting degree of 3.9 wt% was synthesized and used as a polymeric compatibilizer. ABS/EP composites with different ratios of EP were prepared by a continuous one‐step melt mixing method. Thermogravimetric and morphological analysis, tensile tests, limiting oxygen index (LOI) and UL‐94 vertical burning tests of the composite materials were investigated. EP significantly decreased the decomposition rate of ABS and promoted char formation. EP provided a UL‐94 V‐1 flammability rating with great fire resistance and self‐extinguishing properties to the ABS matrix without any melt dripping. The LOI of ABS was greatly improved, reaching a value of 28.5% by adding only 5 phr EP. Zinc borate (ZB) also played a significant role in enhancing thermal stability and flame retardancy by creating a good synergism with EP. The composite containing 5 phr ZB showed a flame retardant grade of UL‐94 V‐0 and an LOI value of 27.5%.Highlights Flame retardant ABS/EP composites were successfully prepared by melt mixing. The EP ratio of 10 phr provided the highest resistance to flammability. ZB showed good synergy with EP in enhancing the flame retardancy of ABS. ABS/EP10/ZB‐5 composite had a UL‐94 V‐0 rating with an LOI value of 27.0%. This study proved the potential use of natural EP as a flame retardant filler.

Enhancement of fire resistance and mechanical performance of polypropylene composites containing cellulose fibres and extracellular biopolymers from wastewater sludge

In the present research, a bio-based flame retardant (FR) was prepared using a biopolymer derived from wastewater sludge to improve the fire performance of polypropylene (PP). Extracellular polymeric substances (EPS), which were extracted from wastewater aerobic granular sludge, were absorbed into cellulose-based fibres, such as flax and toilet papers. Thermogravimetric analysis results indicated that the EPS-cellulose fibres played a significant role in enhancing the char formation of PP composite. Furthermore, the incorporation of the bio-based FR into PP restricted its vertical burning characteristics, and at the same time enhanced the tensile moduli of the composites. The reaction between phosphoric acids from EPS and hydroxyl groups of cellulose fibres improved dehydration and char formation of the composites to enhance the overall fire reaction properties. This study opens up new possibilities for the wastewater-derived biopolymer “EPS” to prepare the bio-inspired FRs for cellulose-based fibres and composites, and enhance sustainability of wastewater sludge treatment.

Preparation of novel hollow metal organic framework for enhancing flame retardancy of paraffin/EP thermal energy storage materials

AbstractParaffin is a potential thermal energy storage material, but leakage and flammability are the two major problems affecting its storage and safe use. Here, a novel flame retarded paraffin/epoxy resin composite was developed by using paraffin, epoxy resin and hollow metal organic framework (W‐UiO66‐PPA) as thermal energy storage material, supporting material and flame retardant, respectively. The thermal energy storage and flame retardancy performances were examined with differential scanning calorimetry, vertical burning, limiting oxygen index and cone calorimeter tests. The results show that the paraffin/epoxy resin retains intact without leakage when the content of paraffin reaches 40 wt%, and this material exhibits high melting latent heat and remarkable thermal recycling property. In addition, the flame retarded paraffin/epoxy resin shows excellent flame retardancy, which is attributed to the following three aspects: (1) the hollow structure with open vertices of W‐UiO66 is capable of absorbing and collecting the combustible gasses produced by the combustion of epoxy resin; (2) the Zr and W elements of W‐UiO66 can facilitate catalytic charring and form a dense char layer; (3) phosphorous‐containing free radicals are able to capture OH· and O· free radicals during the combustion of paraffin and epoxy resin, thus interrupting the combustion chain reaction. On the whole, the flame retarded paraffin/EP possesses excellent thermal energy storage, thermal recycling, and flame retardancy properties. Our work provides a fantastic inspiration for the rational design of other flame retarded form‐stable phase change materials.

Expandable graphite embedded in flexible polymer surfaces for fire detection in multiple modes

AbstractFire detection sensors are a necessary facility to ensure fire safety. The long fire response time and the false fire alarms caused by a single fire response mode are urgent problems for fire detection sensors. Here, a strategy of embedding expandable graphite (EG) in the sample surface of a styrene‐butadiene‐styrene block copolymer/intumescent flame retardant is used to endow the sample with fire detection in multiple modes and early warning functions, thus shortening the fire warning time and preventing the false fire alarms. The EG improved the flame retardancy of the samples from failing to V‐0 in the vertical burning rating test. The EG also gave the samples the ability to sense tensile and bending deformation. The negative temperature effect of the EG resistance gave the sample an early warning capability for fires with warning temperatures as low as 200°C. The rapid expansion of EG exposed to flame into graphite worms was used for the rapid response of the sample to fire (response time < 1 s). The Seebeck effect with response voltage of up to 0.3 V was used for fire detection of samples based on the temperature difference of EG on the sample surface caused by the flame. This study has potential application prospects for rapid fire warning in buildings.

Study on the Flame Retardancy of Rigid Polyurethane Foam with Phytic Acid-Functionalized Graphene Oxide.

A rigid polyurethane foam (RPUF) composite was prepared by compounding phytic acid (PA)-functionalized Graphite oxide (PA-GO) with flame-retardant poly (Ammonium phosphate) (APP) and expandable graphite (EG). The effects of PA-GO on the thermal, flame-retardant, and mechanical properties of RPUF were studied using a thermogravimetric analyzer, a limiting oxygen index (LOI) tester, a UL-94 vertical combustion tester, a cone calorimeter, scanning electron microscopy, and a universal tensile testing machine. The results indicated that there was a significant synergistic flame-retardant effect between PA-GO and the intumescent flame retardants (IFR) in the RPUF matrix. Compared with RPUF-1, the addition of 0.3 wt% PA-GO could increase LOI from 25.7% to 26.5%, increase UL-94 rating from V-2 to V-0, and reduce the peak heat release rate (PHRR) and total heat release rate (THR) by 28.5% and 22.2%, respectively. Moreover, the amount of residual char increased from 22.2 wt% to 24.6 wt%, and the char layer was continuous and dense, with almost no holes. Meanwhile, the loss of mechanical properties was apparently lightened.

Multifunctional design integrating the flame-retardant and antifouling functionality into superhydrophobic cotton fabric

Here, we construct a stable flame-retardant superhydrophobic cotton fabric (FRS-CF) via simple impregnation method. The firstly deposited ammonium polyphosphate/zinc borate (APP/ZB) and silicon dioxide form an inorganic hierarchical structure, which not only endow the fabric with flame retardancy, but also provide appropriate roughness for the construction of superhydrophobicity coating. The latter deposited polydimethylsiloxane function as low surface energy materials to achieve the superhydrophobic performance, and the added epoxy resin could strongly increase the overall mechanical stability of the coating through providing interfacial adhesion. Importantly, the hierarchical micro-sized structure generated by the deposition of APP/ZB can supply particular protection for the constructed superhydrophobic coating from flame. Thus, the modified cotton fabric can self-extinguish during vertical combustion and display excellent flame retardancy with oxygen limitation index above 30 %. Additionally, the coating shows excellent water repellency, self-cleaning, anti-fouling properties and oil-water separation to a variety of liquids. The constructed coating holds durable flame-retardant and robust mechanical stability. After cycled friction test, the FRS-CF still maintains excellent superhydrophobicity and the oxygen limitation index remains above 30 %. We believe that the design of robust superhydrophobic/flame-retardant coating may advance the development of flame-retardant cotton fabric and provide new possibilities for the practical application of superhydrophobic coating.

Effect of Al‐based metal‐organic frameworks/halloysite nanotubes on the flame retardancy of silicone rubber foam

AbstractTwo kinds of Al‐based metal‐organic frameworks (Al‐MOFs), MIL‐53(Al), and MIL‐96(Al), were synthesized by the solvothermal method and then characterized using SEM, XRD, and FTIR. The Al‐MOFs and halloysite nanotubes (HNTs) were blended and added to silicone rubber foams (SiFs). The mechanical properties and flame retardancy of the composites were tested and analyzed using universal tensile tester, limiting oxygen index (LOI), vertical combustion tester, cone calorimeter, TG, SEM, EDS, and FTIR. The results show that Al‐MOFs synthesized by the solvothermal method have high crystallinity and purity. Compared with pure SiFs, the LOI of SiFs with 2 wt% MIL‐53(Al) and 2 wt% HNTs increased to 29.4%, while total heat release and total smoke release decreased by 36.9% and 32.4%. The flame retardant mechanism of the composites is mainly reflected in the condensed phase. MIL‐53(Al) and HNTs can synergistically promote the formation of a dense carbon layer, blocking heat and oxygen from entering the SiFs matrix.

Low‐flammability epoxy resins with short solidification time and good mechanical properties

AbstractA novel fire‐resistant epoxy resin (EP) material has been prepared using EP, 9, 10‐dihydro‐9‐oxa‐10‐phosphaphenanthrene‐10‐oxide (DOPO), maleic anhydride, and 2‐aminobenzothiazole. Maleithiazolephosphaphenanthrene (MSD) was synthesized and its chemical structure was characterized using infrared spectroscopy (IR) and nuclear magnetic resonance (NMR). Fire‐resistant additive MSD was introduced into EP. The flammability and mechanical properties of the modified EP materials were then investigated using limiting oxygen index (LOI), UL‐94 vertical burning, cone calorimeter (CC), tensile, three‐point bending, and izod unnotched impact tests. EP blend containing 4%MSD displayed a UL‐94 V‐0 rating and an LOI value of 32.2%. Heat release and smoke release determined using cone calorimeter for the sample containing 4% MSD were lower than the sample of EP alone. Further, introduction of 4% MSD to EP material improved its izod impact, tensile strength, and flexural strength by 13.3%, 13.9%, and 21.6%, respectively. Inferences for the mode of fire‐resistant action were available from MSD, XPS, SEM, Raman, and Py‐GC/MS. MSD has a positive effect on fire resistance in both the condensed phase and gas phase.Highlights A novel flame‐retardant (MSD) was synthesized. MSD endowed EP with excellent fire safety and improved mechanical properties. MSD shortened solidification time of EP during preparation. MSD plays a flame‐retardant role in both condensed and gaseous phases.

Construction of a durable superhydrophobic flame-retardant coating on the PET fabrics

In order to meet the increasing demand for fire prevention and pollution prevention of polyester fiber fabrics (PET) in different scenes, it is imperative to develop surface coatings with superhydrophobic and flame retardant properties. However, how to realize all these functions at the same time is still a big challenge. In this work, fluorinated PDMS was obtained through the cross-linking reaction between fluorosilane and PDMS, which was evenly mixed with the combustion product of silicone rubber (mainly composed of SiO2) and ammonium polyphosphate (APP), and the mixed coating was deposited on the surface of PET fabrics by spraying method to construct a superhydrophobic flame-retardant coating. The coated fabrics shows good superhydrophobicity (water contact angle is 155.61 ± 1.42°, sliding angle is 3.2 ± 0.4°) and self-cleaning performance. In particular, the prepared coated fabrics also has excellent mechanical durability, and it still does not lose its superhydrophobicity after 10 abrasive paper rubbing cycles, 60 min washing and even 300 bending and twisting cycles. In addition, compared with the original fabrics, the coating shows excellent flame retardant performance, which can realize self-extinguishing within 10 s in vertical combustion experiment.

A versatile, highly effective intumescent flame-retardant synergist for polypropylene and polyamide 6 composites

A novel phosphorus-based macromolecular flame-retardant synergist named DPS was designed and synthesized via three steps from 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO), dihydroxybenzophenone (DHBP) and pentaerythritol (PER). The prepared synergist was used in combination with a base flame-retardant (melamine-coated ammonium polyphosphate (APP-M), or aluminum diethylphosphinate (ADP)) to create novel binary intumescent flame retardant (IFR) systems for polypropylene (PP) and polyamide 6 (PA6) matrices. The structure of DPS was characterized by fourier transform infrared (FTIR), phosphorus nuclear magnetic resonance spectroscopy (31P NMR) and gel permeation chromatography (GPC) analysis. The thermal stability and combustion behaviors of the flame-retardant polymer composites were investigated by thermogravimetric analysis (TGA), limiting oxygen index (LOI), UL-94 vertical burning tests. It was found that with a low fraction of DPS (20–25 wt%), the developed binary IFR systems significantly enhanced the flame-retardant performance of both PP and PA6. The results indicate that owing to the rich phosphorus content and abundant aromatic structures, DPS has synergistic actions with the base flame retardants to scavenge free radicals and promote char formation in the gaseous and condensed phases, respectively. Additionally, the mechanical properties of the PP composites were also evaluated, revealing the mechanical reinforcement effect of the binary IFR, i.e., simultaneous improvement of tensile modulus, ultimate tensile strength and impact toughness. This further demonstrates the effectiveness of the developed IFR formulations in terms of well-balanced flame-retardant performance and mechanical properties.

Freeze-casting production of thermal insulating and fire-retardant lightweight aerogels based on nanocellulose and boron nitride

Cellulose aerogels exhibit biocompatibility and biodegradability, rendering them promising candidate for application in building energy conservation and insulation materials. However, the intrinsic inflammability of pristine cellulose aerogel causes unneglectable safety concerns, hindering their application in energy-efficient buildings. Herein, a thermal insulating, fire-retardant, strong, and lightweight aerogel was produced via freeze-casting suspensions of cellulose nanofibril (CNF) and l-glutamine functionalized boron nitride nanosheets (BNNS-g). The aerogel with a BNNS-g:CNF concentration ratio of 15:5 exhibited outstanding mechanical strength owing to the strong interaction between BNNS-g and CNF as well as satisfactory thermal insulating performance (0.052 W/m·K). Particularly, this aerogel showed excellent fire-retardant and self-extinguishing capabilities in the vertical burning test, which remained unscathed after over 60 s of burning in a butane flame. Further, the limit oxygen index (LOI) of this aerogel was 36.0 %, which was better than the LOIs of traditional petrochemical-based insulating materials. This study provides a promising strategy for producing aerogels with excellent properties using cellulose and other inorganic nano-fillers.

The coating based on phenolic resin gives rigid polyurethane foam excellent flame retardant properties

AbstractA flame retardant coating was designed and synthesized using phenolic resin (PF), 9,10‐dihydro‐9‐oxa‐10‐phosphazephenanthrene‐10‐oxide (DOPO), and nano‐SiO2 as raw materials. The coating is applied to the surface of rigid polyurethane foam (RPUF) to give it a flame retardant effect. Based on the excellent adhesion of PF, the coating effectively suppresses heat transfer, and the synergistic effect of DOPO and nano‐SiO2 improves the flame retardancy of RPUF. In addition, vertical combustion experiments have shown that when the ratio of DOPO to nano‐SiO2 is 2:1, there is no dripping, the flame is self‐extinguishing, and the internal structure remains basically unchanged, resulting in the best flame retardant effect. The cone calorimetric test shows that the coating can effectively reduce the total heat release and heat release rate of the substrate, and the smoke release rate and total smoke release data show that its smoke suppression effect is significantly improved. Thermogravimetric analysis shows that the coating can effectively improve the residual carbon rate of RPUF, and its mechanical properties are good. This study confirms that coatings based on PF/DOPO/Nano‐SiO2 can effectively improve the flame retardancy of RPUF, providing a potential direction for the development of green insulation materials.

Electrolytic manganese residue to metal phosphides via ball milling: Enhancing flame retardancy, mechanical properties, and electrical conductivity of epoxy resin

Landfill or open-air stacking of waste electrolytic manganese residue (EMR) poses environmental pollution risks due to the presence of harmful substances. EMR contains SiO2, Al2O3, and Fe2O3, which offer resource utilization and flame retardancy potential. A ball milling-based surface treatment strategy was proposed to modify EMR by incorporating red phosphorus (RP) and graphitic carbon nitride (g-C3N4), resulting in flame retardant EMR-PCN containing metal phosphides. Adding EMR-PCN to epoxy resin (EP) enhanced the flame retardancy of EP, addressing its inherent fire hazard. The EP composite incorporating 5 wt% EMR-PCN (EP/5EMR-PCN) demonstrated a limiting oxygen index of 33.0% and achieves V-0 level in vertical combustion test. Compared to EP, EP/5EMR-PCN showed significant reductions in peak heat release rate (65.3%), total heat release (62.2%), total smoke production (40.7%), and average CO yield (53.8%). Notably, EP/5EMR-PCN achieves a Flame Retardancy Index of 8.37, outperforming most g-C3N4-based flame retardants. Besides, increased hydrophobicity optimized the storage of EMR-PCN. Improved compatibility of EMR-PCN with EP enhanced its mechanical properties. Additionally, volume and surface resistance reductions in EP/5EMR-PCN mitigated static cumulative effects, expanding its application potential.

Facile Synthesis of Melamine/G-C3N4 Covalent Organic Framework (COF) by Indirect Intercalation and Its Flame Retardant

In this paper, a covalent organic framework (COF) based on g-C3N4 was designed firstly. The COF is arranged through an indirect interrelation method among melamine and g-C3N4. During the reaction, Cu2+ was used to expand the layer space of g-C3N4. The as-prepared COF were characterized by SEM, TEM, FTIR, and XRD. The obtained product is a melamine interrelation g-C3N4 composite material (MCN) with COF structure. The MCN was used as flame retardant for cable sheath material. The thermal stability, thermal shrinkage, oxygen record and vertical burning of link sheath material contain MCN were tested. The results showed that the MCN flame retardant increases the thermal stability time of the sheath material from 89 min to 131 min, and the thermal shrinkage rate diminished from 4.17% to 2.00%. The LOI is 29.5, and the flame retardant grade reaches UL-94 V-0. The SEM analysis of the carbon residue of the cable sheath material after burning, it was found that the state of the carbon layer of the link sheath material transform into a thick honeycomb structure by the impact of the MCN flame retardant, which forestalls the dispersion of oxygen and burnable gases, in this way hindering the transmission of flame.

Effect of polycarbonate‐polydimethylsiloxane block copolymer and two commercial toughening agents on the flame retardancy and smoke emission of rigid polyvinyl chloride

AbstractIn this work, different test methods were used to investigate the flame retardancy and smoke emission of polyvinyl chloride (PVC) toughened with polycarbonate‐polydimethylsiloxane block copolymer (PC‐b‐PDMS) and two other commercial toughening agents. The oxygen index result and heat release curves in the cone calorimetry test showed that toughened PVC has reduced flame retardancy compared to unmodified PVC. However, the vertical combustion test showed that all samples have achieved the highest flame retardant rating, indicating that the flame resistance of these toughened PVC is still adequate for use. In terms of smoke emission, the results of the cone calorimetry test and the smoke density test showed a significant difference. In the smoke density test, it was found that PVC toughened with PC‐b‐PDMS has less smoke generation in the early stage of combustion. In the cone calorimetry test, the total smoke production was lower for PVC and significantly higher for toughened PVC. This difference was mainly due to the different test conditions of these two tests.

Biomass‐functionalized graphene oxide toward waterborne polyurethane composite with enhanced flame retardancy and hydrophobicity

AbstractIn this study, phytic acid‐polydopamine functionalized GO (GO@PA@PDA) was first synthesized. The DOPO derivatives, hydroxyl‐terminated polydimethylsiloxane (PDMS) and GO@PA@PDA were incorporated into waterborne polyurethane (WPU) by in situ polymerization. The chemical structure of GO@PA@PDA was characterized by Fourier transform infrared spectroscopy, Raman spectroscopy, X‐ray diffraction, ultraviolet–visible (UV–vis) spectroscopy and scanning electron microscopy. A cone calorimeter test and a universal testing machine investigated the flame retardancy and mechanical properties of GO@PA@PDA modified waterborne polyurethane (GPD‐WPU). The results showed that the incorporation of GO@PA@PDA into WPU significantly enhanced the flame retardancy by reducing the heat release rate, total heat release, smoke production rate, and total smoke production. Furthermore, the mechanical properties of the GPD‐WPU composite films increased with the dosage of GO@PA@PDA from 0 to 2.0 wt%, and decreased slightly afterward. The contact angle and atomic force microscope measurements showed that the addition of GO@PA@PDA increased the surface roughness of GPD‐WPU composite film, thereby improving the hydrophobicity of GPD‐WPU composite films. Afterward, GPD‐WPU as a finishing agent was coated on polyester fabric. The experimental results of limiting oxygen index (LOI) and the vertical burning test indicated that when the dosage of GO@PA@PDA was 2.5 wt% in GPD‐WPU, after‐flame time, after‐glow time, damage length and LOI value of the coated polyester fabric were 2.9 s, 0 s, 6.8 cm, and 28.6%, respectively.

Preparation of Porous Silver Nanowires‐Melamine Formaldehyde Hybrid Composite Materials and Their Electromagnetic Shielding and Flame‐Retardant Properties

Along with the booming development of communication technology and electronic equipment, higher requirements of flame‐retardant and EMI shielding performances for electromagnetic interference (EMI) shielding materials are put forward. Herein, the ultralight and porous silver nanowires (AgNWs)‐melamine formaldehyde (MF) hybrid composite with unique micro‐/nanostructure is developed by a facile dip‐coating method, which uses the AgNWs as 1D conductive coating and MF foam (MF foam) as 3D skeleton template. Benefiting from the unique porous micro‐/nanostructure, the resultant hybrid composite displays low density, excellent EMI shielding performances, and superior flame‐retardant property. The EMI shielding effectiveness (SE) and specific EMI SE (SSEt) of the hybrid composite in X‐band (8.2–12.4 GHz) can be up to 77 dB and 26971.4 dB cm−2 g−1, respectively. At the same time, the hybrid composite also passes the vertical burning test and shows an increased LOI value of 40.6%. The combination of flame‐retardant and EMI shielding performances for EMI shielding materials makes the AgNWs‐MF hybrid composite great application potential in civil and military fields. This work provides a new guide for the design of multifunctional high‐performance EMI shielding materials.

A phosphorus/silicon‐containing flame retardant based on eugenol for improving flame retardancy and smoke suppression of epoxy resin

AbstractEpoxy resin (EP) has excellent comprehensive properties, but its inherent flammability limits its further application in high‐end industries. The present study focuses on the preparation of an efficient phosphorus/silicon‐containing flame retardant for improving the flame retardancy and smoke suppression of EP. The intermediate product ED was first obtained by the addition reaction of 9,10‐dihydro‐9‐oxa‐10‐phosphaphenanthrene‐10‐oxide (DOPO) with eugenol, and then the target flame retardant DPSi‐ED was synthesized by the Williamson etherification reaction between ED and dichlorodiphenylsilane. The flame retardant was further incorporated into EP/4,4′‐diaminodiphenylmethane (DDM) system to prepare the modified epoxy thermosets. The flame‐retardant performance and mechanism were investigated by limiting oxygen index (LOI) test, vertical combustion test, cone calorimetry, thermogravimetric analysis‐infrared spectroscopy (TG‐IR), and so forth. At the same phosphorus content (0.5 wt%), EP/DPSi‐ED thermosets exhibited superior flame‐retardant properties to EP/ED thermosets. Moreover, EP/DPSi‐ED7 achieved a LOI of 35.3% and V‐0 rating in UL‐94 testing, and compared to EP/ED7, its peak heat release rate (pHRR) and total smoke production (TSP) were reduced by 31.5% and 10.9%, respectively. The phosphorus and silicon elements synergistically contributed to the formation of a stable char layer, which acted as a physical barrier to effectively enhance the flame‐retardant properties of the thermosets. Meanwhile, the incorporation of DPSi‐ED containing flexible SiO bonds and rigid DOPO groups to some extent also improved the mechanical properties of the cured EP. Hence, this study provides an effective strategy for the preparation of bio‐based phosphorus/silica‐containing high‐efficiency and smoke‐suppressing flame retardants.