Synergistic Flame-retardant Mechanism Research Articles

DOPO chemically modified mesoporous silica composites: Preparation, flame retardancy, and thermodynamic properties

AbstractOrganic flame retardant 9,10‐dihydro‐9‐oxa‐10‐phosphaphenanthrene‐10‐oxide (DOPO) was used to decorate the pores of mesoporous silica (m‐SiO2) nanospheres to prepare a new composite flame retardant (DK‐SiO2). The content of DOPO in DK‐SiO2 is about 17 wt%. Due to the chemical bonding, DK‐SiO2 not only enhances the flame retardant performance, but also effectively avoids adverse effects of DOPO on the glass transition temperature and mechanical properties of epoxy resin (EP). At 9 wt% loading, the limiting oxygen index of the EP increased from 25.7 to 31.2, and successfully passed the UL‐94 V‐0 rating. Besides, DK‐SiO2 can significantly reduce the peak heat release rate, total heat release, and total smoke production of EP, with reductions of 26%, 32%, and 20.8%, respectively. Compared with the simple blended sample, DK‐SiO2 not only has better flame retardant performance but also shows significant advantages in thermodynamic properties. The glass transition temperature, impact, and tensile strength, as well as storage and flexural modulus have been improved. This excellent flame retardant performance is mainly attributed to the gas‐condensed synergistic flame retardant mechanism between DOPO and m‐SiO2. The good thermodynamic performance is due to the excellent dispersion of DK‐SiO2 nanospheres in the EP.

Preparation and properties of phosphorus-containing thermotropic liquid crystal copolyester fibers with excellent flame retardance and mechanical property

In order to acquire polymeric fibers have both excellent flame retardance and mechanical properties, high molecular weight phosphorus-containing liquid crystal copolyesters derived from 6-hydroxy-2-naphthenic acid (HNA), terephthalic acid (TA) and 10-(2,5-dihydroxypheny)-10-hydro-9-oxa-10-phospha phenanthrene-10-oxide (DOPO-HQ) were synthesized via “one-pot” melt polymerization, and then the fibers were obtained by melt spinning method. The structure and property of the copolyesters were studied elaborately by experimental characterization technique and molecular simulation method. Shear shinning behavior was observed from rheology measurement, indicating that the copolyesters had excellent melt fluidity and spinnability. The rigidity of molecular chain was efficiently improved by the phosphorus-containing monomer DOPO-HQ and naphthalene HNA units which could be reflected by the molecular simulation results as well as high Tg values. The flame retardant mechanism of the phosphorus-containing flame retardant copolyester was systematically studied via limiting oxygen index (LOI), vertical burning (UL-94) test, cone calorimetry, scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The results showed that the copolyesters exhibit synergistic flame retardant mechanism of gas phase and condensed phase. Meanwhile, mechanical property of the as-spun fibers could be significantly improved by increasing the spinneret draw ratio (SDR) attributed to high molecular chain orientation. The maximum tensile strength of the as-spun fiber was 0.77 GPa observed for P-HNA60P20 at a relatively low SDR of 29. It was shown the unique combination of good thermal stability, spinnability as well as mechanical and flame retardant properties of the copolyesters would make them could be used as high-performance flame retardant materials.

Preparation of phosphorus-containing organic-hybrid layered double hydroxide as a flame retardant for thermoplastic polyurethane

Developing polymers with both flame-retardant and smoke-suppressing properties is a great challenge in the field of fire-safety thermoplastic polyurethane (TPU). This study involved synthesizing a synergistic organic-hybrid layered double hydroxide (O-LDH) and phosphorus/nitrogen-containing substance (PD) inspired by the observed synergistic effect between them. The incorporation of PD significantly enhanced the flame-retardant properties of TPU in conjunction with cobalt/aluminum- layered double hydroxide. The composite containing 10 wt% O-LDH achieved a limiting oxygen index of 26.5% and met the vertical burning V-0 rating. Moreover, the heat and smoke release were decreased compared to pure TPU in cone calorimeter tests. The systematic characterization of the synergistic flame-retardant mechanism emphasized the crucial contribution of cobalt and phosphorus species in catalyzing charring effects, resulting in the compact and highly carbonized char layer in the condensed phase. The incorporation of the hybrid flame retardant significantly enhanced the advancement of the flame-retardant TPU materials.

Noncombustible gel polymer electrolyte inspired by bio-radical chemistry for high voltage and high safety Ni-rich lithium batteries

For high energy density lithium-ion batteries (LIBs) with nickel-rich ternary cathodes, the chemical degradation of electrolytes caused by free radical reactions and the hazards of thermal runaway have always been significant challenges. Inspired by the free radical scavenging of living organisms and multiphase synergistic flame retardant mechanism, we innovatively designed and prepared a multifunctional flame retardant HCCP-TMP that combines flame retardancy and free radical scavenging by combining hindered amine and cyclophosphazene. Only 1 wt% HCCP-TMP can make the polyacrylate-based gel polymer electrolyte (GPE) incombustible. Moreover, the equipped NCM811//Graphite pouch cells don't exhibit combustion behavior after thermal runaway and can resist mechanical abuse. Based on the above noncombustible GPE, the NCM811//Li battery exhibits capacity retention rate of 82.2 % after 100 cycles at a current density of 2 C and in the voltage range of 3.0–4.7 V, exhibiting excellent cyclability under high voltage. This simple molecular design simultaneously improves the fire safety and high voltage stability, demonstrating enormous application potential in the field of advanced LIBs with high safety and high energy density.

Real-time monitoring of charcoal layer resistance for investigating the synergistic flame retardant mechanism of zinc oxide and intumescent flame retardants in SBS

Metal oxides as synergists of intumescent flame retardant (IFR) lead to an extremely complex formation process of intumescent char layers. The lack of means to detect the evolution of the char layer in real time makes it challenging to investigate the synergistic flame retardant mechanism between metal oxides and IFR. Herein, an innovative method of detecting real-time changes in the resistance of the char layer under flame ablation is used to investigate its changes in morphology, thus assisting in revealing the synergistic flame retardant mechanism of zinc oxide (ZnO) in IFR/SBS. ZnO showed a significant synergistic flame retardant effect with IFR without MEL and no synergistic effect with MEL-containing IFR. The analysis of the char layer structure revealed that ZnO played a role in promoting gas release and char layer formation and increasing the viscosity of the molten char layer regardless of the presence or absence of MEL.The difference in the morphology of the char layer could not reveal the experimental phenomenon that there is no synergistic flame retardant effect between ZnO and MEL-containing IFR. The analysis of the real-time resistance of the charcoal layer reveals that ZnO achieves its synergistic flame retardation with the MEL-free IFR by increasing the expansion of the charcoal layer at the initial stage of its formation. For MEL-containing IFR, 0.5% ZnO inhibits the rupture of the char layer by promoting its formation in the early stages of ablation, and 1% ZnO leads to the rupture of the char layer instead, due to the promotion of gas release. Excess ZnO (2%) caused pyrolysis gases to escape from the voids of the char layer rather than allowing it to expand. The analysis of the real-time resistance of the charcoal layer can help to accurately reveal the flame retardant mechanism.

Biomimetic Multifunctional Graphene-Based Coating for Thermal Management, Solar De-Icing, and Fire Safety: Inspired from the Antireflection Nanostructure of Compound Eyes.

Due to the ubiquitous and inexhaustible solar source, photothermal materials have gained considerable attention for their potential in heating and de-icing. Nevertheless, traditional photothermal materials, exemplified by graphene, frequently encounter challenges emanating from their elevated reflectance. Inspired by ocular structures, this study uses the Fresnel equation to enhance the photo-thermal conversion efficiency of graphene by introducing a polydimethylsiloxane (PDMS)/silicon dioxide (SiO2) coating, which reduces the light reflectance (≈20%) through destructive interference. The designed coating achieves an equilibrium temperature of ≈77°C at one sun and a quick de-icing in ≈65 s, all with a thickness of 5µm. Simulations demonstrate that applying this coating to high-rise buildings results in energy savings of ≈31% in winter heating. Furthermore, the combination of PDMS/SiO2 and graphene confers a notable enhancement in thermal stability through a synergistic flame-retardant mechanism, effectively safeguarding polyurethane against high temperatures and conflagrations, leading to marked reduction of 58% and 28% in heat release rate and total heat release. This innovative design enhances the photo-thermal conversion, de-icing function, and flame retardancy of graphene, thereby advancing its applications in outdoor equipment, high-rise buildings, and aerospace vessels.

Eco-friendly preparation of advanced epoxy composites and their pyrolysis and flame retardant mechanisms

Traditional additive flame retardants pose issues including high dosage, easy precipitation, and poor compatibility with the matrix. Designing efficient organic-inorganic synergistic flame retardants can enhance the flame retardancy and mechanical properties of epoxy (EP) composites while reducing their smoke toxicity. In our study, we initially employed Tetrakis(hydroxymethyl)phosphonium sulfate (THPS) for intercalation modification of montmorillonite (MMT). Subsequently, we achieved a green and efficient exfoliation of MMT by reacting urea with hydroxyl groups, resulting in the simultaneous preparation of efficient organic/inorganic synergistic flame retardants (THPSU-MMT). EP composites containing 5wt% THPSU-MMT can attain UL-94 V0 classification. Furthermore, the peak heat release rate (PHRR), total heat release (THR), and peak release rates of CO can be reduced by up to 78.42 %, 62.26 %, and 72.50 %, respectively. Simultaneously, we systematically investigated the synergistic flame retardant mechanism of the EP composite. The findings reveal that THPSU-MMT exhibits a dual flame retardant effect in both the gaseous and condensed phases. Moreover, the combination of MMT and THPSU substantially enhances the presence of phosphorus-containing pyrolysis products in the condensed phase. The fire performance index (FPI) of the flame retardant EP increased from 0.05 m2/s/W in pure EP to 0.36 m2/s/W, attributed to the enhanced catalytic carbonization and assisted gas-phase free radical capture. Additionally, the flame spread index (FGI) decreased from 11.55 kW/m/s in pure EP to 1.18 kW/m/s, signifying a substantial enhancement in fire safety. Furthermore, the THPSU-MMT synergistic flame retardants improved the tensile strength of EP composites. This study offers an environmentally friendly and efficient approach for the effective exfoliation of MMT, while also presenting novel concepts for the design of efficient organic-inorganic synergistic flame retardants.

Calcium gluconate-based flame retardant towards simultaneously high-efficiency fire safety and mechanical enhancement for epoxy resin

Flame retardants containing biomass receive growing interest in environmental friendliness and sustainability but usually face the low flame-retardant efficiency and deterioration on mechanical property of matrix. Herein, a calcium gluconate-based flame retardant (CG@APP) was chemically prepared using calcium gluconate (CG) and ammonium polyphosphate (APP) via ion exchange reaction, and enabled the excellent fire safety and mechanical enhancement for epoxy resin (EP). The resulted EP composites containing 6 wt% CG@APP (EP/CG@APP6) exhibited V-0 ratings in UL-94 test. Furthermore, with respect to EP/APP6, the peak of heat release rate (pHRR) and peak of smoke production rate (pSPR) of EP/CG@APP6 decreased by 70.5 % and 50.0 %, respectively. The well synergistic flame-retardant mechanism of CG@APP between gaseous and solid phases was revealed to generate denser and more continuous charring residuals, which could do well work on insulation for heat transfer and fuel diffusion. In addition, the shell rich in hydroxyl group and Ca2+ on the surface of CG@APP well enhanced the interface compatibility through the hydrogen bond and coordinated bond, thus the tensile strength, flexural strength and impact strength of EP/CG@APP6 increased by 18.2 %, 4.5 % and 9.1 % compared with pure EP, respectively. This work provided a simple and sustainable way to construct excellent fire-safety composites.

Balanced Thermal Insulation, Flame-Retardant and Mechanical Properties of PU Foam Constructed via Cost-Effective EG/APP/SA Ternary Synergistic Modification.

To address the challenge of balancing the mechanical, thermal insulation, and flame-retardant properties of building insulation materials, this study presented a facile approach to modify the rigid polyurethane foam composites (RPUFs) via commercial expandable graphite (EG), ammonium polyphosphate (APP), and silica aerogel (SA). The resulting EG/APP/SA/RPUFs exhibited low thermal conductivity close to neat RPUF. However, the compressive strength of the 6EG/2APP/SA/RPUF increased by 49% along with achieving a V-0 flame retardant rating. The residual weight at 700 °C increased from 19.2 wt.% to 30.9 wt.%. Results from cone calorimetry test (CCT) revealed a 9.2% reduction in total heat release (THR) and a 17.5% decrease in total smoke production (TSP). The synergistic flame-retardant mechanism of APP/EG made significant contribution to the excellent flame retardant properties of EG/APP/SA/RPUFs. The addition of SA played a vital role in reducing thermal conductivity and enhancing mechanical performance, effectively compensating for the shortcomings of APP/EG. The cost-effective EG/APP/SA system demonstrates a positive ternary synergistic effect in achieving a balance in RPUFs properties. This study provides a novel strategy aimed at developing affordable building wall insulation material with enhanced safety features.

Synthesis of aluminum bis(hydroxy‐phenyl‐methyl)phosphinate and its synergistic flame retardant mechanism in PLA

AbstractIn this paper, we report on the synthesis of a new aluminum bis(hydroxy‐phenyl‐methyl)phosphinate, AlBPi, under mild reaction conditions. The product structure was confirmed via characterization, and its thermal stability and flame retardant properties were assessed. To improve the flame retardant properties, we employed ammonium polyphosphate (APP) as a synergist with AlBPi. The PLA composite material containing 10% AlBPi and 5% APP achieved an LOI of 28.1% and a UL‐94 rating of V‐1. Cone calorimetry tests showed a significant reduction in PHRR, THR, PSPR, and TSP for the PLA/AlBPi/APP composite compared to the pure and PLA/AlBPi materials. SEM analysis revealed a continuous and dense char layer on the residual surface of the synergistic flame retardant sample. AlBPi and APP exhibited excellent synergistic flame retardant effects, with both releasing a large amount of PO·free radicals. APP was also able to release inert gas, exhibiting excellent flame retardant effects in the gas phase. Additionally, APP improved the charring performance of AlBPi and formed a compact char layer on the material surface, achieving good flame retardant effects in the condensed phase. Therefore, the AlBPi and APP synergistic flame retardant system can be considered a viable flame retardant additive for PLA.Highlights A novel flame retardant AlBPi was synthesized. AlBPi and APP demonstrate good synergistic flame retardant performance in PLA. AlBPi and APP play a flame retardant role in both gas and condensed phases.

Improving flame retardant and smoke suppression function of ethylene vinyl acetate by combining the piperazine pyrophosphate, expandable graphite and melamine phosphate

Ethylene vinyl acetate copolymer combined with the expandable graphite (EG), pyrophosphate piperazine (PAPP) and melamine polyphosphate (MPP) was adopted to prepare the flame retardant EVA (FREVA) composites by melt blending. The research results showed that the PAPP/EG/MPP mixture with a mass ratio of 2:2:1 presented the optimal flame retardant effect. With the 25 wt% additive amount, EVA composites passed UL-94 V-0 level (1.6 mm), and the limiting oxygen index (LOI) reached 35.2 %. The peak of heat release rate (PHRR), total heat release (THR) and total smoke release decreased by 67.6 %, 60.9 % and 67.4 %, respectively. The Fourier Transform Infrared Spectroscopy (FTIR), X-ray Photoelectron Spectra (XPS), scanning electron microscope (SEM), and thermal gravimetric analyzer (TGA) were used to research the synergistic effect flame retardant mechanism of PAPP, EG and MPP in combination with the FTIR spectrometer (TG-FTIR) and the cone calorimeter test (CCT). The polyphosphoric acid non-volatile substances generated by PAPP, attached to the surface of the EG carbon layer, effectively restrained the “popcorn effect”, and the char layer presented a compact and stable structure.

An amino trimethylene phosphonic acid‐based chelated boric acid complex that works as a synergistic flame retardant for enhancing the flame retardancy of cotton fabrics

AbstractThe chelating ligands of boric acid and amino trimethyl phosphonate prepared a novel flame retardant (BAP) for the cotton fabric. A stable chemical and coordination bond was formed on the surface of the cotton fibers by a simple three‐curing finishing process to make the fabric exhibits excellent durable flame retardancy. Cotton fabrics' tensile strength and whiteness got substantially retained after BAP treatment. 90 g/L BAP‐treated samples (3 curing times, 50 laundry cycles) showed good flame retardancy and durability, holding the largest limit oxygen index, 29.7%, and the shortest damage length, 61 mm. A condensed phase and gas phase synergistic flame retardant mechanism was concluded by thermogravimetric, cone calorimeter tests, and thermogravimetric infrared analysis.

Preparation and properties of flame retardant biobased polyamide elastomer with shape memory

AbstractNylon is the general name of high molecular polymers with amide bonds repeat structure in the main chain. Because of its good wear resistance, excellent chemical resistance and outstanding impact resistance, it is widely used in various fields of national life, such as automobile parts, oil pipelines, electronic parts, gears, connectors, coating materials and medical applications. Using isocyanate terminated polyamide prepolymer as hard segment, polypropylene glycol as soft segment and triethanolamine as crosslinking agent, polyamide elastomer was flame retardant modified by adding reactive P flame retardant and P/N synergistic flame retardant mechanism. The sample was named IAHDP‐x, in which IAHD is the synthetic hexamethylene diamine polyaitaconic acid, and x is the mass of the added flame retardant DDP. Its tensile properties, fatigue resistance, self‐recovery and tear resistance were investigated. The results revealed that the synthesized phosphorus flame retardant (9,10‐dihydro‐9‐oxa‐10‐[N,N‐bis‐(2‐hydroxyethylamino methylene)]‐10‐phenanthroline‐10‐oxide (DDP)) could not only enhance the flame retardancy, but also strengthen the mechanical properties of polyamide. Among them, the LOI and UL‐94 of IAHDP‐1.2 were 27.6% and V‐0, respectively, indicating that it could be used as flame retardant material; Cyclic tensile test demonstrated that it had good fatigue resistance and self‐recovery; Besides, the tear resistance of IAHDP‐1.2 could reach 35.24 kJ/m2. Interestingly, IAHDP‐1.2 also displayed shape memory characteristics, and the sample could be restored to its original state at 60°C. The synthetic IAHDP‐x also had excellent flame retardancy, high mechanical properties, fatigue resistance, tear resistance, shape memory, so the material can be used in satellite wings, solar panels, electronic and electrical equipment, and smart materials.

Boosting fire safety and mechanical performance of thermoplastic polyurethane by the face-to-face two-dimensional phosphorene/MXene architecture

• A black phosphorus-MXene@polydopamine nanohybrid was synthesized. • The TPU/BP-MXene@PDA nanocomposite simultaneously showed reinforcing and toughening effects towards TPU. • The TPU/BP-MXene@PDA nanocomposite could be achieved excellent thermal stability, mechanical properties and flame retardancy. • A synergistic flame-retardant mechanism between black phosphorus and MXene in the TPU were discussed and clarified. Black phosphorus (BP), as one of the most promising fillers for flame retarding polymer, has been seriously limited in practical application, due to the agglomeration and poor structural stability challenges. Here, the BP was modified by MXene and polydopamine (PDA) via ultrasonication and dopamine modification strategy to improve the structural stability and dispersibility in the matrix. Then, the obtained (BP-MXene@PDA) nanohybrid was employed to promote the mechanical performance, thermal stability, and flame retardancy of thermoplastic polyurethane elastomer (TPU). The resultant TPU composite containing 2 wt.% of BP1-MXene2@PDA showed a 19.2% improvement in the tensile strength and a 13.8% increase in the elongation at break compared to those of the pure TPU. The thermogravimetric analysis suggested that BP-MXene@PDA clearly enhances the thermal stability of TPU composites. Furthermore, the introduction of the BP-MXene@PDA nanohybrids could considerably improve the flame retardancy of TPU composite, i.e., 64.2% and 27.3% decrease in peak heat release rate and total heat release, respectively. The flame-retardant mechanisms of TPU/BP-MXene@PDA in the gas phase and condensed phase were investigated systematically. This work provides a novel strategy to simultaneously enhance the fire safety and mechanical properties of TPU, thus expanding its industrial applications.

Synergistic flame‐retardant effect of modified hydrotalcite and expandable graphite for silicone rubber foam

AbstractSilica gel‐coated hydrotalcite (LDHs) flame retardants (SiLDHs‐Ce) are prepared by the sol–gel method. The synergistic effect of SiLDHs‐Ce and expandable graphite (EG) on the silicone rubber foam (SRF) is studied through limiting oxygen index (LOI), Cone Calorimeter Test (CC), thermogravimetric infrared spectrometer (TG‐IR), and scanning electron microscopy. The results show that SiLDHs‐Ce and EG can improve the flame retardant properties of the SRF materials. The LOI value of the SRF material can reach 40.1% when the ratio of EG to SiLDHs‐Ce is 2:1, and the heat release rate (HRR) and total heat release (THR) are reduced by 66.60% and 52.76%, respectively, compared with the original. The minimum SPR of the SRF material is 0.010 m2 s−1 when 1 wt% SiLDHs‐Ce has been added. TG‐IR results show that the addition of EG and SiLDHs‐Ce increased the carbon residue rate of SRF materials. Results show that the residual carbon‐containing EG and SiLDHs‐Ce is denser. It is inferred that the synergistic flame retardant mechanism of SiLDHs‐Ce and EG on the SRF is mainly condensed phase flame retardant, augmented by gas‐phase flame retardant. The results of this study can provide guidance for the development of environmentally friendly silicone rubber foam.

Making polycarbonate flame retardant: Flame retardant selection and calorimetric analyses

Polycarbonate (PC) has been widely applied in aerospace and railway industries, and it is imperative to improve its fire safety related properties, especially heat release properties. Particularly, the MARHE value (maximum average rate of heat emission) directly obtained from the cone calorimeter (CONE) test is a comprehensive property that is presented in the EN45545-2 standard developed by the EU. In order to study the effect of flame retardants on the MARHE of polycarbonate, four flame retardants with different flame retardant mechanisms were used to prepare low heat release PC. CONE was used to characterize the heat release performance of PC, focusing on exploring the factors affecting MARHE and the method of preparing low heat release materials. The flame-retardant mechanism of PC was studied by SEM and TG/DTG. Meanwhile, the flame retardant index (FRI) is calculated as a reference for the flame retardant performance of PC. Results show the MARHE of HPCTP/PC is reduced by 31.12%, and it is confirmed that MARHE is influenced by time to ignition (TTI), peak heat release rate (PHRR), total heat release rate (THR), and the shape of the peak. Mica-RDP/PC materials were prepared based on the conclusions of MARHE derivation. RDP and Mica play a typical synergistic flame-retardant mechanism, with MARHE reductions from 20.31% to 20.00% of the single-component systems to 31.39%. All FRI values of PC materials are in the range of Good flame retardancy. This study provides a feasible way for the deep understanding and wide application of MARHE and the improvement of the fire safety performance of PC.

Reactive Flame-Retardant Cotton Fabric Coating: Combustion Behavior, Durability, and Enhanced Retardant Mechanism with Ion Transfer.

In recent years, we have witnessed numerous indoor fires caused by the flammable properties of cotton. Flame-retardant cotton deserves our attention. A novel boric acid and diethylenetriaminepenta (methylene-phosphonic acid) (DTPMPA) ammonium salt-based chelating coordination flame retardant (BDA) was successfully prepared for cotton fabrics, and a related retardant mechanism with ion transfer was investigated. BDA can form a stable chemical and coordination bond on the surface of cotton fibers by a simple three-curing finishing process. The limiting oxygen index (LOI) value of BDA-90 increased to 36.1%, and the LOI value of cotton fabric became 30.3% after 50 laundering cycles (LCs) and exhibited excellent durable flame retardancy. Fourier-transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM) methods were used to observe the bonding mode and morphology of BDA on cotton fibers. A synergistic flame-retardant mechanism of condensed and gas phases was concluded from thermogravimetry (TG), cone calorimeter tests, and TG-FTIR. The test results of whiteness and tensile strength showed that the physical properties of BDA-treated cotton fabric were well maintained.

A novel lanthanum‐based phosphorus‐containing flame retardant agent and its application in polylactic acid

AbstractCurrently, intumescent flame retardants (IFR) are often used in the flame retardant modification of polylactic acid (PLA). Due to the high loading, it will weaken the mechanical properties of PLA. In this study, lamellar lanthanum‐based DOPO derivative (La@DDP) is prepared by solution method, and it acts as a flame retardant agent was added into PLA with IFR. The results show that PLA composite passes the UL94 V‐0 rating with a limiting oxygen index (LOI) of 32.0, in the addition of 4.5 wt% IFR and 1.5 wt% La@DDP. Moreover, the peak heat release rate (PHRR) and total heat release (THR) of the PLA composite reduces by 31.0% and 23.2% compared to pure PLA, respectively. IFR/La@DDP agents assign the PLA composite with excellent thermal stability and carbon‐forming ability. Through the analysis of residual char, the synergistic flame retardant mechanism between IFR and La@DDP in PLA composite is discussed. Notably, the tensile strength and elongation at break of the PLA composites are only reduced by 4.03% and 9.51% compared to pure PLA. This work provides a novel lanthanum‐based flame retardant agent for designing PLA composites with good fire safety and mechanical properties, and it will broaden the application range of PLA.

Preparation and performance of nitrogen–phosphorus–silicone-containing flame retardant UV–curable coatings with high transparency

UV-curable transparent silicone-modified flame retardant materials are highly desired because they usually serve as protecting polymer matrix from moisture, ionic contaminants and particulates in vast fields such as coatings, electronic devices attributed to their merits such as high flame-retardant efficiency, high curing efficiency and low volatile organic chemical emissions. In this paper, nitrogen–phosphorus–silicone-containing flame retardant UV-curable coatings were prepared from nitrogen–phosphorus–silicone-containing acrylate and thiol-containing silicone hyperbranched polymers by UV initiated thiol-ene click reaction. It shows that these coatings were with fairly high transmittance, pencil hardness and initial decomposition temperature (Td5) of 80.7–96.9 % (400–800 nm), 9H, and 159–185 °C, respectively. Vertical burning behavior of the UV-curable coatings prepared with different acrylate derivatives was investigated and the self-extinguish time for the coatings prepared from POPHA was about 9 s. To make clear of the flame retardant mechanism, cone calorimetric test and XPS spectra of UV-curable coatings, and SEM images for the surface morphology of the chars were carried out. SEM images of the chars show that there is fine and dense white SiO2 “in-situ” generated during the course of combustion spreading on the surface. It also shows that honeycombed-like structures attributed by nitrogen and phosphorus form a quite good barrier to heat, oxygen and other flammable gas. Therefore, a ternary synergistic flame retardant mechanism of phosphorus, nitrogen and silicone elements in the UV-curable coatings was proposed. This work denotes that it is a good method to develop nitrogen–phosphorus–silicone-containing flame retardant transparent UV-curable materials.

Mechanically Reinforced Flame-Retardant Epoxy Resins by Layered Double Hydroxide In Situ Decorated Carbon Nanotubes

Epoxy resins (EPs) are widely used as structural materials in airplane compartments due to their lightweight merits and corrosion resistance. However, the flammability of polymers necessitates the exploration of high-performance flame retardants to improve aircraft fire safety. In this study, an in situ composite structure of layered double hydroxides (LDHs) and carbon nanotubes (CNTs) is constructed via a one-pot strategy in which LDH nanosheets are grown in situ on the skeleton of interwoven CNTs. The composite structure of LDH–CNTs acts as a mechanical support to further accommodate nanoparticles of 9,10-dihydro-9-oxa-10-phosphorus-10-oxide (DOPO) to obtain the flame retardant LDH–CNTs–DOPO. The in situ composite structure of LDH–CNTs realizes the uniform dispersion of the nanoscale flame-retardant components in the polymer substrate and endows the flame-retardant-treated EP substrate with both desirable mechanical strength and flame retardancy. Notably, the total heat release and smoke release of the flame-retardant composite EP@LDH–CNTs–DOPO are reduced by 19.0 and 25.56%, respectively, relative to those of neat EP, and a limiting oxygen index (LOI) of 31.0% and a flame-retardancy level of V-1 are achieved. A synergistic flame-retardant mechanism coordinated by LDH nanosheets, a supportive LDH–CNTs composite structure, and DOPO nanoparticles is proposed and elaborated by extensive fire-resistance evaluations and intensive analysis of the char residue after combustion.