UL-94 Test Research Articles

Enhancing the thermal and mechanical properties of sulfonated peek fiber composites with reduced smoke density and toxicity

AbstractPolyether ether ketone (PEEK) sulfonation process is a reasonably easy but time‐consuming to manufacture composites. This study focuses on altering PEEK powder in a sulfuric acid solution via a sulfonation process to develop sulfonated PEEK (SPEEK) resin for the fiber‐reinforced thermoplastic composite manufacturing and characterization steps. In this study, about 5 wt% PEEK powder was sulfonated in 98% sulfuric acid solution for 12 h at 65°C. The water bath technique was used for the precipitation process to obtain the SPEEK polymer. After proper washing and drying, the SPEEK matrix (resin) was obtained by dissolving it in dimethylformamide in a ratio of 1:2. This resin solution was then used to manufacture thermoplastic Kevlar and glass fiber‐reinforced composites employing wet layup process and cured at an elevated temperature under pressure. These SPEEK composites passed the flame retardancy UL94 test with a V0 rating. The average water contact angle of the glass fiber‐ and Kevlar‐SPEEK composites is 93.67° and 102.24°, respectively. The average tensile strength values of these composites were found 222.22 and 284.35 MPa, correspondingly. The smoke density and toxicity tests of the glass fiber‐SPEEK composite confirmed lower smoke generation with the modifications. These SPEEK‐fiber composites can be considered for various industrial applications, including aviation, energy, drone, defense, and automotive.

Construction of phosphorus-containing polyimine vitrimer film by incorporating ionic liquid BMIM∙PF6 for enhanced mechanical, flame-retardant and reprocessable properties

A composited flame-retardant phosphorus-containing polyimine vitrimer films (Ionic-PIs) were synthesized by using ionic liquid BMIM∙PF6 containing flame retardant elements N, P and F as the regulator. The effects of the addition amount of BMIM∙PF6 on the mechanical properties, degradation, recycling, and flame retardancy were investigated. Compared to intrinsically phosphorus-containing polyimine film (PI), the composited Ionic-PIs exhibited better mechanical strength and toughness. Hydrogen bonding interactions between BMIM∙PF6 and polyimine network greatly increased Ionic-PI’s mechanical strength at a low addition of 1 wt%, and the microphase separation caused by the aggregation of BMIM∙PF6 drastically enhanced their toughness as the addition increased. Ionic-PIs exhibited excellent reprocessability at 85 °C and degradable recyclability under acidic conditions. In addition, due to the synergistic effect of condensed-phase and gas-phase flame-retardant mechanisms, the Ionic-PIs possessed good flame retardancy with LOI above 27 % and a UL-94 test reaching VTM-0 grade, which was important for the high-fire safety of polyimine vitrimer. This work is helpful to provide a simple and feasible strategy to modulate the comprehensive properties of cross-linked polyimine vitrimer film and to expand their applications in many fields.

Equol-based epoxy resin as an ideal substitute for the diglycidyl ether of bisphenol A (DGEBA)

The development of high-performance bio-based epoxies with excellent mechanical properties, heat resistance and flame retardant properties is essential to mitigating the resource and environmental burdens caused by the widespread utilization of petroleum-based epoxies. This work focuses on the synthesis of a bifunctional epoxy resin (EEU) with the rigid tetrahydrobenzopyran ring derived from equol. The structure of the EEU epoxy resin was characterized, and using 4,4′ diamino diphenyl sulfone as the curing agent, the rheological properties, curing behavior and comprehensive properties of cured resin were studied. The results demonstrate that EEU-DDS presents the same curing behavior as DGEBA-DDS. The mechanical properties heat resistance and flame retardant properties of EEU-DDS are superior to DGEBA-DDS. The tensile strength, tensile modulus and glass transition temperature reached to 94.0 MPa, 3.62 GPa and 221 °C, respectively, higher than those of DGEBA-DDS (83.2 MPa, 2.81 GPa and 203 °C). EEU-DDS reached the V-1 rating in UL-94 tests with a high limiting oxygen index (LOI) (28 %), and the peak heat release rate and smoke release rate of 631 kW/m2 and 0.155 m2/s were significantly lower than that of DGEBA-DDS. The flame retardant mechanism was proven to be gas-coacervated phase synergistic flame retardant. In addition, the interlamellar shear strength (ILSS), bending strength, and impact strength of carbon fiber reinforced resin matrix composites prepared by EEU-DDS reached 97.9 MPa, 1281 MPa, and 81.3 kJ/m2, respectively, higher than those of DGEBA-DDS. Therefore, equol-based epoxy resin can serve as an ideal alternative to petroleum-based bisphenol A-type epoxy resin, offering superior comprehensive properties.

Interface engineering of multi-component core-shell flame retardant towards enhancing fire safety of thermoplastic polyurethane and mechanism investigation

Polymeric materials usually present substantial hazards to human health and the environment as a consequence of their flammability which leads to the emission of a great deal of heat and toxic fumes. To address this issue, it is imperative to urgently enhance the flame retardancy of polymer materials. This study focuses on the synthesis of a novel gel-silica/polydopamine double-layer microencapsulated cobalt ions (Co2+) modified ammonium polyphosphate (APP-Co@PDA@Si) and its utilization in thermoplastic polyurethane (TPU) composites. The resulting TPU composite, containing 10.0 wt% APP-Co@PDA@Si, exhibited excellent flame-retardant properties, i.e. achieving a limiting oxygen index of 30.0 % and the V-0 grade in the UL-94 test. Furthermore, peak heat release rate, total heat release, peak smoke production rate, and total smoke release of the TPU composite were decreased by 88.51 %, 66.06 %, 61.73 %, and 74.01 %, respectively, in comparison to those of pure TPU. The enhanced fire safety of the TPU composite was attributed to the synergistic effect among Co2+ catalytic carbonization, the free radicals capture effect of APP, and the flame-retardant functions of PDA and silane. This innovative strategy proposed in this work holds great promise for improving the fire-resistance of TPU.

Phosphorus and nitrogen supramolecule for fabricating flame-retardant, transparent and robust polyvinyl alcohol film

Supramolecular flame retardants have attracted increasing attention recently due to their simple and eco-friendly preparation process. In this study, a novel flame retardant HEPFR was prepared using supramolecular self-assembly technology between piperazine and 1-hydroxy ethylidene-1,1-diphosphonic acid (HEDP). It was introduced into polyvinyl alcohol (PVA) matrix to form PVA/HEPFR composite film. Subsequently, the transparency, mechanical properties, thermal stability, and flame retardancy of PVA/HEPFR films were studied. Due to the hydrogen bonded cross-linked network structure between PVA and HEPFR, the mechanical properties of PVA/HEPFR films have been improved, while maintaining good transparency. With 10 wt% addition of HEPFR, PVA films can reach the VTM-0 level in UL-94 testing. And the limiting oxygen index can be increased from 18.5% of pure PVA to 26.5%. The peak heat release rate was reduced by 61.5%. The flame retardancy and thermal stability of PVA/HEPFR films have been greatly improved. This study provides a “one stone, three birds” strategy for preparing flame-retardant, transparent, and robust PVA film.

A macromolecular intumescent flame retardant with thermal cross-linking groups for poly(ethylene terephthalate) with enhanced fire safety

To improve the flame retardancy of poly(ethylene terephthalate) (PET) without loss of its mechanical properties, a macromolecular intumescent flame retardant (SPPO) with thermal-responsive groups was developed in an effective way. As 8 wt% of SPPO was melt-blended into PET, the prepared PET/SPPO composite achieved a V-0 rating during UL-94 tests without melt-dripping, and exhibited substantial reduction in the total heat release (THR), peak heat release rate (PHRR), total smoke production (TSP) and average carbon monoxide yield (av-COY) by 44.8 %, 39.0 %, 63.3 % and 45.8 %, respectively, in comparison with pure PET. The improved flame retardancy of this composite was considered to be ascribed to the formation of intumescent residues of SPPO. The generated physical barrier increased the melt viscosity by triggering the cross-linking reactions of the C≡N groups in SPPO, effectively inhibiting the melt-dripping of PET during burning. The tensile strength was also well-retained for PET composites when different contents of SPPO were added into PET, demonstrating the good compatibility between SPPO and PET matrix, which can meet the requirements of industrial application.

Advancing flame retardancy, mechanical properties, and hydrophobicity of epoxy resins through bio-based cinnamaldehyde derivative

Developing flame retardants based on biomass materials to improve the flame retardancy and multifunctionality of epoxy resin (EP) is crucial. Herein, we synthesized a novel derivative, PPABCA, combining cinnamaldehyde and 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide to serve as flame retardants for EP. Incorporating 5 wt% PPABCA into EP (EP/PPABCA-5) demonstrated remarkable flame retardancy, with a limiting oxygen index of 33.7% and a V-0 rating in UL-94 test. It also reduced the peak heat release rate, total heat release, and peak CO2 production by 32.9%, 29.9%, and 42.8%, respectively. The enhanced flame retardancy was facilitated by the capture of phosphorus-containing free radicals coupled with dilution of combustible gas characterized by the blow-out phenomenon and formation of a dense char layer enriched with triazine and phosphorus. Furthermore, EP/PPABCA-5 exhibited enhanced flexural and tensile strengths by 20.5% and 16.5% compared to EP, attributed to the increased cross-linking density and π-π conjugation from the high rigidity of PPABCA, along with its good compatibility with EP. Additionally, the improved hydrophobic properties of PPABCA, confirmed by electrostatic potential analysis, further enhanced the hydrophobicity of EP composites. Overall, this work underscored a strategic development of multifunctional, bio-based flame retardant, showcasing efficient flame retardancy, enhanced mechanical properties, and boosted hydrophobicity in EP.

Construction of an organic iron phosphate/graphite carbon nitride hybrid system for improved fire safety of epoxy resin

Enhancing the fire safety of epoxy resin (EP) is crucial due to its widespread but inherent flammability, necessitating the integration of additive flame retardants (FRs) that are effective in small quantities and exhibit efficient flame retardancy. This study constructed a novel, efficient FR by synthesizing organic iron phosphate (ATMP-Fe) and loading it on graphitic carbon nitride (g-C3N4). The resulting hybrid flame retardant (ATMP-Fe/g-C3N4) was added to EP in minimal amount to bolster its flame retardancy and safety features. Incorporating a mere 3 wt% of ATMP-Fe/g-C3N4 into EP significantly improved its flame retardancy and thermal stability. This was evidenced by an increase in the limiting oxygen index from 25.5% for EP to 30.1%, achieving a V-1 rating in the UL-94 test, and producing a 22.0 wt% char residue. Moreover, there was a substantial reduction in peak heat release rate, total heat release, and total smoke production by 36.3%, 27.5%, and 39.3%, respectively. The reduction in pyrolysis products, along with the formation of a dense and stable char layer facilitated by the synergistic effects of phosphorus and iron elements, significantly improved the fire safety of EP. Additionally, the enhanced hydrophobicity, mechanical properties, and electrical conductivity of the EP/3ATMP-Fe/g-C3N4 composite suggested potential for wider application of EP in various fields.

Preparation of a Polymeric Phosphoramide Flame-Retardant and Its Effect on the Flame-Retardant Properties of Epoxy Resin.

The flammability of epoxy resins and knowing how to achieve curing are particularly important factors during use. A novel approach for enhancing the fire resistance and reducing the smoke emission of epoxy resin during the curing process is suggested, which involves the utilization of a three-source integrated polymerization intumescent flame-retardant. In this study, the synthesis of poly 4,4-diaminodiphenylsulfone spirocyclic pentaerythritol bisphosphonate (PCS) is achieved through using solution polymerization, utilizing 4,4'-diaminodiphenylsulfone (DDS) and spirocyclic pentaerythritol bisphosphorate disphosphoryl chloride (SPDPC) as initial components. Following that, the EP underwent the inclusion of PCS to examine its resistance to heat, its ability to prevent flames, its effectiveness in reducing smoke and its curing effect. Compared to the unmodified epoxy resin, the addition of PCS can not only cure the epoxy resin, but also decompose before the epoxy resin and has a good carbonization effect. With the addition of 7 wt.% PCS, the LOI value can achieve 31.2% and successfully pass the UL-94 test with a V-0 rating. Moreover, the cone calorimeter experiment demonstrated a noteworthy decline of 59.7% in the maximum heat release rate (pHRR), 63.7% in overall heat release (THR), and 42.3% in total smoke generation (TSP). Based on the examination of TG-FTIR and SEM findings, there is ample evidence to suggest that PCS, functioning as a phosphorus-nitrogen intumescent flame-retardant that combines three origins, has the potential to exhibit a favorable flame-retardant impact in both its gas and condensed phases.

Epoxy resin/ aluminium hydroxide/expanded graphite synergistic effects on advancing flame retardancy, mechanical structure and thermal management of octadecanoic acid and octadecanol-based eutectic phase change materials

In the present research, a novel approach wherein a flame-retardant composite phase change material (PCMs) is devised by incorporating eutectic PCMs, epoxy resin (ER), aluminium hydroxide (ATH), and expanded graphite (EG). This innovative formulation capitalizes on the synergistic interaction between ER and ATH, alongside the porous structure of EG, resulting in a triple-layer encapsulation of the eutectic PCMs. The outcome of this formulation is marked by remarkable thermal stability, even under extreme conditions such as exposure to temperatures as high as 800 °C. Notably, one of the representative samples, denoted as S5, showcases impressive attributes with a thermal conductivity of 1.335 W∙m-1K−1 and a substantial phase change latent heat of 150.4 J∙g−1. It was observed an increase in latent heat up to 181.3 J∙g−1 after 100 heating–cooling cycles of composite PCMs. This indicates the good thermal reliability of the form-stable composite PCMs synthesized. Moreover, the composite PCMs exhibit outstanding mechanical properties, especially S5 which showed a 14.69 % and 400.12 % increase in compression strength and compression modulus compared with pure eutectic PCM (S0), respectively. Besides, the ternary composition of ER, ATH, and EG enhances the flame retardancy of the composite PCMs, yielding a substantial reduction of 67.33 % in peak heat release rate and 50.38 % in total heat release. This collaborative effect also establishes a robust defense mechanism against the rapid propagation of flames, as exemplified by the attainment of a V-0 rating in the UL-94 test. As a result, the flame-retardant ER/ATH/EG ternary-based form-stable composite PCM presents itself as a promising candidate for ensuring both safety and efficiency in thermal management applications.

Characterization and Flame-Retardant Properties of Cobalt-Coordinated Cyclic Phosphonitrile in Thermoplastic Polyurethane Composites.

Halogen-free organophosphorus flame retardants have promising application prospects due to their excellent safety and environmental protection properties. A cobalt-coordinated cyclic phosphonitrile flame retardant (Co@CPA) was synthesized via a hydrothermal method using hexachlorocyclotriphosphonitrile (HCCP), 5-amino-tetrazolium (5-AT), and cobalt nitrate hexahydrate (Co(NO3)2∙6H2O) as starting materials. The structure was characterized using Fourier transform infrared (FTIR), nuclear magnetic resonance spectroscopy (1H-NMR), scanning electron microscopy (SEM), and thermogravimetric analysis (TGA). Thermoplastic polyurethane (TPU) composites were prepared by incorporating 10-(2,5-dihydroxyphenyl)-9,10-dihydro-9-oxa-10-phosphame-10-oxide (ODOPB), Co@CPA, and silicon dioxide (SiO2) via melt blending. The flame-retardant performance and thermal stability of the TPU composites were evaluated through limiting oxygen index (LOI), vertical combustion (UL-94), TG, and cone calorimetric (CCT) tests. SEM and Raman spectroscopy were used to analyze the surface morphology and structure of the residual carbon. A synergistic flame-retardant effect of ODOPB and Co@CPA was observed, with the most effective flame retardancy achieved at a TPU:ODOPB:Co@CPA:SiO2 ratio of 75:16:8:1. This composition exhibited an LOI value of 26.5% and achieved a V-0 rating in the UL-94 test. Furthermore, compared to pure TPU, the composite showed reductions in total heat release, CO production, and CO2 production by 6.6%, 39.4%, and 48.9%, respectively. Our research findings suggest that Co@CPA demonstrates outstanding performance, with potential for further expansion in application areas. Different metal-based cyclic phosphonitrile compounds are significant in enriching phosphorus-based fine chemicals.

Non-covalently functionalized black phosphorene to efficient flame retardant EVA with improved mechanical properties

The development of flame-retardant polymer materials play a vital role in reducing fire hazards and protecting both lives and property. Black phosphorus (BP) is an extremely promising flame retardant since its synergistic flame retardancy with different modifiers. Nevertheless, the issue of unven dispersion within the polymer matrix has severely restricted its practical applications. Herein, BP nanosheets functionalized with ionic liquid (IL-BP) were prepared and then compounding with EVA to improve the mechanical and the flame-retardant properties of EVA matrix. The results demonstrated enhanced compatibility of IL-BP nanosheets within the EVA matrix, leading to the 1.5 %IL-BP/EVA composite displayed a 25 % and 9.6 % increase in tensile strength and elongation at break, respectively. Remarkably, the flammability test results demonstrated that the 1.5 %IL-BP/EVA sample featured a significant decrease of 18.1 % and 21.5 % in total heat release (THR) and peak heat release rate (PHRR), respectively. Meanwhile, the composite also achieved a V-0 rating in UL-94 test and demonstrated superior resistance to melt dripping. The flame-retardant mechanisms of IL-BP/EVA composites in both gas phase and condensed phase were studied. This work provides a promising strategy to design synergetic flame retardants that simultaneously enhanced the fire safety and mechanical properties of EVA.

Camellia meal-based adhesive with synergistic crosslinking of physical and chemical interaction for preparing aldehyde-free, anti-mildew, water-resistant wood-based composites

Wood adhesives containing toxic aldehyde-based adhesives play a vital role in the performance of wood-based panels, while the mechanical properties and water and mildew resistance of aldehyde-free adhesives are lacking. In this study, a high-strength aldehyde-free adhesive was constructed via a combination of physical and chemical crosslinks. Inexpensive alum was used to ensure a high degree of crosslinking and to increase the crystallinity. Metal ions in alum opened the protein helix, exposed the active groups, increased the number of hydrogen bonds, and ultimately improved the internal physical crosslinking ability of the adhesive. The compound formed by the Schiff base reaction formed coordination bonds with metal ions, thus forming a covalently-crosslinked network. The high-strength polymer produced in this study contained multiple physical and covalent crosslinks, resulting in significantly improved mechanical properties of the adhesive. Its water-resistant adhesive strength reached 1.96 MPa, which was 180.2% higher than that of ordinary phytogenic protein adhesive (0.69 MPa), and it can still reach 1.28 MPa after hot water circulation soaking experiment. The adhesive also possessed antifungal properties and flame-retardant capabilities, achieving a V-1 rating in the UL-94 test. This strategy expanded the application of phytogenic protein adhesives in environmentally friendly wood composite materials by replacing synthetic resins that released formaldehyde and provided an economical and feasible industrial scale production method for the preparation of high strength, water, and mildew resistant, flame retardant indoor and outdoor wood-based panels.

Effect of Phosphorus-Nitrogen based Flame-Retardant Combined with Zinc Borate on Thermal Stability and Flame Retardancy of Epoxy Clay Nanocomposites

A phosphorus-nitrogen containing 6,6'-(piperazine-1,4-diyl)bis(6H-dibenzo[c,e][1,2]oxaphosphinine 6-oxide) (DOPO-PZ) flame-retardant was synthesized and its effect combined with zinc borate (ZnB) and nanoclay (NC) on thermal stability and flame retardancy of epoxy resin was studied. Various epoxy composites containing DOPO, DOPO-PZ, ZnB and NC using curing agent diaminodiphenylsulfone (DDS) were prepared. The X-ray diffraction (XRD) and transmission electron microscope (TEM) micrographs of the composites showed intercalated nanostructure of epoxy-clay nanocomposites. In thermogravimetric analysis (TGA), pure epoxy gave 3.4% char yield at 700 ºC in nitrogen atmosphere, while in case of EP/DOPO-PZ/ZnB/NC sample having 1% phosphorus content, 5 wt.% zinc borate (ZnB) and 3 wt.% nanoclay (NC), the char yield is increased to 24.0%. Differential scanning calorimetry (DSC) study showed decrease in the glass transition temperature (Tg) on the addition of flame-retardant due to plasticization effect and increase in Tg on addition of nanoclay due to formation of nanostructure of epoxy composites. The EP/DOPO-PZ/ZnB/NC nanocomposite sample exhibited a limiting oxygen index (LOI) value of 29.2% and passed the UL-94 test with a V-0 rating and thus achieved a sufficient flame retardancy.

Development of a Polypropylene-Based Material with Flame-Retardant Properties for 3D Printing.

In this study, a nanocomposite based on a heterophasic polypropylene copolymer containing 5 wt% of nanoclays and 3 wt% of compatibilizer was formulated via melt compounding to obtain a material suitable for Fused Filament Fabrication (FFF) processing with enhanced flame-retardant properties. From rheological analyses, the nanocomposite showed an important increase in the non-Newtonian behavior, and, therefore, improved FFF printability compared to the pristine PP COPO. A filament with suitable characteristics for FFF was produced using a single-screw extruder and subsequently 3D printed. Finally, cone calorimeter and UL94 tests were carried out on both 3D-printed and compression-molded specimens. The obtained results showed that the 3D-printed samples exhibited even better flame-retardant properties than the compression-molded ones, thus demonstrating not only the possibility of successfully developing and using functionalized PP-based filaments in 3D printing but also the possibility of obtaining enhanced flame-retardant properties compared to conventional compression molding.

The effects of property variation on the dripping behaviour of polymers during UL94 test simulated by particle finite element method

Abstract The dripping behaviour of polymers is often observed experimentally through the UL94 flammability standard test. In this work, polymeric dripping under fire is investigated numerically using particle finite element method. A parametric analysis was carried out to observe the influence of a single property on overall dripping behaviour via a UL94 vertical test model. Surrogates and property ranges were defined for variation of the following parameters: glass transition temperature (T g), melting temperature (T m), decomposition temperature (T d), density (ρ), specific heat capacity (Cp), apparent effective heat of combustion of the volatiles, char yield (µ), thermal conductivity (k), and viscosity (η). Polyamide, poly(ether ether ketone), poly(methyl methacrylate), and polysulfone were used as benchmarks. Simulated results showed that specific heat capacity, thermal conductivity, and char yield allied with viscosity were the properties that most influenced dripping behaviour (starting time and occurrence).

Preparation of cresyl diphenyl phosphate‐loaded halloysite nanotube composite and its flame retardancy in epoxy resin

AbstractTo address the shortcomings of poor thermal stability, easy migration, and over‐plasticization of the liquid organic phosphorus flame retardant, cresyl diphenyl phosphate (CDP), we employed halloysite nanotube (HNT) as a carrier to load CDP, thus forming a novel composite (HNT‐CDP). The results demonstrated that the CDP loaded into HNT channels was 41 wt%. HNT‐CDP composites exhibited higher thermal stability, water resistance, and flame retardancy than mixtures of HNT and CDP in epoxy resin (EP). With a loading of 15 wt%, the limiting oxygen index of EP/HNT‐CDP increased to 48.3 and achieved a V‐0 rating in UL94 tests. Additionally, HNT‐CDP exhibited better inhibitory effects on the peak heat release rate and total heat release of EP, as well as a longer time to ignition, compared with the mixture. Moreover, as opposed to EP/HNT + CDP, EP/HNT‐CDP exhibited a significant 114.5% increase in tensile strength. These excellent thermal, water resistance, and mechanical properties can be primarily attributed to the loading of CDP by HNT channels. HNT effectively utilizes the channel confinement effect to isolate CDP from directly interacting with EP. The outstanding flame retardancy is mainly due to the synergistic effect between HNT and CDP after the formation of the composite.

Comparative study of flame retardancy in polyimine vitrimers and composites: Evaluating additive and reactive flame retardants acting via gas-, solid-, and combined-phase mechanisms

We developed flame retarded polyimine type vitrimers and carbon fibre reinforced composites using two additive and a reactive flame retardant containing phosphorus: ammonium polyphosphate (APP), resorcinol bis(diphenyl phosphate) (RDP); and N,N',N’’-tris(2-aminoethyl)-phosphoric acid triamide (TEDAP). We characterised the vitrimer matrix materials by differential scanning calorimetry (DSC), thermal analysis (TGA), limiting oxygen index (LOI), UL-94 test and mass loss calorimetry (MLC), while the vitrimer composites by LOI, UL-94 test, MLC and dynamic mechanical analysis (DMA). We compared the performance of the vitrimer systems to a benchmark pentaerythritol-based aliphatic epoxy resin system (PER). The vitrimer reference had higher thermal stability but lower fire performance than the PER aliphatic reference epoxy. At lower phosphorus content, the vitrimer systems exhibited a melting above their vitrimer transition temperature, which negatively affected their LOI and UL-94 results. From 2% phosphorus content, rapid charring and extinguishing of vitrimers prevented the softening and deforming. The superior performance of these same flame retardants in vitrimer systems could be attributed to the high nitrogen content of imine-based vitrimers in combination with phosphorus flame retardants, exploiting nitrogen-phosphorus synergism. In both matrices, flame retardants with solid phase action lead to better fire performance, while in composites, the lowest peak heat release rates (152 kW/m2 in vitrimer composite) were achieved with RDP acting predominantly in the gas phase, as carbon fibres hindered the intumescent phenomenon.

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.

Vanillin-derived epoxy-coated flexible cellulose nanofiber film for multifunctionality and energy harvesting applications

Cellulose nanofiber (CNF), a state-of-the-art sustainable material, often suffers from high hydrophilicity, flammability, and emaciated UV-blocking properties, hampering its broad growth in high-performance applications. This paper reports a novel multifunctional bio-based-epoxy-coated CNF film promising to cope with the addressed challenges. Key to this approach is the etherification reaction, which favors excellent compatibility between CNF film and vanillin-derived epoxy (VDE) resin, resulting in a robust crosslinked network structure with a remarkable adhesion strength (16.12 ± 0.7 MPa), tensile strength (211.6 ± 7.2 MPa), and Young's modulus (8.6 ± 0.4 GPa). A thin VDE layer coating on CNF (VDE/CNF) film significantly presented the film's hydrophobicity of around ⁓93.0 ± 1.5° and UV shielding performance of ⁓100%. Additionally, the coated VDE/CNF film exhibited higher thermal stability (213 °C) and char residue (36%) than the CNF film. Most importantly, despite the high flammability nature of CNF film, the VDE/CNF film passed a V-0 rating under the UL-94 test with a limited oxygen index of 31.8%. The VDE/CNF film was utilized for a triboelectric nanogenerator (TENG) to demonstrate its broad technological impact. Notably, the VDE/CNF-TENG exhibited a significant output power of 18.33 μW. This critical approach offers a promising way to extensively utilize sustainable and multifunctional VDE/CNF nanocomposite materials for high-performance applications.