Search Results (326)

External heat flux is a primary thermal input parameter in cone calorimeter tests, with the nominal value conventionally established at the center of the specimen surface. However, the radiant heat flux generated by the cone heater specified in ISO 5660-1 is known to be spatially non-uniform. This study quantified the spatial distribution of external heat flux at nominal levels of 20, 35, and 50 kW/m² and applied area-weighted spatial averaging to quantify the relationship between the nominal heat flux and the spatially averaged external heat flux over the specimen. The measured heat flux decreased radially toward the specimen boundaries, with local relative deviations reaching approximately −30% near the corners of a standard 0.100 × 0.100 m specimen. Despite this local non-uniformity, the normalized spatial distributions were similar across all three heat flux levels. For the entire specimen, the area-weighted relative deviations were −3.54%, −3.28%, and −3.41% at 20, 35, and 50 kW/m², respectively, with comparable deviations in total external radiant power. These findings demonstrate that the magnitude of local heat-flux deviation should be distinguished from the specimen-wide spatially averaged deviation. The proposed area-weighted spatial interpretation provides a quantitative basis for relating the nominal external heat flux established at the specimen center to the spatially averaged external heat flux over the specimen under the ISO 5660-1 cone calorimeter configuration. Full article

To overcome the flammability and formaldehyde-emission problems associated with plywood, a novel soy protein-based intumescent flame-retardant adhesive with phosphorus–nitrogen–silicon (P-N-Si) synergism (C@Si@APP) was developed in this study. C@Si@APP was initially prepared by coating silane-modified ammonium polyphosphate with collagen. Subsequently, C@Si@APP was combined with lignin and adenine and incorporated into a soy protein, collagen, and isocyanate (MDI)-based adhesive matrix to fabricate a flame-retardant adhesive for eucalyptus plywood. Cone calorimeter (CONE) analysis demonstrated that the flame-retardant plywood bonded with SPI/C/MDI/C@SiAPP18 achieved the most effective flame-retardant and smoke-suppression performance, and the peak heat release rate, total heat release, and total smoke production were reduced by 23.5%, 20.7%, and 43.9%, respectively, and the release rates of CO and CO₂ were also effectively suppressed. Mechanistic analysis indicated that the enhanced flame retardancy was mainly governed by a condensed-phase mechanism, in which phosphorylation and siloxane crosslinking promoted the formation of a compact and thermally stable char layer that protected the underlying material, whereas a gas-phase contribution involving the dilution of flammable volatiles by non-combustible gases (NH₃, H₂O, and CO₂) and possible radical scavenging by phosphorus-containing species is proposed as a plausible complementary pathway inferred from the TGA-FTIR results and the previous literature. Full article

Recycled cotton fibers offer a promising route for sustainable thermal insulation, but their flammability limits wider application. This study evaluated rigid recycled cotton insulation boards bonded with a polyvinyl acetate (PVAc)–starch system and modified with kraft lignin or aluminium trihydroxide (ATH) at dosages of 10 and 15 wt.%. Board density, thermal conductivity, volumetric heat capacity, thermal diffusivity, cone-calorimeter behavior, and ignitability under single-flame exposure were assessed. Thermal conductivity remained within a narrow range of 0.071–0.075 W·m⁻¹·K⁻¹, indicating that the basic insulation function was preserved despite formulation changes. Greater differences were observed in volumetric heat capacity and thermal diffusivity, particularly in lignin-modified boards at higher PVAc contents. Fire behavior was strongly formulation-dependent and showed no uniform dose-dependent response. The lowest peak heat release rate (pHRR) was obtained for the formulation containing 10 wt.% ATH and 20 wt.% PVAc, while the lowest total heat release (THR) was obtained for the formulation containing 10 wt.% ATH and 18 wt.% PVAc, reaching 170.31 kW·m⁻² and 62.30 MJ·m⁻², respectively. Lignin produced a less consistent effect on heat release. Under single-flame exposure, edge application was generally more critical than surface application, while ATH, particularly at 15 wt.%, provided the most consistent reduction in ignition and early flame spread. Overall, ATH was the more promising fire-modifying additive, although further formulation optimization and formal reaction-to-fire classification are required. Full article

Soybean protein isolate (SPI) adhesives are eco-friendly but suffer from poor water resistance and bonding strength. Waterborne epoxy (WE) can effectively improve these properties; however, WE-modified SPI adhesives can hardly satisfy the growing stringent flame-retardant demands for plywood. Herein, we report a composite adhesive (SPI/20WE/THPS@CS/MMT) that simultaneously exhibits favorable flame retardancy and dry and wet shear strengths. In this system, a phosphorus-, nitrogen-, and sulfur-containing polyelectrolyte complex (THPS@CS) is fabricated by vacuum-drying an ionically crosslinked polyelectrolyte hydrogel derived from bis[tetrakis(hydroxymethyl)phosphonium] sulfate (THPS) and chitosan (CS) and subsequently incorporated into the SPI/WE matrix (SPI/20WE) together with montmorillonite (MMT). The plywood bonded with SPI/20WE/THPS@CS/MMT achieves a limiting oxygen index (LOI) of 28.0% and shows significantly reduced heat release in cone calorimeter tests. Meanwhile, the resultant plywood possesses high dry and wet shear strengths that fulfill the interior-use plywood criteria specified in GB/T 9846–2015. This work offers new insights into the design and fabrication of high-performance eco-friendly plywood adhesives. Full article

Wood-based composite panels are renewable and low-carbon materials, but their inherent flammability limits their broader use in applications requiring improved fire safety. In this study, expanded graphite (EG) was incorporated into a melamine–formaldehyde (MF) adhesive system to fabricate fire-retardant Japanese cedar (Cryptomeria japonica) plywood. Two EG types with different expansion ratios, 200-fold expanded graphite (200EG) and 450-fold expanded graphite (450EG), were added to the bonding layer at 10, 20, 30, and 40 phr. The effects of EG expansion ratio and content on the physicomechanical properties, combustion behavior, char morphology, and pyrolysis gas evolution of plywood were investigated. EG had limited effects on air-dried density and moisture content, but increasing EG content reduced bonding shear strength and parallel-direction flexural properties, particularly in the 450EG series. Cone calorimeter analysis showed that EG reduced the heat release rate and total heat release by promoting the formation of an expanded carbonaceous barrier layer. Among the tested formulations, 30 phr 200EG provided the most favorable balance between mechanical performance and fire-retardant efficiency, showing a visually more continuous char coverage while maintaining acceptable bonding properties. High-temperature furnace–FTIR analysis indicated that excessive EG loading or high-expansion-ratio EG increased CO₂ and CO-related signals at 400–700 °C, probably because of a visually looser char morphology, structural disruption during expansion, and gas release from EG intercalating agents. Although the tested panels did not fully meet the CNS Grade 3 fire-retardant requirement, the results provide a useful basis for the modification and performance optimization of halogen-free fire-retardant wood-based composite panels. Full article

In this study, the effects of the type and content of phosphorus-based flame retardants, namely melamine polyphosphate (MPP) and aluminum diethylphosphinate (AlDPi), as well as their hybrid systems (MPP:AlDPi ratios of 1:1, 1:3, and 3:1), on the fire performance of acrylonitrile-butadiene-styrene (ABS) composites were investigated. The obtained results indicate that the synergistic action of MPP and AlDPi, including simultaneous inhibition of combustion in the gas phase and action in the condensed phase, leads to a significant improvement in the fire-retardant properties of ABS composites. For unmodified ABS, the peak Heat Release Rate (pHRR) and Total Heat Released (THR) values were 808.7 kW/m² and 86.5 MJ/m², respectively, while for the ABS/MPP_15/AlDPi_5, these values decreased to 292.9 kW/m² and 32.3 MJ/m². Simultaneously, the Effective Heat of Combustion (EHC) decreased from 22.3 to 15.5 MJ/kg, indicating inhibition of combustion processes in the gas phase. Fourier Transform Infrared Spectroscopy (FTIR) analysis of post-combustion residues (peaks 1280 and 1168 cm⁻¹) confirmed the contribution of additives to the formation of phosphorous derivatives in the condensed phase. The hybrid system ABS/MPP_15/AlDPi_5 exhibited the most favorable fire performance in cone calorimeter tests, characterized by reduced heat release and fire growth parameters. This was confirmed by the calculated fire performance indicators, including Fire Growth Rate Index (FIGRA), Maximum Average Rate of Heat Emission (MARHE), Fire Potential Index (FPI), and Flame Retardancy Index (FRI). Full article

To investigate the effects of different surface coating treatments on the fire resistance of Qing Dynasty traditional corridor-style timber structures, the Long Corridor of the Beijing Summer Palace was selected as the case study. Two representative timber species, red pine and larch, were examined under three treatment conditions, including no treatment, traditional treatment (“San-dao-hui” and “Yi-ma-wu-hui”), and composite treatment combining traditional treatment with modern flame-retardant coatings. Cone calorimeter (CC) testing and Fire Dynamics Simulator (FDS) simulation were used to systematically investigate their combustion performance and fire spread patterns. Results indicate a clear, gradual improvement in timber reaction to fire: composite treatment coating performed best, followed by plaster layer protection, and untreated wood performed the worst. Among these, the composite treatment of red pine with “Yi-ma-wu-hui” (one hemp layer and five lime plaster layers) combined with modern flame-retardant coating showed the highest overall efficacy. The time to ignition (TTI) reached 76.7 s, a 210.5% increase compared with untreated wood. Meanwhile, peak heat release rate and carbon monoxide production were both significantly reduced. Notably, the selected modern flame-retardant coating cures colorless and transparent, preserving the original appearance of the wood, and the composite treatment maintains the historical texture and color consistency required for heritage restoration. The flame-retardant efficiency of the “Yi-ma-wu-hui” plaster layer was superior to that of the “San-dao-hui” (three lime plaster layers), owing to its denser structure that provides a stronger physical barrier effect. Larch exhibited better inherent reaction to fire than red pine, and surface coating treatments effectively reduced differences between substrates. FDS simulations confirmed that the composite treatment could keep peak heat release rate below 6000 kW under the most adverse meteorological conditions, confining high temperatures and dense smoke near the ignition point and effectively restraining sequential fire spread in traditional corridor-style timber structures. These findings provide a scientific basis and practical guidance for the fire-resistant restoration of Qing Dynasty traditional corridor-style timber structures and similar heritage buildings. Full article

This study investigates the influence of surface-modified fly ash particles on the fire behavior of polyamide 6 (PA6) composites containing two types of flame retardants: melamine polyphosphate (MPP) and aluminum diethyl phosphinate (AlPi). The objective was to evaluate how interfacial modification of fly ash using amino-silane (APTES), glycidoxy-silane (GPTES), or titanate coupling agents affects dispersion, thermal stability, and combustion performance. A series of 18 formulations containing up to 25 wt% of additives was prepared by melt compounding and characterized by thermogravimetric analysis (TGA) and cone calorimetry. TGA results showed that MPP-based systems favored char formation, with residues up to 21%, whereas AlPi provided higher thermal stability (T₅₀% ≈ 445 °C). The incorporation of untreated or surface-treated fly ash improved both thermal stability and char yield, depending on the nature of the coupling agent. Cone calorimeter results confirmed a strong synergistic effect between flame retardants and fly ash. The peak heat release rate (pHRR) decreased by 65–75% compared to neat PA6, while total heat release (THR) and mass loss were also significantly reduced. Titanate-modified fly ash showed the most homogeneous dispersion and provided the highest residue and lowest pHRR values. Energy-dispersive X-ray (EDX) analyses confirmed enhanced phosphorus retention in the residues (up to 100%), evidencing the formation of stable inorganic species and protective ceramic-like structures. These results demonstrate that surface-modified fly ash can act as an efficient synergistic additive in PA6 flame-retardant formulations, simultaneously improving fire performance and promoting the valorization of industrial by-products for sustainable polymer design. Full article

In the framework of plastic circularity, managing end-of-life plastics containing flame-retardant (FR) additives represents a significant challenge. Although FRs are essential for enhancing fire safety in polymeric materials, many FR-containing products are never exposed to fire during their service life. As a result, substantial amounts of still-active FR remain in plastic waste streams. Since mechanical recycling is currently the most widely implemented strategy for plastic waste management, it is crucial to evaluate whether this process affects the flammability and combustion behavior of FR plastics. In this study, polypropylene (PP) containing 21 wt.% intumescent FR (IFR) was reprocessed up to five times to simulate mechanical recycling. After each cycle, the materials were systematically characterized in terms of rheological, morphological, combustion, and mechanical behavior. Although the agglomeration of IFR particles was observed after multiple cycles, the materials maintained stable processability and thermal stability. Importantly, the charring efficiency of the IFR system was preserved, resulting in consistent flammability performance; furthermore, all reprocessed samples achieved UL 94 V-0 classification and exhibited comparable limited oxygen index values. Mechanical properties were likewise largely maintained. Overall, these findings demonstrate that mechanical recycling represents a viable end-of-life strategy for this PP/IFR system, supporting its compatibility with circular material flow. Full article

Carbon fiber-reinforced polymer (CFRP) has been widely used in various fields due to its significant advantages. However, research on their pyrolysis and combustion behavior under fire conditions, which directly affects structural integrity and safety, remains insufficient. To challenge this issue, thermogravimetric analysis was employed to investigate the pyrolysis characteristics of the CFRP in both air and nitrogen atmospheres at heating rates of 20–40 °C/min with relevant pyrolysis kinetic parameters calculated using the Kissinger method. Fourier-transform infrared (FTIR) spectrometer was utilized to analyze pyrolytic gas species and concentrations at 40 °C/min in nitrogen atmosphere. Cone calorimeter tests at 50 kW/m² were conducted to obtain combustion characteristic parameters. Based on atomic conservation and oxygen-consumption principles, the equivalent molecular formula (CH_5.787O_0.541) of the epoxy resin pyrolysis gas and its combustion reaction equation were derived through reverse deduction. The heating, pyrolysis, and combustion processes of the CFRP (cone calorimetry specimen) were numerically simulated using Fire Dynamics Simulator (FDS). The predicted heat release rate, mass loss rate, and gas production rate showed good agreement with experimental results. Full article

Fire smoke, rich in toxic ultrafine particles and polycyclic aromatic hydrocarbons (PAHs), poses significant health risks to first responders and vulnerable populations. In this study, a reproducible combustion–smoke simulation platform was developed to mechanistically quantify fire behavior, particle emissions, and PAH toxicity under controlled heat flux and oxygen conditions. Consistent combustion and smoke emissions were achieved by measuring heat release rate, particle mass, particle number concentration, and PAH concentration, with an overall average coefficient of variation below 15%. Systematic experiments with representative biomass (pine, oak) and plastics (PVC, polystyrene) demonstrate that fuel composition, heat flux, and oxygen availability jointly govern particle formation and PAH partitioning. Regardless of the combustion factors, ultrafine particles dominated the particle number concentration (55.5–86.2%). Plastic combustion generated 7 to 59 times particle mass, up to 260 times higher PAH emissions, and up to 58,500 times greater PAH toxic equivalent quotient (PAH-TEQ) than wood. Oxygen-deficient and smoldering regimes shifted emissions toward fine and ultrafine particles enriched in high-molecular-weight PAHs, revealing a coupled physical–chemical hazard not captured by bulk PM metrics alone. These results establish a quantitative framework linking combustion regime, particle size, and PAH toxicity, providing critical insight for exposure assessment, PPE design, and mitigation strategies in ventilation-limited and mixed-fuel fire scenarios. Full article

Melamine polyphosphate (MPP) is a widely employed additive-type flame retardant for polyamide 6. Generally, a higher loading of MPP leads to improved flame retardancy of polyamide 6 composites. Nevertheless, excessive addition tends to cause problems such as flame-retardant migration, leakage, and exudation. Against this background, this work focuses on covalently grafting melamine polyphosphate onto the surface of carbon nanotubes via a facile chemical reaction, with the aim of alleviating the migration and leakage of the flame retardant in the polyamide 6 matrix. Carbon nanotubes (CNTs) were surface modified with a silane coupling agent (KH560) to obtain CNTs bearing epoxy groups (CNT-KH560). Subsequently, a ring-opening addition reaction was conducted between the CNT-KH560 and melamine polyphosphate (MPP) yielding carbon nanotubes with surface-bonded flame-retardant MPP (CNTM). Polyamide 6 composite slices (PA6/CNTM) were prepared via twin-screw extrusion blending and compounding and then by hot-press molding into test specimens. The modified carbon nanotubes were characterized using Fourier transform infrared spectroscopy, scanning electron microscopy, and thermogravimetric analysis. The results confirmed the successful grafting of MPP onto the carbon nanotube surface, with a grafting degree of 9.1 g/100 g measured. The flame retardancy of the PA6/CNTM composites were evaluated through UL 94 vertical burning and limiting oxygen index (LOI) tests and cone calorimeter. These flame retardancy results indicated that when the content of flame-retardant-modified carbon nanotubes was 10 wt%, the PA6/CNTM10 composites achieved UL 94 V-2 and the limiting oxygen index increased from 24.5% of pure PA6 to 29.1%. The PHRR value of pure PA6 decreased from 750 kW/m² to 614 kW/m². This design of surface-grafted flame retardant provides a new strategy for the preparation and application of high-performance polyamide 6 flame-retardant composites. Full article

This work deals with the impact of surface acoustic treatment (holes and grooves) and primary material (plywood, MDF, solid wood panel) of acoustic panels on their fire characteristics. Fire characteristics were determined based on the cone calorimeter method, single-flame source test, and smoke generation assessment. In general, birch plywood demonstrated the highest values for heat release rate (HRR), maximum average rate of heat emission (MARHE), and effective heat of combustion (EHC), indicating its higher flammability compared to the other tested materials. MDF generally exhibited the lowest values for heat release rate (HRR) and maximum average rate of heat emission (MARHE); yet, under certain perforated configurations, it generated the highest amount of smoke. Solid wood panels exhibited the lowest heat release rate (HRR) but developed the largest charred areas during the single-flame source test. Among the surface treatments, the 16/8 mm treatment resulted in the highest values of effective heat of combustion (EHC) and maximum average rate of heat emission (MARHE), while the 8/1.5–15T treatment exhibited the most rapid increase in heat release rate (HRR), attributed to the swift degradation of its thin surface layer and high void fraction. The presence of holes and grooves increased smoke production, which was most evident in MDF and plywood panels. The results demonstrate that acoustic surface geometry significantly modifies the fire behavior of wood-based panels and should be considered alongside material selection when evaluating fire safety in interior applications. Full article

The characteristics of litter combustion have a significant impact on the spread of surface fires in the central Yunnan Province, a high-risk forest fire zone. The burning behavior of individual and mixed-species litter samples from five dominant tree species (Pinus yunnanensis Franch., Keteleeria evelyniana Mast., Quercus variabilis Blume., Quercus aliena var. acutiserrata, and Alnus nepalensis D. Don.) was assessed in this study using cone calorimeter tests. Fern fronds and fine branches were included in additional tests to evaluate their effects on specific combustion parameters, such as Fire Performance Index (FPI), Flame Duration (FD), Time to Ignition (TTI), Mass Loss Rate (MLR), Residual Mass Fraction (RMF), Peak Heat Release Rate (PHRR), and Total Heat Release (THR). There were remarkable differences in the burning properties of the three types of litter (broadleaf, pine needles, and short pine needles). The THR and PHRR values of P. yunnanensis were the highest, whereas the PHRR of the other species varied very little. Short pine needle litter showed incomplete combustion and a long flame duration. When measured against pure pine needle litter, mixtures of P. yunnanensis and broadleaf litter showed lower PHRR. When set side by side to pure pine needle litter, P. yunnanensis and broadleaf litter showed lower PHRR. THR rose when fine branches were included, underlining the significance of fine woody fuels in fire behavior. The insertion of ferns increases the percentage of unburned biomass, prolongs TTI, and dramatically reduces PHRR. Full article

Polybutadiene has excellent mechanical properties and flexibility. It is widely used in elastomers and industrial fields. However, it has the characteristic of high flammability. The low LOI and rapid heat release upon ignition pose significant fire hazards. This results in a significant fire safety risk during service. Therefore, its application in some key fields has been restricted. In this study, polybutadiene with high-performance flame-retardant properties was developed by adding phosphorus–nitrogen synergistic flame retardants to address this challenge. This flame retardant mainly enhances its flame retardancy through the synergistic gas-phase and condensed-phase mechanisms. Dense and continuous carbon layers could be promoted by flame retardants during combustion. It provides an effective thermal barrier and oxygen barrier. In addition, phosphorus-containing volatiles can function by suppressing flame propagation via radical quenching in the gas phase. The modified polybutadiene reached UL-94 V-1 grade at the optimal load of 1.0 wt%. Meanwhile, its LOI increased to 27%. The cone calorimeter test further confirms a high reduction in peak heat release rate (pHRR). This work provides a feasible strategy for developing advanced polybutadiene materials. It can effectively enhance its fire safety. At the same time, it maintains a balance between flame retardancy and the overall material performance. Full article