Reduced Heat Release Research Articles

Eco-friendly wearable textiles: Asymmetric structures for EMI shielding, thermal management, and fire safety

This work focuses on developing multifunctional wearable fabrics, specifically targeting the challenge of flammability in this context. An eco-friendly, asymmetrically structured nylon/cotton blend fabric is prepared through the surface modification of phytic acid-induced polyaniline, the application of silver nanowires (AgNWs) and MXene on both sides and encapsulated by polydimethylsiloxane (PDMS). The AgNWs coating suppresses thermal radiation from the human body to achieve radiative heating, while the MXene coating enhances solar heating, ensuring thermal comfort in cold conditions. The treated fabric also exhibits electrical heating for heat compensation in the absence of sunlight, remarkable EMI shielding performance (55.6 dB) is also achieved. Enhanced fire safety is demonstrated as the treated fabric extinguishes when exposed to flame, reducing heat release by 45.9 % relative to the control nylon/cotton blend fabric (CO/NY). Additionally, the treated fabric exhibits significant antibacterial properties against Gram-negative E. coli and Gram-positive S. aureus, along with a notable water contact angle (WCA) of 130.2°. This work provides a promising method for the development of eco-friendly wearable smart fabrics with well-balanced desirable properties.

Enhancing water resistance and flame retardancy of wood through phytic acid catalyzed in-situ polyesterification

The treatment of wood using in-situ polyesterification with citric acid and D-sorbitol (SCA) is a novel method for enhancing wood properties. This method can effectively improve the dimensional stability and biological durability of wood. However, achieving effective fixation of polyester in wood at lower curing temperatures has not been achieved. In this study, phytic acid was used to catalyze in-situ polyesterification of SCA. The autocatalytic reaction pattern of SCA polyesterification was elucidated through an investigation of the kinetics of the curing reaction. It was also confirmed that phytic acid reduces the curing temperature and activation energy of SCA. The investigation of polyesters revealed that phytic acid catalysis enhances the esterification degree and thermal stability of the polyester. Wood treated with SCA and 2%wt phytic acid exhibited a 44% reduction in polyester leaching. Moreover, it demonstrated high water resistance and dimensional stability, with water repellency efficiency of up to 33.8% and anti-swelling efficiency of up to 46.2%. Remarkably, it exhibited excellent flame retardancy, with an oxygen index of 33.1% and a 47.5% reduction in total heat release. The outstanding flame retardancy is attributed to the dual action of phytic acid in both the solid phase and gas phase.

Digital fabrication material processing strategy for bespoke low clinker mass concrete components

Digital manufacturing techniques are seen to be very promising in concrete construction because of their potential for increasing productivity, as well as their potential to increase sustainability due to reduced material usage via nonstandard geometry. Concrete 3D printing via extrusion has received the most attention as a method, however the problem of implementing reinforcement remains unresolved; therefore, printed concrete typically serves as either a formwork or as unreinforced masonry. The recently developed technique of Digital Casting allows for digitally produced concrete components that implement standard reinforcement bars. The technique was developed especially for digitally produced, nonstandard formworks, and relies on controlled set acceleration of a self-compacting concrete to control formwork pressure during production.Digital fabrication techniques such as Digital Casting (and 3D Printing), however, have notoriously high cement contents due to processing requirements, and this may negate any sustainability benefit that can be realized through material savings in a bespoke concrete component. Research efforts to bring these cement contents closer to standard concretes have focused on: 1) reducing paste content through increased aggregate content and 2) reducing clinker content through substitutions, with most recent efforts focused on the latter. A recent project demonstrated, additionally, that elevated clinker contents negatively impact the casting of mass concrete elements due to high heat generation, which limits the applicability of digital fabrication for mass concrete applications.In this study, the use of a CEMIII (slag substituted cement) based mix design for this type of application was examined. The mix was successfully accelerated to control formwork pressure in a digital casting process of a thick (>1 m) bespoke element with overhang, and internal temperatures monitored. The reduced heat release generated temperatures of only half of those generated by a previous mix design with higher clinker content.

The investigation of flame-retardant fiber mats for high performance composites: flame retardancy and structure performance

The flame-retardant performance of carbon fiber reinforced composites serves as a critical metric for structural stability. Nonetheless, the prevalent methodologies for improving the flame retardancy of composites struggle to reconcile the dual objectives of flame retardancy and mechanical robustness, due in part to the constraints imposed by the conventional additive-based approach on the material interface. This study introduced a novel method involving a glass fiber mat, which was augmented with a polyurethane-based treatment integrated with flame-retardant substances, in particular ammonium polyphosphate and nickel hydroxide. This fiber mat was strategically applied to the composite surface, conferring both flame retardancy and enhanced structural resilience. The structure performance and flame retardancy of composites were characterized by Fourier transform infrared spectroscopy, scanning electron microscopy, and the cone calorimeter test. Experimental comparisons with nontreated controls indicated that the innovative composites exhibited a reduction in total heat release and total smoke production by 13.7% and 18.8%, respectively. Concurrently, a notable enhancement in mechanical properties was observed, with increases of 20.9% and 23.1% for tensile and flexural strength. This well-balanced performance is attributable to the structure design, with toughened glass fiber mats to protect the composite surfaces from structural failure, and flame-retardant agent composition for combustion resistance and smoke suppression. Consequently, the proposed integrative flame-retardant structural design, enriched with specific flame-retardant treatments, offers a promising avenue for fabricating high-performance composite materials with potential utility in the aviation and aerospace sectors.

Enhancing the flame retardancy of polylactic acid nonwoven fabric through solvent-free transparent coating

Polylactic acid (PLA) nonwovens, recognized as eco-friendly substitutes for petroleum-based synthetic fibers, face a significant challenge due to their inherent flammability. This work addresses this concern by synthesizing a hyperbranched polyphosphoramide flame retardant (TPDT) through a one-step polycondensation process without using solvent and catalyst. TPDT is subsequently applied to PLA nonwovens using a dip-pad finishing technique. Notably, with a mere 7 wt% weight gain of TPDT, the PLA nonwovens exhibit a substantial increase in the limited oxygen index (LOI) value, reaching 32.3 %. Furthermore, the damaged area in the vertical burning test is reduced by approximately 69.2 %. In the cone calorimeter test, 17 wt% weight gain of TPDT results in a 51.4 % decrease in peak heat release rate and a 56.0 % reduction in total heat release compared to the control PLA. Additionally, char residue increases from 1.5 wt% to 31.1 wt% after combustion. The strong affinity between TPDT and PLA molecules persists even after repeated abrasion, ensuring sustained flame retardancy. Importantly, the introduction of TPDT also imparts increased softness to the PLA nonwovens. This work addresses this concern by synthesizing a hyperbranched polyphosphoramide flame retardant (TPDT) through a solvent-free, catalyst-free, and one-step polycondensation process.

The effect of organophosphorus flame retardants on the combustion behavior and performance of poly (methyl methacrylate)

Maintaining transparency poses a challenge in the preparation of flame-retardant poly (methyl methacrylate) (PMMA). The feasibility of preparing flame-retardant transparent PMMA by incorporating oligomeric resorcinol bis(diphenylphosphate) (liquid), 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) and hexaphenoxycyclotriphosphazene (solid) as additives has been explored. The impact of the flame retardants on the processing performance, thermal stability, combustion behavior and mechanical properties of PMMA has been investigated. The presence of organophosphorus compounds does not impact the transparency of PMMA and has a significant plasticizing effect. The modified PMMA displays a UL94 V-2 rating largely due to the formation of noncombustible droplets. However, the blend exhibits lower heat resistance, modulus and strength than does unmodified PMMA. The presence of organophosphorus compounds induces a higher limiting oxygen index (LOI) and reduced heat release for combustion of the blends than observed for PMMA without relying on charring, among which DOPO has a higher flame retardant efficiency due to its higher phosphorus content and lower decomposition temperature.

Seeding effects of submicron CaAl-NO3 LDH particles on the hydration and properties of Portland cement and sulfoaluminate cement pastes

Layered double hydroxide (LDH) is reported to improve the durability of concretes, primarily due to its ability to exchange anionic species, including chloride, which is implicated in corrosion-driven durability issues. However, there is no comprehensive study investigating the effect of LDH on the properties of different cement systems at both early and mature ages. In this study, the early age and mature age properties of Portland cement (OPC) and calcium sulfoaluminate (CSA) cement pastes seeded with submicron-sized calcium aluminum-NO3 LDH (CaAl-NO3 LDH) were investigated. The effects of the 1–5%mass dosage of LDH on the hydration of both cement systems were characterized by rheology, isothermal calorimetry, porosimetry, compressive strength tests, thermogravimetric analysis, and x-ray diffraction. Time-dependent rheology results indicate that CaAl-NO3 LDH seeding enhanced the buildability of cement pastes, as evidenced by increased plasticity loss, hardening, and yield stress. While LDH seeding accelerated hydration kinetics for both CSA and OPC pastes, interestingly, the OPC exhibited reduced heat release, suggesting potential applications of LDH as heat sink in various areas, including building in hot climates, reducing heat and crack-propensity in mass concrete placements, and 3D-printed OPC-based concretes. Although LDH slightly decreased compressive strengths at both 1d and 28d, its primary role was to expedite the hydration process without enhancing the microstructure or strength of the final product.

Enhancing the Flame Retardancy of Polyester/Cotton Blend Fabrics Using Biobased Urea-Phytate Salt.

The use of biobased flame-retardant (FR) agents for reducing the flammability of polyester/cotton (T/C) blend fabrics is highly desirable. In this study, a novel and sustainable phosphorus/nitrogen-containing FR, namely, phytic acid-urea (PA-UR) salt, was synthesized. The PA-UR salt was further used to enhance the FR performance of T/C fabric through surface modification. We further explored the potential chemical structure of PA-UR and the surface morphology, thermal stability, heat release capacity, FR properties, and mode of action of the coated fabric. The coated fabric achieved self-extinguishing and exhibited an increased limiting oxygen index of 31.8%. Moreover, the coated T/C blend fabric demonstrated a significantly reduced heat release capacity, indicating a decreased fire hazard. Thermogravimetric analysis revealed the anticipated decomposition of the coated T/C blend fabric and a subsequent increase in thermal stability. The burned char residues also maintained their fiber shape structures, suggesting the presence of condensed FR actions in the PA-UR-coated T/C blend fabric.

Mechanical and Fire Properties of Flame-Retardant Laminated Bamboo Lumber Glued with Phenol Formaldehyde and Melamine Urea Formaldehyde Adhesives.

This study investigated the effects of different adhesives, phenol formaldehyde (PF) and melamine urea formaldehyde (MUF), on the mechanical and fire properties of flame-retardant laminated bamboo lumber (LBL). The results demonstrated that the flame-retardant treatment using phosphorus-nitrogen-boron compounds endowed the LBL with excellent flame retardancy and smoke suppression properties, even though the bending strength and bond shear strength were slightly reduced. The PF-glued LBL exhibited superior mechanical and shear properties to the MUF-glued ones, primarily due to its higher processing temperature and deeper adhesive penetration. In addition, the MUF-glued flame-retardant LBL displayed better heat release reduction and smoke suppression properties than the PF-glued LBL, which resulted from the synergistic flame retardancy between the melamine element in MUF and the applied flame retardant. The analysis of the influence of adhesive type on the mechanical and fire properties of flame-retardant LBL holds significant importance for the future design and production of high-performance LBL material.

Effect of synthesized lignin-based flame retardant liquid on the flame retardancy and mechanical properties of cotton textiles

The flammability of cotton (Gossypium hirsutum) is a significant concern for technical applications, prompting ongoing research into solutions to mitigate this risk. Traditional flame-retardant methods utilizing acid-based approaches are complex and can negatively affect the mechanical properties of textiles. To address these challenges, this study focuses on developing a liquid bio-based flame retardant (LBF) utilizing a lignin-silica-based liquid (LSL) extracted from rice husk (RH) (Oryza sativa ssp. japonica) and 9, 10-Dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO). A one-pot dip-coating technique is utilized to treat cotton with the LSL, and the flammability and mechanical properties of the treated cotton are subsequently tested. Fourier-transform infrared spectroscopy (FTIR) confirms the covalent bond formation of the LSL with DOPO and the hydrogen bond formation of the LBF with cotton. Scanning electron microscopy (SEM) confirms the uniformity of the coating. The experimental results demonstrate that the treated cotton exhibits self-extinguishing behavior during a vertical burning test (VBT), with a 78% reduction in peak heat release and a 65% reduction in total heat released during pyrolysis combustion flow calorimetry. Surprisingly, the treatment also improves the tensile behavior of the cotton by 21.7% and thermal stability by producing a protective char layer that accounted for 36.9% of the final residue. This study provides a promising approach for improving the flame resistance and mechanical strength of cotton for technical applications.

Comparison of multi‐component and mono‐component intumescent flame retardants for thermoplastic polyurethane composites

AbstractConventional intumescent flame retardant (IFR) is comprised of multiple components (acid, carbon, and gas source). In comparison, “all‐in‐one” design of mono‐component IFR is effective to impart the homogeneity to functional sources in polymer matrix, which is significant to improve the synergy against combustion. In this work, a core‐shell structured mono‐component IFR (MAPP@FDS) are prepared with ammonium polyphosphate (APP) and furfural‐derived Schiff base (FDS) and applied to modification of thermoplastic polyurethane (TPU). TPU composite with the as‐prepared mono‐component IFR (TPU/MAPP@FDS) exhibits V‐0 rating in UL‐94 test and a limiting oxygen index (LOI) value of 32.0%, with prominent bulkiness of carbonaceous layer. Cone calorimetry tests (CCTs) showed a significant reduction in total heat release (THR) and peak heat release rate (pHRR) for TPU/MAPP@FDS compared with the TPU composites with multi‐component IFR. By analyzing the morphology and composition of residual char, the flame‐retardant mechanism of TPU/MAPP@FDS is reasonably proposed. This work illustrates the superiority of the integration to prepare mono‐component IFR and provides a potential method in developing TPU composites with remarkable flame retardancy.Highlights TPU/MAPP@FDS achieves a LOI value of 32.0% and UL‐94 V‐0 rating. TPU/MAPP@FDS exhibits significantly enhanced flame retardancy compared with TPU composites incorporated multi‐component IFR. The synergy in multi‐component IFR is prominently strengthened.

Bio‐marine shell powder‐filled jute fabric/epoxy composites: Chemical, combustion, and mechanical properties

AbstractNatural fiber/resin composites exhibit poor fiber–matrix compatibility and easy combustion. In this study, jute‐fiber‐reinforced epoxy resin was used to prepare composite materials by adding marine shell powder, which is a natural non‐combustible inorganic filler that originates from a variety of sources. The morphology, composition, thermal stability, combustion performance, and mechanical properties of the prepared composites were tested using several characterization methods. The results show that the marine shell powder was evenly distributed in the epoxy resin and did not affect the adhesion between the epoxy resin and the jute fiber. When 20% marine shell powder (SMJF20) was added to the jute‐fiber‐reinforced epoxy resin composite, the pyrolytic residual content was 21.88% (60.2% higher than that without), and the maximum heat release rate was 350.75 kW/m2 (22.8% lower than that without). The total heat release and total smoke release of SMJF20 were also 13.9% and 30% lower than that of MJF, respectively. The addition of marine shell powder did not significantly affect the tensile strength, whereas the tensile modulus of SMJF20 increased by approximately 13.9%, the fracture strain decreased by approximately 13.4%, and the bending strength and modulus decreased by approximately 12.9% and 13.0%, respectively. Marine shell powder is an ideal biomass filler for jute‐fiber‐reinforced epoxy resins.Highlights Jute‐fiber‐epoxy composites fortified with non‐combustible marine shell powder. Effective filler distribution without compromising epoxy‐jute fiber adhesion. 20% marine shell powder significantly reduces heat release and smoke release. Tensile strength unaffected; tensile modulus and residual content increased. Marine shell powder proves ideal for enhancing epoxy resin with jute fibers.

Reasonable multi-functionality of cotton fabric with superior flame retardancy and antibacterial ability using ammonium diphosphate as cross-linker

Ammonium phosphates have been proven to be efficient and durable flame retardants for cellulose fabric. However, a facile process for their multifunctional flame-retardant modification has not yet been reported. In order to achieve this goal, we synthesized an ammonium diphosphate of ethylene glycol (AP) and used it as a crosslinker to fabricate flame-retardant and antibacterial cellulose fabric with a dihydroxyl N-halamine precursor (BD) via a one-pot process. The AP/BD modified fabric exhibited superior flame retardancy, with a LOI value of 32.9% and self-extinguishing behavior at only 11.0% weight gain. The heat release was significantly inhibited, with an 81% reduction in peak heat release rate (PHRR) and a 60% reduction in total heat release (THR). Furthermore, the modified fabric maintained its self-extinguishing properties even after undergoing 50 washing cycles, demonstrating excellent washing durability with a LOI value of 30.5%. In addition to its outstanding flame retardancy, the AP/BD modified fabric also displayed excellent biocidal efficacy due to the formation of N-Cl bonds through simple bleaching treatment. All inoculated bacteria were killed within just 5 min of contact without any noticeable dissolution occurring. Moreover, the oxidative chlorine that acted as an antibacterial factor could be recharged after long periods of storage and washing. Importantly, no significant changes in whiteness, air permeability or hand feeling were observed after the AP/BD modification process. Therefore, this work presents a common and facile approach for preparing highly-efficient flame-retardant cellulose fabrics with multifunctionality.

Employing the spray system to alleviate the thermal action of air-conditioning in summer

Widespread adoption of air-conditioning significantly enhances indoor thermal comfort in summer, but the heat dissipation from these outdoor units contributes to an increase in ambient air temperature, exacerbating urban heat island effects. Consequently, as outdoor thermal conditions worsen, the energy consumption associated with air-conditioning is likely to escalate. The spray system becomes a suitable choice due to the obvious advantage of heat absorption through the droplet evaporation. To assess the effectiveness of the spray system in reducing heat release, a comparative study was conducted between two identical buildings with the same air-conditioning system, but only one of which incorporated the spray system. Three installed locations are considered with the spray location in inlet (Case 1), outlet (Case 2) and both inlet & outlet (Case 3) of outdoor units. The results demonstrated the average temperatures of air outlet were reduced by 4.0 °C, 6.3 °C, and 7.9 °C for Cases 1–3, respectively, accompanied by a reduction in energy consumption of the air-conditioning system by 18.8%, 13.9%, and 37.3% respectively. The most significant benefits were observed when the spray location was installed in both outdoor unit inlet and outlet (Case 3). The spray system established a virtuous cycle in heat dissipation improvement, evaporation enhancement, and air temperature reduction.

A durable coating constructed by metal-organic framework and polyphosphazene for flame retardant cotton fabric with enhanced mechanical properties

The extremely flammable cellulose macromolecules in cotton fabrics seriously affect their application in the field of flame retardancy. In this paper, the surface of cotton fabric was modified with citric acid, and then metal-organic framework (UiO-66), cationic starch (St) and polyphosphonitrile (PZS) microspheres containing the transition metal element Zr were sequentially deposited to prepare an efficient and economical cotton fabric. St-PZS double-impregnated cotton fabrics have better thermal stability, flame retardancy and mechanical properties. And the coating does not affect the whiteness and stiffness of the cotton fabric. The results of thermogravimetric analysis showed that cotton/UiO-66/2St-PZS had a higher residual char rate (25.34%) under N2 atmosphere, which was 200.1% higher than that of control cotton (8.28%). In addition, cotton/UiO-66/2St-PZS had a 46.6% reduction in peak heat release, a 31.7% reduction in total heat release, and a 35.3% reduction in the peak of CO2 production compared to control cotton. It is worth noting that the average gross calorific value is 63.3% lower than that of the control cotton, indicating that flame retardant cotton fabrics can effectively inhibit the production of flammable gases. In addition, the tensile strength and elongation at break of cotton/UiO-66/2St-PZS are 458.79 N and 11.04%, respectively. After 20 laundering cycles, the mechanical properties remained almost unchanged.

The synthesis of biphenyl ether/vanillin‐based flame retardants for enhancing both the flame retardant properties and mechanical performance of epoxy resin

AbstractImparting good flame retardancy and mechanical properties to epoxy resin (EP), while pursuing the sustainable and safe application of EP, we synthesized a novel reactive phosphorus/nitrogen flame retardant for biomass through nucleophilic addition reaction, which contains flexible ether bonds and rigid aromatic ring structure (DVD). Owing to the cooperative effect of aryl ether diamine, phosphorus phenanthrene, and biomass vanillin, the DVD exhibited excellent flame retardancy. EP/DVD‐1 (0.4 wt% phosphorus content) achieved UL‐94 V‐0 rating, with an improvement in limiting oxygen index value from 26.5% (pure EP) to 32.5%. In the CCT, the modified DVD EP showed a 44.5% reduction in peak peak of heat release rate (PHRR) and a 38.0% reduction in total heat release compared to pure EPs. And flame retardant epoxy resin (FREP) still had good transparency after the addition of DVD, which indicated the nice compatibility between DVD andEP. What was noteworthiness was that at high levels of addition, the mechanical properties of modified EP for DVD was still improved compared to pure EP. These results demonstrate that DVD is an excellent and multifunctional bio‐based flame retardant with broad application prospects in the field of EP material modification.

Optical diagnostics in impact of ammonia energy ratio and diesel split ratio on combustion process and flame propagation in an Ammonia-Diesel Dual-Fuel engine

In the context of ammonia-diesel dual-fuel (ADDF) engines, challenges such as ignition difficulties and misfires emerge prominently at elevated ammonia energy ratios. To alleviate these challenges, this study aims to elucidate the effects of ammonia energy ratios (AER) and diesel split ratios (DSR) on the combustion process and flame propagation in an optical ADDF engine configuration. Utilizing optical diagnostics, including flame luminescence and high-speed photography, the study provided insights into combustion boundary conditions specific to ADDF engine operation. The results highlight that an increase in AER to 60 % results in a marked decrease in peak cylinder pressure, peak apparent heat release rate (AHRR), and the in-cylinder pressure rise rate. This is accompanied by a reduction in IMEP from 4.16 bar to 3.24 bar, indicating a decline in combustion efficiency upon greater ammonia addition. Flame luminosity exhibits a shift from a diesel-like blue hue to an ammonia-tinted pale yellow. This change coincides with a significant reduction in soot formation and restrictions in flame area and propagation speed, largely due to ammonia's intrinsically slower burning velocity and its chemical interplay with diesel. Implementing a dual injection approach further accentuates the peak in-cylinder pressure and AHRR, with the second injection playing a crucial role in ignition. Optimizing the DSR to 40 % improves combustion efficiency, attributed to enhanced fuel-oxygen interactions. Conversely, DSR values of 60 % and 80 % pose challenges. A reduction in diesel content in the subsequent injection leads to a leaner blend, subsequently affecting combustion efficiency, as indicated by reduced heat release rate and diminished IMEP. This study emphasizes understanding the ammonia-diesel interaction and the importance of choosing the appropriate DSR to exploit the advantages of ADDF engines.

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.

Combination effect of ADP‐intercalated kaolinite and ammonium polyphosphate on simultaneously enhancing the flame retardancy and smoke suppression of epoxy resins

AbstractIn this article, ammonium dihydrogen phosphate (ADP) was successfully intercalated into kaolinite (Kaol) to prepare a novel synergist named ADP‐intercalated kaolinite (K‐ADP). The chemical structure of K‐ADP was thoroughly characterized using various analytical methods, and then K‐ADP was combined with ammonium polyphosphate (APP) to enhance the fire safety of epoxy resins (EPs). The flammability results indicate that the combination of K‐ADP and APP exerts super positive effects on reducing the heat release and smoke emission of EPs than the mixture of Kaol and APP. Especially, the EP/8 wt% APP/2 wt% K‐ADP has a super LOI value of 33.2% and reaches a UL94 V‐0 rating accompanying with a 29.1% reduction in total heat release (THR) and a 72.7% reduction in total smoke production (TSP) compared to pure EP. The morphology and component analyses show that the combination of K‐ADP and APP facilitates the formation of more phosphorus‐rich crosslinking and aromatic structures in the condensed phase to enhance the compactness and intumescence of char layer, which effectively segregates heat, combustible compounds and smoke particles. Thermogravimetric analysis shows that the combination of K‐ADP and APP exerts super char‐forming ability in EPs, and the residual weight of EP/8 wt% APP/2 wt% K‐ADP at 800°C increases from 7.8% of pure EP to 19.7%. Mechanical test shows that the addition of K‐ADP displays the less adverse effect on the mechanical properties of EP composites compared to Kaol due to the better compatibility of K‐ADP and epoxy matrix with DSC analysis support.Highlights A novel ammonium dihydrogen phosphate‐intercalated kaolinite (K‐ADP) was synthesized. APP/K‐ADP system exerts super positive effect on reducing fire hazards of EPs. APP/K‐ADP system takes effect in both gas phase and condensed phase. APP/K‐ADP has a satisfying balance between fire safety and mechanical properties in EPs.

Synthesis of phosphaphenanthrene derivatives as flame retardants and their properties in epoxy resin composites

AbstractIn order to further improve the flame‐retardant properties of epoxy resins (EPs), two hydroxyl‐containing phospha‐phenanthrene derivatives, DOPO‐PHBA and DOPS‐PHBA, were prepared from the molecular structure design by using 9,10‐dihydro‐9‐oxa‐10‐phospha‐phenanthrene‐10‐oxide (DOPO), 9,10‐dihydro‐9‐oxa‐10‐phosphaphenanthrene‐10‐sulfide (DOPS), and 4‐hydroxybenzaldehyde (PHBA) as the raw materials. These composites of DOPO‐PHBA/EP and DOPS‐PHBA/EP were prepared by melt blending. The results showed that UL‐94 V‐0 was achieved with an LOI of 31.9% when just 7.5% DOPS‐PHBA was added to EP, while a limited oxygen index of 35.2% was achieved with 10% DOPO‐PHBA/EP. Moreover, in comparison with 7.5% DOPO‐PHBA/EP, 7.5% DOPS‐PHBA/EP has the lower peak of heat release rates, total heat release values, and fire growth rate, demonstrating that the flame‐retardant DOPS‐PHBA is more effective at reducing heat release, enhancing the material's flame retardancy, and lessening the intensity of EP burning. The Thermogravimetric‐infraredspectrometry (TG‐IR) results showed that the phosphorus‐containing radicals generated by DOPS‐PHBA/EP pyrolysis trapped the free radicals, such as H˙, O˙, or HO˙, thus providing free radical quenching. Furthermore, combining the macro and micro Scanning electron microscopy (SEM) test results, DOPS‐PHBA/EP has a better char formation ability and a denser char layer, which can play a better role in heat and oxygen insulation.