Reduction In Peak Heat Release Rate Research Articles

Enhanced mechanical property and flame resistance of phosphorylated cellulose nanofiber based‐aerogel combined with boric acid

AbstractAs for cellulose‐based aerogels, a feature of inadequate mechanics and easy‐flammability seriously restricts their practical applications. To address this issue, herein a lightweight, mechanical elastic and flame‐retardant phosphorylated lignin‐based cellulose nanofiber (PLCNF‐B) aerogel with the aid of boric acid was successfully obtained by freeze‐drying method. Due to the uniform and tough network structure benefitting by strong hydrogen bond between phosphorylated fibers and boric acid, the resultant aerogel showed excellent mechanical performance, that is, high compressive strength of 8.9 kPa (strain: 50%) and outstanding cyclic reliability (remain 90% after 10 cycles). Meanwhile, PLCNF‐B aerogel possesses highly improved flame‐retardant property, that is, a high LOI value (up to 46%), significantly reduced peak heat release rate (11.2 W/g) and total heat release rate (0.47 kJ/g). Based on structural observation and analysis, the flame‐retardant behavior should be attributed to the formation of PxOy/amorphous boron oxide protective layer, which is derived from the phosphorus containing group of PLCNF and boric acid. The splendid overall performance of aerogel material offers a potential material tactic for design and development of advanced bio‐based aerogels for practical applications.

Green synthesis of a P/N/B-containing aggregate for boosting fire-retardancy of PA6/aluminum diethylphosphinate composites

The intrinsic flammability of polyamide 6 (PA6) has significantly impeded its broad application regardless of its balanced physical properties. Aluminum diethylphosphinate (ADP), as a P-containing fire retardant, has been demonstrated to be effective in reducing flammability of PA6 because of its dual-phase modes of action by creating an intact protective char layer and inhibiting the burning process. However, the efficiency of ADP needs to be further improved for creating cost-effective fire-retardant PA6, in addition to its relatively high cost. To boost its efficiency, we, here, report a P/N/B-containing aggregate (MBA) as an effective synergist via green self-assembly of melamine (MA), boric acid (BA) and amino trimethylene phosphonic acid (ATMP) in an aqueous medium. The results show that the inclusion of 5 wt% MBA and 10 wt% ADP leads to a significantly reduced peak heat release rate (PHRR) by 52.5% compared to neat PA6, in addition to a desired UL-94 V-0 rating. A synergistic effect of 55.4 % is observed between MBA and ADP in terms of the PHRR value. This work provides a facile green strategy for developing eco-friendly multiple elements-containing fire retardants, which can be used as fire retardants alone or high-efficiency synergists for other fire retardants.

Design synthesis of melamine amino tris-methylene phosphonate modified halloysite nanotubes for epoxy resin with simultaneously improved flame retardancy, dielectric properties and mechanical performance

The development of epoxy resin (EP) with simultaneous enhancements in flame retardancy, mechanical performance, and low dielectric properties represents a significant and complex challenge. In this study, halloysite nanotubes (HNTs) were modified with melamine amino tris-methylene phosphonate (MA) to produce MA-modified HNTs (HMA), which were then integrated into EP to form EP/HMA composites. The incorporation of 1 wt% HMA significantly enhanced the flame retardancy (limit oxygen index up to 29.7%, UL-94 V-0 rating), reduced peak heat release rate by 23.4%, decreased total heat release by 11.9%, reduced total smoke production by 18.4%, and improved mechanical properties (tensile strength by 17.0%, impact strength by 61.0%) compared to pure EP. Additionally, EP/HMA showed a low dielectric constant (3.16) and a dielectric loss (0.019) at 1 GHz. This research presents a versatile strategy for creating multifunctional EP composites with high potential for applications in microelectronics, electronic packaging, and other relevant fields.

A novel phosphorus/nitrogen-containing polyacrylonitrile fiber with excellent flame retardancy and mechanical properties

To improve the flame retardancy, smoke suppression and mechanical properties of polyacrylonitrile (PAN) fiber, it was first modified with diethylenetriamine to prepare the aminated PAN fiber (A-PAN). Second, diethyl phosphite (DEP) was grafted onto the A-PAN to fabricate flame retardant PAN fiber (DEP-A-PAN). XPS and FTIR analysis confirmed that phosphorus and nitrogen elements were covalently bonded to the surface of PAN fiber. TGA revealed that the incorporation of DEP promoted char formation of PAN matrix and suppressed the thermal degradation. DEP-A-PAN exhibited a significantly reduced peak heat release rate (pHRR) compared to the control sample. Moreover, the limiting oxygen index (LOI) of DEP-A-PAN was up to 34.3 %, and remained at 26.6 % even after 50 laundering cycles (LCs), demonstrating excellent durable flame retardancy. Interestingly, DEP-A-PAN exhibited improved tensile strength of 2.97 cN/dtex. This work developed a simple and feasible method for preparing mechanical-enhanced flame retardant and smoke suppressive PAN fiber, which could be large-scale preparation.

Using renewable phosphate to decorate graphene nanoplatelets for flame-retarding, mechanically resilient epoxy nanocomposites

Eco-friendly, safe yet highly effective nanomaterials play an essential role in providing flammable polymers with a flame-retarding merit. However, there is a lack of research into bio-based, sustainable phosphate together with graphene for flame-retarding polymer nanocomposites. We herein report a method of electrostatically assembling renewable adenosine triphosphate (ATP), melamine, and graphene nanoplatelets (GNPs) into hybrid particles (ATP-melamine-GNPs). Demonstrating a relatively uniform dispersion in an epoxy matrix with strong interfacial adhesion, ATP-melamine-GNPs at 3 wt% increased Young's modulus, fracture energy release rate, and glass transition temperature by 91.5 %, 92.7 %, and 15.6 %, respectively. ATP-melamine-GNPs reduced peak heat release rate, total heat release, and total CO production by 30.7 %, 22.2 %, and 27.9 %, respectively. ATP-melamine-GNPs resulted in a far more continuous and compact char than individual ATP-melamine or GNPs. Synergy was observed for both mechanical properties and flame retardancy of the nanocomposites. The findings of this work provide a new platform for using bio-based, sustainable materials and GNPs in the development of flame-retarding, mechanically resilient polymer nanocomposites.

Thermal management ability and flame retardancy of silicone rubber foam filled with flame retardant phase change capsules

A novel phase change capsule with layered double hydroxide (LDH) modified SiO2 shell (named M-EPCM) was designed and prepared, which was used to improve the thermal regulation performance and flame retardancy of silicone rubber foam (SRF). The SRF-3 composite containing 18 wt% M-EPCM presented greatly improved thermoregulation ability, and excellent thermal reliability even after 100 cycles. Besides, SRF-3 also exhibited excellent flame retardancy, with the limiting oxygen index exceeding 31.0%, reduced peak heat release rate (36.4%) and low total smoke yield (13.8 m2). The flame retardant mechanism analysis revealed that barrier effect, catalytic crosslinking and polyaromatic reaction provided by LDH played an important role. Moreover, SRF composites have outstanding mechanical properties, especially SRF-3 which showed a 150% and 85% increase in tensile strength and compression strength compared with pure SRF, respectively. This article provides a new idea for further application of LDH in the field of thermal management.

Eco-friendly in-situ mineralization of bamboo for flame retardancy

An inorganic-organic structure including calcium carbonate (CaCO3) and bamboo was prepared via in-situ mineralization to improve the flame retardant properties of bamboo. During the mineralization, CaCO3 deposited mostly in parenchyma cells with pits and multilayer cell walls, which contributed to a stable cross-linked structure in bamboo by binding negatively charged calcium ions to carboxyl groups. Also, mineralization reduced the relative content of carbohydrates but promoted the formation of char residue. Cone calorimetry tests demonstrated that the mineralized bamboo had substantially reduced peak heat release rate (pHRR), lower total heat release (THR), lower peak smoke produce rate (pSPR) and total smoke release (TSR) than control bamboo. The improved flame resistance and smoke suppression properties of bamboo were primarily attributed to the even and dense coverage of non-combustible CaCO3.

Synthesized acrylate monomers to improve photothermal conversion efficiency and fire safety of PEG/black phosphorus (BP) phase change composites

The combination of photothermal components and phase change materials (PCMs) has received extensive attention. However, the incorporation of photothermal functionality into PCMs confronts the fatal problems of low utilization efficiency and performance compromise during processing. In this work, an acrylate monomer-passivation strategy was proposed to wrap photosensitive black phosphorus nanosheets (CG-BPs) to retain their intrinsic properties for high photothermal conversion efficiency. In addition, a flame-retardant acrylate (MCBDB) was further synthesized to crosslink with CG-BPs and build a framework for PEG1000 encapsulation. The resulting composite (cPCMs-1.2) was able to achieve a photothermal conversion efficiency of 85.3% even with a low content of CG-BPs (1.2 wt%) and unconcentrated irradiation. And benefiting from the synergistic flame-retardancy of CG-BPs and poly(MCBDB), the PCM composites displayed a reduced peak heat release rate of 38.7% compared with that of pristine PEG1000, indicating improved fire resistance. Considering its appropriate phase-change temperature, the application demonstration of the fabricated cPCMs-1.2 for human body hot compress was conducted, in which the promoting effect on blood circulation was observed. This work provides us with a new idea for the simple fabrication and new application of photothermal PCM with high photothermal conversion efficiency and application safety.

Biomass-derived polyphosphazene toward simultaneously enhancing the flame retardancy and mechanical properties of epoxy resins

As one of the most widely used polymers, the intrinsic brittleness and high flammability bring about a stringent requirement for the practical application of epoxy resins (EPs). It is difficult to toughen EP without compromising its mechanical and thermal properties for many conventional toughening agents. Here, a novel furan-derived bio-based polyphosphazene (PFMP) with a flexible backbone and rigid side groups was prepared by the nucleophilic substitution reaction between polydichlorophosphazene (PDCP) and furfuralcohol. The resultant PFMP was incorporated into EP to realize exceptional toughening, strengthening, and flame retardant function. By adding 15% of PFMP, the limit oxygen index value is from 25% (EP) to 33% (EP/PFMP-15) and reaches the UL-94 V-0 rating. According to the cone calorimeter results, EP/PFMP-15 exhibits exceedingly reduced peak heat release rate (pHRR) (50.2%) and total heat release (THR) (49.6%). The significantly increased fire performance index (FPI) and decreased fire growth rate index (FIGRA) of EP/PFMP-15 demonstrate an improvement in its flame retardancy. The catalytic carbonization effect (condensed phase) and radical quenching effect (gas phase) of PFMP account for the greatly improved flame retardancy. Moreover, the impact and tensile tests indicate that PFMP can ameliorate the mechanical performance of EP with a maximum increase of impact strength (111.8%) and elongation at break (35.2%) for EP/PFMP-5. With 15% PFMP added, the tensile strength of EP/PFMP-15 increases by 40.4%. This work demonstrates that PFMP is expected to overcome shortcomings (flammability, toughness, and strength) of EP and spread its applied fields.

Enhanced Flame Retardancy of Rigid Polyurethane Foams by Polyacrylamide/MXene Hydrogel Nanocomposite Coating.

Rigid polyurethane foam (RPUF) has been widely used in many fields, but its high flammability and frequent release of large amounts of toxic smoke during combustion limit its application. Hydrogel coatings, as a kind of environmentally friendly material, contain large amounts of water, which is beneficial to flame retardance of RPUF. MXene, as a two-dimensional inorganic nanomaterial, possesses a large specific surface area and good thermal stability, performing well in smoke suppression and as a physical barrier for flammable gas products and heat. Herein, to address the fire hazards of RPUF, MXene nanosheets were first grafted with double bonds, and then introduced into a polyacrylamide hydrogel system by radical polymerization to prepare MXene-based hydrogel coating (PAAm-MXene). The flame-retardant RPUF (coated RPUF) was prepared by painting the PAAm-MXene coating onto RPUF surface. The dispersion of modified MXene nanosheets (m-MXene) in hydrogels is improved compared with pristine MXene, and the addition of m-MXene contributes to the thermal stability enhancement of PAAm-MXene. Cone calorimetry, water retention test, and open flame combustion test were used to study the flame retardancy, smoke suppression, and water retention of flame-retardant RPUF. The coated RPUF exhibited significant flame retardancy, including reduced peak heat release rate (pHRR) at a maximum by 25.8%, and total heat release rate (THR) at a maximum by 24.6%, and total smoke production at a maximum by 38.9%. The results show that both MXene and m-MXene can improve the flame retardancy, smoke suppression, and water retention of hydrogels, but m-MXene has a better smoke suppression effect than MXene. That can be ascribed to the better dispersion of m-MXene than pristine MXene. The detailed performance improvement mechanisms are proposed. This work will not only improve the flame retardancy of RPUF, but also promotes the exploration of new flame-retardant strategies for RPUF.

Effect of using laser incising treatment and fire-retardant coating on Larix kaempferi wood to improve fire retardant performance

To improve fire-retardant performance of Japanese larch (Larix kaempferi) wood, this study analyzed the effect of pinholes made by laser incising and fire retardant (FR) coating on the surface of Japanese larch wood. Combustion properties such as peak heat release rate (PHRR) and total heat release (THR) of Japanese larch and Korean red pine (Pinus densiflora) wood without FRs showed similar tendencies. The comparison of the combustion properties on wood injected with an inorganic water-soluble FR under vacuum revealed that the PHRR and the THR of Korean red pine wood decreased by 37 and 62%, respectively. FR was injected into the Japanese larch specimens with pinholes on the surface and additionally coated with 5% sodium silicate and 35% potassium bromide. The results indicated a 16 to 25 and 19% reduction in PHRR and THR, respectively, compared to those without the FR. Despite the pinholes and FR coating, the FR employed in this study did not meet the standards set in Korea (THR of 8 MJ/m2). This study serves as a reference for future studies on the application of pressurized conditions and other surface treatments to improve the FR percent injection and performance of Japanese larch wood.

A flame‐retardant and optically transparent wood composite

AbstractTransparent wood (TW) is an emerging functional wood composite with attractive advantages and promising applications. The versatile functions of the impregnating polymers offer various properties to the TW, but also threaten its fire safety and restrict its applications. Herein, fire retardant TW (FRTW) is prepared by ultraviolet (UV)‐assisted lignin modification followed by refractive‐index matched transparent fire‐retardant coating (TFRC) impregnation. FRTW has a compact structure with a homogeneous interface between the TFRC and cell wall. It presents excellent optical and structural properties with 95% optical transmittance, 88% UV absorption, 96% high haze, and 154.3 MPa tensile strength. Moreover, FRTW shows great flame retardancy against high‐temperature heating. It has a 68.2% reduced peak mass loss rate and a 2.8‐fold increased char residual than natural wood (NW). Compared to the conventional epoxy‐based TW, FRTW has a weaker combustion behavior with an 81.4% reduced peak heat release rate. The enhanced flame retardancy is due to the synergistic flame retardancy (combining cooling, dilution, insulation and radical capture effects) of the TFRC. FRTW provides a new wood composite alternative with excellent optical properties and flame retardancy, which broadens the application potential of conventional TW with excellent fire safety.

Assembled hybrid films based on sepiolite, phytic acid, polyaspartic acid and Fe3+ for flame-retardant cotton fabric

Abstract To impart durable flame retardant property to cotton fabric, a kind of multilayered hybrid film based on environmentally friendly phytic acid, sepiolite, polyaspartic acid, and Fe3+ were deposited on the surface of cotton fabric by layer-by-layer and spraying method to form a dense protective layer. Compared with cotton fabric, hybrid film coated cotton showed excellent flame retardant property and low fire hazard, which can be demonstrated by vertical flame test, limiting oxygen index (LOI) and cone calorimeter test. After-flame time and after-glow time of hybrid film coated cotton is 1 s and 1 s, respectively. LOI value of hybrid film coated cotton increased by 44.4% compared with control sample. Cone calorimeter test revealed a total heat release rate reduction of 52.6% and peak heat release rate reduction of 73.6% for hybrid film coated cotton fabric. This work demonstrates that the hybrid film composed of phytic acid, sepiolite, polyaspartic acid, and Fe3+ could improve the durable flame retardant property of cotton fabric.

A green, durable and effective flame-retardant coating for expandable polystyrene foams

Expandable polystyrene (EPS) foam, one of the most widely used thermal insulation of building materials, is highly flammable, while its traditional flame-retardant coating has been severely restricted by the low efficiency and the use of toxic formaldehyde adhesive. Herein, we demonstrate a formaldehyde-free phosphorus-containing polysiloxane coating that acts as both an adhesive and a flame retardant for EPS foams. In this design, on one hand, the high adhesion of the polysiloxane can evenly and tightly bind the EPS beads and expandable graphite (EG, a flame-retardant synergist filler) at a relatively low additive loading, thus leading to durable thermal insulation even under high humidity conditions. On the other hand, the functional coating can promote the formation of P/Si-containing graphited char layers during the combustion of the EPS composite, which can effectively isolate oxygen, heat, combustible compounds, and smoke particles. As a result, the EPS composite showed excellent flame retardancy with a high limiting oxygen index of 36%, a UL-94V-0 rating, and a significantly reduced peak heat release rate (−76%), while the smoke release can be greatly suppressed both in cone calorimetry and smoke density tests. This work provides a new strategy for the design of environmentally friendly coatings, which can give EPS foam high fire safety and excellent comprehensive performance.

Halogen-free and phosphorus-free flame retardants endow epoxy resin with high flame retardancy through crosslinking strategy

Epoxy resin (EPs) has been widely used in many fields in recent years, such as electronics, adhesives, coatings, and so on, which mainly benefiting from its excellent mechanical and chemical properties, low price and easy preparation. However, conventional EPs tend to be flammable, which significantly prevents their applications especially in high flame-resistance required areas. In this work, we introduce nitrile groups and the benzoxazine ring into the flame-retardant, followed by a simple heat treatment for a multiple cross-linking reaction in EPs. The resultant halogen/phosphorus-free and environmentally friendly network not only suppress the migration of the functional flame retardants from the substrate, but also shows much enhanced flame-retardant property, including the UL-94 rate, total heat release and reduced peak heat release rate. As a result, the thermosets can pass the UL-94 V-0 rate and reach a LOI value at 32.7% at a very low addition amount (10 wt%) of this cross-linked flame retardant.

Epoxidation of pillar[5]arene with three dimensional macrocyclic structure and host-guest capability for epoxy coatings

To expand the properties of epoxy coatings for emerging technologies, herein, a pillar[5]arene-based epoxy compound (PAEP) containing unique pillar-shaped three dimensional macrocyclic structure was prepared and cured with conventional 4,4′-diaminodiphenylmethane (DDM). Interestingly, the PAEP exhibited a strong host-guest complexation with 1,4-dibromobutane (DBrBu), a potential organic antibacterial agent, with a complex constant of 215.7 ± 11.02 M−1. Furthermore, the PAEP/DDM resin possessed enhanced mechanical and thermal properties, probably due to the increase of chain-entanglement brought about by the cyclic structure. Also, the PAEP/DDM resin exhibited excellent intrinsic flame retardant properties, including significantly reduced peak heat release rate (153.5 W·g−1) and high limit oxygen index (LOI) (34.7%), and a V-0 rating in the UL-94 test. Moreover, the PAEP/DDM resin exhibited a remarkably low dielectric constant of 2.25 at 106 Hz for telecommunication applications, which is much lower than the current epoxy resins with nanoporous inorganic modifiers. Therefore, the incorporation of pillar[5]arene is a fruitful pathway to expand the properties of epoxy resins and provides a new platform for decoration for various applications.

Preparation of soybean root-like CNTs/bimetallic oxides hybrid to enhance fire safety and mechanical performance of thermoplastic polyurethane

The three main fatal factors considered when Thermoplastic polyurethane (TPU) products catch fire are massive heat radiation, suffocation by smoke inhalation, and poisoning by toxic gases (CO and HCN). In this study, to weaken these adverse impacts, soybean root-like zeolitic imidazolate frameworks (ZIFs)-derived carbon nanotubes/bimetallic oxides (CNTs/BMO) hybrids are designed and prepared. In addition, we studied its performance in improving the fire safety of TPU. The in-situ growth of ZIFs on the surface can suppress the entanglement of CNTs (main roots), enhancing a uniform dispersion in the hybrid. Porous BMO and ultrathin N-doped CNTs (N-CNTs) functioned as conversion stations for organic and inorganic, similar to the root nodules and root hairs, respectively, resulting in the increased generation of char residues and suppressed emissions of smoke and toxic gases. Compared with neat TPU, there are 32.11%, 27.91%, and 41.91% reductions in peak heat-release rate, total smoke production, and total CO production, respectively, with 1 wt% of well-dispersed CNTs/BMO hybrids. In addition, the soybean root-like hybrids also have enhanced the mechanical performance of composites. On the basis of the satisfactory mechanical strength of neat TPU, the tensile strength and elongation (at break) of the soybean root-like hybrids are further increased by 70.61% and 16.49%, respectively. This work provides a feasible method to construct a well-dispersed inorganic hybrid with complex structure and excellent performance, which will deliver a new perspective for the development of multifunctional polymer composites.

Effects of layered double hydroxides on the thermal and flame retardant properties of intumescent flame retardant high density polyethylene composites

SummaryIn this study, two layered double hydroxides (LDHs), ZnAl‐LDH, and MgAl‐LDH, were combined with intumescent flame retardant (IFR) consisting of ammonium polyphosphate and tris (2‐hydroxyethyl) isocyanurate to prepare flame retardant high density polyethylene composites. The thermal and flame retardant properties of these composites were investigated by thermogravimetric analysis, limiting oxygen index measurement, and cone calorimetry, while the morphology and chemical structure of the char residue were analyzed by scanning electron microscopy, Fourier transfer infrared spectroscopy, and laser Raman spectroscopy. The results showed that the peak heat release rate (PHRR) of both HD/IFR/Zn‐LDH and HD/IFR/Mg‐LDH composites was 52.0% and 12.0% lower than that of HD and HD/IFR, respectively, suggesting that there was no difference in the reduction of PHRR between the two LDHs. The use of LDHs resulted in the formation of compact char residue with a high graphitic degree, but no significant increase in tensile strength.

Fire and mechanical properties of polymeric composites with keratin-based flame retardants

Due to the high flammability of polymeric materials, the development of a flame retardant with high-performance, low-toxicity and cost-effectiveness has been one of the most important issues in the polymer industry. To address these requirements, keratinous fibres have been employed for a novel intumescent flame-retardant fabrication. Phosphate loaded keratinous fibres through the sequential infiltration of phosphoric acid and reactive amines have shown a successful demonstration of the self-extinguishment (V0 grade) and ~80% reduced peak heat release rate in the vertical burn test (UL94) and cone calorimeter test, respectively. Owing to the unique char formation behaviour of the fibres with the combined effects of phosphorus compounds, the composites have achieved the improvement of flame retardancy compared to the commercial ammonium polyphosphate/polypropylene composite. Furthermore, the fibre addition has contributed to enhance the mechanical properties of the composites. For the practical application of the new FR, cost reduction capability depending on the type of reactive amine used for the phosphate production in the fibre, has also been investigated.

Iron-phosphorus-nitrogen functionalized reduced graphene oxide for epoxy resin with reduced fire hazards and improved impact toughness

Novel iron hexamethylenediaminetetrakis-(methylenephosphonate) (Fe-HDTMP)-reduced graphene oxide (Fe-rGO) hybrids were prepared by in situ immobilization of Fe-HDTMP nanoparticles and the reduction of graphene oxide via a hydrothermal strategy. Fe-rGO modification of epoxy resin (EP) improved mechanical properties, flame retardancy, smoke suppression, and thermal stability by combination with flame retardant elements (i.e. Fe, N, and P) and graphene nanoplatelets. The incorporation of 1% Fe-rGO increased the impact strength and storage modulus of EP by 19.2, and 27.9%, respectively. Additionally, the incorporation of 5% Fe-rGO helped EP/5Fe-rGO achieve UL-94 V0 rating with a limiting oxygen index of 30.5%. Compared to untreated EP, the modified EP exhibited 68.2% lower release of total smoke, 54.5% decreased peak CO production rate, 66.3% lower total heat release, and 47.7% reduced peak heat release rate of EP/5Fe-rGO. In addition, the glass-transition temperature of EP/Fe-rGO nanocomposite was maintained at a high level. The improved fire safety performance of EP/2Fe-rGO nanocomposite was due to the catalyzing carbonization effect, the release of inert compounds of Fe-rGO in condensed and gas phases, and the barrier effect of graphene.