Limiting Oxygen Index Value Research Articles

Preparation and performance of waterborne polyurethane coatings based on the intumescent flame retardant of boron, phosphorus, and nitrogen

AbstractPNB organic flame retardant was synthesized using 4‐formylphenylboronic acid, 4‐aminophenylthiophenol, 9,10‐dihydro‐9‐oxa‐10‐phos‐phaphenanthrene‐10‐oxide (DOPO), and then introduced into the hydroxyl‐terminated polybutadiene acrylonitrile (HTBN) molecular chain to successfully prepare a macromolecular flame retardant, which was used to prepare flame retardant waterborne polyurethane. The mechanical properties, thermal properties, and flame retardancy of waterborne polyurethane (FR‐WPU) were studied using thermogravimetic analysis (TGA), limiting oxygen index (LOI), scanning electron microscope (SEM), cone calorimeter, and universal testing machine, respectively, and the flame retardant mechanism of macromolecular flame retardants was explored. An LOI value of 29.76% and a UL‐94 V‐0 rating could be realized when the APFBH conjugation is 7.5 wt%, showing a significant improvement of melt dripping behavior and flame retardancy. It indicated that the fire resistance of FR‐WPU remarkably improved and displayed both gas and condensed phase mechanism. As the content of APBDH increased, the tensile strength and the elongation at break of FR‐WPU increased firstly and then decreased.

Green synthesis of a novel P/N/S containing bio-based flame retardant and its applications in poly(lactic acid): rapid self-extinguish, anti-dripping, and excellent mechanical performance

Poly(lactic acid) (PLA), which is recognized as a potential biodegradable material, brings serious fire concern because of its flammability with heavily molten drips. In this investigation, a bio-based flame retardant named CS@ATMP@MI (CAM) consisting of chitosan (CS), amino trimethylene phosphonic acid (ATMP), and methionine (MI) was developed through a simple and environmental-friendly synthesis approach. CAM provided effective flame retardancy and anti-dripping ability without compromising mechanical properties. PLA/CAM composites achieved a UL-94 V-0 rating with 1.0 wt% CAM and a limited oxygen index value of 28.4 % with 3.0 wt% CAM. The high efficiency is due to the high phosphate content in ATMP and the strong coordination between CS, ATMP, and MI. The cone calorimetry tests showed that adding 2.0 wt% CAM increased the total smoke production from 0.2 to 0.6 m2, and thermogravimetric analysis/infrared spectrum analysis indicated that combustible gas production was reduced over 50 % with 3.0 wt% CAM, demonstrating that phosphorus-nitrogen synergy in CAM could effectively capture free radicals and released inert gases. Char analysis showed that the PLA/CAM composites could form a thicker and denser char layer during combustion due to phosphorus-sulfur synergy, which promoted char formation to shield mass transfer. PLA/CAM composites maintained excellent mechanical performance, with a 3.0 wt% CAM increasing tensile strength from 53.9 to 57.3 MPa and Young's modulus from 1782 to 2262 MPa. This study presented a sustainable method for synthesizing an effective bio-based flame retardant and a strategy for producing eco-friendly, fire-resistant PLA composites for industrial applications.

Durable flame retardant and UV-resistant coating for Poly (ethylene terephthalate) fabric with recyclability and reusability

Poly (ethylene terephthalate) (PET)fabric is widely used in our lives due to its excellent mechanical strength, high elasticity, wrinkle resistance, and anti-abrasion. However, the inflammability and droplets produced during combustion restricted its application. Herein, a novel PET fabric with fire resistance, anti-dripping, and UV resistance is proposed to resolve this problem. Firstly, the finishing agent (AAD) was synthesized using adipoyl chloride, 9-anthracenemethanol, and diethyl(hydroxymethyl)phosphonate. Then AAD was introduced to the surface of PET fabric by dip-pad-cure process. The limiting oxygen index (LOI) value of AAD-treated PET enhanced to 23.8% from 19.3%. Besides, the fabric passed the vertical burning test (VBT) with no droplets generated. The fabric could still pass the VBT and maintain an LOI value of 23.3% after washing. Meanwhile, the AAD-treated PET fabric showed outstanding UV resistance with a high UPF value of 4318.27. The breaking force of AAD-treated PET was also improved. More importantly, the AAD coating could be easily removed from the fabric using dichloromethane and recycled using a rotary evaporator with a recovery rate of 98.6%. The recycled AAD could also recoated on the PET fabric to impart similar properties. This work proposed a novel strategy to prepare durable flame retardant and UV-resistant PET fabrics with recyclability.

A novel phosphorus/boron-containing flame retardant for improving the flame retardancy of ramie fiber reinforced epoxy composites

As a kind of plant fiber, ramie fibers (RFs) are widely used in fiber reinforced resin matrix composites, however, both of RFs and resin matrix are flammable. Enhancing the flame retardancy of ramie fiber reinforced epoxy composites is important. In this study, a highly efficient flame retardant, PBXY, was synthesized from phytic acid, boric acid, and xylitol to improve the flame retardancy of ramie fibers, and flame-retardant ramie fiber reinforced epoxy composites (EP/RF-PBXYs) with different weight gain were prepared by coating PBXY on the surface of ramie fibers. The effects of different weight gain of PBXY on the thermal stability, flame retardancy, and mechanical properties of EP/RF-PBXYs were investigated. Compared with that of EP/RF, the limiting oxygen index value of EP/RF-PBXY2 was increased from 23.0% to 31.4% and a UL-94 V-0 rating was obtained, the total heat release and total smoke production were reduced by 33.2% and 31.0%. However, the presence of PBXY had a negative effect on the mechanical properties of EP/RF when the weight gain of PBXY was more than 10wt% (related to RFs). This study offers a promising avenue to improve the flame-retardant resistance of EP/RF.

Fire-safe and mechanically robust polycarbonate composite enabled by novel copolymerization/macromolecular blending strategy

Polycarbonate is a widely used engineering plastic material, but its limited flame retardancy has restricted its application in high-end fields such as aviation and railways. In this study, we propose a novel copolymerization/macromolecular blending strategy to produce a high-performance, fire-safe polycarbonate composite. By copolymerizing with polydimethylsiloxane oligomer and blending with macromolecular polyarylate, the resulting PC-BPDMS5/PITR successfully achieved a UL-94 V-0 rating and a high limiting oxygen index value of 34.2%. The peak heat release and total smoke release were significantly reduced by 45.2% and 27.4%, respectively, compared to pure PC. SEM, Raman, and XPS analyses confirmed the condensed-phase dominated flame-retardant mechanism, attributed to the char-forming ability of the polyarylate and polydimethylsiloxane segments. Polydimethylsiloxane segments can decompose to produce small molecules such as methane, and the left structure with silicon, which undergo cross-linking reactions with the substrate during combustion to promote char formation. The polyaromatic ring structure of PITR can also participate in the formation of a dense and stable char layer. The excellent compatibility between the polyarylate and the PC matrix, combined with the superior flexibility of polydimethylsiloxane, allowed the composite to maintain mechanical properties comparable to pure PC. Additionally, the increased molar volume resulted in a low dielectric constant for PC-BPDMS5/PITR. This work presents a promising approach for the development of high-performance polycarbonate composites.

Construction of epoxy resin with enhanced flame retardancy, mechanical properties, and satisfactory transparency based on a novel bi‐DOPO and hydrogen‐bonding network

AbstractEstablishment of high‐performance epoxy resin with satisfactory fire safety, mechanical properties, and excellent transparency is urgently desirable, but still remains significant challenges. Herein, a super‐tough yet high flame retardant epoxy resin (EP/BTD) was designed and prepared by incorporating bi‐DOPO structure and hydrogen‐bonding networks. Although the phosphorus content was only 0.69 wt% (10 wt% of bi‐DOPO flame retardant [BTD]), EP/BTD‐10 showed a high limiting oxygen index value (33.4%), satisfactory UL‐94 rating (V‐0), and good heat suppression ability (total heat release [THR] and peak heat release rate [PHRR] reduced to 29.0% and 42.2%, respectively). Furthermore, the flame retardant mechanism of EP/BTD was illustrated and attributed to dual‐phase fire‐retardant effect. Additionally, EP/BTD‐7.5 featured notably mechanical properties, of which the tensile strength, elongation at break and impact strength increased by 44.6%, 40.0%, and 232.6%, respectively, due to hydrogen‐bonding network and π–π interaction. More importantly, EP/BTD maintained high visible light transmittance and excellent UV‐blocking properties. In summary, this work provided a guidance for the development of high‐performance epoxy resin and was expected to expand the practical applications.

Preparation and Characterization of Glucose-Based Self-Blowing Non-Isocyanate Polyurethane (NIPU) Foams with Different Acid Catalysts.

The preparation and application of non-isocyanate polyurethane (NIPU) from biomass raw materials as a substitute for traditional polyurethane (PU) has recently become a research hot topic as it avoids the toxicity and moisture sensitivity of isocyanate-based PU. In the work presented here, self-blowing GNIPU non-isocyanate polyurethane (NIPU) rigid foams were prepared at room temperature, based on glucose, with acids as catalysts and glutaraldehyde as a cross-linker. The effects of different acids and glutaraldehyde addition on foam morphology and properties were investigated. The water absorption, compressive resistance, fire resistance, and limiting oxygen index (LOI) were tested to evaluate the relevant properties of the foams, and scanning electron microscopy (SEM) was used to observe the foams' cell structure. The results show that all these foams have a similar apparent density, while their 24 h water absorption is different. The foam prepared with phosphoric acid as a catalyst presented a better compressive strength compared to the other types prepared with different catalysts when above 65% compression. It also presents the best fire resistance with an LOI value of 24.3% (great than 22%), indicating that it possesses a good level of flame retardancy. Thermogravimetric analysis also showed that phosphoric acid catalysis slightly improved the GNIPU foams' thermal stability. This is mainly due to the flame-retardant effect of the phosphate ion. In addition, scanning electron microscopy (SEM) results showed that all the GNIPU foams exhibited similar open-cell morphologies with the cell pore sizes mainly distributed in the 200-250 μm range.

Construction of a hydrophobicity, phosphorus‐ and nitrogen‐containing layered double hydroxides‐based synergistic effect flame retardant for poly (lactic acid)

AbstractIn this work, a synergistic effect strategy was explored for fabricating hydrophobicity, phosphorus‐ and nitrogen‐containing layered double hydroxides nanosheets (LDHs) based flame retardant (LDHs‐K@DM). This fabricating process was achieved by amination of the surface of LDHs and, subsequently, interfacial self‐assembly with high P content of diethylenetriaminpenta (methylene‐phosphonic acid) (DTPMP) and high N content of melamine (MEL). The chemical construction and thermal stabilization properties of LDHs‐K@DM were confirmed via different characterization approaches. The results revealed that LDHs‐K@DM was successfully prepared and the surface of LDHs‐K@DM was transformed into hydrophobicity with high water contact angle. Moreover, LDHs‐K@DM had better thermal stability. After that, LDHs‐K@DM was molten compounded with biobased polylactic acid (PLA). It was suggested that LDHs‐K@DM were uniformly dispersed in the PLA matrix and could accelerate the decomposition of PLA to form char residues. Most importantly, the addition of 20 wt% LDHs‐K@DM into PLA can endow the composite to achieve a desirable UL‐94 V‐0 rating and the limiting oxygen index value of 30.9%. Finally, the synergistic effect flame retardant mechanism of LDHs‐K@DM was comprehensively analyzed. This synergistic decorating strategy for preparing LDHs‐K@DM flame retardant is promising for industrial production.

Double cross-linked biomass aerogels with enhanced mechanical strength and flame retardancy for construction thermal insulation

Biomass aerogels are expected to be a popular material in construction field due to their sustainability, eco-friendliness and excellent thermal insulation properties. In this paper, high modulus biomass aerogels based on the principle of double cross-linking of physics and chemistry were synthesized by freeze-drying technique using gelatin, sodium carboxymethyl cellulose, glutaraldehyde, phytic acid and diatomite as raw materials. The presence of a double cross-linked network structure endowed the prepared aerogels with a low thermal conductivity (0.021–0.029 W·m−1·k−1). The density of only 0.0865 g·cm−3 biomass aerogel exhibited an extrastrong compression modulus of 31.5 MPa, which was superior to common biomass aerogels. Biomass intumescent flame retardant system composed of sodium carboxymethyl cellulose (carbon source), gelatin (gas source) and phytic acid (acid source) was used in combination with diatomite to enhance flame retardancy (limit oxygen index value up to 36.5 %, UL-94 V-0 rating and total smoke production reduced from 0.31 m2 to 0.18 m2) and thermal stability (the residue up to 48.91 %). Remarkably, the modified aerogel showed incredible hydrophobicity (hydrophobic angle of 137°). In summary, the results indicated this study proposed a novel green idea for the preparation of construction thermal insulation materials with a combination of high modulus, flame retardancy and hydrophobicity.

Synchronously enhanced flame retardancy and mechanical properties of polylactic acid via in-situ assembly of polyphosphazene nanoparticles on ammonium polyphosphate

Polylactic acid (PLA) exhibits wide potential applications in many fields ranging from textile, packaging material to biomedical devices. However, the relatively low mechanical properties and inflammability are obstacles to the expansion of its application. Here, a kind of polyphosphazene nanoparticles with tannic acid (TA) as template, hexachlorocyclotriphosphazene (HCCP) and 4,4′-Sulfonyldiphenol (BPS) as comonomers were prepared (named as HTB), and then combined with ammonium polyphosphate (APP) to enhance the comprehensive properties of PLA composites. The introduction of HTB strengthened the interfacial adhesion of composites via constructing the hydrogen bond interaction between PLA and APP, promoting the homogenous dispersion of APP in the composite and the formation of APP network. The flame retardant measurements presented that incorporating 10 wt% APP and 5 wt% HTB in PLA increased the limit oxygen index (LOI) value to 31.0% and endowed the composite with the V-0 rating of UL-94 test and simultaneously, the peak of heat release rate (PHRR) and total heat release (THR) of the composite decreased by 14.2% and 13.2% compared with pure PLA. Specially, there was almost no melt drip appeared during the combustion process, which was distinctly different from the combustion behavior of the composite containing only 20 wt% APP with the V-2 rating of UL-94 test. The uniform dispersion of APP in the PLA matrix and the strong interfacial adhesion between APP and the PLA matrix contribute to the enhancement of the mechanical properties of composites, and the elongation at break, Young’s modulus and impact strength of the composite were increased by 52.9%, 7.6% and 24.2%, respectively. The present study offers novel insights for the trade-off between flame retardancy and mechanical properties with PLA composites.

A New Approach for Improving Flame Retardancy of Automotive Interior Upholstery

This study presents the flame retardant (FR) performance of chemically treated automotive upholstery fabrics using two different impregnation methods of Resin Transfer Molding (RTM) and supercritical carbon dioxide (scCO2). Referring to the related standards, untreated seat fabric obtained from seat upholstery of a bus (neat fabric, NF) and treated fabric samples underwent burning rate (BR) and limiting oxygen index (LOI) tests to compare effect of treatment and impregnation methods on FR performance. Thermal analysis was also conducted on the samples considering onset degradation temperatures and char yields. The results showed that BR and LOI of all samples were in acceptable range and treatment provided enhancement in FR performance of NF. The treated sample using scCO2 method gave the highest LOI value of 32% and the lowest BR of 21 mm/min subtending to 18.5% increase in LOI and 30% reduction in BR compared to those of NF. The performance of treatment in RTM was worse than that of scCO2 and better than that of NF. The results confirm that both treatment and methods used in this study give promising results for safety against fire in transportation vehicles.

Double-crosslinked polyvinyl alcohol/starch bioplastic with superior water-resistance and flame retardancy

The high water solubility and flammability of polyvinyl alcohol (PVA) limits its further widespread use in areas such as bioplastic and green packaging. In this study, double-crosslinked polyvinyl alcohol/starch bioplastics (named PDA) were fabricated using PVA, dialdehyde starch (DAS), and phytic acid (PA), resulting in a material with superior water resistance, flame retardancy, and excellent degradability. PA not only plays the role of catalyst for the chemical crosslinking but also as the physical crosslinker to form the intermolecular hydrogen bonds with PVA and DAS. This chemically and physically double cross-linked network structure results in PDA bioplastics with excellent toughness and water resistance. Specifically, the optimal formulation with 15 % PA content, designated as PDA15, exhibited a high toughness of 35.5 MJ/m3 and demonstrated prolonged shape retention in the boiling water. Additionally, PA also serves as a flame-retardant and antibacterial agent; the PDA15 achieved a high limit oxygen index (LOI) value of 40.0 % and passed the UL-94 V-0 rating without melt dripping, along with better degradability compared to pure PVA film. These outstanding performances make the PDA bioplastics highly promising for various applications, particularly in disposable plastics and laminated flexible packaging materials.

Improvement of the flame retardancy of polyamide 6 by the incorporation of UiO-66 and UiO-66/melamine

The flame retardancy of polyamide 6 (PA6) has been investigated through the incorporation of the metal–organic framework (MOF) UiO-66 and a composite of UiO-66/melamine during the extrusion process. The prepared materials have been characterised by various techniques: XRD, XPS, FTIR, TGA, DSC, SEM, EDX and mechanical properties. Moreover, to examine the efficiency of the flame retardants, the composites have been tested using the UL-94 vertical and, horizontal burning test, as well as the limiting oxygen index (LOI). The UL-94 V-2 standard has been achieved with only a 4 wt% load of either UiO-66 or UiO-66/melamine, compared to pure polyamide, which is not classified. The best results have been achieved with the UiO-66/melamine sample at 7 wt%, which prevents the agglomeration of UiO-66 alone. The highest LOI value was also obtained with this sample, achieving a value of 35.5 %, compared to pure PA6 and with UiO-66, which reached values of 22.4 % and 23.2 %, respectively. A flame suppression mechanism of the UiO-66/melamine composite is proposed, based on the formation of zirconium oxide, gas adsorption by the MOF and release of NH3.

Superior flame retardancy, thermal insulation, and mechanical properties of konjac glucomannan/sodium alginate biomass aerogel modified by supramolecular assembled phytic acid-melamine nanosheet

The development of biomass-based eco-friendly aerogel with superior flame retardancy, thermal insulation, and mechanical properties at the same time has long been a tough challenge. In this study, the polysaccharide-based aerogels composed of konjac glucomannan, sodium alginate, and supramolecular assembled melamine phytate (MPA) nanosheets were successfully fabricated through the freeze-drying method. Owing to the excellent charcoal-forming and non-combustible gas-releasing effect of MPA nanosheets, the thermal stability and flame retardancy properties of the aerogels were both significantly enhanced, with the highest limiting oxygen index value reaching 42.4 %. Meanwhile, appropriate MPA embedded in the pore walls greatly enhanced the compressive strength of the aerogel (364.9 kPa) and can withstand >7100 times its weight without visual deformation. Moreover, the thermal insulation effect was quite attractive with a thermal conductivity of 0.0385–0.0420 W/mK. The present work provided an environmentally friendly method for the fabrication of multifunctional sustainable fire-resistant aerogels, which showed promising prospects in the future.

Phytic acid-induced durable fire-proof and hydrophobic complex coating for versatile cotton fabrics

To address the current development requirements for multifunctional cotton fabrics, a phytic acid-induced flame-retardant hydrophobic coating containing nitrogen (N), phosphorus (P), and silicon (Si) was grafted on the surface of cotton fabrics using a facile step-by-step immersion method. The limiting oxygen index value improved to 31.2 %, decreasing to 26.7 % after 50 laundering cycles, while the fabric remained self-extinguishing effect in the vertical flammability test and showed a water contact angle of 126.1°. Cone calorimetry test showed that the modified fabric could not be ignited at the irradiation heat flux of 35 kW/m2. When the irradiation heat flux was raised to 50 kW/m2, there was a significant decline in the peak heat release rate of the modified cotton fabric, which decreased by 43.2 % to a remarkably low value of 114.0 kW/m2, indicating excellent flame-retardant properties. The analysis of the flame-retardant mechanism uncovered that the modified coating exhibited a significant dual flame-retardant mechanism involving both the gaseous phase and the condensed phase. Additionally, the oil-water separation tests revealed that the separation efficiency of the modified cotton fabrics was as high as 97.1 % and remained around 96 % after 10 cycles, which made them reusable for the clean-up of hazardous chemicals.

Development of a novel elastomer with unique properties as fire and radiation resistance

This study aims to create a novel, distinct form of elastomer with superior ability to resist fire, high resistance to radiation, and resistance to environmental conditions such as temperature and solvents. This type of natural-based elastomer was prepared using carboxymethyl cellulose CMC, polyacrylic acid PAA, crosslinked with tannic acid TA. Most techniques in elastomer manufacture technologies are unfriendly and participate in increasing carbon emissions. Gamma radiation was used as a clean tool for copolymerization and crosslinking the elastomer. The irradiation dose of 5 kGy with a rate of 3.32 kGy/h was enough to produce CMC/PAA/TA elastomer. The properties of the produced elastomer were investigated by Fourier-transformed infrared spectroscopy (FT-IR), X-ray diffraction, thermal gravimetric analysis (TGA), and limiting oxygen index (LOI). CMC/PAA/TA has high resistance to solvents such as acetone, benzene, HCl, and HNO3. The tensile strength is 3.376 MPa, the elongation percent is 501.689%, and the LOI value is 30%. The produced elastomer possessed excellent gamma radiation resistance. The elastomer was exposed later to 1864 kGy of gamma radiation without showing degradation and retained its properties, as confirmed by FTIR, TGA, and mechanical properties. After investigation, it can be inferred that the produced CMC/PAA/TA elastomer exhibited outstanding properties.

Biomass aerogel with humidity sensitive for thermal runaway suppression of battery modules and flame-retardant application

The propagation of thermal runaway (TR) is a critical safety issue in lithium-ion battery modules, which can be mitigated by using aerogels, a new nano porous material with exceptional thermal insulating capabilities and flame resistance. In this study, we developed an environmentally friendly aerogel by combining chitosan (CS) and phytic acid (PA) through ambient pressure drying. The optimal PA composition was 5 wt%, and the corresponding aerogel achieved a limit oxygen index (LOI) value of 45.6 % and V-0 rate in UL-94 tests, demonstrating excellent flame retardancy. With a low density of 0.163 g/cm³, the aerogel exhibited a thermal conductivity of 0.0309 W/(m·K), making it an effective thermal insulator. The rigid porous structure of the composite aerogel provided a maximum compressive strength of 25.8 MPa and a compressive modulus of 5.58 MPa. To study the effect of the aerogel in mitigating TR, we simulated TR conditions by heating blocks to 300 °C. The aerogel significantly reduced the temperature rise in adjacent blocks, effectively inhibiting TR propagation. These findings indicate that the CS/PA aerogel offers superior thermal insulation, flame-retardant properties, and robust mechanical strength, making it a promising material for enhancing the safety of lithium-ion battery modules.

Sustainable lignosulfonate-modified PA6.6 fabrics to improve durable flame retardancy, hydrophilicity and mechanical performance

Creating durable flame retardancy, enhanced mechanical performance, and hydrophilic polyamide 6.6 (PA6.6) textiles via cost-effectiveness from sustainable renewable sources is a considerable challenge. This study introduces a pretreatment process involving the application of sodium lignosulfonate (LS) to the surface of PA6.6 fabrics, thereby enhancing their hydrophilic and flame-retardant properties. Subsequently, a layer-by-layer (LbL) nanocoating treatment is employed, utilizing renewable polyelectrolytes—chitosan (CS), LS, and poly (sodium phosphate) (PSP)—to create 8-bilayer (BL) and 4-quarda layer (QL) structures that further improve the hydrophilicity and durable flame resistance of PA6.6 fabrics. The combined LS-modified and LbL coatings notably increased the limiting oxygen index (LOI) values from 19.5 % to 22.5 %, eliminated melt dripping, and secured a V-1 rating in the vertical burning (UL-94) tests. Moreover, the treated fabrics exhibited a 43 % reduction in the peak heat release rate (PHRR) and a lower fire growth rate (FGR) of 0.84 W/g·s, with a significant increase in char yield% in both air and nitrogen (N2) atmospheres. A cross-linked network structure is responsible for the superior hydrophilicity, enhanced tensile strength, and fabric softening properties. The self-crosslinking of sulfur-containing radicals with amide units ensures an anti-dripping performance that can withstand up to 30 home laundering cycles, demonstrating remarkable washing durability. However, a convincing approach has been developed for sustainable and high-performance materials for the textile industry, and a simple LbL technique using renewable polyelectrolytes that have traditionally been utilized in water treatment and food processing has been developed.

Resveratrol-derived halogen-free phosphate flame retardant for fire-retarding polylactide composites

Despite regarding as one of the most promising alternatives to petroleum-based plastics, polylactide (PLA) suffers from its highly flammable nature, which restricts its application range. Taking the impact on the environment into consideration, it can hold great importance to develop bio-based flame retardants for PLA. Herein, bio-derived flame-retardant resveratrol trisphosphate (RTP) is synthesized by a simple strategy without any fussy treatment. By adding only 4 wt% RTP, the PLA-4RTP composite exhibits desired flame retardancy including UL-94 V-0 rating and limiting oxygen index value of 28.6 vol%. Furthermore, PLA composites with the additive of RTP show comparable tensile strength to the pure PLA sample. RTP can inhibit the combustion process via releasing inert radical and incombustible gas to capture energetic radical and dilute combustibles.

Flammability of Novolac epoxy cured with aromatic diamines

The modification of Novolac epoxy with the organophosphorus compound 9,10-dihydro-9-oxa-10-phosphaphenanthren-10-oxide (DOPO) to reduce flammability and its influence on curing reactions has been investigated. Three aromatic diamine curing agents were used, namely 4,4′-diaminodiphenylmethane (DDM), 4,4′-diaminodiphenylsulphone (DDS), and diethyltoluenediamine (DETDA). The thermal stability and dynamic-mechanical behaviour of the cured resin depend on interactions of the curing agent with DOPO. The onset degradation temperature decreased with increasing phosphorus content, indicating the influence of DOPO on thermal stability. The DDM 3 %P sample exhibited the highest glass transition (Tg) of 136 °C, while DDS-crosslinked simples displayed the highest Tg of 147 °C among all samples. An improvement in the reaction of Novolac epoxy to fire was achieved by incorporating DOPO compound, as indicated by cone calorimetry results, showing up to a 67 % reduction in the peak heat release rate (pHRR) and 53 % reduction in total heat release (THR) for DDM 3 %P. The modified samples containing DOPO presented a self-extinguishing performance, displaying a UL-94 V-0 rating and a limiting oxygen index (LOI) values reached a maximum of 37.1 % for DDM 3 %P, with less flame propagation than for neat Novolac epoxy.