UL-94 Vertical Burning Test Research Articles

A phosphate covalent organic framework: Synthesis and applications in epoxy resin with outstanding fire performance and mechanical properties

To prepare epoxy resin (EP) with satisfied fire performance and mechanical properties, a novel phosphoric acid modified triazine covalent organic framework (PCOF) was successfully synthesized. The structure and microtopography of PCOF were fully characterized. By the presence of 12wt% PCOF, the limiting oxygen index value of EP composite was increased from 24.8% to 28.6%, and V-0 rating was achieved in UL-94 vertical burning test. The cone calorimeter test showed that the peak heat release rate and total heat release of the 12PCOF-EP sample were decreased sharply by 78.9% and 68.9% compared with that of the control EP. The flame retardant effect was maintained after soaked in 75 °C for 168 h, indicating an excellent water resistance. The thermogravimetric analysis of the composites indicated that more char residue was formed, especially at a high-temperature range. Moreover, both the tensile and impact properties of EP composites were improved by adding appropriate amount of PCOF. By analyzing the products formed during combustion, it was proposed that PCOF took effects in both gas and condensed phase.

A novel phthalazinone-based epoxy resin with excellent rheological property and intrinsic flame retardancy

Phthalazinone is a critical structural factor for high-performance polymer material, which is achieved by polar structure and the structure characteristic of unsymmetrical and kink non-coplanar. In this study, a novel phthalazinone-based epoxy (EEPZ) has been designed and synthesized. The rheological behaviors, thermal stability and combustion behaviors of cured systems have been investigated by dynamic rheology, TGA, DMA, UL-94 vertical burning and cone calorimetry tests. It was found that the phthalazinone-based EEPZ epoxy resin had the lower melting viscosity within broader processing window and enhanced char forming ability for bisphenol A epoxy/4′4-diamino-diphenyl sulfone (E44/DDS) system. When combined with only 20 wt% EEPZ in the E44 system, the E44/20%EEPZ/DDS, passed the UL-94 V-0 rating. In the combustion test, the total heat release, total smoke production and peak of heat release rate were sharply respectively decreased by 44.7%, 24.3% and 44.6% in the case of E44/20%EEPZ/DDS compared with E44/DDS. The results of morphology characterization chemical structure and component for residue char in EEPZ epoxy resin confirmed that the phthalazinone group can lead to form nitrogen-containing compact char layer during combustion. The combined technologies (TGA-FTIR, Py-GC/MS) was utilized to detect the pyrolysis process of the crosslinks system and the charring mechanism. Simultaneously, the tensile strength and tensile modulus of the composites were also improved.

Comparison of Flame-retardancy Property and Mechanism between a Phosphate Ester and a Phosphoramine Flame-retardants

A halogen-free flame-retardant (hydroquinone bis (N, N’-diarylphosphoramidate), 4N-HDP) containing phosphorus-nitrogen was synthesized. Its structure was characterized by infrared spectroscopy (IR), nuclear magnetic resonance (1H-NMR and 31P-NMR). Thermogravimetric analysis (TG), limiting oxygen index (LOI), UL-94 vertical burning test (UL-94), thermogravimetric-infrared instrument (TG-IR) and scanning electron microscopy (SEM) were used to compare the flame-retarding performance and mechanism of hydroquinone bis (diphenyl phosphate) (HDP) and 4N-HDP. TG, IR and TG-IR were used for comparative analysis, indicating that both HDP and 4N-HDP are flame-retardants, and the gas phase and condensed phase act synergistically. In the pyrolysis process, it is divided into two steps: the first step is the breakage of large molecules to small molecules; the second step is the gasification and carbonization of small molecules, and eventually produces phosphate ester and non-flammable gases. Through the comparison of various results, it could be found that 4N-HDP has better flame-retarding performance compared to HDP in the composite with polycarbonate (PC).

Preparation of a novel functionalized magnesium-based curing agent as an intrinsic flame retardant for epoxy resin

In this study, a novel organic-inorganic hybrid flame retardant 10-(1,4-dicarboxylic acid magnesium salt)-9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DMMH) was synthesized via neutralization and addition reaction of maleic acid, magnesium hydroxide and 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO), and subsequently used in an intrinsic flame retardant epoxy resin. The chemical structure and morphology of DMMH were analyzed by Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). Further, the prepared DMMH was combined with ammonium polyphosphate (APP) to form an intumescent flame retardant system. The thermal stability and flame retardance were evaluated by thermogravimetric analysis (TG), UL-94 vertical burning test, limiting oxygen index (LOI) and cone calorimetry. It was observed that the addition of 1.7% DMMH and 5.3% APP led EP-7 to acquire UL-94 V-0 rating, with the limiting oxygen index of 26.0%. As compared with pure EP, the peak heat release rate, total heat release, smoke production rate and total smoke production of the sample was noted to decrease by 54.5%, 35.1%, 43.6% and 38.1%, respectively. In addition, the introduction of DMMH did not negatively impact the mechanical properties of the epoxy resin.

Low-melting phosphate glasses as flame-retardant synergists to epoxy: Barrier effects vs flame retardancy

In this research, low-melting phosphate (LMP) glasses (G1, G2, G3) were employed as green flame-retardant synergist additives in epoxy (EP)/ammonium polyphosphate (APP) composite. To investigate their performance as flame-retardant additives, comprehensive fire tests and characterizations were carried out, including limiting oxygen index test, UL-94 vertical burning test, cone calorimeter test, real-time temperature detection, X-ray microtomography, and char residue strength analysis. A prominent improvement of flame-retardant properties was observed in EP composites containing LMP glasses. EP/9%APP/1%G1 reached V-0 rating in UL-94 test and showed a decreased peak heat release rate by around 40% over EP/10%APP in the cone calorimeter test. It found that LMP glasses mainly showed the physical barrier effect in the condensed phase flame retardancy. Interestingly, via simulating different combustion temperatures, LMP glasses reveal different flame-retardant performance. The mechanism was further elucidated as: A match between the LMP glass phase-transition temperature range and the combustion temperature contributed to the optimized flame-retardant performances. This result provided enlightenment for the design and application of phase-transition additives toward improving the flame-retardant properties in polymer composites.

Synthesis of a hyperbranched polyamide charring agent and its flame-retarding and toughening behavior in epoxy resin

A hyperbranched polyamide charring agent (HPCA) was synthesized by amidation of 1,2,3,4-butanetetracarboxylic acid and melamine, and its chemical structure was characterized. Such a charring agent, combined with ammonium polyphosphate (APP), was applied in epoxy resin. V-0 rating in the UL-94 vertical burning test and 32.3% of Limiting Oxygen Index were achieved with only 10% total flame retardant loading. A HPCA/APP ratio of 1/1 showed better flame retardant properties than the system with only HPCA or APP involved, indicating an apparent synergistic effect. The residual char at high temperature was analyzed by using FTIR and X-ray Photoelectron spectroscopy (XPS) to further explore the above synergistic mechanisms. Additionally, HPCA, as a co-curing agent, was grafted into the crosslinking net of epoxy resin due to the reactivity of carboxylic acids with epoxy group and hydroxyl group. The introduced hyperbranched polyamide structure effectively improved the toughness of original rigid crosslinking net of epoxy resin.

Synergistic effects of aluminum hydroxide, red phosphorus, and expandable graphite on the flame retardancy and thermal stability of polyethylene

AbstractThe flame‐retardant low‐density polyethylene (LDPE) composites loading aluminum hydroxide (ATH), red phosphorus (RP), and expandable graphite (EG) were successfully prepared. The flame retardancy, the thermo‐oxidative stability, and the mechanical property of the composites were investigated. The synergistic effect of ATH, RP, and EG on the flame‐retardant property and thermal behavior of LDPE were observed. The limiting oxygen index value of LDPE significantly increased from 17.1% to 25.4% upon the incorporation of 15 wt.% of the mixture of three fillers with ATH:RP:EG mass ratio of 1:1:1; and this composite achieved the V‐0 classification of the UL94 vertical burning test. The thermogravimetric analysis of this composite under air atmosphere revealed that its residue weight remained 27.89% at 900°C. Furthermore, the results of tension tests indicated that the surface modification of ATH by magnesium stearate and RP by poly(methylhydrosiloxane) noticeably improved the tensile strength and the elongation of the composite.

Thermal degradation and flame retardant mechanism of sulfonated polyoxadiazole fibers modified by metal ions

The sulfonated polyoxadiazole (SPOD) flame retardant fibers are prepared by wet spinning and modified by metal ions (Na+, Ca2+, Ba2+, and Mg2+). The structures of SPOD fibers are characterized by Fourier transform infrared spectrometry (FTIR), elements analysis (EA), inductively coupled plasma emission spectrometry (ICP), scanning electron microscopy (SEM) and energy dispersive spectrometry (EDS). Results show that sulfonate groups were successfully grafted on the POD fiber polymer, and metal ions are adsorbed in the fiber by physical and chemical adsorption. The micro-scale combustion calorimeter (MCC), limiting oxygen index (LOI), and UL-94 vertical burning tests are used to test the flame retardant properties of the fibers. Results show that the Mg-SPOD had the best flame retardant performance with LOI of 40% and the lowest heat release rate (HRR). The thermal degradation mechanism of the fiber is analyzed by thermogravimetric analysis coupled with infrared spectrometry (TG-FTIR), and the char residues were investigated by X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). The rapid and sharp emission of non-flammable SO2 and high content char residue covered with dense MgO and MgSO4 improve the flame retardant properties of Mg-SPOD fibers significantly.

Experimental characterization and modeling of boundary conditions and flame spread dynamics observed in the UL-94V test

Abstract To characterize the UL-94 vertical burning test (UL-94 V), temperature, oxygen content, and heat flux of the burner flame were measured using an R-type thermocouple, oxygen analyzer, and water-cooled Schmidt–Boelter gage, respectively. To account for sample geometry, mock samples from Kaowool PM insulation board were used during the burner measurements. Temperature and heat flux measurements were used to express the heat flux of the burner as a linear, piecewise function of burner flame temperature and a constant convective heat transfer coefficient. UL-94 V tests were conducted using 0.27 cm thick poly(methyl methacrylate) (PMMA) samples with and without insulated sides to investigate edge effects. All UL-94 V tests were recorded on video using a 900-nm narrow-band filter to focus on emissions from soot for tracking flame length over time. In some of these tests, a heat flux gage was embedded into the sample to measure PMMA flame heat flux to verify a previously developed laminar wall flame heat feedback submodel. PMMA flame heat fluxes of insulated samples confirmed the wall flame submodel, while non-insulated samples had significantly greater heat fluxes; the flame submodel was scaled accordingly. The burner and wall flame heat flux submodels were combined with an independently developed pyrolysis model of PMMA to conduct two-dimensional, time-resolved simulations of the UL-94 V test. Burner flame oxygen content was measured to be about 5 vol% and was found to enhance PMMA decomposition. Inclusion of the oxygen effect was essential to predict ignition. The simulation predicted flame length and spread on insulated UL-94 V samples reasonably well, validating the submodels. However, the simulation underpredicted flame length on the non-insulated samples; discrepancies were attributed to burning and spread on the edges which were not modeled explicitly. The developed model can be applied to non-charring polymeric solids with no to moderate amount of dripping. Its applicability for charring and intumescent materials will be explored in the future.

Facile preparation of uniform polydopamine particles and its application as an environmentally friendly flame retardant for biodegradable polylactic acid

The demand for environmentally benign flame retardants for biodegradable polymers has become particularly necessary due to their inherently “green” nature. This work reports intrinsically non-toxic polydopamine (PDA) particles as an efficient and environmentally friendly flame retardant for polylactic acid (PLA). 5 wt% PDA loading resulted in a 22% reduction in the peak heat release rate, 34.7% increase in the fire performance index, and lower CO2 production compared to neat PLA. A limiting oxygen index (LOI) value of 27.5% and a V-2 rating was achieved in the UL-94 vertical burning test. Highly aggregated amorphous particulate char was formed with the increasing content of PDA, and a significant reduction in evolved pyrolysis gaseous products was achieved for the PLA/PDA composites as compared with control PLA. This work provides important insight into the potential commercial application of PDA alone as an efficiently green, environmentally benign flame retardant for bioplastic PLA.

An environmentally friendly approach to fabricating flame retardant, antibacterial and antifungal cotton fabrics via self-assembly of guanazole-metal complex

Cotton fabrics are prone to ignite fire accidents as well as breed bacteria and fungi, which have hampered their applications in the field of packaging and home decorations. Guanazole complexes with silver and zinc ions were deposited to cotton fabrics through self-assembly to prepare the flame-retardant and antibacterial cotton fabrics. The effect of the guanazole-metal complexes on the morphological structure, flammability and thermal degradation of cotton fabrics was studied by field emission scanning electron microscopy, limiting oxygen index (LOI), UL-94 vertical burning test, and thermogravimetric analysis. The antibacterial and antifungal activities of the coated fabrics were evaluated as well. The guanazole-zinc and guanazole-silver treated cotton fabrics showed a high LOI of 29.5% and 27.5%, respectively. In the vertical burning test, both the guanazole-zinc and guanazole-silver treated cotton fabrics self-extinguished when removing the ignition source, displaying a UL-94 V-0 classification, while the untreated one and the guanazole-treated one burned out. Thermogravimetric analysis results confirmed that the guanazole-metal complexes promoted the thermal decomposition of cotton and thus improved the char yield significantly. Micro-scale combustion calorimeter measurements clarified that the guanazole-zinc and guanazole-silver treated cotton displayed dramatically decreased peak heat release rate (64.4% and 59.1%, respectively) and total heat release (26.4% and 14.8%, respectively) in comparison to the untreated one. The significantly improved flame retardancy of guanazole-metal complexes treated cotton fabrics could be attributed to their enhanced charring capability that blocked flammable volatiles into flame zone. The treated cotton fabrics with guanazole-metal complexes exhibited better antibacterial capacity against Staphylococcus aureus and Escherichia coli than the untreated and guanazole-treated ones. Furthermore, the guanazole-silver treated cotton fabrics also showed good antifungal activity against Penicillium, Fusarium chlamydosporum and Aspergillus niger.

Deposition growth of Zr-based MOFs on cerium phenylphosphonate lamella towards enhanced thermal stability and fire safety of polycarbonate

The fabrication of engineering plastics combining high efficiency flame retardancy and thermal resistance are essential for practical applications. A novel halogen-free binary hybrid with lamellar and porous structure, Zr-BDC@CeHPP, was created by hydrothermal reaction, thereafter blended with polycarbonate (PC) to improve its thermostability and fire safety. With 2 wt% Zr-BDC@CeHPP, temperatures under peak decomposition rates (Tmax1 and Tmax2) of PC were increased by 28 and 34 °C under oxidizing atmosphere. Time to reach PHRR (t-PHRR) and time to ignition (TTI) and of PC were effectively prolonged to 145 and 18 s, respectively. In comparison with pure PC, the peak of heat release rate (PHRR), total heat release (THR), peak specific extinction area (PSEA) and total smoke release (TSR) of PC composites were reduced by 45%, 20%, 74% and 18%, respectively. Moreover, the flame retardant PC reached V-0 rating in UL-94 vertical burning test. The results indicated that the hybrid was able to fully utilize the advantages of Zr-BDC and CeHPP. In the ignition and middle periods of combustion, Zr-BDC@CeHPP played roles in delaying and suppressing explosive combustion. In severe combustion stage, Zr-BDC@CeHPP could catalyze the char-forming process and serve as a barrier.

Synergistic effect of a hypophosphorous acid-based ionic liquid and expandable graphite on the flame-retardant properties of wood–plastic composites

A hypophosphorous acid-based ionic liquid [Bmim]H2PO2 (BMP) was synthesized and characterized by FTIR, 1HNMR, 13CNMR and 31PNMR. Moreover, a new intumescent flame-retardant system composed of BMP and expandable graphite (EG) was used to improve the flame retardancy of high-density polyethylene-based wood–plastic composites (WPC). The retardant properties and thermal decomposition behaviors were investigated by the limiting oxygen index (LOI) test, UL-94 vertical burning test, thermogravimetric analysis (TGA) and cone calorimeter test, respectively. When the mass ratio of BMP to EG was 1:2 and the total amount was kept at 30 mass%, WPC/EG-BMP composite passed UL-94 V-0 rating, and its LOI value increased to 31.5% from 21.4% for neat WPC. In addition, both the peak heat release rate and the total heat release of WPC/BMP-EG composite decreased significantly relative to WPC and WPC/EG composites according to cone calorimeter analysis. The TGA results suggested that BMP had good ability of char formation, and when combined with EG, it could greatly promote the formation of the protective char layer. The surface morphology and chemical structure of char residues were examined using scanning electron microscope–energy-dispersive spectrometer and Raman spectroscopy. It revealed that a compact and thick char layer was formed with the combination of BMP and EG, which hinder the transfer of heat flow and combustible gases in the condensed phase, thus exhibiting excellent flame retardancy. This study demonstrated that BMP and EG had a synergistic effect on the flame retardancy of WPC.

Synthesis of Novel Polymeric Acrylate-Based Flame Retardants Containing Two Phosphorus Groups in Different Chemical Environments and Their Influence on the Flammability of Poly (Lactic Acid).

Novel polymeric acrylate-based flame retardants (FR 1–4) containing two phosphorus groups in different chemical environments were synthesized in three steps and characterized via nuclear magnetic resonance (NMR) spectroscopy, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and mass spectrometry (MS). Polylactic acid (PLA) formulations with the synthesized compounds were investigated to evaluate the efficiency of these flame retardants and their mode of action by using TGA, UL94, and cone calorimetry. In order to compare the results a flame retardant polyester containing only one phosphorus group (ItaP) was also investigated in PLA regarding its flame inhibiting effect. Since the fire behavior depends not only on the mode of action of the flame retardants but also strongly on physical phenomena like melt dripping, the flame retardants were also incorporated into PLA with higher viscosity. In the UL94 vertical burning test setup, 10% of the novel flame retardants (FR 1–4) is sufficient to reach a V-0 rating in both PLA types, while a loading of 15% of ItaP is not enough to reach the same classification. Despite their different structure, TGA and cone calorimetry results confirmed a gas phase mechanism mainly responsible for the highly efficient flame retardancy for all compounds. Finally, cone calorimetry tests of the flame retardant PLA with two heat fluxes showed different flame inhibiting efficiencies for different fire scenarios.

Flame retardancy and thermal properties of rigid polyurethane foam conjugated with a phosphorus–nitrogen halogen-free intumescent flame retardant

In this work, a halogen-free intumescent combining phosphorus and nitrogen, flame-retardant 2-((2-hydroxyphenyl)(phenylamino)methyl5,5-dimethyl-1,3,2-dioxaphosphinane 2-oxide (HAPO) was successfully synthesized. It had been synthesized by reaction of 5,5-dimethyl-1,3, 2-dioxphosphinane 2-oxide with Schiff base. Its chemical structure was characterized in detail by Fourier transform infrared spectroscopy, 1H NMR, and 31P NMR spectrum. The flame-retardant polyurethanes were prepared with different loadings of HAPO. The thermal properties, flame retardancy and combustion behavior of the pure polyurethane foam thermosets were investigated by a series of measurements involving thermogravimetric analysis, limited oxygen index measurement, UL-94 vertical burning test, and cone calorimeter test. The results of the aforementioned tests indicated that HAPO can significantly improve the flame retardancy as well as smoke inhibition performance of polyurethane foam. Compared with the PU-Neat, the limited oxygen index of flame-retardant polyurethanes (15%) thermoset was increased from 19.5% to 23.8% and its UL-94 reached V-0 rating. In addition, the cone test results showed that the heat release rate, total heat release, rate of smoke release, and total smoke production of flame-retardant polyurethanes (10%) were decreased obvious sly. The apparent morphology of carbon residue was characterized by scanning electron microscopy, and results revealed that the modified polyurethane foam can form dense carbon layer after combustion. Thermogravimetric analysis results also indicated that the char amount of flame-retardant polyurethanes was obviously increased compared with PU-Neat. Based on the above analysis, we can draw the conclusions which in the condensed phase, phosphorus-based acids from the degradation of HAPO, this could promote the formation of continuous and dense phosphorus-rich carbon layer. In the gas phase, the flame-retardant mechanism was ascribed to the quenching effect of phosphorus-based radicals and diluting effect by non-flammable gases.

Synthesis and characterization of a novel Schiff base and its enhancement on flame retardancy of epoxy resins

A novel Schiff base, namely N1,N2-bis{3,4-bis(5,5-dimethyl-2-oxide-1,3,2-dioxaphosphinan-2-yl)oxy]benzylidene}ethane-1,2-diamine (PN), was synthesized by the condensation of 3,4-bis[(5,5-dimethyl-2-oxido-1,3,2-dioxaphosphinan-2-yl)oxy] benzaldehyde (PCHO) and ethylenediamine. Its chemical structure was characterized by 1H, 13C, 31P NMR, mass spectra and elemental analysis. PN was used as an additive flame retardant to improve the flame retardancy of diglycidyl ether of bisphenol A (DGEBA) cured by 4,4′-diaminodiphenylsulfone (DDS) with different phosphorus mass fraction. The incorporation of PN promoted DGEBA/DDS to yield more char residues under both nitrogen and air atmosphere, and exhibit good flame retardancy. With 1.5 wt% phosphorus mass fraction, PN-1.5/DGEBA/DDS could reach the highest flame retardant level of V-0 rating for UL-94 vertical burning test, obtain a limiting oxygen index (LOI) value of 32.4%, and keep relatively good mechanical properties by 81.52% of flexural strength and 90.40% of Izod impact strength compared with DGEBA/DDS. The flame-retardant mechanism researches revealed that PN presented a comprehensive mechanism of condensed phase, gas phase and phosphorus-nitrogen synergistic effect in DGEBA/DDS system.

Effects of a Macromolecule Spirocyclic Inflatable Flame Retardant on the Thermal and Flame Retardant Properties of Epoxy Resin.

A new strategy for the preparation of an integrated three-source intumescent flame retardant (IFR) has been developed to improve the flame-retardant and smoke suppression performance of epoxy resin (EP) with a synergistic flame retardant effect. Herein, the synthesis of a macromolecular spirocyclic phosphorus/nitrogen-containing IFR poly sulfonamide spirocyclic pentaerythritol bisphosphonate (SAPC) is reported via a two-step method that uses pentaerythritol, phosphorus oxychloride and sulfonamide (SAA) as raw materials. Subsequently, the SAPC was incorporated into EP to prepare the composite to investigate its thermal stability, flame retardancy, and smoke suppression performance. Herein, a differential scanning calorimetry (DSC) analysis showed that the addition of SAPC increased the glass transition temperature (Tg) of the composite. Cone test results indicated that the incorporation of 8 wt % SAPC significantly improved the flame-retardant performance for the composite, with a 43.45% decrease in peak of heat release rate, a 28.55% reduction in total heat release, and a 30.04% decrease in total smoke release. Additionally, the composite received the V-0 rating in a UL-94 vertical burning test, accompanied by the “blowout” phenomenon. After the addition of SAPC, the amount of flammable gas products from the EP composite decomposition was obviously suppressed, and the amount of non-flammable as was increased. All of this suggests a good dilution role of SAPC. There are enough reasons to believe that the enhanced flame-retardant and toxicity suppression performance for the EP composite can be attributed to the good coordination of carbonization agent, acid source, and blowing agent in the SAPC structure.

Flame retardant efficiency of modified para-aramid fiber synergizing with ammonium polyphosphate on PP/EPDM

This paper investigates the char forming effect of para-aramid fiber and the flame-retardant efficiency of para-aramid fiber synergizing with ammonium polyphosphate on polypropylene/ethylene propylene diene monomer. Para-aramid fiber was firstly modified by phosphoric acid, and then modified by 3-aminopropyltriethoxy. Para-aramid fiber and modified para-aramid fiber were characterized by field-emission scanning electron microscope, energy-dispersive analysis and Fourier transform infrared spectroscopy. Fourier transform infrared spectroscopy illustrated that P–O groups and Si–O groups appeared on the surface of modified para-aramid fiber. The intumescent flame retardants containing para-aramid fiber/ammonium polyphosphate or modified para-aramid fiber/ammonium polyphosphate was introduced into polypropylene/ethylene propylene diene monomer. The flame-retardant efficiency of polypropylene/ethylene propylene diene monomer composites were investigated by limiting oxygen index, UL-94 vertical burning and cone calorimeter test. The polypropylene/ethylene propylene diene monomer composite containing 34.5 wt% ammonium polyphosphate and 0.5 wt% modified para-aramid fiber achieved a UL-94 V0 rating with a limiting oxygen index of 28, as well as showed a 23.6% reduction of total heat release and a 47.0% reduction of total smoke release. The thermal stability of polypropylene/ethylene propylene diene monomer composites were investigated by thermogravimetric analysis. The residual char layers of polypropylene/ethylene propylene diene monomer composites were analyzed by field-emission scanning electron microscope. The tensile and tear strength of polypropylene/ethylene propylene diene monomer composites were also tested. After 1 phr modified para-aramid fiber was added, the tensile strength and tear strength increased by 33.3% and 35.9%, respectively. The results indicated that modified para-aramid fiber/ammonium polyphosphate/polypropylene/ethylene propylene diene monomer had better flame-retardant efficiency, thermal stability, smoke suppression and mechanical properties with the synergistic effect of P, N, Si elements.

Preparation of methacrylic acid modified microcrystalline cellulose and their applications in polylactic acid: flame retardancy, mechanical properties, thermal stability and crystallization behavior

Microcrystalline cellulose (MCC) extracted from bamboo powder was used as bio-based carbon source in intumescent system. Before using, MCC was modified with methacrylic acid (MA) by grafting polymerization to prepare MA-MCC, which may improve both the dispersibility and compatibility of in/with polylactic acid (PLA). MA-MCC, together with ammonium polyphosphate, was blended into PLA by melt compounding. The flame retardant properties of the composites were characterized by the limiting oxygen index (LOI), UL-94 vertical burning test and cone calorimeter test. The results showed that the LOI of PLA composite sample containing 3% MA-MCC and 7% APP could reach up to 26.8% and pass V-0 rating in UL-94 test. The addition of APP and MA-MCC could also decrease the peak heat release rate from 556 kW/m2 of neat PLA to 456 kW/m2 and form a continuous, dense, homogeneous residue char to prevent PLA from further burning. Thermogravimetric analysis showed that the presence of APP and MA-MCC could enhance the thermal stability of the composites, which is also essential for the improvement of fire performance. The mechanical properties of PLA composites were also improved with the unnotched impact strength increased to 8.16 kJ/m2 and Young’s modulus increased to 1612.8 MPa. The possible mechanisms for the improvement of flame retardancy and mechanical properties had also been proposed.

Highly flame retardant zeolitic imidazole framework-8@cellulose composite aerogels as absorption materials for organic pollutants

In the current study, Zeolitic Imidazole Framework-8 (ZIF-8) was in situ grown on the surface of cellulose fibers and the ZIF-8@cellulose composite aerogels were fabricated by a freeze-drying method. The flame-retardant, thermal and mechanical characteristics of the cellulose-based aerogels were investigated. SEM images indicated that ZIF-8 was evenly deposited on the surface of the cellulose fibers in the aerogel owing to formation of hydrogen bonding with cellulose molecules. The addition of ZIF-8 enhanced thermal stability and flame retardancy of the host cellulose aerogel. The peak of heat release rate of the ZIF-8@cellulose-3 composite aerogel exhibited a drastic decline from 128 W g−1 to 63 W g−1 and the total heat release from 25.9 kJ g−1 to 14.8 kJ g−1. In the UL-94 vertical burning test, the samples showed self-extinguishing behavior. Additionally, ZIF-8 induced a dramatic enhancement in the mechanical properties of the host cellulose. Specifically, the compressive stress of the ZIF-8@cellulose composite aerogel showed a significant increase from 0.45 to 34.80 MPa. Moreover, the ZIF-8@cellulose composite aerogel can selectively remove the organic pollutants from water and adsorb a wide range of liquid oils with considerable capacities. The current study presented a feasible approach to synthesis of strong and flame-retardant cellulose-based aerogels for waste water purification.