Polylactic acid (PLA) is a new type of biodegradable material with good mechanical properties, and is widely used in many fields. However, as PLA is highly flammable, it is necessary to conduct ...flame‐retardant modification research on PLA. Phosphorus heterophilic flame retardants are low smoke, non‐toxic and have high flame‐retardant efficiency, and also have broad application prospects. In this study, a phosphazene flame retardant, 9,10‐dihydro‐9‐oxa‐10‐phosphazene‐10‐yl‐hydroxy‐phenol (abbreviated as DOPO‐PHBA), was synthesized. The PLA/ECE/DOPO‐PHBA flame‐retardant composites were prepared by adding DOPO‐PHBA and epoxy chain extender (ECE) into PLA. Thermal, mechanical, and flame‐retardant properties, as well as microscopic morphology of the PLA flame‐retardant composites were characterized and analyzed, and the flame‐retardant mechanism was discussed. Results show that when the flame‐retardant DOPO‐PHBA is added at 5 wt%, the PLA composites can reach the V‐0 level of combustion, and the corresponding LOI value is 30.0% at this time, and the LOI value increases from 22.5% to 33.6% with the increase of the flame‐retardant content. In addition, PLA composites still have good mechanical properties, and the cone heat, carbon residue and the thermal decomposition process shows that the flame‐retardant causes a two‐phase flame‐retardant mechanism on PLA with the gas and condensed phases acting in synergy. High flame retardancy is mainly attributed to free radical quenching, gas dilution, and the thermal barrier caused by the carbon layer. This work provides a simple and scalable method for the preparation of high‐performance flame‐retardant PLA materials.
In this study, a phosphazene flame retardant, 9,10‐dihydro‐9‐oxa‐10‐phosphazene‐10‐yl‐hydroxy‐phenol (abbreviated as DOPO‐PHBA), was synthesized. The PLA/ECE/DOPO‐PHBA flame retardant composites were prepared by adding DOPO‐PHBA and epoxy chain extender (ECE) into PLA. The thermal properties, flame retardant properties, microscopic morphology and mechanical properties of the PLA flame retardant composites were characterized and analyzed, and the flame retardant mechanism was further discussed.
DOPO based flame retardants demonstrate exceptional flame retardancy efficiency when applied to epoxy resins. However, the crosslinking degree of epoxy resin may decrease due to the addition of DOPO, ...leading to a deterioration in flame retardancy and mechanical properties. Herein, a reactive DOPO derivative flame retardant 6‐((1H‐benzodimidazol‐2‐yl) amino) dibenzo oxaphosphinine 6‐oxide (BADO) was successfully synthesized, which contains multiple reactive sites, thus ensuring a higher degree of crosslinking in the system. As a result, the modified epoxy resin exhibits excellent flame retardancy. The limiting oxygen index value of the modified epoxy resins increased from 19.8% to 29.7% by adding 7.5 wt% BADO, and its UL‐94 test passed V‐0. Flame retardancy mechanism analysis reveals that BADO exhibits both gas‐phase and condensed‐phase flame retardant effects. In particular, the formation of a porous inside‐char layer is a significant factor in reducing smoke release. The 7.5% BADO/EP composite exhibited a 43.2% reduction in total smoke production and a 43.6% reduction in total smoke rate compared to neat epoxy resins (EP). Furthermore, the addition of BADO slightly deteriorates the mechanical properties of the modified epoxy resin.
The flame‐retardant mechanism of BADO/EP.
Alternative flame retardants (FRs) have now replaced legacy FRs (such as polybrominated diphenyl ethers, PBDEs), but little is known about their fate in the aquatic environment. In this study, a ...range of legacy FRs (n=10) and alternative FRs, including halogenated FRs (HFRs, n=32) and organophosphorus FRs (OPFRs, n=19), were screened in water samples collected from 23 rivers covering the whole latitudinal range of Sweden. Of the 61 targeted FRs, 26 were detected in at least one of the river samples, with ΣFR concentrations ranging up to 170ngL−1 (mean 31±45ngL−1). In general, higher concentrations and a larger variety of FRs were detected in southern Sweden (ΣFR=60±56ngL−1) compared with the north (ΣFR=9.0±16ngL−1). In the south, HFRs were dominant, constituting on average 59% of ∑FRs, whereas in the north, OPFRs were dominant, constituting on average 82% of ∑FRs. This difference was best explained by higher population density in the south. The total daily flux of FRs into the Baltic Sea was estimated to be ~31kg and comprised mainly tetrabromobisphenol-A (TBBPA), 3,4,5,6-tetrabromophthalic anhydride (TEBP-Anh), and 2,4,6-tribromophenol (TBP). To the best of our knowledge, this is the first report of environmental occurrence of TEBP-Anh, which was detected in two rivers and is suggested to originate from airports located near the sampling sites.
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•OPFRs were detected both in the north and south of Sweden, HFRs mainly in the south.•Correlations indicate different sources for OPFRs compared with HFRs and PBDEs.•Population density proved to be a strong predictor of levels of FRs in the rivers.•Occurrence of TEBP-Anh in the environment is reported for the first time.•Total ∑FR (PBDEs, HFRs, OPFRs) flux to the Baltic Sea was estimated to ~31kgday−1.
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Polypropylene (PP), one of five general-purpose plastics, is widely used in many fields. However, the intrinsic alkane structure of PP makes it relatively easy to burn, leading to ...limiting its scope of application. Here, this article reviews the most commonly flame retarding strategies used in PP matrices, including the flame-retardant compounds, application methods as well as flame-inhibition mechanism and also focuses on recent advances and foresees the future outlook of such applications. It is seen that traditional flame retardants and some new compounds are considered in modifying the fire behaviors of PP. At present, with the enhancement of environmental awareness, the application frequency of novel materials in this field is increasing. Thus, the harmonious combination of traditional flame retardants with the newly derived flame retardants has broadened the choice of researchers to come up with novel strategies for improving the fire performance of PP matrices.
In this study, a high effective phosphorus‐containing flame retardant (DOP‐DDM) was synthesized using phenylphosphonic dichloride, p‐hydroxybenzaldehyde, 9,10‐dihydro‐9‐oxa‐10‐phosphaphenan‐ ...threne‐10‐oxide (DOPO) and 4,4′‐diaminodiphenyl methane (DDM) as raw materials. The chemical structure of DOP‐DDM was confirmed by Fourier transform infrared spectroscopy (FT‐IR), 1H nuclear magnetic resonance (1H NMR) and 31P nuclear magnetic resonance (31P NMR). The epoxy resin (EP) material with 4.7 wt% DOP‐DDM (EP‐4.7) can reach V‐0 degree in UL 94 test and has LOI value as high as 33.5%. If neat EP (EP‐0) material is used as a control, even if the loading of DOP‐DDM in the flame‐retarded EP material reached 7.6 wt%, the transmittance can reach 96.8% of EP‐0. From cone combustion (CC) test, the peak of heat release rate (pHRR), total heat release (THR) and total smoke release (TSR) values of EP‐4.7 material were decreased in comparison to those of EP‐0. Compared with EP‐0 material, differential scanning calorimetry (DSC) and dynamic thermo mechanical (DMA) results showed that the glass transition temperature of EP‐4.7 material slightly increased, and the storage modulus (E′) and loss modulus (E′′) increased 65.7% and 47.3%, respectively. The morphology and graphitization degree of residual char after CC test were measured by SEM and Raman spectroscopy, respectively. Concurrently, the gas components of EP‐4.7 material were well analyzed by thermogravimetric analysis FTIR. All these results demonstrated that the DOP‐DDM played a role in gas‐phase and condensed‐phase.
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•Flame retardant interfacial compatibilizer is synthesized.•The GUPR composites can achieve eminent flame retardant effect.•The mechanical properties are improved to a large ...extent.•The flame retardant mechanism for enhanced fire safety are analyzed.
The low flame retardant efficiency and poor interfacial property are the main problems that confine the wide application of glass-fiber reinforced unsaturated resin (GUPR) composites. Herein, these problems are effectively solved by grafting modified silane coupling agent on the surface of glass fiber and adding multi-element hybrid flame retardant to matrix. Firstly, phosphorus-containing flame retardant interface modifier (PKH550) and Sulfur-containing flame retardant (PCH3-S) were synthesized, and the structures were confirmed by Nuclear Magnetic Resonance spectroscopy (NMR) of 1H and 31P. Then PKH550 was successfully grafted on the surface of glass-fiber. Notably, compared with PGF/UPR 20% which had no rating in UL-94 test, the use of PKH550 modified glass-fiber made MGF/UPR 20% reached the V0 rating, and the limiting oxygen index (LOI) value was as high as 38%. In addition, with the increase addition of PCH3-S, the flame retardant properties of GUPR composites were gradually improved. Finally, the mechanical properties of GUPR composites had been improved further by the plasma method. Compared with the 296.93 MPa tensile strength of PGF/UPR, the tensile strength of P-PGF/UPR prepared after plasma treatment of glass-fiber increased to 319.27 MPa. This work provides a new angle to simultaneously improve the fire safety performance and mechanical properties of materials, which will not only be limited to the application of unsaturated resins, but can also have a rather good application prospects in other flame-retardant materials.
•The summary of flame retardants used in asphalt, the flame retardancy mechanisms and research approaches was presented.•Warm mix flame retardant asphalt, mix design method and influence on ...environment were discussed.•Prospect of novel flame retardants and environment-friendly technologies were suggested.
Asphalt pavement is widely used in highway tunnels duo to its excellent skid resistance, comfortability and fast maintenance, however, the flammability suppression of the asphalt pavement in tunnel is still one intractable issue considering the serious accidental consequences. This review starts with the mechanism of asphalt material burning. Secondly, an introduction of flame retardants from conventional to novel is presented. Subsequently, the research approaches for flame retardant is summarized and discussed. In the following chapter, performance evaluation of flame retardant asphalt is reviewed. In chapter 6, the warm mix flame retardant asphalt technology is presented. In addition, the preparation and economic efficiency of flame retardant asphalts were evaluated. Moreover, the environmental effect of flame retardant was explored in chapter 8. Finally, conclusions and remarkable future research interests are presented.
Most organic polymeric materials have high flammability, for which the large amounts of smoke, toxic gases, heat, and melt drips produced during their burning cause immeasurable damages to human life ...and property every year. Despite some desirable results having been achieved by conventional flame‐retardant methods, their application is encountering more and more difficulties with the ever‐increasing high flame‐retardant requirements such as high flame‐retardant efficiency, great persistence, low release of heat, smoke, and toxic gases, and more importantly not deteriorating or even enhancing the overall properties of polymers. Under such condition, some advanced flame‐retardant methods have been developed in the past years based on “all‐in‐one” intumescence, nanotechnology, in situ reinforcement, intrinsic char formation, plasma treatment, biomimetic coatings, etc., which have provided potential solutions to the dilemma of conventional flame‐retardant methods. This review briefly outlines the development, application, and problems of conventional flame‐retardant methods, including bulk‐additive, bulk‐copolymerization, and surface treatment, and focuses on the raise, development, and potential application of advanced flame‐retardant methods. The future development of flame‐retardant methods is further discussed.
Flame‐retardant methods for polymeric materials are reviewed with particular focus on advanced flame‐retardant methods developed in recent years. Both the advantages and drawbacks of these methods are discussed, and prospects for the future development of flame‐retardant methods are presented. It is hoped that this review will guide the development of flame‐retardant polymeric materials.
•A bio-based flame retardant (PF) is synthesized by green and one-step method.•4 wt% PF enables PLA to achieve a high LOI of 28.5% with a UL-94 V-0 rating.•PF simultaneously takes action in gaseous ...and condensed phases during combustion.
The synthesis of bio-based high-efficiency flame retardants in accordance with green and facile method is critical yet very challenging for bioplastics, e.g., poly (lactic acid) (PLA). In this study, a bio-based flame retardant named as PF is synthesized by the reaction between phytic acid (PA) and furfurylamine (FA) in water. PF improves the flame retardancy of PLA at low addition. For instance, PLA composite containing only 2 wt% PF passes a UL-94 V-0 classification, and that containing 4 wt% PF exhibits a limiting oxygen index (LOI) of 28.5%, which is 46.2% higher than that of pure PLA. PF slightly reduces the peak heat release rate (PHRR) and total heat release (THR) of PLA in cone calorimeter test (CCT). In detail, 4 wt% PF reduces the PHRR from 362.2 kW/m2 to 332.7 kW/m2 by 8%. Additionally, PLA/PF composite is comparable to the neat PLA in terms of mechanical properties and thermal stability when a UL-94 V-0 rating is achieved. The flame-retardant mechanism analyses demonstrate that PF takes action in both gaseous and condensed phases. It is proposed that PF accelerates the generation of melting droplets to take away heat, suppresses the release of combustible gases and improves the compactness of char layer during combustion. This study provides a green and facile strategy to create bio-based high-efficiency flame retardants for the preparation of fire-safe bioplastics holding a promising future in the industry.
A solid reactive organophosphorus‐nitrogen flame retardant 4N‐BDP was devised and synthesized in order to address the flaws of the widely used organophosphorus flame retardants BDP as well as the ...issue of flame retardant modification of epoxy resin (EP). A series of flame‐retardant EP composites were prepared by adding 4N‐BDP and BDP to EP in a specific proportion. The flame‐retardant properties of the two were compared, and the flame‐retardant mechanism of 4N‐BDP was deeply analyzed. The results of the UL‐94 test revealed that sample 4N‐BDP‐6 obtained the greatest V‐0 level, while BDP‐6 had no level, when the addition ratio of flame retardant was 8.03%. In the cone calorimeter test, the peak smoke production rate (pSPR) and total smoke production (TSP) of BDP‐6 were not significantly different from those of pure EP. In contrast, TSP and pSPR of 4N‐BDP‐6 decreased by 39.50% and 50.00% respectively compared with EP. Compared with BDP, 4N‐BDP shows better flame retardancy and smoke suppression performance, which can significantly improve the fire resistance of EP. The flame‐retardant mechanism of 4N‐BDP was resolved by scanning electron microscopy, XPS, and thermogravimetric analysis/infrared spectrometry. 4N‐BDP can increase the residual carbon rate of the composites, improve the residual carbon strength, play an excellent condensed phase flame retardant effect, and avoid further decomposition of the materials. In the gas phase, the decomposition of 4N‐BDP produces PO·, PO2· and NH3, which play a good quenching effect and dilution effect. The escape of NH3 will leave bubbles in the residual carbon, making the residual carbon more fluffy, further improving the ability of heat insulation and oxygen insulation, and enhancing the flame retardant effect of the condensed phase. In general, the flame‐retardant mechanism of 4N‐BDP is a synergistic combination of condensed phase and gas phase flame retardant mechanism. This work provides a new approach to improve the defects of organophosphorus flame retardant BDP commonly used in the market and enhance the fire resistance of EP.
