Phosphorylated cellulose/Fe3+ complex: A novel flame retardant for epoxy resins

A novel flame retardant containing cellulose, phosphorus and ferrum complex (Cell‐P‐Fe) was successfully synthesized and then it was used as flame retardants in epoxy resins (EP). Due to the present of acid sources and carbon sources, the Cell‐P‐Fe exhibits improved thermal stability and flame retardant properties. The EP/Cell‐P‐Fe composites with 10 wt% of Cell‐P‐Fe show remarkably improved LOI and UL‐94 values compared with the flame retardants without ferrum. At the loading of 10.0 wt% flame retardants, the char yield for EP/Cell‐P‐Fe composites increased to 29.1 wt%, indicating the improved thermal stability at high temperature. Moreover, thermogravimetric analysis, morphology of char residues and FTIR results demonstrate that stable char layers are formed on the surface of the composites during the combustion, attributing to the catalytic carbonization effect of Fe and phosphorus and the present of cellulose as carbon source. The stable char layers, which can protect the underlying materials from heat and oxygen, play an important role in the flame retardancy enhancement.     

Effect of ethyl‐bridged diphenylphosphine oxide on flame retardancy and thermal properties of epoxy resin

Three commercialized flame retardants, 1,2‐bis(diphenylphosphinoyl)ethane (EDPO), 6,6‐(1,2‐phenethyl)bis‐6H‐dibenz[c,e][1,2]oxaphosphorin‐6,6‐dioxide (HTP‐6123), and hexa‐phenoxy‐cyclotriphosphazene (HPCTP), were used to prepare the flame retardant diglycidyl ether of bisphenol A (DGEBA) epoxy resin (EP) under the same experimental conditions. The effects of T_g, thermal stability, and water absorption properties of EP caused by the three flame retardants were investigated and compared, together with their flame retardant efficiency. Results showed that the introduction of the three flame retardants improved the flame retardant performance of EP but led to decreases in T_g and decomposition temperature. EDPO showed higher flame retardant efficiency than the other two flame retardants. EP/EDPO showed higher thermal stability, better flame retardant performance, higher T_g value, and lower water absorption than EP/HTP‐6123 and EP/HPCTP. The study discovered that EDPO and HTP‐6123 primarily act through the gas phase flame retardant mechanism, while HPCTP is primarily driven by the condensed phase mechanism.     

(Photo)oxidative degradation and stabilization of flame retarded polymers

Flame retarded polymer formulations are mainly used in long-term applications whereas antioxidants, light stabilizers and co-additives provide the requested lifetime of plastic materials. However many flame retardants influence the oxidative and photooxidative stability of polymers often in a negative way resulting in early failure and loss in value. Moreover insufficient (photo)oxidative stability of the flame retardant itself may reduce the flame retardance performance over time. Therefore, there is a need to develop adjusted stabilizer systems considering the type of flame retardant, the polymer substrate and the intended application. Therefore, the influence of flame retardants on the (photo)oxidative stability of selected polymers is reviewed and strategies to extend the lifetime of flame retarded polymers are provided. In addition, the specific requirements of the stabilization of nanocomposites as potential flame retardant components are covered.     

磷系阻燃剂阻燃聚碳酸酯研究进展*

磷系阻燃剂具有阻燃效率高、低烟、低毒、与基质材料相容性好等优点,在阻燃高分子材料领域得到广泛应用。本文介绍了磷系阻燃剂的分类及阻燃机理,综述了近年来磷酸酯阻燃剂、膦酸酯阻燃剂、DOPO磷杂菲类阻燃剂、磷腈类阻燃剂和无机磷阻燃剂在阻燃聚碳酸酯领域的研究进展,为新型磷系阻燃剂的研发提供参考。     

Synergistic effect of flame retardants and graphitic carbon nitride on flame retardancy of polylactide composites

In order to improve the flame retardant of polylactide (PLA), the synergistic effect of graphitic carbon nitride (g‐C₃N₄) with commercial‐available flame retardants melamine pyrophosphate (MPP) and 9,10‐dihydro‐9‐oxa‐10‐phosphaphenanthrene‐10‐oxide (DOPO) was investigated. The PLA composites containing 5 wt% g‐C₃N₄ and 10 wt% DOPO had a highest limited oxygen index (LOI) value of 29.5% and reached the V‐0 rating of UL‐94 test. The cone calorimeter tests exhibited that DOPO had a better synergistic effect with g‐C₃N₄ than MPP to improve flame retardancy of PLA. The peak heat release rate (pHRR) and total heat release (THR) of PLA composites containing 10 wt% DOPO could be reduced by 25.2% and 23.6%, respectively, as compared with those of pure PLA. The presence of rich phosphorus element and aromatic groups in DOPO contributed to obtain continuous compact char layer and increase the graphitization level of char residues, thereby, resulting in improving the flame retardancy of PLA together with g‐C₃N₄. In addition, the incorporation of DOPO can serve as a plasticizer to reduce the complex viscosity, improving the processability of PLA composites.     

Organically modified montmorillonite as a synergist for intumescent flame retardant against the flammable polypropylene

Low flame retardant efficiency is a key bottleneck for currently available retardants against the flammable polypropylene (PP). Herein, the organically modified montmorillonite (OMMT) was utilized as a synergist for our previously reported intumescent flame retardant (IFR) that was constructed from ammonium polyphosphate (APP) and hyperbranched charring foaming agent (HCFA) to further enhance the retardant efficiency against PP. The resultant's combustion behavior was thoroughly investigated by cone calorimetry, limiting oxygen index (LOI), vertical burning test (UL‐94), and scanning electron microscopy (SEM). The results showed that 20% addition of IFR with OMMT showed a positive effect and improved the flame retardancy of the PP systems. Especially, addition of 2 wt% OMMT obviously increased the LOI values of PP systems with 20% total loading flame retardants from 29% to 31.5% and the samples meet V‐0 rating as well as the reduction of the heat release rate (HRR), total heat release (THR), CO₂, and CO production occurred. On the other hand, the SEM images were also revealed that OMMT initiated a dense and strong char on the surface of the material, which resulted in efficient flame retardancy of PP matrix during combustion. In addition, thermal degradation behavior discussed by thermogravimetric analysis (TGA) indicated that OMMT could improve the thermal stability of PP systems under high temperature, and promoted char residues of PP/IFR systems. Copyright © 2016 John Wiley & Sons, Ltd.     

Studies on the effect of different levels of toughener and flame retardants on thermal stability of epoxy resin

A thermoplastic toughener, polyether sulphone (PES) and a number of different types of flame retardants were blended in different ratios with a commercial epoxy resin triglycidyl-p-aminophenol (TGAP) and 4,4-diamino diphenyl sulphone (DDS) a curing agent. The effect of type and levels of flame retardants (FR) and the toughening agent on the curing, thermal decomposition and char oxidation behaviour of the epoxy resin was studied by the simultaneous differential thermal analysis and thermogravimetric techniques. It was observed that the toughener slightly increases the curing temperature (by up to 20 °C) but had minimal effect on the decomposition temperature of the resin. Flame retardants, however affected all stages depending upon the type of flame retardant used. The curing peak for samples containing tougher and flame retardants although slightly changed depending upon the type of FR, was not more than ± 20 °C compared to that of samples containing toughener only. All flame retardants lowered the decomposition temperature of the epoxy resin. Phosphorus- and nitrogen-containing flame retardants reduced the char oxidation leading to more residual char, whereas halogen- containing flame retardants had less effect on this stage.     

Combination effect of nanoparticles with flame retardants on the flammability of nanocomposites

Polystyrene based nanocomposites (PNCs) with and without flame retardant additives were successfully prepared through a single-screw extrusion technique. The combination effect of nanoparticles and flame retardants was investigated with nanosilica and attapulgite clay as nanofillers, and with a NASA formulated SINK flame retardant. A comprehensive study was done by Cone Calorimetry, UL94 and TGA.The addition of nanoparticles to polystyrene generally improved the OI of polystyrene. The horizontal burning tests suggested that nanofiller types have different impacts on the flammability of nanocomposites. According to the vertical burning tests and oxygen indices, it was found that polystyrene/silica and polystyrene/attapulgite clay PNCs alone are not flame retardant. In fact, the materials burned faster. However, the combination of nanocomposites with the SINK flame retardant significantly altered the thermal stability, and flammability of the materials. A remarkable reduction in heat release rates of polystyrene was achieved for both silica and attapulgite with flame retardant nanocomposites. For instance, the introduction of 20% SINK into PS reduced the PHRR of PS from 1212 to 838 (−31%); 10% silica reduced it from 1212 to 1060 (−13%), while the combination of silica and SINK reduced it to 530 (−56%), which clearly shows interaction between nanosilica and SINK.     

聚乳酸阻燃性能的研究进展

聚乳酸作为一种资源与环境友好材料已得到了广泛深入的研究。如果能够提高聚乳酸的阻燃性能,则能进一步扩大其应用范围。目前对聚乳酸的阻燃改性主要采用添加阻燃剂的方法,并以磷系、氮系、硅系、金属化合物阻燃剂以及多种阻燃成分的复配为主,而聚乳酸的反应型阻燃也在不断研究发展中。本文在介绍阻燃作用机理的基础上,综述了聚乳酸阻燃研究发展现状,并对聚乳酸的阻燃提出展望。     

Properties and characteristics of polylactide blends: Synergistic combination of poly(butylene succinate) and flame retardant

A study on the influence of flame‐retardant types, poly(butylene succinate) (PBS) contents, and combination of flame retardant and PBS on the mechanical, thermal, morphological, and flame retardancy properties of polylactide (PLA) and PLA/PBS blends was investigated. Blending of PLA, PBS, and flame retardant was prepared by a twin screw extruder. Tricresyl phosphate (TCP) and montmorillonite (MMT) were used as a flame retardant, whereas PBS acted as a flexible material for enhancing the fire resistance and toughness of PLA, respectively. The results revealed that the introducing of TCP and MMT greatly improved the impact strength of the PLA. The impact toughness of PLA blends with 20 wt% of PBS increased to about 244% that of neat PLA. The addition of flame retardants markedly improved the limiting oxygen index of PLA from 18.0% to 30.1% and 24.3% for the blends containing TCP and MMT. The V‐0 rating in UL‐94 testing was achieved with PLA/TCP blend. Elongation at break, impact toughness, and thermal stability of PLA significantly increased with the increment of PBS concentration. The synergistic effect of flame retardant and PBS afforded the PLA blends with outstanding increase of impact resistance. Furthermore, the flame retardant of TCP in the system not only affected dripping behavior and total flame time of PLA/PBS blends but also improved limiting oxygen index values due to the forming of char layer and inhibiting of burning mechanism.     

Flame retardant chemical mechanisms of flame retardant viscose fibres and blends with polyester

A systematic investigation of structurally identical flame retardant viscose, modal and polyester blended fabrics and fibres was carried out in order to develop a chemical basis for more effective products based on organic and inorganic flame retardants. The oxygen indices and chemical compositions of phosphorus-nitrogen flame retardants (P-N) were used in efficiency and synergy evaluations. A new flame retardant viscose fibre containing silicid acid was included in the comparative evaluation procedure. Thermal gravimetry and X-ray diffractometry were used for determine physical factors during pyrolyzing of fibres. Charred residues were analyzed by applying elementary and solid 13-C NMR (CPMAS) spectrometry. The pyrolysis gas-liquid chromatographer connected with a gas phase FT infrared spectrometer was applied to identify the decomposition products of P-N-containing fabrics.     

Synthetic hydromagnesite as flame retardant. Evaluation of the flame behaviour in a polyethylene matrix

Synthetic hydromagnesite obtained from an industrial by-product was evaluated as a non-halogenated flame retardant. It was used in combination with aluminium hydroxide (ATH) and compared with commercial flame retardants like magnesium hydroxide (MH) and natural hydromagnesite-huntite (U) in a polyolefin system of low-density polyethylene/poly(ethylene-co-vinyl acetate) (LDPE/EVA).The thermal stability and flame behaviour of the halogen free flame retarded composites were studied by thermogravimetric and differential thermal analysis (TG-DTA), limiting oxygen index (LOI), epiradiateur and cone calorimeter. It has been shown that synthetic hydromagnesite could be an alternative solution to the use of MH in non-halogenated flame retardant systems in EVA.     

Development of additives possessing both solid-phase and gas-phase flame retardant activities

Effective additives are required to impart a measure of fire retardancy to polymeric materials used in a variety of applications. Traditionally, these have been gas-phase active additives, most commonly organohalogen compounds or solid-phase active agents, often organophosphorus compounds. Organosphosphorus flame retardants are often very effective but may suffer from a cost disadvantage when compared with their organobromine counterparts. Organohalogen flame retardants are usually quite effective but their use is a subject to several environmental concerns. The development of additives that could simultaneously promote both types of fire retardant action could make available flame retardants that are both more cost effective and more environmentally friendly than those currently in use. Several sets of compounds with the potential to display both solid-phase and gas-phase flame retardant activities have been prepared and evaluated.     

In situ synthesis of a novel transparent poly (methyl methacrylate) resin with markedly enhanced flame retardancy

A novel phosphorus‐containing monomer, (6‐oxido‐6H‐dibenzo[c,e][1,2]oxaphosphinin‐6‐yl)methyl acrylate (DOPO‐AA), is first synthesized and characterized by Fourier transform infrared spectra (FTIR), ¹H nuclear magnetic resonance (NMR) and ³¹P NMR. The monomer is then introduced into poly (methyl methacrylate) (PMMA) matrix via in situ copolymerization to produce a new PMMA based copolymer (PMMA/DOPO‐AA). From UV–vis spectra, microscale combustion calorimeter (MCC) and thermogravimetric analyses (TGA) results, the as‐fabricated PMMA/DOPO‐AA copolymers not only keep relatively high transparency, but also exhibit remarkable improvements in the flame retardancy and thermal stability, such as increased T_0.5 by 60.2°C and limited oxygen index (LOI) by 4.1, and decreased peak heat released rate (PHRR) by 34.7%. Thermal degradation behaviors investigated by real time Fourier transform infrared spectra (RTIR), char structure analysis studied by scanning electron microscope (SEM) and pyrolysis gaseous products studied by TGA coupled with FTIR (TGA‐FTIR) demonstrate that the catalytic charring function of DOPO‐AA in condensed phase and DOPO flame retardant systems in the gas phase are two key factors for the property enhancements. This work not only provides a promising flame‐retardant monomer for polymers, but also will stimulate more efforts on the development of DOPO‐containing flame‐retardant monomers. Copyright © 2015 John Wiley & Sons, Ltd.     

A review on flame retardant technology in China. Part II: flame retardant polymeric nanocomposites and coatings

The progress of flame retarded polymer nanocomposites and coatings in China over the past decades are described in this review. Emphasis on flammability performance of polymer nanocomposites containing nanofillers, mainly layered inorganic compounds, nanofibers and nanoparticles, combined with conventional flame retardant additives are addressed based on the open literature. Polymeric coatings with improved flame retardancy prepared using a wide variety of additives and UV‐curing technology are also introduced. Derived from this research, the combination of multiple methods and technologies including catalyst and nanotechnology, is predicted to have a high probability to enhance char formation and improve the flame retardancy of polymeric materials. Copyright © 2011 John Wiley & Sons, Ltd.     

硅橡胶复合材料阻燃研究进展

将功能填料引进到硅橡胶及其复合材料中可以获得特定功能的硅橡胶复合材料,已经成为近些年研究热点。目前阻燃剂种类繁多,但是性能比较单一,这已经不能满足人们的需要。人们在关注硅橡胶复合材料阻燃性能的同时,也考虑与其它性能兼备以及成本等问题。因此,本文综述了铂化合物、磷系阻燃剂、阻燃涂层、阻燃填料和微胶囊化阻燃剂等阻燃体系下硅橡胶复合材料的阻燃研究现状,总结了不同阻燃剂的阻燃机理,并且给出了其今后的改进方法,最后对硅橡胶复合材料阻燃研究的发展做了展望。     

Ternary structure design based on hydrogen bonding for transparent and flame retardant PMMA with good mechanical properties

The synthesis of intrinsic flame retardant copolymer by copolymerization with reactive flame retardants is the most potential method to prepare transparent and flame retardant poly (methyl methacrylate) (PMMA) at present,but the main challenge of this method is that the copolymer usually has poor mechanical properties and heat resistance. In this work, the hydrogen bond enhancement strategy is adopted, and the flame retardant PMMA with excellent comprehensive properties is obtained by ternary copolymerization with methyl methacrylate (MMA) as matrix unit, diethyl (methacryloyloxymethyl) phosphonate (DEP) as flame retardant unit and methacrylamide (MAA) as hydrogen bond unit. Due to the formation of intermolecular hydrogen bond via MAA unit, the storage modulus, flexural strength and impact strength of the terpolymer containing 15 mol% MAA are 48%, 19%, and 24% higher than those of the copolymer of MMA and DEP, and its hardness, glass transition temperature and load thermal deformation temperature (increased by 7°C) are also superior. Moreover, owing to the gas-phase dilution and charring flame retardancy of MAA unit, the terpolymer shows increased limiting oxygen index (24.3%) and UL94 rating (V-1). This work not only provides a promising flame retardant PMMA for practical application, but also offers a new strategy to design flame retardant polymers with good mechanical properties.     

Thermal properties of compounds possessing both solid-phase and gas-phase flame retardant potential

Effective additives are required to impart a measure of fire retardancy to polymeric materials used in a variety of applications. Traditionally, these have been gas-phase active additives, most commonly organohalogen compounds, or solid-phase active agents, often organophosphorus compounds. Organosphosphorus flame retardants are often very effective but may suffer from a cost disadvantage when compared with their organobromine counterparts. Organohalogen flame retardants are usually quite effective but their use is subject to several environmental concerns. The development of additives that could simultaneously promote both types of fire retardant action could make available flame retardants that are both more cost effective and more environmentally friendly than those currently in use. Several sets of compounds including bromoanilino triazine derivatives and bromoaryl phosphates with the potential to display both solid-phase and gas-phase flame retardant activity have been prepared and evaluated by a variety of thermal methods.     

Influence of phosphorus valency on thermal behaviour of flame retarded polyurethane foams

This paper reports decomposition/pyrolysis studies of polyurethane (PU) rigid foams containing phosphinate, phosphonate or phosphate as flame retardant in order to study the effect of phosphorus oxidation state on their gas and/or solid phase action. The flame retardants analyzed were aluminium phosphinate (IPA), dimethylpropanphosphonate (DMPP), triethylphosphate (TEP) and ammonium polyphosphate (APP), which differ in oxidation state and/or decomposition temperature. Gases evolved during TGA analyses as well as solid residues have been studied by means of MS and FTIR.The results show that phosphorus flame retardants which significantly lose weight at temperatures lower than those of neat PU foams act in the gas phase irrespective of their valency: indeed, they are completely volatilized before polymer decomposition starts and thus no interaction between flame retardant and polymer can be expected. The effect of phosphorus oxidation state becomes important when flame retardant decomposition takes place in the same temperatures range as neat polymer. In this case, it seems that at lower P oxidation state (+1) a combined gas and solid phase action takes place while at higher P oxidation state (+5) only solid phase action was observed.     

Vanillin‐derived phosphorus‐containing compounds and ammonium polyphosphate as green fire‐resistant systems for epoxy resins with balanced properties

Flame retardants from vanillin when utilized together with ammonium polyphosphate (APP) yield excellent synergistic flame retardancy toward epoxy resins. Bisphenol A epoxy resins have been widely used due to their excellent mechanical properties, chemical resistance, electrical properties, adhesion, etc., while they are flammable. Environment‐friendly and bio‐based flame retardants have captured increasing attention due to their ecological necessity. In this paper, 3 bio‐based flame retardants were synthesized from abundant and more importantly renewable vanillin, and their chemical structures were determined by ¹H NMR and ¹³C NMR. They were used together with APP (an environment‐friendly commercial flame retardant) to improve the fire resistance of bisphenol A epoxy resin. With the addition APP content of 15 phr, the modified bisphenol A epoxy resin could reach UL‐94V0 rating during vertical burning test and limit oxygen index values of above 35%, but reducing APP content to 10 phr, the flame retardancy became very poor. With the total addition content of 10 phr, the epoxy resins modified by 7 to 9 phr APP and 1 to 3 phr bio‐based flame retardants with epoxy groups or more benzene rings showed excellent flame retardancy with UL‐94V0 rating and limit oxygen index values of around 29%. The T_gs of the epoxy resins could be remained or even increased after introducing bio‐based flame retardants, as the control; those of APP alone‐modified epoxy resins compromised a lot. The green synergistic flame‐retardant systems have a great potential to be used in high‐performance materials.