Fire retardant action of mineral fillers

Endothermically decomposing mineral fillers, such as aluminium or magnesium hydroxide, magnesium carbonate, or mixed magnesium/calcium carbonates and hydroxides, such as naturally occurring mixtures of huntite and hydromagnesite are in heavy demand as sustainable, environmentally benign fire retardants. They are more difficult to deploy than the halogenated flame retardants they are replacing, as their modes of action are more complex, and are not equally effective in different polymers. In addition to their presence (at levels up to 70%), reducing the flammable content of the material, they have three quantifiable fire retardant effects: heat absorption through endothermic decomposition; increased heat capacity of the polymer residue; increased heat capacity of the gas phase through the presence of water or carbon dioxide. These three contributions have been quantified for eight of the most common fire retardant mineral fillers, and the effects on standard fire tests such as the LOI, UL 94 and cone calorimeter discussed. By quantifying these estimable contributions, more subtle effects, which they might otherwise mask, may be identified.     

阻燃高分子复合材料中氢氧化镁的制备及其表面改性

以氢氧化镁为代表的无卤阻燃剂,由于其具有良好的阻燃、抑烟性能及环保特点,已日益得到学术界和产业界的重视.在实际应用过程中,人们发现阻燃剂的形貌对其阻燃性能具有较大影响,因此本文重点综述了化学沉淀法制备不同形貌及尺寸的氢氧化镁和各影响因素对其制备的影响,以及当前氢氧化镁表面改性的一些新方法,如:大分子改性等,使得其在复合加工过程中,能与高分子材料具有良好的相容性.     

绿色环保型氢氧化镁阻燃剂

介绍了阻燃剂的种类和发展趋势,并重点介绍了氢氧化镁阻燃剂的阻燃机理、特点、应用和发展。指出氢氧化镁阻燃剂是一种新型的、对环境友好的无机阻燃剂。     

Etude ATD-ATG du polyethylene ignifuge par l’hydroxyde de magnesium

Fire resistance of polyethylene is realized by magnesium hydroxide which is distinguished from halogenated fire-proofing agents by its lower cost and its non toxicity. Magnesium hydroxide decomposed by an endothermic reaction with liberation of water, contributing to fire proofing. The sample used (Kisuma 5A-N^*) is constituted from a powder (0.6–0.8 micrometre) its surface is treated by plastic material in order to ameliorate its compatibility. We studied the thermal decomposition by DTA and TG, of mixtures constituted by polyethylene and magnesium hydroxide. A sudden decomposition began at 385°C for pure polyethylene and decomposition took place at 429°C for the mixture polyethylene-Kisuma (50–50). Incorporation of magnesium hydroxide in polyethylene increases fire resistance.     

Mechanism of action of a fire retardant chloroparaffin

The mechanism by which a typical fire retardant chloroparaffin imparts fire retardant characteristics to high density polyethylene, polypropylene and polystyrene is studied by comparing the oxygen indices of these mixtures measured before and after dehydrochlorination. It is shown that flame poisoning by HCl evolved from the chloroparaffin is negligible in polystyrene and high density polyethylene, whereas it is noticeable in polypropylene. The results obtained are related to previous data on the thermal degradation of these mixtures. It is concluded that the chloroparaffin acts mainly by modifying the mechanism of pyrolysis of these polymers in the burning process. Only in the case of polypropylene is there an appreciable contribution by flame poisoning.     

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.     

使用裂解气相色谱对几种阻燃聚丙烯材料热稳定性及阻燃机理的探讨

用裂解气相色谱（PyGC)考察了经三种类型阻燃剂（含磷、含溴、含溴和磷）改性的聚丙烯的热稳定性。利用PyGC-MS法分析不同样品的高温裂角产物,以此来推测阻燃材料受热分解时气相以及凝聚相所发生的反应,推断阻燃机理,分析影响阻燃效果的因素,为阻燃剂的开发提供有益参考。结果证实,它们都影响聚丙烯的热降解。溴系阻燃剂和磷系阻燃剂是分别从气相阻断、凝固相加速成炭实现阻止燃烧的,而磷-溴型阻燃剂同时具备单纯含磷或者含溴阻燃能力。     

Study of hydromagnesite and magnesium hydroxide based fire retardant systems for ethylene-vinyl acetate containing organo-modified montmorillonite

A new flame retardant (FR) system for ethylene-vinyl acetate, mainly based on the combination of hydromagnesite (HM, obtained from an industrial by-product) and organo-modified montmorillonite (oMMT) has been compared with a magnesium hydroxide (MDH) and oMMT flame retardant system. The presence of oMMT in association with both hydrated minerals gave a strong decrease of heat release rate in cone calorimeter tests. Moreover, the HM/oMMT combination leads to a better improvement of resistance to ignition and self-extinguishability in comparison with the MDH/oMMT one. The study of residues formed during thermal decomposition revealed the formation of forsterite (Mg₂SiO₄) when either MDH or HM was used in combination with oMMT. SEM observations of residues showed sintering of the mineral particles at high temperature particularly in the case of HM/oMMT composition.     

Thermal decomposition of polymer mixtures of PVC,PET and ABS containing brominated flame retardant: Formation of chlorinated and brominated organic compounds

The thermal decomposition of various mixtures of acrylonitrile butadiene styrene copolymer (ABS), ABS containing brominated epoxy resin flame retardant and Sb₂O₃, poly(ethylene terephthalate) (PET) and poly(vinyl chloride) (PVC) has been studied in order to clarify the reactions between the components of mixed polymers. More than 40 halogen-containing molecules have been identified among the pyrolysis products of mixed samples. Brominated and chlorinated aromatic esters were detected from the mixtures containing PET and halogen-containing polymers. A series of chlorinated, brominated and mixed chlorinated and brominated phenols and bisphenol A molecules have been identified among the pyrolysis products of polymer mixtures containing flame retarded ABS and PVC. It was established that the decomposition rate curves (DTG) of the mixtures were not simple superpositions of the individual components indicating interactions between the decomposition reactions of the polymer components. The maximal rate of thermal decomposition of both ABS and PET decreases significantly if the mixture contains brominated epoxy flame retardant and Sb₂O₃ synergist. The dehydrochlorination rate of PVC is enhanced in the presence of ABS or PET.     

Fire protection of polypropylene and polycarbonate by intumescent coatings

An innovative way to improve fire‐retardant properties of different polymers by applying intumescent coatings on their surface has been studied. Two polymers have been investigated: polypropylene and polycarbonate. The surfaces were first subjected to a flaming treatment in order to clean them and to increase their wettability and thus improve the adhesion of the coatings. Two different formulations were then applied: a transparent intumescent varnish, based on an acrylic resin, and an intumescent coating based on polyvinylacetate resin. Different parameters have been obtained using several fire tests. The cone calorimeter, the limiting oxygen index and UL94 tests have been carried out to evaluate the fire‐retardant properties obtained for both the intumescent coating and the intumescent varnish. Results clearly evidence an outstanding improvement of the fire‐retardant properties using intumescent coatings without any incorporation of flame retardants in the bulk. Copyright © 2010 John Wiley & Sons, Ltd.     

Date palm fibre filled recycled ternary polymer blend composites with enhanced flame retardancy

Flammability of recycled polypropylene (PP)/low density polyethylene (LDPE)/high density polyethylene (HDPE) ternary blends containing date palm fibres is investigated in this study. Melt blending is used for the composite preparation and the palm fibres induce good mechanical strength to the blend composites. The effect of flame retardant magnesium hydroxide, is studied through the limiting oxygen index analysis and cone calorimeter studies. Morphology of the palm fibres in presence of fire retardant reveals interesting facts of base hydrolysis. Since the polymers used are recycled ones and the fibres are obtained from the date palm leaves, the whole composite manufactured stands as low cost, less energy consuming and environmental friendly. Though the flame retardant reduced the mechanical properties, the palm fibres strengthened the whole composite thus helping to achieve the flame retardancy and mechanical properties simultaneously. Flame retardancy is correlated with the thermal degradation and thermal conductivity of the blend fibre composites as well.     

Thermal degradation of fire retardant chloroparaffin-metal compound mixtures: Part III—A comparison of the behaviours of antimony trioxide and bismuth compounds

The characteristics of the evolution of the flame inhibitors HCl and metal chlorides from thermally degrading mixtures of a chloroparaffin and antimony trioxide or Bi compounds are compared with reference to the behaviour of these mixtures as fire retardant additives for polymers.     

Evaluation of various fire retardants for use in wood flour-polyethylene composites

Wood-plastic composites represent a growing class of materials used by the residential construction industry and the furniture industry. For some applications in these industries, the fire performance of the material must be known, and in some cases improved. However, the fire performance of wood-plastic composites is not well understood, and there is little information regarding the effectiveness of various fire retardants in the public domain. We used oxygen index and cone calorimeter tests to characterize the fire performance of wood flour-polyethylene composites, and compared the results with unfilled polyethylene and solid wood. We then evaluated the effect of five additive-type fire retardants on fire performance. Generally, magnesium hydroxide and ammonium polyphosphate improved the fire performance of WPCs the most while a bromine-based fire retardant and zinc borate improved fire performance the least.     

Characterization of fire retardant polymer blends by temperature resolved in-source pyrolysis mass spectrometry

The characterization of fire retardant polymer blends by temperature resolved in-source pyrolysis mass spectrometry (PYMS) is demonstrated with a few examples. Electron impact (EI) and electron capture negative ionization (ECNI) were used to identify the thermal degradation products of polymer blends containing brominated fire retardants. PYMS (EI mode) offers an analytical instrument for a fast analysis of unknown mixtures of polymers and for the presence of fire retardant additives. Under electron impact conditions, in vacuo, low-molecular weight additives like fire retardants mainly evaporate from the polymer matrix. PYMS (EI mode) has been used for the characterization of addition polymers like polystyrene and acrylonitrile-butadiene-styrene copolymer, and for condensation polymers like the polyester poly(butylene terephthalate). Applying electron capture negative ionization, at low argon pressure in the ionization chamber, a more realistic pyrolysis situation is created because the premature loss of volatile additives is suppressed. The selectivity of ECNI for electron accepting groups like bromine makes it possible to study the influence of brominated compounds on the degradation processes in the melt. This is demonstrated by our studies on polystyrene and acrylonitrile-butadiene-styrene copolymer. High-molecular weight pyrolysis products in the m/z range of 1000 - 2000 are detected for p-bromopolystyrene and for a blend of high impact polystyrene with the fire retardant system decabromodiphenyl ether/antimony(III) oxide. In addition to the formation of antimony bromides shown in earlier studies, the emission of the synergist antimony(III) oxide as a dimeric cluster (Sb₄O₆) or as a reduced Sb₄ cluster is observed under PYMS conditions.     

The Future of Flame Retardant Polymers – Unmet Needs and Likely New Approaches

ABSTRACT

Thermoplastic and thermoset polymers in use today have fire risk and fire hazard associated with them that is not always well known to the public or material scientists. Recent events in the United Kingdom and California show that, if not considered carefully, use of flammable materials can result in catastrophic losses of both life and property. Further, current understanding has shown that simply adding flame retardant chemicals to polymers to address fire hazard and risk is not sufficient, as there is an increased demand from consumers, government, and industry for improved durability, recyclability, fire safety, and reduced environmental impact. These new requirements are beginning to change flame retardant chemistry for polymers, which has been mostly unchanged for the past 50 years. Existing flame retardant chemical technology will be briefly reviewed to show what is available today, followed by a discussion of potential future flame retardant approaches. Future possibilities such as polymeric, reactive, inorganic, and transition metal chemistries will be surveyed and discussed, with emphasis on what is not fully understood or validated for commercial use or future research and development investment. Current unmet fire safety needs of polymers, based upon current information and technological trends, will also be discussed.     

Structural and thermal interpretation of the synergy and interactions between the fire retardants magnesium hydroxide and zinc borate

The mechanism of cooperative action of commercial fire retardants is interpreted as resulting from specific chemical reaction and phase changes. This investigation focuses on the thermally initiated interactions between two forms of commercially available fire retardant compounds. The fire performance of a polyolefin with a metal hydroxide fire retardant, magnesium hydroxide, can significantly reduce the heat release rate through absorption of heat during conversion to its metal oxide. Formation of water, followed by vaporisation, decreases heat and dilutes volatiles from polymer degradation. The second form of fire retardant compounds are zinc borates (2ZnO·3B₂O₃·3H₂O and 4ZnO·B₂O₃·H₂O), that undergo dehydration with increasing temperature. Differential thermal analysis and wide-angle X-ray spectroscopy indicated that various structural changes occurred during heating. Endothermic transitions were observed for all components, while zinc borate (2ZnO·3B₂O₃·3H₂O) showed an exothermic crystallisation transition at relatively high temperature. The exotherm was modified by the development of a new crystalline phase, magnesium orthoborate (3MgO·B₂O₃) that formed on reaction with magnesium oxide (MgO) at temperatures greater than 500 °C. Formation of crystalline zinc oxide (ZnO) was also detected. From zinc borate (4ZnO·B₂O₃·H₂O), ZnO was primarily formed. No new crystalline phases were observed in the presence of MgO over the temperature range investigated.     

Performance and mechanisms of fire retardants in polymers—A review

The fundamental mechanisms by which fire retardant additives can interrupt the self-sustained combustion cycle of organic polymers are reviewed. Evaluation of fire retardant performance and methods used for mechanism assessment are discussed. Examples are given of recent mechanistic studies of halogen-based and intumescent systems indicating that some previous generalisations should be revised. It is shown that a deeper understanding of fire retardance mechanisms acquired through detailed thermal degradation studies is the only way to answer the ever increasing demand for polymeric materials characterised by minimised overall fire hazard.     

Thermal Degradation and Fire Behavior of High Performance Polymers

Abstract

High performance and high temperature polymers are a class of polymeric materials exhibiting high thermal stability and their resistance to fire makes them valuable assets for many applications. Those applications include as typical examples high temperature gas separation membranes, automotive and aerospace industry as well as the construction industry. The high performance polymers have been synthesized since the early 1960s, and have developed rapidly over the past few decades. Most high performance polymers comprise a highly aromatic backbone, linear chains, and strong inter-chain interactions. This review deals mostly with commercial polymeric materials. Studies regarding their thermal behavior, degradation mechanism and their reaction to fire have been synthetically combined in order to bring out potential insight concerning the effect of the thermal decomposition and thermal behavior on the fire properties of those polymers.     

Surface modified aluminium hydroxide in flame retarded noise damping sheets

Flame retarded polyethylene compounds were prepared using a series of aluminium hydroxide of different particle size applying a milling processes and special precipitation technologies. The processability and flame retardant efficiency of the flame retarded systems were compared. The effects of various surface modifications were analysed in case of one selected type of aluminium hydroxide. A silicone terminated reactive surfactant promoted not only the processability but also the flame retardant efficiency. Noise damping sheets were prepared by simultaneous application of aluminium hydroxide and barium sulphate in an elastomer blend matrix. V0 flame retardant grade could be achieved this way accompanied with improvement in the acoustic properties and maintenance of the mechanical properties.     

Flammability characteristics and synergistic effect of hydrotalcite with microencapsulated red phosphorus in halogen-free flame retardant EVA composite

The flammability characteristics and synergistic effect of hydrotalcite with microencapsulated red phosphorus (MRP) in halogen-free flame retardant ethylene vinyl acetate (EVA) composite have been studied by cone calorimeter test (CCT), thermogravimetric analysis (TGA), limiting oxygen index (LOI) and UL-94 test. The results obtained by comparing the flame retardancy of hydrotalcite with magnesium hydroxide (MH) and aluminium hydroxide (AH) for their EVA composites showed that hydrotalcite has higher flame retardant effect than MH and AH at the same loading level. The CCT tests indicated that the heat release rate (HRR) and mass loss rate (MLR) of EVA composite blended with hydrotalcite greatly decreased compared with those blended with MH and AH. The LOI values of EVA/hydrotalcite composites are 3-4% higher than those of the corresponding MH composites at 40-60 wt% loading levels, and 6% higher than that of the corresponding AH composite at 40 wt% loading level. Moreover, the addition of a given amount of MRP apparently resulted in the increase of LOI value and decrease of the HRR and MLR as well the loading of hydrotalcite in EVA blend while keeping the V-0 rating in UL-94 test. However, the smoke release increased during the combustion of EVA/hydrotalcite blend containing MRP.