Phosphorus based flame retardants

With a recent push toward non-brominated flame retardants, phosphorus-based alternatives, such as phosphate esters, are used more frequently for various applications. Their use as plasticizers is also well known. However, their function as environmental stress crack agents of various thermoplastics is less well recognized. Two case studies, one - in which a triaryl phosphate was a component of the formulation, the other - in which it was migrating from an adjacent component illustrate some of the problems with their use. Fractographic analysis and various analytical techniques were used to determine a root cause of each of the two failures. 

Houde [24] has investigated the composition and mode of operation of flame retarding additives based on antimony, bromine, chlorine, nitrogen, and phosphorus. 

Several approaches have been used to make polymers fire-retardant. Phosphorus-based flame retardants have been effectively used in a wide variety of polymeric materials. The efficiency of phosphorus compounds is often dramatically increased in the presence of certain nitrogen compounds. Thus, the improved flame resistance of polyesters in the presence of triphenylphosphine oxide and Nylon-6 has been attributed to the synergistic effect of phosphorus and nitrogen atoms. However, the fire-retardant additives (1) frequently influence the decomposition reaction in... 

Wang Zheng, Wu Wei, Zhong Yuhua, Ruan Mingzhu, and Hui Lin Lin. Flame-retardant materials based on phosphorus-containing polyhedral oligomeric silsesquioxane and bismaleimide/DBA with improved thermal resistance and dielectric properties. J. Appl. Polym. Sci. 132 no. 9 (2015) 41545-41555. 

For more than a decade potential environmental problems associated with organo-bromine flame retardant systems have motivated the search for non-halogen-based approaches to reduce polymer flammability. Initially, research focused on development of new phosphorus-based flame retardants, and numerous publications and patents have been issued in this area. Similarly motivated research has also produced nonhalogen flame retardant approaches based on other elements, such as boron and sihcon. At the same time, work on the use of additives, or flllers, with nanometer-scale primary particle sizes, produced polymer nanocomposites. These materials exhibit enhancement in a variety of physical properties at one-tenth the loading required when micrometer-size additives are used. ... 

The mode of action of phosphorus-based flame retardants is believed to take place in either the condensed or the vapor phase (refs. 1,2) depending on the type of phosphorus compound and the chemical composition of the polymer. Phosphorus has been reported to be 3 to 8 times more effective than bromine depending on the polymer type (ref. 3). 

The use of n-butylamino-derivatives of cyclophosphazenes in flame-proofing cellulose-based fabrics has been described in a patent application. The topic of fiame retardants is also covered in a recent review, where phosphazenes are important because of their relatively high phosphorus and nitrogen contents. 

When used purely as an insulator, foam densities can be as low as 0.02 to 0.08 g/cm3. In structural applications the foam s density can rise to 0.4 to 0.7 g/cm3. The use of fluorocarbons as blowing agents has largely given way to more environmentally friendly agents, such as low molecular weight hydrocarbons. We can impart flame retardancy by incorporating chlorine-or phosphorus-based compounds. 

Generally, flame retardants for engineering PET compositions are based on bromine-containing compounds (such as brominated polycarbonate, decabro-modiphenyl oxide, brominated acrylic, brominated polystyrene, etc.). Such compounds are available commercially (such as from the Ethyl Chemical Corporation, Great Lakes Chemical Corporation, Dead Sea Bromine Company, etc.) In addition, the flame-retardant package generally contains a synergist, typically sodium antimonate. PET may also be flame-retarded with diarylphosphonate, melamine cyanurate or red phosphorus. 

While there are a large number of both phosphorus additive and comonomer compounds available, no direct comparisons have been reported between the effectiveness of the two methods of incorporation, aside from some references to the lack of permanency of many additive compositions. The use of additives, on the other hand, may provide a greater flexibility, allowing the production of polymeric compositions of varying degrees of flame retardance, from the same base resin. The purpose of this study was to determine whether any real differences in effectiveness are detectable due to the method of incorporation of phosphorus into a polymer system. 

Highly toxic phosphine gas, PH3, is used in industry to produce flame retardants. One way to make phosphine on a large scale is by heating elemental phosphorus with a strong base. 

TBBA, a brominated flame retardant, is used in the epoxy resin laminate in printed circuit boards in most manufacturers products. In 1997, a phosphorus-based alternative to TBBA was developed by the German engineering giant, Siemens,... 

In 2000, NEC developed an epoxy resin with what it describes as a fire-retardant structure that avoids the need for either TBBA or phosphorus-based flame retardants in circuit boards. The new resin contains a metal hydroxide retardant. The company claims the new board is almost totally free of pollutants, and is easy to process and thermally recycle. By also integrating flame retardant properties within the board, use of the metal hydroxide is minimised, while offering good electrical properties, higher heat resistance and improved processing characteristics. ... 

The early patent disclosures have claimed the application of a wide spectrum of gas-evolving ingredients and phosphorus-based organic molecules as flame retarding additives in the electrolytes. Pyrocarbonates and phosphate esters were typical examples of such compounds. The former have a strong tendency to release CO2, which hopefully could serve as both flame suppressant and SEI formation additive, while the latter represent the major candidates that have been well-known to the polymer material and fireproofing industries.The electrochemical properties of these flame retardants in lithium ion environments were not described in these disclosures, but a close correlation was established between the low flammability and low reactivity toward metallic lithium electrodes for some of these compounds. Further research published later confirmed that any reduction of flammability almost always leads to an improvement in thermal stability on a graphitic anode or metal oxide cathode. 

Figure 75. Flammability of the electrolytes containing various phosphorus-based flame retardants (FR). All electrolytes are composed of these flame retardants in 1.0 m LiPFe/EC/EMC. (Reproduced with permission from ref 529 (Eigure 1). Copyright 2003 The Electrochemical Society.)...

Benzoylresorcinol based phosphate esters are obtained by reacting a benzoylresorcinol compound with a chlorophosphate, e.g., benzoylresorcinol with diphenyl chlorophosphate or phosphorus oxychloride. These esters can function both as flame retardants and UV stabilizers for PC/ABS and a series of other polymers (78). 

Flame retardants - [TEXTILES-FINISHING] (Vol 23) - [ALUMENUMCOMPOUNDS - INTRODUCTION] (Vol2) -antimony as [ANTIMONY AND ANTIMONY ALLOYS] (Vol 3) -antimony compds as [ANTIMONY COMPOUNDS] (Vol 3) -antimony compds as [ANTIMONY COMPOUNDS] (Vol 3) -based on ammonium sulfamate [SULFAMIC ACID AND SULFAMATES] (Vol 23) -bromine in [BROMINE] (Vol 4) -in electronic applications [PACKAGING - ELECTRONIC MATERIALS] (Vol 17) -iron fluoride in mfg of [FLUORINE COMPOUNDS, INORGANIC - IRON] (Vol 11) -nickel compounds as [NICKEL COMPOUNDS] (Vol 17) -phosphorus for [PHOSPHORUS] (Vol 18) -polycarbonates in [POLYCARBONATES] (Vol 19) -from propylene oxide [PROPYLENE OXIDE] (Vol 20) -for rubbers [RUBBERCHEMICALS] (Vol 21) -use m electrical connectors [ELECTRICAL CONNECTORS] (Vol 9)... 

Condensed-Phase Mechanisms. The mode of action of phosphorus-based flame retardants in cellulnsic sy stems is probably best understood. Cellulose decomposes by a noncalalyzed route lo tarry depolymerization products, notably levoglucosan, which then decomposes to volatile combustible fragments such as alcohols, aldehydes, ketones, and hydrocarbons. However, when catalyzed by acids, the decomposition of cellulose proceeds primarily as an endothermic dehydration of the carbohydrate to water vapor and char. Phosphoric acid is particularly efficaceous in this catalytic role because of its low volatility (see Phosphoric Acids and Phosphales). Also, when strongly heated, phosphoric acid yields polyphosphoric acid which is even more effective in catalyzing the cellulose dehydration reaction. The flame-retardanl action is believed to proceed by way of initial phosphory lation of the cellulose. 

The largest volume use of phosphorus-based flame retardants may be in plasticized vinyl. Other use areas for phosphorus flame retardants are flexible urethane foants. polyester resins and other thermoset resins, adhesives. textiles. polycarbonate-ABS blends, and some Other thermoplastics. Development efforts are well advanced lo find applications for phosphorus flame retardants, especially ammonium polyphosphate combinations, in polyolefins, and red phosphorus in nylons, Interest is strong in finding phosphorus-bused alternatives to those halogen-containing systems which have encountered environmental opposition, especially in Europe. 

In tile 1990s. two lypes lit flame retardants are preferred lor outdoor fabrics, i.e.. a system based on phosphorus and nitrogen such as the precondensuie-NHi finish and an antimony-bromine system based on decahromodiphetiyl oxide and antimony)III) oxide. 

Two examples have been selected to demonstrate this process. The first involves a selective catalysts development program at Akzo Nobel under collaboration with Mark E. Davis of the California Institute of Technology (Caltech). Catalysts with greater selectivity were needed to improve the performance of a product line of phosphorus-based flame retardants and functional fluids. The Akzo Nobel... 

Phosphorus-Based Inorganic Additive Flame Retardants.109... 

PHOSPHORUS-BASED INORGANIC ADDITIVE FLAME RETARDANTS... 

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