Flame retardant additives on the

The effect of a flame-retardant additive on the flexural modulus provides an indication of its effect on long-time creep. 

This paper reports the results of a molecular-level investigation of the effects of flame retardant additives on the thermal dedompositlon of thermoset molding compounds used for encapsulation of IC devices, and their implications to the reliability of devices in molded plastic packages. In particular, semiconductor grade novolac epoxy and silicone-epoxy based resins and an electrical grade novolac epoxy formulation are compared. This work is an extension of a previous study of an epoxy encapsulant to flame retarded and non-flame retarded sample pairs of novolac epoxy and silicone-epoxy compounds. The results of this work are correlated with separate studies on device aglng2>3, where appropriate. 

In some cases, several of these processes occur simultaneously, depending on the sample size, the heating rate, the pyrolysis temperature, the environment, and the presence of any additives. Although polymer degradation schemes can be greatly altered by the presence of comonomers, side-chain substituents, and other chemical constituent factors, the ultimate thermal stability is determined by the relative strengths of the main-chain bonds. Many additives and comonomers employed as flame retardants are thermally labile and as a result the thermal stability of the polymer system is reduced. In order to reduce the observed effects of the flame-retardant additives on the thermal stability of the polymeric materials, more thermally stable and hence inherently flame-resistant polymers are of increasing interest. 

Bae S-Y, Shim E-G, Kim D-W (2013) Effect of ionic Uquid as a flame-retarding additive on the cycling performance and thermal stability of lithium-ion batteries. J Power Sources 244 266-271. doi 10.1016/j.jpowsour.2013.01.100... 

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. 

Selection of Fire Retardants. The choice of flame retardants depends on the nature of the polymer, the method of processing, the proposed service conditions, and economic considerations. Although the processing, service, and economic factors are impor.pa tant, the flame-retardancy potential of an additive is of primary importance, and this factor can be readily evaluated by thermal analysis. 

As stated above, conventional synthetic fibres may be rendered inherently flame retardant during production by either incorporation of a flame retardant additive in the polymer melt or solution prior to extrusion or by copolymeric modification before, during, or immediately after processing into filaments or staple fibres. Major problems of compatibility, especially at the high tanperatures used to extrude melt-extruded fibres like polyamide, polyester, and polypropylene and in reactive polymer solutions such as viscose dope and acrylic solutions, have ensured that only a few such fibres are commercially available. A major problem in developing successful inherently flame retardant fibres based on conventional fibre chemistries is that any modification, if present at a concentration much above 10wt% (whether as additive or comonomer), may seriously reduce tensile properties as well as the other desirable textile properties of dyeability, lustre and appearance, and handle, to mention but a few. 

The general paucity of FR polyamides reflects their high melt reactivities and hence poor potential flame retardant additive compatibilities. The only additive currently marketed as a potential flame retardant for polyamide fibres is Clarianf s Exolit OP930/935, which is based on a fine particulate (Dj(, 2-3pm), aluminium diethyl phosphinate. This phosphinate may be used alone or combined with melamine polyphosphate, although in bulk polymers total levels of 15wt% or so are required for acceptable levels of flame retardancy. To date it is not known whether commercially successful PA6 and PA6.6 fibres based on this agent are available. 

The chemical fibers rayon and cellulose acetate are made fireproof by adding flame-retardant additives to the spinning solution. The active substance in this case is distributed throughout the whole fiber and is not only on the surface, as in the case of wool and cotton. 

Various workers have discussed the fire retardancy of polyvinylchloride (PVC) [55-59] using ammonium treated clay montmorillonite nanocomposites [52], hydroxyapatite nanocomposites [56] and antimony trioxide [57]. Lum [60] examined the effect of flame retardant additives on polymer pyrolysis reactions with a PVC composition containing 3 phr of SbiOs. It is well known that a synergistic flame retardancy effect is observed when SbiOs is incorporated into organic halide materials such as PVC. 

These phenomena also were observed in the case of the lithiated synthetic graphite. Prakash also reported the effect of the addition of hexamethoxycyclotri-phosphazene as a solid retardant on thermal stability of the charged cathode. In his paper, addition of 1.68 wt% flame-retardant additives into the Li/LiNi gCo cell... 

In later work Baillet and Delfosse examined the effect of the flame retardant fillers on the formation of carbon oxides during pyrolysis of an EVA polymer and tested various additives for incandescence suppression effects [50]. Using the same quartz reactor described previously, they demonstrated that below the self-ignition temperature, the filled systems gave much more complete oxidation (higher C02 C0 levels) than the unfilled polymer. This supports the greater degree of char combustion referred to previously. 

Wilkie and co-workers [69, 70] synthesized two organically modified clays to produce nanocomposites of PS, HIPS, and ABS terpolymer. They used the following copolymers to modify clay vinylbenzyl chloride (COPS) and methyl methacrylate and vinylbenzyl chloride (MAPS). The cation head for clay modification with these compounds was ammonium. After melt-blending, styrene copolymer-modified clays yielded exfoliated nanocomposites, whereas the methacrylate copolymer clays yielded a mixture of immiscible and intercalated nanocomposites. In general, all nanocomposites exhibited improved thermal stability and mechanical properties, in addition to improvements in flame retardancy, depending on the quality of clay dispersion. 

It is also believed that the large heat capacity of hydrogen halides and their dilution of the flame results in a decrease in the mass concentration of combustible gases and the temperature of the flame. The physical effect of halogen halides is comparable to that of inert gases, CO2, and water. There is no contradiction between the radical trap theory and the physical theory apparently, they complement each other. The contribution of each mechanism depends on the temperature of decomposition of the flame retardant additive and the polymer. 

Molybdenum Oxide. Molybdenum compounds incorporated into flexible PVC not only increase flame resistance, but also decrease smoke evolution. In Table 10 the effect of molybdenum oxide on the oxygen index of a flexible PVC containing 50 parts of a plasticizer is compared with antimony oxide. Antimony oxide is the superior synergist for flame retardancy but has Httle or no effect on smoke evolution. However, combinations of molybdenum oxide and antimony oxide may be used to reduce the total inorganic flame-retardant additive package, and obtain improved flame resistance and reduced smoke. 

A series of compounded flame retardants, based on finely divided insoluble ammonium polyphosphate together with char-forming nitrogenous resins, has been developed for thermoplastics (52—58). These compounds are particularly useful as iatumescent flame-retardant additives for polyolefins, ethylene—vinyl acetate, and urethane elastomers (qv). The char-forming resin can be, for example, an ethyleneurea—formaldehyde condensation polymer, a hydroxyethylisocyanurate, or a piperazine—triazine resin. 

Bromine compounds are often used as flame retardant additives but 15-20ptsphr may be required. This is not only expensive but such large levels lead to a serious loss of toughness. Of the bromine compounds, octabromo-diphenyl ether has been particularly widely used. However, recent concern about the possibility of toxic decomposition products and the difficulty of finding alternative flame retarders for ABS has led to the loss of ABS in some markets where fire retardance is important. Some of this market has been taken up by ABS/PVC and ASA/PVC blends and some by systems based on ABS or ASA (see Section 16.9) with polycarbonates. Better levels of toughness may be achieved by the use of ABS/PVC blends but the presence of the PVC lowers the processing stability. 

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