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Recent Advances in Flame Retardant Compositions

Reffer:Editor:Author:Hits:-InputTime:2014-09-24 10:22:00
Hindered amines are known for their ability to provide UV stability as well as long term thermal stability. Recently, there have been new classes of hindered amines, based on the novel NOR functionalization, that afford additional benefits beyond UV or long term thermal stability. For example, over the last several years we have clearly established the utility of novel NOR type hindered amines, such as NOR 1, either as a flame retardant, or flame retardant synergist in combination with conventional halogenated flame retardants in polyolefin thin section substrates, e.g., polypropylene fibers. In this paper, we will provide an update on the recent advances in thick section substrates including both flame retardant efficacy and UV stability. Overall, we have found that these novel NOR type hindered amines not only allow for substantial reduction in the overall concentration of the bromine compounds, mineral fillers, or/and the elimination of antimony trioxide flame retardant synergist but also, they provide superb UV stability in the presence of halogenated flame retardant. Antimony free, UV stable flame retardant systems for polypropylene homopolymer molding with UL 94 V-0 and V-2 ratings respectively, have been achieved. Introduction Currently, there is an increasing need for flame retardant polyolefin applications. 1 Typical polyolefin flame retardant systems contain either bromine or phosphorous in combination with fillers such talc or inorganic synergists such antimony trioxide. Although these particular systems are very effective in providing flame retardant efficacy at relatively low cost, they raise a lot of concerns from a practical and environmental point of view. Also, halogenated flame retardants, especially the aromatic ones, detrimentally affect the polymer light stability. Moreover, there are processing problems such as odor, toxicity, and significant negative impact on the physical and mechanical properties of the polymers associated with the high levels of use of the flame retardant additives. 2.In some European countries there are proposals to ban the use of halogenated and heavy-metal containing flame retardants. 3,4.Accordingly, a market need to replace these conventional flame retardants has been developed. In this report, the efficacy and advantages of the non-halogenated NOR 1 (Appendix 1) as a flame retardant synergist in halogenated and non- halogenated systems are discussed. Historic Background N-alkoxy hindered amines (NOR) were first introduced as non-interacting light stabilizers for automotive coatings, flame retarded fiber and agricultural film applications. 5 NOR hindered amines have low basicity and are in a more active oxidation state than conventional hindered amines. In agricultural film applications, pesticides generate acidic species and deactivate conventional hindered amines. Similarly, hindered amines are deactivated by the thermal or photo generation of HBr from flame retardants resulting in inferior light stability. Light stabilization studies which were conducted with brominated flame retardants, conventional hindered amines (HALS), and NOR HALS confirmed that NORs perform significantly better than conventional light stabilizers in the presence of brominated flame retardants. Similar observations were made in agricultural films in the presence of pesticides. Papers have been already presented demonstrating the efficacy of N-alkoxy hindered amines with brominated flame retardants and UV absorbers. 6 These papers however, only describe the light stabilization performance and do not show any flame retardant efficacy data. It was believed at that time that the non-interactive nature of NOR HALS with the halogen in the brominated flame retardant positively influenced the performance. Subsequently, when NORs were tested for flame retardancy without the presence of brominated flame retardants, it was observed that they provide flame retardant efficacy to polypropylene fibers. The efficacy of Flamestab NOR 116 as a flame retardant in passing flame retardant industry standard tests such as NFPA 701 at surprisingly low concentrations was discussed in a previous paper.

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