Stability red phosphorus

Although the P-4 primer was only in use for approximately 1 year, it was further improved in 1961 by coating the stabilized red phosphorus with PETN, RDX (cyclotrimethylenetrinitramine), or TNT giving the following primer mix ... 

A special and also unusual case of destruction through contact with metal, in this case with copper or copper bronze, is that of red phosphorus, as mentioned in Chapter 12. The oxidation in the presence of air and moisture is also strongly promoted by impurities such as iron or copper within the material (not necessarily as metals). Stabilized red phosphorus, JAN-P-670A, is not only low in iron and copper but particles of less than 10 n diameter are mostly removed and 2.5% of alumina is added as a stabilizer. From experiences in the match industry, the author would confidently say that the special manipulations of red phosphorus leading to the stabilized variety are quite unnecessary since several percent of effective neutralizers such as zinc oxide prevent any acidification of the system in storage. 

Red Phosphorus. This aHotropic form of phosphoms is relatively nontoxic and, unlike white phosphoms, is not spontaneously flammable. Red phosphoms is, however, easily ignited. It is a polymeric form of phosphoms having thermal stabiUty up to ca 450°C. In finely divided form it has been found to be a powerful flame-retardant additive (26,45—47). In Europe, it has found commercial use ia molded nylon electrical parts ia a coated and stabilized form. Handling hazards and color have deterred broad usage. The development of a series of masterbatches by Albright Wilson should facihtate further use. 

A detailed understanding of the course of a reaction between a polymer and an additive will permit one to use that information to design new flame retardants. The reaction between poly(methyl methacrylate), PMMA, and red phosphorus is described and that information used to determine that CIRh(PPh3)3 should be used as a flame retardant. The results of this investigation are then used to choose the next additive. A recurring theme is the efficacy of cross-linking as a means to impart an increased thermal stability. 

In this paper we describe the reaction of poly(methyl methacrylate), PMMA, and red phosphorus and use that information to predict that the reaction of Wilkinson s catalyst, CIRh(PPh3)3, and PMMA may be a worthwhile investigation. Finally information from this reaction is utilized to identify other potential additives and the reaction of these cobalt compounds with PMMA is described. Part of the strategy that will be explored is a strategy of cross-linking to produce materials with greatly increased thermal stability. 

The evidence presented above clearly indicates that red phosphorus attacks PMMA at a carbonyl site with the elimination of methyl and methoxy and the formation of anhydrides. The evidence indicates that anhydride formation occurs via an intra-molecular process, this second bond along the polymer chain does provide added stability that will render depolymerization more difficult and the polymer more thermally stable. The suggested course of the reaction between red phosphorus and PMMA is delineated in Scheme 1. 

The previous conflicting investigations may now be rationalized. Red phosphorus is known to thermally convert to white phosphorus, which will burn in air. If white phosphorus is formed, a fire is expected and no flame retardant activity will be observed. On the other hand, if the phosphorus reacts with the polymer as in Scheme 1, then thermal stabilization is expected. The efficacy of red phosphorus seems to be closely related to the efficiency of mixing of the additive and the polymer, when they are well-mixed the phosphorus will react with the polymer and lead to flame retardant activity, if the mixing is poor then the phosphorus will be converted to the white allotrope and burning will result. Since all of the work reported herein was carried out in sealed tubes under vacuum, the phosphorus must react and lead to stabilization of the polymer against molecular weight loss and fuel production, i.e. thermal stabilization. 

Red Phosphorus smoke mix production. Evaluation of the Sprout Waldron 35 cubic foot Jet Airmix unit for production of Red Phosphorus (RP) M8E1 Smoke Mixtures was conducted (12). Results indicated the mix was stabile and not easily initiated by heat, but sensitive to friction and snark stimuli. The burning time was slow with dense smoke emission. 

Uneven open shell Pn clusters are easier to ionize than even closed shell ones and the stability of the closed shell uneven P cluster cations is higher. For very large Pn+ cations with n = 25 + 8x (x — 0.1.2. 8) islands of stability were observed in the time of flight mass spectrum (TOF-MS) obtained by laser ablation of red phosphorus, suggesting that the more stable P clusters have connections with units of eight P atoms [71d]. A lot of effort has been put into the calculation of the most stable Pn+ cation structures. The respective global minimum structures of the more stable uneven P3+, Ps+, P71 and P<)h cluster cations are shown in Figure 2.6-10 [73, 74],... 

Their stability is comparable with that of disubstituted oxadiazoles. For instance, 5-hydroxy-3-phenyloxadiazole is not decomposed by heating up to 300° and it is stable towards hydrochloric, nitric and sulfuric acid. The hydroxyl group cannot be substituted by chlorine when treated with phosphorus pentachloride or oxychloride at 100° 27, 28). It is reduced to benzamidine with hydroiodic acid and red phosphorus 81). The silver salt treated with ethyl iodide gives an N-ethyl derivative XLVI 28, 58, 59). 

Applications for Red Phosphorus RP is commercially used in a wide variety of industrial applications safety matches, flame retardants, phosphides and pyrotechnics. (Figure 5.4). In most applications, the red allotrope is favored over the white because of its greater stability in air and also its easier handling characteristics. RP is also not considered problematic with regard to environmental and occupational health issues. It is not soluble in water and is considered nontoxic when pure. When the content of WP is less than 0.02%, the LD50-value is >15000mg/kg (rat). 

Red phosphorus will react with atmospheric moisture to form toxic phosphine gas and will ignite readily in air. As a result, the commercial product is often encapsulated in an appropriate polymer matrix. Suitable stabilization and encapsulation have led to commercial concentrates containing 50% red phosphorus. Handling hazards and the color of the final flame-retardant products may be a deterrent for wider use. 

F. Laoutid, L. Ferry, J.-M. Lopez Cuesta, and A. Crespy, Red phosphorus aluminium oxide compositions as flame retardant in recycled PET, Polym. Degrad. Stabil., 2003, 82 357-363. 

L. Du, B. Qu, and Z. Xu, Flammability characteristics and synergistic effect of hydrotalcite with microencapsulated red phosphorus in halogen-free flame retardant EVA composite, Polym. Degrad. Stabil., 2006,91 995-1001. 

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