Stabilization with diphenylamine

At a temperature of 75°C in a dry atmosphere, a powder with an admixture of 2/ diphenylamine gave off only about one quarter the amount of gases evolved by a powder with an admixture of 8% amyl alcohol heated for the same period of time. At a temperature of 110°C the stability of the powder containing diphenylamine proved to be 2.5 times greater than that containing amyl alcohol. 

A powder with an admixture of 1.5% diphenylamine, when heated at a temperature of 75°C in a dry atmosphere showed signs of decomposition only after 512 days, whereas powder containing 2% amyl alcohol began to decompose after 122 days. In a damp atmosphere at a temperature of 75°C a powder containing 

2% diphenylamine decomposed much more slowly (at least four times more slowly) than the powder containing 8% amyl alcohol. 

Berger [66] defined the degree of decomposition of powder at temperatures of 40-110°C, by determining the amounts of heat emitted by the fresh powder on burning and by partly decomposed powder. From this difference he calculated the amount of heat emitted on decomposition. Berger thus examined the behaviour of powder without a stabilizer (AT), powder with amyl alcohol (AM) and D powder with diphenylamine he obtained curves (Fig. 196), the shapes of which are charac- 

Investigations have shown that the basic properties of diphenylamine are so weak that it cannot hydrolyse nitrocellulose, but they are sufficiently strong to neutralize any acid product arising either from the decomposition of impurities in the nitrocellulose, from the oxidation of residual solvent or even from decomposition of the nitrocellulose itself. It was also demonstrated that the basic properties of diphenylamine may have a deleterious effect on the powder if the diphenylamine content exceeds 5%. The best stabilizing results are achieved by using 1.0-2.5% diphenylamine. 

---

Stabilization of smokeless powder Stabilization with diphenylamine Inorganic stabilizers Organic stabilizers Apparent stabilizers I-iterature... 

As Likhtenshtein has shown [75], such a case is realized when polypropylene is stabilized with diphenylamine, if polyphenylene or diphenyl-picrylhydrazyl is introduced into the polymer as the second substance. 

The original catalyst for this reaction is Pd(PPh3)4. Heterogenization of this catalyst was attempted by grafting it onto functionalized polystyrene or modified silica gels,185 which increased significantly the selectivity for the reaction of 3-acetoxy-5-carbomethoxy-l-cyclohexene with diphenylamine. Data concerning the stability of these solids are, however, not reported. 

Sunlight is a factor which hastens the decomposition of smokeless powder. Experiments carried out by D. Berthelot and Gaudechon [60] showed that powders containing various types of stabilizers behave in different ways towards light. E.g. powder stabilized with amyl alcohol proved to be more resistant to sunlight than that containing diphenylamine. The latter darkens very rapidly under the influence of light, which no doubt accelerates the decomposition of diphenylamine. 

Other letters and subscripts show the stabilizer used and its amount, thus BM7AM8 means a powder BM7 stabilized with an addition of 8% amyl alcohol. BSP D1.5 is a powder for siege howitzers stabilized with an addition of 1.5% diphenylamine. BM5 powder is thin since it is extruded through a die of about 2.3 mm, and BM17 powder through a die of about 7.5 mm. 

D. A letter added to the designation of Fr proplnts to signify that diphenylamine (DPhA) is used as a stabilizer. For example, BD is Poudre B (See Vol 2, p Bl) and when stabilized with DPhA, BFD2 is Poudre B, for rifle, contg 2% DPhA... 

Stabilizers are necessary because nitrocellulose decomposes with age. The decomposition reaction yields dinitrogen tetraoxide which acts as an autocatalyst and accelerates the decomposition.58 Stabilizers act as dinitrogen tetraoxide scavengers consequently shelf life is increased. Stabilizers are normally added in the region of 0.5 to 2.0%. To neutralize the decomposition products, which could cause corrosion of the firearm, calcium carbonate is added to some propellants. A common stabilizer is diphenylamine or its nitro derivatives (Figure 10.2). 

Properties Colorless liquid stabilized with either hydroquinone or diphenylamine inhibitors. The hy-droquinone stabilized material can be polymerized without redistillation. The DPA-stabilized material must be distilled before polymerization. D 0.9345 (20/20C), fp -100.2C, bp 73C, refr index 1.3941, bulk d 7.79 lb/gal, flash p 30F (-1.1C) (TOC), aut-oign temp 800F (426.6C). Soluble in most organic... 

Fortunately, no such conflict of interests arises with diphenylamines 9 and phenylenediamines lla-d. Various DPA were tested and approved as AO not only in rubbers, their traditional application field the physically persistent 9b and 9a have also been approved for stabilization of plastics in contact with nonfatty food [307]. Derivatives of PD are the most versatile nowadays as mbber antidegradants. Oral administration to experimental animals indicated some danger of necrosis of skeletal and/or cardiac muscles [311]. This has been explained by in vivo oxidation of PD lid into quinone imine by muscle mitochondria and establishing an alternative pathway for electron transport in the physiological respiratory chain. 

A II single base propellant stabilized with 0.9 % acardite II DPA single base propellant stabilized with 1.1 % diphenylamine C I single base propellant stabilized with 0.6 % centralite I... 

The same study revealed that antioxidants in general provide little if any additional stability to bromobutyl vulcanisates at temperatures below 150°C, that many antioxidants contribute significantly to heat stability at higher temperatures, and that exceptional heat resistance is achieved with MBI/MgO, with diphenylamine/acetone reaction products plus MgO or, particularly, with combinations of these two antioxidant systems. The author states that magnesium oxide was included with each system because, although its role in bromobutyl vulcanisation is not clear, there is no doubt that it contributes to processing safety, shelf life and heat resistance when used in conjunction with curing systems that do not contain elemental sulphur. 

The beater additive process starts with a very dilute aqueous slurry of fibrous nitrocellulose, kraft process woodpulp, and a stabilizer such as diphenylamine in a felting tank. A solution of resin such as poly(vinyl acetate) is added to the slurry of these components. The next step, felting, involves use of a fine metal screen in the shape of the inner dimensions of the final molded part. The screen is lowered into the slurry. A vacuum is appHed which causes the fibrous materials to be deposited on the form. The form is pulled out after a required thickness of felt is deposited, and the wet, low density felt removed from the form. The felt is then molded in a matched metal mold by the appHcation of heat and pressure which serves to remove moisture, set the resin, and press the fibers into near final shape (180—182). 

In explosives, diphenylamine stabilizes cellulose nitrate by reacting with nitrogen oxides (see Explosives and propellants). The products formed include /V-nitrosodiphenylamine and mono andpolynitro derivatives. 

Because nitrile rubber is an unsaturated copolymer it is sensitive to oxidative attack and addition of an antioxidant is necessary. The most common practice is to add an emulsion or dispersion of antioxidant or stabilizer to the latex before coagulation. This is sometimes done batchwise to the latex in the blend tank, and sometimes is added continuously to the latex as it is pumped toward further processing. PhenoHc, amine, and organic phosphite materials are used. Examples are di-Z fZ-butylcatechol, octylated diphenylamine, and tris(nonylphenyl) phosphite [26523-78-4]. All are meant to protect the product from oxidation during drying at elevated temperature and during storage until final use. Most mbber processors add additional antioxidant to their compounds when the NBR is mixed with fillers and curatives in order to extend the life of the final mbber part. 

Acid-treated clay catalyst Engelhard F-24 was found to be very effective for the alkylation of diphenylamine (DPA) with an olefin such as a-methyl styrene (AMS) to obtain a mixture of mono and dialkylated diphenylamines (Chitnis and Sharma, 1995). For example, alkylation of DPA with AMS produced a mixture of 4-(a,a-dimethyl benzyl) diphenylamine, i.e. monocumyl-diphenylamine (MCDPA) and 4,4 -bis(a,a-dimethylbenzyl) diphenylamine, i.e. dicumyldiphenylamine (DCDPA) (Eqn.(l 1)). The dialkylated diphenylamine, i.e. DCDPA, is indu.strially important as an antioxidant and heat stabilizer. DCDPA is reported to be an ideal antioxidant for many materials like polyethylene, polypropylene, polyether polyol, polyacetals, nylon 6, synthetic lubricants, hot melt adhesives, etc. 

Although diselenonium-, ditelluronium- and mixed sulfonium-selenonium dications can exhibit either oxidative or electrophilic properties in reactions with nucleophiles, substitution at the onium chalcogen atom is more typical.96 Owing to the increased stability of heavier dichalcogenium-dications, they react only with highly activated substrates such as aniline and tV,A-dimethylaniline, while no reaction is observed with phenol and diphenylamine.113 Reactions of ditelluronium dications with activated aromatics are also not known (Scheme 44).114... 

Adoption in 1906 by the French Navy of propint with 8% amyl alcohol stabilizer did not prevent the disastrous expin in 1907 of battleship Iena. As a result of this, previously tested DPhA (diphenylamine) was approved as stabilizer of Naval cannon proplnt, which became known as poudre B(Bo) (Ref 44, p 249) (See also Vol 1 of Encycl, p A395-L)... 

The presence of N02 and other nitrogen oxides and/or acids in explosives (especially in smokeless powders and dynamites)is very undesirable because they act as catalyzers and promote further, more rapid decomposition. Most of the stabilizers used in smokeless powder, such as diphenylamine, centralites, urethanes etc are really inhibitors because they react with N02 and other nitrogen oxides to form nitroso- and nitrocompounds. 

Jacque Stability Test. Jacque, director of the Spanish plant Cantabrica at Guldacano, near Bilbao, proposed a test for NC which was simple, rapid, and did not require complicated apparatus. It is not advisable to use this test when it is known in advance that the NC is of low stability Procedure. A NC sample of 2-3g, previously-dried in a loosely covered weighing dish or crystallizer to constant wt, is transferred to an oven maintained at 130—40° and left there for 2 hrs. It is cooled in a vacuum desiccator and reweighed. The sample is again heated at 140° and weighed at intervals of 2 hrs until it decomposes, as indicated by an abnormal loss of wt. After termination of the test, it is advisable to wash the NC with distilled water, add a few drops of 0. IN KMn04 soln and determine the amt of HN03, either by the nitron or diphenylamine method... 

Stability. In order to have maximum effectiveness over long periods of time, an antioxidant should be stable upon exposure to heat, light, oxygen, water, etc. Many antioxidants, especially in the presence of an impurity when exposed to light and oxygen, are subject to oxidation reactions with the development of colored species. Alkylated diphenylamines are least susceptible and the />-phenylenediamine derivatives the most susceptible to direct oxidation. 

Duration of test, days Powder without stabilizer Powder with an addition of 7% amyl alcohol Powder with an addition of 1% diphenylamine... 

---