CHEMICALS chemistry of Kel-F elastomer vulcanization is n o t fully understood, the marked increase in strength a n d solvent resistance after cure indicates t h a t the elastomer has undergone a chemical change, producing a network o r crosslinked t y p e of structure. CS 1 Sodium Hydride A s Oil Dispersion Metal Hydrides has developed a process whereby micron-range sodium hydride is prepared as a n oil dispersion. X h e oil coating on the sodium hydride crystals thus protects t h e reactive surface when h a n d l e d in t h e air. Dust a n d fire hazards are eliminated. Company says dispersion is ready t o use, as shipped, and can b e poured in air, p u m p e d , and m e t e r e d for accurate control. Sodium hydride in this finely divided state is also more reactive a n d company says cuts i n reaction time and increased production results. CS % Sample at very top is Kel-F elastomer which has undergone a week's exposure to red fuming nitric acid. It remains unafiFected. Remaining samples consist of other rubbers, Buna-N, Butyl, neoprene, natural, and GRS. Exposed to red fuming nitric acid for only 10 minutes, they are in various stages of disintegration. Kel-F stocks, when exposed to white fuming nitric acid, reach an equilibrium volume swell of 20 to 30% -within one week. Extensibility and hardness, however, show virtually no change C o m m e r c i a l Production Ahead For Kellogg's Kel-F Elastomer
m e r can b e readily compounded, mixed, molded, and extruded using standard r u b b e r processing equipment. Because it is fully saturated, it is not readily vulcanized by normal rubber curatives. The organic peroxides, polyisocyanates, polyamines, and isocyanate-amine combinations may b e used. Kellogg says t h a t although t h e
Kel-F fluorocarbon elastomer, unique synthetic r u b b e r developed by M. W . Kellogg in cooperation with the Office of t b e Quartermaster General, U. S. Army, will be a commercial reality sometime i n the first quarter of 1955 (C&EN, S e p t . 27, 1954, page 3 8 5 0 ) . The elastomer, notable for its high tensile strength (2000 to 3500 p.s.i.), You C a n ' t Wash Them O u t good extensibility (400 to 6 0 0 % ) , and tear strength (150 to 400 p.p.i.), will then be offered as a white spongy c r u m b or i n the form of compressed sheets. So far it has been available only in experimental quantities as the spongy c r u m b or as a water dispersion. Chemically, the elastomer is a fully saturated chlorotrifluoroethylene copolymer. I t s elasticity results from the incorporation of methylene groups in the normally rigid, highly fluorinated polymer c h a i n . X-ray diagrams show that the polymer is amorphous at temperatures a s low as —40° C. On stretching t o 300%, typical fiber diagrams are observed, indicating susceptibility to orientation and crystal formation. Thermal stability is shown by the fact that t h e r e is no evidence of chain scission or halogen loss after prolonged exposure a t 400° F . Kellogg says t h e fluorocarbon poly552
New S o l v e n t Has Unusual Properties Stepan Chemical is in pilot plant production of a n e w solvent, dimethyl sulfoxide, which is said t o h a v e many unusual advantages. It is a clear» water-white, very hygroscopic a n d completely water-soluble liquid. D e spite t h i s , it dissolves many organic compounds and is unusually selective in its solubility characteristics for hydrocarbons. It can thus be used for the selective separation of paraffinic and aromatic hydrocarbon mixtures Company says preliminary tests indicate t h a t dimethyl sulfoxide is nontoxic.
Monsanto's Resîoom, a fabric «rusher, a pleating company, and textile resin chemists all combine in this "Wash-APleat cotton skirt. The recipe, which gives cotton stayin pleats offered in nylon and other synthetics, involves not only the right Resloom resin formula to impregnate the cotton, but also the right amount of heat a n d curing time to hold the pleats. The pleats endure washing in automatic washing machines, and if hung up wet, drip dry into fancy pleating without benefit of ironing
CHEMICAL
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ENGINEERING
NEWS
I t is also odorless and relatively tasteless. Potential uses for dimethyl sulfoxide are a s an antifreeze a n d as a hydraulic fluid. Freezing points in water mixtures a r e considerably below those obtainable with mixtures of ethylene- glycol. Certain synthetic fibers—polyacrylonitrile, acetate rayon, and others—are completely soluble in dimethyl sulfoxide. Company says another interesting potential is as a solvent for acetylene gas. I t is said to absorb 3 3 % more acetylene than acetone and has three times longer life in acetylene cylinders.
csa Resins Are Light-Stabilized And Very Light Colored T w o new Balcelite polyester resins are designed to minimize color fading and maintain favorable light transmission in structural panels of reinforced plastic for skylights, greenhouses, factories, and other sucli uses. Designated as PLLB-5O03 Natural, one of t h e resins resists color fading under direct sunlight. T h e other, P L L A 5006 Natural, h a s the same light colorbut is recommended for fabricators who wish to a d d their own lignt-stabilizing agent. Company says both resins exhibit good resistance to cracking a n d crazing and have good r e sistance to weathering and most chemicals. CS 4 W a x Has Low Penetration Characteristics An emulsifîable wax, Petronauba D , developed b y Bareco Wax, h a s a n exceptionally l o w penetration of 3.5 (at 7 7 ° F.) to 28.0 (at 130° F.). Company says this is the result of a refining process which tends t o remove t h e soft, tacky fractions. In addition, w a x has good emulsifîable characteristics and is easily handled d u e to its low viscosityCompany anticipates widespread acceptance of Petronauba D from t h e liquid floor polish industry w h i c h has been using increasingly greater q u a n t i ties of emulsifîable petroleum waxes.
I O N EXCHANGE RESINS for w increased Yields •
Processing Shortcuts
•
Continuous or
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A d d e d Safety
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Lower Costs
•
Simple Product Isolation
Process
Yes, but these and other advantages are being obtained in reactions such as esterifieation, epoxidation, hydrolysis, etc. A technical bulletin, complete with literature survey, is yours for the asking· JL\_MAZING?
NATIONAL
ALUM IN ATE
6199 West 66th Place
CS5
In Canadaz
·
CORPORATION
Chicago 38, Illinois
Alchem Limited, Burlington,
Ontario
• Binney & Smitrs is offering a n improved high color black lacquer dispersion, DCY Coblac, which, although having same composition as D C Coblac, h a s greater jetness. CSS For further information on a n y process or item mentioned here,
see coupon OR page 556
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7, 1 9 5 5
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