THE CHEMICALS WORLD THIS WEE
R. E. Brooks (left) and W. F. Busse, both of D u Pont, examine samples of D u Pont's new chlorosulfonated elastomer, Hypalon. Right. R. Houwink of Rubber Stichting, Delft, The C&EN
REPORTS:
ACS
Division of
Netherlands, shows CyanamicTs Norman A. Shepard (left) sample articles prepared from latex ebonite. E>r. Houwink predicted a rosy future for ebonite because of i t s latex form
Rubber Chemistry
Revolutionary Developments Seen In Synthetic Elastomers Field N e w products, processes could effect major change in r u b b e r industry markets C I N C I N N A T L - T h e market outlook for a number of natural and synthetic elastomers is in for some serious reappraisal, if re ports presented at the 60th meeting of the ACS Division of Rubber Chemistry are indicative—and they undoubtedly are. About 7 5 0 of the division's nearly 3000 members were on hand here April 30 to May 2, to gather facts on a new series of chlorosulfonated polyethylenes, on the promising alfin catalyzed synthetic rubbers, and on oil-extension of elastomer stocks. Any or all of these developments, if pushed to full commercialization, could work a major change in the balance of rubber industry markets (if this ever-changing field can be considered to possess some kind of "balance"). Many of the rubber industry's other problems, too, were up for a new look during the three-day con vention. In the first public announcement of the new, rubber-like chlorosulfonated poly ethylenes, dubbed Hypalon, D u Pont chemists presented an integrated trio of papers dealing with preparation, proper ties, and potential uses of the elastomers. They are made, said R. E. Brooks, by treat ing polyethylene with chlorine and sulfur dioxide. The particular compound now being offered is one having a useful bal ance of properties for general service, and is based on a polyethylene having an
1966
average molecular weight of about 20,000. It contains 1.3 to 1.7% sulfur and 26 to 29% chlorine, or approximately one chlo rine for each seven carbons, and one sulfonyl chloride group for every 90 carbons. By varying molecular weight and its distribution, chain branching, and the de gree of crystallinity, said Dr. Brooks, a wide variety of derivative types may b e prepared. The one now offered commer cially can b e readily compounded and processed in conventional rubber machin ery; it is shipped as a white, fluffy crumb which has a specific gravity of about 1.1 when molded. Tensile strengths of gum
The Week's Events Loss of Vitamin Potency N o t Ex cessive in Food Processing . . Potentiometry Gives Insight into Thermodynamics o f Chelates . . Chamber of Commerce Endorses Amendment to Limit Taxing Power Bailey Selected as Herty Medalist for Fats and O i l s Research . Λ Radioactive Sulfur Lends Itself t o Exploration of Proteins . . . . Equation for Reaction Rates Gives Agreeing Results New Insecticides N o More Toxic than O l d e r Ones Chemistry Highlighted at Drew During Open House
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stocks are as high as 350O to 4000 pounds per square inch, and are n o t dependent on fillers such as carbon blacks or silica gels. Carbon Black Unnecessary. The com bination of high tensile strength and modulus without t h e use of carbon black, unique in a synthetic elastomer, permits the compound to enter many uses inde pendent of color. A n example is the prepa ration of a white sidewall stock for auto mobile tires; the product's good flex life and abrasion resistance, its mechanical strength, and especially its complete re sistance to ozone degradation, make it a sure contender in this and other important applications. Chlorosulfonated polyethylene is a com pletely saturated elastomer, depending primarily on reactive sulfonyl chloride groups for cure, said M. A. Smook. The most practical curing systems for the poly mer are based on a polybasic metal oxide, or a polybasic metal salt of a weak acid, h e said. The metal oxide reacts to give a metal sulfonate crosslink. Organic acids and accelerators are necessary components of a complete curing system, although their exact function is not y e t known, Dr. Smook stated. The material m a y also be cured by reac tions other than the formation of salt bridges, said W. F . Busse. Some of the best vulcanizates have been obtained with organic curing agents, especially aromatic diamines such as benzidine, thiourea and its derivatives, aliphatic a n d cyclic dioximes, thiurams, and carbamates, Dr. Busse observed. Chlorosulfonated polyethylene cured with these reagents tends to give higher elongations than cures with metal oxides, and sometimes m u c h higher values for tensile strength, equivalent to those exhibited by natural rubber. Alfin Rubber. A prediction made four
AND
ENGINEERING
NEWS
years ago by Avery A. Morton of MIT, to the effect that alfin (from alcohol and olefin, components of the catalyst used) rubber might eventually replace all natural rubber and GR-S in automobile tires, stands much closer to realization today, because of work reported by H. Leverne Williams of Polymer Corp., Ltd. Chief drawback to the use of alfin-catalyzed rubber has been its extreme toughness, which made it very difficult to process. This problem has been largely overcome, said Dr. Williams, through adaptation of the oil-extension principle developed in 1949 and 1950 for use with cold rubber. It has been found possible, Dr. Williams reported, to prepare the alfin rubber in the presence of a light oil and carbon black, yielding a mixture easy to process but still possessed of its desirable properties of toughness and low heat build-up. The toughness of the new rubber suggests that even higher percentages of oil than are used with cold rubber may be feasible. Besides softening the rubber for easier processing, this oil addition should result in substantial reductions in cost, since rubber raw materials at 20 to 30 cents per pound are extended by oil at 3 to 5 cents per pound. Further cost reductions may be realized through the use of commercial grade butadiene, said Dr. Williams. Laboratory experiments indicate that technical grade raw materials can be employed for the preparation of both catalyst and rubber. In the case of butadiene, this would obviate the need for the distillation step; an expensive as well as a very hazardous operation would thus be eliminated. Further savings in manufacturing costs may be possible because the polymerization can be carried out near room temperature, minimizing the need for heating or cooling as now practiced in synthetic rubber production. In addition, Dr. Williams stated, the high speed of polymerization may lead to large-scale continuous production as a replacement for the less rapid batch processes now in general use. Rubber Processing Oils. All hydrocarbon oils taken from petroleum for use in rubber processing do not have the same characteristics, warned Stewart S. Kurtz, Jr., of Sun Oil, and allowances must be made for the differences which exist. Two types of hydrocarbon molecules are the major components of the oils : ( 1 ) aromatic hydrocarbons which vary in proportions of aromatic rings, naphthene rings, and paraffin side chains; ( 2 ) naphthene hydrocarbons which vary in proportions of naphthene rings and paraffin side chains. The concentration of paraffin hydrocarbons in dewaxed oils is very small. Describing examples of a "relatively aromatic oil, a relatively naphthenic oil, and a relatively paraffinic oil," Dr. Kurtz showed that the different oils could all have about the same average molecular weight as a commonly used oil extender, but vary widely in composition and properties. In an evaluation program being conducted jointly with General Tire & Rubber, Dr. Kurtz reported, preliminary results have indicated that oils relatively high in aromatic content yield rubbers which excel VOLUME
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in processability, tensile strength, and modulus. Oils low in aromatics but high, in naphthenes, on the other hand, give products with better low temperature properties, rebound, and color. For general utility and best ail-around performance, Dr. Kurtz said, an intermediate composition is probably the most desirable. Water Bomb. During a half-day session on problems related to the oxidation of elastomers, William H. Haines of Gates Rubber described a new "water bomb" apparatus and technique for accelerated oxidation tests on rubber or other materials. In some tests, said Dr. Haines, a period of three hours in the water bomb has proved the equivalent of about eight days in a conventional oxygen bomb. Data secured with the new apparatus have been in agreement with previous work on such problems as deterioration of physical strength through oxidation, and the catalytic effect of carbon black in the oxidative degradation of elastomers, Dr. Hines said. Whether carbon black actu-
ally behaves as a catalyst in this way, or merely gives the appearance of doing so while absorbing, adsorbing, or reacting with the oxygen available, is still a controversial point, as indicated by comments from members of the audience following Dr. Maine's paper. Those who commented appeared to be about evenly divided, pro and con. The water bomb is a steam-jacketed autoclave with agitator. Elastomer samples are immersed in water in the heated reactor, and a charge of oxidizing agent in solution is pressured into the system. Samples of the liquid in the bomb are withdrawn periodically through a sampling tube, and titrated for residual oxidizing power. So far, according to Dr. Haines, the bomb has been used to study the oxidation of natural rubber and GR-S. The effects of temperature and pH on oxidation rate have been determined, and mbber poisons, such as manganese, have been studied for their role in accelerating oxidation.
C&EN REPORTS: American Oil Chemists Society
Oilseed Industry Shows N e w Trends In Returning to Prewar Levels Cottonseed processing combines solvent extraction with forepressing HOUSTON.—"Per capita supply of oilseeds in the world was in 1951 back to prewar levels for the first time—the first exports of soybean oil in years were received from Manchuria—a bumper crop of olive oil was made in the Mediterranean countries—there is no reason to expect higher oil prices." These excerpts from the remarks of W. H. Goss, Pillsbury Mills, in opening the technical sessions of the American Oil Chemists Society here April 28 to 30 held an optimistic note continued throughout the meeting. Combination of forepressing cottonseed, followed by solvent extraction, overcomes much of the difficulty in obtaining maximum oil extraction by use of solvents only, and is in Mr. Goss' opinion a trend of sensational importance. Wet corn and castor beans have been processed in this way for years in Europe, but American processors have been slow to adopt the technique for cottonseed. Other significant trends Mr. Goss mentioned are movement of cotton oil mills to the West, increased use of foreign improvements in solvent extraction equipment, and application of a German method for direct steam stripping of solvent from soybean meal. On a somewhat different tone he mentioned the increased attention being paid to the question of toxicity of meal from trichloretnylene-extracted seeds. Eight mills in this country are using trichloroethylene for solvent extraction and increased deaths of cattle fed on meal from
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this type of extraction indicate that perhaps more attention should have been paid to reports of such danger published 35 years ago. Recent German reports on cattle deaths due to this may be somewhat speculative and not backed by sufficient experimentation, Mr. Goss said, but a flurry of such deaths in Japan, and Havana, traceable to trichloroethylene-extracted meal, gives cause for alarm. Perhaps to be sure that he wasn't accused of complacency as far as the oilseed situation is concerned, Mr. Goss predicted as one trend increased competition from animal fats, which are undergoing an intensive improvement program. Filtration-Extraction for Cottonseed. One of the promising trends in solvent extraction pointed out by Mr. Goss is the simplified direct extraction method for cottonseed developed by the Southern Regional Research Laboratory. This method is based on use of a continuous horizontal vacuum filter and incorporates a mild cooking operation with direct solvent extraction. Advantages cited by Henry L. E. Vix are high filter capacity for small filter units (up to 7 tons of cottonseed per square foot of filter area per 24 hours ), practical elimination of the fines problem, low solvent requirements, and a better quality meal. Preliminary results on using this method for processing soybeans, rice bran, and tung meats have been successful. Babassu Problems.
O i l f r o m the ba1967
