TECHNOLOGY
Evolutionary process to improve elastomers may have dramatic effect on industry
TESTING. Exhaustive trials produce favorable results
Alfin rubber goes commercial next year The revolution in tire cord materials (to polyester and glass fiber from nylon and rayon) and tire design (to bias-belted from bias-ply) is pretty well decided, for the near future at least. However, a new battleground is shaping up for the rubber industry: the tire rubber itself. Although a revolution in the kinds of elastomers used isn't expected, an evolutionary phase of improving the existing ones has started. The first commercial process to produce alfin rubbers, 1,3-diene polymers, will be on stream early next
year. Nippon Alfin Rubber Co. is building a 20,000 metric-ton-per-year unit in Japan. The alfin rubber will be produced by the Hytrans solution polymerization process developed by U.S. Industrial Chemicals Co., which is licensing it to Nippon Alfin Rubber Co. on a nonexclusive basis. The Japanese firm will produce copolymers of butadiene-isoprene ( 9 0 / 10 and 9 7 / 3 ) and butadiene-styrene (85/15 and 9 5 / 5 ) ; both virgin and oil-extended types will be marketed. U.S.I, will reveal no process details until its patent on the commercial
U.S.I, process aims for the tire market 1600
Synthetic elastomer consumption, thousands of long tons
1200
800
400
1960
1965
Tires and tire products ^ U aC&EN estimates.
46 C&EN OCT. 27, 1969
1968
1969*
Wire and cable
Source: Rubber Manufacturers Association
|
1974' Other
process has been issued. The company indicates that the alfin catalyst is less expensive than those of traditional processes and that its process will probably prove to be more economical, too. Another advantage of the process is that the tire material is produced as a copolymer, which eliminates the blending step. Currently, the most popular tire rubber is a blend of styrene-butadiene rubber (SBR) and polybutadiene. If the alfin rubbers prove to have a cost advantage besides the claims for improved properties, then Akron*s tire makers may beat a path to U.S.I.'s door. Alfin rubbers get their name from the catalyst used in their production—the combination of an a/cohol and an olefin. They were invented by Dr. Avery A. Morton at Massachusetts Institute of Technology in 1944. The distinguishing feature of these polymers is a straight chain, trans-rich (65 to 75%) configuration coupled with extremely high molecular weight. The problem until now was in providing molecularweight control for the alfin rubbers to make them suitable for commercial processing. The microstructure of these controlled polymers is identical to polymers obtained without molecularweight control, U.S.I/s Raymond G. Newberg told the ACS Rubber Division meeting in Buffalo, N.Y., earlier this month. Also, he says, the resulting copolymers have better wear, abrasion resistance, and other properties than most rubbers now used in tires. The first molecular-weight control agent for alfin polymers was 1,4-dihy-
drobenzene, discovered by Mr. Newberg's coworkers Dr. Harry Greenberg and Dr. Virgil E. Hansley in 1959. Subsequently, 1,4-dihydronaphthalene has proved to be many times more active than 1,4-dihydrobenzene, Mr. Newberg says. Of the many molecular-weight control agents tested, a general pattern of structure has emerged, he says, namely, the 1,4-diene structure which may be either straight chain or cyclic. With all these control agents, the alfin polymerization process is effective for not only 1,3-butadiene, but also for isoprene, piperylene, styrene, and several other dienes, he points out. "Combinations of these dienes to give copolymers or terpolymers can be prepared easily with molecular-weight control. Thus, moderator action coupled to the alfin process makes it possible to prepare an infinite number of polymer and copolymer combinations at predetermined molecular weight or Mooney viscosity levels." Radioactive tracer experiments indicate that molecular chain length control uses only one molecule of moderator per chain and involves some form of hydrogen transfer, he says. The alfin catalyst is an insoluble heterogeneous system, he explains. It is composed essentially of equimolecular quantities of a sodium alkyl (usually sodium allyl), a sodium alkoxide (usually sodium isopropoxide), and sodium chloride. They are prepared simultaneously in an inert hydrocarbon medium.
Exhaustive tire testing of the new polymers has produced highly favorable results, Mr. Newberg says. The tests were done by the U.S.L Division of National Distillers and Chemical Corp., Nippon Alfin Rubber Co., and several U.S. and Japanese rubber and tire companies. The tests have established the alfin polymers as useful and economical candidates for commercial passenger car tire use, he adds. U.S.I, data (see graphs) show the alfin rubbers to be superior to 65% SBR/357c cte-polybutadiene for tread wear, traction, braking, and skid resistance in passenger car tires. Beyond the passenger car tire market, Nippon Alfin Rubber is testing the new elastomers for other uses in products such as boots and other footwear, industrial belts, mechanical rubber goods, and truck tires. The firm will market the rubbers in the U.S. as well as in Japan. The company is so confident that the new rubbers will be accepted by the rubber industry that it is building the first commercial plant with provisions for doubling the capacity in the near future. If the alfin rubber process lives up to U.S.I/s expectations, it could have a dramatic effect on the U.S. and world rubber industry. About two thirds of the U.S/s predicted consumption of 2 million long tons of synthetic rubber this year will go into tires. However, for such a lucrative market, improvements in other processes and other elastomers will probably provide plenty of competition in the near future.
MEMMPTO COMPOUNDS THIOLS-MERCAPTANS-R-SH Ammonium Thioglycolate Benzyl Mercaptan p-Chlorobenzyl Mercaptan 2 Diethylaminoethanethiol Hydrochloride Iso-octyl Thioglycolate 2-Mercaptoethylamine Hydrochloride 3-Mercaptopropionic Acid Octadecyl Thioglycolate Thioacetic Acid (thiolacetic acid) Thiobenzoic Acid 1-Thioglycerol
Thioglycolic Acid Thiolactic Acid
Thiomalic Acid Thiosalicylic Acid POLYTHIOLS-POLYMERCAPTANS-R-
