TECHNOLOGY
Three who attended the symposium are ( left to right ) : Graham Meacock, British Nylon Spinners, J. B. Speakman, University of Leeds, and L. B. Morgan, ICI Dyestufïs Division. Speakman described production of 6-polymer polyamide from 6-hexanolactam
N e w Fiber Formers Condensation polymers developed in Britain show promising possibilities; commercial feasibility is keyed to low-cost hydrazine and sebacic acid LONDON.-Polyaminotriazoles ( P A T ) , produced in t h e laboratories of British Celanese, have been used to produce filaments possessing high strength and having striking dyeability characteristics. The PAT's may well occupy a n important position among synthetic fibers in the future. Celanese research leader J. W. Fisher described the d e velopment in a paper before the symposium on the Chemistry and Physics of Synthetic Fibers, sponsored by t h e Society of Chemical Industry here recently. A polymer can be prepared which, according to Fisher, has a melting point between 256° and 260° C . Fibers can be formed from the melt which can readily b e orientated b y cold drawing, thereby combining high tenacity with good elasticity. The PAT fibers have good affinity for dyestuffs of the acid type and of the dispersed type, as used for cellulose acetate rayon. New polymer is very resistant to hot aqueous alkalies but is rather reactive to acids and bleaching agents. The tensile strength and elongation of yarns made from the polymer are unaffected by acid solutions down to p H 2 on immersion for one hour at 25° C. Fisher a d d e d that chlorinated hydrocarbons d o not affect polyoctamethyleneaniinotriazole fiber. Polymerizations of hydrazides, dihydrazides, and combinations of hydrazine with dicarbonyl compounds are not new. But past work has led to only 1470
unsuitable polymers of varying composition. Key to the reaction had apparently been overlooked, said Fisher. Most important condition for securing uniformity in the PAT product is an excess of hydrazine, he said. Fisher outlined this polymerization procedure: A mixture of 100 parts of sebacic acid, 100 parts of 60' 't aqueous hydrazine, and 0.8 parts acetamide is heated in an autoclave at 210° C. for 15 hours. Temperature is raised to 270° C. and maintained for three hours while pressure is gradually reduced to 500 pounds per square inch. Questioned regarding the long polymerization time, Fisher replied that under "proper conditions" this time could be reduced to eight or nine hours. The acetamide functions as a "chain-stopper. " It renders the hydrazide functional end groups inactive. Fisher said that tests on PAT fibers had been very encouraging. Celanese is now waiting for low-cost hydrazine and sebacic acid to become available in Britain. With the availability of these raw materials, the economic picture and commercial potentialities of the new fiber could change overnight. Polyamides Compared. Fibers formed from the three commercially available polyamides have similar characteristics, but a recent investigation has revealed that there are also striking differences in physical properties. The 6,6-, 6,10- and the 6-polyamides have undergone physical and chemical testCHEMICAL
ing in the laboratories of British Nylon Spinners. Manufacture of 6,6-fibers (nylon) has predominated i n Britain and the U. S., but in Europe, particularly Germany, the main product has been 6-polyamide (Perlon). The relative simplicity of producing the 6-polymer from 6-hexajnolactam aroused his company's interest in comparing properties, explained Graham Meacock. High pressures .and the elimination of large quantities of water are not involved. Unfortunately the monomer-polymer equilibrium is not so favorable in the 6-polymeir and a n extra washing or evaporation! step i s necessary in the process, he admitted. Stability of the 6-polymer \v^as found superior to that of either of t h e other two. T h e 6,6-type polymer was described as least stable of t h e th_ree. The amino end group content risers rapidly at the same time as the carl>oxyl end group content decreases. When it came to processing the fiber, the 6-polymer did not rate so well. Evolution of monomer close? t o the spinneret and subsequent hulld-up o n the guides are nndesiriihle features, said Meacock. At eqnilibriunri, the 6 polymer contains about 1 0% imonomer, which leads to the difficulty in the yarn processing. The melting point of 6,6-pelymer i s about 5(Γ C. higher than that of the other two. This means 6,6-fïher will be superior in applications zreqxiiring a retention of strength a t higher temperatures, but on the other h a n d , t h e other two polymers can r>e extruded a t lower temperatures. Sa ran Process Details. Monofilaments are now being made i n Britain from the vinylidene chloricle-vinyl chloride copolymer (Saran). Ma_nufaeturing details were outlined by J a m e s Jack and R. A. Horsley, B. X. Plastics." Plasticizing vinylidene polymers is not easy because of erystaJ-forming tendencies. However, this i s vitally necessary if the working temperature is to be kept within limits of thermal decomposition, said Jack. Adldition of about 7c/f diphenyl diethyl either will depress the softening point ancH increase thermal stability, he said. Described a s a light stabilizer or filler: 2lr/c of 5 chloro-2-hydroxybenzoplienon^. Design of a Saran extruder is primarily determined by thermal instability of the polymer and, 3:o a less extent, by low bulk densitw of t h e powder feed. Metals irt contact with the polymer must contain no i r o n , copper, zinc, or tin. These are catalysts for thermal decomposition. Favored alloys, according to Jack, are/ Ζ nickel (Duranickel) for screw; Ζ mickel, X alloy 306 (cast form), Hnstelloy D AND
ENGINEERING
ME^S
(cast form), or Stellite for cylinder liner; and Ζ nickel or nickel for the right-angle head and dies. A maximum temperature of 170° C. is required for extrusion. Steam heat ing is preferred to oil o r electrical re sistance types of heating. The extruded monofils drop vertically into quench hath, controlled at a b o u t 10° C , and pass around a fixed or rotating guide to the draw rollers. A draw ratio of about 4 to 1 is applied and for an 11-mil monofilament the stretching tension will normally be about 150 grams per filament, he explained. The drawn filament is wound on bobbins at speeds approaching 400 to 500 feet per minute. Two wind-up systems are in current usage: winding first on large drums and then rewinding on the final package, and winding directly on the final spool. The latter system is rapidly gaining favor and permits a low winding tension which can be controlled accurately. Helical Spherulites? A helical struc tural theory, applied t a fiber-forming polymers, came in for considerable at tack from the floor. I C I ' s L. B. Morgan defended his theory an
