US2461602A - Method of manufacturing synthetic sutures and the like - Google Patents

Description

Patented Feb. 15, 1949 METHOD OF MANUFACTURING SYNTHETIC SUTURES AND THE LIKE John P. Hollihan, Jr., Garden City, at, assignor to American Viscose Corporation, Wilmington, Del., a corporation of Delaware No Drawing. Application January 17, 1946, Serial No. 641,865

This invention relates to improvements in methods for manufacturing synthetic suture material and similar products comprising an integral mass of fibers which occur in animal parts, as for instance, animal tendons or sinews, such as beef tendons.

One method of producing filaments or threads comprising such animal fibers involves the steps of suspending the fibers, whether in their elementary condition or after cutting thereof to selectively controlled lengths, as describedin the pending application of Hall, Hollihan'and Morehead, Serial No. 630,686, filed November 24, 1945, in an organic or inorganic acid, extruding the suspension into a coagulating and/or dehydrating medium, raising the pH on the thus formed filaments by treating them in an aqueous bufier ing system and thereafter drying the buffered filaments simultaneously with stretching thereof.

Stretching of the buffered filaments concomitantly with their drying is an essential step of the process, and I have found that in order to obtain final filaments or threads having the most desirable properties as respects tenacity and. extensibility, it is necessary to stretch the filaments about 14 to 16% during the drying step, which is equivalent to subjecting the filament bundle to a tensioning load which varies in accordance with the size of the filament, from about 70 gms. for a 200 denier filament to about 200 to 250 gms. for a 1000 denier filament, as measured by any standard strength-testing device. I have discovered, further, that in order to produce filaments capable of accepting the required stretch during drying without rupture at the weaker portions which inevitably occur along the filament length, it is important to avoid excessive swelling of the filaments when the pH on the acidic filaments is raised by treating them with a bufiering solution. Thus, excessive swelling of the filaments in the bufier system has been found to reduce the capacity of the filaments to withstand, at all portions along their length, the stresses and strains developed therein when they are stretched during drying,

Theacidic filaments invariably swell when they are subjected to the action of alkaline solutions, but I have found that if the extent of the swelling is controlled so that the buffered filaments are swollen to about twice their normal (dry) size, the filaments accept a stretch of 14 to 16% during drying without rupture, and the final filaments are characterized by high tensile strengths andextensibilities. 1 I

Li The object of thepresent invention thereiore,

5 Claims. (CI. 1854) is to provide a method for raising the pH on the acidic filaments while controlling the extent of swelling of. the filaments during bufiering thereof.

This and other objects are achieved by treating the acidic filaments with an aqueous alkaline solution which, under the conditions of treatment, has a limited swelling action on the filaments such that the buffered filaments .are swollen to. only about twice their normal (dry) size after withdrawal thereof from thebufiering medium.

One buffer system which has been suggested for use in treating the acidic filaments comprises an aqueous solution of ammonium hydroxide and ammonium chloride. It has been found that all solutions of ammonium hydroxide and ammonium chloride are not satisfactory for use in treating the acidic filaments from the point of view of controlled swelling of the filaments and ability of the buffered filaments to withstand stretching. tow the required 14 to 16% without rupture duririgidrying thereof. I 'havefou'nd that both dilute and highly concentrated solu tions of the ammonium compounds have a pronounced swelling action on the filaments and that the filaments thus swollen have a markedly decreased capacity to undergo stretching without rupture. I have discovered, however, that-there is an optimum concentration of the ammonium hydroxide and ammonium chloride in the buffering solutions at which the pH on the filaments is raised while at the same time the filaments are swollen only to a minimum controlled extent which does not prevent their accepting a stretch of about 14 to 16% without rupture. Thus I have determined that when the dry acidic filaments are immersed in water to whichhas been added about 6 to 6.5 cc. of concentrated am monium hydroxide and about 1 to 1.2 grams of ammonium chloride, per liter, for about eight minutes the filaments leaving the buffering medium are swollen to a size which is only about twice their normal (dry) size. The term concentrated ammonium hydroxide is used here in its usual sense to define an aqueous solution containing approximately 28% NH; by'weight and of sp. gr. 0.90, (Handbook of Chemistry, Lange, p. 1165, 1944; Talbots Quantitative Chemical Analysis, 1939, p. 284; Qualitative Chemical Analysis, Prescott and Johnson, p. 618)". In contrastto, this comparatively slight swelling of the filaments when they are buffered in aqueous; media containing the amm nium like, which comprises suspending the fibers in an aqueous acid solution, extruding the suspension into a non-basic coagulating and dehydrating medium to form acidic filaments, withdrawing and drying the thus formed acidic filaments and raising the pH on the filaments while swelling the fibers to approximately twice their normal dry size by treating them with water to which has been added about 6.3 cc. of concentrated ammonium hydroxide and about 1.07 grams of ammonium chloride, per liter, and thereafter drying the filaments while stretching them from 14 to 16%.

3. Method for the manufacture of threads and the like comprising an integral mass of fibers which occur in animal sinews, tendons, and the like, which comprises suspending the fibers in an aqueous acid solutionfextruding the suspension into a non-basic coagulating and dehydrating medium consisting of an organic solvent, to form acidic filaments, withdrawing and drying the thus formed acidic filaments and raising the pH on the filaments, while swelling the filaments to approximately twice their normal dry size, by treating them with water to which has been added from about 6 to 6.5 cc. of concen-.

trated ammonium hydroxide and from about 1 to 1.2 grams of ammonium chloride, per liter, and thereafter drying the filaments while stretching them from about 14 to 16%.

4. Method for the manufacture of threads and the like comprising an integral mass of fibers which occur in animal sinews, tendons, and the like, which comprises suspending the-fibers in an aqueous acid solution, extruding the suspension into a non-basic coagulating and dehydrating medium consisting of acetone to form acidic filaments, withdrawing and drying the thus formed acidic filaments and raising the pH on the filaments, while swelling the filaments to approximately twice their normal dry size, by treating them with water to which has been added from about 6 to 6.5 cc. of concentrated ammonium hydroxide and from about 1 to 1.2 grams of ammonium chloride, per liter, and thereafter drying the filaments while stretching them from about 14 to 16%.

5. Method for the manufacture of threads and the like comprising an integral mass of fibers which occur in animal sinews, tendons, and the like, which comprises suspending the fibers in an aqueous acid solution, extruding thesuspension into a non-basic coagulating and dehydrating medium consisting of acetone to form acidic filaments, withdrawing and drying'the thus formed acidic filaments and raising the pH on the filaments, while swelling the filaments to approximately twice their normal dry size, by treating them with Water to which has been added about 6.3 cc. of concentrated ammonium hydroxide and about 1.07 grams of ammonium chloride, per liter, and thereafter drying the filaments while stretching them from about 14. to 16%. 1

JOHN P. HOLLIHAN, JR.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS FOREIGN PATENTS Country 7 Date Great Britain May 28, 1931 Great Britain Apr. 1, 1938 Number Number