US2445042A

US2445042A - Method of treating oriented acrylonitrile structures

Info

Publication number: US2445042A
Application number: US496396A
Authority: US
Inventors: Silverman Shirleigh
Original assignee: EI Du Pont de Nemours and Co
Current assignee: EIDP Inc
Priority date: 1943-07-28
Filing date: 1943-07-28
Publication date: 1948-07-13
Anticipated expiration: 1965-07-13
Also published as: CH283374A; GB585367A; NL128726B; FR924369A; BE464523A

Description

y 3, 1948. s. SILVERMAN 2,445,042

IBTHOD 0P TREATING ORIENTED ACRYLONITRILE STRUCTURES Filed July 28, 1943 .Wai

IN V EN TOR. SH/R4 5/6 5/4 VERMN h/im/ A TTOR/VEX Patented July 13, 1948 IV IETHOD OE TREATING ORIENTED ACRY- LONITRILE STRUCTURES Shirleigh Silvcrman, Baltimore, Md., assignor to E. I. du Pont de Nemours & Company, Wilmington, Del., a corporation of Delaware Application July 28, 1943, Serial No. 496,396

Claims. 1

This invention relates to shaped articles, such as yarns, films, tubings, fibers, etc., of an acrylonitrile polymer. More particularly, it relates to a method for improving the physical properties of such shaped articles which have been subjected to a drawing operation during or after their formation and which show a definite orientation on X-ray analysis.

For convenience, this invention will be discussed in connection with the treatment of yarns of an acrylonitrile polymer.

It has been proposed to dissolve an acrylonitrile polymer in a suitable organic solvent and extrude the resulting solution through an orifice to form a shaped structure, such as a yarn. When little or no tension is exerted on the yarn during the spinning operation, the yarn obtained is somewhat brittle and possesses undesirably low properties. A typical yarn will possess a tenacity of approximately 0.8 gram per denier and an elongation of about 8%. X-ray analysis indicates that the yarn is crystalline in nature but substantially unoriented.

There have recently been proposed two methods involving the. stretching of an acrylonitrile polymer yarn, whereby it is possible to greatly increase the tenacity of such a yarn without causing any substantial decrease in its elongation. According to one of these methods, which is fully described in copending application of Daniel T. Meloon, Serial No. 496,397, filed July 28, 1943, the substantially unoriented yarn mentioned above is heated to a temperature of at least 100 C. and drawn while at this temperature to from 4 to 10 times its original length. According to the second method. which is fully disclosed in copending application of William W. Watkins, Serial No. 496,376, filed July 28, 1943, now Patent No. 2,426,719, the yarn is spun by a wet-spinning technique into a bath comprising, for example, a glycerol bath heated to a temperature of 140 C. or an aqueous 40% calcium chloride bath heated to a temperature of at least 100 0., the yarn being subjected during its passage through the bath to a tension of at least 0.5, and preferably 0.7 to 1.0 gram per denier.

The yarns obtained by either of these two methods are highly oriented and generally possess a tenacity of at least 3 grams per denier. However, they still possess an elongation that is relatively low, it being of the order of 8% to 12%. While they can be used for certain specialized purposes, wherein a low elongation is desirable,

- the yarns are not generally suited for use in the textile art, which requires a yarn possessing an elongation of from 15% to 25%, and preferably of from 18% to 22%.

It is the object of this invention to provide an acrylonitrile polymer yarn suitable for use in the textile art. It is a further object of this invention to provide a method for improving the elongation of an oriented acrylonitrile polymer yarn. It is a still further object of the invention to provide a method for improving both the tenacity and elongation of an oriented acrylonitrile polymer yarn. Itis a specific object of the invention to provide an acrylonitrile polymer yarn possessing a tenacity of at least 3 grams per denier and an elongation of at least 15%. Other objects will become apparent hereinafter,

The objects of this invention are accomplished, in general, by heating an oriented acrylonitrile polymer yarn in a relaxed state to a temperature of at least 6., whereby the yarn is caused to shrink, and then maintaining the yarn at a temperature of at least 80 C. for a period of from 1 to 24 hours, the yarn during this time being maintained in a relaxed state or under very low tension, for example, a tension of approximately 0.05 gram per denier. The term oriented acrylonitrile polymer yarn, as used in this specification, refers to an acrylonitrile polymer yarn that possesses a tenacity of at least 3 grams per denier and an elongation of from 8% to 12% and that showspn X-ray analysis a degree of orientation at least equal to that of an acrylonitrile polymer yarnspun by the dry-spinning technique without the application of stretching tension, as disclosed in Example I of copending application of George H. Latham, Serial No. 447,466, now abandoned, subsequently stretched to at least twice its original length while passing through a glycerol bath maintained at a temperature of C., as disclosed in said copending application of Daniel T. Meloon, Serial No. 496,397, filed July 28, 1943.

The initial step of this process; involving the hot relaxing of the yarn, causes it to shrink 10% to 25% of its length, this shrinkage of the yarn not affecting its tenacity but causing a large increase in its elongation, substantially all of this shrinkage showing up as increased elongation. This latter result is surprising and is in sharp contrast to the action of other stretched polymeric yarns, wherein only a portion of the total shrinkage of the yarn at elevated temperatures shows up in increased elongation. At the same time, this hot relaxing of the yarn causes an appreciable improvement in its other properties, including an approximate 50% increase in such properties as knot, loop and impact strength.

The final step of the process involving a prolonged heating of the shrunken yarn, preferably accomplished under no or only very slight tension, does not generally cause a further shrinkage of the yarn but rather causes an appreciable and surprising increase in its tenacity without any accompanying substantial loss in its elongation. The yarn thus ebtained is in condition for subsequent use, for example, in the textile art.

In contrast to the untreated yarn, it possesses a somewhat increased tenacity, a greatly improved elongation and a desirable increase in its other physical properties, including such properties as knot, loop and impact strength, etc. Moreover, the final yarn does not appear to'have been degraded by the successive heat treatments involved in the process of this invention.

The practice of this invention is not limited to the use of a particular type of apparatus and, generally speaking, any form of apparatus capable of heating the yarn in the desired manner can be used.

In the drawings,

Figure 1 shows a diagrammatic form of one embodiment 01' an apparatus suitable for use in the invention; and

Figure 2 is a perspective view of one form oi. heating device which is suitable for use in the invention.

Referring now to Figure 1, an oriented acrylonitrile polymer yarn I is unwound at a constant rate from a supply bobbin 2 by a metering device comprising a positively driven roller 3 and displacement guide I, and is led through a heating means 5 by a second metering device comprising a positively driven roller 6 and displacement guide I. The speed of the positively driven roller 6 is so adjusted with respect to that of the positively driven roller 3 that the yarn I, passing through the heating means 5, is in a relaxed state and free to shrink. The shrunken yarn leaving the second metering device is then collected in package form on a rotating bobbin 8, the yarn being preferably wound into the package under the lowest possible tension commensurate with good winding and unwinding performance. The wound package is then placed in an oven where it is maintained at a temperature of at least 80 C. for a period of 1 or more hours.

The heating means 5 must, of course, be so constructed that it is capable of heating the yarn passing through it to the desired temperature without exerting any tension on it, the yarn being free to shrink at all times during its passage through the device.

Referring now to Figure 2, wherein there is shown one form of apparatus capableiof operating in such a manner, the reference numeral 20 designates a solid block provided along one 'surface with a. slot 2| throughwhich the yarn I is led." The block 20 is provided with a bore 22 in which there is positioned an electrical resistant 23 capable of maintaining the block at the desired temperature of at least 80 C. The block 20 is preferably made of metal whereby the yarn I, passing through the slot 2 I, will be heated both by convection and radiation. As shown, the slot II is preferably enlarged at that portion thereof through which the yarn passes.

The following examples which are intended to illustrate, and not restrict, the invention represent several preferred embodiments of the invention,

and the percentages therein given are by weight:

Exam: I

An acrylonitrile polymer yarn was prepared by the extrusion oi. a 25% solution of an acrylonitrile polymer having a molecular weight of 66,000 in tetramethylene cyclic sultone through a, Ill-hole spinneret into a tubular cell through which heated air was circulated in an opposite direction. The yarn issuing from the cell had a denier of 310 and possessed a tenacity of 0.8 gram per denier and an elongation 01' 8.0%. X- ray analysis showed it to be crystalline in nature but substantlallyunorlented. The yarn was then stretched between positively driven rollers and, while passing about a stationary pin, heated to a temperature of C. to 8 times its original length. The stretched yarn possessed a tenacity 01 3.7 grams per denier and an elongation of 10.1%. x-ray analysis showed it to be crystalline in nature and highly oriented in the direction of its fiber axis. 1 7

The yarn was then passed in the continuous, relaxed manner of Figure 1 oi! the accompanying drawings through a slot formed in a metal block 10 inches long and maintained at a temperature of 130 C. The yarn, which shrank approximately 20% while passing through the slot, was then collected on a rotating bobbin under the lowest tension commensurate with good winding and unwinding performance. The bobbin package thus formed was then heated in an oven' (dry air) for a period of 1 hour at a temperature of C. The final yarn possessed a tenacity of 4.66 grams per denier and an elongation of 20%, with loop and knot tenacities 01' 3.3 and 2.3 grams per denier respectively. The yam was substantially colorless and showed no signs of having been degraded by the heat treatment.

, Earn: 11

A crystalline oriented acrylonitrile polymer yarn was formed by extruding a 20% solution of acrylonitrile polymer possessing an average molecular weight of appnoximately 120,000 in dimethyl formamide into a glycerol bath maintained at a temperature of 125 C., the yarn being passed through the bath for a distance of 24 inches and subjected to a spinning tension of approximately 1 gram per denier. The physical properties of this yarn, as spun, are given in the accompanying table.

One portion'or this yarn was wound into skeln form and suspended in a tensionless, relaxed manner for a period of 1 hour in a glycerol bath heated to 100 C., whereupon the yarn shrank approximately 20% of its original length. A second portion or the yarn was heated for 1 hour in air at 100 C., the yarn being maintained at constant length during the heating period so that no shrinkage could take place. The physical properties of the yarn obtained in these manners are given in the accompanying table, which clear- 1y indicates the nature of the improvement obtained by the practice of this invention:

Table d Yum 'llamolflec (g p Elongation, per cent Straight Knot Loop Straight Knot Imp As spun a 15 1.1: 1. so 10.0 s. s a. 1 Heated 100 0., 1 hour. relaxed in yoerol 4.11 2.2 2. 75 21.0 14.0 18.0 Heated III)" 0., 1 hour, in llr0% 4.10 2.2 2.5 13.0 6.0 6.3

tures employed'in these operations should generally be of the order of at least 80 C.; for example, desirable results are obtained with the use of a temperature of 100 C. to 150 C., and even higher temperatures, such as up to and including 300 (Lean be used if desired. 1

For the relaxing step,- it is essential that the yarn be maintained in a tenslonless manner so that it will be completely free to shrink. As indicated in the examples, this step can be performed in a continuous manner (on the run by leading the yarn in a relaxed manner through a heating'means) or in a batch manner (by suspending a quantity of yarn in a relaxed manner,

as in the form of a skein, in a heated medium).

- The exact manner of heating the yarn in this operation is not critical to the invention, it only being necessary that the yarn be free to shrink during the heating operation; for example, the yarn may be heated by passing through a slot formed in a heated block, as in Example I, or it can be passed about a heated roller, or it can be passed through a heated inert fluid, such as air,

glycerol, etc., the yarn being maintained in a relaxed, free-to-shrink condition.

The second step of the process of this invention, involving the prolonged heat treatment of the yarn, may also be conducted in either a continuous or batch manner. However, because of the time involved, it is generally preferred to employ the latter procedure, wherein individual masses of yarn, such as bobbin packages, are placed in a heating means, such as an oven, for the necessary length of time. The exact time required for the development of optimum physical properties in the yarn is, of course, dependent on the temperatures employed. Desirable results are obtained when using a heating period of 3 hours at 150 C. while somewhat longer periods should be used at a temperature of 80 C. The heated medium employed for this operation comprises an atmosphere of air maintained at the desired temperature. However, this is not essential and in order to more substantially prevent discoloration the yarn is preferably heated in any inert atmosphere, such as carbon dioxide or nitrogen gas, or even in an inert liquid, such as glycerine, glycol, etc.

The process of the invention preferably comprises the combined steps of successively subjecting an oriented acrylonitrile polymer yarn to a hot relaxing treatment and to a prolonged heat treatment because of the desirable effects of such treatment on both the tenacity. and elongation of the yarn. However, such a combined treatment is not essential for the production of an improved yarn, and desirable yarns for certain purposes can be obtained by the application of only the relaxing treatment or the heat treatment; for example, in the case of the yarn of Example I above, the omission of the final heating of the bobbin package yields a yarn possessing a tenacity of 3.5 grams per denier and an ,6 s elongation of 23%. On the other hand, as shown in Example II, the omission of the relaxing step results in the formation of a yarn that possesses a greatly improved tenacity but only a slightly improved elongation.

Though in the preferred form of the invention the two steps are performed separately in different' apparatus, the two steps may becombined and performed in a single apparatus. In such an embodiment, the yarn is placed'into a heated chamber and maintained therein at the appro priate temperature until the yarn has completely shrunk and the shrunken yarn has been'given I the prolonged heat treatment.

Although the specific examples of this case dis- I close only jthe'treatment of yarns prepared from a simple acrylonitrile polymer, the process of the invention is also applicable to the treatment: of

other shaped articles of sucha polymer, including films, tubings, fibers, B120.- The'acrylonitrile polymer constituting the shaped articles treated in accordance with this invention must, of course, be of a-sumciently high molecular weight to pos sess filmor filament-forming properties, and

polymers possessing an average molecular weight (determined from viscosity measurements by the Staudinger formula) of from 7,000 to 400,000'or more'are suitable for use. Preferablvhowever, the polymer possesses a molecular weight of from 50,000 to 150,000. Though the polymer preferably comprises a simple polymer of acrylonitrile, the invention is not restricted thereto. Interpolymers of acrylonitrile and other polymerizable substances, such as vinyl compounds, unsaturated carboxylic acid and their derivatives, oleflnic' compoun'cL'and other polymerizable substances, may also be used. However, for the final article to possess the desirable properties of polymerized acrylonitrile (such as resistance to acids and common solvents), it is necessary that the interpolymer contain a major portion of acrylonitrile, and those interpolymers that are prepared from at least 80 parts of acrylonitrile and no more than 20 parts of another polymerizable substance are preferred. As previously mentioned, it is, of course, necessary that the structure to be treated possess an orientation as determined by X-ray analysis; that is, at least equal to that of an unoriented acrylonitrile polymer yarn that has subsequently been drawn to at least twice its original length. If the structure does not possess an orientation of at least this value, the process of this invention will not generally improve its physical properties.

This invention makes possible the production or an acrylonitrile polymer yarn that is eminently suited for use in the textile art. The practice of the invention not only greatly increases the elongation of such a yarn but also makes possible a substantial improvement in its tenacity. It also serves to greatly improve the knot and loop tenacities and elongations of the yarn. The invention makes possible for the first me the production of an acrylonitrile polymer yarn possessing a tenacity of at least 4 grams per denier and an elongation of the'order of 20%. At the same time the yarn retains such other desirable properties, characteristic of acrylonitrile polymer yarn, as high resistance to chemical agents, such as common organic solvents, cleaning agents,etc. Moreover, the process of the invention does not cause the yarn to become colored to any appreciable extent. This fact, together with their greatly improved physical properties, makes the yarn of this invention highly suited for use in the textile art. Moreover, the yarns do not tend to shrink to any appreciable extent on subuquent exposure to elevated temperatures for example, shrinkage of the yarns under conditions Since it is obvious that many changes sntl modifications can be made in the above-described details without departing from the nature and spirit of the invention, it is to be understood that the invention is not to be limited thereto except as set forth in the appended claims.

I claim:

1. A method oi improving the physical properties of an oriented shaped article formed -1'rom a polymer containing a ajor proportion or acrylonitrile which comprises heating the shaped article 'in a relaxed, iree-to-shrink condition. at a temperature of 80C. to 300 C. andmaintain ing the shrunken shaped article under a tension insuihcient to stretch said shrlmlr'en article at a temperature oi 80 C. to 300 C. for at least one hour. both of said heating stepsbeing carriedvout in the presence of an inert heating medium.

2. The'method of improving the physical properties oran oriented yarn formed. from: polymer containing a major proportion otacrylonitrile which comprises heating. the yarn in a relaxed, i'ree-to-shrink condition at a temperature of. 89 C. to 300 C. and maintaining theshrunken yarn under a tension insumcient to stretch said shrunken yarn at a temperature of 80 C. to 300 is P ., 8 CJoratleastonehounbothoteaid heatingstepsbeing elected in the presence of an inert heating medium.

3. Themethod of claim2,characterizedinthat said second heating step iscarried out-in an inertatmosphere.

4. The method of claim 2, characterized in that said second heating step is carried out while the yarn is maintained ulder a tension 01 not more 10 than 0.05 gramper denier.

a tile of this patent:

Number 6 Name Date 1,367,297 Zart July 12, 1932 2,161,766 Rugeley et a1. (1) June 6, 1939 2,170,439 Wiezevich Aug. 22, 1939 2,176,153 Semon Oct. 17, 1939 2,199,411 Lewis May 7, 1940 2,239,730 Fikentscher et al. Apr. 29, 1941 2,273,071 Rugeley et al. (2) Feb. 17, 1942 2,309,370 Williams Jan. 26, 1943 2,317,409 Seaton Apr. 27, 1943 2,325,060 Ingersoll July 27,1943 2,346,203 Conaway Apr. 11, 1944 85 I V FOREIGN PATENTS Number Country Date 387,956 Great Britain Feb. 16, 1933