US2597557A

US2597557A - Nitric acid treatment of polyethylene terephthalate structures

Info

Publication number: US2597557A
Application number: US95379A
Authority: US
Inventors: Amborski Leonard Edward
Original assignee: EI Du Pont de Nemours and Co
Current assignee: EIDP Inc
Priority date: 1949-05-25
Filing date: 1949-05-25
Publication date: 1952-05-20
Anticipated expiration: 1969-05-20

Description

Patented May 20, .1952

FFICGE 2,597,557 mere on) QTBEATMENT F POLYETHYL- ENE TEREPHTHALATE STRUCTURES Leonard Edward Aniborski, Buffalo, N. Y., as-

signor to E. I. du Pont de Nemours & Company, Wilmington, DeL, a corporation of Delaware No Drawing. Application May 25, -1949, Serial No. 95,379

3 (liaim's. (o1. s 115.5)

This invention relates to the manufacture of synthetic organic filaments, yarns, fibers, etc. and more particularly, to a novel process for treatingfilarnents, yarns and like structures of polyethylene terephthalate whereby to improve certain physical properties thereof.

In many instances, e. g. where yarn is to be usedas rug pile, etc, it is desirable to enhance the toughness, resilience, work recovery and allied physical properties of the filaments, fibers, or yarn. In general, filaments having a high degree of toughness, resilience, etc., also have high el ngations-at the breaking point, and it should therefore be possible to increase, say the toughness, of a given filament or yarn by in creasing its elongation. However, expedients heretofore employed to improve elongation of filaments of synthetic organic materials, such as hot relaxing of a stretched filament, etc, for the most part work an improvement in elongation at the expense of the tenacity or tensile strength of the filament and often, while the desired degree of toughness is achieved, the tenacity of the resulting filaments are so low that the filaments are commercially inutile. These generalizations are particularly valid for filaments, fibers and yarns made from the synthetic linear polyethylene terephthalates disclosed in Whinfield and Dickson U. S. Patent No. 2,465,319 which filaments, fibers and yarns, because of their excellent physical and chemical properties, especially recommend themselves for broad application in the textile arts.

Obviously a treatment of such nature that satisfactory improvement in elongation, toughness, work recovery, etc., is obtained while retaining good tenacity, is to be highly desired. The improvement in these properties is attendant with a decrease in orientation of the polymer molecules along the fiber axis and an increase in the crystallinity 'of the polymer structures. Orientation along the fiber axis is achieved by submitting the fibers to the action of mechanical stress or stretching either at the time of spinhing or subsequent thereto, and results in improved tensile properties and pliability. This trieiiistisnisarso evidenced by a characteristic X-ray diffraction diagram. In general, highly oriented yarn will exhibit relatively low elongation, resilience, Work recovery and toughness.

.An object of this invention therefore is to provide a simple, economical process for increasing the elongationof filaments, fibers, yarns and like fun ular st uct r s f. po ethylene erephthw latewithoutreducing the tenacity thereof to a detrimental level.

Another object is to produce tough filaments, fibers, yarns and like funicular structures of polyethylene terephthalate which have a desirably high tenacity at the breaking point.

A further object is to provide a simple, econoinical process for dec'reasing the orientation along the fiber axis of oriented filaments, fibers, yarns and like funicular structures of polyethylene terephthalate without reducing the tenacity thereof to adetrimental level.

A still further object is to render filaments, fibers, yarns and like structures of polyethylene terephthalate more crystalline and hence more stable. I M

These and other objects will more clearly appear hereinafter. I H

These objects are realized by the] present invention which, briefiy stated, comprises treating oriented filaments, fibers, yarns and like funicular structures of polyethylene terephthalate with nitric acid solution. H

The polyethylene terephthalate structures with which this invention is concerned may be prepared by melt-sp'inning or casting the polymeric material by the usual techniques. The polymeric ethylene terephthalate may be prepared by the esterification of terephthalic acid with ethylene glycol under normal melt-polymerization conditions or again in a similar fashion by the ester exchange reaction between dimethyl terephthalate and ethylene glycol. Thedetails of the preparation and shaping of polyethylene terephthalate are fully disclosed in the aforesaid patent to Whinfield and Dickson. Orientation alon the fiber axis of the funicular structures is accomplished by a stretching operation, either integral with the spinning of the polyethylene terephthalate or at a subsequent time. 7 7 v The concentration of the nitric acid solution may be varied within wide limits depending upon the extent of change of properties of the polyethylene terephthalate structures desired. For relatively short treatment times (from 10 J seconds to 40 minutes) at room temperature,

56-89% nitric acid covers the most useful range. However, if shorter treatment times ore desired, a higher concentration of acid and/or a higher temperature may be utilized if desired. Of course, it is to be understood that lower concentrations may be used if the increased length of'ti'rne necessary to get the desired effect is unimportant.

With respect to the temperature conditions of the process of this invention, the range 0 C.- C. is the most useful. For odinary purposes,

however, room temperature is preferred as being the most convenient operating temperature.

The treatment of this invention may be carried out on oriented filaments and yarns of polyethylene terephthalate under either relaxed conditions or under moderate tension, 1. e. constant length. However, if treating tensions are too high, e. g., near the breaking point, an inferior product from the viewpoint of tenacity and elongation is produced.

The following examples of certain preferred embodiments further illustrate the principles and practice of this invention.

Inasmuch as this invention is concerned, in great part, with securing the maximum elongation while retaining good tenacity the tenacity-at-break, To, calculated from the equation:

E T -T(1+ where T is the usual tenacity in grams per denier (g./d.) based on the measured denier (d.) and the measured break load (g.), and E is the measured percent elongation to break, serves as an excellent measure for comparing yarns and is used in the following examples to demonstrate the improvements herein realized.

Example I A 77-denier polyethylene terephthalate yarn that has been completely drawn with no subsequent relaxation is immersed in skein form in a 70% nitric acid solution at room temperature for a period of one minute. At the end of this time, it is withdrawn and immediately washed in a water bath. The following table shows the before and after properties and dem-- onstrates clearly the large elongation increase at a useful level of tenacity.

Treatment, Time gjg 5 33 Denier To Control 6. 5s 12. a 77 7. a5 1 Minute 2. 97 95. 0 132 5.8

The following example shows the effect of the nitric acid treatment on a polyethylene terephthalate funicular structure that has been drawn in two stages at two different temperatures without subsequent relaxation.

Example II Tenacity Elon- Ticatment, Time gafion Denier To 7.38 11.3 61 8.35 to 4. 4 62. 3 85. 3 7. 12 No Acid Treatmen Hot Relaxed 2.8 62.0 80. 0 4. 53

The hot-relaxed sample above shows comparatively that for a high degree of relaxation, the acid treatment results in a far better yarn than is possible by hot-relaxation alone. An acidtreated yarn having properties in this range is an extremely tough yarn (as indicated by the large area under its stress-strain curve) particularly useful for carpets.

Example III To show the usefulness of the process of this invention when applied to a partially relaxed yarn, a sample of the oriented yarn of Example II before treating was relaxed 10% and then given the same nitric acid treatment with the before and after results as shown below:

ment of this invention seems to be that of a fiber penetrant which causes relaxation and does not appear to induce crosslinking or, for that matter, any irreversible effect. The following example shows that it is possible to redraw a nitric acid treated polyethylene terephthalate structure and get as a resultant product a funicular structure that has tenacity and elongation properties similar to the original starting material prior to nitric acid treatment. The following example illustrates the improvement in work recovery and initial tensile modulus over the control yarn for this particular modification of the treatment.

Example IV P u goubleg j roper es rawn Control g g g n Tenacity-51. 7. 38 7. 2 Elongation-Per Cent.... 11.3 3 To 3. 35 7.6 initial Tensile Modulus I 120. 0 144. 0 Work .Recovery from 0.5% Elongation 80.8 100.0 1.0% Elongation... 72. 2 84.0 2.0% Elongation 49. 2 58.0

1 Initial tensile modulus is defined as the slope of the first reasonably straight portion of a stress-strain curve of the yarn obtained by plotting tension as the vertical axis vs. elongation as the horizontal axis as the structure is being elongated at the rate of 10% per minute.

i Work recovery is defined as the ratio of the amount of work done by the yarn in recovering from deformation to the work recovery; 9. stress-strain curve, as described previously, is used under the following conditions: The yarn specimen is extended at a constant rate of elongation of 1% per minute; the specimen is held at the maximum elongation desired for 30 seconds and then is allowed to retract at the same rate at which it was extended. The same specimen is extended successively, 0.5, 1.0, and 2.0% for each determination. The areas under the elongation curve and the retraction curve respectively, represent work performed on the specimen, and work returned. These areas may be measured with a planimeter and the percent work recovery computed by means of the relationarea (work returned) X Ork teem ery area (work performed) gation or initial tensile modulus. This is preferably done by treating the polyethylene terephthalate under constant length conditions, for example, on a stainless steel bobbin. The following example gives an illustration of this process an also shows the use of this invention at a temperature other than room temperature.

Example V A polyethylene terephthalate yarn was doubledrawn so that it had a final denier of 61 by drawing to 4 times its original length at 85 0., followed by a draw of 1.5 times its original length at 155 C. and had the properties as shown below as control. This yarn was then wound on stainless steel bobbin so that it was held taut at constant length. The yarn on the bobbin was then immersed in a 70% nitric acid solution for a period of 5 minutes at a temperature of 85 C. At the end of this time, it was withdrawn and washed and had the following physical properties:

Additionally, the process of this invention operates to give a resultant structure that, on X-ray analysis, proves to be considerably more crystalline than the untreated control. This is probably due to the fact that nitric acid as a fiber penetrant allows the crystallites in the structure greater freedom of movement. The increased crystallinity is a useful result inasmuch as it represents a more stable configuration. That such an increase does occur is clearly shown by the conventional X-ray diffraction diagrams. Such diagrams show e. g., that the spots in the diagram obtained from crystalline double-drawn polyethylene terephthalate are made narrower by nitric acid relaxation, indicating increased crystallization. At the same time the spots are narrowed, they are lengthened into arcs, which phenomenon corresponds to decreased orientation. 1

Although the invention has been described herein above with specific reference to funicular structures such as filaments, fibers and yarns it is obvious that the novel effects and advantages thereof will pertain as well to other structures 6 such as film, ribbons, rods, etc., of polyethylen terephthalate.

The invention provides an inexpensive method of relaxing large quantities of yarn in a short time, and yield in an economical and simple fashion an extremely tough yarn, which has a relatively high tenacity, an improved work recovery, a high initial tensile modulus, and a high degree of crystallinity.

As many apparent and widely different embodiments can be made without departing from the spirit and scope of this invention it is to be understood that said invention is in no wise restricted except as set forth in the appended claims.

I claim:

1. A method for improving the elongation characteristics of drawn, oriented yarns, filaments, and fibers of polyethylene terephthalate which comprises contacting said structures with an aqueous nitric acid solution at a temperature of from 0 C. to C. until structures of the desired elongation and tenacity are obtained and thereafter washing said structures and drying same, whereby to produce drawn structures hav- (ing increased elongation.

2. .A method for improving the elongation characteristics of drawn, oriented yarns, filaments, and fibers of polyethylene terephthalate which comprises relaxing said structures in an aqueous nitric acid solution at a temperature of from 0 C. to 95 C. until structures of the desired elongation and tenacity are obtained and thereafter washing said structures and drying same, whereby to produce drawn structures having increased elongation.

3. A method for improving the elongation characteristics of drawn, oriented yarns, filaments, and fibers of polyethylene terephthalate which comprises relaxing said structures in a 50-80% nitric acid solution for 10 seconds to 40 minutes at room temperature.

LEONARD EDWARD AMBORSKI.

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

UNITED STATES PATENTS Number Name Date 2,465,319 Whinfield et a1. Mar. 22, 1949 FOREIGN PATENTS Number Country Date 610,135 Great Britain Oct. 12, 1948

Claims

1. A METHOD FOR IMPROVING THE ELONGATION CHARACTERISTICS OF DRAWN, ORIENTED YARNS, FILAMENTS AND FIBERS OF POLYETHYLENE TEREPHTHALATE WHICH COMPRISES CONTACTING SAID STRUCTURES WITH AN AQUEOUS NITRIC ACID SOLUTION AT A TEMPERATURE OF FROM 0* C. TO 95* C. UNTIL STRUCTURES OF THE DESIRED ELONGATION AND TENACITY ARE OBTAINING AND THEREAFTER WASHING SAID STRUCTURES AND DRYING SAME, WHEREBY TO PRODUCE DRAWN STRUCTURES HAVING INCREASED ELONGATION.