US2428603A - Process for hardening protein fibre - Google Patents

Description

Patented Oct. 7, 1947 curren STATES PATENT OFFICE PROCESS FOR HARDENING PRoTEIN new Francis C larke Atwood, NewtongMassl assignor,

bymesfne assignments, toNational Dairy Broducts Corporation, New York,

tion of Delaware N. Y., a corpora- No Drawing, Application October 29,1941, Serial No. 417,024

Claims. (01. ix-427.6)

used, such as the alkali-dispersible acid-coagulabl'e proteins derived from cotton seeds, castor beans, natural wool, etc. All of such proteins are dispersible in water with an alkaline material and can be formed into fibre by spinning the dispersion into an acidic coagulating bath. All of these proteinsalso are hardened by formaldehyde and are therefore adapted for treatment in accordance with this invention.

The complete process, in which my invention is an improvement, includes the step of dispersing the protein with an alkaline material, preferably caustic, but also including other inorganic alkaline materials, such as bases and alkaline salts, ammonia, organic bases, such as the various amines, soaps and similar alkaline materials. This dispersion is accomplished preferably by heating thetprotein and the alkaline material in a suitable quantity of water to obtain a dispersion of high viscosity. After suitable filtering, centrifuging, cooling and deaerating steps, the dispersion is forced through a spinnerette intoan acidic coagulating bath. The composition of thisbath preferably includes such a portion of acid as to achieve a relatively low pH value preferably generally within the range of .75 to 2.5 and preferably about a valueof 1.50. This bath may also contain a mineral and a vegetable tanning agent such as an alum and Goulac, respectively, and a soluble salt, such as sodium chloride or sulfate, or both, for dehydration. The fibre is p plished in one or more baths containing an alkali metal salt of a strong, m ne-grand, such, as so-drum chloride orfsodiumfsulfate, a riiin'eral hardening agent such asalum, and formaldehyde in solution. The composition jofsuch 'a,'ba th or baths may Vary over relatively wide lirnit s It is poss'ible, for example, to useiaplurality of. baths in which the first contains a relatively smaller proportion of formaldehyde or none fatall, and a higher proportion of salt, with for. withoutfan alum. such a. bath acts .pnmaniygas ahyiiertonic solution andca'uses dehydration or sh'rinkmg 'of the bre, butsome haras ing. action may occur depending on thefinclus'ion a damour p cr formaldehyde. A subse qlient bat 1 or'batlis'rnay include a much greater, concentration of v formale dehyde,..for example from .7 to 40%, preferably about to 20%.. These baths may include asalt and also may incl'udef'a'n alum, if desired. The latter is no t so essentialat .thisflaterstag'e. -The salt is preferred in order to maintain the nit-e in a dehydrated condition.

The first bath is referred to as a pickling. particularly it doe s not contain any formalde hyde or contains a small amount such as aco ncentration of under, 5%., The second orsub se quent baths which contain higher concentrations of formaldehyde 'forexeifting a pronounced hard ening action are referred to as hardening baths. One reason forusing two ba'ths instead, of one is occasioned by the fact that water eliminated from the fibre which dilutes the bath, This is undesirable if. the bath is to contain a high percentage.oflformaldehyde. {It is preferable to ha ve the dilution occur in the first bath, and to treat the, relatively, dehydratedfibre with more concentrated formaldehyde. ;l 3 ut asingle bath may be used if .the above disadvantage is of no commercial significance. A, a a V In all of these prior proposals, utilizing one or more baths varying in composition asabove described and for the purposes above mentioned, there has been no attempt insofar as; am aware, to control the pl l value ofthe baths withina range which exerts a maximum hardening action. Particularly is this so inthe case ofthe bath or baths containing a relatively large concentration of formaldehyde in which the primary hardening actionocc'urs. b L; J

It will be appreciated that the fibre being introduced into these baths is in avery. acidic condition because itiis wet withthe coagulating liquid, and eventhough an attempt is made tdiflein vs the acid which genera e thesurface of the fibre, the fibre is permeated with this acid and at a pH approximately that of the coagulating liquid. Since relatively large quantities of fibre are passed continuously through these baths, the baths take on the pH value of the fibre or at least are not of such a composition as to alter appreciably the pH value of the fibre. Experience has shown that under actual manufacturing'conditions the pH value of the formaldehyde hardening bath will vary from 2.45 to 3.17, depending upon the composition of the bath, the amountof fibre that has been treated in the bath, etc. As far. as I am aware, no attempt has been made heretofore to alter the composition of these baths except by varying the salt, alum and formaldehyde content.

Such variations do not result in pH values outside of the range mentioned above. While 'such baths. may have a pH value somewhat higher when ini tially fresh and before any fibre is introduced into H them, they very quickly fall to a pH value within Y the above range as .soon as the acid fibre is introduced into them.

I have discovered that a decidedly superior hardening action is obtained if the pH value of the formaldehyde containing bath, such as the tity of it renders it more easily controlled as to pH value. A bath which contains sufficient formaldehyde to exert an appreciable hardening action is much more difiicult to control as to pH value and has a more pronounced tendency to remain in an acid condition despite attempts to raise the pH value. This phenomenon may pos- 'sibiy be explained by the action of the formaldehyde onthe protein. If it is assumed, as some authorities say, that the formaldehyde acts primarily to block or react with the amino or alkaline groups in the casein or render them inactive, this wouldrender the casein itself more acidic which would tend to maintain the bath in this condition. The maintenance of this pH value may be accomplished in a number of ways. For example, it is possible to add alkaline material directly to the baths, but this has the danger that portions of the solution will have a pH value higher than the remainder of the bath with consequent nonuniformity of the fibre. to circulate continuously the liquid of the baths through a treating chamber to which appropriate amounts of caustic or carbonates may be added so as to keep the pH value at the desired point. In a continuous operation in which the bath is continuously full of fibre passing therethrough,

it 'is not particularly convenient to use this method. This also has the difliculty that such a control is very difficult since it'requires constant analysis, and within this pH range small amounts of caustic may effect an appreciable increase in pHvaluef V r N While any method maybe used for maintaining the pH value within the range above set forth, and preferably at one point, within this range in order that the fibre being processed may be uni form, I prefer to achieve this pH control by means ofa buffering salt in the treating'baths, particularly thebath containing'formaldehyde in a hardfactory results. To this solution is added sodium It may also be possible 4 ening concentration. The buffering salt to be selected will depend somewhat upon the pH value selected.

An alkaline material, such as caustic or soda ash, may be used to raise the pH value to the desired amount, in combination with an appropriate buffering salt to hold the solution at about the pH value achieved by the addition of the al- .kaline material. a

An alkali metal acetate, such as sodium acetate, is very desirable when the pH range is to be maintained in the neighborhood of 4.5 to about 5.5 or possibly 6.0 under certain circumstances.

In an embodiment of my process that is particularly practicalunder present day manufacturing conditions, the pickling solution may comprise an aqueous solution containing 3 to 15%,.

preferably 5 to 10% of a soluble salt, such as sodium sulfate or sodium chloride, or both, formaldehyde in an amount 0 to 5%, preferably 1 to 3%. and sodium acetate and alkaline materials i amounts to achieve and maintain a pH value within the range of 4.5 to 5.2. Thehardening bath may contain formaldehyde in an amount of 5 to 40%. limit are not required, however, for good results, and a range within 7 to 10% is desirable for satisacetate and alkaline materials in such amounts as to achieve and maintain 'a pH value within the range of 4.5 to 5.2. If desired other soluble salts, such as sodium chloride or sodium sulfate or both, may be included, but this is not so essential for a hardening solution, although desirable to maintain the fibre in a dehydrated condition. Alum may also be added but is generally not necessary, V g r When utilizing a higher pH value, this is obtained by the use of, other buffering salts, as is well known in the art; for example, suitable proe portions of citric acid and di-sodium phosphate,

and also suitable proportions of mono-so'dium diacid phosphate and di-sodium mono-acid phosand probably superior resultspas indicated here particularly if a rapid'reaction is de-j inafter, sired.

tained in accordance with my invention,'a fibre prepared in the conventional mannerby hardening it in an ordinary bath containing20% formaldehyde, 5% salt and 5% alum and having a pH value of 1.5, was compared with a fibre hardened in a bath containing 20% formaldehyde and other ingredients similar buthaving the pH value of 6.5. The samples offibre treated in the two harsh and welded together, whereas inthehard whereas the fibre formed in the bath with a higher pH value is more firm and of afib rous nature. These results were checked 'byfcomparing the fibre treated in bathssuch as mentioned above] Concentrations as high as the upper As indicative of the results thatmay be obbut having pH values of 2.7 and 5.7, respectively. The results were quit similar.

As further illustrative, the following example is given with reference to a bath containing a lower concentration of the formaldehyde. A bath containing 7% formaldehyde, 2 /2% salt, 2 /2% alum, and havin a pH value of 3.45 was compared with a similar hardening bath containing the same amount of formaldehyde but buffered to a pH value of 6.56. A comparison of the fibres treated in these two baths shows that in the more acidic bath after one hour treatment, the fibre was brittle and welded together, whereas after hardening in the bath of higher pH value for twenty minutes, a fibre was obtained which was soft, not welded, and readily carded. This indicates that much lower concentrations of formaldehyde may be used upon increasing the pH Value of the formaldehyde bath. In a commercial operation operating at a pH value of 6.0, a formaldehyde concentration of 5% gives excellent results.

As a further example, a hardening bath containing 18% formaldehyde and without any salt or alum was adjusted to a pH value of 3.5; a fibre I treated therein for one hour and dried resulted in a brittle welded mass; a fibre treated in an identical bath but buffered to a pH value of 6 was an excellent fibre in ever respect. This indicates that upon proper control of the pH value, the amount of salt or alum in the hardening bath may be greatly reduced if not entirely eliminated, and the time of reaction may be greatly shortened.

I have also discovered that when utilizing formaldehyde baths in which the pH value is controlled as above noted, that superior results are obtained if the temperature is maintained within relatively critical limits; and also a much more shorter treating operation is required.

While the desirable results in accordance withv my invention may be obtained utilizing a bath at room temperature, providing the treatment is prolonged somewhat, I have ascertained that the maximum speed in hardening and the greatest superiority in the fibre is obtained if a temperature range of from 100 to 125 F., preferably 115 to 120 F.'is maintained in the formaldehyde hardening bath. Investigations indicate that a bath containing 5% formaldehyde buffered to a pH value of 6.0 or 6.5 and at a temperature of 115 to 120 F. gives a satisfactory hardened fibre in 10 to 30 minutes. This is to be compared with the prior art known requirements of from 10 to 12 hours.

I have also discovered that when utilizing a formaldehyde bath maintained at the above pH value and preferably within preferable temperature ranges, that desirable results are obtained with respect to strength and fibre diameter if the fibre is kept at constant length while in the bath or baths so that it is not permitted to shrink, particularly in the case of the hardening bath. This action is referred to more generally as tensioning. While the fibre may actually be elongated during this treatment, it is practical that the fibre, while in the hardening bath, may be suspended between rollers or run in loops between rollers or other suitable means whereby it is maintained at the same length during the treatment in the bath and thus preventing shrinkage. As further illustrative of this aspect of my invention, a fibre which is introduced into an ordinary hardening bath at the rate of 220 feet'p'er minute and permitted to stand in the bath for one hour without being subjected to any tension, would be withdrawn from the bath at the rate of. to feet per minute. This indicates the shrinkage in length of the fibre that takes place during the hardening. If the fibre, while it is in the hardening bath, is maintained at constant length, such as passing it continuously between rollers so as to be in loops of fixed lengths, whereby the continuous strand entering and leaving the hardening bath moves at the same rate, it has been found that the fibre is greatly improved in strength and is of a much smaller desirable diameter. The results are indicated in the following table:

Tension Strength in During Pounds per Hardening Square Inch Diameter Fro-m the above it will be seen that an increase in strength from 15 to 50% is obtained and a reduction in fibre diameter of about 25%.

Throughout this specification I have indicated what I believe to be the upper and lower critical limits of the various factors when such limits are critical for securing the new results in accordance with my invention. I have also included a more limited range which I regard as the optimum conditions either from the commercial standpoint or for securing the most favorable results. The inclusion of a statement of the optimum conditions in order that 'my invention maybe practiced with the greatest benefit and advantage is not intended to be inconsistent with the critical nature of the range over which the new result may be obtained.

Fiber made in accordance with the invention is admirably suited for treatment in subsequent processes such as acylating with ketene or acetic anhydride, deaminizing by nitrous acid, etc.

' It will be obvious that many variations may be made within my invention as outlined above and that various expedients apparent to those skilled in the art may be resorted to for carrying'into effect the invention as described herein. I intend all such equivalents and variations to be included within the scope of my invention.

This application is 'a continuation-in-part of application Serial No. 309,028, filed December 13, 1939, now Patent No. 2,342,994.

Iclaim:

1. In a process of hardening a proteinaceous fibre that ha been formed from an alkali-dispersible acid-coagulable protein by dispersing said protein with an alkaline material and spinning the dispersion into an acidic coagulating bath whereby the fibre is impregnated with the acid in said bath, following which the fibre is stretched; the steps which comprise placing said acid coagulated and stretched fibre in a hardening bath containing formaldehyde, and maintaining the pH value of said bath at not less than 4.5 and not more than '7 .0 during which time the fibre is hardened in said bath.

2. In a process of hardening a proteinaceous fibre that has been formed from an alkali-dispersible acid-coagulable protein by dispersing said protein with an alkaline material, spinning the dispersion into an acidic coagulating bath, and stretching the coagulated fibre; the step which comprises hardening said coagulated and stretched fibre in a formaldehyde hardening bath maintained at a temperature of 100 to 125 F;

and at a pH value of not less than 4.5 and not over 7.0. V r A -3. Ina process of hardening a proteinaceous fibre'that has been formed from an alkali-dispersible acid-coagulable protein by dispersing said protein with an alkaline material, spinning the dispersion into an acidic coagulating'bath, and stretching the coagulated fibre; the step which comprises hardening said coagulated and stretched fibre while maintained against shrinkage in a formaldehyde hardening bathhaving a temperature of 100 to 125 F. and a pH value of not less than 4.5 and not over 7.0.

4.'In a process of hardening a'proteinaceous fibre that has been formed from an alkali-dis! persible acid-coagulable protein by dispersing said protein with an alkaline material, spinning the dispersion into an acidic coagulating bath, and stretching the coagulated fibre; the step which comprises hardenin said coagulated and stretched fibre in a hardening bath containing formaldehyde in a concentration of at least and buffered at a pH value of not less than 4.5 and not over 7.0 by a buffering salt. I

5. In a process of hardening a proteinaceous fibre that has been formed from an alkali-disand stretching the'coagulated fibres; the steps which comprise introducing said coagulated and stretched fibre into a first stage hardening bath containing not more than 5% formaldehyde, and 3 to'15% of an alkali metal salt of a strongmineral acid and'buffered to apH value of not less than'4.5 and not over 7.0 by a buffering saltjand transferring the preliminarily hardened fibre to a second stage hardening bath containing at least 5% formaldehyde and buffered to a pH-value of not less than'4.5 and not over 7.0 by a buffering salt. I 10; In a'process of hardening a proteinaceous fibrethat has, been formed from an alkali-dis- V persible acid-coagulable protein by dispersing said protein with an alkaline material, spinning the dispersion into an acidic coagulating bath, and stretching the coagulated fibre; thesteps which comprise introducing said coagulated and persible acid-coagulable protein by dispersing said protein with an alkaline material, spinning the dispersion into anacidic coagulating bath, and stretchin the coagulated fibre; the step which comprises hardening said coagulated and stretched fibre in a hardening bathcontaining formaldehyde in a concentration of at least 5% and maintained at a pH value of not less than 4.5 and not over 7.0 by the buffering action of sodium acetate included in said bath.

6. In a process of hardening a proteinaceous fibre that has been formed from an alkali-dispersible acid-coagulable protein by dispersing said protein With an alkaline material, spinning the dispersion into an acidic coagulating bath, and stretching the coa'gulatedfibre; the step which comprises hardening said coagulated. and.

stretched fibre in a hardening; bath containing formaldehyde in a concentration of at least 5% and maintained at a temperature of 100120 125 F., and a pH value of not less than 4.5 and not an alkaline material, spinning the dispersion into an acidic coagulating bath, and stretching; the coagulated fibre the step which comprises hardening said fibre while maintaineclragainst shrinkage in a hardening bath containing formaldehyde in a concentration of at least 5% and maintained at a'temperature of 100 to 125 F;, and a'pHvalue of not less than 4.5 and not over 7 .0 by the buffering action of sodium acetateincluded in said bath.

8. In a process of hardening 'a proteinaceous fibre that has been formed from analkali-dise persible acid-coagulable protein by dispersing said protein with an alkaline material, spinning.

I containing not more than 5% formaldehyde, and

3 to 151% of an alkali metal salt of a strong mineral acid, and having a pH value of not less than 14,5 and not over 7 .0; and transferring the prelim inarily hardened fibre to" asecond stagehardeni-ng bath containing atleast 5% formaldehyde stretchedfibre into a first stage hardening bath containing not more than 5% formaldehyde, and

3 to 15% of an alkali metal salt of a strong min and-a pH value of not less than 45 and not over 11. In a process of hardening a casein fibre that has been formed by dispersing said casein with an alkaline material, spinning the dispersion into an acidic coagulating bath, and stretching the coagulated fibre; the steps which comprise introducing said coagulated and stretched fibre into a first stage hardening bath'containing not more than 5% formaldehyde, and 3 .to.15% of an alkalimetal salt of a strong mineral acid; and hav-- V in apH value'of. not less than 4.5- and not'over. 7.0 and transferring the preliminarily har dened fibre to second stage hardening bath con tainingjat least 5% formaldehyde and buffered to a pH value of notless than 4.5 and not over 7.0 by means of sodium acetate.

12. In aprocess of hardening a casein fibre that hasfbeen formed by dispersing said casein with an alkaline material, spinning the dispersion, into an' acidic coagulating bath," and stretching r the coagulated fibrej the steps which comprise introducing said coagulated and stretched fibre into a first stage" hardening bathrcontainingnot more'than 5% formaldehyde, 3 to 15% of sodium chloride,:anol buffered to a pHvalue of not: less than 4L5and not over 7.0 by'sodium acetate, and transferring the preliminarily hardened fibre to a secondstage hardening bath containing at least 5% formaldehydeand maintained at a temperature of 10o to fF. and buffered to apH value of not less than 4.5 and not.over7.0 by means.

of sodium acetate; v

13. In a process of hardeninga has been formed by dispersing said ;'casein with an alkaline material and continuously spinning the dispersion into an acidic coagulating bath 7 whereby the fibreis impregnatediwith the acid in 5 said. bath, following which the'coagulated fibre 'l isstretched; the steps whichcomprise continu-. ously introducing said: acid coagulated iand stretched fibre into a first stage hardening bath containing not more than formaldehyde, 3 to 15% sodium chloride and buffered to a pH value of 4.5 to 5.2 by the inclusion of sodium acetate in said pickling bath and the neutralization of any acid introduced with the fibre into said bath, permitting the fibre to remain in said bath for from 10 to 60 minutes, continuously removing the fibre from said bath and transferring the preliminarily hardened fibre to a second stage hardening bath containing at least 5% formaldehyde, 5 to sodium chloride, and maintained at a temperature of 110 to 125 F. and buifered to a pH value of 4.5 to 5.2 by means of sodium acetate.

14. In a process of hardening a proteinaceous fibre that has been formed from an alkali-dispersible acid-coagulable protein by dispersing said protein with an alkaline material and spinning the dispersion into an acidic coagulating bath whereby the fibre is impregnated with the acid in said bath, following which the coagulated fibre is stretched; the steps which comprise continuously introducing said acid coagulated and stretched fibre into a hardening bath containing formaldehyde and an alklai metal salt of a strong acid, and maintaining the pH value of said lastmentioned bath at not less than 4.5 and not over 7.0 by neutralizing any acid introduced into said bath by said fibre and by incorporating in said bath an alkali metal salt of a weak acid.

15. In a process of hardening a proteinaceous fibre that has been formed from an alkali-dispersible acid-coagulable protein by dispersing said protein with an alkaline material and spinning the dispersion into an acidic coagulating bath whereby the fibre is impregnated with the acid in said bath, following which the coagulated fibre is stretched; the steps which comprise continuously introducing said acid coagulated and stretched fibre into a first stage hardening bath containing a small amount of formaldehyde and alkali metal salt of a strong mineral acid, maintaining the pI-I value of said bath at not less than 4.5 and not over 7.0 by incorporating therein buffering salt and by neutralizing any acid introduced into said bath by said acid coagulated fibre; continuously transferring the fibre to a second stage hardening bath containing at least 5% formaldehyde and an alkali metal salt of a weak acid to maintain said bath buifered to a pH value of not less than 4.5 and not over 7.0.

FRANCIS CLARKE ATWOOD.

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

UNITED STATES PATENTS OTHER REFERENCES Brother and McKinney, Protein Plastics From Soybean Products from Ind. and Eng. Chem, Nov. 1938, pgs. 1236-40.

La processus de durcissement dans ldustrie de la galalithe J. DelormeRev. Gen. Mat. Plastiques, 1936, T. 12, No. 3, pgs. 74-76, Mars. from Chemie and Industrie, Cas. Dig.

Mougeot, Formaldehyde in the Hardening of Casein Objects from Rev. Gen. des Matieres Plastiques, Feb. 1928, vol. 14, No. 2, pages 35-37.

Certificate of Correction Patent No. 2,428,603. October 7, 1947.

FRANCIS CLARKE ATWOOD It is hereby certified that errors appear in the printed specification of the above numbered patent requiring correction as follows: Column 7, line 56, claim 7, after the word said insert coagulated and stretched; column 8, line 48, claim 11, for "to second read to a second; column 9, line 25, claim 14, for alklai read alkali; column 9, line 15, beginning with In a process strike out all to and including the Word and period acid. in line 30, comprising claim 14, and insert the same after claim 1, as claim 2; same column, line 31, beginning with In a process strike out all to and including the numeral and period 7.0. in column 10, line 9, comprising claim 15, and insert the same after claim 8, as claim 10; and for the claim numbers 2, 3, 4, 5, 6, "7", 8, 9, 10, 11, '12, and 13, read 3, 4, 5,6, 7', 8, 9, 11, 12, 13, 14, and 15, respectively; and that the said Letters Patent should be read with these corrections therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 27th day of January, A. D. 1948.

THOMAS F. MURPHY,

Auistant oommiasiogwr of Patenta.