US2580491A - Reducing the crystallinity of native fibrous cellulosic material - Google Patents

Description

Patented Jan. 1, 1952 REDUCING THE CRYSTALLINITY OF NATIVE FIBROUS CELLULOSIC MATERIAL Kyle Ward, Jr., and Carl M. Conrad, New Orleans, and Leon Segal, Metairie, La., assignors to the United States of America as represented by the Secretary of Agriculture No Drawing. Application August 8, 1950,

Serial No. 178,339 r Claims. (Cl. 260--212) (Granted under the act of March 3, 1883, as

, l 1 The invention herein described may be manufactured and used by or for the Government of the United States of America for governmental purposes throughout the world, without the payment to us of 'any royalty thereon.

- This invention relates to native fibrous cellulosi'c material, in particular cotton, linen, ramie, and other vegetable fibrous materials, in which the crystal form of cellulose I (native cellulose), as well as the fibrous structure, of the original native material is retained but in which the degree'of crystallinity is reduced.

The objects of the present invention are, first, to provide a fibrous cellulosic material, such as cotton, in-which the original high degree of crystallinityof 85-80% has been reduced to varying and controllable degrees down to as low as" about and where such reduction has been retained to a greater or less degree after completionof the treatments necessary to accomplish the reduction; second, to prepare this cellulosic material of low crystallinity in a manner such that there is substantially no chemical degradation and substantially no loss or impairment of the fibrous structure; and third, to prepare this cellulosic material of low crystallinity without changing the crystal form from that of celluloseI (native 'cellulose) ,For an understanding of the present invention, an exposition .of the present view of cellulose, as it occurs in nature, especially in the vegetable fibers, is pertinent; Such cellulose is considered to be composed of two modifications, or phases. One of these is the dense crystalline ,phase, giving rise to characteristic X-ray diffraction patterns, and believed to consist of minute fibrous crystals, composed of many parallel cellulpse molecules,Qlying side by side, and held together in exact relation by forces known as hydrogen bonds. The crystals are not, in fact. discrete, but are considered to be connected by long cellulose molecules which, in proceeding from one end of the moleculeto the other,fmay pass through a dozen or more crystallites and intercrystalline regions. There is produced,"thus, a discontinuous crystalline structure, held together by the interconnecting, but widely diverging, cellulose chains. The intercrystalllne portions of the cellulose molecules constitute a continuous network, and thus represent the less dense. so-called, amorphous modification or *phase. .Unllkethe" crystalline fraction, thls lat- LtrFphasegjives rise to a broad halo whenirradiated in the X- raybeam,

' One of the principaldrawbac'ks of the native amended April 30, 1928; 370 O. G. 757) cellulosic fibers is their brittleness and tendency to fail when subjected to combined strain and shock. Thus, in spite of the great strength of such cellulosic fibers as fiax and ramie, they have never attained much use in automobile tires and'other mechanical fabrics due to their inability to resist shock. This shortcoming is considered to be associated with the high degree of crystallinity of these fibers, being in the range of 90-95%. Cotton fibers do not show the degree of failure from shock that is shown by the flax, ramie, and other best fibers generally, and

this is believed to be due to the somewhat lower crystallinity of cotton fibers, which vary from -90%. However, it is considered that the crystallinity of cotton fiber, notwithstanding its somewhat lower value, is nevertheless considerably greater than optimum, and that a material improvement would be accomplished by the production of a fiber otherwise the same, but lower in crystallinity.

The crystallinity of cotton fiber, and native cellulosic fibers generally, militates against their maximum usefulness in still another way. The fibers are dense and rather impervious to gases, liquids, reagents, etc. This is manifest in a number of ways. Cotton fibers, together with cellulosic fibers in general, as is well known, are rather poorly sensitive to dyeing, and. must be dyed with certain substantive dyes, i.. e., dyes that will adsorb on cellulose, or with mordant dyes. It is believed that the relatively large dye molecules cannot penetrate the crystalline areas, but only the relatively large areas, crevices, and pores existing in the amorphous areas. Many types of dye molecules being relatively small can pass into the amorphous areas, but due to the open structure, can pass out readily and are not retained on removal of the dye bath and washing. Since the amorphous areas can thus be considered to be the active adsorbing center of the acted in the fibrous condition with such reagents as acetyl, propionyl, butyryl and benzoyl anhydrides; methyl, ethyl, and proplonyl alcohols; and numerous other substances. Forexample,

lthe acetylation reaction, as is well-known, takes place very rapidly up to an extent corresponding approximately to the amount of amorphous cellulose present, and then much more slowly throughout the remainder of the reaction. The interpretation is that the reaction occurs principally in the amorphous areas and perhaps on the surfaces of the crystallites. If the cellulose were first transformed into a product with a high proportion of amorphous cellulose, it is considered that the rate of reaction could be greatly acc'er erated and the cost of manufacture correspondingly reduced.

It is considered, in fact, that all reactions withfibrous cellulose must take place in two ways; first, very rapidly in the accessible, exposed, regions, i. e., in the amorphous areas; and secondly on the surfaces of the crystallites, by a much slower topochemical reaction. The surfaces of the crystallites being necessarily small in comparison with the surfaces exposed by the amor phous regions, it follows that the relative proportion of the latter must be the predominant factor in determining ease and rate of reaction. Any process which generates amorphous cellulose at the expense of the erystalline fraction must facilitate and favor the desired reaction.

In genera according to the present invention, the native fibrous c'ellulosic material, particularly cotton, is treated by immersion in an anhydrous, liquid primary alkylamine containing 1 or 2 carbon atoms preferably primary ethylamine, er in a mixture. of such amines and an anhydrous primary alkyl amineeontaining 6 or '7 carbon atoms, preferably primary hexylamine. A substantial amount of the treating agent is then mechanicallyremoved from the treated material, substantially all of the remaining agent being removed by extraction with a non-polar solvent, such as chloroform, This produces a fibrous ,cellulosic material with crystallinity ranging from about 20% to about 59%, according to the conditions of treatment. Reduction of crystallinity varies with-the time of immersion in the amine, periods of from 4 16 hours resulting in the lowest crystallinity. The physicalcondition of the fiber during tre'atmentis such that handling is not dimcult. There are no visible signs of fiber damage, which fact is verified by the results of accepted tests on the material.

X-ray diffraction patterns of such treated celluloses are those of cellulose I, but; the heights ,of the characteristic. difiraction peaks are much reduced, indicating reduced crystallinitiesin qualitativeagreement with the results of the principal crystallinity determinations used. V Determinations of thechange in the crystallite size. in the treatedcelluloses show that this decreases from about 210 glucose units for the untreatedcotton to about 110 glucose units for the treated cotton. 4 n

Immersion of the treated cellulose in boiling water for as long as 3 hours causes onlya partial restoration of crystallinity provided it has been reduced below that 50%., and with no change in are accepted asindicative of increased amorphous material, i. e., of reducedcrystallinity. V

The results of accepted tensile tests made on yarns and cords show that, first, the breaking strength has not been significantly changed by 4 the treatment; second, the percent elongation.- at-break has been more than doubled thus resulting in nearly doubling the toughness. These efiects are in'agreementwith the concept of re-' duced crystallinity. Determination of twist by an accepted method shows that there has been no significant change in the twist of the yarn by the treatment.

Higher alkyl amines, such as normal hexylamine,.'even though anhydrous when used alone 1 as-the treating-agent, do not reduce crystallinity.

However, these higher amines, particularly primary' hexyl and primary heptylamines, when preceded by a short-chain amine, particularly i anhydrous liquid ethylamine, can efiect a further Varying the proportions will afiect the amount of reduction. Thus, no reduction isiound ifi'th amines. are in the proportions. where the shortchain amine ispresent as 50% or less, .by weight.

Since the short-chain amines-have low boiling points and since a continuous cyclic methodot extraction is' employed to remove from the swollen cellulosic material such mine. as remains after washing with. the. non-polar solvent. 9. means must be provided t6 prevent. them from cycling with the. solvent. A suitable. methodoi' doing. this was to form in the. boiling flask Of the extractor a non-volatile amine salt which may or may not be soluble in the solvent. Aqueous solutions of acidic material are unsuitable since the presenceofwat r is to be avoided';.vo1au1eami substances are to be avoided for reasons obviousto those skilled in, the art; whatever the stance, or substances, there must not bev an adverse reaction withthe solvent. 'Co'ncentrated orthoph'o'sphoric acid plus a small amcunt of phosphoric anhydride was found to be suited fer this purpose. Sulfamic acid can serve the purpose also, but concentrated sulfuric acid not suitable since it reacts adversely with the sol.-

vents. w

The fellowi'ng', exam ies, whicha're not t?) be considered as limitihg illustrate the process of treating the 'enumsm fiber.

EmampZe 1,

Approximateiy 10 g. or bleached cotton fiber, obtained from a cbm'merciai scurce anc cut to short lengths, was immersed overnight at 5 Q. in anhydrous liquid monoethylamine, contained in a screw-cap bottle. No attempt was'made toe-xelude air during the handling or processing. After preliminary removal of the amine bystation, followed by washing and extracting of the remainder with chloroform, the cotton was allowed to dry. The crystallinity of this material was found to be'about 23%. It was stillfibrous and visually apparently undamaged; however", by viscosity measurements it was found to show some chemical degradation which was attributed to alkaline oxidation due to-expo'sure tc'atmoe pheric oxygen. V

I Example 1 1 I About 100 g. of the" out cotton described in Example I was immersed for 4' hoursiin anhydrous, liquid'monoethylamine at 0? Q. contained in a vessel open to the atmosphere. Excess amine 5 was removed by suction. The cotton, still damp with ethylamine, was placed in a large screwcap bottle and then covered with anhydrous normal hexylamine. The bottle and contents were allowed to stand overnight at room temperature. The excess hexylamine was removed by suction, then by washing and extracting with chloroform. No attempts were made to exclude air during the handling and processing. After drying, this material was found to have a crystallinity of about 19%, and was still fibrous and apparently undamaged.

Eaample III Approximately g. of cut cotton as described in Example I was immersed overnight at room temperature in a mixture of amines. The mixture consisted of 75% by weight of anhydrous monoethylamine and by weight of anhydrous normal hexylamine. The cotton and amine mixture was contained in a closed glass jar of sufficient strength to withstand considerable internal pressure. By morning some pressure had developed, evidently from the high content of ethylamine in the mixture, but this was easily vented before attempting to open the jar. The liquid was removed by suction, followed by washing and extracting with chloroform. After drying, the fibrous material was found to have a crystallinity of 50%.

Example IV Approximately 10 g. of cut cotton, as in Example I, was treated exactly as given in Example I, with the exception that normal hexane was used instead of chloroform for washing and ex- 1 tracting the treated material. After air-drying, the crystallinity of the fibrous material was found to'be about 20%.

Example V One pound of raw cotton fiber, in the form of card sliver, was treated with anhydrous ethylamine. Batches of 100 g. each of the sliver, in continuous form, were immersed 4 hours in the anhydrous amine. All operations were carried out under nitrogen, including the first two washings with chloroform to begin removal of the amine. The remainder of the amine was removed by extraction with chloroform. After airdrying, the fiber was found to have a crystallinity of 24%. Critical examination of the fiber revealed that there was very little degradation. The sliver had a harsh hand, due to the removal of the waxes by the treatment.

Example VII The exact treatment as described in Example VI above was repeated on 10 g. skeins of a 20s singles, kier-boiled cotton yarn of loose twist.

After drying, the yarn, of undamaged appearance and slightly harsh hand, had a crystallinity of 31%.

Example VIII The exact treatment described in Example VI above was repeated on 10 g. skeins of the 20s singles yarn. In this case the crystallinity of the extracted, dry yarn was 34%. There was little degradation and only a slightly harsh hand. The yarn was still suitable textile material as evidenced by tensile tests for breaking strength and elongation.

Having described our invention, we claim:

1. A process of reducing the degree of crystallinity of a native fibrous cellulosic material with no substantial chemical degradation and impairment of the fibrous structure comprising immersing the cellulosic material in a liquid treating agent selected from the group consisting of an anhydrous primaryalkylamine containing from 1 to 2 carbon atoms, and a mixture of at least by weight of an anhydrous primary alkylamine containing from 1 to 2 carbon atoms and an anhydrous primary alkylamine containing from 6 to '7 carbon atoms, mechanically separating a substantial amount of the treating agent from the treated material, and separating substantially all of the remaining treating agent by extraction with a non-polar organic solvent.

2. The process of claim 1 in which the treating agent is anhydrous primary metIhylamine.

3. The process of claim 1 in which the treating agent is anhydrous primary ethylamine.

4. The process of claim 1 in which the treating agent is a mixture of at least 50% by weight of an anhydrous primary alkylamine containing from 1 to 2 carbon atoms and an anhydrous primary alkylamine containing from 6 to '7 carbon atoms.

5. The process of claim 1 in which the treating agent is a mixture of at least 50% by weight of anhydrous primary ethylamine and anhydrous primary hexylamine.

6. The process of claim 1 in which the nonpolar solvent is chloroform.

7. The process of claim 2 in which the nonpolar solvent is chloroform.

8. The process of claim 3 in which the nonpolar solvent is chloroform.

9. The process of claim polar solvent is chloroform.

10. The process of claim 5 in which the nonpolar solvent is chloroform.

KYLE WARD, JR. CARL M. CONRAD. LEON SEGAL.

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

UNITED STATES PATENTS 4 in which the non- Number Name Date 2,186,101 Dreyfus Jan. 9, 1940 2,200,452 Kosslinger et al. May 14, 1940 2,218,479 Peterson Oct. 15, 1940 2,270,326 Miller Jan. 20, 1942

Claims (1)

1. A PROCESS OF REDUCING THE DEGREE OF CRYSTALLINITY OF A NATIVE FIBROUS CELLULOSIC MATERIAL WITH NO SUBSTANTIAL CHEMICAL DEGRADATION AND IMPAIRMENT OFF THE FIBROUS STRUCTURE COMPRISING IMMERSING THE CELLULOSIC MATERIAL IN A LIQUID TREATING AGENT SELECTED FROM THE GROUP CONSISTING OF AN ANHYDROUS PRIMARY ALKYLAMINE CONTAINING FROM 1 TO 2 CARBON ATOMS, AND A MIXTURE OF AT LEAST 50% BY WEIGHT OF AN ANHYDROUS PRIMARY ALKYLAMINE CONTAINING FROM 1 TO 2 CARBON ATOMS AND AN ANHYDROUS PRIMARY ALKYLAMINE CONTAINING FROM 6 TO 7 CARBON ATOMS, MECHANICALLY SEPARATING A SUBSTANTIAL AMOUNT OF THE TREATING AGENT FROM THE TREATMENT MATERIAL, AND SEPARATING SUBSTANTIALLY ALL OF THE REMAINING TREATING AGENT BY EXTRACTION WITH A NON-POLAR ORGANIC SOLVENT.