US2029481A - Esterification of cellulosic materials - Google Patents

Description

Patented Feb. 4, 1936 UNITED STATES PATENT OFFICE ESTERIFICATION OF CELLULOSIC MATERIALS No Drawing. Application March 29, 1933, Serial No. 668,372

11 Claims.

This invention relates to methods of manufacturing things from cellulose. The invention also relates to new compositions of matter. The invention also relates to new processes of esteriiying cellulose. The invention particularly relates to the improvement of formed cellulosic articles without making substantial changes in their appearance. The invention also relates particularly to cellulose acetate thread and/or fibers having weaving and fabricating properties approximately equal to regenerated cellulose thread and/or fibers. The invention will be described in part in its application to certain manuiacturing processes but the particular descriptions are given for purposes of facility only and do not limit the scope of the invention.

Regenerated cellulose, when wet or moist or when subjected to changes in atmospheric humidity, tends to stretch or to deform and suffers a decrease in strength. As 'a result of this property filaments or fabrics made from this material are sometimes damaged in laundering, pellicles of regenerated cellulose swell and are distorted by contact with water or by changes in humidity, lessening their usefulness for wrapping purposes, and regenerated cellulose articles which have been wet andhave been allowed to dry while not under tension do not dry flat. While these qualities in no wise balance the good qualities of regenerated cellulose, they are undoubtedly detrimental.

The word spinning originally meant the twisting of short fibers to form a thread. It was accomplished by the spinning wheel and its equivalents. More recently the word has also come to mean the formation of an artificial thread by the extrusion of a cellulose solution, such as viscose, through an orifice into a precipitatng bath. This chemical process is spinning only in the sense that a thread is formed. Fibers produced from cellulose acetate and from viscose are sometimes spun (in the original meaning) into thread, but these two types of fiber diler greatly intheir spinning qualities. The

cellulose acetate fibers are so slick that theyare spun into thread only with difliculty, and are apt to produce a thread of inferior strength, whereas regenerated cellulose fibers have excellent spinning qualities. When usedii'n knitted or wov n fabric c llulose ace a fi ame ts ten be cause of their slickness, to impair the value of w the fabric by slipping out of position, which is not true of regenerated cellulose threads. Various treatments have been applied to cellulose acetate thread, fibers, and fabrics to overcome this difficulty; roughening agents have been used on the surface of the filaments, pigments have been included in or on the filaments, and the fibers of the completed fabric have been swollen by means of solvents to superficially Weld them into position, but each of these expedients modifies the thread, and none of them is entirely satisfactory.

It is an object of the invention to produce pellicles, filaments, molded articles, and fabrics which shall be resistant to the action of water or water vapors while maintaining the pleasing appearance of similar prior art materials. Another object of the invention is to produce cellulosic filments and threads whose ratio of wet strength to dry strength is increased while the appearance remains substantially unchanged. It is another object of the invention to produce new compositions of matter. It is another object of the invention to produce new esters of 2 cellulose. It is another object of the invention to prepare articles of an alkyl or aryl acid ester or esters of cellulose without forming an ester solution. It is another object of the invention to manufacture such esters substantially without degradation of thecellulose. Another object of the invention is to produce cellulose esters which are not soluble in the usual solvents for prior art esters of equal degrees of esterification. Another object of the invention is to produce cellulose esters in any form, including filaments,

.pellicles, fabrics, and molded articles containing any desired degree of acyl content, to do this directly without putting the ester in solution, and to do it by going directly to the desired percentage 0 of esterification, omitting the necessity of completely esterifying and thereafter breaking down the ester. Another object of the invention is to produce a material having the appearance but not the dyeing properties of regenerated cellulose. Another object of the invention is to prepare ,a cellulose ester thread, particularly a cellulose acetate thread, having spinning and .weaving properties approximately equal to the spinning and weaving properties of regenerated cellulose.

Other objects of the invention are in part apparent and in part set forth elsewhere herein.

The objects of the invention are attained, generally speaking, by making from cellulose hydrate, cellulose, or a lowly esterified cellulose ester or lowly etherified cellulose ether an object in the desired form and of the desired appearance,

and by acting upon this object with a bath containing an arylor alkyl monocarboxylic acid an hydride, a tertiary amine hydrohalide which remains substantially constant in quantity throughout the reaction, and suflicient pyridine or hydrohalide acid in excess of that needed to make the pyridine hydrohalide to make the active ingredients of the bath from slightly acid to someby the means, methods, and products herein described.

The following examples .serve only to illustrate the invention.

Example I A viscose solution was extruded through an orifice, passed through a coagulating bath, was regenerated, desulfured, bleached, and washed free from acid and, without drying, was passed through several changes of glacial acetic acid to displace the water present. The dehydrated pellicle was immersed in about 100 times its own dry weight of a bath of the following composition and was left for twenty-four hours at 35 0.:

Parts Pyridine hydrochloride 15 Pyridine 5 Acetic anhydride 25 Glacial acetic acid as a diluent '55 In this example and in those that follow the proportions are given by weight.

At the end of the treating time the material was removed from the bath, washed free of bath liquor, and dried. Analysis showed the material to have an acetyl content of 25% (35% calculated as acetic acid) of the weight of the finished pel- The material was much more resistant to' licle. changes in humidity and to wetting than the usual regenerated cellulose pellicle and deformed much less under this treatment; the presence of a plasticizer in the pellicle improved its softness and pliability and made it more suitable for use as a wrapping material; the usual softeners for cellulose acetate proved satisfactory as plasti-- cizers for the new material and could be introduced into the pellicle either before or after drying; the softened pellicles of the new material were softer and more pliable than pellicles ,of

straight regenerated cellulose impregnated with the same plasticizers. The new material was not dissolved bychloroform, acetone, or acetic acid and was consequently-more suitable than ordinary cellulose acetate for purposes which require contact with the usual cellulose acetate solvents. The new material did not take the direct dyes used for native or regenerated cellulose, but took many of the dyes used for cellulose esters, such as cellulose acetate. The new ma e al had a higher dielectric value than regenerated cellulose pellicles, took a static electrical charge more readily and, consequently, will find use in electrical insulators and condensers. The new material did not fuse at as low a temperature as prior art cellulose acetate pellicles having a corresponding acyl content.

Example If A regenerated cellulose pellicle after coagulation, regeneration, desulfuring, bleaching, and washing free from acid, as in Example I, was

soaked in several changes of glacial acetic acid to displace the water present, and was immersed in about 100 times its own dry weight of an acid bath of the following composition, heated to a temperature of 45 C.

' Parts Pyridine hydrochloride 15.00 Glacial acetic acid 59. Acetic anhydride 25.00 Hydrogen chloride 0.35

At the end of twelve hours the pellicle was removed, washed in water, and dried. It had an acetyl content of 37% (52% calculated as aceticacid) on the basis of the dry weight of the finished pellicle. The dried pjellicle was more resistant to the changes induced by wetting by water, water vapor, or by humidity changes than regenerated cellulose, and than the products of Example I, had electrical insulating properties superior even to those of the product of Example I, was even more compatible with the softeners for ordinary'cellulose acetate than were the products of Example I, was insoluble in chloroform, acetone, acetic acid, and other ordinary solvents for the prior art cellulose esters; and did not take the direct dyes used for native or regenerated cellulose, but was dyed by the dyes used for cellulose esters, such as the dyes used for cellulose acetate.

Its valuable properties make this material of reat value where a nondeforming pellicle is desirable, as wrapping materials and for uses which require greater resistance to solubility than prior 'art cellulose esters possessed.

Example III A pellicle of regenerated cellulose after coagulation, regeneration, desulfuring, bleaching, and washing free from treating liquids was soaked in several changes of glacial acetic acid to displace the water. present, and the dehydrated pellicle was immersed in approximately 100 times its own dry weight of a bath of the following composition I Parts Pyridine hydrochloride 15 Pyridine 5 Glacial acetic acid 5 Acetic anhydride At the end of 48 hours the pellicle was removed, washed first in glacial acetic acid, then in water and dried. It had an acetyl content of 37% (52% calculated as acetic acid) based on the weight of the dry finished pellicle. The acetyl content of the pellicle produced in this example and its properties were found to correspond with those of the product of Example II. It was insoluble in chloroform, acetone, and acetic acid.

Example IV Pellicles of regenerated cellulose after coagulation, regeneration, desulfuring, bleaching, and

washing free from acid, and which were not subwater present.

jected to drying, were soaked in several changes of glacial acetic acid to displace the water present. The dehydrated pellicles were immersed in about 100 times their own dry weight of a bathhaving the following composition:

Parts Pyridine hydrochloride 15 Pyridine Glacial acetic acid 5 Acetic anhydride 75 for approximately one hour at room temperature in order to allow the pellicles to become thorough- 1y impregnated with the bath, after which they were removed and placed while still wet with adhering reagents, in a sealed container which was kept at 35 C. for 120 hours. The pellicles were removed, washed with glacial acetic acid, and then with water and dried. 1

The pellicles had an acetyl content of 36% (51% calculated as acetic acid) based on the dry weight of the finished pellicles. The pellicles produced in this example contained an acetyl content very close to that of the pellicles produced in Examples II and III, and had corresponding properties. They were insoluble in the usual solvents for prior art cellulose acetates of equal esterification.

Example V Regenerated cellulose bottle caps were coagulated, regenerated, desulfured, bleached, washed free of treating fluids and were soaked in several changes of glacial acetic acid to displace the These dehydrated caps were immersed in about 100 times their own dry weight of a neutral bath of the following composition at 65 (3.:

Parts Pyridine hydrochloride 16.6 Acetic anhydride 77.8 Acetic acid; 5.6

At the end of 72 hours-the caps were removed, and Washed in water. The caps had an acetyl content of 41% (57% calculated as acetic acid) on the basis of the weight of the caps when dried. When dried over the necks of bottles, the caps shrank and clung tightly and immersion in water failed to swell them enough to make them come ofi; they shrank more than prior art cellulose acetate caps; they were insoluble in the usual solvents for prior art cellulose acetate of equal esterification including chloroform, acetic acid, or acetone; they did not take the direct dyes which are used for native or regenerated cellulosic materials, but were dyed by the dyes used for the cellulose esters, including dyes for cellulose acetate.

Pellicles of this new material in the form of caps and hands because of their water resistance are suitable as caps on milk bottles which are packed in ice or come in con act with water, and because of their comparative insolubility are suitable as caps on bottles which contain liquids, or which are exposed to liquids, which are solvents for the usual cellulose acetates.

Example VI Regenerated cellulose pellicles (in cap form) were coagulated, regenerated, desulfured,

bleached, washed free from treating liquids withwater, were soaked in several changes of glacial acetic acid to displace the water, and were immersed in aboutlOO times their own dry weight of a bath of the following composition at 35 C.:

Parts Acetone 50 Pyridine hydrochloride Acetic anhydride Pyridine 5 Glacial acetic acid 5 At the end of 72 hours the pellicles were removed, washed in water, and analyzed; they had an acetyl content of 25% calculated as acetic acid) based on the weight of the finished pellicle when dried. They were compatible with cellulose acetate plasticizers, contracted similarly to prior art caps when placed wet over bottle openings and allowed to dry but, once dried, did not wet up or swell readily in Water. The new pellicles are not soluble in the usual solvents for cellulose acetate, and are satisfactory for capping bottles which contain liquids or are exposed to liquids which dissolve the usual cellulose acetates. For example, they may be satisfactorily used as caps on bottles containing cosmetics, pharmaceutical preparations and the like even when solvents for the older cellulose acetates are present. They do not take the direct dyes which are used for native or regenerated cellulosic materials, but are dyed by the dyes for cellulose esters, including dyes for cellulose acetate.

Example VII Viscose rayon threads were coagulated, regenerated, desulfured, washed free from treating liq- I nor with water, steeped in several changes of glacial acetic acid to-remove the water present, and immersed in a bath at room temperature which has been prepared by mixing parts acetyl chloride, 77 parts glacial acetic acid, and 123 parts amyl acetate, and parts of pyridine added while stirring. At the end of 48 hours the rayon was removed, washed with methyl alcohol, dried, and analyzed. It proved to be a cellulose acetate thread containing 37% acetyl (52% calculated as acetic acid) on the basis of the weight of the finished thread. It did not take the direct dyes used for native or regenerated cellulosic materials, but was dyed by the cellulose ester dyes such as are used for cellulose acetate; it had the same appearance as rayon threads which were not subjected to the action of the acetylating bath; it was not soluble in the usual solvents for the prior art cellulose acetates; it did not fuse at as low a temperature as prior art cellulose acetates of identical esterification; it possessed better electrical insulating properties than the prior art threads; it .had a better wet-dry strength ratio and was more resistant to damage on handling while wet, than regenerated cellulose thread.

,Because of its valuable dyeing properties this thread can be used in the production of effects in fabrics: When knitted with prior art threads of identical appearance into a fabric and dyed, first by a dye for regenerated cellulose and afterwards by a dye for cellulose acetate, remarkable two-color effects may be produced, the prior art threads taking the first dye but not the second and vice versa. Fabrics woven or knitted from such threads resist damage from the solvents or heat used in dry cleaning or laundering better than do similar fabrics made from ordinary cellu lose acetate threads, and by reason of their insulating properties are suitable as cable wrappings or electrical appliance cord coverings.

' erings, their better strengthwhen wet making I Example VIII Thread was coagulated from viscose, regenerated, desuliured, and washed free from treating liquids with water. Some of it was dried and reserved for subsequent testing, and some of it without drying was steeped in several changes of glacial acetic acid to remove the water present, and treated at 100 C. in a hath made up of 5 parts acetyl' chloride, parts glacial acetic acid, and 6 parts pyridine. At the end of three hours the rayon was washed with water, and dried under tension. The product was a lustrous thread containing 26% acetyl, based on the weight of the finished thread. This thread was compared with that dried and reserved for testing and was found to have a better dry tenacity per denier and a wet tenacity per denier about 20% better. The treated thread showed the crenelated cross section of the original viscose rayon and was immune to direct dyes. When dyed with acetate dyes, it took the dyes more readily than prior art commercial acetate thread of equal esterification.

The new threads are suitable for use alone or for use in the production of tone efiects by cross dyeing in woven or knitted textile materials as described in Example VII. Garments woven or knitted from these threads, due to their increased wet strength, are more resistant to damage when wet, as when laundered, than non-acetylated threads. The threads are useful as umbrella covthem more satisfactory than regenerated cellulose. The threads are insoluble in the usual solvents for the ordinary types of cellulose acetate, and garments or articles made from them are more resistant to damage by cleaning fluids than garments made from prior art cellulose ester threads. The new threads do not fuse at as low a temperature as the correspondingly esterified ordinary cellulose acetate threads, and garments or articles woven or knitted from such threads are more resistant to damage in pressing, ironing or laundering. The new threads possess electrical insulating properties superior to those of regenerated cellulose and are more suitable for wrapping electric cord and other electrical insulating purposes.

Example IX drogen chloride. The product was removed from.

the'bath, washed with water and dried. It had a propionyl content of 24.9% based on the weight of the finished staple, possessed a greater wetdry strength ratio than the dried unacylated fibers, possessed better electrical insulating properties than the untreated fibers, did not dye with the direct dyes used for native or regenerated cellulose, but was dyed by the dyes used for cellulose acetate and similar cellulose esters, was insoluble in the usual solvents for the ordinary types of cellulose acetate, and fused at higher temperatures than prior art cellulose acetate fibers having a corresponding acetyl content.

- Fabrics made from threads spun from this fiber are more resistant to damage when wet, as

" in laundering or in umbrella fabrics, than the untreated fibers, are more valuable in the manufacture of electrical insulating mediums for example in the threads of coverings on electrical lamp cords, and in the construction of cables. The new staple fibers may be used in the manufacturing of threads to be used in, woven or knitted fabrics, and, by combining them with fibers which take a difierent dye, can be used to produce excellent color effects. Threads spun from these fibers, or fabrics woven from these threads, prove to be more resistant to damage from the solvent 'used in dry cleaning than similar threads or fabrics. made from prior art cellulose acetates of equal esterification and threads spun, or fabrics manufactured from them are more resistant to damage by heat.

Example X Thirty parts of finished staple fiber, which after coagulationhad been washed free of acid and subjected to drying, were steeped for 12 to 15 hours in glacial acetic acid and then the staple was drained of all but three times its weight of acid. The staple fiber swollen by acetic acid was then placed in a bath consisting of:

- I Parts Acetic anhydride 114 Glacial acetic acid 108 Pyridine hydrochloride 65 Free pyridine 1'7 The bath was heated at 85 C. for ten hours,

was allowed to cool to room temperature, and was drained off. The staple fiber was washed free of any trace of the acetylating bath, subjected to a finishing treatment, and dried. The finishing treatment may be one of soaps, sulfonated oils, or other materials used on textiles to produce a good feel or hand and is not essential. The staple fiber was apparently cellulose acetate and had an acetyl content of 34.8% (48.5% acetic acid). Quantities of this fiber, examined under a microscope, showed crenulations in kind and number corresponding to the crenulations of regenerated cellulose fiber.

Example XI Twenty-five parts of staple-fiber in the gel condition were steeped in glacial acetic acid to remove the water present, the excess acid was 'drainedofi and the staple was swollen by acetic acid and was placed in an acetylating bath consisting of 250 parts acetic anhydride, 200 parts glacial acetic acid, 48.5 parts pyridine hydrochloride,,and 1 part free pyridine. The mixture was heated at 70 C. for three hours, the staple was removed from the bath, washed free of acid, and dried. The acetyl content of the finished staple was 26% (36.3% acetic acid). Quantities of this fiber, examined under a microscope, showed crenulations in kind and number corresponding to the crenulations of regenerated cellulose fiber.

Example XII Cotton gauze was pretreated by steeping in 19% sodium hydroxide, washed free from sodium hydroxide with warm water, dehydrated in glacial acetic acid, and treated at 70 C. in a hath made by mixing 25 parts acetic anhydride, 20 parts glacial acetic acid, 9 parts benzoyl chloride and 6 parts pyridine. This bath contained essentially acetic and benzoic anhydrides, and/or .the mixed anhydride of acetic and benzoic acids, since in the presence of pyridine the benzoylchloride reacts with acetic acid to form the mixed anhy- 8 hours.

dride and pyridine hydrochloride. At the end of 21 hours the cloth was removed from the bath, washed with water and dried. The product was an acetylated cellulose containing 22% acetyl, based on the weight of the finished gauze, was insoluble in chloroform, acetic acid, or acetone, the usual solvents for prior art cellulose acetate containing a corresponding amount of acetyl, did not fuse at as low a temperature as the ordinary cellulose acetates having a corresponding acetyl content, was not dyed by the direct dyes used for regenerated or native cellulose, but wasdyed by the dyes for cellulose esters, such as for cellulose acetate, did not wet as readily in water as the untreated cloth, and possessed electrical insulating properties superior to those of untreated cotton cloth. It finds a valuable use in the fabrication of synthetic resin-impregnated cloths for insulating purposes.

Example XIII The mixture is warmed at 100 C. until the fibers are highly swollen. This should require about The bath is filtered off, the fibers washed with alcohol, and dried. The dried material is a fibrous cellulose stearate insoluble in organic solvents.

Y Example XIV The procedure was the same as in Example XIII, except that there was used 20 parts of benzoicacid instead of 47 parts of stearic acid. The time of heating was somewhat longer, about 16 hours yielding a suitable product. The product was a fibrous cellulose benzoate insoluble in ordinary ester solvents.

The homologs of benzoic acid, the other acids of the monobasic aromatic series, including toluic acid and ethyl benzoic acid, can be used in place of benzoic acid with equally good results,

desired. The prior art methods of esterification were accompanied by severe degradation of the cellulose, and yielded products soluble in chloroform, acetone, acetic acid, or even less powerful solvents. Our process produces a product insoluble in these solvents.

In Examples XII and XIII and in other examplesare disclosed new filaments which are substantially cellulose acetate (or which by the use of proper reagents may be any other cellulose ester) and which have spinning and weaving properties substantially equal to the spinning and weaving properties of regenerated cellulose filaments. We; believe that cellulose acetate filaments having these properties are entirely unknown to the art. When examined under a high powered microscope a cross-section of prior art cellulose acetate filaments shows only a few crenulations running longitudinally of the filament. By this is not meant that some cellulose acetate filaments selected from a large number of prior art cellulose acetate filaments would not have a relatively large number of crenulations but that the average number of crenulations per filament is low compared to regenerated cellulose filaments. Furthermore, the crenulations of cellulose acetate filaments were more or less smooth and large curved. On the other hand the average crenulations per filament of, for instance, a regenerated cellulose filament made by the regeneration of viscose is comparatively high, the crenulations are small and the curves rough and sharp compared .to crenulations of cellulose acetate. Comparatively speaking, consequently, the regenerated cellulose filament is rough and the cellulose acetate filament is smooth. In spinning, consequently, the rough regenerated cellulose fiber spins easily and makes a closely knit thread while the cellulose acetate thread spins only with difficulty and tends to slip with respect to associated fibers. By our invention we have been able to produce a cellulose acetate (or other cellulose ester) fiber having crenulations on the average approximately equal to the average crenulations found in regenerated cellulose thread.

In the new process we prefer to use as the raw material regenerated cellulose in any form and without regard to the process by which made, or cellulose, or a lowly esterified or etherified cellulose. The meaning of the term lowly esterified or etherifiedcelluose varies somewhat with the particular acyl group involved, as will be understood by any chemists, but can be comprehended by a reference to a specific example. In cellulose acetates, for instance, a lowly esterified cellulose would be one corresponding very roughly to a mono-acetate. Many of the advantages of the invention can be obtained by using materials which are somewhat more highly esterified than a monoacetate, but it will be obvious to all persons skilled in chemistry that the more highly esterified is the cellulosic raw material the less opportunity there is for our esterifying bath to perform its function, and the more opportunity there has been for prior treatments to degrade the cellulose and form an inherently soluble product.

The raw cellulosic material with which we start is treated in our process in an esterifying bath which contains an anhydride of alkyl or aryl monocarboxylic acid or a mixed anhydride of aryl or alkyl acids or a mixed anhydride of acids of either class or a mixture of different anhydrides.- The majority of examples directed to the aliphatic acids refer to acetic acid because cellulose acetate is now of commercial interest and We wish to illustrate the manipulation of the process in regard to it, but examples have been included to illustrate the manipulation of the process with the higher members of the aliphatic monocarboxylic acid series and its manipulation with the aryl monocarboxylic acids. The

bath also contains as a catalyst a tertiary amine hydrohalide such as pyridine hydrochloride,

pyridine hydrobromide, or a hydrohalide of a pyridine homolog, such as picoline, lutidine, and quinoline. The cyclic tertiary amine hydrohalides are preferred to other tertiary amine hydrohalides although hydrohalides of a tertiary amine such as triethyl amine, tributyl amine and dimethyl aniline are useful in our process. A particular feature of our process is that the amount of catalyst present is kept substantially constant throughout the reaction. In the reaction bath there may also be either a quantity of pyridine which serves particularly as an acid buifer or a quantity of hydrogen halide. It is our discovery that the reaction proceeds with great efilciency when the active ingredients (which are usually the ingredients other than the diluent) have a reaction which may vary from slightly acidic (due to the presence of halogen acid in excess of that needed to form pyridine hydrohalide with the pyridine present) to rather strongly basic (due to the presence of an excess of pyridine over that needed to form pyridine hydrohalide with the halogen acid present). Thus, in Example I isdescribed a bath whose active ingredients are basic; in Example II is described a bath whose active ingredients are slightly acid; in Example III is described a bath whose active ingredients are neutral.

We have found that the action of pyridine hydrochloride in the esterification of cellulose by means of organic acid anhydrides may be divided into three parts: First, it is strongly adsorbed and causes the cellulose to swell markedly and in swelling to absorb the organic acid anhydride uniformly, with resulting uniform esterification. Second, it exerts a true catalytic action on the esterification, for which action only relatively small amounts are necessary. We have found, for example, that the amount of acyl introduced in a given time is practically as great when the ratio of cellulose to pyridine hydrochloride is 50:1 as it is when the ratio is 1:1, prpvided the cellulose is initially sufiiciently swollen to insure even penetration of the reagents. solubilizing or degrading one. ='I'he latter action is relatively slow but, we have discovered, proceeds with marked increase in velocity at the higher temperatures. We have applied these discoveries by using a comparatively small amount of pyridine hydrochloride, by keeping the quantity of the catalyst constant throughout the reaction, and by operating at relatively low temperatures. By these means the catalytic effect of pyridine hydrochloride, which is efiicient but mild compared to sulfuric acid, zinc chloride orsimilar catalysts, can be obtained without inducing any substantial degradation of either the raw material or the product, and uniform esterification is secured throughout the entire mass of the cellulosic material even to the extent of converting the raw material completely to a triester. without producing a soluble product.

In making an esterification bath containing pyridine hydrochloride or other tertiary amine hydrohalide it may be difiicult to bring exactly 'equimolecular amounts of pyridine and hydrogen chloride into combination but this is not undesirable because to have in the bath either an excess of pyridine or a small excess of hydrogen halide over that required for the formation of pyridine hydrohalide furnishes a means of aifecting the speed and energy of the reaction. A large excess of pyridine is less detrimental than a considerable excess of hydrogen chloride, but

large excesses of either of these compounds, and

particularly of the acid, may tend to produce a degraded product which is not completely insoluble in the usual organic solvents. To obtain the most insoluble products the reaction bath should contain about 1% or less excess hydrogen chloride (based on the weight of the bath), although flve and under certain conditions even ten percent excess acid have sometimes been successfully used.

The third action is a- There is a greater permissible latitude within which this process may be carried out on the basicside than there is on the acid side. The

presenceof uncombined pyridine in reasonable excess (above that required for the making of the pyridine hydrohalide) does not substantially afiect the solubility or properties of the products. Even relatively large quantities of uncombined excess pyridine may be used advantageously without seriously afiecting the nature of the products and, when present, tend to increase the rateof esterification. An advantageous amount of excess pyridine, economy also being considered, has been found to be between 5 and 10% of the weight of the bath, although excesses up to 30%, or even 50% are sometimes employed.

If insoluble, esterified, cellulosic products in the same physical form as the starting material are to be obtained, it is advantageous to keep within the indicated approximate limits of excess base or excess acid. More precise directions as to the exact'and specific proportions or quantities which should be used need not be given for the reason that this invention applies to a large number of difierent reactions whose optimum operating conditions and whose variations can be determined with ease by any chemist. To a person skilled in the art the method of determining the best operating conditions will be apparent and obvious under the above disclosures.

Practically any of the common diluents may be used in the reaction mixture of our process, and a number of materials may be used as diluents which in prior art processes would completely dissolvev the product and which are in fact accepted as the standard by which the solubility of the various types of cellulose acetate'or other cellulose esters may be judged. Among the ordinary diluents which are useful are benzene, toluene, dioxan, chlorobenzene, amyl acetate, and

ethers, and among the extraordinary diluents though esterification has proceeded (in the case,

for instance of cellulose acetate as far as the tri-ester) to the limit ofpossibility. When it is desired to operate at temperatures above 100 C. the choice of diluents becomes more limited and those with higher boiling points, such as kerosene and other non-solvent hydrocarbon diluents, are advantageous.

The acidity or basicity of the diluent appears to have no substantial effect upon the reaction.

The presence of a diluent does not appear to materially affect the rate of esterification- (except in the case of acetic acid which slows the reaction down somewhat) other than by the dilution effect. 7 The temperature of the bath afiects the rate of esterification, an increase in temperature of 10 C. approximately doubling the rate. With an increase in the temperature, the solubilizing action of the bath upon the cellulosic material is increased to a greater extent than the rate of esterification. Hence, in order to avoid destroying the form of the cellulosic materials and in order to form insoluble end products, it is advantageous to carry out the treatment at as low a temperature in their action by the use of a basic and diluted bath.

The operating conditions of the process may be varied by the chemist to suit the needs of the moment. For instance, if it is desired to prolong the time of reaction, or if the reaction is to be carried out at a relatively high temperature, it is advantageous to use smaller excesses of hydrogen-chloride, or better, to react with a neutral bath or with a bath having an excess of pyridine. On the other hand, if the temperature is to be low, and/or if the time of the reaction is to be shortened, large excesses of pyridine may be employed, or the reaction may be carried out on the acid side, but extremely large excesses of pyridine are to be avoided under extreme conditions of esterification, such as high temperature and long time.

, In carrying out this treatment of cellulosic materials two general methods are applicable. It is convenient in some instances to simply immerse the cellulosic material in the esterification bath for the desired time period at the desired temperature. The esterification can also be carried out by impregnating the material with the bath, or by soaking the material in the bath, and allowing the esterification to proceed for the time period and at the temperature desired while not actually immersed in the bath but while placed in a closed container which prevents the liquid carried by the material from being lost. For example, flat regenerated cellulose pellicles may be impregnated and stored in a roll until the reaction is completed.

It is advantageous, when treating pellicles, to carry out'the removal of the bath from the material while the material is under tension. In this manner the many creases which usually appear in the finished material when the material is treated not under tension are avoided.

The bath is usually removed from the cellulosic materials by displacement by water but it is advantageous in some instances to displace it by the use of some liquid inert towards the bath, such as glacial acetic acid. The organic acid anhydrides in the bath react with the water, which may be present, to form the corresponding acids with the evolution of heat. This phenomenon sometimes (particularly when the cellulosic materials are somewhat swollen during the esterifi-,

cation treatment) causes a slight tendering of the materials. In case of transparent cellulosic pellicles, sheets or molded articles this tendering tends to make the thing opaque. This tendency is avoided by the use of a non-aqueous washing bath.

The standard method of making the esterification bath by mixing given quantities of the selected reagents has been described in detail hereinbefore. Analternative method of making this esterification bath consists in mixing an organic acid chloride with an organic acid having the same or a different acyl group in the presence of pyridine, forming a plain or a mixed anhydride and pyridine hydrochloride in a reaction indicated by the following formula:

stances are tricresyl phosphate, triphenyl phosphate, diphenyl methane, diphenyl oxide, acetov phenone, benzyl acetate, and their homologs. Ordinary regenerated cellulose when impregnated with these substances is only slightly improved in flexibility, but the new material is more highly compatible with these substances and is greatly improved in flexibility by them. Being compatible and non-hygroscopic, these softeners form a valuable adjunct to the new materials.

Among the many advantages of our invention are the accomplishment of each of the objects of the invention which have been hereinbefore set forth.

Another advantage of the invention is in its application to the manufacture of caps and bands, such as bottle caps, which are allowed to dry over the necks of bottles and to shrink into place to form a seal. Bottle caps of regenerated cellulose were rather unsatisfactory for use in places where they would be affected by moisture because they would wet up and come off the bottle but caps of the new materials are less affected and retain their shape and position. Caps and bands of this cellulose acetate shrink somewhat .mcre than prior art cellulose acetate caps and bands making fewer sizes necessary. The better compatibility of the new materials for non-hygroscopic materials useful as softeners is of particular value in this connection.

The new materials have electrical insulating properties superior to those of ordinary cellulosic materials in any form. The new materials possess higher softening temperatures than prior art cellulose esters of equal degrees of esteriflcaprior art esters, may be used as non-active diluenis in the new esterification reaction. As a result of this property pellicles or other forms of the material are not damaged by contact with pharmaceutical preparations even when they contain solvents for the usual esters of cellulose and tubes made of the new material can be used as transparent containers for a wide variety of pharmaceutical and cosmetic preparations. Garments made from filaments of the new material may be readily cleaned by solvents which would be damaging or destructive to prior art products.

A particular advantage of the process is in the direct production of cellulose esters in any form such as filaments, pellicles, fabrics, or molded articles which contain any desired degree of acyl content; The prior art processes for the production of cellulose esters appear to be limited to the products of cellulose esters having acyl contents within narrow limits determined by the solvents which are employed in the casting operation. The new process is not limited in this manner and eliminates entirely the problem of selecting solvents to be used in the casting process.

Another advantage of the process lies in the choice of a catalyst. Prior art processes have used catalysts, such as sulfuric acid, modified sul furic acid, zinc chloride, or the like, whose use induces, we have discovered, a degrading effect on the raw material or on the product, whereas discovered-that by starting with a fixed, predetermined quantity of pyridine hydrochloride and by maintaining this quantity constant throughout the course of the reaction, however long this may be, the bad efiects which are attendant upon the prior processes are avoided.

Another advantage of the invention consists in accomplishing the esterification of the starting material to any selected degree of esteriflcation in a reasonable time, without destroying the original physical ,form of the material, without producing a substantial change in its appearance, and with an actual increase in its strength.

I For example, rayon filaments after esterification are at least as strong indry strength as before the reaction and are usually about at least 20% stronger in wet strength.

Another advantage of the invention is the production of cellulose acetate, or of other cellulose ester, fibers having spinning properties approximately equal to the spinning properties of regenerated cellulose fibers of equal size. Another advantage of the invention is the production of a cellulose acetate, or other cellulose ester, thread having crenulations approximately equal on the average in number and character to the average crenulations of thread of the same size regenerated from viscose. These properties are of great advantage in connection with staple fibers.

Another advantage of the new materials lies in their stability toward moisture. Ordinary glycerine-plasticized regenerated cellulose pellicles deform in the neighborhood of 3 to 5% in the machine direction and as much as 'l to in the cross direction when the relative humidity changes between 90% and 5% at 35 C." The new materials in pellicle form, when plasticized with one of the non-hygroscopic softeners hereinbefore referred to, have been observed to deform as little as 1% in both machine and transverse directions during the identical change in relative humidity at the identical temperature.

' It is to be noted that the extent to which deformability by moisture is eliminated depends to a material degree on the degree of esterification, an increase in the degree of esteriflcation entailing a decrease in deformation.

This esterification treatment of cellulosic materials, such as regenerated cellulosic threads, filaments, films, sheets, ribbons, bottle caps, or tube; such as sausage casings, produces cellulose esters in the same physical forms, which fuse at higher temperatures when heated, than the prior art cellulose esters of equal esterification. This property of the new cellulosic materials makes them more satisfactory than the usual cellulose esters in uses where they are subjectedto heat. For instance, pellicles of the new materials can be used in color screens for theatre spotlights,

- for photographic or moving pictureyfihn, and for other similar purposes requiring "resistance to i fusion on heating.

As many apparently widely difierent embodi-' ments of'this invention may be made without departing from the spirit and scope thereof, it ll to be understood that we do not limit ourselves to the specific embodiments thereof except as defined in the appended claims.

We claim:

1. The method of making an ester of cellulose which comprises reacting at about 35 C. upon one of a group of substances consisting of regenerated cellulose, cellulose, arid lowly esterified or etherified cellulose with a bath containing an aliphatic monocarboxylic acid anhydride, a substantially constant amount of the addition product of pyridine and hydrogen chloride, one of said last-named constituents being present in an uncombined state.

2. The method of making an ester of cellulose which comprise; reacting on one of a group of substances consisting of regenerated cellulose, cellulose, and lowly esterified or etherified cellulose with a bath containing a monocarboxylic' acid anhydride, a substantially constant amount of the addition'product of pyridine'and hydrogen chloride, one of said last-named constituents be-- ing present in an uncombined state. 3. The method. of making an article which comprises making viscose from cellulose, coagulating the viscose in the shape of the desired article,

regenerating and purifying the article, and reacting the undried article with the ingredients of a bath containing a monocarboxylic acid anhydride, a substantially constant amount of the additionproduct of pyridine and hydrogen chlbacting the undried article at a relatively low temperature with the ingredients of a bath containing a monocarboxylic acid anhydride, pyridine hydrochloride in a quantity which remains substantially constant throughout the reaction, and pyridine in quantity to make the active ingredients of the bath slightly basic.

5. The method of making an article which comprises casting and regenerating an article from viscose and reacting the undried article with the ingredients of a bath containing a m'onobasic acid anhydride, a'substantially constant amount of the addition product of pyridine and hydrogen chloride, one of said last-named constituents being present in an uncombined state.

6. The method of making an article which comprises casting and regenerating an article from viscose and reacting the article with the ingredients of a bath containing an aliphatic monocarboxylic acid anhydride, a substantially constant amount of the addition product of pyridine and hydrogen chloride, one of said last-named constituents being present in an uncombined state. U

7. The method of making an article which com-.

prises making and regenerating the article from viscose, and in a continuous process reacting it at relatively low temperature with the ingredients of a bath containing acetic anhydride, pyridinehydrochloride, and pyridine.' I 1 8. The method of making an article which or said last-named constituents being present in an uncombined state.

9. The method of making' an article which comprises making viscose from cellulose, coagulating the viscose in the shape of the desired article, regenerating and purifying the article, and reactingthe undried article at a temperature below about 100 C. and preferably near room temperature, with the ingredients of a bath containing a monocarboxylic acid anhydride, a substantially constant amount of the addition product of pyridine and hydrogen chloride, one of said last-named constituents being present in an uncombined state.

10. The method of making an ester of cellulose which comprises reacting one o! the group or substances consisting of regenerated cellulose,

cellulose, and lowly etherifled or esterified cellulose with'a bath containing a monocarboxylic acid anhydride and the addition product of a tertiary amine and a hydrogen halide, one of said last named constituents being present in an uncombined state.

11.'The method of making an article which comprises making viscose from cellulose, coagulating the viscose in the shape of the desired article, regenerating the article, and reacting the undried article with the ingredients of a bath containing a monocarboxylic acid anhydride and the addition product of a tertiary amine and a