US2994924A

US2994924A - Cellulose ether

Info

Publication number: US2994924A
Authority: US
Publication date: 1961-08-08
Anticipated expiration: 1978-08-08

Description

Aug. 8, 1961 D. T. MILNE cELLULosE ETHER FILM Original Filed Jan. 29, 1953 of? to ds vom :En 9G United States Patent Oli 2,994,924 Patented Aug. 8, 1961 2,994,924 CELLULOSE ETHER FILM David T. Milne, Fredericksburg, Va., assignor to American Viscose Corporation, Philadelphia, Pa., a corporation of Delaware Original application Jau. 29, 1953, Ser. No. 334,067, now Patent No. 2,902,334, dated Sept. 1, 1959. Divided and this application June 23, 1959, Ser. No. 822,988

'I'his invention relates to the coagulation of hydrophilic colloids and more particularly to the coagulation or precipitation of cellulose derivatives.

Heretofore, it has been found to be impractical to use certain groups of cellulosic colloids for the formation of useful objects, such as films and filaments, because, after shaping, casting or spinning, and coagulation in the con ventional or known manner, the coagulated colloids, while still in the wet gel state, were too weak and too easily torn, broken, ruptured, or punctured to be handled conveniently. While the present invention will be described in connection with cellulose derivatives such as alkali-soluble cellulose ethers of the hydroxyalkyl type, for example alkali-soluble hydroxyethyl cellulose, this s merely illustrative and not limitative, since the invenion is also applicable to other colloidal cellulosic macrials.

In the past it has always been found to be practically mpossible to cast or spin a solution of an alkali-soluble tydroxyalkyl cellulose ether into a ilm of sufficient trength while in the wet gel state to permit handling on t conventional cellophane machine without xanthation of he ether before casting or without mixing the ether solulon with another colloid, such as viscose and the like.

Accordingly, it is a principal object of this invention 3 provide a method for the coagulation of cellulosic olloidal materials so that they will have improved proprties While still in the wet gel state.

Another object of the invention is to employ an im roved bath for the coagulation ofthe cellulosic colloidal laterials.

Another object of the present invention is to employ n alkaline solution of an alkali-soluble hydroxyalkyl :llulose ether having present the minimum amount of kali to improve the properties of the coagulated ether oresaid while still in the Wet gel state.

Other objects of the invention will appear hereinafter.

Typical of baths commonly recommended for coaguting colloids of the type set out above is one composed 5% sulfuric acid, 10% sodium sulfate and 85% water.

ie standard, hereinafter referred to, refers to films agulated by immersion in a bath of the above compoion. When alkali-soluble hydroxyalkyl cellulose ethers a coagulated in such a bath, the resultant lrns, while the Wet gel state, are weak and subject to tearing and ucturing, and as a result incapable of being cast or 'med on a conventional film-forming machine, such that employed in the manufacture of cellophane.

I'he objects of the present invention are accomplished :l the disadvantages of prior attempted practice as imerated hereinbefore are overcome by employing a tgulating bath containing large amounts or relatively h amounts or proportions of the phosphate radical or sphate ion (POF) and an alkali metal radical such the sodium radical or sodium ion (Na+). The phos- ,te radical is present in an amount at least about 2.5

m-moles per kilogram of solution or corresponds to hosphate content of at least about 24.9% calculated ghosphoric acid. The alkali metal such as the sodium radical is present in an amount at least about 2.1 grammoles per kilogram of solution or corresponds to an alkali metal content of at least about 8.3% calculated as sodium hydroxide. The pH of the coagulatiug bath may vary from about l to 8.

The bath may be formed from an alkali metal salt or salts such as a sodium salt or sodium salts of phosphoric acid or their hydrates with or Without added phosphoric acid in relatively high amounts or proportions. The amounts may be sutiicient so as to produce a nearly saturated solution at a temperature of 25 C. or greater concentrations may be employed by elevating the temperature of the bath.

Alternatively, the bath may be formed from phosphoric acid and the alkali metal hydroxide such as sodium hydroxide and the amount of phosphoric acid and alkali metal hydroxide may vary above the aforementioned limits.

The drawing illustrates the phase diagram of the system phosphoric` acid-sodium hydroxide-water, the irregular curve representing the solubility at a temperature of 25 C. Oblique lines A, B and C represent the compositions 3NaOH:lH3PO. 2NaOH:lH3PO., and

1NaOH:lH$,PO,l

respectively. Oblique lines AA, BB and CC represent the compositions 3NaOHz1H3P04 plus 10% H3PO4, 2NaOHz1H3PO4 plus 10% HsPO,A and lNaOHzlHaPO, plus 10% H3PO4, respectively.

Point l on the graph represents the limit of solubility of tn'basic sodium phosphate at 25 C. and expresses the composition of a saturated solution in terms lof the amount of sodium hydroxide and phosphoric acid present. Similarly, points 2 and 3 represent the limit of solubility of dibasic sodium phosphate and monobasic sodium phosphate, respectively, at 25 C. As will be pointed out hereinafter, it is not merely a matter of the degree of saturation of the specific bath but rather the amounts or proportions of the alkali metal and phosphate radicals present in the bath which accomplish the purposes of this invention.

The lower limit of the compositions of the baths satisfactory for the purposes of this invention is represented by the point 4 of the graph. The preferred compositions of the coagulating baths comprise solutions correspond ing to at least 25% of an alkali metal salt or a mixture of alkali metal salts of phosphoric acid and at least 10% phosphoric acid. The points 8, 9 and 10 represent the compositions of baths formed from 10% phosphoric acid plus 25% of monobasic, dibasic and tribasic sodium phosphates, respectively. Thus, the preferred bath compositions lie within the pentangular area 5, 6, 7, 8, 9, l0 and 5 and may be considered as being formed from 10% phosphoric acid and at least 25% salt selected from the group consisting of monobasic, dibasic and tribasic sodium phosphates, mixtures of monobasic and dibasic sodium phosphates, and mixtures of dibasic and tribasic sodium phosphates. The preferred upper limit of compositions of the baths contain about 4.9 gram-moles of the phosphate radical and about 6.75 gram-moles of the alkali metal radical per kilogram of solution, corresponding to about 47.8% calculated as phosphoric acid and about 27% calculated as sodium hydroxide, as represented by point 6 of the graph.

Where the composition of the bath, above the lower limit, lies beneath line C and above line 4, 7 the phosphate and sodium radicals will be present as monobasic sodium phosphate and free phosphoric acid. Where the relative proportions of sodium and phosphate radicals are such that the compositions fall on line C, the radicals will be present as monobasic sodium phosphate. Cornpositions between line C and line B will consist of a mixture of monobasic sodium phosphate and dibasic sodium phosphate. Compositions falling along line B will consist of dibasic sodium phosphate. Compositions lying above line B will consist of a mixture of dibasic sodium phosphate and tribasic sodium phosphate.

The use of a coagulating bath having a composition above the specified low limit results in the production of films having superior strength, clarity, elongation and the like particularly in the wet gel state. The characteristics of the films are dependent upon the proportions or amounts of the alkali metal and phosphate radicals contained in the coagulating bath. Coagulating solutions having compositions outside the specified range do not produce products having the superior properties contemplated by the present invention. The physical properties of products formed by the use of coagulating baths having compositions outside the specified range are of the order of or lower than the physical properties of products obtained by the use of the standard type coagulating baths.

The coagulation media described and contemplated by this invention are particularly effective for the coagulation of hydrophilic cellulosic colloids among which, in addition to alkali-soluble hydroxyalkyl cellulose ethers, may be named aqueous alkaline dispersions of degraded cellulose, cellulose ethers (other than those aforenamed) cellulose xanthates, cellulose etherxanthates in dilute caustic soda, cuprammonium cellulose and the like. They are also effective for the coagulation of mixtures of such colloids.

In the practice of the lose is made from a starting material such as wood pulp. cotton linters, etc., as by steeping in caustic soda, pressing to an approximately 2.5 or 3 to l ratio of alkali cellulose to original air-dry cellulose, shredding in a Werner- Peiderer mixer, for example, and then aging in covered cans at constant temperature and humidity. The aging process of the alkali cellulose or the degradation process is regulated carefully since the degree lof polymerization of the alkali cellulose is determinative of the final viscosity of the cellulose ether solution. The aged alkali cellulose is placed in a Werner-Pfieiderer mixer and sutiicient etherifying agent is added with mixing so as to introduce approximately the equivalent of 0.05 to 0.5 substituent ether gnoups into the nal product. Any of the usual etherifying agents employed in the art are suitable in this connection. The alkali-soluble cellulose ether o so produced is then dissolved in sodium hydroxide of from 2% to 10% strength. The concentration of the ether may vary from 2% to 10% depending on the degree of polymerization of the particular ether used and hence the resultant viscosity of the alkaline solution. It may be necessary in some instances, in order to produce a geland fiber-free solution, to lower the tempera ture of the same to -10.0 to +l0.0 C.

The solution prepared as outlined above, is filtered and deaerated with the usual equipment employed in making viscose for the manufacture of cellophane. The alkali-soluble ether solution is then forced under pressure through an elongated slit into the coagulating bath, the slit opening being such as to produce a final film having a thickness in the range from 0.0002 to 0.0150 inch. The film is coagulated and washed, by passing it through successive baths, and then dried in a manner as is cellophane. If desired, the film may be plasticized inst prior to drying with the same plasticizers that are employed with regenerated cellulose film and in the same manner such as with glycerol, glycol, etc.

Sheets or films may be formed or cast by spreading the alkaline solution of the alkali-soluble cellulose ether on a casting surface, such as that of a stationary or present invention, alkali cellumoving plate, rotating drum, or traveling belt, which surface may be of any suitable material, such as stainless steel, Monel metal, nickel, glass or any material which is resistant to acid and alkali, to the desired thickness, or depth, immersing the same in the coagulating bath, removing the film from the casting surface, then washing and drying the same. Film may also be formed by extruding the alkaline solution of the alkali-soluble cellulose ether under pressure through a slit or die directly into the coagulating bath and removing the film therefrom by means of positively driven rolls or the like.

Films produced by the above outlined means possess increased toughness, puncture and tear resistance, clearness and improved tensile strength and elongation, especially when the film is still in the wet gel state. The films, while still in the wet gel state, show an increased ratio of colloid to solvent. The improvement in the films is due to the coagulant employed as will hereinafter be more specifically pointed out.

lt is to be understood that the same marked improvements, as outlined above, are also noted when the solution is cast in the form of tubes or tubing, filaments, yarns, fibers and other like shaped objects.

In order to more specifically explain the nature of the present invention, the following examples are set forth. But it is to be understood that these examples are merely illustrative and the invention is not intended to be limited thereby.

EXAMPLE I In conventional manner, i.e., by extrusion through a die, films were cast at a thickness, or depth, of 0.015 in. from a composition comprising 6 parts of alkali-soluble, water-insoluble hydroxyethyl cellulose, 8 parts of NaOH 86 parts of water. Before use, this composition was filtered and deaerated. The hydroxyethyl cellulose was characterized as being insoluble in water and soluble in dilute aqueous alkalies on chilling to approximately 5 C. and as having a viscosity of 6 times that of glycerol at 25 C. when made into a composition as described above. This viscosity acts as a practical index of the degree of polymerization of the hydroxyethyl cellulose. The films were coagulated by extruding into a bath comprising an aqueous solution 0f 36% HBPO., and 17% NaOH maintained at 25 C. The composition is represented by point l1 on the graph. The films were rinsed thoroughly in constantly changing water at to 55 C. The still wet films were subjected to physical testing the results of which are tabulated below in Table l.

For the purposes of comparison, films were cast as in Example I, from the same composition therein described, except that the films were coagulated by means of a conventional or standard bath, for example, an aqueous solution of 5% H2504 and 10% NaaSOL. The films were rinsed thoroughly in constantly changing water at 45 to C. Films prepared in such manner will hereinafter be referred to as standard films. These films were characterized by cloudiness whereas films of Example l were clear. Also, the standard films were so weak that they could not be passed between squeeze rolls before plasticizing and drying such as employed on standard film casting equipment thus indicating that the standarcl coagulating bath is incapable of satisfactorily producing films in practical commercial operation. Example I film: were capable of being passed through squeeze rolls while in the wet gel state and were far superior to standar( films in this respect.

Both standard and Example I films were plasticized b1 immersion in 3% aqueous glycerol solution. The plas ticized films were placed on frames, dried, conditionei at F. and 45% relative humidity and subiected t| physical testing, the average results of which are tabu1ate in Table l. The plasticized and conditioned films of Ex ample I were clear while the similarly treated standar films were cloudy.

1 Tests made on a standard Schepper tester.

From the above data it can readily be seen that ilms )roduoed according to the present invention are decidedly tronger than conventional or standard films, especially vhen wet.

It is to be understood that the term iilms as used lerein is meant to include such products as casings for ieats and cheese, bands `for bottles, tubes, and the like, ometimes described `as pellicles.

In place of the die of Example I containing an elonated slit for the production of films, there was employed die containing a plurality of small openings, commonly nown as a spinneret, for the production of fibers, iilalents and yarns. The composition, coagulating bath and rocedure of Example I is generally the: same and such laments, etc., are far superior to those produced when standard coagulating bath is employed.

EXAMPLE II Films were cast as described in Example I from a omposition as therein described and were coagulated by nmersion into an aqueous bath comprising 35% H3PO4 nd 17.5% NaOH at 25 C. The composition is repre- :nted by point 12 on the graph. This bath was nearly iturated. The films were rinsed as described in Example and were clearer than those cast in the standard bath nd were tougher, thinner, and more resistant to tearing ad puncturing, these observations being made just after Jagnlation and rinsing.

Both Example II and standard films were immersed in 1 aqueous 5% glycerol solution, the usual commercial lm plasticizing bath, while still in the wet gel state id were allowed to remain in this solution for a period one week. When examined at the end of this period, e Example II films were still strong and could be reoved from the solution and handled Without breaking tearing. That is to say, they still were self-sustaining ms and capable of being passed between squeeze rolls :fore plasticizing and drying. However, when the stand- `d llms were examined, they were found to be so weak to be incapable of removal from the solution without lling apart. That is to say, they were no longer selfstaining lilms.

Another noticeable difference between Example II and mdard lms was the percentage of cellulosic material the still wet rinsed films (films in the wet gel state). 1e films coagulated in the standard bath were 9.7% llulosic, while those coagulated in the bath of Example were 15.8% ccllulosic showing an increase of 63% llulose content of the latter over the former. In other irds, the ratio off hydroxyethyl cellulose to water was 1.7/ D for the standard lilms and 18.8/ 100 for Exiple II films.

EXAMPLE lII Films were cast, as described in Example l, from an :aline solution of a low substituted cellulose glycollic id, the composition of said solution being the same as :ample I. The sodium salt of this acid was character- :d as being soluble in dilute aqueous alkalies, but inluble in water, organic solvents, etc. Films cast in the Lndard bath were so Weak after rinsing as to be incapas of being passed between squeeze rolls before plasticizg and drying whereas films cast in a bath as described 6 in Example II, having a composition as represented by point 12 of the graph, could be passed between squeeze rolls in routine manner and with no special precautions. The latter llms were also much stronger, tougher and more tear and puncture resistant while still wet.

EXAMPLE IV The procedure of Example I was repeated except that an aqueous coagulating bath comprising 37% H3PO and 20% NaOH was used. The composition is represented by point 13 of the graph. The surface of the film was covered with a beautiful crystalline or frosted" design. This eiiect can be utilized for producing delustered rayons, filaments, staple, etc., for imparting a novel sheen to such materials, etc. Physical data were obtained and will be found in Table 2 following Example V.

EXAMPLE V The procedure of Example I was followed except that an aqueous ooagulating bath comprising 39.6% H3P0, and 16.2% NaOH was used. This bath was a substantially saturated solution of NaH2PO4, of a composition represented by point 3 of the graph and had a pH of 3.1 at 25 C. A crystalline effect was obtained but not to as marked a degree as in Example IV. The still-wet films coagulated in the standard bath were 9.3% cellulosic while those coagulated in the Example V bath were 14.4% cellulosic; an increase of 55%. In other words, the ratio of hydroxyethyl cellulose to water was 10.3/ for the films from the standard bath and 16.8/ 100 for films from the Example V bath. Physical data were obtained and are tabulated in Table 2.

Table 2 VARIATION IN PHYSICAL PROPERTIES OF FILMS (Phosphate" l vs. standard) [Based on lms congulated in standard bath] Thickness Tensile Percent of Film Strength, Change in Type Film Tested, gms., Percent Percent percent Elongatlon Change bange 1 Phosphate refers to a coagulatlng bath composed of HaPOt and NaOH (-1-) =lncreese and =decrease.

EXAMPLE Vl Films were cast as described in Example I from a composition comprising 7.8 parts alkali-soluble, water-insoluble hydroxyethyl cellulose, 7 parts sodium hydroxide and 85.2 parts Water. The hydroxyethyl cellulose, used in this example, is characterized as having a viscosity 6 times that of glycerol at 25 C. when made into a solution comprising 6 parts of hydroxyethyl cellulose and 9 parts sodium hydroxide. The coagulating bath employed comprised an aqueous solution of 15% H3PO4 and 30% NaH2PO4. The composition of this bath corresponds to about 39.5% HgPO, and 10% NaOH and is represented by point 14 of the graph. This bath has a pH of 1.2 at 25 C. The iilms so produced were superior to all others in clearness, toughness, were thinner and more resistant to tearing and puncturing, the observations being made just after coagulation and rinsing. The hydroxyethyl cellulose employed in this example contained approximately the equivalent of 0.2 substituent groups.

It is also to be noted that excellent tubing may be cast into a bath such as the above. This tubing is suitable for the packaging of meats, cheeses, and the like.

It is important in the above examples, from a practical standpoint, to maintain the lowest possible concentration 7 of NaOH in the colloidal solution to maintain solubility of the alkali-soluble, hydroxyethyl cellulose. By proceeding as in Example VI excellent results have been obtained when the NaOH concentration is for certain hydro-xyethyl cellulose ethers, and as low as 2% for others.

The use of the coagulating baths of this invention permits the production of sheet on conventional cellophane equipment from cellulosic colloids heretofore deemed highly impractical with the use of conventional coagulating baths. The following examples illustrate such sheet production:

EXAMPLE VII Film was produced on a semi-commercial scale cellophane machine by continuous extrusion of a cellulose ether solution, as described in Example I, into a coagulating bath having a composition corresponding to 39% HBPO* and 16% NaOH, point 15 of the graph, the tem perature of the bath being maintained at 28 C. to 35 C. The film was extruded with very thin edges, was passed through wash tanks (55 C.) to rinse the sheet free of salts, was passed through a plasticizing solution, 4% glycerin solution at 55 C., and dried by passing over rolls maintained at about 80 C.

The coagulated, wet film or sheet was clear, extremely tough and resistant to tearing and puncturing and was passed through the machine without difficulty. The finished sheet was very clear, tough and possessed a high shatter resistance, high tensile strength and high stretch.

EXAMPLE VIII Film was produced on a semicommercial scale cellophane machine and by the use of the coagulating bath as described in Example VII. The alkali-soluble, waterinsoluble hydroxyethyl cellulose, however, differed from that of the cellulose ether of Example VII in that it was characterized by being soluble in lower concentrations of caustic soda, 3% aqueous caustic soda solution, but had essentially the saine viscosity when made into a solution containing 6% alkali-soluble hydroxyethyl cellulose, 9% NaOH and 85% water. The extrusion solution contained 6% hydroxyethyl cellulose, 5% NaOH and 89% water. The film was extruded as described in Example VII, was passed through wash tanks (85 C. to 95 C.) to rinse the sheet free of salts and dried by passing over rolls maintained at about 80 C. The sheet was produced without the use of a plasticizer.

The coagulated, wet film was extremely tough and comparable to the film of Example VII. The finished sheet which was unplasticized was very clear, tough and had characteristics similar to plasticized films made from viscose.

In the practice of the present invention, its objects are accomplished by the use of phosphate salt in the coagulating bath. If a salt of phosphoric acid, used in the coagulating bath, is effective for the purposes of this invention, it cannot be assumed that the acid itself or only the phosphate radical is the effective agent. For example, films were cast as in Example 1 except that the coagulating bath or baths consisted of aqueous H3PO4 varying in concentration from 5% to 75% H3PO4, inclusive. Still wet films and also plasticized, dried and conditioned films were examined and none of them showed any appreciable differences in properties when compared with films coagulated in the standard bath. Also, these films did not have properties comparable to films such as described in Examples I and II.

Water-soluble sodium carboxymethylcellulose does not dissolve in a solution such as the coagulating bath of Example II, namely, 35% HSPO., and 17.5% NaOH. Hence a 1% aqueous solution of water-soluble sodium carboxymethylcellulose is capable of being coagulated in such a solution (Example II bath) as also is a composition comprising 6 parts by weight of water-soluble sodium carboxymethylcellulose and 100 parts of 8% aqueous caustic soda solution. The present invention can be applied to the production of films, filaments, shaped objects, etc., such as water-soluble yarns, and the same will be clear to tho-se skilled in the art.

The present invention is also useful in coagulating the alkali-soluble hydrophilic cellulose colloids in situ in another body sueh as cotton batting, fabrics, fibrous webs or sheets, and the like. This is pointed out particularly by the following example.

EXAMPLE IX A web of loose cotton batting was supported on a screen and treated with an excess of a composition comprising l part of hydroxyethyl cellulose characterized as in Example I, 3 parts of NaOH, and 96 parts of water. The excess solution was allowed to drain off and the wet batting was treated with an excess of an 'aqueous solution comprising 34% H3PO4 and 16% NaOH thus coagulating the alkali-soluble hydroxyethylcellulose in situ. The composition of the bath is represented by point 16 of the graph. The impregnated cotton was rinsed thoroughly and dried. There was produced a non-woven fabric of exceptional absorbency and wet and dry strength. By means of the procedure of the present example there may be produced non-woven fabrics, bonded webs, paper suitable for wrapping rayon cakes, etc., in accord with the principles of the present invention.

The coagulants are especially useful in connection with cellulosic colloidal impregnants, saturants, coatings, sizes, binders, etc. for textiles, paper, non-woven fabrics, bonded webs, etc. Colloids, applied to textile materials and o0- agulated as herein proposed, exhibit increased laundry resistance, improved retention of hand, etc. With paper and bonded webs improved wet strength is noted.

Films cast from hydrophilic colloids by means of the present invention have superior properties while still wet such as increased toughness, and puncture and tear resistance, decreased brittleness, improved tensile strength and elongation, increased ratio of colloid to solvent, and increased shrinkage of shaped object at the time of coagulation. Dry films may be exceptionally clear, or may have a novel nish or surface character such as a velvet-like sheen or a crystal-like or frosted decorated surface. Multilayered films can be cast from more than one colloid to yield special purpose films, decorated films, tubes, etc.

The following examples illustrate the use of coagulating baths having compositions outside the specified range.

EXAMPLE X Films were also prepared as described in Example I from a cellulose ether solution of a composition specified in Example I by utilizing a bath consisting of approximately 12.3% tribasic sodium phosphate which corresponds to 7.3% H3PO4 and 9% NaOH. This coagulating bath was a substantially saturated solution of tribasic sodium phosphate at 25 C. and is represented by point l on the graph. The physical properties of both the wet and finished films were substantially the same as the films formed in a standard bath. The films were very slightly weaker in the wet condition and slightly stronger in the dried condition as compared to films prepared by the use ol a standard bath. However, the films produced from this bath were more hazy than those from the standard bath.

EXAMPLE XI Films were cast from a composition and by the method as described in Example I utilizing a coagulating bath consisting of approximately 11% disodium phosphate corresponding to .about 7.5% liaPOf, and 6.3% NaOH. This bath was a substantially saturated solution of dibasic sodium phosphate at 25 C. and the composition is represented by point 2 of the graph. The films produced in this bath had a cxinkle or waviness in the surface and were generally inferior in their physical properties to films produced by the use of a standard coagulating bath.

It will be noted that Example V showed the use of a coagulating bath consisting of a substantially saturated solution of monobasic sodium phosphate and the baths of Examples X and XI involve the use of substantially saturated solutions of tribasic sodium phosphate and dibasic sodium phosphate respectively. Although in all three examples the sodium and the phosphate radicals may be considered as being present in a bound state as specific salts, the action of the salts is not comparable. Also, in each instance the solution consisted of a substantially saturated solution of the respective sodium salt. It is apparent that the degree of saturation of the specific bath is not a controlling element. It is clear that in this invention it is the relative amounts of the sodium and phosphate radicals which permits the attainment of the objects of this invention. This is further shown by the following example.

EXAMPLE XII Films were cast from a cellulose ether composition and by the method described in Example I. The coagulating bath employed consisted of a solution containing 20% H3PO4 and 10% NaOH as represented by the point 17 on the graph, The clarity and physical properties of the lms were slightly superior to those of iilms prepared by the use of a standard coagulating bath. The principal difference between the films was a small increase in the proportion of cellulose in the wet film formed by the use of the phosphate coagulating bath as compared to the standard bath. The films did not possess the characteristics and properties f films formed by the use of the ooagulating baths of this invention.

There are a number of advantages of the present invention which are important in connection with the use of the ooagulants. As the coagulants are used preferably at concentrations very near to, or at saturation, recovery is simple and relatively inexpensive since relatively small amounts of solvent need to be evaporated. The effectiveness of coagulation is increased since it takes place at relatively low temperatures which makes heating of the baths usually unnecessary and facilitates temperature control of the sarne. However, good results are also obtained when the temperature is varied from room temperature up to or 50 C.

This application is a division of my copending application Serial No. 334,067, filed January 29, 1953, entitled Coagulation of Cellulosic Colloids, now Patent No. 2,902,334, granted September l, 1959, which is a continuation-in-part of my copending application entitled Coagulation of Colloids, Serial No. 127,801, led November 16, 194.9, and now abandoned.

It is to be understood that the description above is merely illustrative and that changes and variations may be made without departing from the spirit and scope of the invention as defined in the appended claims.

I claim:

As an article of manufacture, an unplasticized, dry, alkali-soluble hydroxyalkyl cellulose ether film characterized by being clear, transparent, tough, flexible and having the physical properties of plasticized viscose lms and by being formed by extruding a dilute alkali solution of the cellulose ether through an appropriately shaped orifice into a coagulating bath composed of an aqueous solution monobasic sodium phosphate, the solution being near the saturation point at 25 C., and drying the coagulated lm.

References Cited in the file of this patent UNITED STATES PATENTS 1,722,928 Lilienfeld July 30, 1929 1,941,278 Schorger Dec. 26, 1933 2,088,642 Dreyfus Aug. 3, 1937 2,150,250 Scott Mar. 14, 1939 2,902,334 Milne Sept. 1, 1959