US2357731A - Solubilized cellulose and method of making - Google Patents

Description

Patented Sept. 5, 1944 Sidney M. Edelsteln, Elizabeth, N. J.

No Drawing. Application April 20, 1943, Serial No. 483,817

9 Claims.

This invention relates to solubilized cellulose and the method of making it.

This application is a continuation in part oi my copending application Serial No. 407,445, filed August 19, 1941, and issued on June 22, 1943, as Patent No. 2,322,427, for Cellulose product. In this copending application there is disclosed a process of dissolving cellulose in sodium zincate the exact nature depending somewhat on the proportion of cellulose used. In any case, the product is more suggestive of undissolved cellulose than ofa solution of cellulose. On dilution of the solution and consequent decrease of ion concentrations; the fact that the cellulose is solubilized first appears, the cellulose then dissolving.

solution at low temperatures, as, for exampe, at

temperatures not substantially above C.

I have now found that a solution may be efiected by sodium zincate solution at much higher temperatures, provided the cellulose is contacted initially with a high concentration of th zincate solution and the resulting mixture is then diluted as by the addition of water, ice or a dilute solution of sodium zincate.

Briefly stated, the invention comprises the method of and the product resulting from contacting a cellulosic material of kind described with an aqueous solution of'sodium zincate of high concentration, so that the zincate solubilizes the cellulosic material but the cellulosic material does not dissolve in the presence 01' the high concentration oi' zincate present, and then treating the product so as to decrease the zincate concentration and cause the solubilized cellulose to dissolve.

The product of the invention is-used in applying cellulosic coating to various products, as, for example, as described in my copending application. The product maybe used also as an adhesive and as a spinning solution for the manufacture of threads and sheets by usual technic for making thread and sheeting of regenerated cellulose. r

The mechanism .by which the higher concentration of sodium zincate used prevents solution of the cellulosic material solubilized by the zincate is herein sometimes referred to as salting out." It is known from the disclosure of my copending application, that a solution of cellulose in a zincate solution undergoes precipitation of cellulose when there is added to the solution a large proportion of salt or like material that, when dissolved in water, is highly ionized.

I have now discovered that strong (highly concentrated) sodium zincate solutions convert cellulose or like celluloslc material to soluble form,

that is, solubilizes it even at ordinary or somewhat higher temperatures. The solubility is not As the cellulosic material to be solubilized, there isused to advantage wood pulp, of which sulfite wood pulp is a satisfactory example, cotton linters or purified linters, ,rayon in fioc or fibrous form,

like cellulosic material, or an alkali-stable cellulose derivative such as one of the common cellulose ethers. Examples of the ethers that may be used are the methyl, ethyl, hydroxyethyl, and glycolic acid ether of cellulose. The cellulose used initially may be modified or even further altered to the condition known as degraded cellulose. Also, the

, modifying or the degrading may be effected as an initial step in my process, as, for example by heating unmodified cellulose to 50 C. or so with a strong solution of sodium zincate. V

In one embodiment of the invention, the cellu-' lose in selected form, say wood pulp sheets, may be wet with about an equal weight of the strong zincate solution and the resulting solubilized product sold in that form for subsequent dilution Just previous to or at the time of use.

satisfactory results with out fibers of such fine-' ness as to pass largely through a 20 mesh and preferably in major proportion through screens as fineas 100 mesh.

readily evident, however, since at the ionic con- The cellulose is used in proportion to give the desired concentration in the finished solution. Thus, cellulose is ordinarily used in the proportion of about 1 to 10 parts for parts of all ingradients including the water added initially with the strong solution of zincate and later as the ion diluting medium. Proportions of cellulose much below 1% in the finished solution give solutions' too thin for most cases, whereas concentrations above 10% are so viscous as to make manipulation difiicult during the forming or use of the solutions. I

The zincate used may be sodium or potassium zincate. Since sodium zincate is entirely satisfactory and less expensive than the potassium salt, sodium zincate is preferred,

The zincate should contain an excess of sodium hydroxide or other alkali metal hydroxide over the amount required theoretically to convert the zinc to zincate. Since the equivalent proportions of sodium hydroxide and zinc oxide are approximately 40 and 40.7, respectively, the proportion of the hydroxide used by weight should be in excess of the zinc oxide. Proportions of sodium hydroxide to zinc oxide that may be used are preferably about 2 to 5 parts of sodium hydroxide to 1 part of zinc oxide by weight. Satisfactory results, particularly when solution is effected under especially favorable condition as to temperature and kind of cellulose used, are obtained when the proportion of zinc oxide used is less than 1, say within the range of about 0.1 to 1 part.

The concentration at which the zincate is initially contacted with the cellulose to give the solubilizing effect may be varied somewhat with the kind of cellulose used and other conditions of. the treatment. The concentration that is preferred is about 25 to 50 parts of zincate, figured as dry weight of the raw materials sodium hydroxide and zinc oxide, for 100 parts of the aqueous solution. Proportions up to the satura tion amounts are satisfactory, although as the zincate solution becomes too concentrated mechanical difficulties are introduced particularly in establishing thorough contact of, the viscous solution or mass with the selected cellulose. Concenerations below 25 partsof the zincate may be used, say down to a proportion corresponding to about 12 parts of total sodium hydroxide in 100 parts of the solution. For best results as to speed of solution and uniformity of product, however, the content of sodium hydroxide in the solution should be not substantially less than 15- parts to 100 parts of the solution contacted with the cellulose and may range from this point up to the saturation proportion of some ingredient of the zincate solution. Ordinarily, there is used a concentration of the sodium zincate solution that is so high as to cause precipitation of cellu- I lose if such a concentration of the zincate is established in a previously made solution of cellulose in sodium zincate solution of relatively low concentration. When the effect of continuous dilution during the dissolving period'is desired, without the feature of dissolving the cellulose in the absence of cooling, then a lower concentrationof sodium hydroxide may be used, as, for example, the concentration of 8 to 15% given in the table on page 1 of my said patent.

The zincate solution itself is first prepared by mixing zinc oxide (this term including the hydroxide or a zinc salt that is soluble in excess of aqueous sodium hydroxide solution) with an excess of such solution or in other conventional manner.

The temperature of contact 01' the strong zincate solution with the cellulose may be any one at which the zincate solution solubilizes the cellulose, as determined by removal'of a portion of the treated batch and diluting with 2 or 3 times its weight of water. In general, the lower the concentration of sodium hydroxide used and the more nearly the cellulose selected approaches the completely unmodified form, the lower is the temperature required to effect a solution. With unmodified cellulose there may, however, be used initial temperatures ranging, say, from about 5 C. to as high as 50 C. or so; at such temperature, the strongly alkaline zincate solution causes a degrading action. When this degrading has been effected, say, after an hour or so, the temperature is lowered as by the addition of cold water.

Examples of temperatures that meet these general requirements and may be used are temperatures ranging from about 10 to 35 C. al-

though any temperature between the initial temperature of degrading and the low temperature at which the solution undergoes crystallization of an inorganic component thereof, as by partial In the contact of the strong zincate solution with the cellulose before the dilution is effected, it is required that the contact be in effect a soaking and that the soaking be continued until there is thorough absorption of the zincate solution or wetting of all parts of the cellulose by the solution. This soaking is considered vto be completed when the particles appear to be uniformly wet. Usually there is required a soaking for not less than 15 minutes and. preferably a half hour or so.

A longer soaking is unobjectionable except that in most instances there is no substantial gain from further soaking once the zincate has contacted and wet all parts of the cellulose used.

Using materials and conditions selected. as described above, I stir the cellulosic material thoroughly with the strong zincate solution until uniform wetting of the cellulose is obtained. Under the usual conditions as to proportions of cellulose, zincate, and water in this initial mixture, the resulting mass is more or less crumbly or dough-like although sometimes mushy, as at lower proportions of cellulose. The resulting mass either at that time or shortly before use of the finished cellulose solution is then diluted by the addition of water, ice which is allowed to melt, dilute sodium hydroxide or zincate solution, or the like, to give the concentration of cellulose which is desired for the particular use to which the product is to be put and also to decrease the ion concentration to less than. the salting out concentration. The dilution is accompanied by stirring. There results disintegration of the original relatively still. or viscous mass to the form of the desired readily fiowable solu-- tion.

In general, the dilution to effect the solution should reduce the proportion of sodium hydroxide (including that combined in the zincate) to less than about 12 parts and preferably 5 to 10 parts for 100 of the finished solution.

It will be understood that the invention is not limited to any particular theory of explanation of the exact mechanism by which the selected chemicals act to give the finished product. It is significant, however, that the cellulose which has been solubilized by contact with the strong zincate undergoes solution, this term being used herein to include dispersion, if the concentration solved cellulose is decreased. Thus, the crumbly mushy or dough-like mass initially formed by contact with the strong zincate may be mixed with water. .When this dilution is large and there is necessarily an attendant large decrease of ion concentration, the cellulose dissolves even though e temperature may not be substantially changed by the dilution. Likewise, the concentrated zincate in the original treated mass may be largely removed by pressing and the remaining treated cellulose stirred into a dilute solution of,

sodium zincate containing, for instance, such an amount 01' sodium hydroxide that, after the dilution and stirring, the concentration of sodium hydroxide is about 2 to 5 parts or so for 100 of the solution. Under this condition also the solubilized cellulose dissolves.

The invention will be further illustrated by detailed description in connection with the tollowing specific examples.

Example 1 Five pounds of viscose rayon doc is mixed with 44 pounds of a solution containing, that is made from sodium hydroxide 18%, zinc oxide 6%, and water 76%. This mixture is agitated for 30 minutes at 25 C. then 51 pounds of tap water are added and the whole stirred. This results in a clear cellulose solution.

Example 2 Six pounds of cotton linters are treated for 8 hours with 22 pounds of a solution containing 37% of sodium hydroxide and 13% of zinc oxide,

the rest being water, at a temperature of 80 C. and in an iron vessel. The resulting doughy mixture is then allowed to cool to 25 C. and enough water of dilution is added to make 100 pounds of total solution.

The clear solution so obtained is considered to be due to breaking down initially of the molecule r or the cotton cellulose and its subsequent dissolving on adding the water of dilution.

Example 3 The procedure of Example 1 or 2 is followed except that the methyl, ethyl. hydroxyethyl, or glycolic acid ether of cellulose is substituted pound for pound for the rayon floc or linters.

Example 4 Fourpounds of medium viscosity 'sulflte pulp are treated with 22 pounds of aqueous zincate solution containing 37% of sodium hydroxide and 13% of zinc oxide for 1 hour and agitated. 22

pounds of cracked ice are added and the mixture is agitated for another 15 to 30 minutes at 12 C. Water at room temperature is then added to make 100 pounds solution.

Example 5 Ten parts of sodium hydroxide are dissolved inten parts of water and then three parts of zinc oxide are added, at a temperature that is preferably moderately elevated, say at 50 C. to

100 C., so as to cause rapid solution of the zinc oxide with the formation of sodium zincate.

The temperature of the zincate solution is made about 50 C.

To this 23 parts of zincate solution I add dry 6 parts of rayon staple fiber and stir the resulting mixture thoroughly, with cooling, to 25 G.

Then I add 46 parts of ice to the mixture and continue stirring until the temperature has reached approximately -3 C. and untilthe cellulose is completely dispersed. The ice in melting cools the. mixture and supplies water so as to lower the concentration of zincatein the solution, the lowering of the concentration being progressive as the ice melts .and the temperature falls.

I then warm the dispersion promptly to ap proximately 15 C.

An aging. reaction'takes place in the containers. The solution is allowed to stand at atmospheric temperature for about 24 hours before use. Thus the solution may be aged (ripened) at about 15 to 35 C. 'for 10 to 24 hours or so. During this period a change occurs that reduces the viscosityof the solution. This aging reaction is particularly noticeable when unmodified cellulose is the kind of cellulose dissolved initial- 1y, and'the cellulose solution is relatively concentrated, say 5% or higher.

It will be understood also that. it is intended to cover all changes and modifications of the example of the invention herein chosen for the purpose of illustration which do not constitute depiartures from. the spirit and scope of the invent on.

What I claim is: 1. The method of forming a solution of a celluloslc material which comprises contacting a cellulosic material selected from the group consisting of cellulose and alkali stable cellulose ethers with an aqueous solution of odium zincate of high concentration adequate to cause precipitation of cellulose previously dissolved in a zincate solution, continuing the contact of the said cellulosic material and aqueous solution of sodium zincate until the cellulosic material is thoroughly wetted by the solution, and then diluting the resuiting mixture by adding water until the cellulosic material dissolves, the said aqueous solution of sodium zincate usedcontaining sodium hydroxide in excess or the proportion required theoretically to convert the zinc to zincate.

2. The method of forming a solution or a cellulosic material which comprises contacting a cellulosic material selected from the group consisting of cellulose and alkali stable cellulose ethers with an aqueous solution of sodium zincate containing at least approximately 15 parts of sodium hydroxide to of the solution, but not more than the saturation proportion, continuing the contact of the said cellulosic material and .aqueous solution of sodium zincate until the cellulosic material is thoroughly wetted by the solution, and then diluting the resulting mixture by adding water until the cellulosic material dissolves, the proportion of alkalinity calculated as sodium hydroxide in the said aqueous solution of sodium zincate being in excess of the proportion of zinc present calculated as zinc oxide.

3. The method described in claim 1, the temwhich comprises forming a slurry of cellulose in an aqueous sodium zincate solution containing an excess of sodium hydroxide over the calculated proportion required to form the zincate, at a temperature above that at which the zincate solution is an effective solvent for cellulose, then cooling the mixture and progressively diluting the zincate solution as the temperature falls to a temperature between the temperature of crystallizing of an inorganic component of the solution and about 5 C., until the cellulose is dissolved, so that the lowest concentration of the zincate solution is present at the lowest temperature reached, and warming, the resulting cellulose solution .to a temperature between about 15 C.

and the temperature of gelation of the solution, the said aqueous sodium zincate solution being of concentration within the range corresponding to alkalinity calculated as sodium hydroxide of at least 8% and not above the saturation proportion of any ingredient present.

'7. In making a solution of cellulose, the method which comprises forming a slurry of cellulose, ice and an aqueous solution of sodium zincate containing an excess of sodium hydroxide over the calculated proportion necessary to form the sodium zincate, the ice being used in amount to cool the mixture to a temperature between the temperature of crystallizing of an inorganic component of the solution and about 5 C. and serving to dilute the zincate solution progressively as the temperature falls, so that the cellulose dissolves.

8. A solubilized but undissolved cellulosic material con'iprising'the water-soluble product of SIDNEY M. EDELs'mm.