US2108125A

US2108125A - Cellulose products and method of making

Info

Publication number: US2108125A
Application number: US53002A
Authority: US
Inventors: Hoddeson Samuel Isaac; Meiklejohn Roy Mackay
Original assignee: General Chemical Corp
Current assignee: General Chemical Corp
Priority date: 1935-12-05
Filing date: 1935-12-05
Publication date: 1938-02-15
Anticipated expiration: 1955-02-15

Description

Patented Feb. 15,1938

UNITED STATES PATENT OFFICE Samuel Isaac Hoddeson, New Brunswick, N. J., and Roy Mackay Meikleiohn, New York, N. Y.,

assignors to General Chemical Company, New

'York, N. Y., a corporation of New York N Drawing. Application December 5, 1935,

Serial'No. 53,002

11 Claims.

This invention relates in general to low viscosity cellulose products and their manufacture.

It is particularly directed to a method of treating cellulose to prepare an initial material which may be nitrated to yield directly low viscosity nitrocellulose products.

The invention further-comprehends low viscosity cellulose as a new article of manufacture. The development of the nitrocellulose lacquer or varnish industry has, in the past, been greatly impeded because of the high viscosity of solutions containing even a small proportion of nitrated cellulose of the laquer or 12%i.50 nitrogen type. This has retarded the general commercial application of such derivatives in the industry since highly viscous products when dissolved or thinned to a usable consistency carry an insuflicient quantity of film-forming ingre-' client to yield a film or coating of substantial thickness in one application. Hence numerous successive applications are required.

While the viscosity of cellulose has in the past been varied over a wide range, it has not been possible, as far as we are aware, to prepare a cellulose of sufficiently low viscosity so that a nitrated cellulose suitable for commercial use in lacquers or varnishes could be prepared directly therefrom. Accordingly it has been the practice to nitrate a cellulose and thereafter to subject the nitrated cellulose to an aftertreatment for reducing its viscosity to within an appropriate range. obtain nitrated cellulose products of sufllciently low viscosity for commercial use in lacquers, paints, varnishes, etc. However, the aftertreatment of nitrated cellulose presents numerous objections. Chemical treatments result in reduced yields and produce a product difilcult to bleach to a satisfactory color. Treatment in water suspension under pressure presents a serious explosion hazard unless equipment is designed to minimize this danger, and this involves additional expense for equipment and operation.

It will be evident, therefore, that a cellulose that may be nitrated to yield directly low viscosity products constitutes a substantial advance in the art.

It is knownthat celluloses such as cotton and 0 wood pulp may be purified by treatment with alkaline liquors, and digestion in weakly alkaline solutions is a customary step in the preparation of cotton for nitration. That such procedures could be manipulated to yield cellulose from which low viscosity second) products could,

In this manner it has been possible to be obtained directly upon nitration was not formerly known.

In accordance with the present invention, it has been discovered that extremely low viscosity cellulose of high alphabeta-cellulose content 5 (i. e. about 98% or more insoluble as determined by the usual soda-soluble test for gamma cellulose) maybe obtained from ordinary cellulose such as cotton, or wood cellulose by employing a series of treatments wherein the cellulose is 10 first treated with a dilute alkaline solution, then mercerized, and subsequently digested in weakly alkaline solution. Furthermore, the low viscosity of the cellulose has been found to inure to the benefit of nitrated cellulose prepared therefrom 15 so that by utilizing nitration methods commonly employed a nitrated cellulose (11%-12.8% nitrogen) of low viscosity is'obtained which may be employed directly without further reduction in viscosity for the preparation of nitrocellulose lacquers, varnishes, etc. of high concentration.

The process of the present invention is especially applicable to cotton linters, which constitute the usual raw material" for the preparation 0! nitrated cellulose. It is also applicable to treat- 25 ment of cellulose from other sources, cotton cellulose or alpha cellulose derived from wood, bagasse, or other vegetable origin to yield products of correspondingly reduced viscosity.

Cotton linters are purified by the preliminary 30 alkaline digestion with the result that the subsequent mercerization liquid may efiectively penetrate the fibers, thus fats, oils, waxes, and any remnants of hulls are removed in the first step. The mercerization serves to effect an important reduction of viscosity of the cellulose and at the same time appears to render the cellulose molecule susceptible to further viscosity reduc tionby subsequent alkaline digestion. Sodium hydroxide or other alkali metal or alkaline earth compounds may be employed as the alkaline reagent. Thus KOH and the salts of sodium and potassium, such as the carbonates, sulfides, sulfites, phosphates, and silicates may be employed but the larger quantities required and/or the high prices of most of these reagents render their useless economical than the use of caustic soda.

The results will vary with conditions of treatment and in order to secure the most satlsfactory products the initial material, such as cotton linters or refined wood pulp, may be digested for 3 to 15 hours at a-temperature of 150 to 200 C. (under a pressure of to pounds per square inch) in a-solution having a hydroxyl ion 55 concentration equivalent to a solution containing .25% to 4.0% of NaOH. This serves to reduce the viscosity of the cellulose in terms of the viscosity of nitrocellulose producible therefrom from as much as several thousand to between about 100 and about 1700. The treatment is preferably regulated to yield a viscosity of 100 to 300 seconds. The treated cellulose is then mercerized, for example by immersion in an aqueous solution having a hydroxyl ion concentration equivalent to a solution containing 14% to 28% NaOI-I maintained at 2 to 32 C. (35 to 90 E.) for a period of 3 minutes to an hour. The mercerization preferably is regulated to further reduce the viscosity to between about 15 and about 60 seconds.

cellulose.

' The cellulose, after mercerization, is then again digested at a temperature of 150 to 200 C. (under a pressure of 60 to 150 pounds per square inch)- for a period from 3 to 24 hours in an aqueous I solution of to 3.0% NaOH or equivalent solution. This digestion serves to reduce the viscosity to that corresponding to second nitro- After'each treatment of the cellulose the excess 26 alkaline solution is drained off and preferably the cellulose is washed well with water and centrituged prior to subsequent treatment.

The customary method of measuring the viscosity of cellulose comprises determining the viscosity of a solution of 2.5 grams of the dried cellulose in 97 cc. of cuprammonium solvent (an aqueous solution containing 3010.5 grams copper, 165 -2.0 grams NHa, and 10 grams of sucrose per liter), referred to as /2 concentration".

85 As far as we are aware .no cellulose has been oflered to the trade or. produced prior to the present invention which has a viscosity below 3 seconds when dissolved in /2 concentration standard cuprammo'nium solution. Acellulose exhibiting a viscosity of 3 seconds in as concentration solution, upon nitration in the customany manner so as to obtain commercial yields,

- gives a nitrated cellulose of approximately 15 to 20 seconds viscosity in a 12.2% solution of standard a viscosity solvent, e. g.'the solvent known to the toluol) trade as 366 (20% ethyl acetate of 85-88% ester content, 25% denatured alcohol 23,

Half second viscosity nitrocellulose has a viscosity in 20% solution (20%dry basis-nitrocellulose in standard solvent) of from 2 to 5 seconds, equivalent to second in 12.2% solution. Viscosity determinations :of products of half second viscosity are customarily made in 20% solution for ease of manipulation.

cuprammonia is so much lower than the viscosity of-the 20% strength of nitrocellulose that the as standard falling ball method can not be applied to the cuprammonia solution. Neither can the cellulose concentration be increased since the cuprammonia solution is not capable of dissolving any appreciable excess over the standard 5 grams of cellulose.

In order, therefore, to establisha directrelae.; ti9nsliip between the viscosity of a cellulose and the nitfofillulowproduced therefrom, and pro-- vide a method of determining ,viscosity that can be applied directly to the cellulose, a di erent In view of the low viscosity of the cellulose Q Full strength ouprammonia Equivalent solution 20% conoontra- 12.2% oonnention nitrocollu: trot-ion nitrolose viscosity cellulose Viscosity Viscosity viscosity. pipette method standard 1 ling #7 pipette ball method 2. 0 11. 0 2. 2 11. 4 2. 6 ll. 6 2. 8 11. 0 3. 4 12- 0 4. 2 12. 4 4. 4 l3. 0 5. 0 13. 0 5. 4 l3. 0 7. 8 15. 0 9. 2 14. 4 l4. 6 16. 6 19. 8 17.2 44. 0 32 2 2. 0 124. 2 l8. 4 3. 2 161. 0 F3. 2 4. 0 104. 0 65. 2 4. 8 3%. 0 10a 4 8. 0 m 0 I 1ft. 6 ll. 8

This tabulation covering 19 samples extends over the range of 2 seconds to 520' seconds for the 20% concentration 01 nitrocellulose and it will be noted that for the direct preparation of A secon nitrocellulose (between 2 and 5 seconds in 20% concentration) a cellulose is required whose full strength cuprammonia solution has a viscosity between 11 and 13 seconds by the pipette discharge method. On the other hand, a cellulose whose full strengthcuprammonia solution has a viscosity 01 2.6 seconds by the standard falling ball method has a viscosity of 32.2 seconds by the other words. requires nearly three times as long to discharge as does the cellulose suitable for direct preparation of 5' second" nitrocellulose.

pipette discharge method or, in

and the 20% solution of nitrocelhiloeedirectly prepared from this 2.6 viscosity of 44.6 seconds. The following examples illustrate the process of the present inventidifsecond; has a Example 1.-1oo parts of rat dotte amen-s were mixed -with' 1100 parts of a 1% aqueous sodium hydroxide solution and heated in a digester at a temperature of about 170 C. pounds per squareinch pressure) -for three hours. The treated cellulose was then separated from the dilute caustic solution, washed.with water, and treated with 1500 parts of an aqueous 18% sodium hydroxide solution maintained at a temperature of about 18 to 14 C. (56 1 for 15 minutes. The mercerized cellulose was separated irom the mercerization. lye; washed with water. and heated with 1100 parts 01' aqueous 2% sodium hydroxide solution for nine hours at a temperature of about C. The product, which comprised more than 98% alpha-beta cellulose.

' was then washed thoroughly with water. The

washed cellulose product, when hitrated under .standard'conditions with the usual nitrating 1 acid mixture yie1ded-'a (12%:.5% nitrogen) nitrocellulose product having'a viscosity of 4.2 w en tested n a 20% solution; 1. e. the

nitrated cellulose product was what is known as second nitrocellulose.

Example 2.100 parts of raw cotton linters were heated with 1100 parts of aqueous .75% sodium hydroxide solution at 170 C. for 16 hours. The treated linters were then separated from the sodium hydroxide solution, washed with water, and mercerized for minutes in 1500 parts of an aqueous 18.25% sodium hydroxide solution maintained at around 12 to 14 C. (53 to 57 F.). The treated cellulose was then separated from the mercerization lye, washed with water, and digested for six hours in 1100 parts of aqueous 2% sodium hydroxide solution at a temperature of 170 C. After this treatment the cotton linters were thoroughly washed with water and nitratedin the customary manner. The nitrocellulose product possessed a viscosity of 4.6 seconds in solution.

Emmple 3.100 parts of bleached sulfite wood pulp (about 85% alpha cellulose) were mixed with 1100 parts aqueous 75% sodium hydroxide solution and heated at a temperature of about 170 C. (100 pounds per square inch pressure) for a period of five hours. The treated pulp was then separated from alkaline solution, washed with water, andtreated with 1500 parts of aqueous 18.6% sodium hydroxide solution for one hour at a temperature of about 22 C. (71 to 72 F.). The m'ercerized pulp was washed with water to remove the concentrated caustic and was digested with 1100 parts aqueous 1.0% sodium hydroxide solution at a temperature of 170 C. for a period of about 16 hours. This cellulose product, when nitrated in the usual manner, yielded a nitrated cellulose having a viscosity of 2.6 seconds in 20% solution.

Example 4.l00 parts of unbleached sulfite wood pulp were digested with 1100 parts of an aqueous solution containing 0.5% sodium hy-' droxide and 0.5% sodium sulfite (NazSOaflHzO) at a temperature of about 170 C. for five hours. The product was separated from alkaline solution. washed with water, and mercerized with 1500 parts of an aqueous 18.4% sodium hydroxide solution for one hour at a temperature of about 22 C. (71 F). The mercerized pulp was washed with water and digested for 16 hours at a tem- 1100 parts of an aqueous 1% sodium sulfite (NarSOaHHsQ) solution, the digested pulp was then separated from sodium sulfite solution and washed with water. The washed pulp was mercerlzed with 1500 parts oi an aqueous 18.4% sodlmm hydroxide solution for one hour at a temperature of 22 C. (71F). The mercerized pulp was washed with waterand digested for '16 hours in 1100 parts of aqueous 1% sodium hydroxide solution at a temperature of 170 C. The

product was then washed as in the preceding,

examples. The cellulose of this treatment. upon nitration, yielded a nitrocellulose having aviscosity of 3 seconds in a 20% solution.

Ezamplefilrwo parts of wood pulp, refined by the soda process, were digested for five hours at a nitrocellulose having a viscosity of 0.8 second in 20% solution.

Example 7.-A kraft wood pulp was digested for five hours with 1100% of its weight ofaqueous 0.75% sodium hydroxide solution at a temperature above 170 C. The digested pulp product was washed with water and mercerized in 1500 parts of 18.6% sodium hydroxide solution for a period of one hour at a temperature of about 22 C. It was then washed with water and redigested this time for a period of 16 hours in 1100 parts of a 1% sodium hydroxide solution at a temperature of about 170 C. This cellulose, when nitrated under standard conditions and with a nitrating acid normally used in the nitratlngindustry, gave a nitrocellulose having a viscosity of two seconds in 20% solution.

The amounts of solutions employed in the three steps of the process are not'critical but may be between 4 and 20 times the weight of the cellulose with highly satisfactory results.

The following example will serve to illustrate the usual nitration processes by which low viscosity nitrocellulose products may be prepared from the cellulose'of the present invention. It is to be understood of course that any of the well-known nitration methods yield nitrocelluloses of similarly low viscosity.

Example 8.The processed cellulose is picked and dried to a moisture content not to exceed 1%. 100 parts of the dried cellulose are then nltrated with 5000 parts of mixed acid containing approximately 21% to 22% HNOs, 60% to 61% H2804, and 17% to 19% H2O. The nitration is carried out for 25 to minutes at a tempera ture of to C. The resulting nitrocellulose is then washed with water and stabilized by boiling in a final aqueous wash having an acidity between .2% and .4% (calculated as H2804). The product represents 140 to 150 parts of nitrocellulose (dry basis), having a nitrogen content of from 11.7% to 12.1% and a viscosity in 20% solution of special solvent No. 366 within the 2 to 5 second range.

After stabilization the nitrocellulose is dewatered either in a filter press or centrifuge and then dehydrated with ethyl alcohol or other suitable dehydrating agent'in order to remove all water which is objectionable in the preparation of lacquers, artificial leather, etc. it is then packaged in containers in an alcohol wet condi: tion, the product for storage and transportation containing approximately 30% alcohol and 70% nitrocellulose.

In the above examples proportions are ex 'fibers low viscosity cellulose, which directly on nitration by the method herein described yields a nitrocellulose of second viscosity, which comprises removing non-cellulosic materials from the cellulose fibers, subjecting the resultant product to mercerization, and thereafter subjecting the mercerized cellulose to the action of a dilute alkaline solution having an alkalinity equal to at least of caustic alkali at a temperature betweenabout 150 C..and about 200 C. for between about 3 and about 24 hours.

2. The method of preparing from cellulose fibers low viscosity cellulose, which directly on nitration by the method herein described yields a. nitrocellulose of ,5 second viscosity, which comprises treating the cellulose fibers with a dilute alkaline solution, subjecting the resultant product to mercerization, and thereafter subjecting the mercerlzed cellulose to the action of a dilute alkaline solution having an alkalinity equal to at least /4% of caustic alkali at a temperature between about 150 C. and about 200 C. for between about 3 and about 24 hours.

3. The method of preparing from cotton low viscosity cellulose, which directly on nitration by the method herein described yields a nitrocellulose of ,5 second viscosity, which comprises removing oils, waxes, fats, and hulls from the cotton cellulose, subjecting the cellulose to mercerization, and thereafter subjecting the mercerized cellulose to the action of a dilute alkaline solution having an alkalinity equal to at least 14% of caustic alkali at a temperature of about 170 C. for between about 3 and about 24 hours.

4. The method of preparing low viscosity cellulose, which directly on nitration by the method herein described yields a nitrocellulose of 39 secohd viscosity, which comprises treating cellulose with an alkaline solution corresponding to an aqueous solution containing between about 34% and about 4% NaOH at a temperature between about 150 C. and about 200 C. for between about 3 and about 15 hours, mercerizing the prodact, and treating the mercerized product with an alkaline solution corresponding to an aqueous solution containing between about and about 3% NaOH at a temperature between about 150 and about 200 C. for between about 3 and about so 24 hours.

5. The method of preparing from cotton, which has been freed from oils, waxes, fats, and hulls,

- low viscosity cellulose, which directly on nitration by the method herein described yields a nitrocellulose of ,5 second viscosity, which method comprises treating cotton thus' purified with an aqueous solution containing between about 14% and about 28% sodium hydroxide at a temperature between about 2 and about 32 C. for between about 3 and about 60 minutes, and heating the resultant cellulose product with an aqueous solution containing between about V and about 3% sodium hydroxide at a temperature or about 170 C. for between about 3 and about 24 hours.

B. The method of preparing low viscosity cellulose, which directly on nitration by the method herein described yields a nitrocellulose of v, sec ond. viscosity, which comprises treating cellulose with an aqueous solution containing between about and about 4% of sodium hydroxide at a temperature between abouti50 and about 200 C. for between about 3 and about 15 hours, treating theproduct with an aqueous solution containing between about 1.4% and about 28% sodium hydroxide at a temperature between about 2 and about 32 C. for between about 3 and about 60 minutes, and heating the resultant cellulose product with an aqueous solution containing between about 14% and about 3% sodium hydroxide at a. temperature of about 170 C. for

between about 3 and about 24 hours.

7. The method of preparing from raw cotton linters low viscosity cellulose, which directly on nitration by the method herein described yields a nitrocellulose of ,5 second viscosity, which comprises treating the cotton linters with an aqueous solution containing between about and about 4% of sodium hydroxide at a temperature between about and about 200 C. for between about 3 and about 15 hours, treating the product with an aqueous solution containing between about 14% and about 28% sodium hydroxide at a temperature between about 2 and about 32 C. for between about 3 and about 60 minutes, and heating the resultant cellulose product with an aqueous solution containing between about and about 3% sodium hydroxide at a temperature of about C. for between about 3 and about 24 hours.

8. The method of preparing from cellulose fibers low viscosity nitrocellulose of the ,5 second type, which comprises removing non-celiulosic materials from the cellulose fibers, subjecting the resultant product to mercerization, thereafter subjecting the mercerized cellulose to the action of a dilute alkaline solution having an alkalinityequal to at least of caustic alkali at a temperature of about 1'70 C. for between about 3 and about 24 hours, and nitrating the" resultant product.

9. The method of preparing from cellulose fibers low viscosity nitrocellulose of the second type, which comprises treating the cellulose fibers with a dilute alkaline solution, subjecting the resultant product to mercerization, thereafter subjecting the mercerized cellulose to the action of adilute alkaline solution having an alkalinity equal to at least 54% of caustic alkali at ,a temperature between about 150 andfabout 200 C. for between about 3 and about 24 hours, and nitrating the resultant product.

10. The method of preparing from cotton low viscosity nitrocellulose of the 55 second type, which comprises removing oils, waxes, fats, a d hulls from the cotton cellulose, subjecting e cellulose to memorization, thereafter subjecting the mercerired cellulose to the action of a" dilute alkaline solution having an alkalinity equal to at least of caustic alkali at a temperature of, about 170 0. for between about 3 and about 24 hours, and nitraflng the resultant product.

11. The method of preparing from raw cotton linters low viscosity nitrocellulose of the ,5 second type, which comprises treating the cotton linters product with an aqueous solution containing bep tween about and about 3% sodium hydroxide at a temperature of about 170 C. for between about 3 and about 24 hours, and nitrating the resultant product.

SAMUEL ISAAC nonmssou. ROY- MACKAY swarm-roan.