Ion Exchange Cottons JOHN D. GUTHRIE U . S . Department of Agriculture, Southern Regional Research Laboratory, New Orleans, La.
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ERTAIN chemically modified cotton fabrics exhibit ion exchange properties similar to those of the ion exchange resins ( 8 , 6, 7 , 8). These ion exchange cottons are made by the introduction of substituent groups with basic or acidic properties into the cellulose molecule under such conditions t h a t fabric structure is retained. Most of these chemically modified cottons were made primarily for purposes other than ion exchange. For example, phosphorylated cotton, a typical cation exchange cotton, was originated by Ford and Hall ( I ) for the purpose of obtaining a flame-resistant fabric, and interest in aminized cotton, a typical anion exchange cotton, centers about its dyeing properties and possible value for further chemical modification (9). Furthermore, the reactions by which these cottons are produced have significance in the field of cellulose chemistry because of the ease with which they may be followed analytically and the fact that most of them may be carried out in aqueous media. The present paper summarizes the preparation of such cottons, most of which have been reported previously and is limited t o a discussion of their ion exchange properties and possible applications.
The succinic acid half ester of cotton cellulose was made by heating fabric with a 10% solution of succinic anhydride in dry pyridine a t 60" C. for 26 hours and washing thoroughly. The cation exchange properties of this material have been previously reported by McIntire and Schenck ( 8 ) . Sulfatoethylated cotton was made by the action of 2-chloroethylsulfuric acid, C ~ C H Z C H ~ O S O on ~ H ,fabric by a procedure similar to that described for sulfoethylated cotton. Phosphatoethylated cotton was made by the use of 2-chloroethylphosphoric acid, C1CH2CH~0P03Hx. The conditions most favorable for the production of these last two cottons have not yet been established nor have their exchange properties been adequately investigated. They behave like cation exchangers of the strong acid type. PREPARATION O F ANION EXCHANGE COTTONS
PREPARATION OF CATLON EXCHANGE COTTONS
PHOSPHORYLATED COTTON. This product was made by the method of Ford and Hall ( I ) by curing cotton with a mixture of phosphoric acid and urea. Typically, cotton sheeting that had been kier-boiled in 2% sodium hydroxide solution wasphosphorylated by wetting it with a solution containing 49.6% urea, 18.4oJ, phosphoric acid, and 320/, water, squeezing out the excess solution, heating the fabric for 30 minutes a t 150' C., and washing thoroughly. Phosphorylated cotton has also been produced in the form of loose fiber, roving, and yarn. The fabric has been produced on a pilot plant scale. I t s cation exchange properties have been described previously ( 7 ) . SULFOETHYLATED COTTON. This material was made by reacting 2-chloroethylsulfonic acid with cotton in the presence of strong sodium hydroxide solution ( 5 ) . For example, a roll of cotton fabric was passed through a solution composed of 5185 grams of water, 2465 grams of sodium hydroxide, and 850 grams of the sodium salt of 2-chloroethylsulfonic acid, ClCHzCHzS03Na (added last t o the cooled solution), and then put through squeeze rolls. The pickup of solution was 146% of the original weight of the fabric. The fabric was passed over rotating steam-heated cans with a surface temperature of about 85" C. a t such a speed t h a t the fabric was in contact with the cans for about 4 minutes. The fabric was washed and then dried by passingit over the steam cans again. The product was a stiff, organdylike fabric having a cation exchange capacity of about 0.51 meq. per gram. Sulfoethyl cellulose has previously been made by Time11 (11)but his product dispersed in water and consequently was of no value as a cation exchanger. I n the presence of strong sodium hydroxide, cotton may be also sulfoethylated by the action of ethylene sulfonic acid, CHs=CHSOaH, or with ethionic acid, HO~SOCHICHZSOIH, to produce products equivalent t o those obtained with 2-chloroethylsulfonic acid. OTHER CATION EXCHANGE COTTONS. Partially carboxymethylated cotton (9) was made by wetting fabric with a 40% aqueous solution of monochloroacetic acid, squeezing out the excess, mercerizing by soaking 1hour in a 42% solution of sodium hydroxide, and washing thoroughly.
AMINIZEDCOTTON. This material was made by reacting cotton with 2-aminoethylsulfuric acid in the presence of sodium hydroxide ( 2 ) . Icier-boiled cotton sheeting was passed through a solution composed of 25 pounds of sodium hydroxide, 65 pounds of water, and 10 pounds of 2-aminoethylsulfuric acid, and then put through squeeze rolls. The pickup of solution was about 100% of the original weight of the fabric. The fabric was then passed over rotating cans heated with steam at a pressure of 20 pounds a t such a rate t h a t the fabric was on the cans for about 15 minutes. The fabric was then washed and dried. To increase its anion exchange capacity, the fabric was put through the process two more times. Its nitrogen content was 0.8% on a dry basis and its anion exchange capacity was 0.6 meq. per gram. Later it was found t h a t this exchange capacity could be obtained in one processing by use of a solution composed of 30 parts of sodium hydroxide, 20 parts of 2-aminoethylsulfuric acid, and 50 parts of water. Cotton may also be aminized in the form of loose fiber, sliver, or yarn. AMINIZED-IMINIZEDCOTTON. Although aminized cotton was found t o have good anion exchange properties, its total capacity was low. Even with repeated treatments the highest anion exchange capacity obtained reached only 1.2 meq. per gram. At about this point the fabric became stiff and boardy and began to disperse. It was found, however, t h a t a higher capacity could be reached without loss of fabric structure by reacting aminized fabric with the vapor of ethylenimine. For example, bleached cotton sheeting was aminized once to obtain a nitrogen content of 0.85% and a n anion exchange capacity of 0.6 meq. per gram. , It was then placed in a vacuum chamber heated a t 70" C. and after the chamber had been evacuated, ethylenimine was introduced in a n amount equal to 16% of the weight of the fabric. After remaining in the chamber for 3 days the ethylenimine treatment was repeated. The fabric had an anion exchange capacity of 2.1 meq. per gram. After four regeneration cycles its capacity was 1.8 meq. per gram and its nitrogen content 3.8y0. QUATERNARYAMINIZED COTTON. Diethylaminoethylated cotton was made by the method of Hartmann (3)by wetting fabric with a 10%aqueous solution of 2-~hloroethyldiethylamine,drying, and then mercerizing with a 25y0 solution of sodium hydroxide overnight a t room temperature. After washing and drying the diethylaminoethylated cotton mas refluxed in a 10% solution of methyl iodide in absolute ethyl alcohol for 2 hours ( 5 ) . It is believed that some of the tertiary amino groups were converted t o quaternary groups by this process.
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of acetic acid, 4.76, and with the pKa for succinic acid, 4.18. TABLEI. IOKEXCHANGE PROPERTIES O F CHEMICALLY MODIAminized cotton had a higher basic strength than the wcalily FIED COTTOXFABRICS IN COMPARISON WITH Iox EXCHANGE basic anion exchange resins, while aminized-iminized cotton had RESINS an intermediate value. The material listed as quaternai:, aminTotal Capacized cotton, although a stronger base then aminized cotton, is ity, 31eq. per p H at Half Gram Capacity llaterial not so strong as a strongly basic anion exchange resin. I t inn\l.? be that only part of the amine groups of quaternary aminixed 7.0 0.5 cotton are in the quaternary form. 3.7 The acidic and basic stiengths of the ion exchange cottons 4.8 Partial succinic half ester of cotton 0.3 Sulfonic acid cation exchange resin 4.2
