LABORATORY PREPARATION OF CELLOPHANE MEREDITH MILLER E. I. du Pont de Nemours 8 Company, Inc., Film Dept., Cellophane Technical Sedion, Riohmond, Virginia
THE conventional procedures for manufacturing cellophane involve a series of steps to convert opaque, fibrous cellulose, such as cotton or wood pulp, into a continuous, thin, transparent sheet. This conversion consists of dissolving the cellulose, casting it into the desired form, and then rendering it insoluble. The procedures, mechanics, and chemistry involved are described in a number of publications.' 2 , 3 . The following simplified procedure defines conditions that are suitable for the preparation of cellophane for small-scale classroom demonstration purposes. SAFETY PRECAUTIONS
The following safety precautions should be observed because of the corrosive and toxic nature of the chemicals and compounds involved.
Acid-proof goggks and rubber gloves should be worn by those conducting the exper$ment. The experiment should be conducted in a n eficient exhaust hood since carbon disuljide and hydrogen suljide are evolved. Affected areas should be rinsed immedialely and thoroughly with large quantities of water i j the slightest amount of sodium hydroxide, acid, or viscose comes in contact with skin or clothes. These chemicals can cause serious irritation or damage if not removed promptly. Only qualified personnel should perform this ex@mat. Glass vessels that are subjected to pressure w vacuum should be wrapped with adhesive tape or cloth to reduce hazards in case of breakage. A n y unused solutions or viscose can be greatly diluted with water and discarded, slowly and with large amounts o f water, into the szwer system. Do not discard m ' d solutions immediately following viscose wasfr. VISCOSE PREPARATION
Loo=, absorbent, medical grade cotton (100 g.) is covered with a 30°C., 18yo solution of sodium hydrox-
' INSHEEP,G. C., AND
P. VAN HORN,Ind. Eng. Chem., 44,
2511-24 (1952). HEUSER,E., "The Chemistry of Cellulose," John Wiley & Sons, Inc., New York, 1947. "Cellulo~c and Cellulosr OTT. E.., AND H. M. SPURLIN. Derivatives," Intersoienor Publishers, Ine., Nrw York, 1954, Vol. V, Part 11, pp. 959-1018. "ONANT, J. B., AND A. H. BLATT,"The Chemistry of Organic Compounds," 3rd ed., The Maomillan Co., New York, 1947, pp. 29%-99.
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VOLUME 35, NO. 10, OCTOBER, 1958
ide. The cotton should remain, or "steep," in this solution for one hour t o convert the cellulose to 'Lalkali cellulose." Decant and transfer the wet alkali cellulose (CeHmOd, Cellulose
+ 3;NnOH
-
+
( C S H ~ O ~ N ~ )2-HsO , "Alkah cellulose"
to a Biichner funnel fitted with a suction flask. Thc alkali cellulose should be hand-pressed and aspirated as dry as possible. After breaking up any large lumps or packed areas into crumbs, the alkali cellulose is transferred to a onegallon, wide-mouth bottle for xanthation. Xanthation is accomplished by adding 40 g. of carbon disnlfide to the alkali cellulose in the bottle and maintaining the sealed bottle at 30°C. for two hours. The bottle should be rotated, if only occasionally, to insure uniform xanthation. The bottle should be opened in (C,H.O,Nn).
+ z-CSz
-
(CeH~05CBNa), Sodium cellulose xsnthste
the hood and 1000 g. of cold (5°C.) water and 200 g. of 18% sodium hydroxide added. The mixture ir then stirred (using a high speed, stainless steel agitator if possible) for two hours while maintaining a 10'-15'C. temperature. The thick orange-colored solution that results is called "viscose." Stopper the bottle, or seal loosely, and store a t 0'-15% for twelve to twentyfour hours. Vacuum may be applied during storage to facilitate removal of air bubbles. CELLOPHANE CASTING
The sheet of cellophane is prepared by spreading a thin (0.010-0.020 inch) layer of viscose on a glass plate and then coagulating the viscose by placing the plate and viscose in a 45'C., 40% ammonium sulfate bath for sixty seconds. Conversion to cellulose is accomplished by immersing the coagulated sheet, still on the plate, in a 45'C., 129& sulfuric acid-18yo sodium sulfate bath for two minutes. The film should be mashed in hot
-
+ X-H~SOI2(CsH,oOs)=+ 22-CS* + x-N&Or
Z(CaHsOsCS3Na),
Cellophane
water for ten minutes and then clamped to a photographic ferrotype plate (or in an emhroidery hoop) t,o prevent shrinkage during air drying at, temperutures less than 100°C. A more flexible cellophane can be obtained by plasticizing the wet sheet for 15 minut,es in a 5y0 aqueous solution of glycerine prior to drying.
