In the Classroom edited by
filtrates & residues
James O. Schreck University of Northern Colorado Greeley, CO 80639
Rayon from Dryer Lint: A Demonstration Michael A. Knopp Miami University Middletown, 4200 E. University Boulevard, Middletown, OH 45042 Chemists are respected for their skill at converting inexpensive raw materials into more valuable substances. Although turning lead into gold by chemical means was abandoned long ago, the notion of converting waste materials into more valuable commodities has an added significance in this era of raw material recycling and conservation. In this demonstration, dryer lint, obtained from the laundering of cotton-containing articles, was made into rayon by an adaptation of the cuprammonium process (1) used to convert cellulose to rayon. Clearly, this demonstration is not a cost-effective means of preparing rayon. It is not economical to collect several hundred tons of dryer lint for this purpose, nor would it be feasible to separate cellulose lint from non-cellulose lint. This activity is best performed as a demonstration by the instructor, rather than as a student experiment, owing to the quantity of ammonia gas that would be present in a room if 20–30 students were to perform the activity. The necessity of properly disposing of a large amount of copper-containing waste would also be a problem if an entire class performed this experiment. Edward Schweizer was the first to report (2) that a saturated solution of copper(II) carbonate in concentrated ammonium hydroxide would dissolve cellulose. This assertion, mentioned in a profile of Schweizer (3) and subsequent history of rayon by Kauffman (4), suggested the use of a solution of copper(II) carbonate in concentrated ammonium hydroxide to dissolve dryer lint. Kauffman has depicted cellulose as having a puckered sheet structure held together by hydrogen bonding between neighboring chains. Kauffman cited a paper by Reihlen (5) stating that the cellulose is held in solution by complexation of the Cu2+ ions with the deprotonated hydroxyl groups of the cellulose chain (eq 1). nCu 2+ + (C6H10O5)n + 2nOH {
(CuC 6H8O5)n + 2nH2O (1)
This process requires a high pH to ensure the deprotonation of the cellulose hydroxyl groups. Other previous rayon preparation experiments (6, 7) used copper(II) sulfate pentahydrate to prepare copper(II) hydroxide, which must be washed, filtered, and then added to concentrated ammonium hydroxide to yield the solution used to dissolve the cellulose. Summerlin and Ealy (8) made copper(II) hydroxide by titrating a saturated solution of copper(II) sulfate with concentrated ammonium hydroxide. The procedure for the experiment outlined below is therefore simpler, as no tedious filtration and washing is needed when copper(II) carbonate is used. Moreover, cellulosecontaining dryer lint already has a high surface area; it can be dissolved in the ammoniacal copper(II) carbonate solution without further treatment. The filter paper, which was used by Summerlin and Ealy, needed to be torn into pieces.
Procedure CAUTION: The use of concentrated ammonium hydroxide requires the use of a fume hood in good working order. Avoid inhaling the dust from powdered copper(II) carbonate, as copper compounds are toxic. Safety goggles and gloves must be worn when working with sulfuric acid and concentrated ammonium hydroxide, since both substances can cause severe burns. Into a 100-mL beaker place basic copper(II) carbonate powder (2.27 g) and a magnetic stir bar. Concentrated ammonium hydroxide (50 mL) is added and the beaker is covered with a watch glass. The mixture is magnetically stirred for five minutes. The dark blue liquid is decanted from most of the excess CuCO3 into a 100-mL beaker. Dryer lint (0.7 g) from the laundering of cotton articles is stirred into the decantate with a glass stirring rod. Any insoluble material is removed with the glass rod; the insoluble material is primarily hair. The resulting solution is decanted into a small plastic screw-cap jar and stored for ca. 2 hours before use. For the demonstration, the mixture is drawn up into a medicine dropper. The tip of the dropper is placed below the surface of a dilute (3 M) solution of sulfuric acid (6) in a large (190 × 100 mm) crystallizing dish. A small amount of the blue viscous liquid is squeezed from the eye dropper and held against the side of the dish with a glass rod. The dropper is then pulled to the opposite side of the dish while squeezing the bulb and holding the tip of the eyedropper under the surface of the acid. A thread several centimeters in length can be pulled in this fashion. If too much liquid is squeezed, some “blobbing” may occur. The thread loses its blue color after a few minutes (6). The color disappears because the Cu2+ ions diffuse from the thread into the sulfuric acid solution. This demonstration was performed using an overhead projector (7) for three classes, each having about 10 students. The solutions must be disposed of in compliance with local environmental regulations. The crystallizing dish containing the 3 M sulfuric acid and rayon threads should not be passed around the room or handled by the students because of the danger of a spill. Literature Cited 1. Shakhashiri, B. Z. Chemical Demonstrations: A Handbook for Teachers of Chemistry; University of Wisconsin: Madison, 1983; Vol. 1, p 247. 2. Schweizer, E. J. Prakt. Chem. 1859, 76, 344. 3. Kauffman, G. B. J. Chem. Educ. 1984, 61, 1095. 4. Kauffman, G. B. J. Chem. Educ. 1993, 70, 887. 5. Reihlen, H. Z. Anorg. Chem. 1948, 257, 340. 6. Tested Demonstrations in Chemistry, 6th ed.; Alyea, H. N.; Dutton, F. B., Eds; ACS Division of Chemical Education: Easton, PA, 1965; p 111. 7. Kauffman, G. B.; Karbassi, M. J. Chem. Educ. 1985, 62, 878. 8. Summerlin, L. R., Ealy, J. L. Chemical Demonstrations: A Sourcebook for Teachers; ACS: Washington, DC, 1985; Vol. 1, pp 126, 178.
Vol. 74 No. 4 April 1997 • Journal of Chemical Education
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