e a u a H I G H - S C H O O L C H E M I S T R Y * m rn m

Demonstrations on the Preparation and Molding of Plastics

JOSEPH F. CASTKA, Boys High School, Brooklyn, New York

THE PRODUCTION of plastics rose steadily I during the depression years to 127 million pounds in 1935 and boomed to almost 300 million pounds in 1939. By 1941 production had again increased by 50 per cent and in 1942 was close to 600 million pounds. This amazing growth coupled with the ready adapta- tion of plastics to wartime needs has done much to stimulate the interest of chemistry students in this most fascinating of chemical fields.

Great difficulty, however, has been encountered in securing adequate directions and reference materials to guide classroom demonstrations and individual laboratory experiments. It is the purpose of this article to mention some of the references, sources of materials, and technics that have helped student groups perform useful and instructive experiments.

One of the most timely demonstrations deals with the production of a sample of synthetic rubber. This material is of the Thiokol type. The Thiokols have been used principally in various fuel and gasoline hoses, gaskets, and more recently in bullet-proof gas tanks, tire retreads, and synthetic tires. The clue to the demonstration was found in an article by Martin and Patrick ( I ) , describing the industrial preparation which took five hours. Discussion with Dr. Leonard Fliedner of Flushing High School, New York City, disclosed the fact that he was preparing samples for his classes in about half an hour.

The following procedure produces a sample within ten minutes. The elastic qualities of the material may then be shown by stretching. Samples have been run through a rubber mill by the Thiokol Corpora- tion of Trenton, N. J., and have been found to be very similar in nature to the first samples produced by Dr. Patrick, the inventor. The materials needed-thyl- ene chloride and sodium polysulfide, technical grade fused-may be readily purchased for less than a dollar a t chemical supply houses.

Demonstration: It is necessary first to change the sodium polysulfide to sodium tetrasulfide. This is done by saturating a saturated solution of the poly- sulfide with sulfur. Add 100 ml. of the tetrasulfide solution to 25 ml. of ethylene chloride. A milk of magnesia pellet or a pinch of magnesium oxide is added as a catalyst. These materials are placed in a 500-ml. flask to which an air or water condenser is attached vertically to serve as a reflux to prevent the

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escape of volatilized ethylene chloride. The mixture is then heated until the ethylene chloride starts to volatilize, after which heating is no longer necessary because the reaction is exothermic. Small particles of the Thiokol are formed a t the interface between the tetrasulfide and ethylene chloride. These float to the top, agglomerate, and then sink to the bottom of the flask. The liquid is decanted and the solid washed several times with water. The water may then be squeezed out and the rubber-lie qualities demon- strated. Forceps or tongs should be used in handling the synthetic material.

The production of bakelite-like plastics from aniline or aniline hydrochloride and formaldehyde is probably the commonest and best-known demonstration in the field. Varying proportions may be used. Exact directions have been given in various sources ( 2 , 3 , 4 , 5 ) .

A more striking demonstration on the formation of a bakelite plastic is the one frequently demonstrated by Professor Hubert N. Alyea of Princeton. Dry hydrogen chloride is passed into a 500-ml. Erleu- meyer flask which contains 50 ml. of glacial acetic acid, 25 ml. of formaldehyde (40%) and 20 g. of phenol. A towel is mapped loosely around the neck and opening of the flask. A large mass of pink plastic is produced with almost explosive violence within five minutes. The time may be controlled by controlling the rate of production of hydrogen chloride. The hydrogen chloride is produced by dropping concen- trated hydrochloric acid into sulfuric acid. The dropping funnel should have a tube drawn to a capillary width dipping below the surface of the sulfuric acid. The hydrogen chloride is then passed through another test tube containing sulfuric acid.

Directions for the production and membrane forma- tion of cellulose nitrate and cellulose acetate appear in various laboratory manuals in organic chemistry. Other valuable suggestions are found in textbooks on cellulose chemistry, such as Doree (6). It is also possible to secure cellulose acetate from safety film or plastics in the home by dissolving them in acetone. The gelatin and silver may be removed by boiling in water. Similarly, cellulose nitrate may be secured from professional 35-mm. film by dissolving in alcohol- ether. Molding of these materials may be performed by evaporation of the solvent (4).

Directions for the preparation of viscose using a 13

variety of cellulosic materials have been given by Doree (6). A very simple and effective experiment on the preparation of viscose and a viscose fiber is described by Soifer (7).' The continuous manufacture of a rayon fiber by the cupraammonium process has also been described (8).

Formation of plastics by straight polymerization is best accomplished by the use of the acrylates or sty- rene. Auylate and methacrylate monomers stabilized with hydroquinone may be obtained from E. I. du Pont de Nemours and C~mpany,~Eastman KodakC~mpany,~ and Rohm and Haas Company.' Direction sheets for demonstrations, distributed by Rohm and Haas Com- pany describe the preparation of the polymer. Benzoyl peroxide is added to remove the inhibitor. Other methods for the removal of the inhibitor, by careful distillation or washing with sodium hydroxide solution, are given by Halenz and Botimer (9), who also de- scribe the procedure for the use of methyl methauylate as an imbedding agent for biological and other speci- mens. Styrene may be purchased from the Eastman Kodak Company and is stabilized by hydroquinone, which may he removed by simple distillation. Extreme caution is urged in handling styrene. Communications from various chemical concerns emphasize the danger in polymerizing styrene by heating in a test tube, al- though this is suggested in one article on plastics and resins.

Various methods for molding, such as casting and evaporation of solvent, have been mentioned (4, 9). If a Carver press is not available, pressure molding may be performed as follows.

Demonstration: A piece of one-inch iron pipe an inch and a half long is capped and preheated for about one minute with a Bunsen burner. About one-auarter -

'See also FROMM, "A simple classroom demonstration of the manufacture of rayon," J. CHBM. DUC, 20, 197 (1943).

E. I. dn Pont de Nemours an? company, Inc., Wilmington, Delaware.

a Eastman Kodak Comoanv. Chemical Sales Division. Roches- . .. ter, New Ymk. ' Rohm and Haas Company, 222 West Washington Square.

Philadelphia. Pennsylvania.

inch of cellulose acetate molding powder is poured in and a two-inch length of iron rod, made to fit into the pipe, is inserted. The pipe and plunger are then placed firmly in a steel vise and heated for about a minute. This will serve to drive out most of the air between the granular particles of molding powder, thereby producing a clear mold. The vise is then tightened as much as possible and the pipe is heated ~trongly for about two minutes. The entire assembly is then cooled with water, the cap removed, and the mold extracted by pushing out the plunger. Of course, the smoother the interior of the pipe the less will he the difficulty in removing the mold. Suitable material to use is Tenite, obtained in various colors from the Tennessee Eastman Corporati~n,~ or transparent cellulose acetate, obtained from the Hercules Powder C ~ m p a n y . ~ Experience will determine the exact time needed for each step, since overheating may cause decomposition and underheating will cause in- complete fusion of the plastic. Of course, conditions are not so easily controlled as with the Carver press but suitable molds can he produced. -

Vennessee Eastman Corporation. Kingsport, Tennessee. Hercules Powder Company, Delaware Trust Building. Wil-

mington, Delaware.

LITERATURE CITED

(1) MARTIN AND PATRICK, "The constitution of polysulfide mbhers,"Ind. Eng. Chcm., 28, 1145 (1936).

(2) FOSTER AND ALYEA, "An introduction to general chemistry," 2nd ed., D. Van Nastrand Co., Inc., New York, 1941.

(3) ART^, "Lecture demonstrations in general chemistry," 1st ed., McGraw-Hill Book Co., Inc., New Ymk, 1939.

(4) JOSEPH, "Demonstrations and pupil projects," The Science Classroom, 22, No. 2 ,4 (Nov., 1942).

(5) HAUT. "Bakelite-twe ~lastics. a demonstration." T. CREK. . - ED&. IS, 43 (193%).-

(6) DOREE, "The methods of cellulose chemistry," D. Van Nostrand Co., Inc., New York, 1933, pp. 268-71, 225-6, 248-9.

(7) SOIFER, "Makina viscose and rayon." The Science Teachcr. 9, No. 3, 34 (1942).

(8) JENKINS, GABUZDA, IWD SANER, "An apparatus to demon- strate the continuous manufacture of rayon." J. CHEM. Eouc., 18, 4 3 3 4 (1941).

(9) HALENZ AND BOTIMER, "Methyl methacrylate as imbedding agent," J. CHEM. EDUC., 19,313-14 (1942).