BAKELITE TYPE PLASTICS-A
DEMONSTRATION
ARTHURHAUT Gmver
Cleveland High School, New York City
A RECENT article' by H. Lindner showed how a Bakelite-type plastic could be prepared in the school laboratory. Using the directions given, the present author found that although a suitable product was obtained, the procedure took too much time and was inconvenient for classroom demonstration. After many trials it was found that the following modification will allow the demonstrator to make a Bakelite-type plastic in one classroom period of about forty-five minutes, followed by subsequent baking. Twenty-five grams of phenol and 50 cc. of 35 per cent. formaldehyde are heated with 3 cc. of 3 M 0 per cent. sodium hydroxide solution in a reflux condenser using a flash of about 40 cc. capacity. As the heating proceeds, the mixture changes to a red color and becomes more viscous. When approximately threequarters of an hour has elapsed the contents of the flask will have assumed the consistency of molasses, and the bubbles which rise through the mass will encounter noticeable difficulty in escaping from the surface. This is the signal for removing the flame and immediately pouring the viscous product into a twoounce wide-mouthed bottle until the latter is about three-quarters full. The substance a t this time changes to a white material resembling dough. It is now ready for baking. The flask in which the mixture was heated should be cleaned as soon as possible with a strong caustic soda solution. If allowed to stand, the hardened product is difficult to remove. The baking operation may be performed in a home-
made oven constructed from a cylindrical can in which laboratory chemicals are shipped. The can should be about fifteen inches tall and six or seven inches in diameter. The cover is discarded and then the can is inverted over an ordinary electric light bulb screwed to a base and resting on the laboratory table. A hole is cut in what is now the top so that a thermometer may be admitted. The product in the wide-mouthed bottle is supported on a tripod and wire gauze over the bulb in the can. The legs of the tripod may be cut off somewhat if the latter occupies too much space in the oven. A few small holes about a quarter of an inch in diameter are bored around the top and bottom of the can to allow for air expansion. The baking should be begun a t a temperature of not more than 50°C. and after about two hours it should be increased to about 75'C. The author found that a fifteen-watt bulb would maintain a temperature in the neighborhood of 50°C. and a twenty-five-watt bulb was good for 75'C. The purpose of the baking is to dry the product, and too rapid heating would crack the plastic. A total of four hours of heating is usually sufficient but a better plan is to leave the material in the oven overnight a t the lower temperature. Shrinkage takes place, and the bottle must be broken to remove the substance which now has a red color and is somewhat brittle but resembles the commercial products in appearance. When a two-ounce wide-mouthed bottle is used for the mold, as suggested above, the shape of the product suggests an umbrella handle. Other molds, such as an ordinary test-tube, may be used. A very ' L m m a , 2. fihysik. c h . Unkwkht, 48, 251 (Sept.-Oct., satisfying result is obtained by using one cover of a Petri dish. 1935).
