Demonstrations on the Premration J.

and Molding of Plastics-Part I1 JOSEPH F . CASTKA

Boys High School, Brooklyn, New York

HE PLASTICS study a t Boys High School has contmned to hold the interest of the students. T .

Since the author's publication of the results of group activities ( I ) , more interesting experiments have been developed. A series of demonstrations on molding by compression, extrusion, and transfer have evolved from the original technique of molding plastics by the use of a capped iron pipe and plunger.

It appeared that better results might be obtained by using uncapped metal cylinders, metal plungers, and a demonstration model hydraulic press. A small tool- a steel cylinder 11/2 inches in height and inch in in- ternal diameter-was produced, and a steel plunger 21/2 inches in height was fitted to the cylinder. The cylinder was then placed upon a small steel plate which was insulated from the upward-moving platform by a layer of asbestos. Molding powders of various types were poured into the cylinder to a height of approxi- mately '/c inch, the piston was inserted, and the cyl- inder was preheated for about one minute by a Fisher burner. Low pressure was exerted, and the cylinder was

heated strongly for one minute. After this, full pres- sure and strong heat were applied for one minute, and the pressure was used alone for another minute. Where cooling was necessaxy before press removal, as in the case of thermoplastics like cellulose acetate, the cylinder and contents were wrapped in a wet towel or had water poured over them. Thermosetting materials like the phenol formaldehydes do not require cooling, but the process was used to facilitate free handling of the cylin- der.

This method of molding plastics was not entirely suc- cessful. Flashes escaped during the molding of discs, or buttons, which formed in the lower part of the cylin- der. The under sides of these buttons often showed evidence of insufficient or uneven heating. Then again, the piston frequently had to be hammered loose from the cylinder because of the fin formed between i t and the cylinder walls.

To overcome these difficulties, another cylinder was made--of the same height but '/4 inch larger in internal diameter. Two brass pistons were produced, designed to insure more even heating. The upper plunger was 2 inches long, and the lower base 1'/* inches in height. The base, or lower piston, was built with '/e inch fitting into the cylinder and 1 inch sewing as a stop inches in external diameter. The top 11/4 inches of the upper piston were slightly tapered to make manual ex- traction easier. Brass was used because i t seemed that the hizher coefficient of expansion of this metal, to-

gether with its greater heat conductivity, would make possible easier extraction of plunger and base, since less fin would be produced. With these improvements successful discs were made from Tenite and Hercules cellulose acetate, Bakelite phenol formaldehyde, Plas- kon urea formaldehyde, Rohm and Haas Crystalite, and Dow Styron. By using great heat it was possible to obtain relatively clear discs of Crystalite. Light transmission qualities of this material were shown when the disc, held edgewise between two fingers, was brought close to an electric light bulb.

Time, heat, and pressure requirements varied with the materials used, but in general no more than five minutes were necessary to produce a disc. Coins were successfully molded in phenol formaldehyde and trans- parent, colorless cellulose acetate. Mottled and layer effects were produced by mixing colored cellulose ace- tate powders.

The next step was to adapt the procedure to extru- sion by adding one-half inch of molding material, clos- ing the mold with slight pressure, heating strongly for two minutes, and applying strong pressure as quickly as possible. For this process a small hole was bored mid- way in the side of the smaller cylinder, and pistons of a newer type were fitted to it. The rods produced tended to swell and curl when they reached the air, but 6-inch samples of cellulose acetate and casein molding materials were obtained.

The possibility of injection molding was considered, but transfer molding, a variation, was substituted. A steel disc '/s inch in height was made to fit into the large cylinder, and a small opening was bored in the center of the flat side. Three overlapping holes were drilled with a '/4-inch steel bit in a steel variation of the base. The extrusion method was used here, and cel- lulose acetate molds of a three-leaf design were pro- duced in various colors. Upon removal from the cylin- der the molded object adhered to the small metal disc. Sprue and runner remnants have to be removed and finished when objects are molded by injection.

A small tapered cup a/4 inch high was produced from a brass mold of the type shown in a Bakelite booklet (2). Although inserting water-soaked cellophane be- fore adding molding powder made removal of the cup from the female half of the mold relatively easy, i t pro- duced steam, causing an uneven exterior.

A variation of an industrial procedure in Sutermeister and Brown (3), one of several experiments in the preparation of plastics, resulted in the production of casein discs and rods. Ten grams of casein, 6 ml. of water, and 1 ml. of glycerin were mixed in a mortar.

Part of this molding material was heated mildly and extruded. The rest was made into casein discs by compression. After two weeks of hardening in a 6 per cent formaldehyde solution, the rod and discs dried into horny casein plastics.

An article in Popular Science (4) was used as a guide in the manufacture of hexamethylenetetramine from formaldehyde and ammonium hydroxide. The white solid "Hexa" is heated with an equal quantity of phenol to produce a yellow resin.

Sources of other interesting and instructive experi- ments on plastics were discovered. Experiments on the formation of a phenol-formaldehyde resin with am- monium hydroxide as a catalyst, the depolymerization of methamylate resin, and the preparation of metha- crylate resin, are explained by Cheronis (5). Sweeney and Arnold (6) give valuable suggestions on a variety of materials. Tests for identification of common com- mercial plastics by combustibility, flame colors, and odors are dcscribrd by Nechamkin (7) and are simple enough to be performed by any high-school student of chemistry. Von Stein (8) described spot testing with uranium nitrate for the detection of phenolic resins. D'Allelio and Guile have written a most useful refer- ence book (9). I t is a laboratory manual which con- tains 43 experiments on the preparation, and I3 on the uses of resinous materials. The preparations of a pro- tein fiber and a cumerone-indene resin, and part of the

experiment on the preparation of a superpolyamide (similar to nylon) may be readily adapted to high- school use, although many of the experiments are suit- able only for the more advanced student.

These experiments were carried out with the help of William Goldberg, laboratory assistant, and Howard Sachar, Stanley Shaw, Wallace Mandel, and Murray Lerner, students.

LITERATURE CITED

CASTIW, "Demonstrations on the preparation and molding of plastics," J., CHEM EDUC., 20,253 (1943).

"Bakelite Moldmg Plastics," Bakelite Corporation. New York, 1940, p. 7.

SUTE~MEISTER AND BROWN, "Casein and ItS Industrial Applications." 2nd ed., Reinhold Publishing Corporation, New York. 1939, pp. 187-98.

WALES, "Try your hand at organic chemistry," Popular Science Mn mine. 134,208 (1939).

C~eno~rs. "&mimicro and Macro Organic Chemistry.'' Thomas Y. Crowrll and Company, Mew York, 1942, p. 345.

(6) SWEENEV AND ARNOLD, "Plastics from agricultural mate- rials." Bulletin 154, Iowa Engineering Experimental Station, Amei, Iowa, February 25, 1942.

(7) NECHAMKIN, "A schematic procedure for identification of common commerrial elastics." Ind. Eric. Chem.. Anal. Ed.. 15,40-41 (1943). '

- (8) VON STEIN. "Detection of straight and modified phenolic

resins." The Chewist Analyst. 32, 35 (1943). (9) D ' A L ~ L I O AND GUILE. ''Labor~torv Manual of Svnthetic

Plastics and ~ e s i n o i s Materials-' Michigan state Col- lege, East Lansing, Michigan, 1942, pp. 57,64,65.