A Schematic Procedure for Identification of Common Commercial Plastics HOWARD NECHAhlKIN 1971 73rd St.. Brooklyn,
T
MELAhiINE FORMALDEHYDE, similar to urea formaldehyde in properties and appearance, is formed by the condensation of melamine and formaldehyde.
HE use of synthetic resins or plastics is daily becoming
more and more important. Not only are these materials being used for original purposes, but, even more important, they are gradually replacing tremendous quantities of metals and other vital materials in war industry. The chemist, especially in the commercial or industrial testing laboratory, has to keep up 115th the great strides taken by the plastics industry if he is to remain valuable in his position. Tables of the properties and characteristics of the synthetic resins are readily available (3) but, to the best of the author’s knowledge, no method has as yet been published to aid the chemist in the identification of a particular plastic. This article presents, in schematic form, a simple and concise procedure for the identification of the more commonly encountered synthetic resins or plastics. Not all the known plastics are considered in this procedure, but only those which are rather uncommon under ordinary circumstances have been omitted. Only those materials which one is likely to find in consumer merchandise submitted for test have been included. Naturally, with the development of new materials and the appearance of new plastics on the commercial market, additions and revisions of the method will become necessary. A novel feature of the procedure is the rather wide application of the olfactory sense. I n most cases the odors are so intense that rather cautious smelling is advised. An important effect to be noted in the classification is the “green zone” around the base of the flame. This green color, when present, will be found a t the area closest to the burning plastic and will be readily discernible. I n all the burning tests a strip or small rod, if practicable, should be touched to the side of a small flame. If it takes fire readily, it should be removed from the flame a t once; if it melts and draws away from the flame, it should be moved so that it is kept in the flame until it takes fire, but not for more than 10 seconds. When the flame of the plastic is to be examined after removal from the Bunsen flame, this should be done immediately following the removal, disregarding any burning characteristics occurring after the first 2 seconds. To determine the odor of vapors produced, the flame should be blown out immediately upon removal from the Bunsen flame and the rising vapors should be smelled cautiously. No valid conclusions can be reached from smelling the plastic while it burns, and too much vapor will produce a deadening effect upon the olfactory organs. I n all cases it is advisable to have specimens of the various plastics in the laboratory, for comparison of the tentatively identified unknown material with a known specimen. The ideal forms in which plastics are to be examined are sheets and rods.
Structural unit:
1 q -N--C
i\i=
1
2”
1
I
Represented by Melamac and Plaskon PHENOLFORMALDEHYDE, the thermosetting resin formed by the condensation of henol and formaldehyde, is one of the most widely used of all pistics. The original work of Baekeland (1) describes the variation of the properties of the polymer with methods of preparation and processing.
Structural unit:
[
-
C
OH H Z
~
]
Represented by Durite and Bakelite PLIOFILM, a thermoplastic resin produced by the addition of hydrogen chloride to the unsaturated linkage present in rubber. I t is widely used in sheet form as a protective covering for various articles. NEOPRENE, a rubberlike synthetic material produced by polymerization of the addition product of vinyl acetylene and hydrogen chloride. It has properties remarkably superior to those of the natural product it can replace, rubber. Structural unit:
[
-CH
C-CH-CHz-
1
VINYL CHLORIDE DERIVATIVES, thermo lastic resins produced by polymerization of vinyl chloride wit[ itself or with other compounds such as vinyl acetate. The products are elastic and may be transparent. Many of the plastic suspenders and wristwatch bands are made of this material. Represented by Vinylite V and Koroseal CASEIN. These are infusible resins produced by the processing and molding of milk protein. The products are usually opaque, but may clear if the casein is hydrolyzed first. The material is very tough. CELLULOSE ACETATE,a thermoplastic product produced by the reaction between acetic anhydride and cellulose, is an ester of the alcohol cellulose. Safety film is prepared from this material. Represented by Lumarith, Tenite I, and Fibestos CELLULOSE KITRATE,the resin produced by the nitration of cellulose with mixed sulfuric and nitric acids. When plasticized with camphor it is known as celluloid. It is a highly flammable material which is finding less and less use with the development of newer plastics because of this hazard. Represented by Celluloid and Hycoloid METHACRYLATE RESISS, thermoplastic products formed by polymerization of one or more compounds of the type or-methyl methacrylate, methyl acrylate, ethyl methacrylate, etc. The product is readily prepared clear and colorless. The aviation industry is becoming one of the chief users of this resin. A disadvantage of the material is its comparatively low resistance to abrasive materials. Represented by Plexiglas and Lucite POLYVINYL FORMAL, ACETAL,AND BUTYRAL, thermoplastic resins produced by the condensation of polyvinyl alcohol with formaldehyde, acetaldehyde, and butyraldehyde, respectively. They are not very frequently encountered in consumer goods, but
Nomenclature UREAFORMALDEHYDE, the thermosetting polymer produced by the condensation of urea and formaldehyde, is usually glassy and infusible. Heating causes the resin to blacken and it ignites only with extreme difficulty.
Represented by Beetleware and Plaskon
N. Y .
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ANALYTICAL EDITION
January 15, 1943
show definite promise of much wider application than they enjoy at present. Represented by Formvar, Alvar, and Butvar KYLON,the condensation polymer formed by the interaction of adipic acid and hexamethylenediamine. It is thermoplastic and has exceptional tensile strength. Nylon stockings, bristles, and tennis racket strings on the market illustrate the versatility of this product. Parachute manufacture consumes most of our present output. Structural unit:
1
-C-(CH2)r-C-(CH2)s-NH-
A
CELLULOSE ACETOBUTYRATE, a thermoplastic resin produced by reacting cellulose with acetic butyric anhydride, CsH,CO0-OCCH,. It may be prepared in transparent sheets or in heavy opaque form. Like cellulose acetate, this product is an ester of cellulose. Represented by Tenite I1 POLYSTYRENE, a thermoplastic material produced by polymerization of the aromatic hydrocarbon, styrene. I t is therefore highly resistant to attack by inorganic acids and alkalies. It is very widely used.
H r-C-CH2-1
Represented by Styron, Lustron, and Loalin ETHYLCELLULOSE, an ether formed by the intermolecular dehydration of cellulose and ethyl alcohol. It is very similar in appearance and properties to the ester cellulose acetate. Represented by Ethocel CELLULOSE, the common transparent material widely used for wrapping packages. Strictly speaking it is not a synthetic resin, but merely reprecipitated cellulose. It is included, however, because of its close resemblance t o other materials used for similar purposes. Represented by Cellophane VINYLIDENE CHLORIDE RESINS,the newly developed very resistant resins produced by the polymerization of vinylidene chloride, unsymmetrical dichloroethylene. It is produced in filament and sheet as well as tube form. Structural unit: [-CCl-CH-] Represented by Saran and Velon
Procedure
41
B. Flame predominantly blue, may have a small white tip 1. Very strong sweet floral fruity odor: methacrylate 2. Odor reminiscent of burning vegetation or fresh celery. Flame is almost entirely blue. The resin is soluble in aqueous 60 per cent (by volume) hydrochloric acid 2 ) : nylon 3. Weak very s ightly sweet odor: polyvinyl formal 4. Odor of rancid butter or cheese a. Sparks produced from flame of burning plastic: cellulose acetobutyrate b. No sparks, burning smooth and steady: polyvinyl butyral C. Flame surrounded by bright green mantle, odor of burnt rubber: pliofilm D. Flame surrounded by a purple mantle, sparks and an acetic odor: polyvinyl acetal E. Flame yellow-white and luminous 1. Odor of butyric acid: cellulose acetobutyrate 2. Odor of burnt milk protein: casein 3. Sweet floral odor (marigold), flame smoky: polystyrene 4. Weak very slightly sweet odor: polyvinyl formal 5 . Odor of burnt paper: cellulose 6. Odor of burnt rubber, flame weak, small green mantle overshadowed by yellow. White flashes may appear in the flame: neoprene F. Flame surrounded b yellow-green mantle 1. Burns with difJ?culty and sparks, producing an acetic odor. The melted burning plastic, when allowed to drip into water, produces heavy black-brown foamy granules or flakes: cellulose acetate 2. Burns readily, once started, producing a slight sweet odor. The melted burning plastic, when allowed to drip into water, produces flat disks which are light tan when the plastic is clear, or not very different in color from the original plastic when the plastic is colored: ethyl cellulose
i
The same resin may occupy more than one position in the scheme. This is to take into account any possible misinterpretations of the characteristics described.
Summary A schematic procedure for identification of the commercial plastic types includes the plastics which the average chemist may encounter in his testing experiences. Seventeen families of plastics are discussed briefly, representing about one hundred plastics which are marketed under different commercial namea
Acknowledgment
The plastic, in strip or rod form, if possible, is held at one side of a Bunsen flame until it takes fire, but not for more than 10 seconds. The following scheme is then consulted: I. No flame is produced. The article retains its shape. The
odor of formaldehyde is present in all cases. A. No other odor: urea formaldehyde B. Strong fishlike odor: melamine formaldehyde C. Phenolic odor: phenol formaldehyde 11. The burnin plastic extinguishes itself on removal from the Bunsen Same. Specimen held just to edge of flame. A. A green zone is produced. 1. Odor of burnt rubber a. Green area pronounced: pliofilm b. Green area small and overshadowed by yellow: neoprene 2. Odor acrid but not that of burnt rubber: vinyl chloride derivative 3. Odpr sweet, heavy black ash: vinylidene chloride resins B. Odor of burnt milk protein: casein C. Sparks from flame of burning_plastic and acetic odor: . cellulose acetate 111. The plastic continues to burn after removal from the Bunsen flame. Flame examined for color during the first second of burning. A. Burning very rapid and intense white flame 1. Odor of camphor: celluloid 2. No camphor odor: cellulose nitrate I
The author wishes to acknowledge the valuable assistance given him by the Dow Chemical Company, the Carbide and Carbon Chemicals Corporation, and the Celluloid Corpors tion in sending him some of the specimens used as standards in the evolution of the method.
Literature Cited (1) Baekeland, L. H., J. IND.ENO.CHEM., 4, 739 (1912). (2) Freedman, E., and Nechamkin, H., Am. Dyestuff Re&., No. 2, 540 (1940). (3) Powers, P. O., CHEM.ENQ.NEWS,20, 536 (1942).
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