Identification of Polymeric Materials P. F. KKUSE, JR.’, AND W. B. WALLACE iwaterials Laboratory, Sandia Corp., Albuquerque, .V. M .
A
METHOD for the identification of polymeric materials by infrared analysis of their pyrolysis products has been developed in this laboratory, apparently almost simultaneously with the work and method reported by Harms (1). One gram of the polymeric material, preferably shredded or cubed, is dry-distilled, and the products of decomposition are collected in 1 ml. of carbon tetrachloride. For the pyrolysis an aluminum cylinder 3.5 X 1.5 inches in diameter was drilled to a depth of 2.75 inches to accommodate a 15 X 100 mm. test tube, fitted with a 4-mm. glass inverted U delivery arm. A potentiometer, with the thermocouple in a S/srinch hole parallel and close to the test tube well, served to measure the temperature of the heating block. Using a hot, blue Bunsen burner flame, the block attains and holds temoeratures in the ranee of 830’ to 870’ F. The tube. containing the sample, is thenlinserted in the well. When del composition products begin to issue from the delivery arm, it is immersed in the carbon tetrachloride. I t is well to carry out the pyrolysis in a hood. For most rubbers and plastics, pyrolysis for 2 minutes produces a sufficiently concentrated solution for identification. I t is well to ensure that some liquid products are collected. The solution is dried by filtering through a column of anhydrous sodium sulfate protected with a calcium chloride drying tube, and then allowed to stand over anhydrous
sodium sulfate. The spectrum of the mixture of products is obtained by compensating for the solvent, This procedure has the advantages of (1)favoring close reproduction of spectra by pyrolyzing all samples a t the same controlled conditions and (2) minimizing fogging of the cell windows by moisture present in the pyrolyzates. As suggested by Harms (I), the solubility of pyrolysis products in carbon tetrachloride poses a problem. Fortunately, in practice, there have been only two experiments (pyrolyzates from urea and urea-melamine plastics) out of more than 100 pyrolyses into carbon tetrachloride where not enough solute was present to yield a characterizing spectrum. The usefulness of the infrared-pyrolysis technique is demonstrat,edin the int,eresting examples given by Harms. LITERATURE CITED
(1) Harms, D. L., A s . 4 ~ CHEM., . 25, 1140 (1953). RECEIVED for review February 14, 1953. Accepted June 12, 1953. Presented at the Eighth Southwest Regional Meeting, AMERICAN CHEMICAL SOCIETY, Little Rock, . i r k . , Decemher 5 , 1952
Two New Forms of Melting Point Calorimeters For Determining the Purity of Liquids of Condensed Gases JOHN T. CLARKE, IIERRICK L. JOHNSTON, AND W.4RREN D E SORBO* The Cryogenic Laboratory and Department of Chemistry, The Ohio State University, Columbus, Ohio
I
S CARRTISG out low temperature calorimetric a ork on gas-
eous hydrides of boron in this laboratory, it was necessary to make relatively accurate purity determinations in advance of introducing the compounds into the condensed gas calorimeter, to avoid the hazard that would be associated with formation of plugs in the narrow inlet tube due to condensable impurity. The two forms of “melting point calorimeter” described in the paper were developed to make these purity determinations. They have proved successful for the purpose, they can readily be utilized for purity determination on other liquids or condensable gases, and are relatively simple to construct and operate. Freezing point determinations have long been used to determine the degree of purity of liquid samples. The method can be made quantitative, without requiring knonledge of the exact nature of the impurity, or impurities, if it can safely be assumed that the impurity is soluble in the liquid but not in the solid phase of the solvent component. Most forms of the method depend on adding or withdrawing heat a t an approximately constant rate and determining the portion melted from a time temperature graph ( 2 , 5 ) . Cooling or warmingrates possess the disadvantage, compared with calorimetry, that the energy measurements are less accurately determined and that constant temperature gradients may exist in the system. Aston, Fink, Tooke, and Cines ( 1 ) 1
Present address, The Samuel Roberts Koble Foundation, Inc , Ard-
more, Okla.
* Research .4ssociate, The General Electric Research Laboratory, Sehenectady, ti.Y.
developed a melting point calorimeter to which heat is added in measured increments and time is allowed b e t w e n heating periods for attainment of thermal equilihrium under adiabatic conditions. This is essentially a simplified form of the more accurate vacuum calorimeters used in the measurement of specific and latent heats at low temperatures, and employs, for the impurity determination, the “premelting heat capacity” treatment employed originally by Johnston and Giauque (3,4 ) . The two melting point calorimeters described in this paper are less suitable than that of Aston and roworkers for determination of premelting heat capacities, arid hence do not employ the accurate premelting heat capacity treatment. They are, however, well adapted for measurement of melting point as a function of fraction melted, and calorimeter I1 is well adapted for heat of fusion measurements. Both calorimeters are simple to construct and to operate and an impurity determination may be made in less than 2 hours, IT-ith calorimeter I, provided there is previous knowledge of the heat of fusion, and in about 3 hours with calorimeter 11, including a fusion heat determination. Calorimetera I and I1 require only 4 and 3 ml. of sample, respectively. CONSTRUCTIOY AND OPER4TIOY OF CALORIMETER I
Calorimeter I is the simpler of the two, both in construction and operation. Its design is shown in Figure 1. The calorimeter proper is a borosilicate glass tube 35 cm. long by 12 mm. in outside diameter, sealed a t the bottom. It contains a platinum resistance thermometer element made of No. 40 B and S gage wire, coiled in a helix, and mounted on a notched mica cross 31 1156
