Infrared Study in Potassium Bromide Disks of the Stability and Hydrolysis of Aromatic Polyurethane Foams Albert S. Tompa Fleet Support Department, Naval Ordnance Station, Indian Head, Md. 20640
of sample in the initial mixture; M 2 is the mass of the initial mixture; and M 3 is the mass of the KBr disk. The KBr mixture and disk d o not have to be weighed if the absorbance ratio method is used. In the absorbance ratio method, the C-H stretching band at 2964 cm-1 was used as the internal standard band. Base lines were drawn as shown in Figure 1. Grinding by hand gave lower absorbance values than when grinding was done in the Wig-L-Bug. This is understandable since a finer and more uniform particle size is produced in the vibrating grinder, and as the particle size decreases, the intensity of a n absorption band increases (5). Kinetic studies were made o n disks stored at 22 “C, and in ovens at 5 5 , 65, and 80 “C. The infrared spectra of the disks were obtained without regrinding or repressing.
RIGIDWATER-BLOWN aromatic polyester urethane foams are used as closure plugs in ordnance. The closure plugs are acceptable if they d o not crack during a gun ram test using dummy cartridge cases. The plugs will crack if they lose their resilience and compression properties. The specifications for these plugs are physical property tests (density, tensile strength, etc.). An infrared study of ten closure plugs which passed specification tests but five of which cracked during the ram test was initiated t o see if a quick, accurate method to distinguish between good and cracked closure plugs could be developed for quality control. In the course of this investigation, it was observed that trapped carbon dioxide was present in KBr disks prepared the previous day. An infrared kinetic study was therefore undertaken in KBr disks of the hydrolysis of unreacted isocyanate to give unstable carbamic acid which decomposes t o form a n amine and carbon dioxide ( I ) . The amine that is produced may also react with isocyanates to form substituted urea.
DISCUSSION
Isocyanate Content. Figure 1 shows the infrared spectrum of a n aromatic polyester-urethane foam sample (cracked) in a KBr disk. The infrared bands of interest are assigned as follows (6, 7): 2964 cm-’ C-H stretch [internal standard), 2334 cm-l carbon dioxide, 2270 cm-1 isocyanate, 1725 cm-I amide I and ester, 1592 cm-l urea and aromatic ring, 1526 cm-* amide I1 and aromatic ring, 1217 cm-l amide 111, urethane, and ester, 1052 cm-I urethane and ester, and 760 cm-1 urethane and ester. The methylene and isocyanate bands were found to obey Beer’s law within experimental error, and therefore the standardized absorbance and absorbance ratio methods of analysis may be used. A least squares computer processing of the data gave the following equation:
EXPERIMENTAL
The aromatic polyester-urethane closure plugs were a commercial product. Approximately 50 mg of sample obtained from the center or along the cracked portion was ground for 1 minute in a Wig-L-Bug (Crescent Dental Manufacturing Co., Chicago, Ill.) vibrating grinder. Then 1.0 to 4.0 mg of ground sample were added to 353 k 5 mg of KBr. The mixture was weighed and ground for 1 minute and then pressed into a disk under vacuum for 5 minutes. The spectrum of the KBr disk was immediately measured o n a PerkinElmer Model 521 infrared spectrophotometer and the disk then weighed. Standardized absorbances were calculated by the equation (2-4):
=
0.0182
+ 1 . 7 4 X 10-6C and 0.003
=
+ 1 . 0 5 x 10-6C
where C is the concentration (lo4 grams cmU2)of the foam in the KBr disks, The results of the analysis of ten samples are given in Table I. The absorbance values (Table I) for the samples which did not crack were always lower. The
As = 1 ,326 (A/M1) (M*/Ms)
where A s is standardized absorbance; 1.326 is the area of the disk in c m 2 ; A is base-line absorbance; M I is the mass
(5) N. E. Sharpless and D. A . Gregory, Appl. Spectrosc., 17, 41 (1963). (6) K. Nakayama, T. Ino, and I. Matsubara, J . Macromol. Sci., Chem., A3, 1005 (1969). (7) L. J. Bellamy. “The Infrared Spectra of Complex Molecules,” John Wiley and Sons, New York, N.Y., 1964.
(1) K. C. Frisch and L. P. Rumao, J . Macromol. Sci., Rec. Macromol. Chem., C5, 103 (1970). (2) A . S. Tompa, Appl. Spectrosc., 22, 491 (1968).
(3) H. Susi and H. E. Rector, ANAL.CHEW,30, 1933 (1958). (4) D. E. Nicholson, ibid., 31, 519 (1959).
W A V E L E N G T H hIICROKS 4 5 6 I 8 9 10 1 2 14 , . I --..1 -A
1
2.5
_A
100
~
’
18 22 ,
35 50
--+
100
-.
il
3 dags/
60
Figure 1. Infrared spectrum of an aromatic polyester-urethane foam in a KBr disk
40
I ’
’
0
.lono
3500
3000
IO ij00
?000
liC0
1400
i f : i Q l CSCY (chI-11
1056
ANALYTICAL CHEMISTRY, VOL. 44, NO. 6, MAY 1972
1100
PO0
500
200
Table I. Relative and Standardized Absorbances of Urethane Bands in Polyester-Urethane Foams in KBr Disks 1. AslAasea
X(cm-l)
-
Passa Failb
2270 0.07 3~ 0.02 0.43 i. 0.12
1725 1 . 5 i 0.1 1.9 =t 0 . 2
1592 0.45f0.05 0.56 =k 0.07
1526 0.82=t0.06 1 . 0 i 0.1
1217 1.2ztO.l 1.5 i0.2
1052 0.69iO.03 0.83 i. 0.08
760 0.50f0.02 0.59 i. 0.04
2. A s cm-1 = 2270 1725 1592 1526 1217 1052 760 102 i 20 72 zt 11 152 f 23 125 =t 23 70 f 14 208 f 28 12 zt 2 Passa 138 i 13 96f 9 224 f 14 175 f 20 94 f 11 285 =t 17 66 f 25 Failb a These numbers represent the mean values and average deviation from that mean for five separate samples which did not crack. b These numbers represent the mean values and average deviation from that mean for five separate samples which cracked.
-
r
Table 11. Second Order Rate Constants for Hydrolysis and Amine Reactions of Isocyanate in KBr Disk Temperature, "C
I-
80 65 55 22 0.65 0.21 1.62 1.17 Rate constant 10.1CP =tO.lCP 1 0 . 0 5 * f0.03b (103 A R - ~min-l)a A R is the absorbance of the 2270 cm-' isocyanate band relative to the absorbance of the 2964 cm-1 methylene band. b Standard deviation values.
C
Q
c
P /
t
I
0
1
2
3
4
I
,
5
6
Time, da. s
Figure 2. Second order plot for hydrolysis and amine reactions of isocyanate in a KBr disk US. time
0, 80 OC 65 "C "C 0 , 22 "C X,
0,55
rriost reliable band for analysis was the isocyanate band as there was at least a fivefold difference in the absorbance of this band for foam samples which cracked and did not crack. A correlation between the isocyanate content and physical properties of aged polyurethane foams has been observed (8, 9). The foams with the lower isocyanate content had better physical properties. A variation in the water content during the manufacture of these foams may account for the difference in absorption of these bands, since the water content would determine the extent of hydrolysis of isocyanate and urethane linkages, a n d consequent decrease in the intensity of absorption of these groups. Thus the infrared (8) G. G. Greth, R. C. Smith, and G. 0. Rudkin, J . Cell. Plasr., 1,
159 (1965). (9) J. K. Buxbaum, ANAL.CHEW,29, 492 (1957).
I
I
I
1
I
I
I
2.8
2.9
'3.0
3.1
3.2
3.3
3.4
0,r-I
Y
1
10'
Figure 3. Plot of second order rate constants for hydrolysis and amine reactions of isocyanate in KBr disks DS. temperature E,
=
7.8 f 0.6 kcal/mole
method for the determination of the relative isocyanate concentration is a quick and reliable way of determining the stability of these polyurethane foams. Hydrolysis Reaction. When KBr disks prepared the previous day were rerun, a new absorption band was observed at 2334 cm-l owing to trapped carbon dioxide. Thus the KBr disk technique presented a convenient way of following the solid state hydrolysis of the isocyanate group in polyesterurethane foams. T h e hydrolysis products were a n amine and carbon dioxide. T h e concentration of trapped carbon dioxide was found to be time dependent; it had its greatest ANALYTICAL CHEMISTRY, VOL. 44, NO. 6, M A Y 1972
1057
increase after the first day and then increased slowly. This may be explained by the fact that the competing reaction rate of a n amine with isocyanate is greater than the hydrolysis reaction rate to give carbon dioxide. The isocyanate concentration can therefore decrease with only a small increase in carbon dioxide concentration. As the amine concentration decreases, the substituted urea and urethane molecules that have been formed can react further with isocyanate to give biurets and allophanates, respectively. Regrinding and repressing a KBr disk liberated the trapped carbon dioxide since its absorption intensity at 2334 cm-’ decreased markedly. A KBr disk that was stored i n a desiccator over drierite for 100 days showed only a pronounced shoulder at 2334 cm-I. This indicated that the hydrolysis reaction is diffusion controlled, and is due to the diffusion of atmospheric water into the KBr disk to react with isocyanate to give COz which is trapped within the disk. The overall reactions (hydrolysis and amine) of isocyanate were found to obey second order kinetics (Figure 2). The reaction between isocyanate and alcohol has been found to be mainly second order (10-13) but (10) H. A. Smith, J. Polymer Sci., 6, 1299 (1968). (11) L. Willeboordse, J. Phys. Chem., 74, 601 (1970). (12) A. E. Oberth and R. S. Bruenner, ibid., 72, 845 (1968). (13) A. Farkas and P. F. Strohm, Ind. Eng. Chem. Fundam., 4, 32
(1965).
zero (14) and pseudo first orders (15) have also been observed The rate constants have been calculated by a least squares computer analysis and are given in Table 11. The activation energy for the isocyanate reactions in a KBr disk was 7.8 i: 0.6 kcal/mole (Figure 3). ACKNOWLEDGMENT
The author thanks George B. Wilmot and Doug Ayers for helpful discussions. RECEIVED for review August 16, 1971. Accepted December 7, 1971. Presented a t the 23rd Pittsburgh Conference on Analytical Chemistry and Applied Spectroscopy, Cleveland, Ohio, March 1972. The opinions or assertions made in this paper are those of the author and are not t o be construed as official or reflecting the views of the Department of the Navy or the Naval Service at large.
(14) N. D. Ghatge, S. D. Yadav, and A. C. Ranade, J. Appl. Polymer Sci., 12, 447 (1968). (15) M. E. Bailey, V. Kriss, and R. G. Spaunburgh, Znd. Eng. Chem., 48,794 (1956).
Rapid Characterization of Salmonella Organisms by Means of Pyrolysis-Gas-Liquid Chromatography E. Reiner, Judy J. Hicks, Mary M. Ball, and William J. Martin Microbial Chemistry Laboratory, Center f o r Disease Control, Public Health Service, U.S. Department of Health, Education, and Welfare, Atlanta, Ga. 30333 FORSEVERAL YEARS the technique of pyrolysis-gas-liquid chromatography (PGLC) has been effectively used to differentiate genera, species, and, in many instances, subspecies of pathogenic bacteria (1-5). Successful use of this technique has stimulated investigations of other pathogens. The present report deals with differentiation and classification of the genus, Salmonella.
Salmonellosis, a common worldwide disease, is most often associated with food poisoning. Difficulties in diagnosis may stem from three sources: use of inadequate isolation procedures, use of time-consuming biochemical tests which often rely o n subjective judgments (e.g., the development of a certain color or the evolution of a gas), and failure to use reliable, well characterized standard reference sera for serological procedures which are used to confirm the identity. I n addition, the serologist may be confronted with confusing cross-reactions from other enteric bacteria. We have compared results from the P G L C technique with those of two methods currently in use. One, a serological method, is exemplified by the Kauffmann-White Scheme (6) ; (1) E. Reiner, Nature, 206, 1272 (1965). (2) E. Reiner, J . Gas Chrornatogr., 5 , 65 (1967). (3) E. Reiner and W. H. Ewing, Nature, 217, 191 (1968). (4) E. Reiner and G. P. Kubica, Amer. Rer;. Resp. Dis., 99, 42 (1969). ( 5 ) E. Reiner, R. E. Beam, and G. P. Kubica, ibid., p 750 (6) P. R. Edwards and W. H. Ewing, in “Identification of Enterobacteriaceae,” 2nd ed., Burgess Publishing Co., Minneapolis, Minn., 1962. 1058
ANALYTICAL CHEMISTRY, VOL. 44, NO. 6, MAY 1972
the other, a biochemical method, is exemplified by the distribution of sugars in Salmonella cell walls (chemotypes) (7). EXPERIMENTAL
Apparatus. All pyrochromatograms were recorded from Barber-Colman Series 5000 gas chromatographs, each equipped with a flame ionization detector and a Model 5180 pyrolysis module. The latter was attached to the gas chromatograph inlet by means of Swagelok fittings. BarberColman (5 mV) and Beckman (1 mV) strip chart recorders were used simultaneously. We also used a n Infotronics Digital Integrator, Model CRS-1l H , to record retention times and peak areas. Column Preparation. Refrigerator grade copper tubing (20 ft long; o.d., 0.125 in.; i.d., 0.065 in.) was cleaned by running through a series of solvents of increasing polarity (methylene chloride last). A stream of nitrogen was passed through the empty column, and its entire length was flamed with a torch. The usual support consisted of 5 Carbowax 20M, terephthalic acid terminated, coated by the vacuum distillation method o n Anakrom ABS, 110/120 mesh. To eliminate fines, the packing was carefully sieved and fluidized. Columns prepared in this manner achieved efficiencies of 600-800 plates/foot. Carrier flow, as measured by a bubble meter, was 16 ml/minute. Sample Preparation. In preparing samples for PGLC study, the enterobacteriologists used standard biochemical and serological procedures which were developed a t the (7) F. Kauffmann, 0. Luderitz, H. Stierlin, and 0. Westphal, Zentralb. Bakteriol. Parasitenik., Abt. I Orig., 178, 442 (1960).
