after elution of the other fixed gases. The analysis time is 11 to 16 minutes, depending on the lengths of the columns. Calibration tests showed that the detector response to the fixed gases was in volume per cent. Each method, based on a sensitive, fast-response detector and the ability to interchange both sides of the cell for reference and sensing, provides a rapid, one-sample analysis of fixed gases. Blast furnace top gases; combustion
gases; fuel mixtures of blast furnace, coke oven, and natural gases; and hydrogen generator gases with hydrogen concentrations varying from 0.05 to 95.0 volume % are ideally analyzed by these methods. Other fixed gases may be determined accurately in concentrations as low as 0.05 volume %. LITERATURE CITED
(1) Bennett, C. E., Martin, A. J., Martinez, F. W., Jr., report, “Linear Programmed
Temperature Gas Chromatography,” F&M Scientific Corp., 1960. (2) Madison, John J., ANAL. CHEM.30, 1859 (1958). (3) Poli, A. A., Taylor, B. W., Pittsburgh Conference on Analytical Chemistry and Applied Spectroscopy, Pittsburgh, Pa. (March 2-6, 1959). RECEIVED for review August 16, 1963. Acce ted November 18, 1963. Pittsburg[ Conference on Analytica.1Chemistry and Applied Spectroscopy, March 1963, Pittsburgh, Pa.
Analysis of Polyester Resins by Gas Chromatography C. C. LUCE and E. F. HUMPHREY Molded Fiber Glass Research Co., Ashtabula, Ohio
L. V. GUILD* and H. H. NORRISH2 Burrell Corp., Pittsburgh, Pa.
JAMES COULL University of Pittsburgh, Pittsburgh, Pa.
W. W. CASTOR Forbes laboratory, Pittsburgh, Pa.
b A method has been developed for comparing polyesters in cured laminates by means of pyrolysis and gas chromatography. The pyrolysis furnace which can be attached to a conventional GC unit is described. The temperature used in the series was 760” C. Chromatographic data and chromatograms of several resins are given.
T
BROAD APPLICATION of gas chromatography to the analysis of volatile materials has resulted in many workers extending this method to less volatile compounds, and finally to materials which would normally not exert sufficient vapor pressure for an analysis. Where there is insufficient vapor pressure, the worker must resort to pyrolysis techniques. The earliest work of the application of pyrolysis in combination with gas chromatography was carried on by Davison, Slaney, and Wragg (1). They collected pyrolysis products of natural and synthetic rubber and subjected them to gas chromatographic analysis. The method was considerably simplified when the pyrolysis system was directly connected to a chromatographic column and continuously swept with carrier, first described by Radell and Struta (7). HE
1 Present address, University of Pittsburgh, Pittsburgh, Pa. 2 Present address, Ace Scientific Co., Linden, N. J.
482
0
ANALYTICAL CHEMISTRY
They indirectly heated a metal loop containing the sample. Two methods of pyrolysis have since been used. The sample is pyrolyzed on a metal filament heated directly by an electric current; or in a small furnace. A number of workers have used the filament method. Janak (4) pyrolyzed a nonvolatile sample on a heated platinum spiral and analyzed the pyrolysis products by gas chromatography. He carefully controlled the current and time of heating, and studied the pyrolysis products of barbiturates, protein derivatives, and other materials. Lehmann and Brauer (6) applied the filament method to the analysis of poly (methyl methacrylate). The pyrolysis furnace method was used by such workers as Hewitt and Whithan (3) and Legate and Burnham (6). More recently Ettre and Veradi (2) have used the furnace method for studying the breakdown products of poly-(n-butyl methacrylate) and nitrocellulose by both pyrolysis techniques. They compared the chromatograms by flash pyrolysis to those done a t a constant temperature. They showed the importance of holding the instrument and pyrolysis parameters constant. The present work confirms that of Ettre and Veradi, and the instrumentation is along similar lines, except the work was done with polyesters. The present study was undertaken with three objectives in mind. The first was to determine the applicability of the pyrolysis technique to the characterization of thermosetting poly-
esters. Of interest was the effect on B pyrolysis chromatogram of changing any given component in a polyester, as well as the effect of changing the ratio of the various components. This information would allow the fingerprinting of a particular polyester composition. A second objective was to study more subtle effects in an effort to relate physical properties of a given polyester to the pyrolysis chromatogram. Such physical properties are usually affected by curing temperature, inhibitor, catalyst, etc. The third objective was to evaluate various instruments and techniques which have been developed, as well as to explore new ones that might be more suited to this problem. EXPERIMENTAL
Instrument. All the present studies were made on a Burrell Model KD instrument using a flame detector. The flame detector was chosen in preference to a thermal conductivity detector for two reasons. First, a smaller sample size could be employed with the flame detector because of its higher inherent sensitivity. The smaller samples were believed to be advantageous in pyrolysis studies, giving more rapid and uniform breakdown. Second, since the flow was interrupted to introduce the sample, the time required for stabilization after sample introduction is much longer with thermal conductivity. With the flame detector, only the pressure drop across the column needs to be reestablished.
f-TO
FLASH VAWRIZER
0 , Iy2
-
LAIR INLET Fig. 1.
Cross section of pyrolysis unit
The first experiments were with an electrically heated filament. Attempts were made to pyrolyze samples upon a single wire filament, as well as within baskets formed from platinum gauze. All were heated by an electrical current in the conventional manner. This technique gave chromatograms which were reproducible in numher of peaks and retention time but had certain limitations: the pyrolysis products of polyesters have a broad boiling range from gases through high boiling liquids, and it was necessary to locate the filament in a flash vaporizer a t several hundred degrees Centigrade to avoid condensation of pyrolysis products. In thermosetting plastics the temperature affects degree of cure of the sample. Under such conditions, post curing of the sample occurred during the stabilization time. In addition, the life of the h a t i n g filaments was quite short. Considerable difficulty was encountered in maintaining a filament for more than perhaps a dozen determinations. Thus, an excessive amount of time was required to maintain the pyrolysis unit in working condition. Furthermore, it was noted that a buildup of materials had occurred on the relatively cold surfaces-e.g. filament leads-indicating that unpyrolysed sample and very high boiling products had splattered off and could well he a source of trouble in obtaining uniform results. While the chromatograms were repeatable for number and kind of peaks, the relative peak areas could not he reproduced to hetter than 20 to 30%. Finally, as Ettre and Veradi found, it was extremely difficult to measure the exact pyrolysis temperature. An instrument was designed to overcome these problems for the present work. Figure 1 shows a cross-section vienr of the pyrolysis unit. The heart of the unit is an electrically heated Inconel tube of '/&-inch 0.d. used as a pyrolysis chamber, the tube itself being the heated element. The tube i s hard-soldered a t either end to mounts which also serve as gas and electrical connections. One end has the carrier inlet and a removable plug for introducing the sample. The plug is finger-tightened against a Teflon seal. A sliding plunger in the plug sealed with silicone is used to position the sample. The other end of the tube exhausts into the flash vaporizer of
Figure 2. the gas chromatography unit and is tailoired to fit the flash vaporizer sample inlet. '. 1 A -bL -~: -ll .a. . i i i i e>.meei ~ jacket, fixed a t one end and insulated from the other by a transite hushing, provides mechanical support and allows for linear expansion. All parts of the unit, except the Inconel tube, transite bushing, Teflon and silicone rubber seals, and the plastic plunger knob are stainless steel. The length of the unit with the plunger in i s 55/s inches, the jacket is 3/4-inch 0.d. and the outer mount is 1-inch 0.d. Heating of the tube required a high current source of the order of 100 amperes. The carrier gas was not preheated. A thermocouple, spoewelded to the Inconel tube, gave direct and accurate pyrolysis temperatures. The upper limit of operating temperature is 1100° C., while the lower limit is of the order of 50' to 100" C. below the flash vaporizer temnerature. If a still lower temperature is desired, or if a shorter cooling time is sought, an air stream can be applied to the pyrolysis tube through an inlet in the jacket. Figure 2 shows a photograph of the pyrolysis unit in place in the instrument. The sample was pyrolyzed in a micro stainless steel or ceramic boat, about 5/16 X ' h X inch. Gas chromatograph operating conditions throughout were as follows, except where noted: Carrier flow rate 60 ml./min.-Helium. Column a/,&nch 0.d. X 8 feet long.
Figure 3.
Pyrolysis unit in place on instrument 30% w./w./Ucon, Type HB-2000 on 30-60 Celite Detector temp. 250' C. Flash vaporizer temp. 300' C. Column programmed from 75" to 200' C. a t 15" per minute. Establishing a Standard. A pyrolysis chromatogram is a function of the various conditions under which the pyrolysis occurs. The pyrolysis technique is therefore primarily one of characterization rather than a n actual analysis. A particular polyester was chosen as a standard to get some kind of bench mark or reference standard as a basis for comnarison. The standard was an unfilled polyester having a molar acid ratio of 3 : 4 of isophthalic acid: maleic acid and a molar glycol ratio of 4: 1 of diethylene glycol :ethylene glycol. Approximately a 1: 1 molar ratio of acid to glycol was used. This was catalyzed with 1% henzoyl peroxide and cured a t 82' C. for 10 minutes, and postcured a t 100" C. for 1 hour. All samples were prepared under these conditions except where noted. Samples were prepared by filing particles from the sample, each time from a fresh surface. The sample size taken was 0.5 mg.& 0.05 mg. except where noted, and the sample placed in a pyrolysis boat. This was positioned in the cold end of the chamber, and flow stabilized, and pyrolysis furnace heated to 760" C. and stabilized. The pyrolysis furnace cooled to below 300" C. where little or no pyrolysis occurs, in about 50 seconds.
.
Chromatogram of standard resin VOL. 36, NO. 3, MARCH 1964
483
For purposes of comparison, identical detector attenuations were used. The chromatogram of this standard is shown in Figure 3. The peaks have been lettered for reference purposes. Extreme caution was used in handling sample and boat to avoid contamination. All t.ools used in preparing and handling sample and boat were thoroughly degreased and baked. The boat was heated in air a t approximately 1100" C. for 1 minute. RESULTS AND DISCUSSION
Reproducibility. For this technique to be of value as a characterization study it is necessary that the relative peak area be reproducible. Table I shows the reproducibility of the relative areas of the standard under identical conditions. While the chromatograms are not shown, the number of peaks and the retention times were sufficiently reproducible that the curves could be superimposed within 2 to 3 mm. Effect of Pyrolysis Temperature. Figure 4 shows the effect of pyrolysis temperature on the standard, pyrolyzed a t 427O, 649O, 871°, and 1093" C. There was not very much evidence of breakdown a t the lowest temperature. As the temperature increases above this level, further break*
: I
t
I
I
I
Table 1.
Peak No. A B2 C D E Fl-F4 F5 F6-F8 G Hl-H3 HPH5 H6-H8 H9-Hl4 H15
1
122 321 530 292 338 1560 1000 887 649 480 808 595 2096 975
2 119 299 632 270 314 1472 1100 874 639 473 803 623 2066 969
Reproducibility of Relative Areas
down takes place with an increase in light products. Maximum molecular fragmentation, indicated by the number of component peaks was a t 649" C. At the highest temperature decomposition is nearly complete, resulting probably in hydrogen and elemental carbon. Hydrogen, of course, could not be determined by the flame detector. Identification of Pyrolysis Products. No extensive identification program was undertaken since much useful information can be obtained from a chromatogram of the pyrolysis products alone. The retention of some
t
Table
II.
So. A B
C D E F2 F5 F7 G H4 H6-H8 H15 ~
484
1.1
1.3 1.6 0.6 0.9
0.25 173 229 563 180 446 153 936 514 738 976 760 1362
Sample size, mg. 0.5 1 133 123 323 263 653 622 240 298 346 361 235 208 1124 1090 683 759 677 737 817 779 649 822 1049 1079
2 132 247 758 311 367 268 1204 773 680 806 501 986
I
STANWRD +IN
Table 111.
427'C,
Effect of change of pyrolysis temperature in standard chromatogram
ANALYTICAL CHEMISTRY
Av. dev., % 2.8 3.1 5.5 2.3 2.2 1.7 3.3 2.4 1.9
Effect of Sample Size on Relative Peaks
Peak
Peak No. A B2 D E5 E7 G H4
Figure 4.
Av. 124 303 581 278 323 1534 1051 859 632 481 815 607 2081 980
I
00005 GRAMS I
4 129 304 594 276 320 1546 1071 819 621 476 819 602 2077 999
3 126 288 568 276 322 1560 1033 857 620 498 833 608 2091 980
Effect of Dwell Time on Relative Areas
Residence time in mseconds 70 140 280 113 147 115 371 315 281 303 259 188 _.978 783 855 660 286 570 589 849 482 710 1001 623
peaks coincided with the retention time for pure compounds so that peaks B2, C, and E are suspected to be benzene, toluene, and styrene. Positive identification was not established. Effect of Changing Sample Size. T h e data in Table I1 show the effect on the relative area varying the sample size from 0.25, 0.5, 1, and 2 mg. Standard conditions were used. The effect of sample size is not great, but for best reproducibility sample size should be held constant. Effect of Carrier Flow. The residence time a t any given temperature affects the pyrolysis products, and therefore the pyrolysis chromatogram. Table I11 shows the effect of changing the flow rate during py-
~
rolysis. A standard sample was pyrolyzed a t carrier flow 1,ates of 30, 60, and 120 ml. per riinute. Under these conditions the residence time was 280, 140, and 70 mseconds, respectively. Immediately after pyrdysis, tl-e flow was restored to the standard rate. It is difficult to rationalize the results obtained, but in general the shorter residence time seemed to increase the concentration of the light ends and decrease the heavy end::, while a t the longer residence time there was a significant reduction in ight ends. Studies of the parameters involved indicate that for the mmt reproducible results, the constant temperature pyrolysis technique is Eest and that all the parameters involved (carrier flow, temperature, sample size, and instrument conditions) affect the results and should be carefully conlrolled. Also, it is likely that the conditions shown in this study would not necessarily be suitable for all polymm, but rather, the optimum pyrolysis conditions would have to be determined for the particular study a t hand. Application of Characterization Technique to Po1yes:ers. Samples were pyrolyzed under standard conditions previously specified. Effect of Changing Composition of a Resin. To determine the effect of composition change, tl-e standard was compared to a polyest2r in which the maleic anhydride of this standard was replaced with fumari: acid. These acids are isomers a n j the heat of transformation is relatively small so that isomerization coulll have occurred under esterification conljitions resulting in composition interck ange. I n this comparison no difference was found in the pyrolysis chromatograms. Orthophthalic anhydride was substituted for isophthalic acid in the standard. A distinct change in the chromatogram is also shown in column I, Table IV. The standard had :t 4 : l ratio of diethylene to ethylene glycol. This ratio was changed to 1 : l . Gross changes did not occur in the chromatogram, but discernible dijyerences in area were shown and indicat?d in column 11, Table IV. Propylene glycol x as substituted instead of 4 : 1 ratio of diethylene glycol to ethylene glycol resulting in large changes in areaas shown in column II?, Table IV. Another application of the method is to fingerprint a particular resin type. A given polyester resin gives a distinct pyrolysis chromatogram, Data from three other polyesters are shown in Table V. The distinctive area ratios of each can readily be seen. It is interesting to note that there seems to be no change in the products but only
Table IV.
Effect of Substitution and Ratio Changes on Relative Areas
Std.
Peak No.
304 584 280 325 221 1056 713 767 428 89 1 539 985
B2 C
D E F2 F5 F7 H4 H6-H7 H9-H 11 H13 Hl5
Glycol changed ethylene and diethylene t o propylene I11
Glycol ratio changed
Acid changed iso- t o orthophthalic I
4 : l to 1 : l
I1
195
343
... ... ... ...
214 259 90
... 437 ... ... ...
...
633 608 344 565 391 2078
943 450
830 882
... ... 1086 *..
... ... ...
...
Blank spaces indicate less than 10% change in peak area.
in product ratios. The codes in Figure 5 refer to the following formulation: Code 1101 PTM. 1:1:2 parts by weight or orthophthalic anhydride: maleic anhydride: propylene glycol Code 4301 PM. 4 : 3 : 7 parts by weight of isophthalic acid: maleic anhydride :propylene glycol Code 7428 P. 7 : 4 : 2 . 2 : 8 . 8parts by weight of isophthalic acid: fumaric acid: dipropylene glycol: propylene glycol
Table V.
Peak Areas of Different Formulations
Square millimeters Peak
KO,
Std.
B2 D F2 F7 H9-HlO H13 HI5
304 280 221 713 645 539 985 ~~~
110n3017 PM 249 387 ._ 201 163 200 179 415 406 1027 642 432 704 3109 1589
PTM ~
~~
The distinctive chromatograms of
PHENOLIC:
428
P
373
240 339 497 910 693 1471
RESIN
. .
I
NYLCN-ZITEL61 I
C0005GRAMS
i
76C'C
I
1
Figure 5.
Chromatograms of other plastics VOL. 36, NO. 3, MARCH 1964
485
different basic resins is shown in Figure 5 : an epichlorohydrin-bisphenol A epoxy resin, a phenol formaldehyde resin, and “Zytel 61” nylon. Effect of Change of Physical Properties on Pyrolysis Pattern. This work is still underway and no definite conclusions can presently be made. CONCLUSION
Both a filament pyrolyzer for flash pyrolysis as well as the furnace type ivere evaluated for use with the characterization of polyesters; the most reproducible results were obtained with the furnace. A simplified pyrolysis furnace was developed for use with a gas chromatograph. Pyrolysis, combined with gas chromatography, provides a rapid means
for the characterization of polyester resins. Gross differences in composition of polyesters can readily be detected. More subtle changes in composition can also be determined, but it is necessary to hold all experimental parameters within close limits. Thus a particular polyester composition can be fingerprinted. I n this preliminary study a correlation between physical properties and pyrolysis chromatograms was not found, Xlthough thermosetting resins were chosen for this work, the technique and instrumentation could probably be estended to all nonvolatile organic materials. The pyrolysis unit may also have an application to microcatalytic studies where the catalyst itself could be placed in the pyrolysis zone and the sample
passed through it; however, this was not investigated. LITERATURE CITED
(1) Davison. W.. Slanev. S.. Wrane. A.., Chem. I.%I n d . i956, 1356. ’ (2) Ettre, K., T‘eradi, P. F., ANAL. CHEM. 35, 69 (1963). \
,
00,
(3) Hewitt, G.. Whit,ham,, B.,, Analust ’ 8 6 . 643 (1961’). (4) Janak,‘ J., Gas Chromatography 185, 387 (1960). ( 5 ) Legate, C., Burnham, H., ANAL. CHEM.32, 1042 (1960). (6) Lehmann. F.. Brauer. G. M.. Ibid.. 33, 673 (1960).’ (7) Radell, E., Strutz, H., Ibid., 31, 1890 (1959). ~
RECEIVEDfor review April 18, 1963. Accepted Xovember 19, 1963. Pittsburgh Conference on Analytical Chemistry and Applied Spectroscopy, Pittsburgh, Pa., 1963.
Analysis of Corrosive Halogen Compounds by Gas Chromatography ROLAND A. LANTHEAUME D.A.M., 6 Avenue Sidoine Apollinaire, lyon (S),France
b Mixtures of hydrofluoric acid and chlorine trifluoride are analyzed by gas chromatography. A special sampling system permits one to vary the hydrofluoric acid concentration. Gas flow rates are controlled by means of a thermic microflowmeter. A corrosion-resistant thermal conductivity detector is used. The gas-introducing device is a nickel sliding valve with a piston and Teflon joints.
Phillips and Owens (6) worked with capillary columns using a flame ionization detector. More recently, other investigators (5) tested performances of various columns in separation of fluorine compounds, including HF and CIFp. A Teflon-lined thermal conductivity
G
analysis Of corrosive halogen compounds was first described by Ellis and Iveson (8) in 1958. The detector used was either a katharometer of conventional design with nickel resistances or a gas density balance. The only suitable materials were nickel, poly(tetrafluorethy1ene) (PTFE or Teflon), and poly(trifluoromonochlorethylene) (Kel-F). Columns were packed Jvith either Teflon or Kel-F, n-ith a Kel-F oil as the stationary phase. Ellis, Forrest, and Allen ( 2 ) proposed a quantitative method for the study of such components as HF, ClF, CL, CIF,, and UFe using a gas density balance of special design. The carrier gas used was argon; the retention times were reported for all these gases on two diff went columns. These results (3) were subsequently used by Iveson and Hamlin (4) in the design of equipment for the analysis of corrosive materials. AS CHROhlATOGRdPHIC
486
0
ANALYTICAL CHEMISTRY
c3
It11 I ! +
b
L . 5mm
Figure 1 .
Thermal conductivity cell a.
b.
Nickel block Composite detector
cell equipped with hot filaments was used as the detector. The purpose of our work was to design and to test equipment for the analysis of corrosive materials. EXPERIMENTAL
Apparatus. Gas Chromatograph. Experiments were conducted with a “Chromodam corrosive gases” type chromatograph, manufactured by the D.A.M. Co., Lyon, France. The apparatus uses a nickel introduction device with Teflon joints and a thermal conductivity cell (1). The helium used as a carrier gas is purified prior to its introduction into the chromatograph in a precolumn provided with a 5 4 11olecular Sieve immersed in liquid nitrogen. The flow rate is 2 liters/hour. The sample volume is 10 ml. The chromatograph temperature is maintained a t 60’ R-ithin 0.1’ C. by an electronic regulating device with proportional setting. The nickel “liquid gas” column, 2 meters long, 6 X 8 mm. in diameter, is packed with Voltalef 300 L D impregnated by Kel-F oil. [Products manufactured by Societe des Resines Fluor6es (S.R.F.), Pierre-Benite (Rhhne), France.] The particle sizes are between 250 and 315 microns. -1Graphispot recorder (Sefram, Paris) is used equipped with spot follower, graduated in 2.5-mv. increments with paper speed of 12 mm./minute. Detection. Each of the two detector components (shown in Figure I ) incorporates a small heater oi
