Pyrolysis- Gas Chromatog ra phic Techniq ue f o r Direc t Analysis of Thermal Degradation Products of Polymers KITTY ETTRE and PETER
F. VdRADl
The Machleft laborafories, Inc., Springdale, Conn.
b The pyrolysis-gas chromatographic technique was modified to determine
products arise instantaneously and are purged as a "plug" into the chromatographic column by the carrier gas. Since the first publications on the application of this method for polymer pyrolysis studies (7, 8 ) , different variations of the technique have been described in the literature and its application was also extended for studies of other complex organic substances (4). These works were, ho\Tever, mainly restricted to the demonstration of the characteristic patterns of the chroniatograms obtained from the pyrolysis products of different compouiids, and actually very little nork was reported on the qualitative and quantitative analysis of the entire pattern. I n our work, we intended not only to show the characteristic over-all picture of the pyrolysis product but also to identify most of the peaks and to accomplish a complete quantitative evaluation of the results. We were primarily interested in the thermal degradation of certain polymers used as binders in vacuum and semiconductor devices-e.g., in the preparation of various electron tube parts such as oxidecoated cathodes, phosphor screens. getters, metal layers for metal-to-ceramic seals. Therefore, vie selected three polymers for detailed investigations: nitrocellulose, poly(n-butyl methacrylate), and poly(viny1 alcohol). Sitrocellulose is the most widely used polymer as binder. Poly(n-butyl methacrylate) has been used recently as binder in a new
both the characteristic pattern and the identity and quantity of the breakdown products of nitrocellulose, poly(n-butyl methacrylate), and poly(viny1 alcohol). The pyrolysis of these polymers was carried out at 650" C. in a helium atmosphere. The tabulated qualitative and quantitative data of the breakdown products are specific for the various polymers and can also be related to the structure of the original macromolecule.
T
of the thermal degradation of polymers is very useful in characterizing and identifying the original macromolecule by the composition and abundance of its breakdown products (3). The execution of such investigation. however, was difficult since the pyrolysis products had to be collected and analyzed u-ithout loss of the cornponents. llicroreactor-gas chroma t o g r a p h i e techniques (g, 5 ) demonstrated the possibility of carrying out a chemical reaction utilizing only microsamples with direct, subsequent gas chromatographic analysis of the reaction products. A niodification of this technique can readily be used for polymer pyrolysis studies. I n this case, a relatively small amount of the sample is heated very rapidly to the desired temperature in an inert atmosphere; thus, the pyrolysis HE STUDY
Table 1.
technique developed in our laboratory for the preparation of high density transfer tape? (1, 10). Poly(viny1 alcohol) can also be used as a binder in the preparation of oxide-coated cathodes, as an example. Besides these particular applications, however, all three materials served a t the same time as good model substances because of their different chemical structures and their charac teristic decomposition. EXPERIMENTAL
Apparatus. A standard PerkinElmer 154-D Vapor Fractometer equipped with a thermistor detector and a gas sampling valve ( 2 1 ) and connected to a Leeds &. Korthrup Speedamax G 5-mv. potentiometer recorder n s used for our investigation. Helium was used as carrier gas. The pyrolysis chamber had essentially the same construction as that used originally by Lehmann and Brauer (6). It consisted of tv-o parts, made of borosilicate glass: the first part was connected to those two ports of the gas sampling valve where the same loop is usually attached; the removable second Dart was fitted into the fixed first part with the help of grounded surfaces. L4 spiral Sichrome wire of 0.010-inch diameter and 4.5-inch length with 2 ohms resistance was installed into the second part of the chamber and connected to a variable transformer (Variac). The sample was placed in a small quartz boat of 2-mm. diameter which was then inscrted into the center of the spiral wire heater Four different separation columns
Column Characteristics and Selected Conditions
Column Characteristics Column Designation
I J
A W
5
Liquid phase, (adsorbent) Linde Molecular Sieve 5A, 30/60 mesh Silica gel, 30/60 mesh Diisodecylphthalate Poly(ethy1ene glycol) (Carbowax 1500)
Support material
ANALYTICAL CHEMISTRY
Column length, meters 2
Chromosorb, 6O/SO mesh Teflon 6, TFE Fluorocarbon resin (duPont), c ‘i times (.sultrt-l ‘Th cnhiinn Tras ’ :ice.’’ prtc.cnditir-Prl z t 16.5’ ( ’ for 2 to 4 h n i w by i v d m g injectioiis of 4 t o 3 pg. 2i promazinc or rhlorj)[omazint. I t boiit 4-rnin:ite I v t i -~
Q
