Polymer characterization by coupled thermogravimetry-gas chromatography

Abstract

A technique combining thermogravimetry (TG) and gas chromatography (GC) is described, which follows the weight changes of a sample as it is heated under controlled conditions, collects the volatiles at various stages as shown on the TG curve, and then analyzes them intermittently by GC. The technique features precise control of temperature and atmosphere and use of minimum thermal energy to perform pyrolysis, therefore reducing the production of secondary products and providing simple and reproducible GC scans. Impurities, such as solvents, monomers, additives, etc., can be analyzed separately from the polymers. Both qualitative and quantitative information on the various components in the sample can be obtained? In favorable cases, polymer blends and microstructures can be studied. Pyrolysis-gas chromatography (GC) has been establishedas a technique for characterization of high polymers (1-3).Pyrolysis of the sample is usually carried out either on a hot wire or ribbon inside the injection port, or in an oven-type unit from which the pyrolysis products can be produced and then injected into the gas chromatograph. The advantages and disadvantages of each method have been extensivelydiscussed by various authors (4-10). Thermogravimetry (TG) is a well known technique for following changes in mass of a material as a function of temperature. Its applications to high polymers have included the study of thermal stability, analysis of additives, and characterization of polymer blends and copolymers (11). The possibility of coupling the two powerful techniques, thermogravimetry and gas chromatography, has been reported (12,13). However, no experimental results have been given in the literature. This presentation describes a combined TG-GC technique which follows the weight changes of a sample as it is heated under controlled conditions, collects the volatiles at various stages as indicated on the TG curve, and then analyzes them intermittently by GC. In a way, this approach is similar to the oven-pyrolysis GC method, except that the extent of pyrolysis is now guided and measured quantitatively by the (1) B.

Reexamination of the Pyrolysis of Polyethylene: Data Needs, Free-Radical Mechanistic Considerations, and Thermochemical Kinetic Simulation of Initial Product-Forming Pathways

“…At low T, DIENEs were at best trivial products compared with ANEs and ENEs for the c ranges reported, even at high x. 32,33,70,72 In a direct comparison at low x, HDPE gave a heavier C 3-13 product than LDPE, 60 and small amounts of branched products, especially at low x, were more prevalent from LDPE, 60,73 consistent with its more branched structure. De Witt and Broadbelt 64 provided data for C 1-5 and C [8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24] ANEs and ENEs (no DIENEs noted) formed from HDPE at 420°C as a function of varying x (t ) 30-150 min; x ≈ 0.04-0.35).…”

Quantitative determination of the vinylacetate content in ethylene vinyl‐acetate copolymers—a critical review

“…A slightly different method was elaborated by Chiu (17,18), who replaced the pyrolysis oven with a device for thermogravimetry (TG). In addition to the VA content determination, TG-GC allowed the study of mass changes of the material as a function of temperature.…”

A Combined TG-GC-MS System for Materials Characterization

“…Unfortunately, in many practical problems, the volatiles are complex mixtures not easily handled by these analytical methods. One logical solution is to couple a separations tool such as gas chromatography (GC) to TG (10)(11). To go one step further, an ideal system would include a TG apparatus as a sample conditioner or reactor, a GC unit to perform separations and then an identification instrument.…”