DRIFT of Kapton After Thermal Decomposition

In the previous chapter polyimide was analyzed after UV laser irradiation using DRIFT spectroscopy. Various intermediates and products of the laser-induced decomposition could be identified. Experiments with the same material were performed to test whether it is possible to distinguish between UV laser-induced decomposition and thermally induced decomposition, i.e., pyrolysis. 

In contrast, diffuse reflectance infrared Fourier-transform (DRIFT) spectroscopy allows one to monitor solid-state structural changes. It is specifically designed to study powder samples, and is well known for its high sensitivity. A wide variety of materials can be analyzed using DRIFT spectroscopy. Some materials can be analyzed neat, without any sample preparation, but polymers have to be diluted normally by embedding them into a matrix. 

The aim of this work is to investigate the reaction scheme of the thermally induced decomposition of Kapton in air and compare it to the UV laser-induced decomposition. This should help to decide whether the laser-induced decomposition (ablation) of Kapton is comparable to pyrolysis. Using DRIFT spectroscopy the changes in the concentration of different functional groups of the polymer are monitored during the thermal decomposition process. This information is used to develop a kinetic reaction scheme and to calculate kinetic parameters. 

The experimental setup consists of a gas dosing system and the DRIFT spectroscopy apparatus. For the pyrolysis experiments KBr was selected as matrix, different to the laser-induced decomposition experiments [141], where SiC was used. KBr was chosen because the emissivity did not increase drastically, as in the case of SiC, where it interfered with the measurements. The Kapton-KBr mixtures are placed in the sample holder of the DRIFT cell and packed using a pressure of 1 MPa as described elsewhere [288, 306]. The sample is heated in an inert gas atmosphere to the desired temperature using a heating rate of 10 K min-1. The spectrum of the Kapton-KBr mixture at a given temperature is collected and used as background spectrum. The following experiments were carried out. 

Thermal decomposition in air. The sample is heated in nitrogen to the desired temperature, then the feed gas is changed to air (compressed air). The 

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