Chemistry and Chemical Biology ETDs

Publication Date

3-28-1972

Abstract

Previous laser-mass spectrometer and laser-gas-chromatographic instruments for study of organic polymer degradation have used high power pulsed lasers (ruby, Nd-glass) which limit sample characterization due to extensive fragmentation.

A new experimental technique has been developed for high temperature pyrolysis and rapid analysis of organic polymers. The experimental technique combines a low power continuous wave CO2 laser for sample pyrolysis and a time-of-flight mass spectrometer to analyze degradation products. The laser built for use in this study was a continuous flow CO2 gas-molecular laser excited by high voltage direct current with maximum power of 10 watts at a wavelength of 10600 nm. The laser was mounted above the mass spectrometer and an optical system of mirrors and lenses which directed and focused the laser beam to impinge on the sample mounted directly below the ion source inside the time-of-flight mass spectrometer. The laser beam controlled by a solenoid actuated shutter provided pulses from 0.01 sec. to 1 sec. whereas operation with the open shutter permitted continuous heating of the sample. Accurate timing of pulse duration was accomplished with a fast response photo-diode used to trigger the oscillograph recorder timing galvanometer.

Various experiments in the continuous and pulsed mode of operation were undertaken to explore the utility of this experimental technique. Polystyrene, polyethylene and three methacrylate polymers, polymethyl­methacrylate PMMA, polyethylmethacrylate PEMA, and polybutylmethacrylate PBMA were continuously irradiated at an attenuated laser power of 0.4 to 0.7 watts at mass spectrometer ionization energy of 100 ev. The results of these studies show close agreement with the results of high temperature degradation studies using conventional electric furnaces.

The analog output system of the time-of-flight instrument permitted the time-resolved study of selected degradation products. In the pulsed mode of operation, laser power was varied from 3.5 to 7.9 watts with pulse durations from 0.05 to 1.03 sec. Pulsed laser degradation studies of polystyrene show a temperature dependency on the formation of degradation products. This temperature relationship shows increased products fragmentation at increasingly higher temperature evidenced by low molecular weight fragments.

Project Sponsors

United States Air Force (USAF)

Language

English

Document Type

Thesis

Degree Name

Chemistry

Level of Degree

Masters

Department Name

Department of Chemistry and Chemical Biology

First Committee Member (Chair)

Nicholas Ernest Vanderborgh

Second Committee Member

Roy Dudley Caton Jr.

Third Committee Member

Edward A. Walters

Fourth Committee Member

Guido Herman Daub

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