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A torsion pendulum has been found to be a sensitive tool to detect the first steps of pyrolysis. It has been shown that some primary bonds break at elevated temperatures, but in the presence of oxygen, new crosslinks can form simultaneously. In resin heated in air, embrittlement due to these crosslinks starts on the surface of the resin and progresses inwards with time.
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G. A. Pogany (1969) studied this question.
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