Changes in structure and in mechanical properties during the pyrolysis conversion of crosslinked polymethylsiloxane and polymethylphenylsiloxane resins to silicon oxycarbide glass

The subject of this study is the thermally induced conversion of cross-linked polymethylsiloxane and polymethylphenylsiloxane resins into inorganic silicon oxycarbide glass. This topic is studied in view of the changes in the chemical structure of the precursor and in the context of the changes in hardness and elasticity, pyrolysis weight losses, density changes, and sample shrinkage. Two aspects of the pyrolysis process were studied: i) the effect of the pyrolysis temperature (tested from 400 to 1000 °C) and ii) the effect of pyrolysis time in cases of isothermal pyrolyses (at 520 °C and 650 °C). The mechanical properties were evaluated by means of micro-indentation tests, while the characterisation of the chemical structure was performed via FTIR spectroscopy, combustion analysis and EDS. The results of these experiments are discussed in the context of the use of examined materials as a precursor for the composite matrix or the sandwich core.