Fig. 4. SEM micrograph of BMY 7378 SiOC foam (MPS precursor was modified by the addition of 12.5 wt% starch; foaming at 230 °C, pyrolysis up to 1000 °C).Figure optionsDownload full-size imageDownload as PowerPoint slide
4.1.1. The release of gaseous products during crosslinking of the MPS resin
On the basis of experiments carried out with starch dispersions in the MPS resin, water vapour released during MPS polycondensation can be recognised as the main pore-forming agent. Starch was found to generate blowing gases mainly in the closing stages of the foaming process (final weight losses at constant T = 250 °C in Fig. 5), via the caramelization process: [C6H10O5]n → Cn + 5n·H2O↑. Fig. 5 compares the release of gaseous products from the pure MPS resin and from the resin with added starch. Both materials underwent a sporangia preparatory heat-treatment for 1 h at 90 °C in one case and for ½ h at 170 °C in the other case.