Structure-property correlation in polyurethane-polyborodimethylsiloxane interpenetrating polymer network foams

This study describes how polyurethane/polyborodimethylsiloxane interpenetrating polymer networks (IPNs) were made and characterised via a two-step in situ foaming process to make foams with different amounts of PBDMS, enabling systematic evaluation to look for structure-property relationships in the resulting IPN foams. FTIR spectroscopy was used to show that the PBDMS was included in the PU matrix because of the appearance of Si–O–Si and Si–CH 3 spectra. Scanning electron microscopy was used to determine the difference in cellular structure of the foams as a result of the addition of PBDMS-e.g., more open cells, interconnected cells, and microporous cell walls. Mechanical testing revealed that the presence of PBDMS in the polyurethane matrix increased the mechanical properties of the foams at intermediate levels of PBDMS, with IPN-2 being the strongest at 5.9 kg/cm 2 tensile strength and 120% elongation to break, compared to 5.2 kg/cm 2 and 79.6% elongation to break for pure PU foams. The increased mechanical performance of the foams with PBDMS was attributed to microstructural changes and induced network interpenetration as a result of adding PBDMS. The results demonstrate that siloxane-based secondary networks significantly influence cellular morphology and tensile behaviour of polyurethane foams.