Effect of blend composition on microstructure, morphology, and gas permeability in PU/PMMA blends

PU and PU/PMMA blends were studied by Fourier transform infrared spectroscopy (FTIR), temperature modulated differential scanning calorimetry (TMDSC), scanning electron microscopy (SEM) and positron annhililation lifetime spectroscopy (PALS), and applied as membranes to the permeation of the gases H2, N2, O2, CH4, and CO2. The blend materials presented partial miscibility associated with hydrogen bond interaction between urethane and PMMA. Polyether flexible segment glass transition was observed at −51 °C and no significantly changes with PMMA content were observed in PU continuous phase in the blends. On the other hand, a PMMA rich phase presented glass transitions between 74 and 90 °C for blends with 80, 60, 40, and 20 wt% PU. Pure PMMA shows Tg of 117 °C. Besides, it was observed a broad thermal event that can be assigned to the interphase between the pure PU phase and the PMMA rich phase. PALS results showed a decrease in the average free volume size of the blends with increasing PMMA content for blends with 80 and 60 wt% PU. In addition, the relative free volume content of the samples does not change significantly. The blends with 90, 80, 70, and 60 wt% PU showed lower permeabilities than those of the PU membrane. The decrease in permeability is well correlated with the decrease in average free volume size. In the case of the H2/N2 gas pair, selectivity increases with blend PMMA content, and no marked changes are observed for the other gas pairs. The improvement in H2 selectivity is associated with the increase in rigid amorphous phases, which induces a complex phase-separated morphology in the blends.