Preparation and characterization of cross-linked Matrimid® membranes using para-phenylenediamine for O2/N2 separation

The cross-linking modification of asymmetric Matrimid membranes with para-phenylenediamine (pPD) has been investigated. The modification was performed by immersing Matrimid membranes in 10% (w/v) pPD/methanol solution at ambient temperature for certain period of time. The effects of immersion time on degree of cross-linking, physicochemical properties and gas transport properties of the membrane have been studied. The cross-linked Matrimid membranes were characterized using gel test, FTIR, TGA, XRD and SEM. The FTIR spectra confirmed that the cross-linking process had taken place, which indicates that imide groups were turned to amide groups during modification process. The degree of cross-linking increased with increasing the immersion time. This study found that, there were small amounts of insoluble materials found from the gel test. The possible reasons were that the proposed cross-linking method using pPD solution occurs only on the surface of the membranes or only low degree of cross-linking takes place. The XRD results revealed that the d-space of the polymeric chains change after the modification due to the methanol swelling and structure-tightening effects induced by cross-linking. The TGA results indicated that the degradation temperature is sufficient for gas separation applications. The gas transport properties of the pure and cross-linked Matrimid membranes were investigated using gas permeation tests. The results showed that the cross-linked Matrimid membranes decrease the O2, N2 and CH4 permeance compared to the unmodified membranes. Interestingly, 10% pPD-120 min samples showed an impressive enhancement of selectivity for O2/N2 compared to the unmodified membrane from 6.19 to 10.01 due to the affinity of nitrogen-containing molecules (pPD) towards oxygen.