Comparison of liquid‐phase and methanol‐swelling crosslinking processes of polyimide dense membrane for CO2/CH4 separation

To overcome the plasticization effect in polyimide membranes, many researchers have proposed crosslinking method. This can reduce an inter‐segmental mobility by tightening and rigidifying the polymer chains. However, it is difficult to modify the whole polymer chains throughout the membrane because the reaction can be hindered by the diffusion rate of the crosslinker. In particular, it is hard for bulky crosslinker to penetrate a dense membrane with a small d‐spacing. This study investigated the effect of crosslinking a dense Matrimid membrane with p‐phenylenediamine (p‐PDA) via two different crosslinking methods (i.e., methanol‐swelling crosslinking process [M‐SCP] and liquid‐phase crosslinking process [L‐PCP]). Most of the crosslinking reaction in M‐SCP occurs on the membrane surface due to difficulty in penetration of the bulky p‐PDA into the Matrimid dense membrane. In contrast, the L‐PCP allows uniform crosslinking across the membrane. The membranes crosslinked using L‐PCP showed excellent chemical resistance. Furthermore, the plasticization phenomenon was not observed in the membranes crosslinked using L‐PCP with p‐PDA more than 15%. Meanwhile, the membrane crosslinked using M‐SCP exhibited poor plasticization and chemical resistance properties. These results showed that the L‐PCP method can be more effective for the crosslinking of dense membrane to deliver both high plasticization and chemical resistance.