Surface Modification of Matrimid® 5218 Polyimide Membrane with Fluorine-Containing Diamines for Efficient Gas Separation

Abstract

Polyimide membranes have been widely investigated in gas separation applications due to their high separation abilities, excellent processability, relatively low cost, and stabilities. Unfortunately, it is extremely challenging to simultaneously achieve both improved gas permeability and selectivity due to the trade-off relationship in common polymer membranes. Diamine modification is a simple strategy to tune the separation performance of polyimide membranes, but an excessive loss in permeability is also generally observed. In the present work, we reported the effects of diamine type (i.e., non-fluorinated and fluorinated) on the physicochemical properties and the corresponding separation performance of a modified membrane using a commercial Matrimid® 5218 polyimide. Detailed spectroscopic, thermal, and surface analyses reveal that the bulky fluorine groups are responsible for the balanced chain packing modes in the resulting Matrimid membranes compared to the non-fluorinated diamines. Consequently, the modified Matrimid membranes using fluorinated diamines exhibit both higher gas permeability and selectivity than those of pristine Matrimid, making them especially effective for improving the separation performance towards H2/CH4 and CO2/CH4 pairs. The results indicate that the use of fluorinated modifiers may offer new opportunities to tune the gas transport properties of polyimide membranes.

Molecularly Mixed Composite Membranes for Gas Separation Based on Macrocycles Embedded in a Polyimide

“…The thermal decomposition had two steps in the Matrimid ® film, whereas it became multistep in the nanocomposite films ( Figure 4 , Figure 5 and Figure 6 ). The high thermal stability of Matrimid ® is indicated by a T onset at 503 °C, a main degradation peak ( T d1) at 530 °C and a second decomposition one ( T d2) at around 609 °C, which is related to the thermal decomposition of the imide group and carbonization [ 28 ]. Nevertheless, at 800 °C, a residue of 56% was registered, indicating that higher temperatures are required for a complete degradation of the polyimide.…”