The evolution of the structure, mechanical, and gas separation properties of P84 hollow fiber membranes from the polymer to the carbon stage

To provide insight into the formation process of carbon molecular sieve (CMS) hollow fiber membranes (HFMs), P84 co-polyimide HFMs were thermally treated at 200, 250, 300, 350, 400, 550, 650, and 800 °C. TG-MS was used to study the weight loss and released gases at all temperatures. In situ SEM, HIM (helium ion microscope) and in situ XRD were used to investigate the structural evolution of P84 HFMs. The structural evolution and changes in the mechanical properties and gas separation performance of P84 HFMs from the polymer to the carbon stages were divided into three stages (sub-Tg, intermediate, and carbon stages) by their Tg (322 °C) and Td (460 °C). The substructure of P84 HFMs began to collapse during the intermediate stage, which impeded the gas permeance of P84 CMS HFMs. At the carbon stage, the permeance of CO2, O2, N2, and CH4 decreased with the increased carbonization temperature; however, the H2 permeance reached a maximum at 650 °C due to the partial pyrolysis and structural reorganization of P84 CMS HFMs.