Two types of polypropylene microporous hollow fiber membranes, Celgard X40-200 and Celgard X50-215, were used to expose to diethanolamine (DEA) aqueous solutions with and without CO2 loading, in order to investigate the impact of amine absorbents on membrane surfaces during the process of CO2 capture in a membrane contactor. The effects of liquids on the membrane surface morphology and surface tension were studied by means of SEM, AFM as well as a Contact Angle Goniometer. Possible interactions between the liquids and the membranes were monitored by XPS. It was found that both Celgard X40-200 and Celgard X50-215 hollow fibers suffered changes in terms of pore structure and surface roughness after being exposed to DEA aqueous solutions. In particular, Celgard X40-200 hollow fiber membranes underwent significant deformation as observed in surface morphology during the initial stage of contact. However, dissolved CO2 was found to cause less deformation of the micro-pores and to retard surface roughening, likely due to the formation of carbamate ions from interactions between CO2 and DEA. XPS analysis suggests that possible chemical reactions between the membranes and DEA may be responsible for the alteration of the surface tension of membranes thereby reducing their hydrophobicity. Therefore, it is possible that polypropylene membranes were partially wetted during CO2 capture, leading to performance deterioration in the membrane contactor. (C) 2003 Elsevier B.V. All rights reserved.