Polymeric membranes dominate the membrane separation field because they are well developed and quite competitive in separation performance and economics [1]. The thermally induced phase separation (TIPS) process is one of the most useful techniques to prepare the porous membranes [2]. A lot of studies have been reported on the effect of different parameters on membrane structure fabricated via TIPS method. There is little research about the extractant effect on membrane morphology. In this work linear low density polyethylene and high density polyethylene were extracted by acetone and hexane extractants and their microstructures were compared. Fig. 1(a) and 1(b) show microstructure of linear low density polyethylene and high density polyethylene were extracted by acetone. Acetone has no effect on their structure and porous structures were obtained. As shown in Fig. 1 (c), LLDPE extracted by hexane is dense. Solubility parameter of hexane and polyethylene is close, so hexane can swell amorphous region of LLDPE. Swelling of polymer cause to closing the pores and dense structure obtained. Figure 1(d), shows the SEM images of HDPE by hexane. It seems that difference in HDPE and LLDPE crystallinity, causes that hexane change LLDPE structure. It can be concluded that in polymers with low crystallinity, solubility parameters of polymer and extractant should be different with each other.
