The potential of polystyrene-block-polybutadiene-block-polystyrene triblock co-polymer as a base-polymer of polymer inclusion membranes (PIMs)

Abstract

The use of polystyrene-block-polybutadiene-block-polystyrene triblock co-polymer (SBS) as the base-polymer of polymer inclusion membranes (PIMs) is studied for the first time. SBS is an inexpensive and accessible thermoplastic elastomer which possesses the required properties to be used as a base-polymer in PIMs, namely mechanical strength and high resistance to acids/bases. Its compatibility with commonly used extractants in PIMs was assessed and it was observed that successful PIMs could be obtained when di(2-ethylhexyl)phosphoric acid (D2EHPA), LIX84I or tri-n-octylamine (TOA) were used as the extractants. The performance of these PIMs was investigated for the extraction of Zn(II), Cu(II) and Cr(VI), respectively, although only the TOA-based PIMs did not perform well. Both D2EHPA- and LIX84I-based PIMs were characterized by water contact angle measurements, atomic force microscopy, differential scanning calorimetry, and Fourier transform infrared spectroscopy. In comparison with PIMs containing other base-polymers, the SBS-based PIMs were found to extract faster and more Zn(II) or Cu(II), and moreover, the LIX84I-based PIM did not require the inclusion of an expensive plasticizer unlike its counterparts containing other commonly used base-polymers. The stability of these PIMs was also assessed over three transport cycles (i.e., simultaneous extraction and back-extraction), and it was observed that the transport rate decreased significantly when using D2EHPA-based PIMs, and in the case of LIX84I-based membranes it stabilized after the first cycle.