usually composed of a polyether or polyester soft segment and a
hard segment. The hard segments consist of urethane and urea
linkages with rigid and bulky units. The strong molecular interaction
of a polar urethane, urea groups and the rigid units makes the
hard segment act as filler or physically cross linked. Many
researchers have investigated segmented PU as a new material to
improve the permselectivity for gas separation. The purpose of
these studies is to find the relationship between the structure of
the PU and their separation properties [11–15].
Mixed matrix membranes (MMM) have been developed with
the old idea of polymer compositing in order to improve mechanical
and separation properties [16–20]. The concept of blending
two materials (polymer/sieve) has appeared over the past two decades,
and many studies were carried out by researchers in this
field. In many cases, the addition of a small amount from a molecular
sieve to a polymer matrix enhances the membrane selectivity
significantly [20–24]. Adams et al. [25] used Polyvinyl acetate
(PVAc) at the polymer matrix to prepare high Zeolite 4Å loading
MMMs. CO2/CH4 mixture is used to investigate the performance
of MMM for natural gas separation. The permeation results show
that for high CO2 partial pressure, CO2 selectivity is increased
63% while permeability remains effectively unchanged. Gorgojo
et al. investigated the effect of the Zeolite Nu-6 particle size on