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Synthetic Saponite Clays as Additives for Reducing Aging Effects in PIM1 Membranes
journal contribution
posted on 2020-08-04, 00:03 authored by Federico Begni, Geo Paul, Elsa Lasseuguette, Enzo Mangano, Chiara Bisio, Maria-Chiara Ferrari, Giorgio GattiPolymers
of intrinsic microporosity represent one of the most promising
polymeric materials for gas separation applications. Their very rigid
and contorted backbone induces unusually high free volumes and high
internal surface area, with high gas permeabilities and moderate ideal
selectivity, especially for O2/N2 and CO2/N2 pairs with values lying above Robeson’s
upper bound. However, the high FFV of PIM1 tends to be short-lived,
soon collapsing to leave fewer transport pathways and reduce gas permeability.
One way to tackle this problem is the addition of fillers within the
polymeric matrix. Here we report the use of synthetic clays named
saponites as fillers to slow down the physical aging of PIM1 membranes.
Mixed matrix membranes (MMMs) based on two different saponite samples
(one completely inorganic and one functionalized with a surfactant)
have been obtained, and their permeation performances have been studied
in the course of one year to explore physical aging effects over time.
Without filler, PIM1 exhibits the classical aging behavior of polymers
of intrinsic microporosity, namely, a progressive decline in gas permeation.
On the contrary, with saponites, MMMs present a plateau after 1 week
within the aging showing that the fillers slow down the aging of PIM1
membranes in the long term. After one year of aging, the total reduction
for CO2 permeability for native PIM1 was 80%, whereas for
the MMMs it was 53% and 59% for the inorganic and the functionalized
saponite, respectively. Interactions between the fillers and the polymeric
matrix in addition to aging effects have been also monitored through
SS-NMR spectroscopy. The 13C spin–lattice relaxation
time (T1) measurements reveal that PIM1
chains intercalation between T–O–T lamellar sheets could
be one of the mechanisms responsible for PIM1 slowing down aging.
Chains confinement between lamellar sheets could play a significant
role in reducing the densification of chains, while maintaining small
free volumes.