FIGURE 2 The FTIR spectra of MMT, DABPPI, and MMT-PI
(a ). The XRD spectra of MMT, DABPPI, and MMT-PI (b ).
The cross-section (c ) and surface (d ) SEM images of
MMT-PI.
Layered silicate, such as MMT, is reported to be impermeable to gas
molecules,[40] which makes gas molecules difficult
to penetrate because of its perfect crystal structure. Therefore, the
addition of MMT to PI would create a physical obstacle to the diffusion
of gas molecules in the composite. From the above SEM results, it could
be inferred that it would be very difficult for gas to pass through the
composite material with such a “brick-and-mortar” layered structure,
which may greatly improve the gas barrier performance of the MMT-PI
composite film.
The results of the gas barrier properties of DABPPI and MMT-PI are shown
in Table 1 . Surprisingly, the WVTR of MMT-PI was significantly
decreased. The value of WVTR decreased from 2.25
g/m2/day for DABPPI to 0.0185
g/m2/day for MMT-PI, a decrease of 99.18%. The
results of previous studies have shown that the improvement in water
vapor barrier properties of nacre-like composites is not very
significant due to the hydrophilicity of the raw materials used. This
concern is ameliorated by using PI as “mortar”. DABPPI is a kind of
water-insoluble PI with relatively low water absorption. Combined with
the dense lamellar structure, the diffusion of water molecules can be
well hampered, thereby improving the water vapor barrier performance.
The nacre-like structure has exceptional barrier properties for
non-condensed, non-polar gases, like oxygen, which has also been
confirmed by early studies.[41, 42] In this study,
the oxygen permeability of MMT-PI was decreased conspicuously.
Specifically, the DABPPI showed an OTR of 1944.69
cm3/m2/day/0.1MPa. While with the
addition of 50% MMT, the OTR decreased to 7.98
cm3/m2/day/0.1MPa, a decrease of
three orders of magnitude. With this simple method, MMT-PI composite
film with noticeably improved water vapor and oxygen barrier properties
can be achieved, which will provide a feasible strategy for the
preparation of flexible high gas barrier films.
TABLE 1 The WVTR, OTR, and LOI of the DABPPI and MMT-PI