Figure 5. OTR of (TA@LDH/PEO)50 hybrid films
with different ratios of TA: LDH.
Hydrogen bonds are much weaker
than electrostatic interactions but stronger than van der Waals forces.
Therefore, hydrogen-bonded films have good tensile
properties.27 Because hydrogen bonding is very
important for mechanical properties, we regulated the ratio of TA to
LDH. The OTR of four kinds of thin films with different ratios and
layers were measured. Besides the (TA@LDH/PEO)50 film
with TA: LDH of 3: 1, the samples with other proportions (1:1, 2:1 and
4:1) also exhibit the same change trend for OTR with increasing the
bilayer number (Figure S4, Support Information).
No matter what the ratio of TA to LDH, the OTR of the films increased
slightly after stretching (Figure 5). The oxygen resistance of the film
is still good after stretching. However, with the decrease of LDH
content in TA@LDH, the attenuation of the oxygen barrier is slower upon
stretching. When the ratio of LDH nanosheets is 50%, the OTR of 120%
stretching is 79% higher than that without stretching (from 99 to
177cm3/(m2·24h·0.1MPa)). When the
ratio of LDH is 20%, the OTR of 120% stretching is only 23% higher
than that without stretching (from 120 to 149
cm3/(m2·24h·0.1MPa)). These results
show a higher content of TA is favorable to the film ductility due to
the presence of elastic hydrogen network, although the incorporation of
LDH nanosheet improves the barrier property.
Considering the balance between oxygen barrier and tensile properties,
the best ratio of LDH is 25% (i.e. TA: LDH = 3:1). At 50-bilayer, the
OTR is 110 cm3/(m2·24h·0.1MPa), and
its oxygen barrier capacity is 28× higher than that of NR substrate.
When the stretch ratio was 25%, the OTR increased by 12% to 124
cm3/(m2·24h·0.1MPa). The OTR is 128
cm3/(m2·24h·0.1MPa) at 50%
stretching, which is 17% higher than that of the unstrained film. It
still has good oxygen resistance at 100% stretching, with OTR increased
by 20% to 133 cm3/(m2·24h·0.1MPa).
As shown in Table 1, the (TA@LDH/PEO)50 hybrid film has
significant advantages over other films in published work. Although the
oxygen barrier property of (TA@LDH/PEO)50 film is not
the best, its tensile deformation ratio reaches 120%, which is not
achieved by other works. And after 120% stretching, the permeability is
only 29% higher than that without stretching. It can be found that
increasing the tensile capacity needs to sacrifice part of the oxygen
barrier capacity. Even so, our (TA@LDH/PEO)50 film shows
simultaneously excellent tensile property and competitive oxygen barrier
capability.
Table 1. Comparative study on gas barrier performance after
stretching between our (TA@LDH/PEO)50 film and reported
materials