(Fig. 3). As shown, the O 2 solubility of crystalline and liquid crystalline polymers
slightly decreases when the crystallinity was increased from 0% to 40% for PLA, 0% to
50% for PET, 0% to 40% for PS, and 0% to 40% for PEN. The O 2 solubility in PE also
decreases when the crystallinity was increased from 20% to 78%, similar to other
crystalline polymers. For example, the O 2 solubility at crystallinities between 22%
and 78% varies from 0.638 cm
3 to 0.014 cm
3 (STP) (cm
3 atm)
À1
, thereby indicating
a 45-fold difference within the same crystallinity for PE. For liquid crystalline polymers,
the O 2 solubility in HBA/HNA is almost constant between 10% and 30% crystallinity,
whereas the value decreases in PPTA between 20% and 40% crystallinity. The solubility
in other liquid crystalline polymers remains constant but somewhat scattered between
the crystallinity of 0% and 50%. The CO 2 and N 2 solubilities in other polymers are
similar to that of O 2 . As seen in these results, the solubility of many crystalline polymers,
such as PE, PLA, PET, PA, and PEN, tends to decrease with increasing crystallinity,
whereas the liquid crystalline polymers show constant values in this analysis. No
increase in the solubility is observed for crystalline and liquid crystalline polymers.
Figure 3 also shows the purely amorphous gas solubility, S a , of crystalline polymers
as a function of their crystallinity. Interestingly, regardless of the gas used, S a in almost
all crystalline and liquid crystalline polymers, with the exception of PEN, are independent of their crystallinity. Only the crystalline PEN shows a slight increase in solubility
between 0% and 40%. This result suggests that the solubility in crystalline and liquid
crystalline polymers with regards to S a and crystallinity is consistent with Eq. 2.
Gas Diffusivity in Crystalline and Liquid Crystalline Polymers
Figure 4 shows the gas diffusivity in crystalline and liquid crystalline polymers as a
function of crystallinity. Liquid crystalline polymers generally have a higher gas
barrier property (i.e., lower gas diffusivity) compared with other crystalline polymers. The O 2 diffusivity, including their deviations, remains almost constant in the
range of 10–30% for liquid crystalline HBA/HNA and 20–40% for PPTA. The
diffusivity in PLA and PS slightly increases at crystallinities between 0% and 25%
and 0% and 40%, respectively. On the other hand, the diffusivity in PET and PEN
slightly decreases at crystallinities between 0% and 50% and between 0% and 40%,
respectively. The O 2 solubility in PE varies from 1.37 Â 10
À6 cm
2 s
À1 for 20%
crystallinity to 3.30 Â 10
À9 cm
2 s
À1 for 78% crystallinity, thereby indicating a
415-fold decrease. These trends are also observed in both CO 2 and N 2 .
Analysis of the Relationship Between Gas Transport Properties
and Crystalline Structure in Crystalline and Liquid Crystalline
Polymers
Although gas transport properties (i.e., permeability, solubility and diffusivity) in
crystalline and liquid crystalline polymers decrease with increasing crystallinity,
based on Figs. 2, 3, and 4, gas permeability and diffusivity are not affected by
534
S. Ando et al.
slightly decreases when the crystallinity was increased from 0% to 40% for PLA, 0% to
50% for PET, 0% to 40% for PS, and 0% to 40% for PEN. The O 2 solubility in PE also
decreases when the crystallinity was increased from 20% to 78%, similar to other
crystalline polymers. For example, the O 2 solubility at crystallinities between 22%
and 78% varies from 0.638 cm
3 to 0.014 cm
3 (STP) (cm
3 atm)
À1
, thereby indicating
a 45-fold difference within the same crystallinity for PE. For liquid crystalline polymers,
the O 2 solubility in HBA/HNA is almost constant between 10% and 30% crystallinity,
whereas the value decreases in PPTA between 20% and 40% crystallinity. The solubility
in other liquid crystalline polymers remains constant but somewhat scattered between
the crystallinity of 0% and 50%. The CO 2 and N 2 solubilities in other polymers are
similar to that of O 2 . As seen in these results, the solubility of many crystalline polymers,
such as PE, PLA, PET, PA, and PEN, tends to decrease with increasing crystallinity,
whereas the liquid crystalline polymers show constant values in this analysis. No
increase in the solubility is observed for crystalline and liquid crystalline polymers.
Figure 3 also shows the purely amorphous gas solubility, S a , of crystalline polymers
as a function of their crystallinity. Interestingly, regardless of the gas used, S a in almost
all crystalline and liquid crystalline polymers, with the exception of PEN, are independent of their crystallinity. Only the crystalline PEN shows a slight increase in solubility
between 0% and 40%. This result suggests that the solubility in crystalline and liquid
crystalline polymers with regards to S a and crystallinity is consistent with Eq. 2.
Gas Diffusivity in Crystalline and Liquid Crystalline Polymers
Figure 4 shows the gas diffusivity in crystalline and liquid crystalline polymers as a
function of crystallinity. Liquid crystalline polymers generally have a higher gas
barrier property (i.e., lower gas diffusivity) compared with other crystalline polymers. The O 2 diffusivity, including their deviations, remains almost constant in the
range of 10–30% for liquid crystalline HBA/HNA and 20–40% for PPTA. The
diffusivity in PLA and PS slightly increases at crystallinities between 0% and 25%
and 0% and 40%, respectively. On the other hand, the diffusivity in PET and PEN
slightly decreases at crystallinities between 0% and 50% and between 0% and 40%,
respectively. The O 2 solubility in PE varies from 1.37 Â 10
À6 cm
2 s
À1 for 20%
crystallinity to 3.30 Â 10
À9 cm
2 s
À1 for 78% crystallinity, thereby indicating a
415-fold decrease. These trends are also observed in both CO 2 and N 2 .
Analysis of the Relationship Between Gas Transport Properties
and Crystalline Structure in Crystalline and Liquid Crystalline
Polymers
Although gas transport properties (i.e., permeability, solubility and diffusivity) in
crystalline and liquid crystalline polymers decrease with increasing crystallinity,
based on Figs. 2, 3, and 4, gas permeability and diffusivity are not affected by
534
S. Ando et al.