polymers have often been investigated because these are crucial in electrical devices
and packaging materials. In these applications, an O 2 barrier property is desired.
Data for other gases, such as CO 2 and hydrocarbons, are few. This study focused on
the gas transport properties of CO 2 as a condensable gas, N 2 as a non-condensable
gas, and O 2 as an often reported gas in crystalline polymers. Data for gas transport
properties were determined via a differential or equal pressure method. The degree of
crystallinity was determined via several methods, including X-ray diffraction
(XRD), thermal analysis, vibrational spectroscopy, volumetric method, and solidstate nuclear magnetic resonance (NMR) (Runt and Kanchanasopa 2008). The
crystallinity calculated via XRD, density, and differential scanning calorimetry
was used in this analysis.
Gas Permeability in Crystalline and Liquid Crystalline Polymers
Figure 2 shows the gas permeability values of crystalline and liquid crystalline
polymers as a function of crystallinity. Liquid crystalline polymers have higher gas
barrier properties (i.e., lower gas permeability) compared with crystalline polymers.
Gas permeability is known to decrease with increasing crystallinity in crystalline and
liquid crystalline polymers because gases cannot diffuse and permeate in the crystalline phase. However, this study shows that gas permeability in the crystalline and
liquid crystalline polymers are independent of their crystallinity at lower crystallinity
values and are almost the same or higher than those of amorphous polymers. For
example, the O 2 permeability of crystalline and liquid crystalline polymers is almost
constant from 20% to 60% crystallinity for PMP, 10% to 30% for liquid crystalline
HBA/HNA, and 20% to 40% for PPTA. By contrast, the permeabilities of PMP,
PLA, and PPTA decrease from 60% to 65%; 25% to 40%; and 40% to 50%,
respectively. This reduction is also observed in PP from 40% to 60%, in PA from
20% to 50%, in PET from 0% to 50%, and in PEN from 0% to 40%. Interestingly,
the O 2 permeability slightly increases between 0% and 25% for PLA, and 0% and
40% crystallinity for PS. Only the O 2 permeability in PE decreases from 20% to 60%
and is sharply reduced from 60% to 80%. The reduction in PE was larger than those
in the other crystalline and liquid crystalline polymers. As shown in PMP and PLA,
the gas permeability begins to decrease beyond a specific crystallinity value. This
result suggests that the phase transitions of the crystalline structure in crystalline and
liquid crystalline polymers occur at these crystallinity values. Hence, the gas permeability of crystalline and liquid crystalline polymers may decrease during phase
transitions. The same pattern is observed for CO 2 and N 2 permeability.
Gas Solubility in Crystalline and Liquid Crystalline Polymers
Figure 3 shows the gas solubility in crystalline and liquid crystalline polymers as a
function of the crystallinity. Liquid crystalline polymers have higher gas barrier
properties (i.e., lower gas solubility) compared with other crystalline polymers
530
S. Ando et al.
and packaging materials. In these applications, an O 2 barrier property is desired.
Data for other gases, such as CO 2 and hydrocarbons, are few. This study focused on
the gas transport properties of CO 2 as a condensable gas, N 2 as a non-condensable
gas, and O 2 as an often reported gas in crystalline polymers. Data for gas transport
properties were determined via a differential or equal pressure method. The degree of
crystallinity was determined via several methods, including X-ray diffraction
(XRD), thermal analysis, vibrational spectroscopy, volumetric method, and solidstate nuclear magnetic resonance (NMR) (Runt and Kanchanasopa 2008). The
crystallinity calculated via XRD, density, and differential scanning calorimetry
was used in this analysis.
Gas Permeability in Crystalline and Liquid Crystalline Polymers
Figure 2 shows the gas permeability values of crystalline and liquid crystalline
polymers as a function of crystallinity. Liquid crystalline polymers have higher gas
barrier properties (i.e., lower gas permeability) compared with crystalline polymers.
Gas permeability is known to decrease with increasing crystallinity in crystalline and
liquid crystalline polymers because gases cannot diffuse and permeate in the crystalline phase. However, this study shows that gas permeability in the crystalline and
liquid crystalline polymers are independent of their crystallinity at lower crystallinity
values and are almost the same or higher than those of amorphous polymers. For
example, the O 2 permeability of crystalline and liquid crystalline polymers is almost
constant from 20% to 60% crystallinity for PMP, 10% to 30% for liquid crystalline
HBA/HNA, and 20% to 40% for PPTA. By contrast, the permeabilities of PMP,
PLA, and PPTA decrease from 60% to 65%; 25% to 40%; and 40% to 50%,
respectively. This reduction is also observed in PP from 40% to 60%, in PA from
20% to 50%, in PET from 0% to 50%, and in PEN from 0% to 40%. Interestingly,
the O 2 permeability slightly increases between 0% and 25% for PLA, and 0% and
40% crystallinity for PS. Only the O 2 permeability in PE decreases from 20% to 60%
and is sharply reduced from 60% to 80%. The reduction in PE was larger than those
in the other crystalline and liquid crystalline polymers. As shown in PMP and PLA,
the gas permeability begins to decrease beyond a specific crystallinity value. This
result suggests that the phase transitions of the crystalline structure in crystalline and
liquid crystalline polymers occur at these crystallinity values. Hence, the gas permeability of crystalline and liquid crystalline polymers may decrease during phase
transitions. The same pattern is observed for CO 2 and N 2 permeability.
Gas Solubility in Crystalline and Liquid Crystalline Polymers
Figure 3 shows the gas solubility in crystalline and liquid crystalline polymers as a
function of the crystallinity. Liquid crystalline polymers have higher gas barrier
properties (i.e., lower gas solubility) compared with other crystalline polymers
530
S. Ando et al.