Crystalline Structure and Morphology of Poly(l-lactide) Formed under High-Pressure CO₂

Abstract

Crystalline structure and morphology of poly(L-lactide) (PLLA) formed under high-pressure CO 2 were studied by comparing the CO 2 -treated PLLA and the annealed one in terms of the crystallization behavior, crystalline forms, and crystalline superstructures. The crystallization temperature dependence of the diffraction peak position (2θ ≈ 16°) and crystallinity for the CO 2 -treated PLLA indicates that the crystal modification changes continuously from the disorder R (R′′) to R forms not through the R′ one with increasing temperature. By using light scattering technique, we clarified that the morphological transition from spherulites on a micrometer scale to rodlike crystalline superstructures on a nanometer scale occurs around 15 °C under 7-15 MPa CO 2 and around 30 °C under 3 MPa CO 2 . By introducing the parameters η and ∆ in the theoretical calculation for Vv light scattering from spherulites, it is indicated that there is a distinct difference in the arrangement of crystalline lamellae within spherulite between the CO 2 -treated PLLA and the annealed one.

Crystallization of polylactide during impregnation with liquid CO2

“…Similar WAXD patterns have been reported previously for PLA crystallized under high-pressure CO 2 in this temperature range, and are distinct from those observed in specimens cold crystallized above T g in the absence of CO 2 or crystallized from the melt [9,10,12,13]. In the present case, isothermal crystallization of the as-moulded specimens at 110°C resulted in sharp Bragg peaks at 2h of 14.5°, 16.5°, 18.8°and 22.2° (Fig.…”

“…the 2.88 Å spacing of the (0 0 1 0) planes in the a modification), the volume of the unit cell is estimated to be some 8 % greater than for the a modification. It follows that CO 2 molecules may have been trapped within the crystalline phase during its formation, as has been suggested elsewhere [10], so that the disorder apparent from the WAXS results may reflect not only the initial state of the crystalline phase, but also modifications induced by desorption. (It would be of interest in this respect to carry out further WAXS measurements in transmission prior to complete desorption of the CO 2 ).…”

Microcellular foaming of polylactide and poly(butylene adipate‐co‐terphathalate) blends and their CaCO3 reinforced nanocomposites using supercritical carbon dioxide

“…This is compatible with the results by Marubayashi, [40] and they also clarified that the morphological transition from spherulites on a micrometer scale to rod-like crystalline superstructures on a nanometer scale with certain temperature and pressure. Meanwhile, for the PLA binary and ternary systems, the crystallinities of those samples are also improved to a certain level of around 37%.…”

“…In literature, the PLLA can be sufficiently crystallized just under CO 2 at 3 MPa and 0°C for 2 hr, exhibiting no cold crystallization behavior during heating. [40] The melting temperatures for PLA samples in this work with the presence of CO 2 are listed in Table 2 and are about 168°C without big difference. Another interesting thing is the disappeared both P ex related to the α′-α transition and typical double endothermic peaks [41,42] of PLA with a certain amount of CO 2 .…”

How high pressure CO2 impacts PLA film properties

“…Based on those considerations, there is a clear interest in studying the interactions between CO 2 and PLA, and the modifications that such molecule could induce in the PLA material, which is suitable as a substitute of PET. For now, most of the related literature is focused on the effects of supercritical CO 2 (or conditions near to it) on the PLA properties, such as foaming properties [16], thermal behavior [17][18][19], hydrophobic drug encapsulation [20,21] or swelling [22,23]. Nevertheless, there is not enough available information related to the effects of CO 2 at conditions lower than its supercritical point, which are often the conditions encountered in food packaging and food processing.…”