The mesophase structuring in melt-quenched poly­(l-lactide) (PLLA) treated in low-pressure CO2 at 2 MPa and 0–35 °C was investigated by using infrared spectroscopy, differential scanning calorimetry (DSC), temperature-modulated DSC, and atomic force microscopy (AFM). It was found that the mesophase formation in glassy PLLA was significantly enhanced, in particular at lower temperature (0 °C), which promoted a distinctly faster formation rate. AFM results revealed that the CO2-enhanced mesophase exhibited nodular morphology with dramatically increased nucleation density. A framework of multistage model in combination with the moderately improved molecular mobility exerted by CO2 was proposed to explain the main findings. Because of the moderate molecular mobility, a tremendous number of metastable mesomorphic layers were formed and stabilized by the accompanying development of the rigid amorphous fraction (RAF), leading to the immobilization of the remaining mobile amorphous fraction (MAF). The mesomorphic phases were converted to more stable crystals via cooperative structural reorganization upon the devitrification of the RAF, requiring high chain mobility, showing time and temperature dependence. Consequently, the amorphous PLLA transiently transformed to the mesophase before transforming into the crystal during treating at a relatively high temperature (35 °C). Alternatively, upon heating, the mesophase underwent disordering–reorganization to form active crystallite, profoundly promoting the cold crystallization of the surrounding restored MAF, resulting in obviously depressed cold-crystallization temperatures. The present results have important implications in understanding and regulation of the crystallization of polymers.

The thermal reduction of GO is the most commonly used strategy for preparation of rGO, and the oxidation degree of GO would influence the chemical structure of prepared rGO, thereby affecting its physical and chemical properties.

The effect of compressed CO 2 treatment on the thermal behavior of poly(L-lactide) (PLLA) with low L-isomer content of 94% was studied by using differential scanning calorimetry (DSC) and temperature modulated DSC. It was shown that the treated samples displayed rich thermal transition signals during DSC heating, which is differ from the PLLA having high L-isomer content, including enthalpy relaxation, endothermic annealing, melting-recrystallization process, and cold crystallization. The results suggested that the crystalline phase obtained has less perfection and low crystallinity regardless of the treatment conditions because of the low crystallizability of the PLLA. This PLLA was induced to crystallize after treatment under CO 2 at 2 MPa and temperature g65 °C and at pressures of 4-16 MPa and temperatures as low as 0 °C. At 2 MPa, the R crystal form is formed predominantly in the crystallized samples. The results also indicated that the PLLA-CO 2 system exhibited the property of retrograde vitrification.