The mesophase of PLA in binary materials with ATBC and in composites with ATBC and mesoporous MCM-41

Several composites of an L-rich polylactide (PLA) with acetyl tri-n-butyl citrate (ATBC), and mesoporous particles of Mobil Composition of Matter No. 41 (MCM-41) have been prepared in order to overcome the important drawback of PLA related to its rather low crystallization rate. Additionally of solving that deficiency, the mesophase of PLA has been spontaneously formed in two specimens just by standing at room temperature. This finding was ascertained from the corresponding X-ray diffractograms, which are similar to those observed for the mesophase obtained by stretching experiments. When the mesophase is initially present, its nucleation ability for recrystallization is significantly higher than the one exhibited by amorphous samples, as shown by both DSC and real-time variable-temperature synchrotron diffraction experiments. Moreover, the mesophase displays relatively small values of the long spacing, around 10–11 nm, compared with the values of about 16–18 nm found in the crystals. On the other hand, the mesophase shows in most cases an intermediate degree of order between the amorphous and crystalline phases, as stated by FTIR measurements. Its most characteristic feature is the observation of a distinctive peak at 916 cm⁻¹, while the crystals show a specific peak at 923 cm⁻¹ for the α′ phase and at 921 cm⁻¹ for the α modification. The low-frequency region of the spectra below around 800 cm⁻¹, scarcely commented in literature, has also been found especially sensitive to ordering.