Conformational and microstructural characteristics of poly(L-lactide) during glass transition and physical aging

Abstract

The glass transition and physical aging processes of poly(L-lactide) (PLLA) were studied by variable-temperature Fourier transform infrared (FTIR) spectroscopy and (13)C solid-state NMR spectroscopy. The glass transition temperature (T(g)) of PLLA can be well determined from the temperature-dependent FTIR intensity. Nearby T(g), a distinct change in the slope of spectral intensity versus temperature plot is detected. FTIR results suggest that the energy-favorable gauche-trans (gt) conformers rearrange into the less energy-favorable gauche-gauche (gg) counterparts with heating over the glass transition region, which becomes more distinct at temperature above T(g). Besides, the 1267 cm(-1) band, which shows different trends of variation from the other bands upon heating, was assigned to be more sensitive to the nu(as)(C-O-C)+delta(CH) vibration mode of the less energy-favorable gg conformers in PLLA. By comparing the FTIR spectra of the aged and deaged PLLA, it was demonstrated that the rearrangement from the high- to low-energy conformers, i.e., gg to gt, occurs with physical aging. (13)C spin-lattice relaxation measurements indicate that the relaxation rate distribution broadens with aging, which agrees with the previous suggestion that the locally ordered domains are formed during physical aging. Because of the larger variation in the conformational state and microstructure, the FTIR intensities vary much more abruptly for the aged sample with heating to nearby T(g).

Properties and structure of polylactide/poly (3-hydroxybutyrate-co-3-hydroxyvalerate) (PLA/PHBV) blend fibers

“…It was recently revealed that structural rearrangements, such as the conformational transition from gg to gt and local ordering [54], occurred during the It is seen in Fig. 5 that all the neat PLA fibers show intensified physical aging peaks together with reduced T c and T m after the 180 days storage.…”

“…The physical aging of PLA has attracted tremendous research interest [53][54][55] because it not only induces macroscopic changes such as embrittlement but also involves profound microstructural evolutions. It was recently revealed that structural rearrangements, such as the conformational transition from gg to gt and local ordering [54], occurred during the It is seen in Fig.…”

Temperature-Variable FTIR and Solid-State 13C NMR Investigations on Crystalline Structure and Molecular Dynamics of Polymorphic Poly(l-lactide) and Poly(l-lactide)/Poly(d-lactide) Stereocomplex

“…These findings resemble those observed in amorphous PLA. 51 NMR spectra of α crystals are of much interest (Figure 6 and Figure a ν, δ, and r denote stretching, bending, and rocking, respectively; as and s represent asymmetry and symmetry, respectively. b vs, s, m, w, and vw are the abbreviations of very strong, strong, medium, weak, and very weak, respectively.…”

Filling behavior, morphology evolution and crystallization behavior of microinjection molded poly(lactic acid)/hydroxyapatite nanocomposites

“…Hence, the aging process of the PLA/HA-C sample is stronger than that of PLA/HA-M sample. Literature [40] shows that there are locally ordered domains formed during aging and these locally ordered domains can reduce the potential energy. During DSC heating process, due to the change of conformational state and Table 1 The DSC parameters of PLA/HA-C and PLA/HA-M samples obtained from Fig.…”