Roles of Conformational and Configurational Defects on the Physical Aging of Amorphous Poly(lactic acid)

Aou, Kaoru; Hsu, Shaw Ling; Kleiner, Lothar W.; Tang, Fuh-Wei

doi:10.1021/jp074509t

Cited by 48 publications

(40 citation statements)

References 64 publications

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“…In addressing the variation of vitrification enthalpy with heating rate, Hodge has used the concept of a "characteristic relaxation time" ( ) [32], while Aou et al [33] For cooling experiments carried out from the memory-erased melt state the plots display a decrease in Tg with increasing cooling rate. This is a similar trend to that observed for the heat of crystallization in Fig.…”

Section: Vitrification Kineticsmentioning

confidence: 99%

Thermal transitions and solidification kinetics of poly(lactic acid) and blends with epoxidized natural rubber

et al. 2016

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Citation: MASCIA, L. ...et al., 2016. Thermal transitions and solidification kinetics of poly(lactic acid) and blends with epoxidized natural rubber. Thermochimica Acta, 633, pp. 82-90. Additional Information:• This paper was accepted for publication in the journal Ther- AbstractThe reactivity of polylactic acid (PLA) with epoxidized natural rubber (ENR50) was confirmed by monitoring the changes in melt viscosity during mixing and by TGA runs.The plasticization resulting from a partial miscibilization of ENR50 during mixing was found to have opposite effects on the crystallization of the PLA matrix, depending on the temperature scanning mode. An increase in heat of crystallization (ΔHc) with increasing temperature scanning rate was observed when heated from the glassy state, while a corresponding reduction in ΔHc was obtained in cooling scans from the melt.Studies on the kinetics of events have shown that the classical Kissinger plots for crystallization by heating from the glassy state display a variable activation energy for the case of the reactive blend. The vitrification kinetics, on the other hand, could be modelled quite accurately with the Mahadevan method for all systems, including an intrinsically amorphous PLA.

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Section: Vitrification Kineticsmentioning

confidence: 99%

Thermal transitions and solidification kinetics of poly(lactic acid) and blends with epoxidized natural rubber

et al. 2016

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“…The glass transition temperatures (T g ) of PLA are also varied to be 45~55 o C, depending on the D-isomer content. [7][8][9] Since the T g values of PLA samples are not far from the room temperature, it is expected that the local segmental motion of PLA is still available at the service temperatures and thus the physical aging takes place.…”

Section: Introductionmentioning

confidence: 99%

Influences of physical aging on enthalpy relaxation behavior, gas permeability, and dynamic mechanical property of polylactide films with various D-isomer contents

2010

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We report the isothermal enthalpy relaxation behavior, gas permeability, and dynamic mechanical properties of melt-quenched amorphous polylactide (PLA) films with various D-isomer contents (1, 4, and 9 mol%) as a function of the aging temperature (T a ) and time (t a ). It was found that the enthalpy relaxation peak area (∆H relax ) and glass transition temperature (T g ) of all PLA samples aged at a given T a increased initially and then remained relatively unchanged with increasing t a . The experimental ∆H relax vs. t a plots were fitted well with the Cowie-Ferguson equation incorporating the Kohlrausch-Williams-Watts (KWW) function. A comparison of the PLA samples aged at a similar degree of subcooling (∆T = T g -T a ) showed that the ultimate ∆H relax was somewhat higher for a PLA film with a lower D-isomer content. In addition, the oxygen permeability of all PLA films decreased linearly with increasing t a , which is due to the densification of glassy PLA films during physical aging. The dynamic mechanical data demonstrated that for the aged PLA films, the storage moduli around glass transition region increased significantly and the loss moduli peak corresponding to the glass transition region shifted to higher temperatures and became narrower.

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“…Apart from the mechanical properties, 19-23 a variety of properties of glassy polymers such as barrier resistance 24,25 and crystallization behavior 26,27 have also been reported to be dependent on the physical aging process. 37,38 Although the enthalpy relaxation of PLLA during physical aging has been investigated by several research groups, [39][40][41][42] the mechanism for the chain movement and molecular reorganization with aging has been still unclear. At present, the effects of physical aging on the macroscopic properties and microstructure of many traditional plastics including polycarbonate, PET, and polystyrene ͑PS͒ have been extensively investigated.…”

Section: Introductionmentioning

confidence: 99%

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

Pan

Zhu

Dong

et al. 2008

The Journal of Chemical Physics

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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).

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Roles of Conformational and Configurational Defects on the Physical Aging of Amorphous Poly(lactic acid)

Cited by 48 publications

References 64 publications

Thermal transitions and solidification kinetics of poly(lactic acid) and blends with epoxidized natural rubber

Thermal transitions and solidification kinetics of poly(lactic acid) and blends with epoxidized natural rubber

Influences of physical aging on enthalpy relaxation behavior, gas permeability, and dynamic mechanical property of polylactide films with various D-isomer contents

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

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