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

Abstract

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.

Effects of chain microstructures on mechanical behavior and aging of a poly(L-lactide-co-ε-caprolactone) biomedical thermoplastic-elastomer

“…Nevertheless, enthalpy relaxations associated to the chain arrangements in the amorphous regions were found particularly in high LA-copolymers as a result of aging. In this context, it is worth mentioning that a comparison of homopolylactides of L-LA-isomer with various copolylactides with several contents of D-LA-isomer, aged at a similar degree of undercooling, showed that the enthalpy relaxation value was somewhat higher for the PLA samples with lower Disomer content (Kwon et al, 2010), in agreement with the results observed for PLCL copolymers. Now in this work, the aging effect was studied on three 70:30 PLCLs having different randomness characters (R = 0.47, 0.69 and 0.92, respectively).…”

How high pressure CO2 impacts PLA film properties

“…Some studies showed a decrease in water and oxygen permeability for different types of PLA (e.g. totally amorphous, semicrystalline, with/without plasticizers) as a result of PLA structure densification during physical ageing [56][57][58]. Based on these considerations, it could be hypothesized that such decrease in the diffusion properties originated from the acceleration of physical ageing during CO 2 sorption.…”

Physical ageing and molecular mobility in PLA blends and composites

“…Physical ageing is a known disadvantage of PLA, which proceeds relatively fast because of the low glass transition temperature of the polymer and which results in considerable changes of properties in a relatively short time [7,8,19]. We discussed the possible effect of molecular mobility on the thermal transitions of PLA, and physical ageing is closely related to and depends on mobility.…”

“…However, besides its advantages, PLA also has several drawbacks. Its slow crystallization [5,6] and fast physical ageing [7,8] result in unstable structure and rapidly changing properties, which might result in brittleness, fast deterioration of properties and finally catastrophic failure. As a consequence, PLA is often modified by various means including copolymerization [9][10][11], plasticization [12][13][14], blending [15,16], incorporation of various fillers [17][18][19][20] and reinforcements [21][22][23].…”