Influence of the addition of water to amorphous switching domains on the simulated shape-memory properties of poly(l-lactide)

Abstract

a b s t r a c tIt is well known that the environmental conditions e.g. humidity can alter the shape-memory properties of polymers. In this work we applied an atomistic molecular dynamics simulation approach to model the influence of the addition of 1 wt% and 2 wt% water on the simulated shape-memory behavior of the amorphous switching domains of poly(L-lactide) (PLLA) with a molecular weight of M n ¼ 52,000 g mol À1 .For the dry as well as the water swollen PLLA-models, two subsequent uniaxial thermomechanical test cycles have been calculated, whereby the applied uniaxial deformation ε m was varied between 50% and 150%.All simulated PLLA models showed high shape fixity ratio of R f ! 84%. The shape-memory properties obtained at ε m ¼ 100% for the dry PLLA and the models containing 1 wt% water were almost identical with a shape recovery ratio in the first and second test cycle around R r ¼ 61%e64%. In contrast PLLA with 2 wt% water exhibited higher values of R r ¼ 76% during the first test cycle, but a lower R r ¼ 52% in the subsequent second cycle. Furthermore, increasing the applied ε m resulted in a decrease of R r from 82% to 42% for the dry PLLA, whereas PLLA with 2 wt% water did not show a dependence of R r on ε m . We anticipate that these observations can be attributed to differences in the initial structure of the various simulated PLLA models e.g. the different distribution of the free volume elements.

Atomistic Simulation of the Shape‐Memory Effect in Dry and Water Swollen Poly[(rac‐lactide)‐co‐glycolide] and Copolyester Urethanes Thereof

“…Whereas, for PLGA‐TMDI, both R r values in the dry and wet state were found to decrease with increasing ε m . A comparable behavior has been also reported for simulated amorphous PLLA samples when the deformation strain during programming was increased . The shape fixation of dry and water‐swollen PLGA‐HDI and PLGA‐LDI models was improved to R f ≥ 87% by increasing to ε m ≥ 50%, while the shape recoveries decrease.…”

“…In this work, we explored the shape-memory behavior of amorphous domains in poly[( rac -lactide)-co -glycolide] (PLGA) and PLGA-based polyester urethanes (PLGA-PUs), containing three different urethane linker units in dry and wet state (with 2 wt% H 2 O) based on recently introduced atomistic simulation methods. [25][26][27] The constructed dry and wet packing models are subjected to a simulated cyclic thermomechanical tensile test, which comprises uniaxial stretching at T high = 500 K, cooling to T low = 250 K under constant stress, unloading at T low = 250 K, and stress free recovery at T high = 500 K. Furthermore, the effect of addition of water on the T g of PLGA and PLGA-PU models was examined. The simulated shape-memory properties of the PLGA-PUs are discussed with respect to the infl uence of: i) the chemical nature of the urethane linker units, ii) the water content, and iii) the applied uniaxial deformation ε m during programming.…”

Biodegradable polyester-based shape memory polymers: Concepts of (supra)molecular architecturing

“…T g is traditionally reduced by plasticizers. For this purpose water [12] and other plasticizers [13] were tried. To avoid the migration of the plasticizer, especially when added in high amount, it is straightforward to crosslink the PLA [13].…”

Shape Memory Systems with Biodegradable Polyesters

“…To overcome this problem two approaches have been followed. Ghobadi et al [9] enhanced the amorphous chain mobility by plasticization with water (≤2 wt.%). Radjabian et al [10] used spun PLA filament, wound in helical form, for SM testing.…”