3 research outputs found
Designing Multiple-Shape Memory Polymers with Miscible Polymer Blends: Evidence and Origins of a Triple-Shape Memory Effect for Miscible PLLA/PMMA Blends
Shape
memory properties of polymers represent one of the most expanding
fields in polymer science related to numerous smart applications.
Recently, multiple-shape memory polymers (multiple-SMPs) have attracted
significant attention and can be achieved with complex polymer architectures.
Here, miscible PLLA/PMMA blends with broad glass transitions are investigated
as an alternative platform to design multiple-SMPs. Dual-shape memory
experiments were first conducted at different stretching temperatures
to identify the so-called âtemperature memory effectâ.
The switch temperature of the symmetric 50% PLLA/50% PMMA blend smoothly
shifted from 70 to 90 °C for stretching temperatures increasing
from 65 to 94 °C, attesting for a significant âtemperature
memory effectâ. Asymmetric formulations with 30% and 80% PMMA
also present a âtemperature memory effectâ, but the
symmetric blend clearly appeared as the most efficient formulation
for multiple-shape memory applications. A programming step designed
with two successive stretchings within the broad glass transition
consequently afforded high triple-shape memory performances with tunable
intermediate shapes, demonstrating that the symmetric blend could
represent an interesting candidate for future developments. Advanced
shape recovery processes are consistent with a selective activation
of specific âsoft domainsâ or nanodomains arising from
the broad glass transition and the large distribution of relaxation
time observed by DSC and dielectric spectroscopy. Polarized IR measurements
pointed out that the composition of activated/oriented âsoft
domainsâ could vary with stretching temperature, giving rise
to the âtemperature-memory effectâ. Consequently, from
a polymer physics standpoint, nanoscale compositional heterogeneities
within the symmetric blend could be suspected and discussed on the
basis of available models for miscible blends and for multiple-SMPs
Shape-Memory Behavior of Polylactide/Silica Ionic Hybrids
Commercial polylactide (PLA) was
converted and endowed with shape-memory
properties by synthesizing ionic hybrids based on blends of PLA with
imidazolium-terminated PLA and polyÂ[Δ-caprolactone-<i>co</i>-d,l-lactide] (PÂ[CL-<i>co</i>-LA]) and
surface-modified silica nanoparticles. The electrostatic interactions
assist with the silica nanoparticle dispersion in the polymer matrix.
Since nanoparticle dispersion in polymers is a perennial challenge
and has prevented nanocomposites from reaching their full potential
in terms of performance we expect this new design will be exploited
in other polymers systems to synthesize well-dispersed nanocomposites.
Rheological measurements of the ionic hybrids are consistent with
the formation of a network. The ionic hybrids are also much more deformable
compared to the neat PLA. More importantly, they exhibit shape-memory
behavior with fixity ratio <i>R</i><sub>f</sub> â
100% and recovery ratio <i>R</i><sub>r</sub> = 79%, for
the blend containing 25 wt % <i>im</i>-PLA and 25 wt % <i>im</i>-PÂ[CL-<i>co</i>-LA] and 5 wt % of SiO<sub>2</sub>âSO<sub>3</sub>Na. Dielectric spectroscopy and dynamic mechanical
analysis show a second, low-frequency relaxation attributed to strongly
immobilized polymer chains on silica due to electrostatic interactions.
Creep compliance tests further suggest that the ionic interactions
prevent permanent slippage in the hybrids which is most likely responsible
for the significant shape-memory behavior observed