Shape-Memory Behavior of Polylactide/Silica Ionic Hybrids

Abstract

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 poly[ε-caprolactone-co-D,L-lactide] (P[CL-co-LA]) and surfacemodified 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 R f ≈ 100% and recovery ratio R r = 79%, for the blend containing 25 wt % im-PLA and 25 wt % im-P[CL-co-LA] and 5 wt % of SiO 2 −SO 3 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.

Recent Applications of Ionic Liquids in the Sol-Gel Process for Polymer–Silica Nanocomposites with Ionic Interfaces

“…The reversible and dynamic ionic bonding between the imidazolium-terminated polymers and the sulfonated silica nanoparticles led to distinct morphologies and very good nanoparticle dispersion within the hybrids. The sum of the improved morphology with an ionic polymer-filler interphase led to an exceptional performance, presenting an extremely long rubbery plateau and longer relaxation times, consistent with the significant shape-memory behavior observed [142].…”

“…Thus, shape-memory effect can be found in systems consisting of ionic interphases, such as, ionic polymers or PILs bearing host-guest interactions with small molecules [139] or with another polymer matrix [140], PIL-metal nanocomposites [141] and IL/PIL containing polymer-silica nanocomposites [9,142].…”

Electrospun hyperbranched polylactic acid–modified cellulose nanocrystals/polylactic acid for shape memory membranes with high mechanical properties

“…The shape fixation ratio determines the ability of the switch segment to be deformed or temporarily shaped. The shape recovery ratio determines the competence of the material to remember permanent shapes . As we can see from the figure, the fixed rate of neat PLA and its composite material was about 90%, which was not changed by the addition of H‐PLA‐CNCs.…”

“…The shape recovery ratio determines the competence of the material to remember permanent shapes. [36][37][38][39] As we can see from the figure, the fixed rate of neat PLA and its composite material was about 90%, which was not changed by the addition of H-PLA-CNCs. Figure 8A indicates the shape memory performances of pure PLA membranes, the pure PLA film has a poor shape recovery rate of only 56%.…”

Design of melt-recyclable poly(ε-caprolactone)-based supramolecular shape-memory nanocomposites

“…While the [4+2] cycloaddition proceeds at room temperature, the reverse reaction (retro-DA) becomes generally favorable above 100 C. The shape reprogramming of some SMPs based on biodegradable polymers such as poly(3-caprolactone) (PCL) and poly(lactide) (PLA) as the switching domain was allowed by the presence of such DA adducts as widely reported in the literature. 5,[10][11][12][13][14][15][16] Simultaneously, relevant non-covalent interactions such as hydrogen bonding, [17][18][19][20] metal-ligand coordination, 8,21 ionic interactions [22][23][24] or p-p stacking 25 were integrated into SMP designing. Among this wide variety of supramolecular interactions, the hydrogen bonds have acquired a specic attention to build reversible polymeric materials, being able to display SMP properties.…”