Thermoreversible Gels of Poly(l-lactide)/Poly(d-lactide) Blends: A Facile Route to Prepare Blend α-Form and Stereocomplex Aerogels

Abstract

The demand for biodegradable polymer-based aerogels with superior comprehensive properties has escalated in various fields of application, such as packaging, tissue engineering, thermal insulation, acoustic insulation, and environmental remediation. In this work, we report a facile strategy for enhancing the thermal and mechanical properties of polylactide (PLA) aerogels through the stereocomplex (SC) formation between the opposite enantiomers. Thermoreversible gelation of poly(L-lactide) (PLLA)/poly(D-lactide) (PDLA) blend in crystal complex forming solvent and the subsequent thermal annealing of the gel resulted in crystalline pure SC gel, which, upon solvent exchange with water and freeze-drying, furnished robust SC aerogel. It was found that the SC content could be tuned by varying the annealing temperature of the blend gel and that we could prepare blend aerogels with pure α crystalline form and a mixture of α and SC. Crystalline pure blend α aerogel showed fibrillar morphology, whereas SC aerogel exhibited unique interwoven ball-like microstructures interconnected by PLLA and PDLA chains. The structural evolution during SC formation at the molecular level and the micrometer length scale instigated better properties in the PLA aerogels. When compared with the homopolymer aerogels, the crystalline pure SC aerogel showed an enhanced melting temperature of 227 ± 2 °C (50 °C higher), better thermal stability (onset of degradation was delayed by ∼40 °C), enhanced mechanical strength (compression modulus of 3.3 MPa), and better sound absorption ability. The biodegradability of PLA and the superior properties induced by stereocomplexation make these aerogels potential candidates for applications such as tissue engineering scaffolds, packaging, acoustic insulation, etc.

Directional-Freezing-Enabled MXene Orientation toward Anisotropic PVDF/MXene Aerogels: Orientation-Dependent Properties of Hybrid Aerogels

“…The PMX aerogels show strong mechanical properties: for example, the PMX-30 aerogel can bear a metal block, which is 2000 times heavier than that of the aerogel (Figure c) without any deformation. These results suggested that the hybrid aerogels have a better compressive performance than the pristine PVDF aerogel, and all of them showed an irreversible buckling behavior similar to that of most of the semicrystalline aerogels. , It is also to be noted that the compressive strength values of the PMX hybrid aerogels are significantly higher than those of the MXene aerogels because of the strong noncovalent interactions between PVDF chains and the surface functionalities of MXene nanosheets. , …”

“…These results suggested that the hybrid aerogels have a better compressive performance than the pristine PVDF aerogel, and all of them showed an irreversible buckling behavior similar to that of most of the semicrystalline aerogels. 6,58 It is also to be noted that the compressive strength values of the PMX hybrid aerogels are significantly higher than those of the MXene aerogels because of the strong noncovalent interactions between PVDF chains and the surface functionalities of MXene nanosheets. 20,28 Other indispensable requirements for the applications of these aerogels in harsh environments are thermal stability and flame retardancy.…”

Impact of polymer chain packing and crystallization on the emission behavior of curcumin-embedded poly(l-lactide)s

“…PLLA is known to form gels in particular solvents that favor the formation of co-crystals or crystalline complexes (e form). 30,[69][70][71] Fig. 8(a) shows the digital photograph of curcumin-PLLA gel in DMF under UV light along with the POM image.…”

Low-Density, Semicrystalline Poly(phenylene sulfide) Aerogels Fabricated Using a Benign Solvent

“…Physical aerogels are one subsection of polymeric aerogels which differ from covalent aerogels in that their network connectivity is derived from non-permanent and often thermally labile junctions, which constitute a physically crosslinked network . Several semicrystalline polymers that are devoid of hydrogen-bonding groups or ionic functionalities have been shown to form aerogels, with polymer crystallites and chain entanglements acting as the physical crosslinks within the open microstructure. − Recent examples of crystallizable polymers that have been shown to form physical aerogels include syndiotactic polystyrene, isotactic polypropylene, poly­(phenylene oxide), poly­(vinylidene fluoride), poly­( l -lactide) and poly­( l -lactide)/poly­( d -lactide) blends, , and poly­(ether ether ketone). − Current applications of physical polymeric aerogels include three-dimensional separation membranes, airborne nanoparticle filters, catalysis supports, thermal insulation, and gel-state platforms for blocky copolymer functionalization. − Expanding the applicability of physical aerogels necessitates the transition to high-performance polymers.…”

“…8 Several semicrystalline polymers that are devoid of hydrogen-bonding groups or ionic functionalities have been shown to form aerogels, with polymer crystallites and chain entanglements acting as the physical crosslinks within the open microstructure. 9−17 Recent examples of crystallizable polymers that have been shown to form physical aerogels include syndiotactic polystyrene, 9 isotactic polypropylene, 10 poly-(phenylene oxide), 11 poly(vinylidene fluoride), 12 poly(L-lactide) and poly(L-lactide)/poly(D-lactide) blends, 13,14 and poly-(ether ether ketone). 15−17 Current applications of physical polymeric aerogels include three-dimensional separation membranes, 12 airborne nanoparticle filters, 18 catalysis supports, 19 thermal insulation, 20 and gel-state platforms for blocky copolymer functionalization.…”