The crystallization and phase transition behaviors of asymmetric PLLA/PDLA blends: From the amorphous state

Abstract

The phase transition behaviors of melt‐quenched asymmetric poly(l‐lactide acid)/poly(d‐lactide acid) (PLLA/PDLA) blends are investigated by the in‐situ wide angle X‐ray diffraction. Results indicate that the crystal structures and their transition of PLLA/PDLA specimens depend on the composition, molecular weight, and temperature. In the specimens with lower molecular weights (∼9 kg/mol), the poly(lactic acid) homocrystallites (HC), mesophase, and stereocomplex crystallites (SC) develop in specific blends. As the content of PDLA increases, the formation temperature of HC increases to a fixed value, while that temperature for SC reduces to a constant value, and the formation temperature of mesophase does not vary with composition. For the specimens with moderate molecular weights (∼30 kg/mol), the HC, modified HC, and SC develop in specific composition, the formation temperatures of both the HC are constant, and the formation of SC reduces to a fixed temperature. In the blends with molecular weight of ∼65 kg/mol, HC and SC develop, and the formation of HC does not vary, but that temperature for SC reduces slightly as more PDLA incorporated. After melting of HC, another enhancement of SC is observed in all the PLLA/PDLA specimens. The unique crystallization phenomena for these PLLA/PDLA specimens are analyzed.

Effect of Chemical Composition Variant and Oxygen Plasma Treatments on the Wettability of PLGA Thin Films, Synthesized by Direct Copolycondensation

“…The PDLA homopolymers were believed to be the same as the amorphous polymer, but the melting peak shows some crystallization, which is attributed to the large amount of l -lactic acid in the monomer, as it is clear from the optical properties of the PLA and PLGA presented in Table 2. The PLLA segments in the homopolymers were crystallized and resulted in a melt transition during the differential scanning colorimetric analysis, but the melting temperature is considerably low compared with the pure PLLA with a similar molecular weight [50]. However, the melt transition of the PLA stereocomplexes of the homopolymers or the copolymers with glycolic acid mostly shifted towards a higher temperature range [28].…”

Photodynamically Active Electrospun Fibers for Antibiotic-Free Infection Control

“…They are cost-effective and versatile as they can be highly tuned to the intended application 18 . Electrospinning is a facile technique used to efficiently produce micro-to nano-scale fibres of polymer solutions at a high production rate with low associated costs 19 . Although the principle of the technique was discovered over 120 years ago 20 , only within the past 15 years has it become widespread due to the straightforward manufacture, enhanced scalability and the increased interest in nanoscience and tissue engineering 21 .…”

“…18 Electrospinning is a facile technique used to efficiently produce micro-to nanoscale fibers from polymer solutions at a high production rate with low associated costs. 19 Although the principle of the technique was discovered over 120 years ago, 20 only within the past 15 years has it become widespread because of the straightforward manufacture, enhanced scalability, and increased interest in nanoscience and tissue engineering. 21 Consequently, there are many papers that focus on the specifics of the electrospinning process.…”

Controllable formation of unusual homocrystals in poly(L-lactic acid)/poly(D-lactic acid) asymmetric blends induced by the constraining effects of pre-existing stereocomplexes

“…meta (Chang & Woo, 2011), -form (Xie et al, 2019), mesophase ] in symmetric L/D (1/1) blends. Previous studies also demonstrate that pre-existing SCs lead asymmetric L/D blends to crystallize as modified HCs (Shao, Sun, Bian, Cui et al, 2013;Lotz et al, 2017;Wang et al, 2018). However, the crystalline structure and crystallization mechanism of modified HCs induced by pre-existing SCs remain unclear.…”