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Abstract The processing–structure–property relationship using poly(lactic acid) (PLA) and poly(ethylene terephthalate) (PET) is explored. Specifically, both pre‐extension and preshear of amorphous PLA and PET above their glass transition temperaturesTg, carried out in the affine deformation limit, can induce a specific type of cold crystallization during annealing, i.e., nanoconfined crystallization (NCC) where crystal sizes are limited to a nanoscopic scale in all dimensions so as to render the processed PLA and PET optically transparent. The new polymer structure after premelt deformation can show considerably enhanced mechanical properties. For example, premelt stretching produces geometric condensation of the chain network. This structural alternation can profoundly change the mechanical characteristics, e.g., turning brittle PLA ductile. In contrast, after preshear of amorphous PLA aboveTg, the NCC containing PLA remains brittle, showing the importance to have geometric condensation from processing. Both AFM imaging and SAXS measurements are performed to verify that premelt deformation of PLA and PET indeed results in NCC from annealing that permits the strain‐induced cold crystallization to take place on the length scale of the mesh size of the deformed chain network.
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This content will become publicly available on March 20, 2026
Elucidations of Crystallization Pathway in Poly(Lactic Acid) Racemate by Solid-State NMR Spectroscopy: Analogies between Glassy and Crystalline Structures
Polymer crystallization is a process which connects the initial amorphous state with the final semicrystalline state. It is important to elucidate the amorphous structure which determines the crystallization pathway. In this work, we report quantitative analysis of the spatial proximity of poly(Lactic acid) (PLA) racemate before and after stereocomplex (SC) crystallization by using 13C selective isotope labeling and two-dimensional solid-state (ss) NMR techniques. It is found that i) the PLA racemate forms SC structure prior to crystallization (chiral recognition), ii) fraction of the chiral recognition segments (f) is extremely high, 94% in a low molecular weight (M) racemate while a high M one possesses only f = 10%, and iii) the f value for the former and latter is surprisingly in accordance with the f value after SC crystallization and SC crystallinity, respectively. From the observed analogies between the initial glassy and final crystalline structures, it is concluded that pre-existing chiral recognition fraction governs the formations of SCC.
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- Award ID(s):
- 2004393
- PAR ID:
- 10645108
- Publisher / Repository:
- APS
- Date Published:
- Format(s):
- Medium: X
- Location:
- Anaheim CA
- Sponsoring Org:
- National Science Foundation
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