Nanoconfined Crystallization in Poly(lactic acid) (PLA) and Poly(ethylene terephthalate) (PET) Induced by Various Forms of Premelt‐Deformation

• Published in: Macromolecular rapid communications. Vol. 44; no. 1; pp. e2200293 - n/a
• Main Authors: Smith, Travis, Feng, Jiansheng, Zou, Lu, Gao, Min, Prévôt, Marianne, Wang, Shi‐Qing
• Format: Journal Article
• Language: English
• Published: Germany Wiley Subscription Services, Inc 01-01-2023
• Subjects: Annealing; Brittleness; Cold crystallization; Crystallization; Deformation; Ductile-brittle transition; ductility; Ethylene; Ethylenes; Glass transition temperature; Mechanical properties; melt‐shear deformation; nanoconfined crystallization; Polyesters - chemistry; Polyethylene terephthalate; Polyethylene Terephthalates; Polylactic acid; Polymers; processing–structure–property relationship; Scattering, Small Angle; semicrystalline polymers; Transition temperatures; X-Ray Diffraction; ductility; nanoconfined crystallization; semicrystalline polymers; processing-structure-property relationship; melt-shear deformation
• ISSN: 1022-1336; 1521-3927
• DOI: 10.1002/marc.202200293

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 temperatures Tg, 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 above Tg, 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.
Both pre‐extension and preshear of amorphous PLA and PET above their Tg in the affine deformation limit can induce nanoconfined crystallization (NCC), with crystal sizes limited to nanoscopic scale so as to render the processed PLA and PET optically transparent. It is shown that a certain type of deformation (pre‐extension) is required to turn brittle PLA ductile.