Role of Shear Flow on Structure Development during Post-Processing Annealing for Poly(lactic acid)

• Published in: Polymers Vol. 15; no. 3; p. 693
• Main Authors: Vo, Hoang-Giang Dai, Kida, Takumitsu, Yamaguchi, Masayuki
• Format: Journal Article
• Language: English
• Published: Switzerland MDPI AG 30.01.2023; MDPI
• Subjects: Annealing; Chains; Cooling; Crystal growth; Crystallization; Dimensional changes; Glass transition temperature; Heat resistance; Lactic acid; molecular orientation; Molecular weight; Orientation; Plastics; poly(lactic acid); Polylactic acid; Shear flow; Shear strain; Viscoelasticity; Japan; United States > US; crystallization; molecular orientation; annealing; poly(lactic acid)
• ISSN: 2073-4360; 2073-4360
• DOI: 10.3390/polym15030693

The effect of shear history on structure development during post-processing annealing was studied using poly(lactic acid) PLA. Since PLA shows a low crystallization rate, quenched films had no crystallinity. Moreover, molecular orientation was not detected in the films. During the annealing procedure beyond its glass transition temperature, however, molecular orientation to the flow direction occurred with the crystallization growth in the films having an appropriate shear history. This peculiar crystal growth during the annealing was most probably attributed to the crystallization from extended chain crystals generated during the applied shear history, although the amount of extended chain crystals was low. The results obtained in this study should be noted because the molecular orientation proceeded due to the annealing history applied. Furthermore, this phenomenon will be used to suppress dimensional change and increase product rigidity.