Linear and nonlinear rheological behavior and crystallization of semicrystalline poly(styrene)–poly(L-lactide) block copolymers
Malek, A., Dingenouts, N., Beskers, T. F., Fehrenbacher, U., Barner, L., & Wilhelm, M. (2013) Linear and nonlinear rheological behavior and crystallization of semicrystalline poly(styrene)–poly(L-lactide) block copolymers. European Polymer Journal, 49(9), pp. 2704-2720.
The rheological behavior of a poly(styrene)-poly(L-lactide) (PS-PLLA) block copolymer was investigated in the viscoelastic linear and nonlinear regime. Large amplitude oscillatory shear (LAOS) experiments in the nonlinear regime led to an exponential decay of the G moduli and the nonlinearity parameter I-3/1. During LAOS, the lamellar microstructure of a low molecular weight PS-PLLA copolymer was orientated parallel to the shear field to achieve a macroscopically ordered material. The degree of orientation was analyzed via small angle X-ray scattering (SAXS) measurements. The crystallization kinetics could be accurately described by the Avrami equation as determined by DSC and rheology. These experiments revealed that the crystallization process was slower for the PS-PLLA copolymers than for the PLLA homopolymers. SAXS was also used to monitor the crystallization of the PS-PLLA copolymers. When the temperature of the crystallization experiments, T-c, was lower than the glass transition temperature of the amorphous PS block, 7; (hard confinement), the lamellar microstructure of the low molecular weight PS-PLLA was maintained apart from a small increase in the domain spacing. When T-c was higher than T-g(a) of PS (soft confinement), the block copolymer also retained its lamellar structure, but the increase in the domain spacing was unexpectedly increased compared to what occurred for crystallization under hard confinement conditions. In addition, two-dimensional (2-D) SAXS diffractograms indicated a loss of the structure periodicity during crystallization under soft confinement.
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|Item Type:||Journal Article|
|Keywords:||Block copolymer; Rheology; Crystallization; Morphology|
|Divisions:||Current > Schools > School of Chemistry, Physics & Mechanical Engineering
Current > Institutes > Institute for Future Environments
Current > QUT Faculties and Divisions > Science & Engineering Faculty
|Copyright Owner:||Copyright 2013 Elsevier Ltd.|
|Deposited On:||21 Jul 2016 23:36|
|Last Modified:||25 Jul 2016 00:39|
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