A synchrotron SAXS study of PLLA crystallized at different temperatures: One-dimensional correlation functions

Time-resolved variable-temperature synchrotron techniques have been employed for learning about semicrystalline structure and morphology of an L-rich (4.2 mol% in D-isomer) poly(lactic acid), PLLA. An amorphous specimen has been isothermally crystallized from the glassy state at different temperatures, aiming to gain knowledge about development of the two polymorphs, α′ and α. Subsequent melting of these cold crystallized samples has been analyzed by DSC and synchrotron techniques. Besides studying Lorentz-corrected SAXS profiles, one-dimensional correlation functions have been determined for two crystallization temperatures, selected for yielding neat α′ and α polymorphs respectively. Long spacing, crystal thickness and local crystallinity have been determined. Results show a clear discontinuity with temperature of some of these parameters when transition from disordered α′ to more ordered α modification occurs. Additionally, a SAXS-determined glass transition has been obtained and compared with that derived from the corresponding DSC results. [Display omitted] •Long spacing peak is sometimes missing when PLLA α′ polymorph is developed.•SAXS invariant derivative is an excellent tool to analyze PLLA phase transitions.•One-dimensional correlation functions (CF) are estimated in PLLA with neat α′ and α forms.•A discontinuity with temperature is seen in some CF parameters along α′ to α transition.