1 Section of Chemistry, The Faculty of Engineering and Science, Aalborg University, VBN2 Supramolekular Chemistry, The Faculty of Engineering and Science, Aalborg University, VBN3 Department of Chemistry and Bioscience, The Faculty of Engineering and Science, Aalborg University, VBN4 The Faculty of Engineering and Science (ENG), Aalborg University, VBN5 Key Laboratory of Polymer Eco-materials Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun6 State Key Laboratory of Polymer Physics and Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun7 School of Materials Science and Engineering, Tianjin University, Tianjin8 State Key Laboratory of Polymer Physics and Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences
The isothermally crystallized poly(L-lactide) (PLLA) samples were obtained at 135 °C under pressures (Pc) ranging from 1 bar to 2.5 kbar. The crystalline structures, the structure transition, and thermal properties of the prepared samples were investigated by wide-angle X-ray diffraction (WAXD), real time synchrotron small-angle X-ray scattering (SR-SAXS) and differential scanning calorimetry (DSC) during this process. The structural parameters, such as the size of crystallites, the inverse spacing, the long periods and lamellae thicknesses decrease with pressure increasing. Based on the peculiarities of crystalline structure and crystallization behaviors, low and high pressure regions were revealed: disordered α crystal was formed in the high pressure region (>1 kbar). A layer located intermediate between crystalline and melt-like regions was observed, which finally took on crystalline order. Reformation, disorder to order transformation, and recrystallization during heating completely changed the previous crystalline and stacking structure, a more stable crystalline structure was newly formed. The melting behaviors of samples indicate the crystalline and stacking structure formed under high pressure are more stable. Operation of lateral growth and thickness growth can explain well the influence of pressure on the structure, stability and the disorder to order transformation.
Crystengcomm, 2013, Vol 15, Issue 21, p. 4372-4378