Thermal Properties and Structural Evolution of Poly(L-lactide)/Poly(D-lactide) Blends

In order to obtain the forming regulation and structural evolution of poly(L-lactide)/poly(D-lactide) (PLLA/PDLA) stereocomplexes (sc-PLA), a commercial high molecular weight PLLA was blended with a series of PDLAs with different weight-average molecular weights (M-w) in the range of 7.5-290 kg.mol(-1) by solution blending. The thermal properties, morphology, and thermal stability of the PLLA/PDLA blends were investigated by differential scanning calorimetry (DSC), field emission scanning electron microscopy (FE-SEM), and thermogravimetric analysis (TGA). The crystallization of sc-PLA and homo-chiral PLA (homo-PLA) was competitive and controlled by the M-w of PDLA. The phase structure of the PLLA/PDLA blends depended on the melting temperature. By quenching sc-PLA from 280 to 290 degrees C, a bicontinuous phase structure was observed for PLLA and PDLA. When quenching sc-PLA from 230 to 270 degrees C, a stereoamorphous mesophase of PLA (sam-PLA) was obtained, which originated from the residual strong hydrogen bonding between PLLA and PDLA. sam-PLA was a new discovery different from sc-PLA and homo-PLA. The PLLA/PDLA blends are not fully compatible among sam-PLA, PLLA, and PDLA. During melting, sc-PLA changed into sam-PLA, and the hydrogen bonding in sam-PLA was destroyed and weakened with increasing temperature at

Automated summary

By investigating the thermal properties, morphology, and thermal stability of PLLA/PDLA blends, a new stereoamorphous mesophase (sam-PLA) structure was discovered, and the relationship between different phases in the PLLA/PDLA blends was explored.