Intermolecular Interactions and Crystallization and Melting Behavior of Poly(L-lactic acid)/4,4′-Thiobis Phenol Blends

The intermolecular interactions between poly (L-lactic acid) (PLLA) and 4, 4'-thiobis phenol (TDP) in their melt blending samples were studied by means of Fourier transform infrared (FTIR) spectrometer. The results show that intermolecular hydrogen bonding forms between carbonyl groups of PLLA and hydroxyl groups of TDP. The glass transition behavior and non-isothermal crystallization, subsequent melting behavior of PLLA and PLLA/TDP blends were studied by differential scanning calorimeter(DSC). The results show that, glass transition temperatures (T-g) of the samples decrease linearly with TDP content. The melt crystallization temperatures(T-c), heat of crystallization (Delta H-c), melting temperatures (T-m), heat of fusion (Delta H-c) all decrease with TDP content, while the cold-crystallization temperatures show reverse tendency. When TDP content reaches 40% (mass fraction) in the sample, neither crystallization exothermic nor melting endothermic peaks appear in the DSC curve, implying that this sample is completely in amorphous state. Wide angle X-ray diffraction(WAXD) analysis reveals that the addition of TDP does not modify the crystal structure of PLLA, but results in less compact crystal structure. Thus, the decrease of melting temperatures ought to attribute to the formation of intermolecular hydrogen bonding, which reduces mobility of PLLA chains and makes the resulting crystals less compact, rather than crystal modification.