Effect Of Physical Aging On The Condensed State Structure Of Poly (L-Lactide Acid) And Its Phase Transition Behavior

In this work, the effects of physical aging on condensed structure andphase transition behavior of poly(L-lactide acid) samples with vavious initialstate were investigated by in-situ infrared spectroscopy (FTIR) anddifferential scanning calorimetry (DSC).First of all, we investigated the structural evolutions and kineticsbehaviors of melt-quenched poly(L-lactic acid)(PLLA) during the process ofisothermal physical aging below the glass transition temperature (T_g) by thetime-resolved infrared spectroscopy. The results showed that the localordered structure and the so called mesophase formed in the physical aging process. Besides, physical aging can enhance the mesophase which alreadyexists in the initial state of melt-quenched PLLA. Heating to the temperatureregion of the physical aging peak, the mesophase could be partially melted,the remnant promoted the formation of crystal nucleus, which ould enhancecold crystallization in the subsequent cold crystallization process.According to the analysis above, the mesomorphic structure would formduring the melt-quench process. Therefore, we systematically investigatedthe relationship between the cooling rates and the formation of themesophase. The results proved that the mesomorphic structure of PLLAcould be formed when the cooling rate was higher than20℃/min. Theslower the cooling rate, the more ordered the mesophase. However, it formsthe stable crystal, when the cooling rate is blow20℃/min.Further more, the condensed structure and the thermal behaviors ofPLLA with different L contents during the physical aging process also beinvestigated. The research result showed that more ordered structure wouldbe formed in PLLA with high content of L during the physical aging process, as a result, the physical aging peak during the glass transition region shifts tohigher temperature.