Study On Control Crystallization Process Of Poly (L-lactic Acid) With P-tert-Butylcalix [6] Arene

Poly (L-lactic acid) (PLLA) is recognized as its biocompatibility and biodegradability. It is a kind of environment-friendly materials and can meet the needs of requirements of environmental protection. So it is one of the most widely used synthetic biodegradable polymers and can be substitute for petroleum-base plastic. Although PLLA has its special physical and mechanical properties, its brittle and poor impact resistance becomes obstruct of engineering application. It is an effective way that adding nucleating agents to increase the crystallization rate and crystallinity of PLLA. Furthermore, with nucleating agents, heat deflection temperature and shaping property of PLLA will be improved. Calixarenes, cyclic oligomer of phenol-formaldehyde condensates, are considered as the third generation of super-molecules for their molecular recognition ability and adjusted cavity size. In this paper, p-tert-butylcalix[4]arene (tBC4) and p-tert-butylcalix[6]arene (tBC6) are investigated as nucleating agents of PLLA. And the affection of these kinds of the nucleating agents is also studied, from which can lay a base of how to design the nucleating agents of PLLA.The tBC4 and tBC6 and their inclusions are prepared, respectively. The crystallization behavior of PLLA with tBC4, tBC6 and their inclusions are studied respectively by DSC. It is found that there is no obviously difference of the peak temperature (Tp) of PLLA with the inclusion complexes which included different solvents as guest. The inclusion complexes are heated at 200℃, temperature of processing. And then their structures are studied by WAXD. The results show that the guest molecules in inclusion complexes escape under the temperature of processing. It is also explained that the function of guest molecules on adjusted cavity size is disappear.And the crystal morphologies of PLLA with tBC4 and tBC6 are studied respectively by POM. The isothermal crystallization kinetics of PLLA, PLLA/tBC4 and PLLA/tBC6 are calculated by Avrami equation. The crystal morphology of PLLA, PLLA/tBC4 and PLLA/tBC6 is spherulitic crystals at 140℃. The Avrami exponent n of them is also implied the crystal morphology. What is more, the addition of tBC6 increases the crystallization rate of PLLA and reduces the size of PLLA crystal.The crystallization mechanism of isothermal crystallization of PLLA, PLLA/tBC4 and PLLA/tBC6 at 140℃is studied by on-line FTIR and Two-Dimensional Infrared (2D-IR) Correlation Spectroscopy. The FTIR spectra of PLLA with the different content of tBC4 and tBC6 show that with increasing of the size of calixarene cavity, the hydrogen bond between PLLA and calixarene (OH…O=C) is more obvious. The 2D correlation analysis of time-dependent IR spectra collected reveals the intermolecular interaction of pure PLLA, PLLA/tBC4 and PLLA/tBC6 during the crystallization process. From the 2D correlation analysis, it is found that during the isothermal crystallization process at 140℃, the change of the COC backbone in PLLA occurs prior to the conformational adjustment of combination of CH3 and COC. And the structural evolution of CH3 group is slower than that of combination of CH3 and COC. In PLLA/tBC4, the change of the COC backbone still occurs at first, that of CH3 happens subsequently and then combination of CH3 and COC interacts. In PLLA/tBC6, the interaction of CH3 group occurs prior to that of COC backbone. And that of the combination of CH3 and COC is slower than both of them. With the interchain interaction of groups, PLLA chain becomes orderly and distorted 103 helix conformation of PLLA chain in a crystals is formed.