Study On Crystallization Behavior And Mechanism Of Poly (L-lactic Acid) By Inclusion Complex Of P-tert-Butylcalix (8) Arene/xylene

Poly(L-lactic acid) is one of biodegradable thermoplastic, it will have a good marketing prospect because it possesses the excellent mechanical properties and thermal performances compared with PE, PP and PS. However, the disadvantages, which hinder the application of PLLA, are that PLLA has a slow crystallization rate and is hard and brittle. In order to improve the crystallization rate and mechanical properties, the most popular way is to added the nucleating agent to PLLA. There are few nucleating agents and the nucleating ability is poor, also the crystallization mechanism of PLLA is not clear to people. Therefore, it's very significant to study the crystallization mechanism between PLLA and nucleating agent, so that we can develop the high nucleating ability of nucleating agent for PLLAThe inclusion complex of TBC8-xy was prepared by recystaling TBC8 from xylene. The crystallization behavior of PLLA added Talc, TBC8 and TBC8-xy were studied by DSC and POM. The conclusion was that the Tp of PLLA/Talc and PLLA/TBC8 is 104.6℃and 110.4℃respectively, when the TBC8-xy was added to PLLA, the Tpof the sample is 125.5℃, and there is no crystallization peak temperature for pure PLLA. And then the isothermal crystallization kinetics of PLLA/TBC8 and PLLA/TBC8-xy were calculated by Avrami equation. The crystal morphology of PLLA/TBC8 was spherulitic and sheaf-like crystals at the low crystallization temperature, when the crystallization temperature was increased; the crystal morphology of PLLA/TBC8 would be three-dimension spherical growth. The Avrami exponent n of PLLA/TBC8-xy was between 4.5 and 5, which implied the crystal morphology of PLLA/TBC8-xy was spherulitic and sheaf-like crystals.The crystallization mechanism of pure PLLA and PLLA/TBC8 was studied by on-line FTIR and Two-Dimensional Infrared (2D-IR) Correlation Spectroscopy. The pure PLLA mechanism result showed that the chain segment become orderly because of the interchain interaction of COC during the isothermal crystallization process at 140℃firstly, secondly, the interaction of CH3 made the conformation of PLLA chain more orderly, the third was that 103 helix conformation would emerge, PLLA would grow into a crystal in the end. The OH…O=C interaction between the C=O of PLLA and the-OH of TBC8 drive the PLLA chain to be adsorbed on the surface of TBC8 during the isothermal crystallization process at 140℃, and then the interchain interaction of CH3 made the conformation of PLLA chain more orderly, the third was that interchain interaction of COC drive the conformation of PLLA chain to be orderly, then a short 103 helix emerges because of the interaction above, there would be a crystal formed.