可同时促进结晶成核和生长的纳米粒子合成及其诱导聚乳酸结晶研究

聚乳酸结晶速率慢、结晶度低的缺点导致其热变形温度低、阻隔性差，很大程度上限制了其制品的应用。纳米粒子可作为聚乳酸的成核剂，大量增加晶核密度，但仍难显著提高其最终结晶度。这是由于纳米粒子虽能有效诱导成核，但不能促进晶体生长。本项目拟将结晶促进剂聚乙二醇接枝到纳米粒子（氧化石墨烯和纳米纤维素）表面，提高纳米粒子表面附近高分子链的运动能力，获得能同时促进结晶成核和生长的高效纳米成核剂。利用高通量、高时间和空间分辨的同步辐射显微红外和X射线衍射等表征手段原位研究表面修饰纳米粒子诱导聚乳酸结晶初期的分子链构象有序、结晶成核、晶体生长动力学及界面结晶形貌等科学问题。获得表面修饰纳米粒子的结构和含量与聚乳酸预有序和结晶的关系，揭示其诱导聚乳酸结晶的机理，为制备高结晶度、高性能的聚乳酸制品提供理论基础和实验依据。

The intrinsic flaws of poly(L-lactide acid) (PLLA), i.e., slow crystallization rate and low crystallinity result in low heat distortion temperature and poor gas-barrier resistance, severely limiting its practical application. Nanoparticles with high specific surface area have been demonstrated as nucleation agents to increase the nucleation density of PLLA; however, the resultant crystallinity of PLLA was not increased substantially. This is because the nanoparticles could serve as heterogeneous nucleation sites, but have little influence on the crystal growth. In this proposal, we proposed to synthesize highly efficient nano-sized nucleation agents by covalently grafting the chain promoter, poly(ethylene glycol) (PEG), onto graphene oxide and cellulose nanocrystals. It is expected that the prepared PEG-grafted nanoparticles could promote nucleation and accelerate crystal growth of PLLA simultaneously. Conformational ordering at the early stage of crystallization, nucleation, crystallization kinetics, and interfacial crystalline morphology of PLLA induced by PEG-grafted nanoparticles were investigated by utilizing in-situ characterization methods, such as synchrotron radiation infrared microspectroscopic imaging and X-ray microdiffraction. In these efforts, we intended to understand the relationship between the structure and content of PEG-grafted nanoparticles and the preordering and crystallization of PLLA, thus unveiling the physical image of PEG-grafted nanoparticle induced PLLA crystallization. The obtained fundamentals based on the aforementioned scientific issues will offer theoretical guidelines and experiment basis for manufacturing the PLLA products with high crystallinity and superior performance.