剪切场下熔体真实流动状态调控及其对结晶影响的研究

Study of shear-induced crystallization (SIC) is the most significant route to clarify the crystallization mechanism of polymer under flow field. In almost all the SIC experiments, researchers tend to consider the melts flow homogeneously in shear device. However, when suffered intensive external flow, melts usually show inhomogeneous flow behavior, which would lead to the mismatch between the intensity of flow and the SIC experimental results. Therefore, the real flow state of polymer melts under shear should be taken into account in researches of SIC. In view of the disconnection of the flow behavior and SIC behavior, the project tend to introduce acceleration of the flow field at start stage into the study of SIC as an apparent flow parameter which could tune the flow behavior of polymer melts. By using this parameter，we will rediscover the mechanism of SIC with the consideration of real flow behavior of the polymer melts under shear flow and deepen the understanding of flow-induced crystallization. In addition, in the view of increasing the response of polymer chain to the flow field at the start stage of the application of shear, the project tend to introduce segments with relatively high mobility into the main chain. With the help of these segments, the response of the whole chain to the shear flow could be enhanced which would suppress the flow inhomogeneity of polymer melts. By combining these two parts of studies, we would like to provide more accurate description of the mechanism of FIC and accumulation of theoretical basis for polymer processing.

剪切诱导结晶的研究对于澄清聚合物流动诱导结晶图像十分重要。在进行剪切诱导结晶实验时，人们往往假设熔体在剪切场下均匀流动。然而，当熔体处于较强剪切场下时，却会出现非均匀流动，导致熔体实际受到的流场强度与外加流场不一致，剪切诱导结晶结果与流场强度错误关联。本项目拟通过控制剪切场启动阶段的时间，引入剪切场加速度这一新的表观流场参数，将熔体流动行为这一长期被忽略的重要特性融入到剪切诱导结晶研究之中，并借助自制的快速降温剪切装置，在考虑熔体流动行为的情况下探索剪切诱导结晶结果。进一步，从提高剪切场施加初期分子链对剪切场响应的角度出发，拟通过分子设计的方法有意识地在聚合物主体链（A）中嵌入运动能力较强的链段（B），通过部分链段的运动带动整链运动，从而有效地提高剪切初期分子链对流场的响应，降低流动非均匀性。两部分研究相结合，深化流动诱导聚合物结晶的理解，同时为实际加工提供理论指导。

项目围绕聚合物流变和结晶行为与性能关系，组首先设计并制造了一台与X射线联用的快速降温平板剪切装置，使用该装置并结合广角X射线散射，采用不同剪切速率和加速时间对不同流动模式下聚合物流变和结晶行为进行了研究，构建加速时间和剪切诱导结晶的关系。随后，项目组采用分子设计的方法对聚合物链结构进行改造，以PLA为研究模板，通过合成和反应共混制备了多种PLA基共聚物，并分别将其添加至PLLA/PDLA、PLLA/PCL和PLLA/PBAT共混体系，研究在实际加工场下各种分子结构的共聚物对基体PLA结晶、共混物中分散相形态和相界面的影响，以得到通过不同结构PLA共聚物和加工外场协同调控PLA及其共混体系流变和剪切诱导结晶情况进行控制，制备高性能PLA制品的方法。此外，项目组设计合成了多种纳米材料，并研究其对PLA结晶行为的影响。该部分研究作为本项目的拓展，为后续流动场下聚合物/纳米材料复合体系流变与结晶行为的研究工作进行铺垫。通过项目的实施得到了对流动诱导聚合物结晶领域研究具有实际指导意义的结论、初步规律，同时为实际加工提供理论指导，具有潜在应用前景，为本领域的后续深入研究奠定了基础。