拉伸和剪切场下半结晶性高分子的非晶结构研究

Polymer systems may exhibit a rich hierarchical structure when crystallize at temperature above the glass transition temperature. There are several aspects that still remain controversial although polymer crystallization has been investigated. The process of crystallization has been historically studied from the viewpoint of the crystalline structure development. However, polymers never crystallize completely and they always present a complex structure, consisting, at least, of two phases: crystalline and amorphous. Polymer crystals arrange themselves into characteristic units consisting of stacks of laminar crystals intercalated by amorphous less ordered regions. In general, SAXS is a very suitable tool to study the development of the arrays of lamella. The nature of the distribution of lamellar stacks in the system has been a subject of extended debate in the last years. Traditionally, the observation of the crystalline phase evolution has been performed by diffraction techniques and microscopy techniques. Both methods pay special attention to the crystalline phase, and very little, or non-at all, to the amorphous one. X-ray scattering and transmission electronic microscopy experiments in different polymers sometimes have been interpreted invoking the formation of a heterogeneous multiple lamellar population arrangement. From the point of view of the dynamics of the chains participating in the crystallization process, also controversial effects have been observed during polymer crystallization. The α-relaxation, that appears at T>Tg, is associated to the segmental motions of the chains in the amorphous state. This α-process is highly affected by the presence of lamellar crystals. In this respect, it has been proposed, on the basis of thermal and dielectric analysis, that the formation of a rigid amorphous phase, i.e. a phase of amorphous chains lacking segmental motion, proposed long time ago and can be located in the interfacial region between the crystalline lamellae and the inter-lamellar amorphous phase. However, dielectric experiments in several polymers seems to indicate that the entire inter-lamellar amorphous phase could be considered as rigid. Dielectric spectroscopy techniques are widely used to study the dynamics of the amorphous chains in polymeric systems..In this proposal, we will selected poly (propylene) and poly(lactic acid) as model samples. The structure, structure transition and the properties of the measured samples will be obtained with dielectric spectroscopy measurements, SAXS/WAXS, DSC and TRIR combined with shear stage, DSC stage and tensile stage. The real time structure evolution investigation and in situ measurement of structure and properties will be performed. Our results would not only be helpful to understand the real relationship between the properties and structures of polymers, but also be helpful to design and process polymer materials.

本基金将主要借助介电谱仪、小角和广角X光同步辐射，结合Linkam 拉伸热台、Linkam剪切热台等手段在线研究拉伸和剪切场下半结晶性高分子的非晶结构。以聚丙烯和聚乳酸为研究对象，在线观测外力场下（拉伸、剪切）结晶高分子形成的多级结构（包括球晶、片晶、微晶，特别是非晶结构等）和结构转变行为，研究非晶结构对结晶结构的影响，进而研究非晶结构对材料性能的影响，认识外力诱导高分子结构转变机理和结构控制机制，理解外力诱导聚丙烯、聚乳酸形态结构与性能和聚合物流体自由能变化之间的内在联系。建立不同外力场作用下高分子的结构尤其是非晶结构及其转变与力学性能之间的关系，争取实现利用外力调控结晶高分子中非晶结构来调控结晶结构进而调控材料性能，为高分子材料的加工条件的遴选和加工条件的优化提供可靠实验依据。

在通用高分子材料中，结晶高分子材料占70%，而中绝大多数结晶高分子的结晶度低于50%，因此结晶高分子材料的非晶部分的结构和性能对高分子材料的宏观结构和性能的影响不容忽视。我们借助介电谱仪、同步辐射小角和广角X光散射，结合Linkam 拉伸热台、Linkam剪切热台等手段在线研究了拉伸和剪切场下结晶性高分子的非晶结构及结构演变。以聚丙烯和聚乳酸为主要研究对象，研究了剪切和不同成核剂对iPP熔体结构的影响，发现不同成核剂可以影响iPP和改变非晶熔体的构象从而导致形成不同结晶结构、结晶度结晶；对PLA的研究发现：结晶和非晶态PLA的非晶结构可以分为柔性非晶区和刚性非晶区、非晶区的链段运动对PLA的宏观性能有重要影响；在拉伸应力作用下，结晶iPP和PLA在应变初期的形变主要发生在非晶区，随着应力、应变增加到一定程度以后才发生晶区的应变。拉伸应力作用下非晶PLA的结构演变随拉伸温度的改变而改变：在PLA玻璃化转变温度以下拉伸只能形成介晶结构；在玻璃化转变温度以上拉伸形成结晶结构的有序性和拉伸温度有关，但是结晶结构的长周期只和非晶聚乳酸的制备条件有关，即非晶聚乳酸形成的结晶聚乳酸的长周期依赖于非晶聚乳酸的非晶结构。这些结果和结论可以为结晶高分子的结构调控和性能调控、为高分子材料的加工条件的遴选和加工条件的优化提供可靠依据。