成核剂对聚乙烯结晶形态的影响及聚乙烯成核剂作用的再认识

添加成核剂是实现结晶高分子高性能化的重要途径。聚乙烯(PE)这种应用广泛的半结晶材料，产量和消费量在所有合成高分子中均高居第一。因其自身结晶生长速率快，人们长期以来认为成核剂对其改性效果不明显，对PE成核剂的研究也较少。但是，在生产实际中许多PE产品中却都添加成核剂类物质。受近年工业界发现一种商品成核剂HPN-20E可显著提高PE薄膜气体阻隔性启发，本项目在研究成核剂对PE结晶动力学、结晶结构影响的基础上，重点研究成核剂对PE结晶取向、晶片排列、织态等“结晶形态”的影响。通过研究熔体中成核剂诱导成核时“真正”的结构特征、成核剂结构特征对结晶形态的影响以及不同层次结晶形态与特定物理性能之间的关系，期望弄清成核剂诱导PE结晶及结晶形态改变的机理，形成对PE成核剂作用效果和作用机理的全面理解，丰富高分子结晶和结构性能关系的内容，为工业上开发新的PE成核剂、形成PE高性能化新技术提供理论依据。

The addition of nucleating agents (NAs) is one of the most cost-effective and easy-to-handle methods to achieve the property improvements of semi-crystalline polymers, which accounts more than 70% of the thermoplastic polymers applied globally, and therefore draws great interest from both academia and industry. Polyethylene (PE) is the first largest volume commodity polymers in use today. However, due to the extreme fast crystal growth rate of PE, it has been generally recognized that the addition of NAs has not very significant effect on its crystallization performance and consequent physical properties in comparison with that of polypropylene (PP), and the academic study on the PE nucleating agents is very limited. Interestingly, contrary to the view of low efficiency of NAs for PE crystallization, NAs are extensively used in commercial PE products. Inspired by the recent fact that the gas barrier property of PE film may be largely improved by adding the first and also only commercial NA specific for PE, Hyperform HPN-20E, we find that the widely accepted viewpoints on the role of NA in PE crystallization is not enough comprehensive. In this work, in addition of the widely investigated effects of NA on crystallization kinetics and “crystalline structure” (crystalline modification, lamellar thickness, spherulite size, etc.), we focus our special attention on the effects of “crystalline morphology” of PE (lamellae arrangement, crystalline orientation, texture structure, etc.) and consequent properties. By investigating the structure evolution of NA in PE melt during the processing, the “real” structure of NA which begin to induce the nucleus formation, the effect of NA structure on resultant crystalline behaviors and morphology, as well as the correlation between crystalline structure and morphology with special application performances of PE, we expect to have a more deep and comprehensive understanding on the roles of nucleating agent in PE crystallization and property improvements.