Molecular Aspects of Flow Effects on Crystallization in iPP

流动对 iPP 结晶影响的分子方面

• 批准号: 9901403
• 负责人: Julia Kornfield
• 金额: $ 31万
• 依托单位: California Institute of Technology
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 1999
• 资助国家: 美国
• 起止时间: 1999-04-01 至 2002-09-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=9901403&HistoricalAwards=false
• 关键词: Molecular; Aspects; Flow; Effects; Crystallization

9901403 KornfieldIn spite of intensive research over the past three decades, the fundamental basis of the effects of processing on structure development in semicrystalline polymers remains elusive. Processing alters the rate, form and anisotropy of crystallization. The goal of the proposed research is to establish the interplay of the conformational relaxation dynamics of the molten chains, the distortion of segmental orientation created by flow, the kinetics and anisotropy of nucleation from a distorted melt and their effects on the subsequent kinetics and morphology of crystallization. A unique apparatus has been developed to create a precisely controlled flow and thermal history and to monitor structure development in real time. It can subject a subcooled melt to precisely controlled intervals of shear at stress levels similar to those encountered in industrial processes. The response during and after shear is continuously monitored in situ using an arsenal of different probes of structure. Polarimetry, light and x-ray scattering will be used in real time, in situ to characterize the interplay of relaxation dynamics and deformation history that is manifested in the effect of flow on crystallization kinetics and morphology. The apparatus facilitates removal of the sample at the conclusion of the experiment to enable thorough characterization of the final structure. Optical and electron microscopies and x-ray scattering will be used ex situ to determine the final solidified structure. Model polymer systems will be used that have controlled stereo regularity and systematically varied distribution of chain lengths and corresponding relaxation times. Guided by evidence that polydispersity strongly affects the dependence of crystallization on flow history, bidisperse samples will be prepared that can reveal the role of the slowest relaxing species (the long chains) in producing flow-enhanced nucleation and anisotropic growth.Our society is heavily dependent on advances in the development of materials with desired combinations of properties: strong but light, flexible but impermeable, stiff but tough. Semicrystalline polymers are a class of materials that has proved extremely versatile in achieving these powerful combinations of properties, precisely because they spontaneously form a nanostructured composite with plate-like crystallites separated by noncrystalline regions. This research will improve our ability to optimize these polymers by clarifying the link form molecular design to processing behavior, and from there to structure development, which ultimately controls their material properties. The potential impact is large, both economically and in terms of quality of life, since semicrystalline polymers are very widely used-over 125 billion pounds a year of polyolefins alone are used worldwide.

9901403 Kornfield尽管在过去的三十年里进行了深入的研究，但加工对半结晶聚合物结构发展的影响的基本基础仍然难以捉摸。 加工改变了结晶的速率、形式和各向异性。 建议的研究的目标是建立的熔融链的构象松弛动力学的相互作用，由流动产生的链段取向的扭曲，从扭曲的熔体成核的动力学和各向异性及其对随后的动力学和结晶形态的影响。 一种独特的设备已经开发出来，以创建一个精确控制的流量和热历史，并监测结构发展的真实的时间。 它可以使过冷熔体在类似于工业过程中遇到的应力水平下经受精确控制的剪切间隔。 在剪切过程中和剪切后的响应连续监测原位使用不同的结构探头的军火库。 将在真实的时间、原位使用偏振法、光和X射线散射来表征松弛动力学和变形历史的相互作用，所述相互作用表现在流动对结晶动力学和形态的影响中。 该装置便于在实验结束时移除样品，以实现最终结构的彻底表征。 光学和电子显微镜和X射线散射将用于非原位确定最终的固化结构。 模型聚合物系统将被使用，具有控制的立体规整性和系统地变化的链长分布和相应的弛豫时间。 在多分散性强烈影响结晶对流动历史依赖性的证据的指导下，将制备双分散样品，以揭示最慢的弛豫物种（长链）在产生流动增强成核和各向异性生长中的作用。我们的社会在很大程度上依赖于具有所需性能组合的材料开发的进展：强而轻，柔性但不可渗透，刚性但坚韧。 半结晶聚合物是一类被证明在实现这些强大的性能组合方面极其通用的材料，正是因为它们自发地形成具有由非结晶区域分离的板状微晶的纳米结构复合材料。 这项研究将提高我们优化这些聚合物的能力，通过澄清从分子设计到加工行为的联系，并从那里到结构开发，最终控制它们的材料性能。 由于半结晶聚合物的使用非常广泛，全世界每年仅聚烯烃的使用量就超过1250亿磅，因此无论是在经济上还是在生活质量方面，潜在的影响都很大。