Rheological and Architectural Control of Flow-Induced Crystallization

聚丙烯（PP）是世界上第二普遍的合成聚合物，在现代日常生活中被广泛用于各种产品中。在几乎所有的应用中，PP和其他半结晶聚合物都是通过熔化、流动和结晶的过程从颗粒转化为最终产品的。流动诱导结晶（FIC）使该工艺具有实用性。在冷却的熔体上施加一个大而突然的剪切流，大大加快了结晶速度，并深刻地改变了最终产品的材料性能。这一重要的商业现象还没有得到很好的理解。先前的研究由于缺乏三个基本要素而受到阻碍：正确的聚合物模型，确认流动如何定向和拉伸聚合物链的流变学，以及基于物理的聚合物结晶理论以及流动如何影响它。我们的方案结合了：1)一种独特的能力，合成具有可控结构的PP模型梳子；2)具有聚合物熔体流变学的实验和理论经验；3)一个成功的聚合物晶体成核理论，可以推广到解决流动的影响。在未来十年，美国塑料工业对PP助剂设计专业的研究生需求量很大。该提案支持的学生将受益于与埃克森美孚公司研究的工业科学家以及谢菲尔德大学的国际专家的合作。这三位pi在来到宾夕法尼亚州立大学之前都在工业界工作，这使他们能够为学生提供强大的工业视角。同时，这个研究领域为本科生在合成、流变学和模拟等方面的研究提供了很多机会。领先的聚烯烃制造商正致力于开发长链分支PP (LCBPP)，以改善熔体加工性能。假设类似的架构可以有效地控制FIC。我们在FIC控制方面的发现可能会转化为工业实践。了解FIC对于电子和光电池应用中半导体和导电聚合物的有效加工也很重要，在这些应用中，器件性能受到晶体尺寸和取向的强烈影响。

1067554MilnerPolypropylene (PP), the second-most prevalent synthetic polymer in the world, is used in a vast array of products that are commonplace in daily modern life. In nearly all applications, PP and other semicrystalline polymers are transformed from pellets to a final product in a process that involves melting, flow, and crystallization. Flow-induced crystallization (FIC) makes the processing practical. Imposing a large and sudden shear flow on a cooling melt greatly speeds up crystallization, and profoundly changes the material properties of the final product.This commercially important phenomenon is not well understood. Previous studies have been hampered by the lack of three essential ingredients: the right model polymers, rheology to confirm how flows orient and stretch the polymer chains, and a physics-based theory of crystallization in polymers and how flow affects it. Our proposal combines:1) a unique capability to synthesize PP model combs with controlled architecture; 2) experimental and theoretical expertise in rheology of polymer melts; and 3) a successful theory for nucleation of polymer crystals, which can be extended to address the effects of flow.Graduate students trained in design of PP additives will be in high demand in the US plastics industry in the coming decade. Students supported by this proposal will benefit from collaboration with industrial scientists from ExxonMobil Corporate Research, and international experts at the University of Sheffield. All three PIs worked in industry before coming to Penn State, enabling them to provide their students a strong industrial perspective. As well, this research area offers many opportunities for undergraduate research in synthesis, rheology, and simulations.Leading polyolefin manufacturers are working to develop long chain branched PP (LCBPP) for improved melt processability. Similar architectures are hypothesized to be effective in controlling FIC. Discoveries we make regarding control of FIC can likely be translated to industrial practice.Understanding FIC may be important as well for effective processing of semiconducting and conducting polymers in electronic and photocell applications, where device performance is strongly affected by crystallite size and orientation.