CAREER: Understanding Process-Structure-Property Relations in Gas/Supercritical Fluid-Injected Polymer Coextrusion Foam Processes

该教师早期职业发展计划（CAREER）拨款将通过贡献与制造轻质多材料泡沫结构的新型制造工艺相关的新知识来促进科学的进步，这些泡沫结构在汽车，航空航天，生物医学，食品和电子包装行业中具有各种应用。大多数新的聚合物产品含有两种或更多种聚合物和功能添加剂，从而产生由每种组分贡献的所需性能。该工艺使用两种或更多种聚合物材料在单步工艺中同时挤出多种材料，所述聚合物材料成形以形成用于独特应用的多层结构。这些包括光学、机械和气体阻挡膜，例如用于电子屏幕的亮度增强滤光片、超强安全和安保窗膜或用于运动鞋中的缓冲气囊的弹性体阻挡膜。泡沫可以由任何塑料通过在加工期间在塑料内引入气体或超临界流体来制备。该奖项支持基础研究，将提供有关制造轻质复合材料的新共挤出泡沫制造技术所需的知识。该工艺还将通过减少材料使用量以及通过适当设计材料微观结构来提高性能重量比来显著降低生产成本。这种跨学科的研究包括制造，聚合物化学，聚合物物理和材料科学。生产高附加值塑料材料的公司将受益于这一结果。 来自代表性不足群体的学生将参与研究，并将与当地博物馆一起开发一个新项目，以激发K-12学生对聚合物材料的兴趣。气体/超临界流体浓度相关的晶体成核/生长，晶体层状取向，以及随后的气泡成核/生长行为的几何约束下提出的基本挑战，在共挤出泡沫过程。此外，材料和工艺参数在很大程度上影响微结构和气泡形态。这些复杂的耦合现象影响最终复合材料的性能。本研究的目的是缩小知识差距的理解微观结构的演变和气泡的成核/生长机制共挤出发泡工艺。研究小组将开发一个基于物理的模型，以了解和预测气体/超临界流体浓度和界面相容性对半结晶聚合物微观结构演变的影响，并将进行实验以验证该模型。该团队还将进行原子和宏观建模模拟，以了解气泡的成核和生长行为，并将通过使用新开发的介电方法来测试各种应力状态影响溶解度和扩散率的假设。根据这些研究结果，将选择工艺参数，以获得令人满意的微观结构和泡沫形态，而无需耗时的试错程序。该奖项反映了NSF的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

This Faculty Early Career Development Program (CAREER) grant will promote the progress of science by contributing new knowledge related to a novel manufacturing process for fabricating lightweight multimaterial foam structures that have a variety of applications in the automotive, aerospace, biomedical, food and electronics packaging industries. Most new polymeric products contain two or more polymers and functional additives resulting in desired properties contributed from each component. The process extrudes multiple materials at the same time in a single-step process using two or more polymeric materials shaped to form a multilayer structure for unique applications. These include optical, mechanical, and gas barrier films, such as brightness-enhancing filters for electronic screens, ultra-strong safety and security window films, or elastomeric barrier films for cushioning bladders in athletic shoes. Foams can be prepared from any plastic by introducing a gas or supercritical fluid within the plastic during processing. This award supports fundamental research that will provide needed knowledge about a new coextrusion foam manufacturing technology for fabricating lightweight composites. This process will also significantly reduce production costs by decreasing material usage as well as increasing performance-to-weight ratios through proper engineering of the material microstructure. This interdisciplinary research encompasses manufacturing, polymer chemistry, polymer physics and materials science. Companies manufacturing value-added plastic materials will benefit from the results. Students from underrepresented groups will participate in the research and a new program will be developed with a local museum to inspire interest in polymer materials for K-12 students. The gas/supercritical fluid concentration-dependent crystal nucleation/growth, crystal lamellae orientation, and subsequent bubble nucleation/growth behaviors under geometric constraints pose fundamental challenges in the coextrusion foam process. Further, the materials and process parameters largely influence the microstructure and bubble morphologies. These complex, coupled phenomena affect the properties of the final composite. The objective of this research is to close the knowledge gap in the understanding of microstructural evolution and bubble nucleation/growth mechanisms in coextrusion foam processes. The research team will develop a physics-based model to understand and predict the effects of the gas/supercritical fluid concentration and the interphase compatibility on the microstructure evolution of semi-crystalline polymers and will conduct experiments to verify the model. The team will also perform atomistic and macroscopic modeling simulations to understand the bubble nucleation and growth behaviors, and will test the hypothesis that various stress states influence the solubility and diffusivity by using a newly developed dielectric method. Based on these research results, the process parameters will be selected to achieve satisfactory microstructure and foam morphologies without time-consuming trial-and-error procedures.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.