CAREER: Multiscale Mechanics of Bio-based, Reprocessable, Recyclable and Mechanically Robust Polymer Composites

这个教师早期职业发展（CAREER）补助金将支持基础研究，以了解生物交联聚合物复合材料的复杂机械行为。交联弹性体和热固性聚合物在工业、国防和日常生活中具有重要的战略意义。虽然强共价交联赋予这些常规热固性材料以理想的性能，但它们也妨碍了修复、再成形、再加工和回收，这造成了严重的环境污染和资源浪费。通过引入生物动力学共价键和添加增强填料，开发了一种新型的绿色聚合物，该聚合物具有潜在的可回收性、可再加工性和可持续性。然而，大多数已报道的生物交联聚合物仍远未被广泛应用于现实世界中的应用，由于其加工-结构-性能关系的理解有限。该研究项目旨在发现生物基聚合物复合材料的机械和化学特性的基本原理，并借助多尺度计算建模，数据科学（统计分析）和实验验证。通过量化的微观结构-性能关系和解开的变形机制，先进的生物基可再加工和机械坚固的聚合物复合材料可以被开发用于广泛的应用，这将显着减轻严重的塑料污染问题。该项目包括一个教育和推广计划，以培训下一代工程师的不同群体：组织研讨会，研讨会讲座和当地回收中心图尔斯参观K-12学生，为高中生提供暑期实习机会，培训本科生和研究生的编码，写作和演示的研究技能。特别是，将为代表性不足的学生，包括身体残疾的学生创造研究机会。 通过开发一个新的多尺度框架，集成密度泛函理论（DFT），全原子分子动力学（AA-MD）和粗粒分子动力学（CG-MD），该项目的目标是建立一个基本的理解，可交换的生物交联的作用，协助聚合物复合材料之间的机械，功能和再加工性能的平衡。研究目标包括：（i）通过力场校准/优化/参数化无缝地桥接DFT、AA-MD和CG-MD;（ii）理解两种代表性的断裂机制：生物基丁苯橡胶（SBR）和生物基环氧玻璃化转变体。将解决以下知识差距：（1）固化过程中去交联/再交联的机制;（2）生物交联相对于常规连接的优势（例如，S-S、C-S键）;（3）纳米填料与聚合物之间的界面相互作用;（4）后处理对再生聚合物结构和力学性能的影响;（5）微观和介观结构与性能的关系。该研究成果将推进生物基聚合物复合材料的力学知识，以及集成的多尺度框架可以扩展到其他无定形材料，如分级生物材料。该奖项反映了NSF的法定使命，并已被认为值得通过使用基金会的智力价值和更广泛的影响审查标准进行评估的支持。

This Faculty Early Career Development (CAREER) grant will support fundamental research to understand complex mechanical behaviors of bio-crosslinked polymer composites. Covalently crosslinked elastomers and thermosetting polymers have been acknowledged as strategically important materials in industry, national defense and our daily life. Although the strong covalent crosslinks confer these conventional thermosets desirable properties, they also preclude repairing, reshaping, reprocessing and recycling, which has caused serious environmental pollution and resource wastage. By introducing bio-dynamic covalent bonds and adding reinforcing fillers, a novel green type of polymers that are potentially recyclable, reprocessable and sustainable has been developed. However, most of the reported bio-crosslinked polymers are still far from being extensively used in real-world applications due to the limited understanding of their processing-structure-property relationships. This research project aims to discover the fundamental principles that govern the mechanical and chemical properties of bio-based polymer composites, with the aid of multiscale computational modeling, data science (statistical analysis), and experimental validation. With quantified microstructure-property relations and unraveled deformation mechanisms, advanced bio-based reprocessable and mechanically robust polymer composites can be developed for wide applications, which will significantly mitigate the severe plastic pollution issue. The project includes an education and outreach plan to train diverse groups of next-generation of engineers: organizing workshops, seminar talks and local recycling center tours to K-12 students, providing high school students with summer internship opportunities, training undergraduate and graduate students the research skills of coding, writing and presenting. Particularly, research opportunities will be created for underrepresented students including physically disabled students. Through developing a novel multiscale framework that integrates density functional theory (DFT), all-atom molecular dynamics (AA-MD) and coarse-grained molecular dynamics (CG-MD), the goal of this project is to establish a fundamental understanding of the role of exchangeable bio-crosslinks in assisting the polymer composites strike their excellent balance among mechanical, functional, and reprocessing properties. The research objectives include: (i) seamlessly bridging DFT, AA-MD and CG-MD by force field calibration/optimization/parameterization; (ii) understanding the fracture mechanisms of two representatives: bio-based styrene-butadiene rubber (SBR) and bio-based epoxy vitrimer. The following knowledge gaps will be addressed: (1) the mechanisms of de-crosslinking/re-crosslinking during curing; (2) the advantages of bio-crosslinks over conventional linkages (e.g., S-S, C-S bonds); (3) the interfacial interactions between nanofiller and polymer; (4) the influence of reprocessing on structure and mechanical performance of reclaimed polymers; (5) microscale and mesoscale structure-property relations. The research outcomes will advance the knowledge of mechanics in bio-based polymer composites, as well the integrated multiscale framework can be extended to other amorphous materials, such as hierarchical biomaterials.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.