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

学院早期职业发展(Career)补助金将支持基础研究，以了解生物交联型聚合物复合材料的复杂力学行为。共价交联弹性体和热固性聚合物在工业、国防和日常生活中被公认为具有重要战略意义的材料。虽然强共价交联剂赋予了这些传统热固性材料良好的性能，但它们也阻碍了修复、重塑、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，具有潜在的可回收、可再加工和可持续发展的潜力。然而，由于对其加工-结构-性能关系的了解有限，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。这项研究项目旨在通过多尺度计算建模、数据科学(统计分析)和实验验证，发现支配生物基聚合物复合材料力学和化学性质的基本原理。通过量化的微结构-性能关系和揭示的变形机制，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得到广泛的应用，这将显著缓解严重的塑料污染问题。该项目包括一项教育和推广计划，以培训不同的下一代工程师群体：为K-12学生组织研讨会、研讨会讲座和当地回收中心之旅，为高中生提供暑期实习机会，培训本科生和研究生编码、写作和演示的研究技能。特别是，将为代表不足的学生，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，结合密度泛函理论(DFT)、全原子分子动力学(AA-MD)和粗粒分子动力学(CG-MD)，本项目的目标是建立对可交换生物交联物在帮助聚合物复合材料在力学、功能和再加工性能之间取得良好平衡的作用的基本理解。研究目标包括：(I)通过力场校准/优化/参数化将DFT、AA-MD和CG-MD无缝连接；(Ii)了解生物基丁苯橡胶(SBR)和生物基环氧玻璃体两种代表性材料的断裂机理。将讨论以下知识空白：(1)固化过程中的去交联/再交联机制；(2)生物交联剂相对于传统键(如S-S键、C-S键)的优势；(3)纳米填料与聚合物之间的界面作用；(4)后处理对再生聚合物结构和力学性能的影响；(5)微观和介观尺度的结构-性能关系。研究成果将促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非晶态材料，如分层生物材料。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势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 (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.