CAREER: Mechanics of Recyclable Thermoset Polymers

这项教师早期职业发展（Career）资助旨在从根本上了解新型可回收热固性聚合物（玻璃体）的微观结构-性能联系。塑料在我们的日常生活中无处不在，由于其低可回收性对环境和自然栖息地构成潜在威胁，因此给我们带来了挑战。传统的热固性聚合物，其吸引人的物理和机械性能使其成为重要的结构材料，特别阴险。分子水平上的不可逆交联严重阻碍了它们的后处理和再循环能力。新的玻璃体化学提供了令人兴奋的途径，以开发机械坚固，可回收的热固性。然而，预测再加工过程中缺陷（组织）的出现及其对力学特性（性能）的影响是困难的。挑战的根源在于揭示与微尺度缺陷结构统计相关的损伤过程，这些缺陷结构是由不同长度尺度和时间尺度的玻璃体化学力学引起的。该研究项目通过新颖的多尺度计算力学来解决这些主要问题。其技术相关性源于对预测建模和仿真框架的需求，以使结构应用的耐损伤玻璃体成为可能。该研究项目被整合到一个更广泛的教育目标中，即在两个层面上创造一种身临其境的学习体验：(i)代表性不足的学生群体，包括残疾学生；（ii）在教育（K-12）中整合颗粒艺术；（iii）开发一门关于材料微观结构敏感失效力学的研究生课程。基于酯交换的共价自适应网络聚合物（玻璃体）通过键交换反应化学获得其后处理能力。回收这类玻璃体的一个有吸引力的方法是将它们粉碎成颗粒状粉末，并通过热机械压实对它们进行再加工。在此过程中，单个颗粒经历非线性、耗散变形，并通过新型化学-机械愈合过程在颗粒间接触区域焊接。由此产生的新固体以微机械缺陷群体的形式体现了回收的指纹。这些缺陷微观结构重新定义了它们的粘弹性硬化、强化和损伤容限，这取决于多个长度尺度的力学：(1)颗粒热化学愈合力学；（ii）损伤演化的缺陷细观力学和（iii）回收部件的连续细观力学。该项目将通过一个多尺度计算力学平台来解决与回收热固性材料力学相关的基本问题：(a)在中尺度上，通过离散元素建模和模拟具有玻璃聚合物的颗粒系，以量化缺陷-损伤联系的紧急统计数据；(b)在宏观尺度上，通过制定和计算实现微观力学信息统计粘弹性损伤力学。计算框架将根据一套现有的实验数据集进行校准、验证和评估，同时为设计耐损伤可回收热固性材料提供机制预测。该奖项反映了美国国家科学基金会的法定使命，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 (CAREER) grant will aim to fundamentally understand the microstructure-property linkages of novel recyclable thermoset polymers (vitrimers). The ubiquity of plastics in our daily lives presents challenges due their potential threats to the environment and natural habitats arising from their low recyclability. Conventional thermoset polymers, whose attractive physical and mechanical properties make them important structural materials, are particularly insidious. The irreversible crosslinking at the molecular level seriously impedes their reprocessing and recycling ability. Novel vitrimer chemistries offer exciting avenues to develop mechanically robust, recyclable thermosets. However, predicting the emergence of defects (microstructure) during reprocessing and their impact on the mechanical characteristics (property) is difficult. The challenge is rooted in unraveling the damage processes associated with the statistics of microscale defect structures resulting from vitrimer chemo-mechanics at various length-scales and time-scales. The research project addresses these principal issues via novel multiscale computational mechanics. Its technological relevance is rooted in the need for a predictive modeling and simulation framework to enable damage-tolerant vitrimers for structural applications. The research program is integrated into a broader educational goal of creating an immersive learning experience at two levels: (i) underrepresented student groups including students with disabilities, (ii) an integration of granular art in education (K-12), and (iii) development of a graduate course on the microstructure-sensitive failure mechanics of materials. Transesterification based covalent adaptive network polymers (vitrimers) derive their reprocessing ability via bond exchange reaction chemistry. An attractive approach to recycling such vitrimers involves pulverizing them into granular powders and reprocessing them via thermomechanical compaction. During this process, individual particles undergo non-linear, dissipative deformation, and welding at inter-particle contact regions through novel chemo-mechanical healing processes. The resulting new solid embodies fingerprints of recycling in the form of micromechanical defect populations. These defect microstructures redefine their viscoelastic stiffening, strengthening, and damage tolerance, which depends on the mechanics at multiple length-scales: (i) granular thermo-chemo-mechanics of healing; (ii) defect micromechanics of damage evolution, and (iii) continuum micromechanics of recycled components. This project will address fundamental questions associated with the mechanics of recycled thermosets via a multiscale computational mechanics platform: (a) at the mesoscale, by discrete element modeling and simulation of granular ensembles endowed with vitrimers chemo-mechanics to quantify emergent statistics of the defect-damage linkages, and (b) at the macroscale, by formulating and computationally implementing a micromechanically informed statistical viscoelastic damage mechanics. The computational frameworks will be calibrated, validated, and assessed against a suite of existing experimental datasets while offering mechanistic predictions for the design of damage-tolerant recyclable thermosets.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.