Chemomechanics in the Solvent-Assisted Recycling of Engineering Composites

许多工程复合材料很难回收，因为这些材料中使用的聚合物是永久粘合在一起的。目前，复合废物的处置主要依靠填埋或焚烧，这给环境和健康带来了巨大的负担。最近开发了一种新的绿色、可持续的回收方法来解决这个问题。它利用溶剂和复合材料之间的键交换反应，在温和的温度下分解聚合物材料，回收清洁的纤维。分解后的产物可用于制造材料和力学性能几乎相同的新型复合材料，用于相同的应用。然而，由于这种回收技术的发展刚刚起步，现有的研究仅限于概念论证。该奖项支持基础研究，以揭示回收热固性材料和复合材料的废物特性、加工条件、回收速度和最终机械性能之间的关系。所提供的科学知识将为这种创新的回收方法的立即应用铺平道路，并大大缓解与传统废物处理方法有关的环境和健康问题。这项研究还将影响其他涉及聚合物分解和回收的行业的大规模应用，如电子产品的可拆卸封装、非破坏性表面涂层、受控药物输送、膜科学和微光刻。此外，该项目将提供教育和培训研究生和本科生的机会，重点是科学、技术、工程和数学方面的未被充分代表的学生。研究目标将使用多个长度尺度的综合实验-理论-计算方法来实现：在微观尺度上，将分子水平的键交换反应与热固性材料在回收过程中的应力场、网络结构和机械性能的演变联系起来。在细观尺度上，将本构关系纳入计算模型，研究纤维-聚合物界面对复合材料层板循环性能的影响。在宏观尺度上，将建立有效的降维计算模型来指导溶剂的选择和工艺条件的选择，以回收具有良好控制几何和力学性能的复合材料结构。这个奖项中定义的化学力学理论将被用来解决复合材料回收行业最关心的三个基本问题：(I)复合材料被回收的速度有多快，(Ii)回收成本最低的是什么，以及(Iii)如何改善回收产品的机械性能？这个奖项反映了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。

Many engineering composites are troublesome to recycle because the polymers used in these materials are bonded together permanently. Currently, the disposal of composite wastes mainly relies on the landfills or incineration, which lead to significant environmental and health burdens. A new green, sustainable recycling method was recently developed to address this problem. It uses a bond-exchange reaction between a solvent and the composite to decompose the polymer material at a mild temperature and reclaim clean fibers. The decomposed products can be used to fabricate new composites with near identical material and mechanical properties for the same applications. However, due to the nascent development of this recycling technique, existing studies are limited to the proof of concept demonstrations. This award supports fundamental studies to uncover the relationships between waste material properties, processing conditions, recycling speed, and final mechanical properties of recycled thermosets and composites. The provided scientific knowledge will pave the road for the immediate applications of this innovative recycling method and significantly ease the environmental and health concerns associated with the traditional waste disposal methods. This research will also impact large-scale applications in other industries involving polymer decomposition and recycling, such as removable encapsulation of electronics, non-destructive surface coatings, controlled drug delivery, membrane science, and microlithography. Additionally, the project will provide opportunities to educate and train graduate and undergraduate students with a focus on underrepresented students in science, technology, engineering, and math.The research objectives will be realized using an integrated experimental - theoretical - computational approach at multiple length scales: In the microscale, constitutive chemomechanics relations will be defined to link the molecular-level bond-exchange reactions to the evolution of stress field, network structure, and mechanical properties of thermosets during the recycling. In the mesoscale, the constitutive relations will be incorporated into a computational model to study the influences of the fiber-polymer interface on the recycling performance of a composite lamina. In the macroscale, an efficient reduced-order computational model will be developed to guide the selection of solvent and processing conditions to recycle composite structures with the well-controlled geometry and mechanical properties. The chemomechanics theory defined in this award will be used to address three fundamental questions that are mostly concerned in the composite recycling industry: (i) how fast can the composites be recycled, (ii) what is the lowest recycling cost, and (iii) how to improve the mechanical properties of recycled products?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.