Chemomechanics in the Solvent-Assisted Recycling of Engineering Composites

许多工程复合材料回收起来很麻烦，因为这些材料中使用的聚合物是永久结合在一起的。目前，复合废弃物的处理主要依靠填埋或焚烧，这导致了巨大的环境和健康负担。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并回收干净的纤维。分解产物可用于制造具有几乎相同的材料和机械性能的新复合材料，用于相同的应用。然而，由于这种回收技术的发展初期，现有的研究仅限于概念演示的证明。该奖项支持基础研究，以揭示废料特性，加工条件，回收速度和回收热固性材料和复合材料的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相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，例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，工程和数学方面代表性不足的学生。研究目标将在多个长度尺度上使用综合实验-理论-计算方法来实现：在微观尺度上，将定义本构化学力学关系，将分子水平的键交换反应与应力场、网络结构、以及回收过程中热固性塑料的机械性能。在细观尺度下，本构关系将被纳入一个计算模型，研究纤维-聚合物界面对复合材料层的回收性能的影响。在宏观尺度上，将开发一个有效的降阶计算模型来指导溶剂和加工条件的选择，以回收具有良好控制的几何形状和机械性能的复合材料结构。该奖项中定义的化学力学理论将用于解决复合材料回收行业最关心的三个基本问题：（i）复合材料回收的速度有多快，（ii）最低的回收成本是多少，以及（iii）如何提高回收产品的机械性能？该奖项反映了NSF的法定使命，并被认为是值得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的支持。

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.