CAS: Reprocessable Thermosets for High Performance Composites

聚合物基复合材料是一种重要的轻质结构材料，用于可持续能源的生产和使用，例如电动汽车和风力涡轮机。这些复合材料的传统材料本质上是不可回收的。解决这个问题的一种方法是利用材料化学的最新进展，使生产具有强化学键的材料能够以可逆的方式断裂和重组。具有这些键的聚合物材料在断裂后可以修复或完全回收，这种能力导致了大量可持续材料的发展。这些类型的材料通常在柔软的橡胶状态下使用和评估，其中材料刚度太低，无法用作结构材料。该项目旨在发展为结构应用生产刚性、可回收材料所需的背景知识。作为项目的一部分，正在测试的一个重要假设是，在刚性材料中加入可逆键也可以导致性能增强，否则无法获得。该项目的成功完成将是朝着坚固、轻质材料的发展迈出的重要一步，这些材料可以在服役期间进行修复。第2部分：技术概述提出的工作是基于在网络结构的各个点上结合芳香二硫键的模型环氧网络的合成。不同的交联剂将用于调节网络的玻璃化转变温度，允许独立控制与玻璃化转变相关的弛豫动力学和与二硫化物交换相关的动力学。三个相互关联的活动将进行，以表征这些材料和发展变形机制的分子水平的理解。其中第一个是一系列的机械测量，表征材料中裂纹扩展附近的材料变形。第二种方法是利用拉曼散射和一系列比色技术，直接可视化二硫键裂解过程中形成的硫基自由基的空间分布。此外，利用石英晶体谐振器进行的一系列薄膜实验将用于评估聚合物的高频流变特性，以及它们在不同环境条件下的降解动力学和稳定性。这些谐振器还将用于开发各种环境监测方法。总的来说，这些实验将导致生产用于结构应用的坚韧，轻质，可回收的聚合物材料的总体策略的发展。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。

PART 1: NON-TECHNICAL SUMMARYPolymer matrix composites are an important class of lightweight structural materials used in applications relevant to sustainable energy production and use, with examples including electric vehicles and wind turbines. Traditional materials for these composites are inherently non-recyclable. One approach to this problem is to take advantage of recent advances in materials chemistry that enable the production of materials with strong chemical bonds that are able to break and reform in a reversible manner. Polymeric materials with these bonds can be repaired after fracture or completely recycled, a capability that has led to the development of a large range of sustainable materials. These types of materials have typically been used and assessed in the soft, rubbery state, where the material stiffness is much too low for use as a structural material. This project is designed to develop the background knowledge needed to produce rigid, recyclable materials for structural applications. An important hypothesis being tested as a part of the project is that the incorporation of reversible bonds in a rigid material can also result in property enhancements that would not be obtainable otherwise. Successful completion of the project will be an important step toward the development of strong, lightweight materials that can be repaired while still in service.PART 2: TECHNICAL SUMMARYThe proposed work is based on the synthesis of model epoxy networks with aromatic disulfide bonds incorporated at various points within the network structure. Different crosslinkers will be used to adjust the glass transition temperature of the network, allowing independent control of the relaxation dynamics associated with the glass transition and the dynamics associated with disulfide exchange. Three interrelated activities will be pursued in order to characterize these materials and develop a molecular-level understanding of the deformation mechanisms. The first of these is a series of mechanical measurements characterizing material deformation in the vicinity of a propagating crack in the material. The second involves direct visualization of the spatial distribution of thiyl radicals that form during cleavage of the disulfide bonds, using Raman scattering and an array of colorimetric techniques. Additionally a series of thin film experiments utilizing quartz crystal resonators will be used to assess the high frequency rheological properties of the polymers, along with their degradation kinetics and stability in different environmental conditions. These resonators will also be used to develop methods for environmental monitoring in a variety of contexts. Collectively, these experiments will lead to the development of a general strategy for the production of tough, lightweight, recyclable polymeric materials for structural applications. .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.