Ultraviolet-light induced Frontal Polymerization in Additive Manufacturing and Repairing of Thermoset Polymer Composite - Understanding the Role of Fiber Reinforcement Phases

紫外（UV）光诱导的前沿聚合（frontal polymerization）是一种自维持的放热化学反应，是用于热固性聚合物的增材制造的有前途的技术，可能适用于纤维增强热固性复合材料。然而，纤维相在正面聚合中的作用仍然难以捉摸，特别是，它如何决定固化和所得的机械性能还没有完全理解。该奖项支持基础研究，通过实验研究和计算建模的综合方法，研究和理解前沿聚合中纤维相行为的机制。所获得的新知识预计不仅将促进增材制造和聚合物加工的科学进步，而且还将使美国工业在广泛的应用中受益，如机身，柔性生物传感器，风力涡轮机叶片和海洋结构等。此外，该团队还将通过夏季研究机会，扩大STEM领域代表性不足的群体的参与，使其能够接触到印度本土的本科生和来自一个学区的高中生，而大多数当地的印度本土学生都在该学区就读。本研究的目的是了解纤维增强相如何影响热固性复合材料的紫外线诱导前沿聚合过程，包括固化动力学，零件微观结构和力学性能。热固性树脂中纤维的存在将使热传递速率和梯度复杂化，这可能会改变激活聚合和形成前沿传播所需的UV能量。为了应对这一根本挑战，不同结构的纤维复合材料，例如，将研究不同重量分数的引发剂在不同UV能量水平下的前沿聚合。固化性能，如固化的速度和程度，沿着产生的微观结构和机械特性，如孔隙率和拉伸性能，将使用原位热成像和固化后材料分析和机械测试进行实验表征。此外，将开发基于物理的反应扩散模型，辅以神经网络机器学习算法，以了解处理现象的行为，并通过实验结果进行验证。此外，增材制造和修复实验将通过将前沿聚合集成到自动纤维铺放3D打印机中来进行，以评估具有不同配置的纤维增强热固性复合材料的固化和机械性能。该奖项反映了NSF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。

Ultraviolet (UV) light induced frontal polymerization, a self-sustaining exothermic chemical reaction, is a promising technique for additive manufacturing of thermoset polymers, potentially applicable to fiber-reinforced thermoset composites. However, the role of fiber phases in frontal polymerization remain elusive, particularly, how it determines curing and resultant mechanical performance is not fully understood. This award supports fundamental research to study and understand the mechanisms governing fiber-phase behavior in frontal polymerization through an integrated approach of experimental investigations and computational modeling. The new knowledge acquired is expected to not only promote scientific advancement in additive manufacturing and polymer processing, but also benefit U.S. industries in a broad range of applications such as airframes, flexible biosensors, wind turbine blades and marine structures, etc. This project will also integrate composites additive manufacturing into course materials. Additionally, the team will broaden the participation of underrepresented groups in STEM through summer research opportunities to the pool of Native Indian undergraduates and to high school students from a school district, where most local Native Indian students attend.The objective of this research is to understand how fiber reinforcement phases influence UV-induced frontal polymerization processing of thermoset composites, including curing kinetics, part microstructures and mechanical performance. The presence of fibers in thermoset resins will complicate heat-transfer rates and gradients, which may alter UV energy required to activate polymerization and shape the front propagation. To tackle this fundamental challenge, fiber composites of different configurations, e.g., varying weight fractions of initiators, will be investigated into frontal polymerization at varying UV energy levels. Curing performance, such as the speed and degree of the cure, along with the resultant microstructural and mechanical characteristics, such as porosity and tensile properties, will be experimentally characterized using in-situ thermal imaging and post-cure material analysis and mechanical testing. In addition, physics-based reaction-diffusion models, complemented by neural network machine learning algorithms will be developed to understand the behavior of processing phenomena and be validated by experimental results. Furthermore, experiments of additive manufacturing and repairing will be conducted by integrating frontal polymerization into an automated fiber placement 3D printer to evaluate curing and mechanical performance of fiber reinforced thermoset composites with different configurations. The fundamental understanding gained is expected to establish the quantitative relationship between curing and mechanical performance of fiber-reinforced thermoset composites and the interplay of the fiber configurations, UV-light energy and curing kinetics of thermoset resins.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.