Intellectual Merit. Electron-beam (EB) curing offers a fast, low-energy, and solvent-free means of polymerizing inks, films, and coatings compared to thermal polymerization. No initiator is required to form the free-radical active centers, making this technique especially appealing for packaging applications where molecular migration would be problematic. In addition, unlike photopolymerization, additives such as pigments, fillers, fibers, and nanomaterials do not prevent penetration of the ionizing radiation, resulting in excellent product consistency. In spite of these advantages, less than 500 low-energy (100 to 300 kV) accelerators are installed worldwide for curing applications. In order to increase use of EB technology, improvements are needed in both the curing process and performance properties of the resulting polymers. While some development has occurred among private companies, there is need for a more fundamental study of process parameters and their effects; however, academic research on EB curing has been limited in part by the high expense of and limited access to EB accelerators. This GOALI will facilitate collaboration between industrial and academic partners (with over 40 years combined experience in radiation chemistry and characterization of polymer kinetics and physical properties) to address these critical needs in EB technology. PCT Engineered Systems develops and manufactures BroadBeam low energy EB accelerators and is located less than an hour?s drive from the University of Iowa (UI) campus.
The goal of this research is to advance EB technologies by increasing the fundamental understanding of the effects of energy deposition and process conditions on kinetics and material properties. To meet this goal, the following four key topics will be pursued collaboratively: (1) compare conversion of EB-cured and UV-cured materials; (2) compare physical properties of EB-cured, UV-cured, and thermally cured materials; (3) develop EB-cured resin formulations requiring little or no nitrogen inerting; and (4) correlate monomer structure with EB dose rate. Conversions as a function of depth will be measured using Raman confocal microscopy to demonstrate the effects of radiation penetration and nitrogen inerting. Molecular weight distributions (for linear polymers), cross-linking density (for polymer networks), and polymer modulus will be measured using gel permeation chromatography and dynamic mechanical analysis to demonstrate the impact of initiation mechanism, monomer structures, and process parameters on polymer physical properties. Epoxide/acrylate and thiol/acrylate systems will be explored to mitigate oxygen inhibition. The results of these studies will provide an improved understanding of both the EB-curing process and the properties of the resulting polymers. This understanding will facilitate the extension of EB technologies to a wider range of applications, including high-performance materials and three-dimensional parts.
Broader Impacts. This advanced characterization of the EB-curing process and the resulting polymer materials will provide a level of understanding of EB-cured systems significantly beyond what is currently available. This knowledge will provide a basis for expanding the applications of EB technologies, especially in the film, coating, adhesives, and composites industries. Results of this research will facilitate establishment of the US at the forefront of EB technologies, increase export opportunities for equipment and products, and provide new jobs as the EB industry expands. This research program will also have a direct impact on the educational experience of students at various levels. Students in engineering and science will benefit from a polymer science course series that will incorporate research results from this project. Several undergraduate and high-school students will be invited to participate in portions of this research, and two graduate students will focus their efforts on investigating these EB-curing systems. Furthermore, through established recruitment and outreach strategies, underrepresented females and minorities will be encouraged to participate in this research. Seminars on EB technology advancements will be held at the UI and PCT, and EB-related symposia will be organized at RadTech 2016, Photopolymerization Fundamentals 2014, and ACS national meetings.
Measurable Industrial Collaboration. PCT will provide EB training, access to its EB pilot line for curing studies, and internship opportunities. PCT will also advise UI researchers on industry needs, help set project milestones and deliverables, and monitor the progress of the studies. Dr. Lapin will serve as a co-advisor for the graduate student committees and will assist in organizing local and national symposia relating to EB technology and its use.
