CAREER: Understanding Process-Structure-Property Relations in Gas/Supercritical Fluid-Injected Polymer Coextrusion Foam Processes

University Of Vermont & State Agricultural College, Burlington VT

Investigators

Abstract

This Faculty Early Career Development Program (CAREER) grant will promote the progress of science by contributing new knowledge related to a novel manufacturing process for fabricating lightweight multimaterial foam structures that have a variety of applications in the automotive, aerospace, biomedical, food and electronics packaging industries. Most new polymeric products contain two or more polymers and functional additives resulting in desired properties contributed from each component. The process extrudes multiple materials at the same time in a single-step process using two or more polymeric materials shaped to form a multilayer structure for unique applications. These include optical, mechanical, and gas barrier films, such as brightness-enhancing filters for electronic screens, ultra-strong safety and security window films, or elastomeric barrier films for cushioning bladders in athletic shoes. Foams can be prepared from any plastic by introducing a gas or supercritical fluid within the plastic during processing. This award supports fundamental research that will provide needed knowledge about a new coextrusion foam manufacturing technology for fabricating lightweight composites. This process will also significantly reduce production costs by decreasing material usage as well as increasing performance-to-weight ratios through proper engineering of the material microstructure. This interdisciplinary research encompasses manufacturing, polymer chemistry, polymer physics and materials science. Companies manufacturing value-added plastic materials will benefit from the results. Students from underrepresented groups will participate in the research and a new program will be developed with a local museum to inspire interest in polymer materials for K-12 students. The gas/supercritical fluid concentration-dependent crystal nucleation/growth, crystal lamellae orientation, and subsequent bubble nucleation/growth behaviors under geometric constraints pose fundamental challenges in the coextrusion foam process. Further, the materials and process parameters largely influence the microstructure and bubble morphologies. These complex, coupled phenomena affect the properties of the final composite. The objective of this research is to close the knowledge gap in the understanding of microstructural evolution and bubble nucleation/growth mechanisms in coextrusion foam processes. The research team will develop a physics-based model to understand and predict the effects of the gas/supercritical fluid concentration and the interphase compatibility on the microstructure evolution of semi-crystalline polymers and will conduct experiments to verify the model. The team will also perform atomistic and macroscopic modeling simulations to understand the bubble nucleation and growth behaviors, and will test the hypothesis that various stress states influence the solubility and diffusivity by using a newly developed dielectric method. Based on these research results, the process parameters will be selected to achieve satisfactory microstructure and foam morphologies without time-consuming trial-and-error procedures. 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.