Microcellular foamed polymers are produced by the use of a decomposing gas in the polymer which leaves behind microcellular voids within stiff, lightweight materials. An objective of the work is to reinforce these materials with plant fibers since such composites have been found to possess highly dissipative, foam-like dynamic response in a rigid, lightweight form. The voids as well as the cellular and vascular anatomy of the natural fibers have been found to play a role in this behavior. The goal of the project is to describe the micro-structural behavior of the biocomposites under dynamic loading, and to connect it to macro-structural response. This knowledge is unavailable for microcellular biocomposites, and will enable the exploitation of the natural properties of the underlying materials and lead to tailored, multi-functional material systems. Building on ideas from polymer crystallization and traditional composites, fundamental research will be conducted concerning micro-structural response, modeling, microscopy, microcellular processing and testing.
Potential applications range from impact safety materials in automobiles and municipal transportation systems to infrastructural materials like specialized flooring, guard rails, seismic panels, and composite slabs, and to less obvious ones like electronics protection and biomedical scaffolds. The participation of a potential large scale user of the materials can help lower the cost of the materials and work to overcome the financial inertia that hinders the use of new materials by smaller manufacturers. Many candidate applications are presently met with petroleum-based materials. The replacement of just a moderate amount of these materials with environmentally-friendly alternatives can produce significant environmental benefit. The project includes education of a graduate student, REU students and educational outreach to kindergarten - 12 students.
A new class of biocomposites possessing unique energy dissipation characteristics has been identified and successfully investigated through a collaboration between researchers at the University of Michigan-Dearborn and Ford Motor Company. These composites have been formulated by combining advantageous features of plant based fibers and micron-sized voids (Figure 1). The resulting biocomposites have highly dissipative, foam-like dynamic response characteristics in a rigid, lightweight form, offering potential for various applications ranging from impact safety materials in automobiles and municipal transportation systems to infrastructural materials like specialized flooring, guard rails, seismic panels, and composite slabs. In addition to plant fibers, conventional materials, such as glass fibers, can also be added to the foamed biocomposites to achieve a wide range of capabilities without losing the energy dissipation characteristics. Various mechanical tests, such as static and dynamic tests under tensile or compressive loading at various temperatures and rates, have been performed using a specially designed and developed apparatus with temperature-controlled chambers (Figure 2). Based on the test results wheat straw fibers, wheat straw powder, cellulose and soy flour have been found to be suitable as fillers for the new composite system, and could replace conventional synthetic fillers for many applications. Compared to conventional counterparts, the foamed biocomposites contain less petroleum and have lower weight and greater potential for recyclability. Computer aided modeling (Figure 3), microscopic inspection (Figure 1) and high-speed imaging studies have also been performed, offering insight into their unique behavior, including energy dissipation and failure mechanisms. These outcomes, including the elucidated mechanical behavior, can serve as a basis for the future exploitation of tailored, multi-functional material systems for the candidate applications mentioned above. The use of the developed, foamed biocomposites over conventional ones can lead to direct environmental, economical, and societal benefits. Many candidate applications presently use glass fibers, that include significant amounts of petroleum in their formulation. The replacement of even just a moderate amount of the presently used glass reinforced materials with environmentally friendly alternatives can produce significant environmental benefit by offsetting petroleum. The use of these materials can also positively impact the country’s agricultural industry by opening it up to more substantial production of industrial raw materials than typical. Also, transportation vehicles having improved safety for occupants and pedestrians can result. Direct project outcomes related to broader impacts include a capstone design project, conducted by a team of mechanical engineering students, in which environmental chambers have been developed for temperature-controlled mechanical tests. Also, a three-week unit on impact characteristics of materials has been developed and incorporated in an undergraduate course. The unit includes a lab that uses equipment and ideas developed as a part of this project. Four different undergraduate students worked on the project and one graduate student has earned his Master’s degree by working on the project. The project has further advanced the collaboration between the University of Michigan and Ford Motor Company’s Materials Research Department including work by students and senior personnel at both the university and Ford’s facilities. A large number of outreach activities have taken place including presentations at local K-12 schools, Ford Take Your Child to Work Day, high school Science Olympiad coaching of the material science event, presentations at the Panel on Women in SAMPE, and recruiting at SWE National Conference. During the course of the award, Ford has hosted numerous research internships to undergraduate and graduate students from around the country and abroad on the production, analysis and design of automotive parts using sustainable materials.
