GOALI: Projection Stereolithography of Gradient Viscoelastic Polymer Nanocomposites

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Polymer reinforced composites are materials that combine reinforcement materials such as carbon or glass fiber, or glass particles with a polymeric base material to produce a material with enhanced mechanical properties. Utilization of these materials has revolutionized industries involved in aerospace, automotive, and sporting goods manufacture. Increasingly, industry is turning to additive manufacturing, or 3D printing, to realize customized components with complex geometries. However, stereolithography, an additive manufacturing process that uses light to locally cure (harden) a liquid polymer resin in layers to build up a solid part, cannot successfully produce polymeric reinforced composites. Nor can the process easily incorporate material property gradients within a single build. This Grant Opportunities for Academic Liaison with Industry (GOALI) project seeks to overcome these limitations by understanding the material processing interactions occurring during a modified stereolithography printing process capable of combining polymers and nanoparticles to produce printed polymer composite materials. Success will advance the performance and range of polymeric materials that can be printed via stereolithography, and in doing so will realize the 3D printing of high performance, customizable, functionally graded components. This has the potential to advance the competitiveness of core US industries involved in the manufacture of aerospace, automotive, and medical components. As Align Technology, a manufacturer utilizing stereolithography in their custom-made orthodontics fabrication process, is a collaborator on this project the students involved in the project will not only be exposed to advanced material science and manufacturing technologies but will also gain an understanding of industrial challenges and drivers. Extended online courses will be made available to students and practicing engineers, providing flexible learning opportunities to keep informed of new developments in materials science and manufacturing.The primary goal of this project is to elucidate the structure/property relationships of gradient composite polymers printed by gray scale stereolithography of a matrix polymer followed by swelling with a reactive filler containing nanoparticles. A secondary goal is to reduce, control or eliminate the large internal stresses caused by polymerization shrinkage and solvent swelling of stereolithographic parts. The latter will be achieved by employing covalent adaptable matrices, e.g. addition-fragmentation chain transfer backbones that rearrange to relax stress in the presence of radicals. To achieve these goals the following tasks will be conducted; 1) precise, macroscopic characterization of matrix monomer-to-polymer conversion as a function of processing conditions and how this partial conversion controls swelling of the filler, 2) validation of the macroscopic predictions on the micron scale via gray-scale stereolithography of the matrix followed by swelling and polymerization of the filler, 3) validation of the predicted viscoelastic behavior of inhomogeneous printed nanocomposites, and 4) demonstration that reversible addition-fragmentation chain transfer chemistry can be leveraged to provide local stress control in bulk composites. If successful the knowledge gained will be used to print and verify the predicted properties of a printed trinary nanocomposite with photo-induced plasticity.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.