GOALI: Additive Manufacturing of High Performance Elastomers via Vat Photopolymerization of Aqueous Polymer Dispersions

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Additive manufacturing processes, often referred to as 3D Printing, have shown promise as a means for fabricating parts featuring complex geometries that can be tailored to an individual customer and application. Vat Photopolymerization is one method of additive manufacturing that offers superior feature resolution, accuracy, and surface finish. However, despite these advantages relative to other processes, Vat Photopolymerization has seen limited industrial adoption for fabricating end-use products primarily due to the limited diversity and quality of its processable materials. The narrow range of suitable materials can be attributed to process-imposed constraints. For example, the resins must have a low viscosity (flow easily) to aid part recoating prior to printing the next layer. This prevents the use of polymers with high molecular weight, which limits the printed material's strength and elasticity. To overcome this limitation, this Grant Opportunity for Academic Liaison with Industry (GOALI) Program research project plans to use resins that consist of high-molecular weight polymer 'particles' suspended in a low viscosity medium, e.g. water and solvent. Successfully understanding the optimal composition and printability of such resins will enable advanced manufacturing capabilities to realize the printing of rubber and latex parts. This can be beneficial to key US based automotive and aerospace industries by facilitating the printing of tires, gaskets, and bushings. As this is an industry-university collaborative project, the graduate students involved will gain an understanding of industrial challenges and drivers, thus increasing their preparedness for the future workforce. Additional educational opportunities will be provided for undergraduate students and underrepresented minorities to further broaden engagement in advanced manufacturing and material science topics. The research objectives of this GOALI program award are to (i) understand requirements for forming stable aqueous polymer dispersions, (ii) understand how characteristics of dispersions influence green body strength and photocuring kinetics, (iii) model the layerwise photocuring behavior of dispersions, and (iv) map the processable material design space. The research will test three hypotheses based on preliminary experiments: (i) improvement in mechanical properties is due to the coalescence of the dispersed polymer particles and formation of a high molecular weight, entangled network throughout the scaffold upon drying, (ii) the observed sharp increase in strength seen at low strains is attributable to the rigid scaffold created in the continuous, aqueous phase during printing, and (iii) existing Vat Polymerization models for relating scattering phenomena with exposure and cure depth must be adapted to account for the dispersions' dynamically changing refractive index. This research will result in (i) fundamental understanding of structure-property-process relationships of Vat Polymerization dispersions, (ii) a model of the photocuring behavior of polymeric dispersions that accounts for dynamically changing refractive index, and (iii) a series of novel Vat Polymerization elastomers with tunable mechanical properties.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.