GOALI: Experimental and Computational Approaches to Tailor Properties of Additively Manufactured Semi-Crystalline Polymers

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Material extrusion, a form of polymer additive manufacturing in which a filament is extruded layer-by-layer onto a bed, can manufacture components with geometric complexity far beyond that possible with conventional manufacturing methods. Building the part in layers, which enables great geometric freedom, also limits the mechanical integrity of the printed part. The bonding quality between printed layers yields parts with lower mechanical strength than if they were manufactured by traditional molding methods. This Grant Opportunity for Academic Liaison with Industry (GOALI) research project seeks to understand how polymer properties and processing conditions interact, and how they can both be manipulated to enhance interlayer bonding in material extrusion additive manufacturing. The knowledge gained will be leveraged to both tailor polymer properties for additive manufacturing processes, and to print components with mechanical properties appropriate for functional applications. Success will greatly enhance the competitiveness of the US additive manufacturing base by providing a pathway towards the manufacture of cost effective, functional polymeric components. This award will also facilitate training of the future workforce; both graduate and undergraduate students will be involved in the research activities and will gain experience in advanced manufacturing and polymer science. As this is an industry-university collaborative project with Henkel Corporation, the students involved will also gain an understanding of industrial challenges and drivers. Planned workshops on polymer additive manufacturing will disseminate the knowledge to industries seeking new opportunities in this manufacturing arena.This research will test the hypotheses that interlayer diffusion is a function of the difference between extrusion temperature and glass transition temperature, and that weld strength is dependent on the difference between the glass transition temperature and melt temperature as well as temperature-dependent wetting. This necessitates an understanding of the thermal characteristics of the material and the additive manufacturing process, and how they affect physical and mechanical properties of a printed structure. Towards this goal, three major research tasks will be undertaken: 1. Determine the role of the difference between the glass transition and melt temperatures in weld strength and residual stress of printed semi-crystalline polymers; 2. Understand the impact of crystallization kinetics on the crystalline morphology formed in additively manufactured structures; 3. Understand how glass reinforcement affects crystallization, heat transfer, and mechanical properties. By understanding the role of assembly conditions on resulting physical and mechanical properties, the work will lead to improved and tailorable physical and mechanical polymer properties essential to structure functionality. This research will also provide guidance in how to formulate polymers for additive manufacturing, based on thermal and physical 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.