The research efforts presented herein examine how <i>tailoring interfacial interactions across the polymer matrix/additive interface governs assembly at the nanoscale and impact thermomechanical properties of parts produced by fused filament fabrication (FFF). </i>Specifically, I examine how physical, non-bonded interactions in poly(methyl methacrylate) (PMMA)-based polymer nanocomposites increases the mechanical properties of FFF-printed parts as the loading level of bare (unfunctionalized) Si NPs increases. Results indicate that at low loading levels (0.1 wt%), bare Si NPs provide minimal reinforcement, while at higher loading levels (1.0 wt%) a notable increase in Young’s modulus is observed. Rheology measurements suggest that increases in Young’s modulus are correlated to the number density of hydrogen bonding interactions between hydroxyl groups present on the Si NP surface and carbonyl groups along the backbone of PMMA. Specifically, at low loadings, the number density of polymer/particle interactions are low, and thus the material properties are similar to unfilled PMMA; however, at high loading levels the number density of interfacial interactions is significantly greater, which enables effective stress transmission from the matrix polymer to the inorganic additive, thereby increasing Young’s modulus and other mechanical properties.<br/>Inspired by the potential to use non-bonded interactions to improve the performance of FFF-printed parts, I also present the first studies that examine how copolymeric additives possessing thermoreversible H-bonding interactions affect thermomechanical properties of FFF-printed parts. The addition of self-complementary, multiple hydrogen bonding random copolymers significantly enhance the mechanical properties of printed parts. Moreover, the hydrogen bonding UPy (UPy = 2-ureido-4-pyrimidone) groups dissociate at high temperatures used for melt processing. Studies show that increasing the number density of hydrogen bonding interactions, which is easily varied by changing the comonomer content (MMA/UPyMA), provides a novel route to effectively manage the mechanical properties. The mechanical reinforcement observed in parts containing thermoreversible additives is attributed to the presence of a dense, interconnected, physical crosslinked network. In total, these reports break new ground and provide fundamental insights regarding how the macroscopic properties of FFF-printed materials can be controlled through molecular design.

Enhancing macroscopic properties of 3D-printed parts by tailoring interfacial interactions at the nanoscale

2019 Fall National Meeting

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