Degree

Doctor of Philosophy (PhD)

Department

School of Renewable Natural Resources

Document Type

Dissertation

Abstract

Filament fused fabrication (FFF) is an extrusion-based 3D printing technology for manufacturing thermoplastic polymers. A major obstacle of 3D printed thermoplastic is the limited crystallinity resulting from a fast quench while material leaving the hot nozzle and solidifying quickly at the low-temperature platform. As a result, the mechanical performances of 3D printed thermoplastic is normally inadequate in comparison with conventionally manufactured ones (e.g., from injection molding). In this work, we developed two strategies for reinforcing and functionalizing 3D printed thermoplastic composites using cellulose nanofibers (CNFs) as nanofillers. Firstly, L-lactide monomers were grafted onto CNFs via ring-opening polymerization. The synthesized poly(lactic acid) grafted cellulose nanofibers (PLA-g-CNFs) compounded with Poly(lactic acid) (PLA) pellets improved storage modulus of the composite in both glassy state (low temperature) and rubbery state (high temperature). Dynamic mechanical analysis, including temperature ramp, frequency sweep, and creep-recovery, confirmed the enhancement of annealed composites to viscoelastic factors. Secondly, we converted CNFs into carbonized CNFs (CCNFs) through pyrolysis. When integrated with carbon black (CB) and polycaprolactone (PCL) matrix, the CCNF-CB-PCL conductive composites found applications for reinforcing, conducting, electromagnetic interference shielding, and deformation sensing. CCNFs also have superior dielectric properties. When irradiating CCNF-PLA composites with microwave, high dielectric loss CCNFs selectively absorbed microwave energy and generated localized heat in the surrounding regions. Such heat transferred to the adjacent PLA, triggering PLA chains to repack and form crystallites, and as a result, enhancing crystallinity as well as mechanical.

Date

3-18-2019

Committee Chair

Wu, Qinglin

Available for download on Monday, June 01, 2020

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