Additive manufacturing enabled by frontal polymerization

Aw, Jia En

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https://hdl.handle.net/2142/115741 Copy

Description

Title

Additive manufacturing enabled by frontal polymerization

Author(s)

Aw, Jia En

Issue Date

2022-04-22

Director of Research (if dissertation) or Advisor (if thesis)

• Sottos, Nancy R
• Geubelle, Philippe H

Doctoral Committee Chair(s)

• Sottos, Nancy R
• Geubelle, Philippe H

Committee Member(s)

• Ewoldt, Randy H
• Baur, Jeffery

Department of Study

Aerospace Engineering

Discipline

Aerospace Engineering

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

Ph.D.

Degree Level

Dissertation

Keyword(s)

• 3D printing
• thermoset
• frontal polymerization
• additive manufacturing
• direct ink writing
• mechanical isotropy
• dicyclopentadiene
• DCPD
• poly(dicyclopentadiene)
• pDCPD
• complex structures
• print fidelity
• free-form printing
• self-regulating
• oxidation
• shape-change
• shape control

Abstract

Additive manufacturing (AM) has emerged as a promising alternative to traditional manufacturing methods due to several advantages, including better design flexibility, precise control over complex geometries, substantial material savings, and an ability for customization. Although significant progress has been made in polymer AM over the past two decades, the 3D printing of high-performance polymers with intricate designs remains a key challenge. Frontal polymerization (FP) was recently demonstrated as a rapid, energy-efficient, and scalable curing strategy capable of producing high-performance engineering polymers. This dissertation describes the advancements in harnessing FP for 3D printing, thus enabling synchronous filament curing during the printing process. Our results show a robust direct ink writing (DIW) technique useful for rapid fabrication of complex architectures. The printed thermoset polymer (poly(dicyclopentadiene), pDCPD) exhibits high-performance properties — high strength, stiffness, plasticity, and thermal stability — which finds broad applicability in many industries including energy, marine, automotive, and aerospace. The direct-writing of frontally polymerizing resin is achieved with a dicyclopentadiene (DCPD) ink. This ink formulation was tuned to ensure that it exhibited the following key rheological characteristics critical for FP printing: (1) distinct shear-thinning behavior for extrudability, (2) a moderate relaxation response for shape retention of printing filaments, and (3) pronounced extensibility to resist the rupturing of filaments. Simultaneous free-form 3D printing and in-situ curing permitted the fabrication of a range of complex architectures. The shape fidelity of the prints is characterized to highlight the precise shape control possible in FP-based direct ink writing (FP-DIW). A self-regulative system is uncovered in FP-DIW in which the curing behavior of the DCPD ink is coupled to the processing conditions. The synergistic interactions between the cure kinetics and printing mechanics resulted in the autonomous compensation for variations in printing speed and environmental conditions (bed temperature). The self-regulating behavior is critical for high-fidelity printing because it enabled sensing and real-time optimization with respect to processing parameters at every stage of the print. Processing maps which define the limits of this self-regulating behavior are experimentally determined and computationally reproduced. These processing maps offer insight on the selection of appropriate parameters for direct-writing of various geometries. A primary concern for additively manufactured parts is the knockdown in mechanical and physical characteristics due to inhomogeneous stresses, insufficient curing, oxidation degradation, defects, etc. FP-printed pDCPD parts are fully cured and do not require post-processing treatments. With the addition of an antioxidant to suppress the surface oxidation can incur in FP-DIW, both thermal and mechanical properties (tensile in longitudinal and transverse direction) of the printed specimens were comparable to the properties of traditional mold-fabricated pDCPD. The mechanical isotropy, scalability, time and cost savings accomplished by FP-based 3D printing compared to traditional manufacturing indicates that it is a suitable manufacturing alternative for high-performance engineering parts. We also investigate the use of FP to achieve shape control at the millimeter scale. Morphological changes observed in a 2-mm wide DCPD resin droplet — the hemispherical droplet transformed into a conical shape as it frontally polymerized — are attributed to volumetric thermal expansion. Experimental results and computational simulations corroborate the effects of multiple processing parameters (bed temperature, resin degree of cure) on the polymerization behavior and the final droplet profile. The shape-morphing phenomenon described herein further our understanding on FP-induced shape control which could be useful in the development of other microfabrication techniques (e.g., polyjet 3D printing of texturized surfaces).

Graduation Semester

2022-05

Type of Resource

Thesis

Copyright and License Information

Copyright 2022 Jia En Aw

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