Design and Synthesis of Polymer Nanocomposites for Additive Manufacturing

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May 2023

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Abstract

Additive manufacturing or 3D printing is a process where the materials are deposited in a layer- by-layer fashion according to a pre-designed computer aided file to fabricate required geometries. There are a wide range of materials from thermoplastics, polymeric resins, metals, alloys, nanocomposites, to hydrogels that have been used in 3D printing, as well as several different types of processes are available for 3D printing. Fused filament fabrication, ink jet printing, stereolithography (SLA) and digital light projection (DLP) can be recognized as the most popular and affordable techniques. This manufacturing technique is very promising as a user friendly, customizable setup without the need to manufacture through expensive molding processes or producing waste from subtractive manufacturing methods such as milling. Even though it possesses all the advantages, poor interlayer adhesion, limited mechanical properties, low resolution and rough surface finish is limiting its applications at large scale. Vat photopolymerization 3D printing techniques provide better resolution as high as 10 μm for the printed parts from SLA and DLP compared to other 3D printing techniques. Here, a photo resin that contains photocurable monomers and oligomers, crosslinkers are polymerized in a print vat using UV irradiation in the presence of a photoinitiator. The photo printed structures show fine resolution and smooth surface finish, yet the mechanical properties of the printed parts are inadequate for end use applications. To address this limitation different approaches were taken and studied, thus the overall goal of this research was to enhance properties of 3D printed objects and to develop methodologies to improve photo printing processes that would ultimately improve intrinsic properties of the photo printed materials. Chapter 1 of the dissertation provides a literature review about 3D printing techniques, materials, and the limitations of additive manufacturing. This chapter further discusses the approaches taken to overcome the limitations by introducing ways to improve the mechanical properties. Chapter 2 describes our work in enhancing mechanical properties through a nanofiller derived from Kevlar and how we successfully 3D printed photoresin formulations using stereolithography without compromising printability. We discuss a methodology that can be used to incorporate unprocessable fibrous fillers in a resin formulation. Chapter 3 provides insights about how supramolecular interactions provide 3D printable materials with noncovalent cross-linking and stimuli-responsive properties to improve their processability and functionality. We evaluated urea formulations with aliphatic and aromatic sidechains and showed physical evidence for the presence of hydrogen bonding using variable temperature Fourier transform infrared (VT-ATR-FTIR) spectroscopy and van’t Hoff analysis. The self- healing efficiency of these formulations was characterized by measuring the recovery of their tensile mechanical properties. Chapter 4 describes our approach to process Metal Organic-Frameworks in vat photopolymerization. A new method is introduced to construct complex structures with fine features by integrating high loading weight percentages of MOF crystals to a photocurable acrylate formulation. Through free radical polymerization in a DLP setup, MOF loaded nanocomposites were 3D printed, and its catalytic performances were studied.

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Chemistry, Organic

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