Increased Interlayer Adhesion of Additively Manufactured Parts
Open Access
- Author:
- Yost, Sierra
- Graduate Program:
- Chemical Engineering
- Degree:
- Master of Science
- Document Type:
- Master Thesis
- Date of Defense:
- November 09, 2022
- Committee Members:
- Bryan D Vogt, Thesis Advisor/Co-Advisor
Christopher Arges, Committee Member
Seong Kim, Professor in Charge/Director of Graduate Studies
Christian W. Pester, Thesis Advisor/Co-Advisor
Stephen C Chmely, Committee Member - Keywords:
- polymers
additive manufacturing
3d printing
anisotropy
vitrimers - Abstract:
- Materials extrusion (MatEx) polymerization is a commonly used type of additive manufacturing (AM) that uses thermoplastic polymers. Compared to other forms of AM, MatEx is less expensive, more user-friendly, and is more versatile in terms of the range of polymers and composites that can be printed. One of the largest disadvantages of MatEx is the anisotropy of the parts, due to limited interlayer diffusion during printing. In this thesis, the merits of utilizing molecular weight distribution and polyurethane vitrimers for increasing interlayer adhesion of 3D printed parts will be discussed. Incorporating lower molecular weight polymer chains in the filament increases the rate of diffusion between the layers, increasing the strength between them and the ductility of the entire part. The addition of high molecular weight polymer chains increases tensile strength to the entire part due to the increase of polymer entanglements. By creating a trimodal molecular weight distribution in a filament, both the high molecular weight and the low molecular weight chains can be utilized to strengthen the printed parts and reduce their anisotropy. Vitrimers are a type of covalent adaptable network that will act as both a thermoplastic and a thermoset, depending on the temperature of the system. Above the topology freezing transition temperature (Tv) the crosslinks in the network will exchange fast enough for the vitrimer to flow. Below Tv, the exchanges are so slow that the vitrimer acts like a thermoset. The crosslinking network is associative, so the crosslinking density is constant. When printed, the crosslinked network can diffuse between the layers because of the crosslinking exchange, then when the part cools, the thermoset-like network will be set between the layers, increasing the isotropy of the printed part.