Material Extrusion based Additive Manufacturing of Semicrystalline Polymers: Correlating Rheology with Print Properties

Filament-based material extrusion (MatEx) additive manufacturing has garnered huge interest in both academic and industrial communities. Moreover, there is an increasing need to expand the material catalog for MatEx to produce end use parts for a wide variety of functional applications. Current approaches towards MatEx of semicrystalline thermoplastics are in their nascent stage with fiber reinforcements being one of the most common techniques. MatEx of commodity semicrystalline thermoplastics has been investigated but most of the current methods are extremely material and machine specific. The goal of this dissertation is to enable MatEx of semicrystalline polymers with mechanical properties approaching that of injection molded parts. Tailored molecular architectures of blends that can control the crystallization kinetics from the melt state are investigated. By modifying the crystallization time window, the time during which chain diffusion can occur across the deposited layers is prolonged, which allows for a stronger bond between layers. Such differences in the crystallization process impact the z-axis adhesion and residual stress state, which directly affect mechanical properties and warpage in the printed parts. The impact of blend composition on polymer chain diffusion, crystallization profiles, and print properties resulting from the repeated non-uniform thermal history in filament based MatEx is studied. The melt flow behaviour is characterized using rheology and its effect on the interlayer adhesion of printed parts and print precision is explored. The extent of polymer chain re-entanglement post deposition on the printer bed is quantitatively determined using interrupted shear rheology protocols. Tensile bars are printed and mechanically characterized to analyze the tensile performance of the printed parts. Correlating the rheological findings with the mechanical performance of the printed parts provides valuable insights into the complex interlayer welding process during MatEx and is critical to improving existing machine designs and feedstocks in order to achieve printed parts with properties approaching their injection molded counterparts. The results will be essential in identifying optimal processing conditions to maximize material specific printed part performance as well as highlight the associated limitations to enable MatEx of next generation materials.

Name thesis:degree_name

Doctor of Philosophy

Level thesis:degree_level

doctoral

Discipline thesis:degree_discipline

Chemical Engineering

Department dc:contributor.department

Chemical Engineering

Grantor dc:publisher

Virginia Tech

Year dc:date.issued

2022

Author dc:creator

• Das, Arit

Chair dc:contributor.committeechair

• Bortner, Michael J.

Committee members dc:contributor.committeemember

• Baird, Donald G.
• Williams, Christopher Bryant
• Martin, Stephen Michael
• McKnight, Steven Hugh

• additive manufacturing
• material extrusion
• polymer diffusion
• rheology
• interlayer adhesion

Statement dc:rights

• In Copyright

Licence dc:rights.uri

• http://rightsstatements.org/vocab/InC/1.0/

Language dc:language.iso

en

Dc Identifier Other

vt_gsexam:35439

OAI identifier oai:identifier

oai:vtechworks.lib.vt.edu:10919/111785