Date of Award
Spring 5-12-2023
Document Type
Thesis
Degree Name
Master of Science in Chemistry (MSChem)
Department
Chemistry
First Advisor
Dr. Jeanne H. Norton
Second Advisor
Dr. Charles Neef
Third Advisor
Mr. Paul Herring
Abstract
Within recent years, 3D printing within the plastics and polymer industries has becoming increasingly prevalent. Also known as additive manufacturing, 3D printing enables the creation of rapid prototypes for short production runs without the need for complex tooling. This allows for runs that are shorter and lower in cost than conventional processes. Polylactic acid (PLA) is a thermoplastic that is widely used in 3D printing for its mechanical properties and low cost. The qualities of PLA however are lacking in the areas of flexibility and toughness which is required in many prototyping scenarios. The solution to this is to incorporate TPU (thermoplastic polyurethane) within the matrix of PLA to address the issue with flexibility. There is another issue that arises with incorporating TPU within the PLA matrix. These materials are immiscible which poses a problem with creating filament within the needed specifications. The goal of this work was to blend PLA and TPU to create a 3D printer filament that exhibits the desirable properties from each material. An additional goal was to optimize the filament diameter to increase compatibility with the feed throat of the 3D printer, which allows for increased consistency of parts.
During the extrusion process, parameters such as screw speed, winder settings, and barrel temperatures were adjusted to try and create circular filament within the set specifications of 1.75 mm (+/- 0.05 mm). Both PLA and TPU were extruded at various ratios by weight percentage. Single-screw extrusion was performed on a Yellow Jacket single-screw extruder in processing labs at Pittsburg State University. After processing, filament was analyzed for its thermal, mechanical, and morphological properties. The methods used for thermal analysis were
differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and melt flow index rheology. TGA was performed to determine degradation onset of the blends and DSC was performed to determine glass transition temperatures and melting temperatures of the crystalline fractions. Mechanical properties were analyzed via Instron tensile testing. Blends increasing in TPU percentage exhibited a change in strength and flexibility. Morphological analysis was performed via scanning electron microscopy (SEM). Furthermore, the transition between thermoplastic behavior and elastomeric behavior with increasing TPU corporation was studied. In prior studies, glass transition temperatures and filament moduli shifted to values similar to TPU when the blend ratio was above 50% TPU. The filament was successfully produced and exhibited properties intermediate to PLA and TPU.
After filament was created successfully via single-screw extruder, filament blends were then created via twin-screw extrusion. This was done in order to determine if processing methods had a significant impact on filament blend properties. Various parameters, such as screw speed, hopper speed, zone temperatures, and winder speed were adjusted to achieve a filament within the desired specifications. Filament extruded via twin-screw extrusion was analyzed for thermal, mechanical, and morphological properties. Twin-screw filament was analyzed by the same thermal and mechanical methods as single-screw filament. The filament produced via twin-screw extrusion was within the specified diameter and was more dimensionally stable than filament produced by single-screw extrusion. Twin-screw extruded filament had less variation in melt pressure than filament produced by single screw extrusion. Thermal stability of filament blends was consistent regardless of processing methods. Mechanical analysis concluded that the modulus of twin-screw filament was slightly lower than single-screw filament. Melt flow index
of pellets was significantly higher in single-screw extruded pellet than twin screw extruded pellet.
Further work added an additional processing step: injection molding. Thermal, mechanical, and morphological analyses were also performed on specimens produced via injection molding. Injection molded samples were analyzed by the same thermal and mechanical methods as single-screw and twin-screw filament. Impact testing was added, as we were able to produce impact bars in addition to tensile testing dog bones in the injection molder. Finally, we were able to 3D print dog bones using the filament produced by single-screw and twin-screw extrusion. Dog bones were tested for tensile strength after printing and compared to injection molded dog bones.
Recommended Citation
Long, Matthew, "OPTIMIZING PROCESS CONDITIONS AND CHARACTERIZING ELASTOMERIC PROPERTIES OF IMMISCIBLE POLYMERS FOR 3D PRINTING APPLICATIONS" (2023). Electronic Theses & Dissertations. 450.
https://digitalcommons.pittstate.edu/etd/450