07/11/2024
By Danielle Fretwell
Candidate Name: AA Mubasshir
Degree: Doctoral
Defense Date: Thursday, July 25, 2024
Time: 10 a.m. - 12 p.m.
Location: ETIC 345
Committee:
Advisor: Joey Mead, Professor, Plastics Engineering, University of Massachusetts Lowell
Committee Members*
1. David Kazmer, Professor, Plastics Engineering, University of Massachusetts Lowell
2. Anson Ma, Associate Professor, Chemical Engineering, University of Connecticut
3. Davide Masato, Assistant Professor, Plastics Engineering, University of Massachusetts Lowell
4. Jay H Park, Assistant Professor, Plastics Engineering, University of Massachusetts Lowell
Brief Abstract:
Integration of fully compounded thermoset elastomers or traditional rubber compounds in additive manufacturing offers exciting possibilities to combine the unique material properties of rubber compounds with the unique characteristics of additive manufacturing, such as design freedom, rapid prototyping, and in-situ fabrication. However, material extrusion additive manufacturing (ME AM) for fully compounded thermoset elastomers is a young field with processing and material-related challenges that prevent the technology from being used in industrial and consumer-scale applications. This dissertation identifies some of the critical challenges associated with using fully compounded thermoset elastomers (traditional rubber compounds) for ME AM applications, derives solutions to these challenges while maintaining minimum compromises to the properties of the original rubber formulations, and finally validates the derived solutions by successfully applying them to other rubber compounds.
This thesis is divided into three chapters. The first chapter identifies critical challenges associated with fully compounded thermoset elastomer for ME AM applications by studying a Nitrile Butadiene Rubber (NBR) compound. Poor printability in the form of substantial shrinkage in the print direction post-print and cured, poor adhesion among adjacent layers, and insufficient processing window were identified as critical challenges. A four-step continuous improvement strategy was successfully employed to mitigate the challenges mentioned above, while minimizing the changes to the original NBR. This strategy successfully transformed the conventional NBR compound into a 3D printable NBR compound. The first chapter investigated the impact of specific modifications (rubber viscosity, filler content, curing agent content, and addition of scorch retarder) on a conventional NBR compound and its printability.
Knowledge from the first chapter was applied to solve similar printability challenges for two other rubber compounds, namely an Ethylene Propylene Diene Monomer (EPDM) rubber compound and a fluoroelastomer (FKM) rubber compound in the following two chapters.
In Chapter Two, a conventional EPDM rubber compound was transformed into a 3D printable material system by successfully applying the strategy learned in Chapter One. Chapter Two also discusses the impact of different cure systems (sulfur vs peroxide) on NBR and EPDM compounds' 3D printability and mechanical properties.
Finally, in Chapter Three, the strategy for transforming conventional thermoset elastomer compounds into a 3D printable material system was applied to an FKM rubber compound. The effects of a perfluoropolyether (PFPE) plasticizer as a viscosity modifier were evaluated, and its effects on printability, interlayer adhesion, and mechanical properties are discussed.
Rubber 3D printing technology shows immense potential for use in a variety of applications, such as seals, footwear, and automotive industries. This dissertation contributes to a deeper understanding of the behavior of conventional thermoset elastomers in the ME AM processing technique. It shows a general strategy for developing 3D printable rubber compounds and successfully applies this strategy to three different rubber compounds, namely NBR, EPDM, and FKM. It also extends the knowledge on the effects of different components of a rubber compound, such as base rubber, curing agent, reinforcing fillers, plasticizers, and scorch retarders, on the overall printability and part properties.