Fused deposition modeling (FDM) is gaining an ever increasing attention for its ability to fabricate complex geometry parts and prototypes at lower cost. The technology is striving to produce parts with high mechanical resistance that can withstand and perform under high stress environment. The adhesion strength between layers, transverse strength, is a limiting factor that need to be quantitatively evaluated to further understand and improve the bonding behavior of thermoplastic polymer in FDM. This interfacial adhesion is derived by the diffusion and penetration of polymer chains across the interface allowing the chain entanglement to form a bonding medium.
This study investigates the bonding behaviour of polylactic acid (PLA) as a function of chain branching. The adhesion strength is quantitatively evaluated by developing and performing a peel test of a two-printed layer samples. It is possible to increase chain branching of PLA by bulk modification with epoxy chain extender. The modification of PLA was carried out using an internal batch mixer with four different concentrations of chain extender. The modified PLA was processed into print filament and characterized by parallel plate rheometry and DSC.
It was found that the addition of chain extender increased molecular weight and degree of branching of PLA and in return the peel testing results reflected a significant increase in adhesion strength. Such improvement can be attributed to the long branched chains of PLA and its ability to create entanglements between layers. These findings can help in producing better PLA filaments to provide a higher stress resistance for FDM fabricated functional parts. / Thesis / Master of Applied Science (MASc) / Fused Deposition Modeling (FDM) is a recent popular method of plastic 3D printing technique, in which plastic filament is heated to a molten state to be then deposited through a layer-by-layer fashion to successfully fabricate parts. One of the drawbacks of that technology is the low bonding strength developed between layers as compared to strength along the length direction of layers. This study focuses on developing a testing methodology to evaluate the adhesion strength between layers and altering the material structure to maximize such strength. Four types of polylactic acid with different degrees of chain branching were successfully processed, printed and tested. Material with higher degree of branching yielded higher adhesion strength.
| Identifer | oai:union.ndltd.org:mcmaster.ca/oai:macsphere.mcmaster.ca:11375/22215 |
| Date | January 2017 |
| Creators | Alturkestany, Mohammed |
| Contributors | Thompson, Michael, Chemical Engineering |
| Source Sets | McMaster University |
| Language | English |
| Detected Language | English |
| Type | Thesis |
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