Blends of modified PLA and biopolyamides for additive manufacturing
(English) The main objective of this work is to counteract the limitations of polylactic acid (PLA) and propose a sustainable manufacturing approach using bioblends of a rheologically modified PLA by reactive extrusion (RExPLA) with predominantly biobased polyamides (BioPA), namely PA10.10 and PA6.1...
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| Tipo de recurso: | tesis doctoral |
| Estado: | Versión publicada |
| Fecha de publicación: | 2023 |
| País: | España |
| Institución: | CBUC, CESCA |
| Repositorio: | TDR. Tesis Doctorales en Red |
| OAI Identifier: | oai:www.tdx.cat:10803/690306 |
| Acceso en línea: | http://hdl.handle.net/10803/690306 https://dx.doi.org/10.5821/dissertation-2117-404652 |
| Access Level: | acceso abierto |
| Palabra clave: | Àrees temàtiques de la UPC::Enginyeria dels materials 620 |
| Sumario: | (English) The main objective of this work is to counteract the limitations of polylactic acid (PLA) and propose a sustainable manufacturing approach using bioblends of a rheologically modified PLA by reactive extrusion (RExPLA) with predominantly biobased polyamides (BioPA), namely PA10.10 and PA6.10. The study was divided in three phases. The first one focuses on the preparation and characterization of bioblends prepared by internal mixer in compositions that ranged from 10% to 50% w/w of BioPA. The aim of the study was to assess the morphological, thermal, and mechanical modifications achieved by modifying the rheological behavior of the matrix. Regardless of the matrix or BioPA, when using a 30% w/w of BioPA the blend showed a ductile behavior. The use of RExPLA resulted in finer morphologies with enhanced mechanical properties. Specifically, RExPLA/PA10.10 bioblends achieved the brittle-to-ductile transition with only 10 wt% and the phase inversion was observed at a 40% w/w of BioPA. Meanwhile, in the other bioblends this situation was not observed in the composition range studied. According to the results of mechanical test, the compositions that offered better balance of performance was 20% and 30% w/w of PA10.10. In terms of thermal behavior, the use of PA6.10 seems to promote PLA crystallization. The second phase focuses on the preparation by twin-screw extrusion of the blends with the compositions previously selected (20% and 30% w/w of PA10.10) and the study of the induction of microfibrillation of the PA phase. Rheological analyses were performed on the parent polymers to assess the microfibrillation potential of PA. The effect of processing conditions, including screw rotation rate (30 and 100 rpm) and take-up rate, were evaluated to establish three draw ratios (DR) on the extruded filaments to determine the microfibrillation potential of the BioPA phase, during compounding of the blends. A preliminary evaluation shows that 20% w/w of PA could not generate a stable microfibrillated morphology; so the study focused on the composition 30% w/w. When RExPLA was used as the matrix, PA microfibrillation was achieved regardless of the applied DR, whereas for unmodified PLA bioblends a higher DR was required. Dynamic mechanical thermal analysis (DMTA) revealed that the use of RExPLA resulted in improved mechanical performance in the rubbery region due to the PA microfibrillation obtained. This microfibrillation morphology seems to improve the PLA crystallization process during the refrigeration stage. The third phase focuses the feasibility of producing in situ microfibrillated composites (MFCs) of RExPLA/PA10.10 using Fused Filament Fabrication (FFF) with pellets as feedstock. The mechanical behavior and structural integrity using Crack Tip Opening Displacement (CTOD) of the bioblends was evaluated. Morphological observations demonstrated that FFF technique enabled the fabrication of in situ MFCs with PA microfibrils of high aspect ratios. According to the mechanical characterization results, it could be concluded that in conventional manufacturing methods the use of blends PLA/PA with a sea-island morphology often results in decreased strength and stiffness compared to neat PLA. However, by tailoring the morphology of PA phase to a microfibrillar structure, the detrimental effects on mechanical properties can be mitigated. Interestingly, when employing FFF as the manufacturing process, a finer microfibrillated morphology can be achieved, while still maintaining similar strength to the matrix with high values of ductility. Even more, the toughness exhibited remarkable improvement, as evidenced by a 206% increase in CTOD values compared to the matrix. In contrast, conventional compression-molding with a sea-island morphology yielded a 44% increase in CTOD values. |
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