Standardization of recycled plastic materials for additive manufacturing

Polymer extrusion-based additive manufacturing (AM) or 3D printing is a process that creates an object from a 3D model, a feedstock polymeric material in the form of wires or pellets, and a 3D-printer equipped with an extruder. Recycled polymeric materials can be used as feedstock for this technology. This thesis aims to enhance the quality of some plastic wastes to meet the standardized thermal and mechanical properties and make them suitable for 3D printing. In the modern manufacturing revolution, which follows the concept of "Industry 4.0", AM plays a key role as an enabling technology, allowing objects with almost any geometry to be created in a more direct way. Material extrusion-based AM can be divided into fused filament fabrication (FFF) and fused granular fabrication (FGF). FFF uses high-quality filament that is not too brittle nor too flexible and has a specific and constant diameter. Therefore, only certain materials with the appropriate mechanical properties could be processed by FFF. In contrast, the FGF method is not so limited by the variety of materials, as all industrial polymers can be found as pellets. Moreover, the preparation of feedstock for FGF eliminates the second thermal processing for wire production, which always results in the reduction of the polymer's molar mass. The most famous polymer for 3D printing is polylactide acid (PLA). It is a biodegradable and renewable thermoplastic polyester derived from renewable sources (mainly starch and sugar). The slow degradation rate in natural environments could lead to PLA accumulation. One way to utilize PLA waste is composting. But this method is used to degrade industrial waste, where a large amount of waste is collected every day, which is not the case for PLA at present. Also recycling the scraps for AM is interesting to save costs because PLA is an expensive polymer, and the construction of composting facilities currently involves large capital investments. In addition, an analysis of the normative base of AM in the polymer sphere revealed that ISO and ASTM organizations only developed seven standards for polymers in AM, without specifying the type of polymer. To achieve the goal of the thesis study, a series of three interrelated experiments was performed. The first experiment on accelerated thermal and hydrothermal ageing of PLA was aimed at studying the temporal dynamics of polymer degradation. Thus, it was found that hydrothermal ageing for 1344 h, which corresponds to more than 1.5 years of operation under real conditions, leads to a significant decrease in the tensile strength of PLA samples. Based on these results, PLA waste from 3D printing up to 1.5 years old from the date of printing was collected for the second experiment. This debris was mixed with pure PLA in proportions of 25%, 50% and 75%, respectively. The results of this experiment showed that a material based on pure and recycled PLA is a feasible material for FFF. In the last experiment, the properties of the mixtures received in the previous research were modified by adding titanium dioxide nanoparticles, and the samples were printed using FGF. The nanocomposite based on primary and secondary (recycled) PLA with the addition of 7% titanium dioxide nanopowder has similar thermal and mechanical properties to the primary polymer, considering the standard deviation. Finally, to ensure the quality of the received nanocomposite and the reproducibility of the properties, the quality indicators have been documented in an organization standard. Thus, in this work, it has been experimentally proved that using recycled PLA for extrusion-based AM is a realistic and achievable task, able to produce parts with improved comparable thermal and mechanical properties to those of primary PLA.

Author dc:creator

• Bergaliyeva, Saltanat

Advisors dc:contributor.advisor

• Sales Lérida, David
• Bolegenova, Saltanat

Statement dc:rights

• Attribution-NonCommercial-NoDerivatives 4.0 Internacional

Licence dc:rights.uri

• http://creativecommons.org/licenses/by-nc-nd/4.0/

Language dc:language.iso

eng

Handle dc:identifier.uri

http://hdl.handle.net/10498/31687

OAI identifier oai:identifier

oai:rodin.uca.es:10498/31687