Controlling the properties of parts 3D printed from recycled thermoplastics: A review of current practices. (February 2022) - Gomes, Tiago EP
Highlights: The properties of thermoplastics used in material extrusion additive manufacturing can be severely affected by thermo-mechanical reprocessing, resulting in a limitation for their recycling potential. Literature shows that, in a distributed recycling context, material degradation can be mitigated or compensated for, in different ways. Advantages and limitations of the application of each upgrading technique are identified and paths for future research, suggested. Abstract: In a world going through a plastic waste management catastrophe with serious environmental, health, social and economic consequences, the ideal step forward would be the creation of circular flows of material which allow for the materials to remain in the value-chain for as long as possible and completing multiple lifecycles. In the case of thermoplastics, a new recycling route is emerging, made possible by Material Extrusion additive manufacturing (MEX): distributed recycling. However, similar to what happens with mainstream recycling of these materials, the thermo-mechanical processes involved, as well as other factors such as exposure to UV-light, result in waste streams with degraded properties. This way, the possible range of applications and functionality of the polymers is reduced along with number of viable lifecycles. On this scope, the application of methods to control and modify the properties of the polymers, enhancing them or compensating for the degradation in a distributed recycling context, becomes important. Not only is this an emerging, less explored recycling route with great potential to complement the existing ones, but it also presents its own set of challenges and advantages to be explored. In this work, a systematic search methodology is followed to conduct a literature review on which the current practices on the modification and control of properties of parts produced from recycled or reprocessed thermoplastics through MEX are assessed. Research gaps and opportunities are presented from the discussion of the results.