Reprocessability of PLA through Chain Extension for Fused Filament Fabrication

Abstract

As additive manufacturing (AM) technologies have been gaining popularity in the plastic processing sector, it has become a major concern to establish closed-loop recycling strategies to maximize the value of the materials processed, therefore enhancing their sustainability. However, there are challenges to overcome related to the performance of recycled materials since, after mechanical recycling, the molecular degradation of thermoplastics shifts their performance and processability. In this work, it was hypothesized that the incorporation of a chain extender (CE) during the reprocessing would allow us to overcome these drawbacks. To attest this conjecture, the influence of 1,3-Bis(4,5-dihydro-2-oxazolyl)benzene (PBO), used as a CE, on mechanical, thermal, and rheological properties of polilactic acid (PLA) was studied. Furthermore, a closed-loop recycling system based on Fused Filament Fabrication (FFF) was attempted, consisting of the material preparation, filament extrusion, production of 3D components, and mechanical recycling steps. PBO partially recovered the recycled PLA mechanical performance, reflected by an increase in both tensile modulus (+13%) and tensile strength (+121%), when compared with recycled PLA without PBO. Printability tests were conducted, with the material’s brittle behavior being the major constraint for successfully establishing a closed-loop recycling scheme for FFF applications.

Materials Requirements in Fused Filament Fabrication: A Framework for the Design of Next‐Generation 3D Printable Thermoplastics and Composites

“…[315] Besides thermoplastic waste from conventional recycling bins, [316] waste printing materials can also be collected and re-extruded into printed filaments, so that a "closed-loop" strategy can be established. [317] As pointed by Mikula et al [318] in their comprehensive review, the ability to re-manufacture 3D printed materials is critical, since AM is still frequently employed as a rapid prototyping tool, which results in a large volume of single-use objects. Moreover, on-site recycling of 3D printing materials into filaments that can be used again for printing (distributed recycling) would mitigate pollution from transportation to centralized collection points.…”

“…[ 315 ] Besides thermoplastic waste from conventional recycling bins, [ 316 ] waste printing materials can also be collected and re‐extruded into printed filaments, so that a “closed‐loop” strategy can be established. [ 317 ] As pointed by Mikula et al. [ 318 ] in their comprehensive review, the ability to re‐manufacture 3D printed materials is critical, since AM is still frequently employed as a rapid prototyping tool, which results in a large volume of single‐use objects.…”

Physical, Mechanical, and Thermal Properties and Characterization of Natural Fiber Composites Reinforced Poly(Lactic Acid): Miswak (Salvadora Persica L.) Fibers

“…Since PLA is costly, has inferior water barrier qualities to more common thermoplastics like PP, and has low heat stability, it is not utilized to produce toothbrushes [71,110,[112][113][114]. However, great attempts have been made to alter PLA's performance to increase its temperature tolerance and mechanical strength as well as to adapt it to increase its uses in high-end markets [72,110,[114][115][116][117][118].…”

Impact of Melt Processing Conditions on the Degradation of Polylactic Acid

“…This degradation process leads to the formation of cyclic polylactic acid oligomers and lactic acid, which is catalyzed by the presence of monomers, oligomers, and hydroxyl groups [ 14 ]. These degradation mechanisms produce significant reductions in molecular weight and narrowing of the molecular weight distribution, which deteriorates the mechanical properties, changes the rheological and crystallization behavior, and causes yellowing of the processed polymer [ 15 , 16 , 17 ]. In addition, other drawbacks of PLA include poor gas barrier properties, low toughness and ductility, and high cost [ 18 , 19 ].…”