Development of toughened PLA filaments by blending with alcoholized PLA-cured epoxidized natural rubber for 3D-printing application

Polylactide (PLA) has become a promising alternative to petroleum-based polymers. However, this has a major drawback as its inherent brittleness limits its use in certain applications. Toughening of PLA by blending with various elastomers have been widely investigated, pertaining to its eco-friendly and cost-effective benefits. In our lab, a chemical recycling process of PLA wastes has been developed by alcoholysis reaction, which yields glycolyzed PLA oligomers (GPLA). In this study, the GPLA products are employed as curing agents for epoxidized natural rubber (ENR), which were then used as toughening agents for PLA resin for use in 3D-printing applications. ENR with 25% degree of epoxidation was used in the reaction with the OH-capped GPLA by using a reactive melt-blending technique in an internal mixer. The effects of GPLA/ENR25 feed ratio on the structures and properties of the resulting GPLA-cured ENR products (GENR) were examined by varying the ratios from 1:1, 1:2, and 1:4 (referring to GENR14, GENR12 and GENR11, respectively). The resulting GENR samples were then blended with neat PLA resin at different GENR contents from 5 to 30%wt. Mechanical and physical properties, phase compatibility and morphology of the blends were examined. Improvements in the toughness were observed, compared to those blended with neat ENR, due to the ductility of the rubber phase and enhanced compatibility from the GPLA segments. The incorporation of 20%wt GENR12 possessed the smallest rubber domains dispersed in the PLA matrix (1 µm), reflecting enhancements in the phase compatibility.PLA-GENR12 blends was selected for extruding as monofilaments with 1.75mm extruder die at different extrusion speeds of 35 and 50 rpm (referring to PGE35 and PGE50, respectively) in a range of extrusion temperature from 140 – 165 oC. However, the optimization of processing needs to be reconsidered to obtain uniform filament diameter at 1.75 mm of 3D filament standard. Izod impact specimens were printed with different printing orientations to examine the printing performances and toughness of the printed products. The prepared filaments can be successfully printed in the flat and on edge orientations, while the up-right orientation cannot be printed due to shape distortion. It was found that the printed specimens of PGE50 filaments exhibited an acceptable printing performance and higher impact strength than others filaments (p-PLA and c-PLA filament). The printed PGE50 impact specimen showed the highest impact strength at 31.6 ± 1.4 J/m with an on-edge printing orientation, which was highly competitive to injection molded neat PLA specimens (33 ± 1.0 J/m of impact strength). Therefore, the blended PLA/GENR12(80/20) material show high potential as new promising material as monofilaments for 3D-printing applications, pertaining to their minimized raw material consumption and environmentally-friendly aspects.