Biodegradation of 3D-Printed Biodegradable/Non-biodegradable Plastic Blends

Abstract

Thermoplastic blends are applied for three-dimensional (3D) printing to obtain improved functionality. While thermal, chemical, and mechanical properties of 3D-printed blends are typically examined, biodegradability of the 3D-printed plastics has rarely been the focus of research. In this study, we evaluated the biodegradation behavior of 3D-printed prototypes fabricated from various plastics and blends, including biodegradable polylactic acid (PLA), poly(3-hydroxybutyrate) (PHB), non-biodegradable high-density polyethylene (HDPE), and polypropylene (PP). Letter-shaped specimens were prototyped using a fused deposition modeling (FDM) printer with various filaments (PLA, PHB, HDPE, PP, PLA/HDPE, PLA/PP, PHB/HDPE, PHB/PP, and PLA/PHB), and their printing performance and optimal printing conditions were evaluated. FDM 3D printing of HDPE and PP has been problematic due to poor adhesion, warping deformation, and crystallization-induced volume contraction. We demonstrate that PLA/HDPE and PLA/PP blends are printable, and PLA/PHB blends exhibit outstanding printing performance. Biodegradation tests on 3D-printed prototypes were performed employing a systematically designed respirometer by simulating (i) controlled composting and (ii) the aerobic aqueous environment. Neat PHB and PLA/PHB blends (50:50 wt %) showed significant biodegradation in controlled composting and an aerobic aqueous test (86.4, 85.0% and 73.3, 32.3%, respectively) in 50 days, while biodegradable/non-biodegradable blends (PLA/HDPE, PLA/PP, PHB/HDPE, and PHB/PP) were barely biodegraded. The immiscible biodegradable/non-biodegradable plastic blends revealed evidence of partial degradation and even antagonism to biodegradation, most likely due to phase separation and the barrier effect. Taken together, although PLA/HDPE and PLA/PP blends exhibited resistance to biodegradation, the low-cost polyolefins (HDPE and PP) as well as some notable improvements in mechanical properties render them promising FDM 3D printing resources. On the other hand, the outstanding printing performance, improved Young’s modulus, and synergetic biodegradation behavior indicate that the PLA/PHB blend can be an excellent fit for sustainable FDM printing resources.