Biodegradation of 3D-Printed Biodegradable/Non-biodegradable\nPlastic Blends

Abstract

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