Assessing the anaerobic biodegradability of PHB filament and its 3D printed sheets through biochemical methane...

The incorporation of biodegradable polymers into additive manufacturing offers a promising pathway to reduce reliance on petroleum-derived materials and close the loop in circular manufacturing systems. This study aimed to evaluate how fused deposition modelling (FDM) processing affects the anaerobic biodegradability of poly(3-hydroxybutyrate) (PHB) by comparing filament and 3D-printed sheet samples. PHB samples were characterized by Fourier Transform Infrared Spectroscopy (FTIR) and X-ray Diffraction (XRD) to quantify changes in chemical bonding and crystallinity, revealing an increase from 40.9 % in the filament to 61.8 % in the 3D-printed sheet. Biochemical Methane Potential (BMP) tests, conducted at 38 °C with acclimatized anaerobic sludge (inoculum-to-substrate ratio 2.85 g VS/g VS), measured cumulative methane production over 50 days according to ASTM D5511-18 protocol. Theoretical methane yields, calculated from elemental analyses, served as benchmarks. Results showed that the filament attained 78.24 % biodegradation in 42 days (corresponding to 389 mL CH₄/g VS), whereas the 3D-printed sheet reached only 70.35 % in 49 days (equivalent to 350 mL CH₄/g VS), indicating an 8 % reduction in conversion and a 10 % lower methane yield for the printed form. This variability is attributed to processing-induced recrystallization, which limits water penetration and enzymatic access in more crystalline regions. To the best of our knowledge, this is the first study to determine the biodegradability of 3D-printable PHB filament and its 3D-printed counterpart using the Biochemical Methane Potential (BMP) assay. As we demonstrated, the decreased biodegradability of the 3D-printed part compared to the filament is likely due to increased crystallinity induced during processing. This insight will aid in designing material formulations and processing strategies that balance printability and end of life biodegradability, advancing the development of truly sustainable additive manufacturing solutions.