Aerobic biodegradation of 3D printed biocomposites containing polylactic acid and industrial residual forest biomass

Abstract

This study investigates the biodegradation of 3D printed biocomposites under aerobic composting conditions. Biodegradable containers were prepared using forest biomass, wood ash (WA), wood sawdust (WS), and cellulose fiber (CF), as fillers and polylactic acid (PLA) as matrix and were processed via fused filament fabrication (FFF). Biodegradability tests were conducted in a laboratory-scale installation using the compost burial method for three months. Weight loss measurements were measured every 7 days throughout testing. The physicochemical and morphological properties of the samples were characterized. Of the biocomposites, PLA with 20 wt% wood sawdust showed the highest water absorption. The kinetic mechanisms followed typical Fickian diffusion behavior. The crystallinity improved with the addition of 20 wt% cellulose fibers. PLA degrades in a two-step process. Initially, temperature and moisture break down the PLA chains into lactic acid monomers. Subsequently, microorganisms in the compost convert these compounds into carbon dioxide, water, and biomass. A 97 % PLA weight loss was achieved after 3 months, with added fillers decreasing the biodegradability rate. Cracks on the surface and color changes were noted. Microorganisms were observed to settle in the spaces between the layers created by 3D printing. Fourier transform infrared spectra, scanning electron microscope micrographs, and synchrotron X-ray microtomographs revealed a microbial biofilm layer on the sample surfaces. After biodegradation, biocomposites can serve as soil fertilizer. Therefore, 3D printed biodegradable containers offer eco-friendly solutions that help minimize agricultural plastic waste accumulation and lower greenhouse gas emissions.