Changes in Chemical and Physical Properties of Bio-based Thermoplastics During Fused Deposition Modelling (FDM) Process

The purpose of this research was to better understand the potential degradation effects of bioderived thermoplastic polymers during fused deposition modeling (FDM). Commercially available filaments made from virgin and recycled polylactic acid (PLA) (named PLA-1 and PLA-2, respectively), as well as a wood flour/PLA composite (PLA-3), were considered. Pre-optimized conditions, satisfying the printing quality of 3D final products, at an extruder temperature of 210 °C, were used to realize samples. The main characterization techniques, were dynamic rotational rheology (in time sweep mode) and infrared spectroscopy (in attenuated total reflectance mode). These methods allowed to verify molecular modifications, occurring in the polymer structure during the 3D printing process. The storage and loss modulus, and complex viscosity over time were presented for both neat and printed specimens. A comparison between the properties of printed and unprocessed materials revealed a decrease in rheological parameters over time as well as a loss in absorbance intensity for typical absorption bands. The viscosity values of PLA-1 and PLA-2 were found to be strongly unstable, with a significant decreasing trend over time. The experimental data were modeled using an exponential decay law, and the original decline was attributed primarily to the interaction of high temperatures and shear stress. Despite the fact that degradation effects were visible in wood/PLA composite materials, such systems remained thermally more stable than pure polymers.