Aging effects on the viscoelastic behaviour of products by fused deposition modelling (FDM) made from recycled and wood-filled polymer resins

In this work, we analyse the thermal aging effects on the thermo-mechanical properties of bio-based specimens realized using fused deposition modelling technology. For the investigations, three commercial filaments made of polylactide acid (PLA) were used. The first filament was a pure virgin PLA (B-PLA); the second one was made from recycled waste production, PLA (R-PLA), and the third one was wood-filled PLA (W-PLA). Such materials were extruded under pre-optimized conditions and thermally aged in an oven at 70 & DEG;C. The as-prepared specimens were subjected to dynamic mechanical analysis (DMA) and infrared spectroscopy (IR). The experimental results are presented in terms of storage modulus (E'), loss modulus (E"), tan delta, and absorption spectra at different aging periods (0, 50, 70, 130, 175 days). For B-PLA and R-PLA, the thermal aging results in a decrease in both storage and loss moduli and in an increase in the glass transition temperature (Tg). On the contrary, for the W-PLA the storage modulus increases with the aging time, while the Tg remains constant. The IR spectra support the hypothesis of a degradation mechanism involving hydrolysis and/or hydrogen atom transfer. Based on these observations, we conclude that heat treatments always lead, through polymer degradation and structural changes, to more stable structures. The presence of wood particles slows down the aging process and makes the final products more durable.