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

Abstract

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 °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.

Effect of Thermal Aging on Viscoelastic Behavior of Thermosetting Polymers under Mechanical and Cyclic Temperature Impact

“…These changes are supposed to shift the behavior of material from viscoelastic to elastic and two separate experiments (creep tests and cyclic heating tests) indicated this phenomenon to exist. Therefore, the hypothesis, which was mentioned in the Introduction (that thermal aging decreases viscosity), is supported by the results of three independent experiments and correlates with other research [19,20].…”

“…Other researchers have got similar results. In [19] the authors studied the effect of thermal aging and performed FTIR analysis. FTIR tests have shown an increase of absorbance after heat treatment.…”

“…In [19], the authors studied the effect of thermal aging of polylactic acid (hereinafter referred to as PLA) resin on its viscoelastic behavior and performed Fourier-transform infrared spectroscopy (hereinafter referred to as FTIR) analysis. The authors concluded that heat treatment led to structural changes.…”

Cellulose/Polyhydroxybutyrate (PHB) Composites as a Sustainable Bio-Based Feedstock to 3D-Printing Applications

“…For the processed polymer (PHB_2), the peak becomes more evident, enlarged, and shifts toward higher temperatures. This variation, due to the extrusion process, is the result of two opposing effects: densification, which reduced polymer chain mobility, and chain scission (due to thermal degradation), which improves macromolecular mobility [55]. The two curves of PHB_2 The storage modulus decreases with increasing temperature, reflecting faster the relaxation processes of the material and the increased mobility of macromolecules at higher temperatures.…”

“…For the pure polymer (PHB), the glass transition temperature is around 23 • C. For the processed polymer (PHB_2), the peak becomes more evident, enlarged, and shifts toward higher temperatures. This variation, due to the extrusion process, is the result of two opposing effects: densification, which reduced polymer chain mobility, and chain scission (due to thermal degradation), which improves macromolecular mobility [55]. The two curves of PHB_2 and PHB/MCC 1.5% overlap, and no significant effect can be observed due to the addition of a 1.5 wt.% filler content.…”