Nanocomposites Made with Poly(Lactic Acid)/Cellulose Nanofibers for Automotive Applications: The Impact of Annealing on 3D Printed Parts

<div class="section abstract"><div class="htmlview paragraph">The advance of regulatory emission standards for light-duty vehicles, trucks and motorcycles, coupled with rising sustainability concerns, particularly United Nations' Sustainable Development Goal 12 (responsible consumption and production), has created an urgent need for lighter, stronger, and more ecological materials. Polylactic acid (PLA), a biodegradable polymer derived from plant sources, offers promising mechanical tensile strength and processability. Nanocomposites, a solution that combines a base matrix with a nanoreinforcing filler, provides a path toward developing sustainable materials with new properties. Cellulose nanofibrils (CNF) are a valuable nanofiller obtained through industrial waste or vegetal fibers, offer a promising avenue for strengthening PLA-based materials. Additive manufacturing (AM) has gained popularity due to its ability to create complex parts, prototyping designs, and to evaluate new nanocomposite materials such as PLA/CNF, showing significant potential for the automotive sector. However, the AM process may result in lower mechanical strength and anisotropy, which can hinder the application and reliability of printed automotive parts. To alleviate this problem, chemical treatments can soften layers, while annealing can reduce voids and relieve internal stress. This article aims to study the impact of the annealing process on a PLA/CNF nanocomposite. Two combinations of temperature-time were evaluated: 75 °C for 1 and 2 h, and 90 °C for 1 and 2 h. Tensile tests of 3D-printed specimens were conducted according to ASTM D638 type V and differential scanning calorimetry analyses. The results revealed that the nanocomposite exhibited an increase in thermal properties and crystallinity, but lower mechanical strength when compared to the pure PLA, mainly attributed to printing defects that may have acted as stress concentrators. It is expected that this research will help to expand the use of additive manufacturing technologies applied to the automotive industry and development of new PLA nanocomposites with CNF.</div></div>