Selective Laser Sintering of Lignin-Based Composites

Lignin is introduced as a suitable component for selective laser sintering (SLS) of polyamide (PA12) to reduce costs while maintaining or improving processability and performance. Alkali lignin (sourced as a polydisperse, amorphous powder) was used at a volume concentration of up to 60 vol % for three-dimensional (3D) printing of complex, layered structures. The latter were obtained as high axial aspect objects, produced in flat, flipped (90°), and vertical directions, which were further examined to elucidate the effect of lignin as a suitable component in SLS. The composite withstood heating during SLS, and sintered PA/lignin showed 30% less degradation at elevated temperatures compared to pure PA. The morphological, wetting, mechanical, and thermal characteristics associated with the 3D-printed structures were compared. For instance, the strength and wettability were highly dependent on processing orientation. Compared to objects produced from neat PA, those that included lignin presented a higher porosity (∼10%) with a simultaneous increase in stiffness (increased Young modulus, by ∼16%, and reduced tensile strength, by ∼7%). Owing to differences in surface roughness and composition, an important difference in the water contact angle (CA) of the samples printed in the flipped and flat orientations was observed (55 and 126°, respectively). Overall, SLS is shown as a developmental step toward lignin valorization in composites while allowing reduced cost, scalability, and facile processing.