Evaluation of biomass as bio-additive in 3D printing

The petrol-based polymer has been widely applied in current daily life. The end-of-life of polymeric products has drawn environmental concerns. One of the solutions to such issues is to use bio-renewable materials to replace or reduce the use of petrol-based materials. Lignocellulosic materials are one of the potential candidates. Along with the features of 3D printing and the unique properties of biomass, 3D-printed biomass-based materials could be promising in preparing sustainable alternatives.

In this dissertation, lignin and other biomass were applied to various 3D printing techniques for sustainable composites. Stereolithography (SLA) was first used, and the kraft softwood lignin was incorporated into the commercial clear resin. The printed composites showed a reinforcing effect after fully curing. Inspired by such a reinforcement, wood flour, where lignin is isolated, was also applied as a biomass filler. The 3D-printed wood flour composites showed a unique stress-whitening phenomenon, which displayed a potential for stress indicators.

To further improve the loading amount of lignin in 3D printing, fused depositional modeling (FDM) was also involved. To improve the interfacial interaction between lignin and the polymer matrix, organosolv hardwood lignin was demethylated with improved phenolic hydroxyl groups. Enriched phenolic hydroxyl structures improved the interfacial interaction, thereby promoting tensile performance. A similar demethylation was executed on the softwood lignin. Due to the inherent difference in the functional groups, the obtained enriched polyphenol structures showed different but positive influences on tensile properties. In addition, the enhanced phenolic structures also showed great anti-aging performance, which brings more functions to the resultant composites, making lignin/polymer composites a promising functional and renewable material for the sustainable materials world.