Decolorization of Lignin for High-Resolution 3D Printing of High Lignin-Content Composites.

Lignin, one of the most abundant biomaterials and a large-scale industrial waste product, is a promising filler for polymers as it reduces the amount of fossil resources and is readily available. 3D printing is well-known for producing detailed polymer structures in small sizes at low waste production. Especially light-assisted 3D printing is a powerful technique for production of high-resolution structures. However, lignin acts as a very efficient absorber for UV and visible light limiting the printability of lignin composites, reducing its potential as a high-volume filler. In this work, the decolorization of lignin is presented for high-resolution 3D printing of biocomposites with lignin content up to 40 wt.%. Organosolv lignin (OSL) is decolorized by an optimized low-energy process of acetylation and subsequent UV irradiation reducing the UV absorbance by 71%. By integration of decolorized lignin into bio-based tetrahydrofurfuryl acrylate (THFA), a lignin content of 40 wt.% and a resolution of 250 µm is achieved. Due to the reinforcing properties of lignin, the stiffness and strength of the material is increased by factors of 15 and 2.3, respectively. This work paves the way for the re-use of a large amount of lignin waste for 3D printing of tough materials at high resolution.

Generation of precision microstructures based on reconfigurable photoresponsive hydrogels for high-resolution polymer replication and microoptics.

Microstructured molds are essential for fabricating various components ranging from precision optics and microstructured surfaces to microfluidics. However, conventional fabrication technology such as photolithography requires expensive equipment and a large number of processing steps. Here, we report a facile method to fabricate micromolds based on a reusable photoresponsive hydrogel: Uniform micropatterns are engraved into the hydrogel surface using photo masks under UV irradiation within a few minutes. Patterns are replicated using polydimethylsiloxane with minimum feature size of 40 µm and smoothness of Rq ~ 3.4 nm. After replication, the patterns can be fully erased by light thus allowing for reuse as a new mold without notable loss in performance. Utilizing greyscale lithography, patterns with different height levels can be produced within the same exposure step. We demonstrate the versatility of this method by fabricating diffractive optical elements devices and a microlens array and microfluidic device with 100 µm wide channels.