*2.3. Lignin Precipitation*

Sulphuric acid was slowly added to the cooking liquor under agitation until final pH of 2.5. A color change from black to brown was observed at pH 5.5. In addition, a viscosity change was observed, the liquid was more viscose at lower pH. These changes occur due to the initial stage of the lignin precipitation. The mixture was then centrifuged (3500 rpm, 10 min) to recover the lignin. The lignin was repeatedly washed with water, then dried in an oven at 105 ◦C overnight. Volatile organic compounds (VOC) were removed after drying in a 2L Parr reactor (N4622, Parr Instruments, Illinois, USA).

#### *2.4. Filaments and 3D Printing*

Neat PLA (100%) and blends of PLA and lignin (20 wt % and 40 wt %) were extruded through a Noztek Xcalibur (Table 1). The temperatures in the three heating chambers were 200 ◦C, 205 ◦C, and 210 ◦C. The speed of the screw extruder was set to 15 mm/s. The target diameter of the filaments was 1.75 mm. The filaments were extruded twice in order to improve the mixing of the PLA and lignin.


**Table 1.** Mechanical properties of PLA and PLA/Lignin biocomposites.

Et (tensile elastic modulus); σM (tensile strength); M (elongation at tensile).

An original Prusa i3 MK3S was used for 3D printing by fused deposition modeling (FDM), using a 0.4 mm nozzle and a printing speed of 35 mm/s. Dogbone samples (length 63 mm, width 3 mm) were printed for mechanical testing. Three sets of dogbones were printed with varying printing temperatures of 205, 215, and 230 ◦C. The printing direction was 45◦. In addition, a smartphone protective case was printed as a demonstration.
